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October 23

Phase of quantum probability amplitude for reflection from a potential change

Part of my quantum mechanics assignment is to calculate the probability amplitude that an unbound particle will reflect back from a potential well. The final answer is given, and I keep getting an answer that differs from the given one by a constant phase factor but is otherwise identical. Am I correct in thinking that this phase difference is caused by considering the reflection as taking place at a different point within the potential well, and that the particle picks up the phase difference between the two nominal reflection points? If so, how is the phase relationship between the incoming and reflected wavefunctions usually specified? Do you always need to specify both a reflection probability amplitude and a nominal reflection point, or is there a simpler way? —Keenan Pepper 03:46, 23 October 2007 (UTC)

Let me guess: Does the phase factor that you've calculated make the answer a little less simple to express? In that case, my guess is that the difference between the answers is just a matter of a constant phase factor being considered unimportant to the problem at hand. After all, the overall phase of a quantum mechanical wavefunction is arbitrary. The only time a phase relationship between two unbound wavefunctions is important is when you're dealing with an interference effect between two parts of what's really one wavefunction, such as with a double slit experiment or something. An unbound particle reflecting back from a potential well is basically a scattering experiment, in which I don't think one usually cares about the phase relationship between the incident and reflected wavefunctions. The phase relationships between different parts of a bound state, however, is a different matter. MrRedact 05:39, 23 October 2007 (UTC)

Right, but our professor is very attentive to detail, even pedantic. I doubt he would just arbitrarily change the phase without telling us. Anyway, thanks for your answer. I feel confident it's not an error on my part now. —Keenan Pepper 12:38, 23 October 2007 (UTC)

Lobe-Finned Fish

My biology teacher owns a very peculiar preserved fish which appears to be a lobe-finned fish, though only the two front fins appear to resemble primitive limbs. It appears very primitive (non-bony, thick body and long thick tail) and is covered in large, thick, plate-like scales (the underside is bare and flat, and has two seemingly vestigial fins tucked flat against the body) and has a worm like lure on it's head. It almost resembles a frog without the tail, but with backwards bending knees (the limb like structer of the front fins is highly pronounced). The lobed-fins look like they were used for crawling, as the fish is most likely a bottom feeder. It is about 6 inches long, and the original color is no longer apparent. It was caught off the coast of florida on the ocean floor (unkown depth) and even after extensive research my teacher and the troller fisherman who caught it have found no-other like it nor anyone who is able to identify it's taxonomy. I'll try to get some pictures of it but for now I was wondering if anyone might be familiar with this description. BeefJeaunt 05:42, 23 October 2007 (UTC)

Part of the description sounds like some sort of angler fish - which have the bait, look a bit froggy, and despite not being lobe-finned fish have quite lobe shaped fins..87.102.17.104 11:16, 23 October 2007 (UTC)

Is it possible that your teacher is spinning you a story about what's going on here - "even after extensive research my teacher and the troller fisherman who caught it have found no-other like it nor anyone who is able to identify it's taxonomy". So your teacher somehow gets his hands on this bizarre unidentifiable fish, researches it with the troller (trawler?) fisherman, and then can't get it identified. Surely he would take it to a reputable university department or something like that to try to get identified professionally, and they would be very interested in it if it was really unable to be classified; I can't imagine them just shrugging their shoulders, saying they don't know, and giving it back to him to sit on a shelf (consider the reaction to the coelacanth when one was first caught in 1938 for example). --jjron 13:40, 23 October 2007 (UTC)

It seems reasonably improbable that the fish is actually lobe-finned (there are very few extant species). There are many species of fish, so finding one which even an experience fisherman is not familiar with is not terribly unusual. Your best bet is to take it to a fisheries collection (Florida Museum of Natural History is a good place to contact), but you'll probably need an expert to make the identification. --TeaDrinker 03:57, 25 October 2007 (UTC)

Speed of light

When we say that speed of light cannot be exceeded, what is the frame of reference? Keria 08:54, 23 October 2007 (UTC)

That's true in every inertial frame of reference! The speed of light is exactly the same in every inertial frame of reference. That's one of Einstein's postulates of special relativity. For more information, see the Introduction to special relativity article. MrRedact 10:16, 23 October 2007 (UTC)

And not to be totally pedantic, but the most simple and accurate way of stating it is the speed of light is independent of the velocity of the light emitter. The reason for the restatement is that 1. it emphasizes what is really going on in terms of its constancy (the speed of a wave is always independent of the velocity of its emitter; if it wasn't, the Doppler effect wouldn't work. Light isn't terribly special in THAT regard, though because it is light, it has very important implications for space and time, ergo Special Relativity) and 2. light can, in fact, vary in speed: the speed of light in a vaccum is different than the speed of light in a medium (that is, it can be slowed down in, say, water). So rather than saying it is "constant" I think it is a little more clear to say that it is "independent"—it also avoids the appearance of tautology that baffles many new physics students (the analogy with sound is an easy one), makes it more clear why Einstein and his buddies knew it was "constant" from a theoretical point of view, and reminds people that thinking of light as little particles only reflects some aspects of its nature. --24.147.86.187 12:01, 23 October 2007 (UTC)

Yes inded and that's exactly my problem (now I see I might have worded the quesion poorly): How do you know when the speed of an object or particule (say some intergalactic one) would be approaching the speed of light if we don't have a frame of reference to calculate from? Would we consider the known universe as stable and not moving so that all absolute speed should be seen as the speed relative to our universe? But then how can we be so sure our universe is not moving and say in one direction an object could go 1.5 times the speed of light relative to the universe and the opposite direction never more than 0.5 times the speed of light while never actually exceeding the absolute speed of light? Keria 12:15, 23 October 2007 (UTC)

Well, you can measure the speed of an object from any reference frame, but no matter what the case it will not bypass the speed of light. Which is to say, they will not be exceeding the speed of light in any reference frame. Sound a little weird? Well, that's sort of the essence of Special Relativity. Instead of another observer seeing them as bypassing the speed of light, they will have disagreements about the amount of space they have covered in that time, or the amount of time it took them to cover that amount of space. In either case they will never see them go faster than 300,000,000 meters per second. (At least, that's my basic understanding of it. Someone correct me if I am mistaken about my reasoning.)

In any case, you have to use a different velocity-addition formula when working within special relativity—it doesn't work quite the same way as it does with simple Galilean velocity additions. Unlike Galilean relativity, where you could have one observer see the other exceeding the speed of light, the relativistic velocity-addition formula has the inability to exceed the speed of light hard-coded into it in a rather elegant way. --24.147.86.187 13:07, 23 October 2007 (UTC)

To take the first part of your question, you can't. There's no absolute measurement of speeds in relativity—only (surprise) relative ones. If you take a sealed box that's travelling at some constant speed, there's no experiment that you can do inside that box that will tell you anything about how fast the box is travelling relative to anything outside the box. The idea of the luminiferous aether has no place in relativity.

If you have an intergalatic particle travelling at some constant speed, the physics works whether you say the particle is moving quickly and the galaxy it's passing is at rest, or if you say the galaxy is moving quickly and the particle is at rest. It's totally equivalent; you may run across the phrase 'There are no privileged frames of reference' in your reading.

In a larger sense, the Universe is just like that sealed box. We don't get any information about what's going on 'outside'; heck, there probably isn't any 'outside' to talk about. You can, if you wish, treat the entire Universe as moving with some constant velocity, and you'll get the same results out of your equations and experiments. (Indeed, all you accomplish is making the math slightly more complicated.) TenOfAllTrades(talk) 13:20, 23 October 2007 (UTC)

Perhaps the simplest way to say this is: For everyone and every thing in the universe, every other thing has to be moving slower than the speed of light relative to them (unless it's a photon when it's moving at exactly the speed of light). SteveBaker 14:05, 23 October 2007 (UTC)

Hm? No, an object farther away from you than the edge of your observable universe is moving faster than the speed of light relative to you. --Trovatore 15:43, 23 October 2007 (UTC)

Good luck ever observing that ;-) Someguy1221 17:22, 23 October 2007 (UTC)

That's not the point. Whether something is true of "every thing in the universe" is an ontological question, not an epistemological one. --Trovatore 17:37, 23 October 2007 (UTC)

If there were an object that was just outside my observable universe moving faster than light relative to me - then what do you imagine it and I would look like to an observer halfway between the two of us? For that observer, the laws of physics are the same as they are for me. SteveBaker 23:05, 23 October 2007 (UTC)

Who said they weren't? But I admit this does get a little tricky and I don't have it all worked out. The thing to keep in mind is that this is inherently a GR problem; you can't simply apply SR formulas like the addition-of-velocity one and expect them to work unmodified. On a related note, the choice of coordinate systems becomes somewhat less canonical -- we can't speak of an inertial coordinate system that extends from you out to near the edge of your observable universe. I think this is called lack of distant parallelism or some such. --Trovatore 23:14, 23 October 2007 (UTC)

I was hoping a real general relativity expert would step in and explain this, but that hasn't happened, so I'll go ahead and give it my best shot. Hopefully, the following doesn't have any errors that are too blatant:

If an object is farther away from you than the edge of your observable universe, then it's ambiguous as to how fast it's moving away from or toward you. However, it's definitely moving slower than the speed of light.

Speed is fundamentally a local phenomena. The only way you can unambiguously talk about the speed relative to you of something at a distance is if both you and the distant object share an inertial frame of reference. That is, you and the object have to be within a region of spacetime which is flat, or at least close enough that a flat spacetime is a good enough approximation for the problem at hand. But when you're talking about something beyond the observable universe, the curvature of the universe becomes a critically important part of the problem. The problem is that a speed is the spatial distance between two events, divided by the time difference between the two events. But when you're talking about large distances in a curved spacetime, it becomes ambiguous as to how to separate a distant spacetime interval into space and time components. In a curved spacetime, it's impossible to set up a distributed system of clocks that are all synchronized with each other, because the curvature of spacetime makes clocks at different points in spacetime run at different speeds. So unlike with special relativity, with a curved spacetime it's impossible to define any single global coordinate system that keeps time separate from space everywhere. Instead, what general relativity does is to "stitch together" a continuous set of inertial frames of reference, each of which is only used locally. The metric tensor defines the global geometry of the spacetime manifold, and is unambiguous everywhere. But the coordinate system in which one chooses to express the components of the metric tensor at a given event, which is what defines the difference between space and time at that event, varies from point to point, and is to a large degree arbitrary.

Given a local inertial frame of reference used in one place, like an inertial frame of reference in which the earth is more or less at rest, there isn't a single "correct" local inertial frame of reference that should be used at a remote location, such as near a star that's beyond our observable universe. You can arbitrarily choose a local inertial frame of reference near that star, in which the star is moving in any direction at any sub-light speed you want. But in whatever local inertial frame of reference you use for measuring the remote star's speed, it's moving at less than the speed of light in its local inertial frame of reference.

Although in an expanding universe, light from a distant star may never be able to reach us, it's not valid to say it's because the star is moving away from us at faster than the speed of light. Instead, a valid description is that the space in between us and the star is expanding faster than light can overcome. More technically, the metric tensor that describes the distance between nearby points in the space in between us and the distant star is changing over time, such that the distance between any two points gets bigger as time progresses. MrRedact 02:40, 24 October 2007 (UTC)

Well, the above seems a bit internally contradictory -- if speed is fundamentally a local phenomenon (please don't use "phenomena" as a singular), then how can it make sense to say that the star is moving away slower than the speed of light? I do think you're right that the situation is a bit ambiguous because there is no inertial frame including both objects, but that doesn't seem to stop people from describing stars at high redshifts as "moving away from us at 99.999% of the speed of light" or whatever. Whatever definition of speed is used in that description, must surely describe the star past the horizon as moving away faster than the speed of light. --Trovatore 02:49, 24 October 2007 (UTC)

Ah, poking around a little I found the basis of a good candidate for a notion of the speed at which the star is regressing. Give us, and an observer at the distant star, a time coordinate t equal to time since the Big Bang according to a comoving observer -- that is, an observer for whom the background radiation is isotropic; roughly speaking such an observer will be at rest relative to nearby stars or galaxies or maybe galactic clusters. At any t, draw a geodesic between the event point represented by us when we have time coordinate t, and the one at the distant star at time coordinate t. Let s be the length of this geodesic. Now consider ds/dt.

I think it will probably be at least approximately correct that this measure of speed will be less than the speed of light for stars within our observable universe, and greater than the speed of light for stars past the horizon. However it's not my field of expertise and I'm not sure of that. But at least there's a well-defined question on the table; maybe someone who actually does know can settle it. --Trovatore 03:16, 24 October 2007 (UTC)

I didn't actually say that the distant star is moving away slower than the speed of light, merely that the star is moving slower than the speed of light, meaning that in no matter what local inertial frame you use to measure the star's speed in, the star's speed is slower than the speed of light in that inertial frame.

It looks like you're right in that if you choose to define the speed of the star relative to us as being ds/dt, where s is the comoving distance between us and the star (just one of a number of distance measures that could be used) and t is the cosmological time (just one of a number of measures of time that could be used), then the speed of the star relative to us is greater than the speed of light. The principal that "nothing can move faster than the speed of light" isn't violated, however, because the "speed" involved is a measure of the metric expansion of space, not the speed of an object moving within space. Indeed, in the comoving coordinates, both us and the star are roughly at rest. MrRedact 11:48, 24 October 2007 (UTC)

After reading more closely, I see that the definition of the comoving distance is not the same as the length of a spacial geodesic measured along a hypersurface of constant cosmic time. The comoving distance is defined as not changing in time, and isn't even well-defined for an object outside of the observable universe, so it doesn't work to have s be the comoving distance in defining ds/dt as the relative speed. It does work to instead use the length of a geodesic, which is what you used in your definition. MrRedact 14:18, 24 October 2007 (UTC)

Thank you very much for all your answers. Keria 18:54, 24 October 2007 (UTC)

Tap water

hi, i'm now living in the UK, is it safe to drink directly from the tap? in countries i've lived in before it is always recommended to filter the water first... —Preceding unsigned comment added by 82.46.27.191 (talk) 13:37, 23 October 2007 (UTC)

Except under very unusual circumstances, yes, you can drink tap water in the UK (and most other European countries). If not (e.g. due to contamination), that information will be well advertised via TV, radio, and newspapers. You might want to check if you are living in a very old building where the piping may still contain lead. But even in that case, it the risk is only significant for long-term exposure. --Stephan Schulz 13:48, 23 October 2007 (UTC)

In buildings with lead pipes you just need to let the water run for a few minutes so that the water that's been sitting in the pipes for a long time is gone before you take some to drink. But aside from that, yes - it's OK to drink UK tap water. SteveBaker 13:59, 23 October 2007 (UTC)

Every country has its germs. Some more (and more dangerous ones!) than others, but you always run the risk of getting diarhoea when abroad, wherever you go. But at least in (western) Europe you're not likely to get anything serious, so don't worry and drink the tap water. Except when you're just there for a few days maybe, in which case only drinking bottled water would not be too much of a hassle. especially when you're on a business trip, and can't afford to get sick. But even then I would consider it rather over the top. Keep in mind that tap water in (western) Europe is meant to be perfectly safe to drink. I just pointed out the few minor reservations you might have. DirkvdM 19:08, 23 October 2007 (UTC)

Is it possible to use nanomachines instead of electricity?

Like, instead of electricity doing "work", the nanomachines do the work instead. Is this possible? 64.236.121.129 14:54, 23 October 2007 (UTC)

See mechanical work and nanotechnology for some articles that might be relevant. Something has to power the nanomachines, right? That might still be electricity. Friday (talk) 14:58, 23 October 2007 (UTC)

Firstly, we don't have nanomachines - and there are grave doubts that they are even possible. But if we do someday figure out how to make them, they'll need power from somewhere. Most likely we'd power them with laser light - but it's possible they could be powered from chemical sources in whatever media they are working. In that respect they are no different from normal-sized machines. Just as an industrial robot could be powered from electricity or gasoline or solar cells - it would be the same thing with nanomachines. So they aren't going to somehow "replace" electricity - although they may well be powered by electricity. Probably the best way to think of them would be as teeny-tiny robots - or perhaps like bacteria or virusses that we designed ourselves. SteveBaker 15:04, 23 October 2007 (UTC)

Yea I know we don't have nanomachines. If we did, I would already know the answer. Anyway, what powers the nanomachines doesn't necessarily have to be electricity. Hmm, I guess what I'm getting at is, is it possible to create something that is powered by something other than electricity (so it's impossible to be electrocuted) or something that can blow up like gasoline. Our bodies for example aren't powered by electricity (although there are electrical signals), nor by anything that is combustible. 64.236.121.129 15:39, 23 October 2007 (UTC)

Our bodies are powered by combustible materials, it's just mixed with water, so doesn't burn easily. If you take the water out, the remaining protein, carbs, fats, and alcohol burn quite nicely, and will even explode, if converted into an aerosol. StuRat 22:59, 28 October 2007 (UTC)

These machines would probably not carry "batteries" as such - and you wouldn't want to connect them up with wires - so electricity doesn't seem like the natural thing to power them with. They might maybe have an onboard chemical fuel supply - but more likely, I think we'll be powering them by shining laser light onto them from outside - or perhaps using chemicals in whatever fluid they are floating in to generate power. There are other possibilities though - they could be powered by something like a clockwork motor or something like a flywheel that stores energy and can be made to give it back as required. Things work very differently on a nano-scale and things that aren't considered very useful at the macro-scale are often extremely useful at the nano-scale (and vice-versa). For example, it's been widely suggested that nano-bots would use mechanical computing parts - like Babbages Difference engine or the TinkerToy computer that students put together at MIT. Pushrods and gears at that molecular scale would work more quickly than the transistors in an electronic computer! So it's possible that something like a clockwork motor could power such a machine.

But the bottom line is that we don't really know how we'll power these things...if indeed they are possible at all. SteveBaker 16:03, 23 October 2007 (UTC)

It has to be possible to power them. After all, viruses, bacteria, amoebas, cells, etc can utilize energy, so we know that it is possible. If they can do it, then it can be replicated. It's not easy to emulate, but it's possible. 64.236.121.129 16:40, 23 October 2007 (UTC)

Right - those things are (mostly) powered from chemicals in their environments and they have a small on-board chemical fuel supply to tide them over between meals. We could do the same thing. On the other hand single-celled plants are solar powered. We could do that too. If nanomachines are ever built 'for real', and if they are designed to self-reproduce (Drexler's "assemblers" for example) then there is the risk of Grey goo - when the machines go nuts and try to convert the entire planet into more machines! Having them powered by something that's not naturally "out there" is a way to prevent that. If you powered them by shining a laser of a specific frequency onto them - then if they went nuts, you could simply shut off the laser and they'd all switch off. Giving them a fixed internal power source (like a molecule-sized clockwork motor) would have a similar effect. But, as I said before, we are an awful long way from having such things - and it's a bit premature to be discussing details of things like power supplies when there are much more serious problems to be solved. SteveBaker 20:29, 23 October 2007 (UTC)

Grey goo. Pah. Amoebas are self powered and exist solely to make more amoebas. I see no grey ameobic goo. --Psud 10:23, 24 October 2007 (UTC)

See Micropower for a discussion of some nanomachines and nanogenerators (some recent articles on this topic are listed on the talk page but not yet incorporated in the article). Edison 17:01, 23 October 2007 (UTC)

density and volume of electron, proton (atomic structure)

dear sir

i am eswar .nice meeting you.

i would like to ask a question related to basic particles of atom

what is the numerical value of elctron and proton densities in kg/meter cube ?

what is the numerical value of elctron and proton volume in cubic metere ? —Preceding unsigned comment added by Eswar kumar p (talk • contribs) 15:05, 23 October 2007 (UTC)

The very first sentdnce of the Proton article tells you the size and mass. The Electron article also tells you the mass and has some discussion of the size (in terms of the "classical electron radius"). DMacks 15:14, 23 October 2007 (UTC)

But note that the volume of an electron is not well defined. In quantum mechanics, it doesn't really behave much like a particle at all, but more like a wave, which only has a probability function, not a location and volume. StuRat 22:47, 28 October 2007 (UTC)

Anomalous hair

I have a hair follicle which is unusually long, some 2-3 times a normal hair and also white. It is notably to say that it always grows in the same place. I had asked my biology teacher if it was a case of mosaicism but he negated it without offering me an explanation. So guys, any ideas on what is it?—Preceding unsigned comment added by 193.188.46.61 (talk) 16:43, 23 October 2007 (UTC)

Your biology teacher isn't allowed to give out medical advice - and neither are we. SteveBaker 16:06, 23 October 2007 (UTC)

Lighten up. He isn't asking for medical advice. Theresa Knott | The otter sank 17:16, 23 October 2007 (UTC)

Your biology teacher is allowed to give out biological information, and so are we. Having a long white hair should not ordinarily make one suspect mosaicism. Why does a long white hair need explanation, anyway? - Nunh-huh 16:40, 23 October 2007 (UTC)

The melanocytes in this particular follicle have apparently ceased to function earlier than in your other follicles. If you were a mosaic or chimera, there would, I suspect, be a wide range of other readily observable manifestations. Gray hair says that white hairs can appear as early as childhood without any particular or worrisome cause. Just out of curiosity, is it growing more quickly than your other hairs, or is it more robustly rooted, and so does not fall out as readily? Eldereft 22:06, 23 October 2007 (UTC)

It is medical advice he is asking. He presents us with evidence and asks for a diagnosis. Please don't. Questions and answers removed. Lanfear's Bane | t 23:26, 23 October 2007 (UTC)

I felt the question was for an explanation of a biological phenomenon. The was no indication that the questioner regarded this as a medical problem in any way. Are we to assume that any and all questions of human biology are in future to be deleted? DuncanHill 23:39, 23 October 2007 (UTC)

Astonishing. Someone so unacquainted with what medical advice actually is that he removes a question about the causes of a white hair while leaving advice on how to remove ear-wax on the same page. This despite two people who had already indicated there was no advice. - Nunh-huh 00:17, 24 October 2007 (UTC)

I was going for 'here are some possibly related articles,' but fair enough. Eldereft 00:20, 24 October 2007 (UTC)

I agree that this is not a medical question, it's a biology question. I've noticed that people get more of those type of "rogue hairs", which never stop growing, when they get older. They especially appear in the eyebrows and on the ears of men, but can appear just about anywhere. They can be colored or white, but I've also noticed they tend to be thicker hairs. I'm not sure what biological mechanism causes this, but I'd suspect it's a malfunction of the mechanism which normally limits hair length in most places on our bodies. StuRat 22:37, 28 October 2007 (UTC)

safe fungi

how can I tell if fungi is safe to eat? —Preceding unsigned comment added by 213.228.203.153 (talk) 16:57, 23 October 2007 (UTC)

Eat it and see if you die. All joking aside, that's close to the answer. Try to find a local field guide. For instance, I have one for Colorado mushrooms. It lists a number of them, including their safety. It lists some as "Edible, but unsafe" because they are too easily mistaken for poisonous varieties. Failing that, there are methods to test plants for safety, of which you might be able to find in hard-core survivalist stuff. --Mdwyer 17:14, 23 October 2007 (UTC)

Assume it is unsafe unless you already know it is safe or if someone whose expertise you totally trust tells you it is safe. There are a lot of poisinous fungi out there and many of them look very similar to harmless ones. Theresa Knott | The otter sank 17:11, 23 October 2007 (UTC)

Short answer: There is no, clear, simple rule to tell the difference between poisonous and edible fungii.

Longer answer: When I was learning to program simple artificial intelligence systems, one class problem was to write a computer program that could take a lot of facts about classes of object and find rules to distinguish between them. So, for example, you could type in all of the information about 50 different kinds of car (top speed, fuel consumption, 0-60 time, number of doors, weight, etc) - then tell the system which cars were sports cars and which were not. The system would go off and work out which parameters about the car mattered and to what degree they mattered in classifying whether it was a sports car or not (so in this case, it would figure out that top speed and accelleration were important, having two doors was less important but still relevent - but fuel consumption had little or no bearing on how the car was classified). Then you could put in the data for a new car - and the program would unerringly be able to tell you whether it was considered a sports car or not by applying the rules. Anyway most of the class got good working programs to do this and at the end of the class, we were given a database containing all of the characteristics of a bazillion kinds of mushrooms and toadstools (including whether each one was poisonous or not) - and asked to "Find the rule to distinguish poisonous from edible". Nobody's program out of the entire class was able to find a common rule...and the reason for that is: There isn't one...it was a "trick question". SteveBaker 20:21, 23 October 2007 (UTC)

Off-topic: Did you do that in Prolog? I used that language once to write a program with which you could find the ideal place for you to live on Earth. Put in the characteristics and it gave the locations that had all those characteristics (well, actually it was limited to South America and had a very low resolution because I had to manually build the entire database). DirkvdM 09:29, 24 October 2007 (UTC)

From my first answer at 'Edible mold and fungus (mushrooms)' 10 threads up: "If you're not sure if something is edible, first rub it between your fingers, then under your armpit, then on your lips, then put some in your mouth, chew and spit. If any of these tests results in a unpleasant feeling, don't eat it. Then swallow a little bit and wait for a few hours (maybe longer). If you don't get sick, you can eat more and wait. If you still don't get sick, it's safe to eat." This info from a hard-core survivalist (no, not one of those idiots who stock up centuries worth of food in case the world ends). DirkvdM 09:29, 24 October 2007 (UTC)

Bad advise unless the other option is starving to death. The death cap, for example won't irritate your fingers, armpits or lips, but will quite cheerfully kill you a few days later unless you can get a liver transplant in a hurry. Half a cap will likely kill a person. Capsicums (or I think US of Aians call them bell peppers) are tasty and nutritious, and will fail the test. --Psud 10:39, 24 October 2007 (UTC)

It takes days to kill you? That's very unusual. DirkvdM 18:51, 24 October 2007 (UTC)

I agree. The death cap is deadly, but tastes good. Evolution at work right there. Eat food that you know is safe only. Leave the guessing to the starving person who has no choice. 64.236.121.129 13:57, 24 October 2007 (UTC)

So you're saying "look it up". Good advise, but I suppose the questioneer thought of that too. :) I got this from the SAS Handbook by John Wiseman. This time I bothered to look it up and under 'mushrooms' it says that there are no reliable general rules to identify edible mushrooms and boiling doesn't help either. You have to KNOW beyond doubt if it is an edible mushroom. And (translated back into English): "Unlike plants, for which the simple edibility test can be done, they have to be either identified or avoided. The deadly varieties don't taste unpleasant and the intoxication symptoms sometimes set in only after hours." So not days, but still, it turns out you guys are right. However, if identified beyond doubt as edible, they are a good food source which, in the right season, is available in abundance. Fortunately, they can also be easily conserved by drying. The book advises to learn a few real well and stick to those. It also advises to learn to identify amanites, the ones to particularly avoid. The most deadly is amanita phalloides, the death cap, followed by amanita virosa. Symptoms start slowly after 8 - 24 hours. After that a clear improvement, but in 90% of cases one will die after 2 - 10 days due to liver problems. No known antidote. Ah, so it does take days in this case, but it's not the poison itself that kills but the failing liver. Btw, the book also describes some nasty symptoms (including hallucinations) for the famous amanita muscaria, although one will generally recover. Note that I ate a whole muscaria once (for the hallucinations), but noticed nothing. However, that was a few days after I picked it, because I had started with tiny bits, ever bigger, until in the end I ate the remaining half. If only there weren't such idiotic drug laws, then people like me wouldn't do this sort of thing. Anyway, the muscaria article says "The effect is highly variable and individuals can react quite differently to the similar doses. Deaths from A. muscaria are extremely rare. [...] The amount and ratio of chemical compounds per mushroom varies widely from region to region, season to season, further confusing the issue. [...] The vast majority of mushroom poisoning fatalities (90% or more) are from having eaten either the greenish to yellowish to brownish mottled death cap (A. phalloides) or one of the destroying angels (Amanita virosa)." DirkvdM 18:51, 24 October 2007 (UTC)

I'd just like to agree that you should learn one or two easily identifiable species found in your area and stick to them. Use a book and a knowledgable friend if you can (you can get a book out of the library; friends who know about mushrooms may be rarer). For example, in the pine forests near where I live, one can find the delicious Boletus edulis, which is pretty distinctive, and what we call a pine ring (can't find it on wikipedia) whose stalk has a distinctive greenish-blue ring when cut. --Taejo|대조 10:27, 29 October 2007 (UTC)

Bathroom smelling of salt

Whenever I'm away from home for more than a day, when I come back home, my bathroom smells strikingly strongly of salt. The smell goes away by the next morning. What the heck is causing this? JIP | Talk 17:00, 23 October 2007 (UTC)

What does salt smell like? If the plumbing traps are drying out, it might be sewer gasses. It might be things growing in the traps. If you use those giant chlorine pills in your toilet tank, it could be chlorine gasses from it. In other words, I have no idea. --Mdwyer 17:09, 23 October 2007 (UTC)

It's like smelling something pulled up from under the sea. I do not think it's a problem with the house's plumbing, otherwise I would smell it constantly. I first experienced it when undergoing my civilian service training, which took three weeks in a training facility in another town. Weekends were free, so I came back home for every weekend. When I first opened my door on Friday evening, I was met with this salty smell. On Saturday morning, it was completely gone. It must be something related to my senses getting used to something, but how come I only ever notice it in my own apartment, not in my parents' apartments or at my workplace? JIP | Talk 18:47, 23 October 2007 (UTC)

Sounds like the smell of damp/cold places - which you probably get used to when you live there.. I seem to remember a pantry which was unheated having a smell that could be described as salty..87.102.10.72 22:10, 23 October 2007 (UTC)

Assuming you live near the sea, I have two theories:

1. The smell is always there. When you are at home, you get used to the smell and it disappears from your mind. If you go away for a while you get used to different smells so your mind really notices the natural sea smell when you return home.

2. Sea water is mixing with the water in the sewerage system. Without a regular washing out by running water down the outlet and flushing the toilet, the sea water and it's smell seeps further up the drains and into the traps under the your sinks. If the traps are dry, the sea smell could easily escape into your bathroom.

Astronaut 17:11, 25 October 2007 (UTC)

Muscle cells

• On what factor does the strength of the muscle cells rely on ??
• can it be strengthened without increasing its size but by altering its components to make it strong as metal?

plz answer both Qs —Preceding unsigned comment added by 212.71.37.98 (talk) 17:12, 23 October 2007 (UTC)

A muscle's strength is dependent largely on how many myofibrils it contains. Now, saying "as strong as metal" is a meaningless comparison. The strength of a muscle is its ability to exert a force, whereas the strength of a metal is its ability to resist deformation. Someguy1221 17:28, 23 October 2007 (UTC)

The answer is no. The amount of force a muscle can exert is proportional to it's cross-sectional area. So bigger means it can exert more force - there isn't anything you can do to make it exert more force except by making it thicker.

"As strong as metal" is quite utterly meaningless. How strong is Mercury at room temperature? (Hint - it's a liquid!) Which metal are we talking about? What temperature? Are we talking about strength in tension or in compression or in bending? Take a length of electrical wire (copper) and try to snap it by just pulling on it...you'll never manage it. But bend it back and forth a few times and it snaps easily. Even your smallest muscles can be bent back and forth millions of times during your life and they don't snap.

Part of the trouble here is that you are using the word "strength" to mean two quite different things. When we talk about someone being "strong", we are probably talking about the amount of weight they can lift or something. That's a measure of the force your muscles can exert. When we talk about "strength" in metals, we're talking about the amount of weight they can passively hold without breaking. So whilst you MIGHT be trying to compare the amount of weight a steel cable could hold without snapping to the amount of weight a chunk of muscle could hold without snapping - that wouldn't be the same as the weight that could be lifted by contracting that same muscle. SteveBaker 20:05, 23 October 2007 (UTC)

Sanitation

(Aaw, lost what I wrote in an EC...) Is there anything I can do to sanatize my desk besides using clorox wipes and putting on GermX before eating, because we're having staph outbreakes at my school. I could probably get a hold of most things (disenfectants), but I need to know what they are. Thnx!YДмΔќʃʀï^→Г_C← 10-23-2007 • 19:36:16

While it's tempting to recommend that you use the time-honored method of subjecting it to a temperature similar to the inside the sun for a few seconds, I must regretfully assume that you are speaking in practical terms. "Creative" methods such as that excluded, I'd just recommend washing your hands a lot and using the disinfectants, etc you mentioned above. Maybe the article Staphylococcus could give some useful information as well.
Ah, here we go: this section talks about alcohol being a good disinfectant specific to the bacteria:

Alcohol has proven to be an effective topical sanitizer against MRSA. Quaternary ammonium can be used in conjunction with alcohol to increase the duration of the sanitizing action. The prevention of nosocomial infections involve routine and terminal cleaning. Non-flammable Alcohol Vapor in Carbon Dioxide systems (NAV-CO2 systems) have an advantage, as they do not attack metals or plastics used in medical environments and do not contribute to antibacterial resistance.

Hope this is useful. Pyrospirit (talk · contribs) 22:51, 23 October 2007 (UTC)

polymer

which materials are anti_markin about absorbing ink? —Preceding unsigned comment added by 85.133.156.36 (talk) 20:37, 23 October 2007 (UTC)

I'm not entirely sure what you're talking about. Could you provide more context to your question? Pyrospirit (talk · contribs) 23:01, 23 October 2007 (UTC)

You need something with a strong non porous surface, such as glass or metal. The ink will be erasable. FOr polymers you face the additional problem that the solvent in the ink may be able to dissolve the polymer or soften it, allowing the ink to pentrate the surface and be hard to remove. Melamine resin or Formica (plastic) are pretty good at resisting staining. Look at anything that might be used on a kitchen bench or whiteboard. Graeme Bartlett 01:34, 24 October 2007 (UTC)

Toadstools and snakes

I think I know two things: that no shelf mushroom is poisonous, and no snake with longitudinal stripes is venomous. Are these things true? --Milkbreath 21:23, 23 October 2007 (UTC)

There is no simple rule to distinguish poisonous mushrooms from edible ones - although what you say here isn't exactly that. Our article says that most shelf mushrooms are inedible - but doesn't say whether any are poisonous. I'd be VERY skeptical about that rule. About the snakes though. I find your claim here rather surprising too. I guess it depends on what you call a 'stripe' and just how 'longitudinal' it has to be. The Yellow bellied sea-snake is certainly pretty venomous - and I'd call that a black/yellow longitudinal stripe pattern...but maybe you can weasel out of that by saying that it's a 'sea snake' and you meant only land snakes - or that it's not really a "stripe" per-se but merely a top and bottom coloration. SteveBaker 22:37, 23 October 2007 (UTC)

The pit viper Trimeresurus popeorum has ventrolateral stripe. I also came across this bizarre image of what the photographer claims is the deadly Bungarus fasciatus which normally has striking yellow and black lateral stripes, but in this case sports black and yellow longitudinal stripes. The picture has the accompanying text: "Bungarus fasciatus : mutazione genetica. Raro esemplare con una lunga fascia dorsale nera al posto della tipica colorazione ad anelli." I caught the word genetic mutation but that is a pretty drastic change from the normal patterning. Mistaken identity possibly? EDIT: It appears to be the venomous elapid Hemibungarus sauteri an "Asian coral snake" Sifaka ^talk 04:20, 24 October 2007 (UTC)

Actually it seems like a few of the "Asian coral snakes" in the venomous genus Calliophis seem to be longitudinally banded and strikingly colored. See this picture of Calliophis bivirgatus. Sifaka ^talk 04:51, 24 October 2007 (UTC)

Followup: [1] says that the Sulphur Shelf mushroom (Polyporus sulphureus) poisoned seven members of the The Mycological Society of San Francisco (who REALLY ought to know better!). Our article Laetiporus confusingly describes it as edible (and gives it a totally different Latin name?!?) - but then goes on to say "About half of the population has an allergic reaction to this type of mushroom, with cases being more pronounced in older mushrooms."...yeah - so it's edible, but you have a 50/50 chance of being allergic to it. Hmmm - I call your claim "Busted". SteveBaker 22:45, 23 October 2007 (UTC)

Right you are. But, heyyyy...does ya got sumpin against weasels? --Milkbreath 23:00, 23 October 2007 (UTC)

To my knowledge none of the bracket fungi appear to be truly deadly poisonous, but then again some dangerous fungi can grow in a manner where they superficially resemble bracket fungi. It also doesn't help that most bracket fungi taste like tree bark with similar toughness. Incidentally Chicken of the Woods (Laetiporus sulphureus is the correct name for Polyporus sulphureus) is actually very commonly eaten and supposedly tasty; however it needs to be cooked before eating. The poisoning described above was probably at worst an upset stomach, vomiting, and maybe some diarrhea, nothing requiring any hospital attention. Sifaka ^talk 03:16, 24 October 2007 (UTC)

Hmmm - so what you are saying is that it may be true that bracket/shelf mushrooms are not poisonous - but there is no good rule for identifying that something actually is a bracket/shelf mushroom and not a look-alike. OK that makes our OP technically correct - but not usefully/safely correct! If 50% of people have an allergy to the mushroom - I'd be surprised if the symptoms were upset stomach, etc - we'd see allergic reaction symptoms. Of course an allergic reaction doesn't mean that the mushroom is 'poisonous'. But I don't think I'll be eating them anytime soon! Bottom line has got to be that it's just not safe to use this 'rule' to identify edible mushrooms. SteveBaker 04:28, 24 October 2007 (UTC)

Steve you appear to be right. I read it over and found this [[2]], but it seems only mature specimens cause the trouble. Sifaka ^talk 04:36, 24 October 2007 (UTC)

• It's too bad 'shroom-hunting is so tricky. I wonder if you couldn't just come up with some type of litmus test for the most popular substances these things use to kill you. --Sean 21:27, 24 October 2007 (UTC)

internal violation

My big brother wants to join the army but his mates keeps teasing him that during his medical he's going to be internally violated. But I'm to sure about this, I want to know (1) does the doctor internally violate recruits and (2) what purpose does this serve? —Preceding unsigned comment added by Everyone knows someone called Dave (talk • contribs) 22:29, 23 October 2007 (UTC)

What country/army are you asking about? - hydnjo talk 22:47, 23 October 2007 (UTC)

Probably doing a Rectal examination - possibly for Prostate issues. SteveBaker 22:54, 23 October 2007 (UTC)

If that is violation, then I have once been violated by a woman (a doctor). (no prostrate problems, I can happily tell you.) DirkvdM 09:45, 24 October 2007 (UTC)

To paraphrase Tony Soprano, "I don't even let people wag their finger in my face!". 38.112.225.84 15:26, 24 October 2007 (UTC)

• I would be very surprised to learn that young men receive prostate exams in a standard recruiting physical. It's much more likely that your brother will just receive a check for any weaknesses around the inguinal canal, which could lead to an inguinal hernia. This exam gets quite personal, but it's no "unsolicited finger in the anus". --Sean 19:19, 24 October 2007 (UTC)

Is that the legendary stand-in-a-line-and-"please cough whilst I hold your testicles" thing? --Kurt Shaped Box 20:41, 24 October 2007 (UTC)

Yes, although they don't actually hold your testicles. Rather, they "slide" a finger or two up alongside the spermatic cord. Only for some reason, "slide" usually turns out to mean "jam". :-) --David Iberri (talk) 21:14, 24 October 2007 (UTC)

• I get my revenge by turning my head towards the doctor. --Sean 21:29, 24 October 2007 (UTC)

The U.S. Army does do a hemorrhoid check, but it is a visual check and does not involve any probing. These mates are high school students aren't they? --— Gadget850 (Ed) ^talk - 08:10, 27 October 2007 (UTC)

October 24

Frosty Freezer Food

I've gone to my freezer to heat up a prepackaged frozen entree. And when I take it out of the box, I notice the food beneath the plastic wrap is buried in a heavy coat of ice crystals. Usually there are none. Does that mean this entree had defrosted at the store? Is it safe to eat? What causes frozen foods to develop ice crystals? (like that nasty layer of snow on old ice cream?) --24.249.108.133 00:29, 24 October 2007 (UTC)

It could be condensation from the air when it was frozen. The vapour pressure of water is temperature-dependent, so when the food/container was warmer before packaging, there was more moisture in the air. Once the package was sealed and frozen, that amount of moisture became higher than the decreased vapour pressure at the lower temperature. This causes the "excess" moisture to crystallize out as ice. Your food should be safe; the ice simply means it wasn't packed in a vacuum. 142.103.207.10 01:00, 24 October 2007 (UTC)

You might want to see our article about Freezer burn.

Atlant 12:46, 25 October 2007 (UTC)

Does the Earth's magnetic field rotate daily w.r.t the solar system?

Obviously, the Earth's rotation must have an effect on the magnetic field, because of the difference between magnetic and axial north, but can we say the field spins with any certainty, assuming that would be well-defined? 217.43.117.117 01:14, 24 October 2007 (UTC)

The earth's magnetic field spins along with the earth. It does slowy drift over the years, so that the magnetic poles shift over the years. The field will affect the space around the earth, out to the distance where the solar wind dominates the magnetic field. Graeme Bartlett 01:40, 24 October 2007 (UTC)

Yeah - 'true North' (as in "the axis of rotation") and 'magnetic North' (the place where the magnetic field lines converge) disagree. As the earth rotates the location of 'magnetic North' stays still relative to the surface of the earth (at least on the scale of days and weeks - it moves slowly on the scale of months and years). Hence, you would be able to measure a daily rotation of the field-lines if you were stationary with respect to the Sun. SteveBaker 04:15, 24 October 2007 (UTC)

Actually, relative to specified location of the Earth's surface, the magnetic pole describes an rough circle with a radius of tens of miles over the course of the day because it is deflected away from the position of the sun due to the magnetic field of the solar wind. Dragons flight 07:06, 24 October 2007 (UTC)

Wow! Interesting. The wobble due to the misalignment of magnetic and rotational poles is around 1000km (and moving by 40km per year right now) - so this adds a few percent to the overall effect. I guess that makes our answer to the OP's question more like: "97% Yes, 3% No". Of course there is this theory that the earth's magnetic field is about to do one of it's major North/South 'flips' any time now. All bets are off if that happens! SteveBaker 14:23, 24 October 2007 (UTC)

[Original poster]: Thanks for the replies guys - very informative. There's still one thing on which I'm not clear, but I didn't express the question very clearly: If magnetic north was identical to axial north then would the magnetic field be spinning with the earth? Do you see what I mean, the effect of the angle between the magnetic and axial poles gives the field a wobble, but apart from that wobble, is it spinning with the earth? The reason I asked if the question was well-defined is that I'm not sure in what way a spinning magnetic field would be differentiable from a non-spinning one. To illustrate, if i had an magnet and put it inside a spherical shell, and simply span the shell without the magnet spinning, would it be possible to determine from outside the shell whether the magnet span with it or not? What if it was an electro-magnet and was attached rigidly to the shell, but now we turn the magnet off, spin the shell a little and then turn it back on. Can we now tell from outside that the magnet has rotated on its axis? In the limit, would continous rotation be any different to this? Perhaps the answer has something to do with the dynamic nature of ferromagnetism... In any case, further ellucidation would be greatly appreciated. 217.43.117.117 01:53, 25 October 2007 (UTC)

Reading magnetic declination, it would seem that the earth's near-surface magnetic field does rotate along with the earth itself, even if such is not explicitly stated (what is stated is that the magnetic declination at any position on the Earth doesn't change much except over a period of years). It's the case that the magnetic field lines in the space around the earth are more oblong on the dark side due to the solar wind. So I would guess that the currents generating the Earth's magnetic field are roughly in sinc with the Earth's rotation, and the major daily influence on it is the solar wind. Someguy1221 02:21, 25 October 2007 (UTC)

Water, Specifically the acquifer under Pahrump Nevada

I have looked everywhere I can think of for the answer. We bought a home in Pahrump Nevada (Zip Code: 89060)and at the time we were told "The second largest acquifer in America is under Pahrump and stretches from the test site in the north and the Amorgosa valley to under Pahrump.

I was also told that the acquifer is 4755 feet deep, which would be a lot of water!

If you can help me with this problem, I would really appreciate it. I don't know if Wickpedia has ever processed an article on this subject, but I can hope.

Ted Farson (contact information removed to reduce spam) —Preceding unsigned comment added by 12.110.33.171 (talk) 01:25, 24 October 2007 (UTC)

What is your problem, were you misled? Graeme Bartlett 01:43, 24 October 2007 (UTC)

I googled on "pahrump aquifer site:gov" and found this and this (be sure to see the clickable Fig.s). --Milkbreath 03:41, 24 October 2007 (UTC)

Water content of canned tomatoes

How much water is in one 796ml can of ground tomatoes? NeonMerlin 06:18, 24 October 2007 (UTC)

A tomato could have 95% water, so 756 ml of water. Graeme Bartlett 07:07, 24 October 2007 (UTC)

Yeah, but 95% by volume or 95% by mass? NeonMerlin 17:59, 25 October 2007 (UTC)

What is not water in a tomato is mostly carbohydrate with a density near 1, so the difference between mass or volume is not great, and that 95% is only approximate, so that would accomodate any uncertainty. Graeme Bartlett 00:08, 26 October 2007 (UTC)

Charge conservation in electrochemical cells

Hi I am trying to show mathematically that the voltage across an electrochemical cell will decay with time. Is this a valid approach? $I={\frac {Q}{t}}$ and $V=IR$
--> $V={\frac {Q}{tR}}$

Clearly R is a constant, but is Q for particular electrochemical cell? Or should I use $\Delta Q$? Also does this value of Q or $\Delta Q$ change depending on the ratio of concentration of ions in the half cells (according to the Nernst equation initial voltage is the same for the same ratio of product ions and reactant ions)?

My problem comes down to applying the conservation of charge to electrochemical cells. Thanks in Advance

Lots of dupes removed. Lanfear's Bane | t 09:08, 24 October 2007 (UTC)

This slow internet connection is getting annoying. I would've beaten you to the punch if loading didn't take so long. - Mgm|^(talk) 09:14, 24 October 2007 (UTC)

No. It looks like your using a similar method to that used to find find the voltage accross a capacitor. eg see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capdis.html for a solution

The electrochemical cell doesn't store electricity as 'charge' - but as changes in the chemistry of the contents..

The usual method to calculate the voltage is to start with the energy change for the process happening eg Fe + Cu2+ >> Fe2+ + Cu Energy change = E (kJ/mol) then divide by the number of atoms to get the energy change per atom (call this X).. Since a charged particle of charge q requires energy X to move through a potential V ie X=qV gives V=X/q (q is the charge released by the reaction)

If X is constant then V is constant - however X can change for various reasons - mostly due to concentration.. (the are models of this - mostly the Nernst equation)87.102.94.157 11:45, 24 October 2007 (UTC)

Virtual Reality for video games, and resolutions

Is there a limit to how high of a resolution can be displayed in a VR headset? From my understanding, VR headsets have very low resolutions, especially compared to computer monitors or high definition televisions. Also is it possible for VR headsets to replace televisions or monitors for video games? I know it has been tried with some failed attempts (virtual boy, but will it ever catch on? What kind of technological challenges need to be overcome before it becomes a practical technology? 64.236.121.129 14:40, 24 October 2007 (UTC)

The limit is the resolution of the headset itself. Most of the cheap ones use LCD displays of fairly poor resolution (the kind you have in cellphones typically) - and that's the limiting factor. In my last job (Flight Simulation), we had 1600x1200 stereo head-mounted displays - you could buy a REALLY nice sports car (think 'Lamborgini') for the cost of one of them - and they were extremely fragile! The 1280x1024 device is here: [3]. The problem with it 'catching on' is that to do it right is still too expensive and if you do it wrong, people get headaches, nausea, eyestrain, etc. We just need lower cost, higher resolution panels and cheaper optics. The display resolution problem is obvious. The optics problem is 'eye relief' - you can't put a simple pair of screens into some glasses - your eyes don't like focussing down at one or two inches for long periods of time. You need 'collimating' optics to allow them to focus on a virtual image at least half a meter away (preferably more). But it can certainly be done - it's just a matter of cost. SteveBaker 15:38, 24 October 2007 (UTC)

Body Strength

what is the main compononet that gives the muscle cells its strength and can a compononet be added to make it strong as metal????

Please see the section above where this has already been asked and answered. — Lomn 16:46, 24 October 2007 (UTC)

can you permanentaly stop PKC (Protein Kinase C) activity in vivo ?

if yes, with what? —Preceding unsigned comment added by Poppynash (talk • contribs) 17:00, 24 October 2007 (UTC)

Kind of. Isoenzyme-specific PKC inhibitors such as Go6976, safingol or rottlerin, and broad-spectrum PKC inhibitors such as bisindolylmaleimide may partially or fully inhibit PCK function in vivo, but only for as long as you continue to provide the inhibitors to the cells of interest. You can't just apply a single dose of inhibitor an expect PKC to stop functioning permanently. That is not possible. Rockpocket 18:31, 24 October 2007 (UTC)

Some Protein kinase C isozymes have been been knocked out using mice as the experimental system[4]. --JWSchmidt 01:24, 25 October 2007 (UTC)

Time Dilation

Assuming a traveller sets of from the Earth at a constant velocity of half of the speed of light for a round trip of 8 years (as experienced from the Earth's reference frame), would I be correct in saying that the traveller only experiences approximately 6.928 years? --80.229.152.246 21:02, 24 October 2007 (UTC)

Yeah, you got the right answer. A real traveler doing a round trip like that would want to spend a total of on the order of a year doing all the accelerating and decelerating involved, so he doesn't get squished like a bug. Accelerating to half the speed of light in just a day or two is not something you want to do! But special relativity classes tend to just ignore that little detail, and assume that the acceleration duration is a negligible portion of the trip. MrRedact 22:30, 24 October 2007 (UTC)

Er, why would you take longer than a day or two? At constant 9.8m/s^2, you hit the speed of like in about 8.5 hours. --Wirbelwindヴィルヴェルヴィント (talk) 23:05, 24 October 2007 (UTC)

Might want to check your figures there (assuming "like" is a typo for "light"). I think you dropped about three zeroes. Not counting relativistic effects. --Trovatore 00:04, 25 October 2007 (UTC)

Guys - this is not exactly rocket science! v = a.t - so t = v/a - if you want to go at (say) half the speed of light with an accelleration of 1g then you have t = (2.998x10⁸/2)/9.8 seconds which is over fifteen million seconds which is about 177 days. So - yeah - you need six months to get to half the speed of light and another six months to slow down again at a comfy 1g. So MrRedact is exactly right and Wirbelwind needs some more calculator batteries! We are wise to choose half the speed of light because you can pretty much not worry too much about relativistic effects at that speed (for back-of-envelope calculations at least). You can't reach the speed of light no matter what - and even getting reasonably close to it is going to take you an insane amount of time. SteveBaker 01:22, 25 October 2007 (UTC)

I agree with everything Steve says -- except the part where he says "this is not rocket science"! --Anon, 08:04 UTC, October 25, 2007.

Incidentally, the original poster referred to a round trip "at constant velocity", which is impossible if "velocity" is being used as a physicist would to mean a vector quantity. At constant velocity, you can't turn around and come back! But a round trip at constant speed is possible by traveling in a circle, for example. (The half year-or whatever of acceleration would then have taken place before the trip began.)

Sorry, that should be 'a trip of around 8 years'. That's what asking questions when you are far too tired does... --80.229.152.246 11:54, 25 October 2007 (UTC)

For the circular trip to take 8 years at c/2, the circular path must have a circumference of 4 light-years and therefore a radius of 2/π light-years or 6.02×10¹⁵ m. To stay on the circular path therefore requires a continuous thrust (centripetal acceleration) of v²/r = (1.50×10⁸)²/(6.02×10¹⁵) = 3.74 m/s or about 3/8 gee. At least, that's as perceived in our external reference frame; I'm not sure how relativistic effects might change it in the spacecraft's frame. --Anon, 08:07 UTC, October 25, 2007.

Strong Force vs. Electromagnetic Force

How close do 2 protons have to be for the Strong Force to overcome the repulsion of the Electromagnetic Force? Sappysap 18:18, 24 October 2007 (UTC)

It never does. Luckily for us. If Helium-2 were a bound state, all the stars would explode. --Trovatore 18:33, 24 October 2007 (UTC)

Wow! Diprotons, thank you for telling me about them. One follow-up fantastical question if no one minds :) Can an analogy be made between nuclei, which attract at short distances and repulse at long distances, and matter in general which attracts at short distances (say within the range of a galaxy) but seems to repulse at long distances (galaxies are all moving away from each other)? Perhaps the large scale acceleration of galaxies isn't due just to the momentum from the Big Bang. I'll gladly share a Nobel Prize in Physics for any helpful consideration! Sappysap 18:51, 24 October 2007 (UTC)

The movement of galaxies away from one another over long distances is not do to any repulsive force between them, but merely to the expansion of the universe, which only overtakes gravity at long distances. Someguy1221 19:36, 24 October 2007 (UTC)

Possible to generate a magnetic field to repel bullets?

Is it possible? —Preceding unsigned comment added by 64.236.121.129 (talk) 19:31, 24 October 2007 (UTC)

Well, if theyre made from iron, maybe. The earth has such a shield - the magnetosphere - which, according to our article Van Allen Belt is equivalent to 1 millimetre of lead. (That number of course applies to charged particles, not uncharged bullets, so we can be off "by a long shot", but it should give you an idea of the magnetudes (sorry about the silly pun) involved.) — Sebastian 19:46, 24 October 2007 (UTC)

However, since bullets aren't made from iron or other ferromagnetic materials (they're primarily lead, often with a copper jacket), the short answer to the question is "no". Bullets are not magnetic, and so cannot be repelled by a magnetic field. — Lomn 19:51, 24 October 2007 (UTC)

That's not quite right - a non-ferromagnetic conductor moving in a magnetic field will have a current induced in it - and hence become an electromagnet - and could be deflected.. I still imagine that in practice the answer is no - the magnetic generation apparatus would be massive - the best way to utilise it therefor would be to hide behind it!87.102.94.157 19:57, 24 October 2007 (UTC)

What if, the generation device was powered by some kind of advanced Micropower, along with other advanced technologies. Hypothetically, with advanced technology, is it scientifically possible? 64.236.121.129 20:10, 24 October 2007 (UTC)

If we're going to jump that far, why even bother with magnetism? We might as well jump to science fantasy and invent some Treknobabble about reversing the polarity to stop the bullet. In that case, sure. But I'll stick with "no" for my answer. A magnetic field will not stop a bullet. — Lomn 20:47, 24 October 2007 (UTC)

Because we know magnetism exists, and micropower, is also an area of scientific research. "Trecknobabble" as you put it, doesn't and isn't. 64.236.121.129 20:56, 24 October 2007 (UTC)

Magnetism exists -- but there's no reason to expect it to have any effect. Micropower is just a power source, providing the same power as any other power source, and a particularly ill-suited one. Thirdly, your (first) post throws out unspecified "advanced technologies". So you're asking hypothetically, with a theorized power source of dubious merit, using other things that aren't even articulated (much less things that exist), can we use a force that doesn't have a relevant effect to do what we want?" I could say that cold fusion could amplify the strong nuclear force of tissue paper to stop bullets and be just as scientifically useful. — Lomn 21:15, 24 October 2007 (UTC)

An electro magnetic field would affect the movement of bullets. I think 87.102 already pointed that out to you. I don't think the OP was asking you, but he's asking if a powerful electro magnetic field would stop bullets. I think he just added "advanced technology" to mean making the power source small, and extremely powerful. The answer is yes, with enough energy, an electro magnetic field can. Also I must remind you to be civil, and helpful. No need to be condescending with words like "trecknobabble". It's not very helpful, and only serves to ridicule the question. Malamockq 02:59, 25 October 2007 (UTC)

Lomn's mad haha. Anyway I think we already established that a magnetic field would affect a bullet. That's relevant. I'm not sure you have the proper education in this field to answer my question. 64.236.121.129 13:44, 25 October 2007 (UTC)

I feel that it's extremely important on the science reference desk that answers remain grounded in science. With sufficient unfounded assumptions, we can answer "yes" to any "is x possible" question and not do any of them justice. Rather, I find that "is x possible?" needs a healthy dose of "is it possible now or in the near future, with equipment appropriate to the application, etc, etc". It's important to point out to people, then, that "magnetism exists" says nothing about whether it's applicable and that "micropower" is irrelevant in a macropower application. Further, I dispute your allegation that treknobabble is condescending. In fact, I find it a quite precise description of the "solution" presented above. As for "mad" -- not really, though I'm disappointed when hand-waving is seen as a valid method of problem-solving. — Lomn 13:47, 25 October 2007 (UTC)

Well I was just curious if it could ever be made in the future. Of course I know it can't be made now because if we could, then we would have them! No need to explain why it can't be made now because I already know why. I mentioned micropower for obvious reasons. This kind of technology would be most useful on a soldier, you would need some kind of small power source, that's still powerful. Incorporated into a powered exoskeleton perhaps. If you are going to participate in the discussion, it would be nice if you at least concede that magnetism/electro magnetism does affect the movement of bullets. 64.236.121.129 15:43, 25 October 2007 (UTC)

Lead conducts electricity right? Couldn't the kinetic energy in the bullet be converted to electrical energy and get dissipated in internal resistance inside the bullet? 64.236.121.129 20:04, 24 October 2007 (UTC)

Not really. While moving through a magnetic field perpendicular to the bullet's direction of motion, a voltage will be induced across the bullet. However, once the maximum voltage is reached, electron flow stops, and the magnetic force on the electrons in the bullet will still equal that on the protons, and so there will be no net magnetic force on the bullet. Now, since all materials have at least some diamagnetic character, you could try to repell the bullet in this manner. However, it generally takes the most powerful sustainable magnetic fields to simply counteract gravity using diamagnetism, so good luck deflecting a moving bullet with it. Someguy1221 20:18, 24 October 2007 (UTC)

The voltage induced will cause a current eddy current might be useful here - it's possible that using a field strong enough to deflect a bullet would induce such a current that the bullet (lead) is melted due to resistance heating - so now you'd be hit by moltenlead . no good.87.102.94.16 12:47, 25 October 2007 (UTC)

If it were to turn to molten lead, it might not be as bad at all. The bullet would lose most of its armor penetrating ability. Combined with ceramics, kevlar, heat resistant materials, or better, a powered exo skeleton, it would work. 64.236.121.129 16:09, 26 October 2007 (UTC)

An interesting point, since "just use kevlar" is of course the trivial answer to this problem. Since you're absolutely convinced that this must be possible, though, in light of all the problems, what-ifs, maybes, and inaccuracies riddling this discussion -- why even ask in the first place? It seems you've had your mind made up from the beginning. — Lomn 17:38, 26 October 2007 (UTC)

Kevlar can't protect against armor piercing rounds or rounds fired from an assault rifle or similar weapon. If this magnetic field really did melt the bullet before it hits, the kevlar would protect against it even if it was an armor piercing round. Malamockq 00:48, 30 October 2007 (UTC)

"Ribbit"

• If you could diamagnetically accelerate a frog with sufficient velocity towards the bullet, it would stop it. --Sean 21:22, 24 October 2007 (UTC)

Perhaps you should use Electromagnetic radiation to zap the bullet with so much energy that it evaperates before it strikes you — a laser ray gun should do the job, but it will have to be very high power to deliver enough punch! Graeme Bartlett 06:09, 25 October 2007 (UTC)

Since the OP doesn't like my "no" answer, here's the alternate thought problem: suppose you've found a way to repel a bullet with a magnetic field. What happens to all other matter in the vicinity? If you can stop a bullet speeding towards a soldier, what happens to the soldier's rifle and ammunition (or hell, his dog tags?) What happens to his arm as soon as he moves it? It's diamagnetic, too. So here you go: once you solve the utterly impractical problems of stopping a bullet with a magnetic field, you've generated the parallel problems of stopping everything else, too. — Lomn 14:00, 25 October 2007 (UTC)

Uhh, we aren't talking about using diamagnetism to deflect bullets. 64.236.121.129 15:49, 25 October 2007 (UTC)

As best I can tell, that's the only form of magnetism relevant to a copper-jacketed lead bullet. — Lomn 16:31, 25 October 2007 (UTC)

Electro magnetism. 64.236.121.129 17:15, 25 October 2007 (UTC)

That's not really an answer. Materials are ferromagnetic, paramagnetic, or diamagnetic. An electromagnet is presumably what would generate the bullet-stopping magnetic field, but it still has to act on a diamagnetic material -- which is to say, it hardly acts at all. Throw in the loopy-high power requirements (a man-portable nuclear reactor?), posit the room-temperature superconductors that are probably required, consider that the bullet has a high energy to mass ratio (remembering that you have to dissipate the energy while using the mass as your base of magnetic force -- this is far more difficult than, say, levitating a stationary bullet), and by the time you've got something that can stop a bullet, you've got untold other side effects that make the entire exercise moot. — Lomn 18:09, 25 October 2007 (UTC)

Now, I could be wrong on the details, but I just recalled a physics lecture I attended in which the professor swung a pendulum (I think it was copper, could be wrong) through a powerful magnetic field (don't remember if it was static or dynamic), upon which the pendulum stopped essentially instantly. Does an experiment like this sound familiar to anyone? Someguy1221 18:56, 25 October 2007 (UTC)

It sounds like he was using the pendulum as the coil of a generator. In that case, the pendulum is set up to efficiently turn its kinetic energy into electrical energy upon encountering a strong magnetic field. --Carnildo 22:52, 25 October 2007 (UTC)

Yea, that sounds awfully familiar to a post I made earlier. I said a bullet would have its kinetic energy turned into electrical energy if it went through a magnetic field, to which Someguy1221 said it wouldn't. Hah. 64.236.121.129 13:05, 26 October 2007 (UTC)

No, it won't. A bullet travelling through a magnetic field is an open-circuit generator, and won't produce significant amounts of electricity. The pendulum is probably set up as a short-circuit generator, which is very effective at turning kinetic energy into electricity, and from there into heat. --Carnildo 22:00, 26 October 2007 (UTC)

Not to mention your opponent is probably going to use his/her portable nuclear reactor to power an energy gun or something else for his/her robot making your 'bullet stoppind magnetic field' particularly useless. Nil Einne 19:23, 25 October 2007 (UTC)

Ho ho! But we are talking about stopping bullets! We aren't talking about directed energy weapons. If anything, a device that could stop bullets would spur weapons development in that direction, certainly. But we are just talking about if it can be done. 64.236.121.129 20:43, 25 October 2007 (UTC)

I think the most important idea to keep in mind here is that, very simply, any simple magnetic field capable of stopping a non-magnetic object like a bullet would also put significant force on just about anything else passing through it (see the frog, above), which would make this a somewhat impractical method of bullet proofing yourself. Someguy1221 20:53, 25 October 2007 (UTC)

Again, we aren't talking about using diamagnetism, but in all fairness, if you did have a device that powerful, it would be useful for spacecraft. 64.236.121.129 13:09, 26 October 2007 (UTC)

Any extermely powerful magnetic field would set up an eddy current in the bullet as it moves into the field. This will produce a force opposing entry. With Newton's 3rd law the force will also appear on the magnet. I have seen Someguy1221's metal being severly slowed down by a magnetic field. WIth a strong static magnet with poles close together, moving an aluminium plate inf the field was like moving it through honey, the faster it moved the more the resistance. Graeme Bartlett 00:24, 26 October 2007 (UTC)

So if you fired a bullet at a powerful magnetic field, the bullet would slow down then fall harmlessly despite it being diamagnetic? 64.236.121.129 12:57, 26 October 2007 (UTC)

Geeky TV

Do you guys just love Big Bang Theory? Like you've been waiting for this show you're entire lives, right? Beekone 20:45, 24 October 2007 (UTC)

Utter, utter, utter, utter', CRAP. Proper science geeks like: (a) Top Gear, (b) Mythbusters, (c) Junkyard-Wars/Scrapheap-Challenge (before they screwed it up in the last couple of series). SteveBaker 20:51, 24 October 2007 (UTC)

and look around you for a laugh. Theresa Knott | The otter sank 22:43, 24 October 2007 (UTC)

Right - I "lost it" at "H twenty" - hydnjo talk 00:57, 25 October 2007 (UTC)

"Germs originated from Germany, before spreading rapidly to the rest of the world" RHB - Talk 22:51, 24 October 2007 (UTC)

I lost it at the 1000 degree boiling point, then the hand reaches in and just grabs the egg out of the water XD --ffroth 21:57, 26 October 2007 (UTC)

OMG those are funny! I had the best laugh today watching the Maths episode than I've had in many months. I was laughing uncontrollably with tears in my eyes for several minutes, triggered by the absurdity of the first story problem. MrRedact 07:12, 25 October 2007 (UTC)

Top gear? I assume you mean the BBC car show. That's not science, that's everyday technology. No, it isn't even that - the little I have seen of it is not abut the innards of a car, but about how fast it accelerates and how it looks. Yawn. Instead, try World Solar Challenge, a current event, or DARPA Grand Challenge, the next edition of which will be in just over a week, on 3 November. Especially the latter is so much at the forefront of technology that science geeks can't help but be thrilled. And it's bound to be shown at a tv set near you. On top of that, it's about something that could help save the planet ("Oh, Flash, I love you. And we only have a few years left to save the Earth!"). DirkvdM 07:17, 25 October 2007 (UTC)

Am I the only one who thinks that Mythbusters is pretty horrible? Their complete disregard of anything resembling the scientific method, or even basic logical thought anger me to no end. Their typical method is "1)Perform experiment with so many uncontrolled variables that it doesn't come close to proving or disproving anything. 2) If step 1 didn't involve blowing something up, modify the experiment so that something blows up and perform it again. 3) Smugly announce that the myth is 'busted'.69.95.50.15 15:56, 25 October 2007 (UTC)

I got to tell you, I'm a little surprised. Science baffles me to no end, but I think Big Bang Theory is hilarious. If I was a physicist I imagine that would be an accurate portrayal of my life, or if I had a friend who was a geeky scientist I think that's what they would be like. Emphasis for hilarity aside, you got to admit some of their geeky quirks are right on. Right? A little? Beekone 16:02, 25 October 2007 (UTC)

I agree with you about Mythbusters, particularly because they often claim that they're using science. Really, they're all just special effects geeks for hollywood. -- JSBillings 13:33, 26 October 2007 (UTC)

Of course it isn't actual, write-a-paper-publish-in-a-journal kind of science. The point is that they do actually test these myths. Very often with mythbusters, when they announce the myth, I sit up and think "hey yea, I wonder if that's true". And usually they do provide an answer, and usually it's the best answer that you're ever going to get. Real science just can't or won't answer most of these questions. They're not being completely scientific, but they're mimicking the scientific method, to provide enough insight into the question, for me to be satisfied. So it's not just about doing random cool stuff, like so many of these 'cool science' shows. Most of the value comes from the answers that they get. risk 13:45, 26 October 2007 (UTC)

It's not full on hard-core science - but it has a lot of the basics right - they usually have controls for their experiments and they measure things. They make a lot of mistakes and assumptions too - and some of the things they do are clearly flat out wrong. But it has the desired effect of being entertaining and making you think. (Even if it's only "Ooohhh - they got that wrong because they forgot to allow for such-and-such.") If you actually watch the show, they very often use the "PLAUSIBLE" conclusion when something seems true but may not be. They pretty much only use "CONFIRMED" if they managed to reproduce something AND they discovered documentary evidence that it actually happened as described. But some things they are definitely able to bust - conclusively. The old story that if you throw a penny off the top of the empire state building it'll crack the concrete when it hits the ground. They build a miniature wind tunnel - they use it to measure the terminal velocity of a penny - then they make a gun that can fire a penny at speeds well in advance of it's terminal velocity - then they fire pennies at a concrete paving slab of the same kind as the ones used in New York - and the concrete doesn't break. They ramp the speed up and up and they still can't break it even at speeds far in excess of the terminal velocity of a penny. Then (here is the dubious bit) they make a dummy head (yeah - right) and shoot the penny at that and nothing much happens. I don't buy the idea that an old, dried out human skull embedded in ballistics gel necessarily fractures at the same impact loading as a real human skull which is still alive, immersed in fluids and containing a brain. But this test simply gives them the confidence to shoot the penny at each other - and the skin isn't even broken. That's a pretty conclusive "MYTH BUSTED" that it would difficult for a hard scientist to argue with. I feel better off knowing that this is urban legend. Other things they do are much, much worse. Their reliance on the "fact" that ballistics gel mimics all sorts of properties of a human body or that the wooden limbs on 'Buster' the crash test dummy will in fact break when a human limb would break...Nah - nonsense. But some things are genuinely clever and the results are FAR from obvious. SteveBaker 20:16, 26 October 2007 (UTC)

Of course it's pretty obvious that a penny, being a flat piece of metal (not a sphere), would never reach a high enough terminal velocity to do much damage. The idea of having one drop on my head is a different matter, though. But I suppose even that would indeed be safe. This reminds me of when my brother was on top of the Pisa tower he couldn't resist the temptation to 'play Galilei' and drop an orange. When he was back down and inspected the 'drop zone' he found that it had drilled a distinct hole in the ground. Size is nothing. Round is everything. Or pointy, of course. I wonder what a dart would have done. DirkvdM 17:37, 27 October 2007 (UTC)

How do enzymes evolve?

When I asked my Biology teacher, he fobbed me off with "lots of proteins are created, the beneficial enzymes are the only ones that survive further i.e. survival of the fittest except enzymes aren't alive." Our FA on enzymes mentions little on the subject. Is there any proper, researched mechanism for their evolution? Thanks, RHB - Talk 22:47, 24 October 2007 (UTC)

Beneficial is very vague. What's beneficial for one species could be death for another. bibliomaniac15 A straw poll on straw polls 23:10, 24 October 2007 (UTC)

Which of course suggests that organisms which create proteins that kill themselves off are not going to be the fittest. Which illustrates well, of course, the idea that the enzymes are not what is being selected for—its the protein creation by the organism. --24.147.86.187 23:22, 24 October 2007 (UTC)

Your teacher is more or less correct. Enzymes don't evolve. They function like little tools in the cell, so your question is like asking how hammers evolve. But the DNA that gives instructions for how to make an enzyme is subject to random mutations. If that piece of DNA does mutate, then the resulting enzyme may work better, or worse, or show no functional change. If the change makes the enzyme work better, let's say faster or use less energy, then the cell stays alive and that change is passed on to future generations: a different enzyme structure than before. But usually the change makes the enzyme work worse and the cell dies. Delmlsfan 23:27, 24 October 2007 (UTC)

Wikipedia has Molecular evolution. --JWSchmidt 00:12, 25 October 2007 (UTC)

Enzymes don't evolve (indeed, they're not alive), organisms that produce the enzymes evolve, and the ones that produce the right enzymes are the ones that survive, to put it simply. Or do you mean to ask how the first enzymes came about? One theory is that they are being made in certain areas of space (forgot the details) and that some of those landed on Earth and kick-started the evolution of life. I am surprised there is nothing on this in the enzyme and protein articles. At least, I can't find it. DirkvdM 08:06, 25 October 2007 (UTC)

One thing about the phrase "enzymes don't evolve." This may be more semantics than anything. We freely talk about how organs evolve, so why not enzymes themselves? When we talk about wing evolution, for example, we don't need to acknowledge that a wing by itself is alive. We're really talking about the evolution of the genes that are responsible for the wing formation. Same thing with enzymes. While enzymes are non-living, we can talk about how enzymes evolve because we're referring to the evolution of the genes coding for the enzymes. In fact, I did a quick search at pubmed and found that researchers use the term enzyme evolution liberally. 128.163.196.164 17:06, 29 October 2007 (UTC)

A minor quibble—generally when astrobiologists talk about getting the molecules of life from space, they usually mean stuff that's a lot simpler than full-sized proteins. Radio astronomers have detected enormous quantities of a number of small carbon-containing compounds that could be building blocks for biomolecules—simple alcohols like ethanol, and even amino acids like glycine. If the Solar System passed through such a cloud at some point, it could have gotten a nice dose of bioavailable carbon. Another model suggests that life got a helping hand from carbon-containing meteorites (see carbonaceous chondrite). Representing perhaps 5% of all meteorites, these guys are loaded with carbon compounds, again including some of the small molecules of life.

For a discussion of the arrival of more complex 'life from space', you'll want to look at our article on panspermia. Setting aside the flakier bits, the scientific kernel is that life on Earth could have originated on other planets (and possibly in other solar systems). During a powerful meteorite strike, fresh material from the planet's surface can be blown back into space; this material will drift until it hits something else (small meteorites from Mars regularly land on Earth, for example). For small particles, it's possible – at least theoretically – for the solar wind to drive material out of the solar system altogether and into interstellar space. In principle, it's possible that such a particle escaped from another planet billions of years ago, and seeded life on Earth. Inconveniently, however, it still leaves us with the question of where did that life come from.... TenOfAllTrades(talk) 14:00, 26 October 2007 (UTC)

What kind of mechanisms are you specifically wondering about? Because any kind of mutation in a gene will result in a mutant form of an enzyme--after all, DNA codes for enzymes. The basic mutations/recombinations you learn about in genetics-- insertions, deletions, translocations, duplications, etc. all provide the possibility for new and different enzymes to evolve. 128.163.224.198 16:00, 29 October 2007 (UTC)

Size limit of the human body

I remember reading somewhere that there's a theoretical limit to how large we can become evolutionarily speaking due to the fact that as we get larger our weight increases volumetrically but bone strength only increases in cross-section so eventually our skeletons would be unable to support our bodies. Anyone know what the limit might be? Exxolon 23:08, 24 October 2007 (UTC)

Wikipedia has Robert Wadlow, "the tallest person in medical history for whom there is irrefutable evidence". --JWSchmidt 00:03, 25 October 2007 (UTC)

I remember hearing about a much lower limit when falling on you're face becomes potentially lethal. That limit wasn't much larger than our current size. — Daniel 02:57, 25 October 2007 (UTC)

You say "we" and "human body" as if you're talking about humans, but "evolutionarily speaking" as if you're talking about some future species that might be descended from humans but would not be called human. In the latter case, there is much more scope for growth despite the square-cube law by evolving thicker limbs the way hippos and elephants have. The limit in that direction must be at least as large as the largest land animals that have ever lived, i.e. the larger dinosaurs. You could even imagine a being with dinosaur-strength legs but in great numbers like a millipede. I can't imagine any circumstances where that sort of body would be advantageous for an intelligent being (for one thing, the food requirements would be immense!), but it would be physically possible.

On the other hand, if you're talking about beings we would recognize as human, then the limit is set by how far we could evolve in the direction of thicker bones and stronger muscles and still be recognized as human. That is, it's basically arbitrary. --Anonymous, 08:18 UTC, October 25, 2007.

After edit conflict:

Right, that's what I thought too. Our walking on our hind legs makes us rather different from other animals that got to be very big. But of course we could evolve back to four-footers (for whatever 'reason'). In which case I don't see what would stop us from becoming as big as dinosaurs. Btw, do you mean big or tall - weight or length? DirkvdM 08:22, 25 October 2007 (UTC)

A different solution would of course be to go another step 'back' in evolution and enter the water again. Whales are the largest animals that ever lived. And they are supposed to be fairly intelligent, so maybe it wouldn't be such a stupid thing to do. :) DirkvdM 08:25, 25 October 2007 (UTC)

There is no limit speaking in terms of evolution. If an Argentinasaurus can evolve from a macro molecule, then it's possible for human to evolve into an animal that's extremely tall too, but I can't imagine how it could possibly happen with natural or artificial selection. Nothing favors a tall human. The taller you are, the more health problems you have. They aren't better in combat/war, so they don't make better soldiers. They may have some physical advantages (Bubba can make for a good construction worker), but social trends show that humans are using less of their bodies, and spending more time just sitting around doing things that require brain power, rather that physical power (that includes watching TV or playing videogames). And Mr. Brainiac can just build a powerful robot that's stronger than Bubba anyway so it makes for a better construction worker, so who needs Bubba? 64.236.121.129 16:09, 25 October 2007 (UTC)

We also have to consider the effect of the square-cube law in relation to lung capacity. If you maintain the same density, then as you increase the human size further up the scale, the body mass (the cells of which must be oxygenated or die) increases as the cube of the multiplier, but the surface area of the lungs increases only as the square of the multiplier. Eventually you reach a point where the lungs must either undergo an evolutionary change to become more efficient (and thus able to oxygenate the increased mass) or else be unable to support the oxygenation needs of the larger body. Even before that point is reached, the relative effeciency of the lungs would decrease so much that the larger-scaled human would be at a survival disadvantage, with that disadvantage becoming more and more pronounced until the lungs fail to support life functions. 152.16.188.107 02:48, 26 October 2007 (UTC)

Isn't it usually herbivores that achieve the largest sizes? They don't spend quite as much energy as carnivores. They just trot along grazing and use their body size to repel carnivores. SO maybe if we all became vegetarians ... . Another thing is that humans (and other animals) might get bigger if there is more oxygen in the air. I know that is the reason that in somewhere in the past insects (which have very inefficient 'lungs') managed to get very big. DirkvdM 06:58, 26 October 2007 (UTC)

Insects in the past were bigger than they are now - but I don't think that they were ever huge as far as huge things go. Birds have much more efficient lungs than humans, so I suppose that the potential is there for them to become gigantic if flight is abandoned, as demonstrated by the ostrich, moa, terror bird, etc. --Kurt Shaped Box 09:23, 26 October 2007 (UTC)

Gigantic insects were around at the time when there was a lot more oxygen in the atmosphere. Since they absorb oxygen by diffusion through spiracles, a small increase in the partial pressure of oxygen allows a large increase in body size. SteveBaker 19:53, 26 October 2007 (UTC)

Some other factors that limit the size of land animals are circulatory and nervous systems. A single heart eventually can't manage to pump blood quickly enough, so other strategies are needed, like muscle contractions along veins and arteries, combined with one-way valves (and a slower metabolic rate). The nervous system becomes too slow eventually, so more distributed control is needed. We already have reflex actions, which don't need to be processed by the brain. More such distributed reflex action would be needed in a huge land animal, say to control walking and balance. StuRat 20:46, 28 October 2007 (UTC)

About that last bit, it would likely be a very slow animal, so that doesn't seem necessary. And it would probably develop very big feet for stability. Actually, it could probably not lie down to sleep, so the legs would have to 'lock' for that. Of course that would have to be taken to the extreme for a bipedal animal like a human (if we can still call it that). DirkvdM 07:29, 29 October 2007 (UTC)

Honey

I bought some honey, the kind that comes in a plastic bear, and now that it's down to the last quarter or so of the bear I've noticed that the remaining honey is extremely grainy and thick, even to the point where it's a struggle to squeeze it out. Also, the honey is now a different, lighter, color than when I first got it. Was wondering if anyone knew why this might be? Thanks. 38.112.225.84 23:12, 24 October 2007 (UTC)

Sounds like it's crystallizing (probably various sugars that were dissolved in the liquid). DMacks 23:45, 24 October 2007 (UTC)

If you set the bear in a pan of hot water the honey will go back to normal. --Milkbreath 23:52, 24 October 2007 (UTC)

Bear? What bear?

I also assume it's crystallisation, but isn't that caused by drying out? So how would heating it help? And would it remain uncrystallised after it has cooled down again? DirkvdM 08:30, 25 October 2007 (UTC)

Here is a picture of the bear. But I don't know why honey gets fluid again when it's warmed. Lova Falk 09:00, 25 October 2007 (UTC)

The sugar that has crystallised redissolves when warmed. There's a more scientific explanation for why this happens if you ask...87.102.94.16 12:42, 25 October 2007 (UTC)

I know enough science to know that if you don't use mathematics you're talking crap, but I don't mind talking it. I wonder if there's a userbox for proficiency in crap. Honey is a supersaturated solution of sugar in water. If there is nowhere for a crystal to get started, that is, the inside of the container is smooth, it will sit like that a pretty long time, but eventually a crystal will get started and the jig is up. That's how you make rock candy. If you heat the solution the water can hold more sugar in solution, and the crystals redissolve. --Milkbreath 13:05, 25 October 2007 (UTC)

87.102, I thought by posting my question on the Science desk I was asking...:) Thanks for the answer/links Milkbreath, worked like a charm. As to a userbox for proficiency in crap, I believe that

BA	This user has a Bachelor of Arts degree.

would work in a pinch. 38.112.225.84 14:35, 25 October 2007 (UTC)

October 25

String Theory

There have been countless complaints all over the classroom. This weird, nerdy kid in my class is COMPLETELY and UTTERLY obsessed with string theory. He happened to ask every teacher he's met so far about string theory. What is string theory, anyways? Asking just out of curiousity, and a way to shut him up. I looked it up, but I eventually decided that if I devoted my life to deciphering that page, I'd be eternally confused. I'm no math or science geek here. Make your explanation simple enough for my simple mind to understand. Heh. Had to get all complaints out of my system. Sorry 'bout that. —Preceding unsigned comment added by 68.100.133.160 (talk) 02:06, 25 October 2007 (UTC)

No big problem but in the future please edit your posting rather than reposting the entire new version. I've deleted your earlier versions. Also it's a good idea to sign your posts with four tildes like this: ~~~~ . hydnjo talk 02:20, 25 October 2007 (UTC)

Wikipedia insisted that there was a problem when I tried to post my question. Lots of failed attempts.

As basically as I can put it...In physics, fundamental particles (like quarks and electrons, not protons and neutrons, which are made of quarks) are usually considered to be dimensionless (lacking extent in any direction) points in space (when it's a particle, and not a wave, but you wanted simple, so don't ask). In string theory, they are considered to have extent in one direction, making them little curved lines (or strings) instead of points. This leads to a number of very wierd predictions, like the existence of more dimensions than we can see or experience, and particles that have never been observed. The problem with string theory is that while it agrees with "normal" physics, its new predictions are entirely unprovable with any imaginable technology, let alone any existing technology. Someguy1221 04:06, 25 October 2007 (UTC)

I'll try to go even a little simpler, assuming very little knowledge of science: String theory deals with the very smallest parts that everything in the universe can be divided into. If you divide practically anything that exists, like your body for instance, into its very smallest parts, you'll get four kinds of parts: "electrons", which are the smallest pieces of electricity that there can be, "photons", which are the smallest pieces of light that there can be, and a couple other wierd parts called "quarks" and "guons". Those little parts are the smallest things that exist; you can't split them up into anything smaller. In fact, with the normal way that scientists make the most accurate possible calculations about how those parts behave, they treat those parts as not having any size at all. One of those little parts is treated as just being a point with no size.

String theory is a newer way of making calculations about how those little parts behave. In string theory, those little parts are no longer treated as being just a point with no size. Instead, the little parts are treated as being a little curvy line.

Another way that string theory is different from the normal way of making calculations about how the little parts behave is that according to string theory, there exist extra dimensions that we normally don't notice. A "dimension" can be thought of as a combination of a direction and the opposite direction. Space is normally treated as having three dimensions: up and down is a dimension, left and right is a dimension, and forward and backward is a dimension. Any other other direction in space can be treated as being a combination of directions in those three dimensions. Time also counts as a dimension: if you're sitting perfectly still, you can think of yourself as moving forward in the time dimension. Time works a little differently than space does, so space and time are two different kinds of dimensions. String theory says that there also exists a third kind of dimension, that is, a third kind of direction that something can move in. We don't normally notice those extra dimensions because the extra dimensions loop back around, such that if you go just a very little ways in one of the extra directions, you wind up right back where you started from.

To change the subject, if you have any interest at all in gaining some understanding about your classmate, you might want to check out Wikipedia's article on Asperger's syndrome. Weird, nerdy, and completely and utterly obsessed with a topic as geeky as string theory sounds an awful lot like someone who may have Asperger's syndrome. Asperger's syndrome is not too uncommon among people with ultrageeky occupations like mathematicians and physicists. MrRedact 06:17, 25 October 2007 (UTC)

If the questioner has any interest at all in gaining some understanding about their classmate, the best approach is to talk to him, treat him as a person, and drop the "weird", "nerdy", "geeky" labels, which are both insulting and stereotyping. Only a qualified professional can make a diagnosis of Asperger syndrome. Gandalf61 08:45, 25 October 2007 (UTC)

Oh, right, yes, talking to him would be much better than just reading an article that might apply to him. That option didn't even occur to me because I'm not into talking to people much. But that's just me.

It's kind of situational as to whether "nerdy" or "geeky" are insulting. I'm personally not offended at all to be called a nerd or a geek, especially since it's pretty much just me or other nerdy geeks who would call me that, and because I've grown to think of being a geek as being an acceptable, and even enjoyable way to be. But yeah, if those labels are applied to a high school kid who's struggling to try to fit in with the "normal" kids, then yeah, it's probably hurtful. MrRedact 18:33, 25 October 2007 (UTC)

If you indeed have a simple mind, then maybe the simple English Wikipedia article on String Theory is what you are looking for. :) DirkvdM 08:39, 25 October 2007 (UTC)

Well, you don't have to have a simple mind to have difficulty incorporating advanced scientific information. If you don't already know what a quantum and a quark are, much less are ready to accept the idea of 11 dimensions, then it's going to be hard to jump into an article on string theory. --24.147.86.187 12:46, 25 October 2007 (UTC)

Note that the questioneer himself said he had a simple mind. I wasn't being rude this time. :) DirkvdM 19:37, 25 October 2007 (UTC)

A nice, easy book you might recommend your inquisitive-yet-annoying friend is Brian Greene's The Elegant Universe, which is all about String Theory. If you are interested in getting the low-down without reading much, there is a PBS series by the same name which is totally online now. Check it out! --24.147.86.187 12:42, 25 October 2007 (UTC)

No, please don't watch the PBS series. It's shockingly bad. It's made with the visual and narrative aesthetic of a big-budget Hollywood movie, and it will fill your head with wrong and misleading ideas which will then be very hard to unlearn. It doesn't educate. You won't understand anything new after watching it; you won't be able to better evaluate claims about string theory or anything else. But you will think that the rubber sheet model of Newtonian gravity has something to do with general relativity. The book is better, but still pretty bad. I don't know what to recommend in its place, though.

I saw something on PBS that essentially said, over and over, "There are these strings, and they vibrate, and it's awesomely cool." Is that the one? —Tamfang 23:25, 25 October 2007 (UTC)

As for what string theory is, first of all, it's not a theory. It's a research program (that article should exist) whose goal is to find a theory of quantum gravity. The approach is to start with something sort of resembling Feynman diagrams, but using surfaces (manifolds) instead of points and lines. They're called string diagrams because cross-sections through the 2D surfaces look like 1D loops splitting and joining. Feynman diagrams represent a perturbative approximation to quantum field theory, and string diagrams might perturbatively approximate something too. The idea of the string program is to study the string diagrams in the hope of finding hints about, and eventually formulating, the theory that they approximate. The actual theory, if it exists, probably doesn't look much like the string diagrams; for one thing, you'd expect it to be background independent, which string diagrams aren't. The reason people are interested in this program is that there's a bunch of circumstantial evidence that string diagrams are related to quantum gravity, most obviously the fact that you get gravitons in them. People were also excited by the fact that most versions of this idea don't work at all. This is a good thing, because the fewer possibilities there are, the more strongly you're constraining the way the universe has to be. In fact there was a lot of hope/hype in the early days that string theory would constrain the universe so strongly that the standard model would fall out magically without any inputs. But that's not what happened; the general perception now seems to be that the theory has a huge number of effective parameters, leaving it less predictive than the standard model.

Even if string diagrams are connected to the correct theory of quantum gravity (which they quite likely are) it's not necessarily in a way that anyone's going to find. It could be like monstrous moonshine, the famous unexpected connection between modular functions and the representations of finite groups. The connection is real (there's a proof now), but it wasn't discovered until these two branches of mathematics had developed independently and the same large integers suspiciously showed up in both. In principle someone could have discovered representation theory via this connection, but in practice that's not how people think. So I wouldn't be surprised if we found the right theory of quantum gravity by a totally different route, and only then (if ever) figured out how string theory relates to it. -- BenRG 19:17, 25 October 2007 (UTC)

Also, if you want to shut him up, just say, "Well, that sounds interesting, but until they come up with a way to test it, it might as well as be a religion as far as I'm concerned. An untestable theory is not much different than an article of faith." Which might drive him over the edge. ;-) One of the big issues with string theory is that at the moment there is no real way to determine whether it is correct or not; it doesn't make easily testable hypotheses. Some scientists see this as a temporary thing while others consider it to be signs of great flaws. --24.147.86.187 12:46, 25 October 2007 (UTC)

Probably the most time efficient way to get a feel for string theory are the results of a contest that Discovery channel organized recently, posted here. The contest asked people to make a video that explains string theory in two minutes or less. It should give you some idea what it's all about. risk 14:25, 25 October 2007 (UTC)

This one-panel cartoon seems to sum things up pretty well : [5] 69.95.50.15 15:37, 25 October 2007 (UTC)

OK - so we have two problems here: String theory and Annoying Geek.

Let's start with the first one: Annoying Geek...As others have suggested, this kind of obsession with one subject is a common thing with people with Asperger's Syndrome (which I happen to have...so I know what it's like). I didn't know I had it for the first 49 years of my life - but since realising the problem and getting it properly diagnosed - I can look back on some slightly puzzling things from my past and say "Holy Crap! That was me totally failing to get the message from everyone else!". This kid doesn't know he's being annoying - the obsession with one subject (and it could be anything from Dinosaurs to Internet Protocols - this time it happens to be String Theory) is very typical and right now it's the only thing he really cares about. He won't stop being interested in it until something else captures his attention - and that could take a lifetime.

This is bloody annoying for everyone else - but he probably hasn't noticed that yet. You need to try to imagine how he thinks (and since you are 'normal' - that should be easy for you!) The thing with us 'Aspies' is that we need to be told things of a 'social' nature that everyone else kinda somehow "just knows" (it's a complete amazing to me how you 'normal' folks "just know" that stuff). I literally cannot tell when someone is joking or not (particularly not if they can do it with a straight face). I have absolutely no 'innate' comprehension of body language (either my own or anyone elses). I had to LEARN those things...in classes...with an expert. It takes a conscious effort for me to maintain appropriate eye contact in a conversation. I have to think "Have I forgotten to look at people during the last few minutes?" and "Have I been maintaining eye contact for too long - so it's getting freaky for everyone?" and "How is everyone else holding their arms, how are they sitting? That person is sitting like I am - so they are probably agreeing with what I'm saying." Then..."Are my arms mimicking the poses of the people whom I agree with?" - "Could this slightly bizarre turn in the conversation be sarcasm or irony or something?".

So give the kid a break - help him out. Aspies are good at following clearly laid out rules - so if you explain to him (nicely - and directly) that this string theory obsession is annoying everyone and could he perhaps only mention it at most twice per day...then very likely, he'll do what you want. But he simply cannot work that out for himself - especially from things like you "zoning out" and rolling your eyes when he talks to you about it. He doesn't know that you are sick of the subject (after all, he finds it fascinating - and he can't tell that you don't unless you tell him).

OK - second thing: String Theory. Everything in the universe is made of teeny-tiny vibrating strings each much smaller than an atom. When I say "much smaller than an atom", I mean it in much the same way that I'd say that an atom is "much smaller than a galaxy" - just insanely tiny. The way that they vibrate gives them properties like "mass", "charge", "spin" and so on - and in order to have all of those interesting properties they need to vibrate in very complicated ways. Too complicated to do so in just 3 dimensions. Hence string theory says that there have to be something like a dozen dimensions (although some versions of the theory demand more or less dimensions - there are always a lot more than three). These 'extra' dimensions are very 'small' (about the same size as strings are) - which is why we've only noticed the first three. Sadly, all of these weird things happen on a scale that's not only smaller than we can see (even with our finest electron microscopes and such) - but on a scale smaller than we could even theoretically examine. This means that we can't currently prove whether string theory is true or not - we can't even think of ways to try to prove or disprove the theory...it's "unfalsifiable". Calling a scientific theory "unfalsifiable" is pretty much the most damning thing you can say about it. But if it's true, then it may be "The One True Theory Of Everything" - the ultimate explanation of all things. But we can neither prove that it's true nor that it's false. In that respect, it's like religion - you just have to believe in it. This is unsatisfying for scientists (including string theorists) - so the world of fundamental physics is torn between continuing to work on string theory in the hope of someday finding some way to either prove or disprove it - or giving up on it and looking for some other theory of everything instead. Personally, I'm in the latter school...we've spent enough valuable brain power on it...it's time to move on.

SteveBaker 16:52, 25 October 2007 (UTC)

One thing I don't quite understand is why don't the science and maths teachers offer some help. I presume that this is primary school so their level of science and maths may not be extremely high but I would assume they would be better able to learn about string theory then you Nil Einne 18:50, 25 October 2007 (UTC)

Ssshhh ... he really wanted to ask for himself, but was too ashamed, to he made up this boy .... and now this imaginary boy has Asperger's Syndrome ... DirkvdM 19:37, 25 October 2007 (UTC)

Steve, how can a dimension be small? The other dimensions stretch out pretty much into infinity. The universe may be finite (or it may not), but I mean in principle the dimensions themselves have no limits, do they? Except maybe time, but that also depends on the truth of the Big Bang and Crunch. Or does this have to do with MrRedact's remark about the dimension looping back on itself? In which case it's infinite in the sense that it's in an infinite loop, but we stand outside it, so to us it's small? But then each string has it's own dimension? Aaarghhh, that's not possible, a dimension is not a thing, it's something that contains things. Brainmelt .... DirkvdM 19:37, 25 October 2007 (UTC)

See Compactification (physics). MrRedact 20:15, 25 October 2007 (UTC)

(ec) The "extra" dimensions (according to the theory) loop back on themselves in a very short distance, but you're not "outside" them; quite the opposite. You occupy -- in fact, probably every proton in your body occupies -- the entire thickness of the universe in the direction of those dimensions. That's why you don't see any motion in one of those directions. There's nowhere to go. --Trovatore 20:18, 25 October 2007 (UTC)

For an easy to understand explanation, see Steve Baker's previous explanation here. I actually have that page bookmarked so I can find it again. I had always wondered how dimensions were supposed to curl up on themselves, and Steve explained the concept step-by-step in a way that I finally understood. 152.16.16.75 00:43, 26 October 2007 (UTC)

Ok, that put the idea clearer in my head. But it doesn't resolve my issue. Let's take one of those dimensions, say the 8th (which is nonsense of course - we can't point at 'the' 2nd dimension either - but for the sake of the argument). We can't perceive this 8th dimension, but the strings live in them. One for each string. right? Or is that where I go wrong? That 8th dimension is at the same time tiny, but all strings live in it, so it's also as big as the universe. I can't imagine this in any other way than that each string has its own 8th dimension. So that doesn't make it one dimension. By Steve's analogy, if a flatlander's '3rd dimension' were 1 km across, then he could live in it, but everyone would have his own 3rd dimension. The flatlanders would be able to see themselves through binoculars, but would they be able to see each other? DirkvdM 07:56, 26 October 2007 (UTC)

The strings live in all of the dimensions at once - just as we do. Our bodies take up space in all 15 (or so) axes at once - and so do the strings. But for all practical purposes, we are vastly too big to do or see or measure anything interesting in the 'extra' dimensions because there just isn't room in them. So while we exist in all 15 (or so) dimensions, we only NOTICE the three three huge dimensions. Even things as small as atoms don't have 'room' to do anything in the extra small dimensions. But the super-strings (which you'll recall are AMAZINGLY tiny, even compared to an atom) have plenty of room to vibrate in those directions. So they can vibrate up and down (1st dimension) and left and right (2nd dimension) just like a plucked guitar string. They can also vibrate 'in' and 'out' (like a slinky or a sound wave in the 3rd dimension) and they can vibrate squark and floop (sorry - I had to make up two new words for vibrating in the fourth dimension), snork and wibble (5th dimension), finque and gnort (6th dimension)...and so on. So there isn't one dimension per string or anything like that. I don't quite understand how you are misconstruing my flatland analogy...but it is hard to convey these things accurately. SteveBaker 19:00, 26 October 2007 (UTC)

Thank youfor those new words. :) But the problem is I can't see how a dimension can be at the same time small, so that only strings one string can live in it, and as big as the universe, so all strings can live in it. I can accept the idea that a dimension ends where the universe ends (although that is already rather strange (a dimension is a mental construct, a way to look at things - you can't point at it). But if it is smaller (irrespective of how small), then what lies outside it has to have its own version of that dimension to live in. And I can't understand more than one version of a dimension - one for each string in this case. DirkvdM 06:42, 27 October 2007 (UTC)

Consider an ant farm; specifically, consider one not quite as thick as I remember mine having been, so you have lots of available up/down, plenty of left/right, but there is insufficient room for two ants to pass in the in/out dimension. The grains of sand, however, have an extra degree of freedom - they can be displaced in this funny extra dimension that has no meaning for the ants (ok, it does for actual ants, but these are "special" ants). Everywhere an ant-physicist goes in the enclosure, she can measure her familiar two dimensions, but the sand still can be displaced in depth - it is the same direction everywhere even though there is not far to go in it. Eldereft 01:57, 28 October 2007 (UTC)

Ah, I think I've finally got it. The dimension is very small in its own dimension (however weird that sounds), but still stretches out over the entire universe in the other dimensions. I'm ashamed it took a silly ant farm analogy to get it through my thick skull. Now that I get it I don't understand how I didn't before. So the dimension loops back into itself, forming a circle. Add another dimension and you get a tube. Add yet another dimension and the tube gets thickness? I can't imagine that stretching into infinity, though. Btw, that second dimension looping back into itself would result in a torus. And the third one? Oh dear, I guess topological dreams will be keeping me awake tonight (...). DirkvdM 07:48, 29 October 2007 (UTC)

Amateur pyschological evaluations continued

I made a separate header to keep the discussions separate. DirkvdM 07:58, 26 October 2007 (UTC) ps Someone changed the header, so don't blame me. :)

..what if I said that he does this purposely and is fully aware that his classmates are glaring and rolling their eyes or looking for the nearest fire escape or something? He's also one of the best students in the class. I doubt that he has trouble catching up. But he is obsessed, though. I'm pretty sure he doesn't do it just to annoy us. ~~Questioner~~

Maybe he's concerned more with gaining knowledge than with what others might think of him. If he has high self esteem then he might figure everyone already thinks of him as a nerd (which is a good thing), so there is no reason he should impose artificial restrictions on his opportunities for learning. Maybe he has low self esteem and he's seeking acknowledgement of his intellectual abilities. Maybe self esteem doesn't play into it and he's just showing off - "Look at how intelligent I am." Maybe he's simply a genius. Geniuses tend to make their own rules. Maybe you could strike up a friendly, non-confrontational conversation and bring the conversation around to asking him. His actions may annoy you, but imagine how boring life would be if everyone felt an overwhelming need to conform. Personally, I think we need more young people ardently studying the science behind the mysteries of the universe. Go nerds! 152.16.188.107 06:58, 26 October 2007 (UTC)

Changed sub-head. Only a qualified professional can make a diagnosis of Asperger syndrome or any other pyschological condition. We cannot conclude anything on the basis of a few sentences from the original questioner, neither should we try to. This whole sub-thread is inappropriate for the RDs. Gandalf61 09:00, 26 October 2007 (UTC)

Acceleration to near-light speeds

What's the speed of an object moving with a constant acceleration (from its point of reference) with respect to time from its point of reference and from the starting point of reference (when its speed was zero)? Does this question fit better on the mathematics page? — Daniel 03:27, 25 October 2007 (UTC)

It's not terribly hard to work it out -- start from the relativistic addition-of-velocities formula, figure out the change in velocity-in-lab-frame with respect to time-in-ship-frame at a particular velocity (remember to take the existing time dilation into account!) and integrate. From memory I think it may be tanh(at), where a is the acceleration, t the time, "tanh" is the hyperbolic tangent, and you're working in a system of units where the speed of light equals one. But I'd have to re-derive it to be sure. --Trovatore 03:34, 25 October 2007 (UTC)

I just did the integration without assuming special units, and got c*tanh(at/c), which works out to tanh(at) once you put it in said special units. Someguy1221 04:13, 25 October 2007 (UTC)

No, no - everybody knows that the speed of light is 137. In units with ħ and e set to one but the Fine-structure constant retaining its required dimensionless value, that is. For anyone wandering through wondering what is the deal with the funny units, they are useful because physicists like to be lazy efficient. Trovatore's answer is patently dimensionally incorrect to anyone dragging the constants along, but the result must have units of velocity (there is Someguy's first c), and the argument of tanh must be dimensionless (at has units of velocity, so the must be another c to cancel). This only works if both the original formula and the subsequent math are correct, but using c = 1*(3*10¹⁰ cm/s) units actually makes the algebra less cumbersome and clarifies the presentation without sacrificing accuracy or rigor. Eldereft 06:03, 25 October 2007 (UTC)

I really can't tell -- are you trying to make a joke, or are you genuinely crusading for the units that you prefer, or what? For dealing with a relativistic but presumably non-quantum problem, it's much more common, convenient and sensible to choose units such that c=1, rather than to sacrifice the convenience of c=1 in order to make ħ and e be 1. Trovatore's answer is perfectly correct using the very commonly used choice of units for this type of problem. I'm not trying to start an argument or anything; I genuinely just don't understand why you made this comment. MrRedact 06:58, 25 October 2007 (UTC)

See hyperbolic motion (relativity). -- BenRG 13:02, 25 October 2007 (UTC)

I assume the answer given is in respect to time from the point of reference of the observer. What's the answer with respect to the time from the point of reference of the one accelerating? — Daniel 20:20, 25 October 2007 (UTC)

This happens to be equivalent to the same situation as before, except the observer is now sitting in a gravitational field pointing towards the accelerating object, a field of magnitude equal to the acceleration. I'm not so good at GR, so I'm not sure how this affects the observed v/t curve. Someguy1221 20:35, 25 October 2007 (UTC)

You don't need GR here; SR works just fine for this question, acceleration or no. However I don't remember if the "tanh(at)" answer is for t in the lab frame or in the ship frame. Whichever it is, though, you can convert to the other one using purely special-relativistic techniques. --Trovatore 20:43, 25 October 2007 (UTC)

Alright, so I was thinking about this, and I believe that the only difference between the two observers (due to time dilation) is that the accelerating observer should observe the velocity between himself and his starting point to be accelerating at a higher rate than the non-accelerating observer observes...I think. And I think tanh(at) is in the lab frame. Someguy1221 21:15, 25 October 2007 (UTC)

In the equation v=tanh(at), the v is obviously in the lab frame, since in the ship's frame the ship's velocity is just 0. And FWIW, the starting point's velocity in the ship's frame is just -v. However, the t is in the ship's frame. I just derived the tanh(at) from the velocity addition equation myself, so I'm sure of this. An intuitive way to remember that the t is in the ship’s frame is because it’s getting multiplied by a, which is definitely measured in the ship’s frame, since in the lab frame the ship’s acceleration isn’t a constant. It would be weird for there to be an equation that multiplied an acceleration in one frame by a time in another frame, without there being a factor of gamma in there somewhere. —Preceding unsigned comment added by MrRedact (talk • contribs) 20:54, 26 October 2007 (UTC)

Actually, the "a" is only in there as a simplification of f/m, which is what I actually worked with. F and m can certainly be measured from the lab's frame as constant, and the factor of gamma got disected by the integration. Someguy1221 06:49, 27 October 2007 (UTC)

No, that's all wrong. Neither F nor m are constant in the lab frame. As the ship goes faster, the mass of the ship as measured in the lab frame increases. And the equation F=ma doesn’t work at relativistic speeds. See the "Relativistic mass" and "Force" sections of Special relativity. MrRedact 19:27, 27 October 2007 (UTC)

P.S. An intuitive way of knowing that the acceleration of the ship can’t possibly be constant in the lab frame is because if the acceleration were constant in the lab frame, then the ship would reach and exceed c in a finite amount of time (lab time, not proper time). In the lab frame, the ship’s acceleration must asymptotically approach 0 to keep the ship from exceeding c. MrRedact 20:51, 27 October 2007 (UTC)

Yes, I'm well aware of all that, thank you. My "m" refers only to rest mass, which is constant. Thus, we can retain "f" as a constant, or rather, dp/dt as a constant, where "p" is relativistic momentum. It works. Someguy1221 21:24, 27 October 2007 (UTC)

OK, it looks like this was mainly just a misunderstanding. You said that m is measured in the lab frame, which made it sound to me like you were viewing m as being the mass in the lab frame, i.e., the relativistic mass, which certainly isn’t constant.

I’ve figured out to my surprise that F actually is constant in the lab frame, and is the same value as F in the ship’s coordinates. F is obviously constant in the ship’s coordinates, so it’s surprising to me that F happens to also be constant in a frame with respect to which the ship is moving at relativistic speeds and accelerating.

As noted above, the t in v=tanh(at) is the proper time. In terms of the lab’s time, I calculate v=at/sqrt(1+a²t²), where as always c=1 and a is the ship’s acceleration as measured in the ship’s coordinates. MrRedact 18:53, 28 October 2007 (UTC)

I think you’re right about the magnitude of the acceleration of the ship’s starting point as measured in the ship’s coordinates being greater that the magnitude of the acceleration of the ship as seen in the lab frame, at any given event on the ship’s world line. Consider two nearby events on the ship’s world line. The two coordinate systems will agree on the magnitude of the change in velocity that occurred between the two events. But the time measured between the two events will be less in the ship’s coordinates that in the lab frame due to time dilation, so the magnitude of the acceleration will be greater as seen by the ship. MrRedact 05:56, 27 October 2007 (UTC)

TERRESTRIAL PLANT GROWING COMPLETELY IN WATER

I FOUND THAT A TERRESTIAL PLANT IS COMPLETY SUSTAINING IN WATER EVEN IF COMPLETELY DETACHED FROM SOIL.ANOTHER THING IS THAT IT DOESNT HAVE ITS NORMAL ROOT WHILE FALLING INTO WATER.BUT ALSO IT GREW ADVENTITIOUS ROOTS AND SURVIVED.ANOTHER PLANT OF SAME SPICIES GREW ADVENTITIOUS ROOTS EVEN IF IT HAD ROOTS IN SOIL,WHEN ITS SHOOT IMMERSED IN WATER. MY QUESTION IS THAT HOW DO A TERRESTRILE PLAND SHOW SUCH A VARIATION IN CHARACTER? HOW CAN IT GROW IN WATER WHILE IT IS CMPLETELY DATACHED FROM SOIL AND WITHOUT ROOTS? IS IT SHOWING ANCESTRAL CHARACTER? —Preceding unsigned comment added by 59.93.40.184 (talk) 05:21, 25 October 2007 (UTC) --59.93.40.184 05:31, 25 October 2007 (UTC)

Such a plant could grow for a while on the minerals dissolved in the water or stored already in the plant. If the water is ground water, it may in fact have similar minerals available to the plant as it would have in soil. Even rain water will have some nitrates dissolved. However in pure water the plant will eventually suffer mineral deficiency and go yellow, and die. It would not be due to ancestral throw back, but due to the fact that the main ingrediantes plants need are water and air. Graeme Bartlett 05:54, 25 October 2007 (UTC)

Don't shout. Shouting is rude. You are rude. I refuse to read your question. DirkvdM 08:59, 25 October 2007 (UTC)

What Dirk means is that typing in ALL CAPITAL LETTERS is frowned upon in online discussions. It is more difficult to read large blocks of text that are in all caps. On the internet, words in all caps are usually interpreted as 'louder', or 'shouting'; as in the real world people online are more inclined to stand and listen to you if you 'speak' clearly and quietly. I hope you'll keep that in mind in the future, and I'm sorry that Dirk bit your head off. TenOfAllTrades(talk) 13:45, 25 October 2007 (UTC)

I find it extremely unlikely that anyone who knows how to post a question on the ref desk (has found it and discovered how to post a question) has such a limited knowledge of computers (combined with a total lack of common sense) that they don't know that all caps is not normal. It is extremely likely that he intended to draw extra attention, which is rude. Btw, all caps is not harder to read for me. DirkvdM 14:32, 25 October 2007 (UTC)

That's nice, but my experience is otherwise and so apparently is other people's. Skittle 17:17, 25 October 2007 (UTC)

Right, I take that back. Especially when glancing over a text, I pick up less when it's in all caps. DirkvdM 08:03, 26 October 2007 (UTC)

This phenonoma is well known - try hydroponics - also try a web search for "hydroponics + adventitious root"87.102.94.16 12:39, 25 October 2007 (UTC)

The main idea behind hydroponics is that plants don't need soil to grow. All they need is access to certain minerals (about 13 different ones), oxygen and water. If you can get these minerals to the roots, the roots only need to stay dark and moist for the plant to survive. There are many ways of accomplishing this, you can hang the roots in moving water (with minerals dissolved in it). you can let the water flow by the roots on a light slope, you can even hang the roots in a dark chamber and spray them lightly with the mineral solution. The main advantage of hydroponics is that the roots don't need to search for water through the soil, so they have to grow less. That energy can then go into the plant. Also, you need less water to grow plants this way. risk 14:48, 25 October 2007 (UTC)

Power lines noise

Hi,everyone. Whenever I walk under the highly raised power transmission lines,I hear some humming sound(not birds),but it seems to come from the vicinity of the wire circumference.I thought it was because of rainy season.but it appeared in summer too,and in all seasons.later I guessed it couldbe due to capacitance effect, but I'm unsure.Anybody can prove this?.. —Preceding unsigned comment added by Balan rajan (talk • contribs) 05:42, 25 October 2007 (UTC)

Corona discharge. There might be other contributing effects, I'm not sure. Someguy1221 05:58, 25 October 2007 (UTC)

It gets worse where there is salt on the power lines, after rain it can wash off the contamination. This also casues EMI electomagnetic interference. Graeme Bartlett 06:02, 25 October 2007 (UTC)

How did you get salt on the power lines!87.102.94.16 12:37, 25 October 2007 (UTC)

Really long, non-conducting salt shakers, of course! Seriously, in any area near the sea coast, there's actually a surprising amount of salt in the air as a result of droplets of seawater evaporating and leaving microscopic nuclei of salt. These microscopic bits of salt accumulate, partly as a result of electrostatic effects.

Atlant 12:58, 25 October 2007 (UTC)

It's almost certainly 50 or 60 Hz mains hum - just like you can hear from a transformer (power pack) - the interaction of the oscilating current with the earths magnetic field causes a 50 or 60Hz physical vibration. Add the sound of corona discharge (crackly) - and that should be it...87.102.94.16 12:36, 25 October 2007 (UTC)

• I once read that if you ask a person to make a constant hum without specifying the pitch, some high percentage of people will hum at whatever pitch their country's electrical equipment hums at. No sources, of course. :( --Sean 13:14, 25 October 2007 (UTC)

Unlikely. 50 or 60 Hz is a very low bass note. It's well below the lowest notes required of an operatic bass singer. A harmonic of 50 or 60 Hz is slightly more believable. --Robert Merkel 21:19, 25 October 2007 (UTC)

Salt can also of course speed up rusting, so presumably powerlines and the apparatus that holds them near coastal areas not only rust more quickly but hum more frequently and louder on average. Lanfear's Bane | t 13:25, 25 October 2007 (UTC)

Where this salt buildup is a real problem, you'll occasionally see a bizarre-looking power-company tower truck spraying water on the insulators to wash the salt off. (How they avoid causing short circuits with this stunt, or electrocuting themselves, I'm not 100% sure.) —Steve Summit (talk) 00:18, 26 October 2007 (UTC)

To electrocute themselves, they would need to make a path between power line and ground, and put themselves in that path. Same reason crows don't fry when they stand on power lines awaiting their opportunity to strike. --Psud 11:08, 26 October 2007 (UTC)

If you haven't seen a crow fry while trying to land on a power line, you need bigger power lines. I think Steve was thinking that the path of water would form a circuit just like peeing on an electric fence will make a circuit. --DHeyward 07:24, 27 October 2007 (UTC)

("You need bigger power lines." Grin.)

As someone who has grabbed an electric fence, walked on a third rail, and held a live wire in my mouth (and felt pain in only one out of the three), I do understand about completing circuits! I shouldn't have said "avoid electrocuting themselves"; that was for cheap effect. There are lots of varieties of insulated-boom cherry pickers from the buckets of which you can safely work on live wires bare-handed. But it's harder to imagine keeping a powerful pump and a big tank of water (presumably mounted down on the chassis of the truck) adequately isolated from ground. Perhaps they don't try, and use distilled water (which is not significantly conductive) instead. —Steve Summit (talk) 17:47, 27 October 2007 (UTC)

I feel a maxim coming on - The Science Desk, peeing on electric fences on an encyclopedic scale since 2001. Lanfear's Bane | t 13:37, 29 October 2007 (UTC)

color vision

sir, I would like to know more about color vision in different animals.For eg.do bulls and cows recognise differen colours? —Preceding unsigned comment added by 59.93.24.4 (talk) 12:02, 25 October 2007 (UTC)

Have you looked at our color vision article yet? Do you have further questions?

Atlant 13:03, 25 October 2007 (UTC)

Bulls and cows do not have color vision, according to the science podcast Vanguardia de la Ciencia - I'm not able to locate the exact file where I heard this although I have it on my computer (mp3 files aren't easily searchable...). The information is confirmed by this website, which also contains information about other animals.

The description of how color vision "works" in our article is somewhat technical. I'll try to explain it in (hopefully) simpler terms. The reason why we can reproduce just about any color using three primary colors is that our retina has three types of cones, each of which responds to a different range of wavelengths. With the exception of lasers, light is composed of a mixture of wavelengths. Any mixture of wavelengths which stimulate each type of cones by an equal amount, will be perceived as the same color. Thus, two colors that appear identical, may correspond to two quite different mixtures of wavelengths. If a person had a mutation which slightly shifted the response optimum of one of his types of cones, he might be able to distinguish two colors, which appear identical to "normal" people. Even more surprisingly, in some instances, a person who lacks one type of cones is able distinguish colors that appear identical to someone with normal color vision. Check out the reference in the article color blindness. The reference is from 1992, yet I heard about color blind individuals being used by the military for spotting camouflages as a child sometime in the 1960's, and it greatly intrigued me. Many birds have four or even five different types of cones, and experience a world of color that we cannot possibly imagine. --NorwegianBlue ^talk 14:12, 25 October 2007 (UTC)

Just a moment, Mr. Blue! If you're a bird yourself, why aren't you saying that "you" humans can't possibly imagine it? Hmmmm? --Anonymous, 1:43 UTC, October 26, 2007.

Expanding Universe...Are we all getting bigger?

In the ant on a balloon model of the expanding universe is the ant getting bigger too or just the balloon? Sappysap 13:34, 25 October 2007 (UTC)

I've always heard it as just the balloon; e.g. it was the space in between matter that was expanding, not the matter itself. I'm not sure whether that makes total sense though, esp. when talking about large amounts of diffuse matter (e.g. clouds of hydrogen gas out in space). --24.147.86.187 15:13, 25 October 2007 (UTC)

Yeah - just the balloon. If the ant got bigger - then so would the ant's measuring stick - so the little guy would have no idea that his balloon was expanding. Here in the real universe, we can easily measure the expansion of space - so it follows that we are not expanding along with it. Diffuse gas clouds might expand because there is very little in the way of forces holding them together. But the strong, weak and gravitational forces keep things like planets, solar systems and ants firmly glued together. SteveBaker 15:18, 25 October 2007 (UTC)

OK, that makes sense. So basically the expanding action is not very powerful over small distances (like gravity), but does a lot of work over large distances (like gravity). So locally things stay more or less together while the space around them expands. --24.147.86.187 00:05, 26 October 2007 (UTC)

Of course that's for now. --Trovatore 22:39, 25 October 2007 (UTC)

An equally valid explanation would be that the universe remains the same size but matter itself is shrinking. Weird, but is it weirder than an expanding universe? After all, it's the universe, so we can't measure it against anything, so shouldn't we assume it to be of constant size? DirkvdM 08:09, 26 October 2007 (UTC)

Yes, it would be weirder (in my subjective opinion). The "size" of matter, or more specifically the seperation between its consitutient parts, is governed by by equilibrium states among the various relevant forces, especially electromagnetism. The strength of the electromagnetic force governs the size of atoms and the seperation between them in ordinary matter. The strength of the weak and strong forces play similar roles in defining the properties of matter, albeit in more esoteric ways. In order for matter to be shriking (but still appear to have all the same properties), you'd have to posit that all the basic force laws are changing with time. That is much weirder than saying that the average density of the universe is decreasing (which is the effect of the expansion) in a way that is consistent with time invariant physical laws. It's like placing a drop of oil on a sheet of paper: it will spread out over time so that it's average density descreases, but none of that physical processes governing its behavior have changed. It is more aesthetically satisfying to say that physics is fixed and the universe evolves within a physical framework than to say that that universe is fixed and hence physics must be changing. Dragons flight 09:43, 26 October 2007 (UTC)

I agree, from what I've read of Stephen Hawking's work, the universe, not the matter within it, is changing. The matter is just becoming increasingly spaced out. Midorihana_{(talk)(contribs)} 09:48, 26 October 2007 (UTC)

Right, of course, the simplest solution is the one to go for, and constantly changing laws of physics doesn't quite fit that. But then we have a problem with the Big Bang, or, rather, the 'time' before that (or how was that?). Don't the laws of physics even break down there? DirkvdM 07:12, 27 October 2007 (UTC)

I have a problem with the claim that space gets bigger but we don't. As a thought experiment, consider two spherical objects in space 1 million meters apart with a radius each of 1 meter. With the claimed "expanding balloon, nonexpanding ant" model, over time the distance between the objects should increase, say, to 1.1 million meters, but each object would still have a 1 meter diameter. Now place a 1 million meter cable of negligible tensile strength (so it does not forceably prevent the expansion) between them. Its length would have to increase over the time period to 1.1 million meters. Next to it, place 1 million replicas of the standard meter. As individual oblects, each would remain of constant length. But there is no difference between the million meter cable and the million meter sticks. Ergo, the earth, and we ourselves, should expand if the universe expands. Edison 15:35, 26 October 2007 (UTC)

The size of physical objects is governed by chemistry (i.e. electromagnetic forces). As long as the expansion provides neglible force compared to that of chemical bonds, physical objects will continue to maintain the same length, though the spaces between them may increase. Dragons flight 16:34, 26 October 2007 (UTC)

Edison's thought experiment is interesting - but I think the cable would either snap under the "expanding universe tension" or it would have sufficient strength to hold the two balls together or it would simply stretch like a piece of elastic. Since the amount of growth is very small indeed on a scale of a mere million meters, this would have to be an exceedingly fragile or stretchy rope for it to do anything other than keep the two balls a constant distance from each other. There is indeed a difference between your standard meter sticks - they are not attached to each other - so gaps will obviously form between them. I don't see any problem with that. SteveBaker 18:35, 26 October 2007 (UTC)

Actually I don't think the standard meter sticks will separate, at least not for this reason. They aren't attached per se, but the gravitational attraction between them will massively swamp any tendency for them to move apart due to universal expansion.

Here's a very naive calculation -- it may not be accurate, but if it's not completely meaningless, and I don't think it is, then it'll show my point. Consider two particles at distance r from one another, moving along with the Hubble flow, no interaction between them. They move apart at a velocity v = Hr, where H is the Hubble constant. The acceleration is dv/dt = Hdr/dt = Hv = H²r. So the force required to divert one of the particles from that course, and keep it at a constant distance from the other, is just H²rm, where m is its mass.

According to our article, H is about 70 km/sec/megaparsec, and a megaparsec is about 3x10¹⁶ km, so H is about 2x10^-15 sec⁻¹. So at a million meters the acceleration to be overcome is 4x10⁻²⁴ m/s². On the other hand, if one of the meter sticks weighs a kilogram, then the acceleration due to its gravity at a distance of a million meters is 6.7x10⁻²³ m/s², an order of magnitude more. Maybe the meter sticks are lighter than that, but that's going to be completely overwhelmed by the fact that there's a million of them, and they're much closer together. --Trovatore 18:02, 27 October 2007 (UTC)

pH

Can pH be less than zero? One of the articles here says so.

Deepti —Preceding unsigned comment added by 61.2.66.136 (talk) 14:19, 25 October 2007 (UTC)

Yes, see here. --NorwegianBlue ^talk 14:30, 25 October 2007 (UTC)

See also superacid. TenOfAllTrades(talk) 16:17, 25 October 2007 (UTC)

Doesn't this mean pH is ill-defined? Can't it be reduced to SI units? I suppose not, because it is operationally defined. Is it a 'real' unit of measurement (whatever that means)? Oh, hold on, it's a unit-less quantity, or better dimensionless quantity, right? DirkvdM 08:20, 26 October 2007 (UTC)

I don't think pH is really operationally defined. It's defined in terms of the activity of hydrogen (or hydronium) ions through a mathematical formula (see pH). The issue is that most solutions in everyday life are between 0 and 14 and since it's a log scale, that's a large range (10^14) that can usually cover almost everything. But there's nothing that says it has to be within that range. --Bennybp 15:13, 26 October 2007 (UTC)

I did see pH. That's where I got the 'operationally defined' from. I wouldn't have used that expression because I didn't know it, but the nice thing about science-speak is that I instantly understood what it meant. :) DirkvdM 19:11, 26 October 2007 (UTC)

Jeez, maybe I should read the articles I link to rather than skimming :) It looks like it could be defined mathematically (for some solutions) or operationally. Interesting, I'll have to do more research on that :) --Bennybp 00:57, 27 October 2007 (UTC)

giardia parasite

we live in the arctic of alaska and because of the global warming we have experienced an increase of beaver population in our region, which we never use to have before. all the lakes and ponds and rivers are full of more beaver every year, can we drink ice water? is the parasite able to live in the ice? and does it still live after the ice has melted? we do already have a filter that can kill the giardia, i just want to know if we need to use it for the ice water too?

Inupiaqbelle78 15:35, 25 October 2007 (UTC)inupiaqbelle

Giardia can live in ice (and ice cubes), if that is what you are asking. Any water that you may consume that might have giardia in it should be either filtered or boiled first, whether it is in ice or even just used to wash off food. --24.147.86.187 17:01, 25 October 2007 (UTC)

Welcome to Wikiopedia, the encyclopedia that anyonee can edit. The answers you get here can come from anyone. including editors who have no expertise whatsoever that relates to your question. Your question relates to a potentially life-treatening issue. Please seek a professional opinion, Someone in your community could die if you act on the wrong response. That said: if you kill and eat the beaver, the you muwst cook theme completely. duh. -Arch dude 03:28, 26 October 2007 (UTC)

Go away! And stop spreading false medical info. Giardia lethal? Where did you get that idea from? And read the question. And learn to spell. Dude. DirkvdM 08:26, 26 October 2007 (UTC)

I'd say it's a no-brainer that you must always sterilize water from rivers and lakes before drinking it, and this hardly qualifies as "medical advice", it's just plain common sense. Untreated water is potentially dangerous, just about everywhere. StuRat 20:00, 28 October 2007 (UTC)

Where it gets tricky is, is it more or less dangerous than dehydration? In extreme cases the answer is obvious, but the borderline may be tough to define. Suppose you're ten miles into a twenty-mile hike and you twist your ankle; you think you can make it out but you're not sure. You don't have any disinfectant or anything to start a fire with. You have a two-liter canteen, one-third full. Should you fill it up from the running stream, possibly the last one? What about if there's no stream, but there's a pond? My guess is that many people would overestimate the dangers of the water relative to not having the water. --Trovatore 21:16, 28 October 2007 (UTC)

Especially with giardia. It isn't much more than a bloody nuisance, with some sickness and especially foul smelling diarhoea (I speak from experience). The diarhoea dehydrating you then becomes the problem, of course, and I suppose drinking more of the infested water won't matter at that point. Btw, StuRat, the safety of river water depends largely on the presence of humans upstream. And the water in national parks in New Zealand used to be perfectly safe to drink, until it got infested with ... yep, giardia. DirkvdM 07:57, 29 October 2007 (UTC)

I would expect that humans will be present just about anywhere a human is likely to visit. And, even if they aren't, plenty of other animals also carry waterborne diseases that humans can contract. Glacial meltwater coming out of a river from under the glacier ought to be relatively safe, I suppose, but there could still be a thawed/rotting animal corpse in there somewhere, so I'd boil it anyway. StuRat 17:38, 29 October 2007 (UTC)

I was talking specifically about hiking national parks, where normally no-one lives. Then again, if it is a much used national park, as are many in New Zealand, only the water at the highest hut might be considered safe. But then, if there's a track further up (eg crossing a pass) then someone with giardia might have felt a sudden urge and not observed the rule of shitting far away from the river. Point taken. DirkvdM 08:31, 30 October 2007 (UTC)

Dirk, I'm sure we're all happy that you got through your encounter with Giardia with nothing worse than that, but you shouldn't assume that that's the worst that can happen. With GI pathogens particularly (cf Salmonella and Listeria) it often turns out that healthy young adults get a little sick and then get over it, but young children, older people, and the immunocompromised, may die. I never actually heard of anyone dying specifically from Giardia but that doesn't mean it can't happen -- and there are other nasties in water also, like cryptosporidium.

Still, there are lots of scenarios where I'd drink the water rather than go without. I suspect that a lot of people overestimate the risks. But that's just me, and I don't really know much about it, so I offer no warranties of any kind. --Trovatore 20:07, 29 October 2007 (UTC)

Yes, of course, in combination with weakness, caused by whatever, anything can be lethal. I've also had cholera, which is a notorious killer, but mainly because it often breaks out under conditions where people are already weak, such as in refugee camps. But an otherwise healthy person should survive it. DirkvdM 08:31, 30 October 2007 (UTC)

What do beavers have to do with giardia? Dismas|^(talk) 12:28, 26 October 2007 (UTC)

Beaver's pooping in a river where you get your water supply is one of the more common ways to get infected with it. 38.112.225.84 14:42, 26 October 2007 (UTC)

Sounds like we need a global campaign to put diapers on beavers. :-) StuRat 17:40, 29 October 2007 (UTC)

Note that the filter probably doesn't kill giardia. This may be of relevance concerning what you do with the filter. I don't know, just thought I'd point this out. DirkvdM 07:21, 27 October 2007 (UTC)

Why are videogames fun?

What causes the brain to enjoy it? All you are doing really is just pressing buttons. But if you stare at a blank screen and use your imagination, it's no where near as fun. So what's gives? 64.236.121.129 17:38, 25 October 2007 (UTC)

The suspense, the feeling of accomplishment, the entertainment from good storylines? Playing with your friends, the challenge, the anxiety? This is why I play video games. Beekone 17:55, 25 October 2007 (UTC)

I'd agree with this. The conclusion, then, is that you're obviously not "just pushing buttons". While pushing buttons is the physical activity, it's in response to the stimuli that a blank screen does not provide. The same holds true for a great many things: baseball is more fun than batting practice, giving a concert is more fun than solo karaoke, and so forth. — Lomn 18:18, 25 October 2007 (UTC)

Aspects of the most popular video games are basic aspects of classical conditioning. See something flashy, hit the right button, and you get rewarded (praise, adulation, the death of your enemies, etc.) or punished (sad music, game over). Repeat. Obviously it's not just the pushing of buttons — it's the whole context of the system of interactions between your brain and the reward system. In any case though it is worth noting there are very different types of games and they probably appeal to different parts of the brain: pinball, Counter-Strike, and Police Quest all use functionally similar hardware but utilize very different faculties (and don't necessarily appeal to the same people). --24.147.86.187 23:56, 25 October 2007 (UTC)

I think games have a strong biological advantage. We're not the only animals that play games. I remember a scene from the blue planet, where killer whales spend hours tossing a dead seal back and forth with the children. My guess is that these kinds of games provide a safe environment to train motor skills, reflexes and coordination. Of course, for any animal there needs to be a strong biological imperative to perform these mindless repetitions without getting bored, so nature has made these things fun, and made us want to be good at it. Playing the whole thing out in your imagination does not provide most of the benefits of games. First of all, these skills are mostly low level neural processes (like muscle memory), so you need to actually do them to get better at it. Second, it's good to have some independent verification of how good you are at something. In my mind, I can be a fantastic hunter that always catches the prey and never dies, but unless I get actual real world feedback on these skills, I may just be kidding myself (and die the first time I actually try to hunt). That's why nature wants us to play real games, instead of just using our imaginations. risk 03:11, 26 October 2007 (UTC)

I fixed your link. Algebraist 21:28, 26 October 2007 (UTC)

Menopause

Do a) pregnancies, b) oral contraceptives influence the onset of menopause in any way? --KnightMove 19:02, 25 October 2007 (UTC)

I don't know if prenancy has an effect, but taking oral contraceptives will have no effect. However, taking oral contraceptives can hide the symptoms of menopause, and even allow a woman to continue to have periods, even though her ovaries have stopped putting out eggs. [6] Someguy1221 19:09, 25 October 2007 (UTC)

Decibel Meter

Is there any way to make a homemade decible meter? Thanks Deltacom1515 19:03, 25 October 2007 (UTC)

If you had some sort of calibration standard for sound power, you could calibrate any arbitrary microphone, amplifier, and ac voltmeter as a sound meter. Alternatively, if you can borrow a sound level meter, you could calibrate your homemade device against that meter.

Atlant 23:39, 25 October 2007 (UTC)

Sure - a microphone and a voltmeter should do just fine. I bet you could find some freeware software that would let you plug a mike into your computer's sound card and read off the sound levels. But for it to be accurate you'd need a way to calibrate it. If you can borrow a decent sound level meter you could play the same sound into that machine and your home-made contraption and calibrate it like that. The only other way would be to have a sound source of known loudness and set it up that way. I can't really think of anything like that. My HiFi/Home Theatre system has decibel numbers it displays as you wind the volume up and down - but that can't be accurate because it depends on how loud the thing you are playing was recorded at. SteveBaker 23:58, 25 October 2007 (UTC)

Your hi-fi is displaying "relative" decibels (decibels of attenuation); absent a calibration microphone (which some high-end receivers provide), there's no way it can know the absolute sound pressure being produced. As for calibrating sound level meters, ours actually came with a calibrator that, when closely coupled with the meter's microphone, puts out a 94 dB 1000 Hz tone (or, with a switch press, a 114 dB tone). It's that sort of gadget you'd need to calibrate a home-made meter, but even then, there'd still be questions of how well-coupled the calibration source and microphone are and what the frequency response of the microphone is. It'd be far easier to borrow a calibrated meter against which to calibrate the home-made meter.

Radio Shack, by the way, sells sound level meters for not very much money; the meter I use at home came from there (whereas the work meter and calibrator that I was describing above is a very nice Brüel and Kjaer [7]).

Atlant 12:12, 26 October 2007 (UTC)

The above proposals to use a calibrated sound level meter to calibrate a home-brew combination of microphone and amplifier is flawed. Sound pressure level meters have a defined frequency response curve which the home-brew system would lack, so the improvised calibration would be accurate only for the particular frequency used. Edison 15:26, 26 October 2007 (UTC)

I assumed that one would calibrate the home-brew meter using a variety of different single frequencies (tones).

Atlant 23:01, 28 October 2007 (UTC)

You would need a logarithmic amplifier to display the results in the usual decibels if you were to merely use a voltmeter. —Preceding unsigned comment added by 88.109.17.174 (talk) 00:51, 27 October 2007 (UTC)

Or a VU meter or a voltmeter with a "decibel" scale as most analog multimeters (VOMs) used to have.

Atlant 11:48, 30 October 2007 (UTC)

Why do humans rarely eat gull meat?

There are gulls everywhere. The gulls are large and fat. Why do people not shoot them for food like they do with wild duck, pheasant and pigeon? --81.77.116.167 19:25, 25 October 2007 (UTC)

Isn't it said to be bad luck to shoot gulls? Either that or they taste of rancid fish :-) Astronaut 19:43, 25 October 2007 (UTC)

Seagulls are often culled as in many areas they are classified as vermin and can be very aggressive (particularly Herring Gulls. Why they are not used for food is a good question as the largest ones can be bigger than a chicken.GaryReggae 19:56, 25 October 2007 (UTC)

• Avoidance of bad karma, see Jonathan Livingston Seagull. --JWSchmidt 21:15, 25 October 2007 (UTC)

Three reasons:

1. Gulls are scavengers. This means they're likely to carry all sorts of bacteria and parasites, and by eating them, you're likely to get infected.
2. Gulls are scavengers. This puts them very high up on the food chain, so toxic chemicals are likely to bioaccumulate to high levels.
3. Gulls are scavengers. Meat tends to pick up the flavor of whatever the critter eats. Gulls tend to eat decaying food, so guess how gull meat tastes?

--Carnildo 23:38, 25 October 2007 (UTC)

Sorry, this is bad science. Think chickens and ducks which are covered in bacteria, think crabs which scavenge on carrion. Both widely eaten with minimal detrimental effects. That is one reason why we cook food. Richard Avery —Preceding comment was added at 07:43, 27 October 2007 (UTC)

Yeah I suppose so although I'm not too sure about the last point, pigs used to eat all sorts of junk (eg pigswill) but they are still eaten and sheep/cows don't taste like grass either! Pigeons are also eaten sometimes and they eat rubbish off the streets and carry disease too. I would have thought that cooking the bird properly would destroy any bacteria. PS why all the recent questions about gulls? This is the third one I've seen in the last week or so! GaryReggae 12:19, 26 October 2007 (UTC)

Slight note, most beef consumed in the U.S. is from corn-fed cows raised in CAFOs and grass-fed beef does in fact taste appreciably different and is one of the things that distinguishes Argentinian beef, for example. Read The Omnivore's Dilemma for more information on the consequences of raising ruminants on a corn versus grass diet. One of the regular editors/contributors here is some kind of seagull fanatic or something, so the gull questions might be light-hearted trolling of him or something related, FYI. 38.112.225.84 14:37, 26 October 2007 (UTC)

FYI, the pigeons we usually eat are not (usually) the type that scavenge the rubbish in our streets. --Kurt Shaped Box 18:50, 26 October 2007 (UTC)

I always assumed the feral pigeons were Wood Pigeons - you learn something every day!GaryReggae 19:37, 26 October 2007 (UTC)

In my experience, you very rarely get to see Woodpigeon close up - they're very nervy, flighty birds. I suppose that they've learned to beware the hand of man over the years - as it often holds a shotgun. --Kurt Shaped Box 06:57, 27 October 2007 (UTC)

Pffft! Maybe where you live. The woodpigeons in my garden barely move until you're a couple of metres away. Very fat, lumbering things they are. Look quite tasty. Skittle 15:19, 28 October 2007 (UTC)

Shoot a few. Then watch their expressions change when they see you going out. --Kurt Shaped Box 22:26, 28 October 2007 (UTC)

The only real answer here is because chickens are bigger, easier to grow, easier to feed, taste better (apparently), survive much healthier without eating meat etc. It is the same reason why we keep cattle/pigs over any other animals for food - they 'farm' better. There aren't really any wild land animals that most humans eat anymore. Eating small birds was extremely common throughout history (typically the only meat the poor/slaves would eat right up till late 18th century etc). Usually they would eat pigeon or birds that were easier to capture and net. Homeless people in most countries still eat birds like gulls and pigeons, most typically capture by throwing metal pipes at end, believe it or not.--Dacium 00:17, 29 October 2007 (UTC)

-enic vs -eic suffix on acids

I was editing pinolenic acid. It is frequently called pinoleic acid. I'm pretty sure that's a mistake (rather than just an alternative spelling.) That is, pinolenic acid has three double bonds and I think that a compound called pinoleic should have two. I wanted to provide a cite a definitive guide to the chemical notation. But I struck out in the IUPAC Gold Book [8]; maybe I didn't know what term to search for.

Can somebody point me to an authoritative statement about -eic vs -enic, as used in fatty acids? David.Throop 20:45, 25 October 2007 (UTC)

Actually, the suffix is "ic" for carboxylic acid. So the question is whether the proper prefix is "pinole" or "pinolen." Someguy1221 21:04, 25 October 2007 (UTC)

Amphisbaena

I've got to write a report on an animal with near nothing about it, so could someone tell me What signs of health and illness in an amphisbaena would be, and mabey how long it is? I've goth this much so far, but I've got to do a "rehabilitation" thingy for it.

Habitat - Desert Cage - Heavy cage, snip wings, lead under cage, poison fangs Consider - can become two halves Food - Ants

en.wikipedia.com/wiki/amphisbaena http://www.eaudrey.com/myth/amphisbaena.htm

Habitat - Desert Cage - Heavy cage, snip wings, lead under cage, poison fangs Consider - can become two halves Food - Ants Similar in color and appearance to a worm; it can slither in either direction well; medismal uses; 50 feet long, with two heads at each end. It has large bird-like feet and a pair of feathered wings, making it quite an unusual sight to behold; The amphisbaena is a very rare creature that supposedly descends from a legendary serpent that was once long enough to encircle the entire globe and powerful enough to kill gods; An amphisbaena sees four times as well as a human in low-light conditions and twice as well in normal light; An amphisbaena can ascertain other creatures by smell and hearing within 30 feet; According to Greek mythology, the mythological amphisbaena was spawned from the blood that dripped from Medusa the Gorgon's head as Perseus flew over the Libyan Desert with it in his hand; it can't be determined which is the rear head; egenerative abilities - if the amphisbaena is cut in half, the two parts can rejoin venomous fangs - the amphisbaena is venomous, as Pliny the Elder indicates: "The amphisbaena has a twin head, that is one at the tail end as well, as though it were not enough for poison to be poured out of one mouth." efficient duplicity - the amphisbaena's heads can handle more than one task at once. speed - according to some accounts, the amphisbaena can slither (or run) very quickly, and, in the case of the limbless amphisbaena, it can slither in either direction, as Isidore of Seville indicates: "It can move in the direction of either head with a circular motion." The poet Nicander, however, describes the amphisbaena as "slow in motion". rolling - by locking the jaws of its two heads or holding the neck of one in the mouth of the other, the amphisbaena can roll like a hoop, as depicted by medieval artists warmbloodedness - unlike most serpents, the amphisbaena was apparently unperturbed by the cold, as Isidore of Seville indicates: "Alone among snakes, the amphisbaena goes out in the cold." pregnancy - pregnant women wearing an amphisbaena around their necks would supposedly have safe pregnancies; in accord with this, women in power would wear bracelets in the shape of amphisbaenae arthritis - wearing a dead amphisbaena or its skin would cure arthritis chilblains - wearing the skin of an amphisbaena will reduce this swelling of the hands caused by cold cold - wearing a dead amphisbaena or its skin is a cure for a cold woodcutting - nailing the skin of an amphisbeana to a tree before cutting it down will make it easier to fell the tree and keep the lumberjack warm

http://en.wikipedia.com/wiki/amphisbaena http://www.eaudrey.com/myth/amphisbaena.htm http://www.pantheon.org/articles/a/amphisbaena.htm http://www.uvm.edu/~chmartin/amphisbaena.htmll http://www.monstropedia.org/index.php?title=Amphisbaena YДмΔќʃʀï^→Г_C← 10-25-2007 • 21:00:36

Amphisbaena is a mythological animal - there is no such thing! So asking these kinds of question is not going to get you any clear facts because there aren't any facts...all there is is fiction. So all you are doing is reading about the mythology that other people have written. So solid things like how long it is or how you know it's getting sick are going to be figments of someone elses imagination. It's very likely that if you've been given an assignment to write about this creature, then in all likelyhood your teacher is trying to get you to use your imagination. So go nuts! Think up some cool things and write about them (as had all of the other people you've found writing about it). I would like to know how they poop without the necessary apparatus!SteveBaker 23:11, 25 October 2007 (UTC)

Well, the assignment might be a cultural study, in which case all claims need to be sourced. As for the pooping question, maybe the head that doesn't eat, vomits, and they spend all their time trying to out-eat the other head, so they're not the unlucky end. risk 03:18, 26 October 2007 (UTC)

This could be a misspelling of Amphisbaenia which appears to be the real animal from which the mythical one was born (figuratively speaking, of course. Literally speaking the mythical creature was born of the blood of the Medusa). --Psud 09:46, 26 October 2007 (UTC)

Remember, rover gets the pill and fido gets the suppository. (a joke from Futurama) -- Diletante 16:20, 26 October 2007 (UTC)

Hmmm CatDog? SteveBaker 18:22, 26 October 2007 (UTC)

October 26

Benzodrene

In The Diary (Freaks and Geeks episode), one of the characters says that Kerouac was high on "Benzodrene" when he wrote On the Road (something our article disputes).. but I can't find any information on Benzodrene, and only 30 google results. Is this a simple misspelling? I uploaded the relevant clip to youtube. (I guess in the 1980s they still took the beat generation somewhat seriously for some reason..)--ffroth 07:12, 26 October 2007 (UTC)

I think she actually said, "Benzedrine" Rockpocket 07:32, 26 October 2007 (UTC)

Ohh thanks --ffroth 13:49, 26 October 2007 (UTC)

UK - Safest place to live in the world?

I'm leaving aside all man-made aspects of danger here. I'm thinking that maybe the UK is one of the safest places to live in the world when it comes to nature viz :-

We don't get major natural disasters. There are no volcanos. Earthquakes are extremely uncommon and very rarely cause fatalities. We don't get hurricanes. We get occasional tornadoes and high winds but compared to say the USA they are nothing. The temperature rarely gets high enough or low enough to kill you easily. We have exactly ONE species of poisonous fauna - the adder which isn't even all that poisonous - no spiders or scorpions. No dangerous carnivores (barring the odd escaped panther?) - bears and wolves were wiped out. Is there some kind of index for the relative danger from the natural environment by country? Exxolon 13:21, 26 October 2007 (UTC)

Like you mentioned, you are leaving out all the dangers caused by man, which are far more dangerous than any natural disaster. 64.236.121.129 14:25, 26 October 2007 (UTC)

We don't have guns either...or 'militia' groups or KKK members or crazy religious groups who wall themselves off in large compounds and arm themselves to the teeth. On the other hand, we do have terrorist attacks that are more frequent than in the USA (for example). I'm sure there are safer places - but safety isn't everything. Theres jobs, standard of living, friends and family. I'm sure you could find a desert island somewhere with NO risks at all - but what would life be like? SteveBaker 18:20, 26 October 2007 (UTC)

Ireland may be even safer - we don't have adders or wildcats, and never get tornadoes or even heavy snow, and have neither heatwaves (didn't it reach 40 degrees last summer in Cornwall?) nor the extreme cold of Scottish winter. EamonnPKeane 15:03, 26 October 2007 (UTC)

We also don't have malaria-causing mosquitos, rabies or any other diseases that visitors to the the UK would need to be immunised against. The main natural threat has to be climate change (which partially happens naturally as well as being contributed to by man, many parts of the UK would be underwater if sea levels rose and if the transatlantic currents changed, it could drastically alter our climate. GaryReggae 19:33, 26 October 2007 (UTC)

Does 'cuisine' count as a major natural disaster? Mad Cow disease and hoof and mouth disease come to mind as the type of outbreaks that affect U.K disproprtionately. --DHeyward 06:34, 27 October 2007 (UTC)

Mad cow - okay, I'll give you that one. Foot and mouth, however is more of a financial thing for the farmers - it's not (very) communicable to humans and hardly a threat to life. --Kurt Shaped Box 07:13, 27 October 2007 (UTC)

Note that in each instance you're comparing the UK with the worst place. For example, for storms you compare with the USA. But you should be comparing with other places that get little wind. I don't know which that would be, but the Netherlands is sort of shielded by Britain and therefore gets less wind when there is a storm. Of course the Netherlands could get inundated much more severely during such a storm, such as in 1953, but we have fixed that problem since. :) Actually, Britain and Ireland are easy to keep free of dangerous animals because they are islands, but the Netherlands has so little nature left that we don't have anything worse than adders either. Or do we? What about lyme disease, spread by ticks? Doesn't the UK have that too? Speaking of diseases and islands, what about (yes, here it comes again) New Zealand? Almost totally free of dangerous animals and diseases. There is volcanic activity, but that isn't too severe. And it's just in specific areas. Does the entire country have to be safe? That would give big countries a disadvantage, but that's the wrong way around - a big country increases your chances of finding a safe area. DirkvdM 07:44, 27 October 2007(UTC)

UK has the fish n chips a major delicious health hazard. Aside from that why would the UK be safer than say eastern Europe if you only consider natural dangers? If the sea level rises how high and protected is london? Keria 16:56, 27 October 2007 (UTC)

Heh don't live in the North Island of New Zealand. Auckland you're basically living next to an overdue volcano, Wellington you're living directly on the boundary of two plates ready to grind, the Bay of Plenty area gets flooded easily, central areas get the same volcano issues (Mount Ruapehu is the most recent one). --antilived^{T | C | G} 21:04, 27 October 2007 (UTC)

Apropos of nothing, the United Kingdom actually has a higher "tornado density" than any other country in the world. For example, on November 21, 1981, 104 tornadoes hit the country during daylight hours alone. Of course, the overwhelming majority of them were virtually unnoticable. GeeJo ^(t)⁄_(c) • 11:25, 28 October 2007 (UTC)

The UK could be in big trouble if the shutdown of thermohaline circulation occurs. StuRat 19:47, 28 October 2007 (UTC)

Meh. Just a different type of weather for us to whine constantly about... :) --Kurt Shaped Box 22:32, 28 October 2007 (UTC)

A bipedal molecule

This is not a very normal question, but I'm looking for a molecule that, when drawn as a diagram, looks like a human (or a stick figure, to be more precise). I understand that such a molecule may require one to overlook certain rules when it comes to drawing molecules, and I'm afraid my knowledge of drawing molecules is very basic, but it would be great if I could find the closest match to a human figure possible. So far, the closest I've come is allylbenzene, but it requires some manipulation of the molecule. Benzene does seem to make a great head for the figure, though. Any ideas would be greatly appreciated. Many thanks Vvitor 13:26, 26 October 2007 (UTC)

Nanoputian? It says that they've actually been synthesized. Also look at [9] (about halfway down the page) and [10] for the actual journal article. --Bennybp 14:22, 26 October 2007 (UTC)

That's absolutely fantastic! Thank you so much!Vvitor 15:07, 26 October 2007 (UTC)

Three characters of the One over zero webcomic are antropomorphic molecules. – b_jonas 09:45, 29 October 2007 (UTC)

additive nature of heats of reaction

what is it, what does it affect, and if you answer I will thank you. haha. --MKnight9989 14:35, 26 October 2007 (UTC)

Ah, there's a name for this, but I forget. It's the concept that the heat of reaction for A -> C equals the sum of the heats of reaction of the reactions A -> B and B -> C. This also applies to more complex chemical reactions, so long as the reactions you are adding have the same net products and reactants as the final reaction you're calculating the heat of. Someguy1221 17:01, 26 October 2007 (UTC)

Hess's law? —Keenan Pepper 17:37, 26 October 2007 (UTC)

What is the name for this kind of aircraft, and why don't we make them?

http://images.wikia.com/starcraft/images/6/6e/Banchee.jpg

^Would something like that be considered a helicopter? Where you have two covered turbofans (I think they are turbofans), on either side of the body. The tail rotor doesn't make much sense though, because you can just have each turbofan spin in opposite directions... Anyway, why haven't we made an aircraft like that yet? It appears to be far superior to our helicopter designs where you just have one very larger rotor on top, and a tail rotor. This design looks stealthier, not as vulnerable, faster (if combined with a jet engine, which a regular helicopter can't use), doesn't need a tail rotor, potentially can use ejection seats (which are impossible to mount on helicopters for obvious reasons), etc. Anyway I've seen lots of fictional designs that look like the example I gave, so why hasn't it been created in real life yet? 64.236.121.129 15:05, 26 October 2007 (UTC)

• Well, we do have the V-22 Osprey which sort of operates that way. Its history will show why we don't have more of them right now... Arakunem 15:26, 26 October 2007 (UTC)

That's not the same at all. That's a tiltrotor aircraft. It has nothing to do with what I'm talking about. 64.236.121.129 15:38, 26 October 2007 (UTC)

Tiltwing perhaps a little closer? Just because it appears in computer games doesn't actually mean that it is superior to actual helicopters. Perhaps designers simply enjoy the model rather than that of a typical helicopter model? I mean it does look more 'futuristic'. Can you quanitify how it is 'stealthier' or less vulnerable than a regular helicopter? Lanfear's Bane | t 15:46, 26 October 2007 (UTC)

No, Tiltwing has no relevance to this design either. Your second statement, is an assumption. My question is, if that is true, why is it not practical or better than existing helicopter designs. I'm assuming you aren't familiar with the Comanche helicopter. It has a shroud over its tail rotor to help reduce its radar signature. It of course, can not mount a shroud over its main rotor. However this design of aircraft can, and as a result, should help reduce its radar cross section far more, since it lacks the large main rotor, and tail rotor. It appears to be less vulnerable because it lacks a rather vulnerable main rotor. Two smaller turbofans mounted on the sides aren't as exposed to enemy fire. I'm not saying the design I posted is definitely practical or better than existing helicopter designs, I'm asking if it isn't, why? This question is directed to those who are familar with engineering, aviation, etc. 64.236.121.129 16:03, 26 October 2007 (UTC)

(ec)What you're talking about is a cartoon. The tiltrotors include actual, real aircraft. See also Powered lift. There are also real helicopters with more than one rotor like the CH-47_Chinook - see Tandem rotors for more. Friday (talk) 15:47, 26 October 2007 (UTC)

Actually it's from a videogame. Please don't make blank assumptions, it's a little condescending. Yep, those things certainly are real, but you didn't address my questions at all. 64.236.121.129 16:03, 26 October 2007 (UTC)

The "Banchee" (I assume that's the name based on the filename) seems to have a lot of fins and protrudey-bits, which seem to make stealth more difficult. Yes, you can coat them all with Radar absorbent material, but that goes for anything you would want to stealthify, so this design is no more or less stealthy in that regard. Plus, if this design's rotors are just to provide lift, while a jet engine provides forward thrust, that's going to cause a lot of intersting flight dynamics at any kind of high speed... Arakunem 15:55, 26 October 2007 (UTC)

Haha, the protrudey bits aren't relevant to the basic question I'm asking now are they? I'm talking about using two small turbofans to provide lift instead of a large main rotor. So your points about the stealth aren't very relevant. I'm not sure if adding a jet engine would be a good idea or not, so lets throw it out. The basic question I'm asking is, why don't we use the twin turbo lift fan design? 64.236.121.129 16:03, 26 October 2007 (UTC)

Well, you did say it would be more stealthy in your original post... just commenting on that bit too. :) Arakunem^Talk 17:14, 26 October 2007 (UTC)

Sure, it looks cool, but did you look closely at the design? It looks like the props in the "wings" are just holes punched in the wings, with the engines of the fans mounted inside the holes. Apart from obvious problems like fuel lines, it doesn't look like those props could provide much lift, nor are the wings very stable-looking for a very heavy-looking aircraft. If you fixed those problems, you'd probably end up with something looking quite like the V-22 Osprey. I also notice what appears to be an air intake at the front of the vehicle, so there might be a jet engine of some type hidden under the vehicle. -- JSBillings 16:37, 26 October 2007 (UTC)

I'm not sure what you mean by props. Do you mean propeller? There are none. Those are turbofans. Ignore the intake, I'm just talking about the twin turbofans. Hmm, a turbofan should provide lift. The F-35 uses a single small one for STOVL, and has been demonstrated to perform VTOL in testing. Still this is mostly speculation. I was hoping for an answer from an avionics engineer or similarly qualified person. 64.236.121.129 17:10, 26 October 2007 (UTC)

(I used to be a flight simulator designer - now I work in video games - so I'm qualified both ways!)

Your basic answer is "We do - it's called a V-22 Osprey". But you can't possibly say that just because this thing looks cool in a game that it's even feasible in reality. Game designers (of which I am now one) do whatever looks cool with no thought for practicality. That thing looks great as a video game prop - but as an actual, practical aircraft, it's horrible!

• No streamining - all sorts of pointless things to add drag and slow it down. Could they really not put some cheap plastic fairings around some of those knobbly-bits to smooth it off a bit?
• Those gigantic pods (missile launchers?) are ridiculously large for the rockets they deliver. Compare the size with the ones on a real aircraft Image:AH-64 dsc04578.jpg for example. Why do rocket launchers need cooling vanes on them? The rockets come out in a bazillionth of a second - there isn't time for the launcher to get hot.
• It's about as far from 'stealthy' as you could imagine - with all sorts of curved surfaces and bobbly bits that you can't 'stealthify' with any amount of radar absorbing paint. (Did you know: that one time someone didn't fully tighten up one of the screws on the underside of an F117 stealth fighter - and that 'bump' was enough to make the plane visible from ten times the normal range?)
• For some reason, they appear to have used rivets of the kind that would hold a WWI battleship together to construct things like the cockpit canopy and the missile pods. Howard Hughes invented the flush rivet in the 1930's...please use it!
• It's painted with lots of pretty red bits just to be sure that all of our enemies can spot even if they have no radar or somehow didn't hear the ungodly noise from those gigantic engines.
• It's in no way clear how the air from those gigantic drag-inducing ducts would get into the engines. If the engines need that much air, they must be consuming one hell of a lot of fuel. Since there is almost no place to put any fuel (eg, no wings), it's going to have a very short range...unless those air ducts really are a lot bigger than they need to be.
• Why is the tail rotor so goddam huge and how does the power get to it? With twin rotors, it scarcely needs a tail rotor at all.
• Pilot visibility downwards or rearwards would be almost non-existant because of the bulge under the canopy and those two gigantic engines - so this is not going to be easy to land in a vertical manner or use for ground-attack roles.
• With all that drag, and no obvious means of forward propulsion other than the vertical fans - it's going to be slow as all hell - so it's no good for air combat.

Superficially, it looks a bit like an AH-64 Apache - but with overly large everything! It might make a good Disney-land ride attraction - but it's not in any way a useful aircraft design!

SteveBaker 17:13, 26 October 2007 (UTC)

Haha, SteveBaker, you didn't address the turbofans at all! That was kind of the point of the question. I kind of wish I didn't choose that image, because everyone is getting hung up over the doodads it has, but ignoring my questions (one of your points, I even mention in my first post). I was only talking about its twin turbofan design. Also everyone mentioning the V22 is a major -_-;. The only thing it has in common is the fact that it uses two rotors that spin in opposite directions. I'm talking about an aircraft with two smaller turbofans on each side of the body. 64.236.121.129 17:39, 26 October 2007 (UTC)

It's probably worth noting that the wing-prop-things are absolutely not turbofans. While a turbofan is an engine, these are clearly just propellors (that is, no ducting whatsoever exists to send their airflow to a turbofan engine assembly -- they're aligned for vertical thrust and nothing else). Apart from that, I think Steve has covered the bases better than I'm likely to. — Lomn 17:31, 26 October 2007 (UTC)

Well whatever you call them. Although the official webpage on it, http://www.starcraft2.com/features/terran/banshee.xml calls them twin turbofans. I'm just going by what it calls them. 64.236.121.129 17:46, 26 October 2007 (UTC)

That's fine within the context of a game that doesn't have to rely on reality, but if you're going to ask "why don't we actually make/fly/use these?", then you've got to go by what things really are. Also, I noticed in hindsight that SteveBaker did address the "turbofans" -- he noted that there's no way they could force a reasonable amount of air in to the engines (there's your turbofan reference) given the ducting, orientation, and so forth. — Lomn 17:49, 26 October 2007 (UTC)

Haha, you're mad again. In all fairness, I wasn't sure what they were really called, I alluded to that in my first post. ^^. 64.236.121.129 17:57, 26 October 2007 (UTC)

But every time someone called them something else, you jumped in and said "no, no, no, they're turbofans!" Once again, I'm perplexed as to why you bother posing the question when you've already decided what the answer should be. — Lomn 18:00, 26 October 2007 (UTC)

(Incidentally, I am the avionics engineer you were hoping to hear from) — Lomn 18:03, 26 October 2007 (UTC)

Yea, but that was before you pointed out that they weren't. ^^ Oh good, but you haven't really addressed my questions other than pointing out that the fans aren't turbofans. Oh, and you said they were too small, but that's why there's two of them, and the aircraft is small. Also there's the issue with the F-35 using one. 64.236.121.129 18:09, 26 October 2007 (UTC)

...because Steve addressed them. In short, this aircraft does not exist because it is, top to bottom, a hideously impractical engineering liability. It has no redeeming qualities apart from "it looks cool!" -- though I'll grant that it looks cool. — Lomn 18:15, 26 October 2007 (UTC)

Backing up a bit (to a shorter indent), the reason we don't see two small enclosed props providing lift instead of a typical main rotor is -- they're too small. The V-22 has been linked quite a bit above, but it's quite illustrative of the concept. It's a twin-rotor side-by-side configuration and the props are absolutely massive. Additionally, you can't just run small blades faster because you start bumping into the sound barrier, and the associated turbulence is murder on propellors -- this is the primary reason that prop-powered aircraft hit a speed barrier in the mid 1940s. — Lomn 17:55, 26 October 2007 (UTC)

Yeah - exactly. I didn't address that comment because it was meaningless. A "Turbofan" is a kind of engine, not a kind of 'fan'. The "official webpage" doesn't matter a damn - some guy like me thought it sounded cool so he wrote "turbofan" - he could have written "dark-energy powered cyclowidget" for all it matters. You wanted to know how it could be in REALITY. The thing that you drive with that engine is the thing our OP is talking about - and those are "rotors". Which for some arcane reason have been enclosed in some kind of gigantic and heavy-looking donut-shaped fairing. The Osprey uses a pair of 'turboshaft' engines which are essentially turbofans that are designed to rotate a shaft rather than produce jet thrust. I don't really see how you're going to drive those rotors with jet thrust - so I presume your "turbofans" are really "turboshaft engines driving rotors"...which is precisely what an Osprey does...only it does it without the ugly, heavy, radar-reflecting and ultimately pointless fairings. Incidentally, the other aircraft that this fiction thing looks like - the AH64 helicopter - is also powered by a turboshaft engine. SteveBaker 17:56, 26 October 2007 (UTC)

Haha, calm down steve. You're mad. Yea I called it a turbofan, but I wasn't sure what it was. You should know what I was talking about though. I described it well enough, the fans on the sides. Duh. I'm not sure how well they would perform in providing lift, but I do know that the F-35 uses a similar device for STOVL and it can even perform VTOL. Also those fairings WOULD reduce the radar cross section in two ways. One, they are smaller than a main rotor, so that already reduces it. And two, the fairing would act similarly to the fairing on the tail rotor of the RAH-66 Comanche. 64.236.121.129 18:04, 26 October 2007 (UTC)

The F-35 can use such a fan, yes, but there are major caveats. First, it's also using thrust vectoring from its main engine. Second (and far more important), it's hideously inefficient. No aircraft can possibly maintain the fuel capacity to use such a device as its sole lift source and have any practical use whatsoever. Simply executing a VTOL (instead of an STOL) cuts the max takeoff weight of a Harrier by over a third (meaning effectively zero payload) and significantly reduces its range as well. — Lomn 18:12, 26 October 2007 (UTC)

Note: here's an excellent video showing the F-35 rotating its jet exhaust a full 90° for VTO purposes. I would expect, though I have no reference, that the bulk of VTO thrust is derived from this engine with the lift fan providing balance. — Lomn 18:26, 26 October 2007 (UTC)

Uhh, that video specifically states that the lift fan performs without incident. Hence, most of the lifting force, comes from it. Malamockq 00:42, 27 October 2007 (UTC)

That's not a valid "hence" statement. The lift fan works, yes. That's how the video states it. The lift fan is necessary for the VTO to work -- but nowhere in there does it say what the thrust balance from the fan versus the jet is. I'm banking on the jet's far superior power, using thrust vectoring to help counter its off-center location, to provide the bulk of the thrust. It's just a guess, but I consider it quite reasonable. — Lomn 06:33, 27 October 2007 (UTC)

You obviously didn't even bother to read the F-35 article. The lift fan was one of the main reasonsn why the F35 was chosen over the F32. Also use common sense. If it was the jet in the back that was the primary force in VTO, then you would have the jet with its ass up, and its nose planted into the ground without the aircraft getting very far off the ground. The jet assists in VTO yes, but it's anything but the primary force behind it. Malamockq 00:05, 28 October 2007 (UTC)

Actually, I did read the F-35 article -- and found no specifics regarding the lift fan at all. However, this source rather clearly suggests that it's a 50/50 split, give or take (remember, center of gravity is not the same as center of geometry). Of course, it's a moot point. Simply being able to lift with a fan says nothing about the relative merits of this method of propulsion. In short, the merit is: it's small enough to fit in a fighter. The associated problem is the oft-mentioned inefficiency. To take off with this requires a hefty reduction in payload, combat radius, or some combination thereof -- just to take off. God forbid you actually try to sustain lift and propulsion with a system like this. The rich variety of aeronautical experimentation, coupled with the complete lack of a system like this seeing even a trivial level of use, should provide the final nail in the coffin of the theory that Starcraft is a good source of aircraft designs. — Lomn 07:23, 28 October 2007 (UTC)

If it's a 50/50 split, then that means you were wrong anyway. Yes we know it consumes a lot of fuel, no one is saying it doesn't. I believe the point is, that it simply works. Malamockq 13:29, 28 October 2007 (UTC)

My understanding is that "the point" has always been "this design looks obviously superior; why aren't we using it?" — Lomn 15:22, 28 October 2007 (UTC)

(ec)The difference with the F35 is that the enclosed rotor for VTOL is not used to provide lift after it starts moving forward. So far, I'm still not sure how the Banchee is going to get its forward thrust. The difference with the Comanche's fairing is that it is vertical. That design is meant to scatter radar from ground sources, so the tail rotor appears as a sliver from the ground. From the side view in the air, the fairing does increase the radar cross-section. It's a tradeoff based on the Comanche's expected mission profile. Those Banchee fairings will increase cross-section from ground radar, and since they are angled with respect to the horizon, from the air as well. Arakunem^Talk 18:13, 26 October 2007 (UTC)

Also see the CH-47 Chinook. That's kind of like your Banchee turned sideways, so the concept of 2 rotors (or "fans") providing lift and steering has already been done. Arakunem^Talk 18:01, 26 October 2007 (UTC)

As a practical matter, lift will look something like (length of blade)²*(rate of rotation), while air resistance to rotation is closer to (length of blade)*(rate of rotation)². A larger rotor moving slower is more efficient, and hence better from a fuel consumption point of view. Dragons flight 18:08, 26 October 2007 (UTC)

That's true... I didn't know that. But since there's two, wouldn't it help with efficiency and power? There's more air resistance when you use one large rotor. 64.236.121.129 18:15, 26 October 2007 (UTC)

Apart from all the other problems, yes. But only apart from all the others -- namely, that the rotors are too small. You're exactly right in describing why heavy-lift helicopters have two rotors, though. — Lomn 18:26, 26 October 2007 (UTC)

So it wouldn't work on a heavy carbo chopper. But it could work on a light attack/scout aircraft. 64.236.121.129 18:38, 26 October 2007 (UTC)

Wouldn't it be less maneuverable than a single rotor choope? Beekone 19:13, 26 October 2007 (UTC)

Not at all. It would be more maneuverable because the rotors are smaller, and less cumbersome. 64.236.121.129 20:25, 26 October 2007 (UTC)

Wouldn't the extra mechanics needed to drive two rotors and control them and such-like add a great deal to the weight and therefore reduce its maneuverability? --80.229.152.246 20:51, 26 October 2007 (UTC)

The HUGE thing with radar stealthiness is that flat panels reflect the radar beam away in one narrow, focussed direction (like a laser hitting a mirror) which is astronomically unlikely to reflect it back into the radar's receiver. Hence you're pretty much invisible. A curved panel, on the other hand, spreads the narrow incoming radar beam out into a huge arc - so some part of the reflected signal inevitably hits the radar's receiver antenna and you're BUSTED. Radar absorbing paint and gold plated window glass help a little - but they aren't anywhere near enough without having a stealthy shape. That's why the F117 is made of flat panels with sharp angles everywhere. There isn't a curved panel anywhere on the aircraft - and as a result, it's super-stealthy. Now, look at the picture of this fictitious aircraft - there are curved panels all over the place...notably in those useless fairings. If you wanted to be stealthy (with that kind of design) you'd make the fairing octagonal or something - with hard corners. The Commanche is somewhat stealthy - and has lots of flat panels...but it's far from perfect.

I'm not sure that I buy your argument that two smaller rotors makes you more manouverable. The most manouverable helicopters on the planet are the ones with a single rotor. What matters here is your angular inertia. Having large amounts of weight far from the center of gravity of the aircraft is a really bad idea. (Remember the old thing about a spinning skater pulling his/her arms inwards to spin faster...same thing here - keep the weight in the middle to turn faster). Most helicopters have the engine, the 'main mast' the weaponry and the fuel tanks (which are the heaviest bits) as close to the center of the helicopter as possible - with a really lightweight tailplane and lightweight rotors. This fictional plane has two honking great huge engines and two MASSIVE weapons pods mounted far out to either side - and the most complicated, heavy-looking tail assembly I ever saw in my life! To add insult to injury, it's got those huge (and unnecessary) fairings around the rotors - adding lots of structural weight far out from the centerline of the plane. It's certainly going to have a huge moment of inertia compared to (say) the Apache. The Osprey has similar problems with big wings and those complicated gearbox things out where the propellor/rotors are - but it's not a super-manouverable plane either. So without knowing more data - I'd have to say that your fictional plane doesn't look at all manouverable to me. SteveBaker 21:01, 26 October 2007 (UTC)

The B2 Spirit has curved surfaces. So does the F-22 and the F-35. Also it's possible to put radar absorbent materials on a fairing, while it's impossible to put it on an exposed rotor. Malamockq 00:42, 27 October 2007 (UTC)

The operating environment matters, too, though. The aspects of a radar signature a B-2 has to minimize (from below and ahead) are quite different from that of a helicopter (from all sides), and the fighters (1) only aspire to be semi-stealthy (again, from particular aspects) and (2) are still fairly angular. Contrast the F-22 with, say, an F-16 for a good illustration. — Lomn 06:33, 27 October 2007 (UTC)

That has nothing to do with my argument. Steve made the point that flat panels are vital for stealth, but I pointed out examples, where they obviously aren't. In any case, even if he's right, there's nothing stopping a helicopter from having angular, flat panels as a stealthy design. His main point seemed to be that the fairings around the ducted fans were round, therefore they weren't stealthy. But how is an exposed main rotor more stealthy? While I'm at it, it seems he's wrong about Ducted fans being less maneuverable, when the article on ducted fans specifically states that they can be thrust vectored. This greatly aids in maneuverability. Oh, and it seems you were wrong about bashing the original poster for calling those props, turbo fans. Indeed, according to the article on ducted fans, if powered by a turbine, they ARE called turbofans. Malamockq 00:21, 28 October 2007 (UTC)

The B2 flies only a high altitudes and flies pretty much in level flight most of the time - so only the underside has to be flat. The F22 and F35 are really only mildly stealthy - compared to F117, they are hardly stealthy at all. Our OP said This design looks stealthier...and there is absolutely zero evidence for that point of view. The thing is full of disasterously non-stealthy geometry. Things called "corner reflectors" (where three panels meet at right angles like the inside of a cube) are spectacularly visible on radar - they stick out like bright beacons. The obsession the designer of this fictional plane had with cutting channels through the body panels and adding boxes and winglets definitely means that far from being stealthy - it'll stick out like a sore thumb on radar. We know that radar absorbant paint is black - this plane is silver and red...it's not painted with radar absorbent paint. Truly - it's hard to imagine anything that looks less stealthy. Our OP isn't using EVIDENCE to make statements about the probably performance of this thing - it's just wishful thinking - or getting overly immersed in the game. SteveBaker 03:10, 28 October 2007 (UTC)

Uhh, most of your argument are on things the OP said he wasn't referring to at all. Didn't you bother to read his posts? He was just referring to the ducted fans, not the rest of the aircraft. So really, you're arguing a Strawman here. Like I already said, there's nothing stopping a helicopter from having flat panels if they really are most stealthy as you dubiously claim. The RAH-66 Comanche uses stealth technology and, it uses flat panels. Btw, don't make claims about how stealthy the F22 and F35 are. Back up those claims with a source, otherwise you don't have an argument. Malamockq 13:25, 28 October 2007 (UTC)

"Semi-stealthy" is common knowledge among the aviation community, or by anyone with a basic understanding of how stealth works (see the notes about aspect angles above). Apart from that, I'm not sure what points you're trying to score here. Steve and I have addressed both the aircraft as a whole and individual components thereof (particularly the engineering uselessness of the ducted fans), but it's rather frustrating when objectors hop from point to point, ignoring all evidence against them but gleefully proclaiming "you were wrong" when any perceived fault is found. — Lomn 15:20, 28 October 2007 (UTC)

What does "semi stealthy" have to do with anything I said? I'm also giving your baffled bewilderment back to you. I never said ducted fans were practical. But your objections are flawed, mostly because a lot of them don't actually have anything to do with the ducted fans. If you are going to answer his question, stick to what he's asking about. Don't keep harping on design of the aircraft, when he's just talking about the ducted fan design. If you really are an avionics engineer, you should be smart enough to stick to the question, rather than getting hung up over irrelevant points. Malamockq 17:14, 28 October 2007 (UTC)

see the Bell X-22 with it's external ducted fans, seems to be the closest to the concept.—eric 03:46, 27 October 2007 (UTC)

The X-22 wasn't exactly a success - it only flew for a few months (first flew in March'66, and crashed in August of the same year) - and it was the only time ducted fans were tried. The immediate successor to the X-22 (the Bell XV-15) looks a lot like the Osprey - and every other tilt-rotor craft since then. The ducted fans were clearly no the X-22's strong point! SteveBaker 03:10, 28 October 2007 (UTC)

Did he claim it was a success? Stop arguing Strawmen. And no, it wasn't the only time ducted fans were used. There's also the Moller Skycar M400. Malamockq 13:25, 28 October 2007 (UTC)

Geez that one hasnt even flown yet in decades of development. I see a pattern as to why ducted fans are still relegated to video games. And no I'm not argung strawmen... you brought up the Moller. :) —Preceding unsigned comment added by Arakunem (talk • contribs) 15:35, 28 October 2007 (UTC)

No it has flown. Hovered at least, but I'm not sure what your point is. Steve said the X-22 was the only aircraft that used ducted fans. He was wrong. The Moller does too. And you are arguing a strawman by criticizing the performance of ducted fans or the Moller. I never either of them are practical. Malamockq 17:05, 28 October 2007 (UTC)

You can't hold up the Moller skycar as an example of a working aircraft. The X-22 did at least fly...the SkyCar merely hovers at low altitudes...there is a lot of difference! According to our article: "As of late 2002, MI's approximately 40 years' of development has resulted in a prototype Skycar capable of hovering about fifteen feet above the ground." - this is from the SEC complaint about the company. The ductwork around the propellors is said to be mainly a safety thing with some small performance improvements only at very low speeds. But the thing doesn't work - it has been shown hovering at 15 feet altitude (where it's still in "ground effect" and you only need half the amount of thrust) - that's more like a hovercraft than an aircraft. SteveBaker 14:43, 29 October 2007 (UTC)

Hehe you can't make an argument in a discussion and then accuse anyone who responds of strawman. But fine. Here's my final response on this topic, since nobody seems to want to believe the ones who have responded. A direct response to the OP's question, ignoring all the rest: Occam's Razor. We (humanity) have not used this design because any advantage that one piece might have is countered out by disadvantages in so many others, as Steve has pointed out regarding stealth and turning rates. Also, those advantages can usually be realized different ways that are easier and better. Once a ducted fan aircraft can do more than hover while attached to a crane, maybe we will look at that too. But in 100 years of aircraft design, there have been some pretty smart people designing aircraft and rotorcraft. They've tried some way-out concepts and designs. If the OP's design was viable, it would have been done. This is life, not a video game. Arakunem^Talk 18:10, 28 October 2007 (UTC)

tl;dr anyone?

Subsection 1.1: I have seen gravity guns used in lots of films and computer games. Can anyone tell me why we don't make them? After arguing your points I will nitpick and backtrack until all focus is lost and the question becomes a mockery of itself. Any comparisons you try to make I will ridicule and point out that in the totally made up object is not exactly the same as what you are refering to until you question my sources and I will then back down. Lanfear's Bane | t 10:23, 29 October 2007 (UTC)

Yes, indeed. The OP's original question has been clearly and comprehensively answered: If this thing were real, it would be described as a tiltrotor and we don't make aircraft like that because it has no advantages over existing designs.

However, this is not the answer the OP was hoping for ("Wow! Yeah - wouldn't that be cool! Modern aircraft designers are so lame!" might have worked!) - so (s)he started to argue about the answers we gave - which is unfortunate because there is enough expertise here to look at the design rationally and tear it to shreds. That was the cause of the little spiralling debates. The bottom line is the same though - just because you saw it looking cool and behaving nicely in a video game doesn't make it 'real'.

One of the cool things about being a video game designer (and that's what I do for a living) is that you can completely decouple what something looks like from how it performs - and you can make things perform in absolutely any way your imagination leads you - without any reference whatever to real-world science. It's unfortunate that people then take on those utterly unrealistic things and assume that they have some real-world significance. SteveBaker 14:43, 29 October 2007 (UTC)

You could probably attach a decorative fiberglass shell to an Osprey, and wind up with a vehicle very similar to that. Probably about as practical too. 69.95.50.15 15:54, 29 October 2007 (UTC)

plc

what is programming logic control —Preceding unsigned comment added by Londhe.sunil (talk • contribs) 15:51, 26 October 2007 (UTC)

We have an article on Programmable logic controller that is highly relevant. Friday (talk) 15:54, 26 October 2007 (UTC)

Or maybe you're talking about Control flow? -- JSBillings 16:33, 26 October 2007 (UTC)

PLC is primarily a method of controlling things electronically, usually industrial applications such as motors, heating systems, lifts etc but can also be used in consumer products such as washing machines or cars. PLC devices have superseded more primitive electromechanical control systems such as relay arrays and selectors.GaryReggae 19:19, 26 October 2007 (UTC)

Walkie talkies and radios

Why do walkie talkies have a short range compared to radios? Does it have anything to do with the wavelength or frequency of the electromagnetic waves involved? —Preceding unsigned comment added by 86.138.210.65 (talk) 18:53, 26 October 2007 (UTC)

What do you mean by "radios"? Commercial radio stations? "Ham" radio equipment? FRS radios? Citizens Band radios? In any case, the main difference is likely to be power, more than anything else. Both because high power would require heavier, bulkier equipment (and/or shorter battery life), and because having too much range means having more users talking on top of each other, interfering with each others' communications. -- Coneslayer 19:00, 26 October 2007 (UTC)

I more meant what determines the range? 86.138.210.65 19:04, 26 October 2007 (UTC)

Like I said, mostly the power. -- Coneslayer 19:16, 26 October 2007 (UTC)

There are strict regulations dictating the wavelength etc of walkie talkies to ensure that other communication systems (for example Emergency Services) are not interfered with. Power is exactly the thing that dictates the range, your local radio station will have a huge mast which is needed to transmit radio waves miles around while walkie talkies only have a very small aerial. This also ensures the waves don't travel too far. Ham radio is generally slightly more powerful and an antenna of some kind is usually required. You may wonder why mobile phones can operate over such large distances but they use microwaves rather than radio waves to communicate and microwaves can travel much further. GaryReggae 19:24, 26 October 2007 (UTC)

Thank you. Are there an unlimited number of frequencies? What has all this got to do with electromagnetic waves? Im lost. —Preceding unsigned comment added by 86.138.210.65 (talk) 19:46, 26 October 2007 (UTC)

No radio waves occupy a portion of the electromagnetic spectrum. The frequency can be anything between 3Hz and 300 GHz. This is a relatively large gap but the radio waves that you would listen to are generally between 30kHz to 30 MHz, depending on whether they are AM (longwave) or FM (VHF, shortwave). Amateur radio tends to be towards the shortwave end. Radio waves at higher frequencies includes the aforementioned microwaves and UHF tv signals. Radio waves are only one type of electromagnetic waves, light, X-rays and infra-red waves are all part of the electromagnetic spectrum. There is a limit to how many different frequencies you can squeeze into that bandwidth, you can't put channels too close together as they interfere with each other but the same frequency can be used for different things in different places where the waves are not going to intefere with each other. [11] has a good basic explanation of how radio waves work. GaryReggae 19:58, 26 October 2007 (UTC)

You can have radio waves all the way down to not-quite-zero Hertz. (Radio frequencies below a few tens of hertz are useful because they travel through water quite well - so they are used for communicating with submarines). But you can't push the frequency up indefinitely because when you get up high enough (and 300GHz is about it) you start getting infrared "light" instead of "radio" - although it's all really the same kind of thing (electromagnetic waves) - but the properties that make radio work the way it does get less and less useful as the frequency increases. So no, there isn't an infinite range - it's a finite portion of the electromagnetic spectrum. Electromagnetic waves themselves go up MUCH higher in frequency. At the highest frequencies we call them 'X-rays' and eventually, 'gamma rays'. There is also a limit at the high frequency end because as the frequency goes up, so the wavelength goes down. At the very highest frequencies, you start getting wavelengths as small as the planck length and at that point quantum effects start coming into play and it's doubtful you could produce higher frequency waves than that. SteveBaker 20:34, 26 October 2007 (UTC)

However, there are an infinite number of wavelengths within the bounded range. --Elliskev 20:39, 26 October 2007 (UTC)

Yes, but signals being transmitted on one wavelength will overlap and interfere with signals on adjacent wavelengths: the original meaning of the word bandwidth. --Carnildo 22:24, 26 October 2007 (UTC)

If you mean CB walkie-talkies, they are restricted to 4 watts AM, the same as non-walkie-talkie CB sets, because the purpose of citizens' band is short-range communication. That way, a person in Texas can talk on the same channel as a person in Pennsylvania and they won't interfere with each other. There is only so much room in the band allotted to CB. The power is held low for another reason, skip. Radio waves in that frequency range (27 Mhz) bounce off the ionosphere and can come back down thousands of miles from the transmitter, so it's better if they're faint to begin with. --Milkbreath 22:50, 26 October 2007 (UTC)

There are frequencies that you are legally allowed to emit with no limitations on power (but sidebands are not allowed so there are practical limits). 13.56 MHz is one frequency. The microwave oven frequency is another one (somewhere around 2.5GHz) IIRC. --DHeyward 06:58, 27 October 2007 (UTC)

A few questions on Birds

Reading the recent question about gulls has caused me to wonder why certain types of birds (Pigeons, Pheasants and Chickens all definitely do it) nod their heads up and down when they walk? Is there a physical reason for it or is it just a habit these birds have got into over the years?

Also, while I'm on the subject of our feathered friends, I was wondering about the intelligence of them. Some birds, for example parrots and budgies, appear fairly intelligent while others, such as pheasants seem very dopey. Is there a connection between the size of the bird's head compared to its body and its intelligence? Or are all birds equally intelligent (or stupid!)?

Finally, can birds taste or smell things? I know they usually have good eyesight and good hearing (I think).GaryReggae 19:47, 26 October 2007 (UTC)

Regarding your first question. Pigeons' eyes are located on the sides of their heads, permitting them to see over 300 degrees without moving. However, the disadvantage of this positioning is that movement produces motion parallax errors - objects nearby appear to move faster than objects further away. To preserve visual acuity while it takes each step, a pigeon locks its head in position whilst moving its body beneath it. At the last possible moment, the pigeon thrusts its head forward to the next 'lock' position, which it holds for the next step. In this way the parallax effects are minimised. The combined action of the steps and "head locking" gives the characteristic nodding appearance. See here and here for in depth studies. Rockpocket 20:33, 26 October 2007 (UTC)

Regarding your third questions. Traditionally it we thought that birds had a poor sense of smell. However more recent studies seem to suggest it varies dramatically between species and some may have very keen olfactory systems. See here for an overview. Birds also have the ability to taste. It been noted that some species will peck the wings of butterflies to determine whether they taste toxic. If they do the bird will release them, if not they get gobbled up [12] However, in general birds possess relatively few taste buds, on the order of 100 (humans have roughly 9000). Parrots have the highest number (around 350). Rockpocket 20:48, 26 October 2007 (UTC)

Finally, with regards to your second question, see Bird intelligence and there references therein. Rockpocket 20:50, 26 October 2007 (UTC)

I'm personally curious as to whether birds such as pheasants, turkeys, chickens and pigeons are actually as 'stupid' as humans tend to believe, or whether it's simply a form of prejudice/erroneous extrapolation, based on these birds' tendencies to mill around (what would seem to us, aimlessly) in flocks and their general docile demeanour. If so - I've been guilty of it too. --Kurt Shaped Box 06:35, 27 October 2007 (UTC)

And gulls .... you forgot gulls ... how can you forget about gulls? Or are you trying to broaden your horizons?

Anyway, of course it's prejudice. People tend to assume that their way of doing things makes most sense. When we see people from another culture do things their way we often think that's stupid because that sort of behaviour doesn't fit in well in the framework in which they themselves work in. But the other culture has a different framework (set of way to do things), and within that framework what they do does make sense (or not - of course each culture has its stupid habits too). If that is even the case with other peoples, then how can people understand the framework that other animals operate in? DirkvdM 08:19, 27 October 2007 (UTC)

Gulls appear to be pretty smart birds, as it goes. Compare a gull to a pigeon, for example and it certainly *seems* that the gull has more in the way of resourcefulness, interest in social interaction with others of its kind and curiosity about its surroundings. --Kurt Shaped Box 18:50, 27 October 2007 (UTC)

A lot of domesticated fowl are pretty stupid, judging from my own personal experiences -- I don't know if the intelligence has been bred out of them, or the fact that they were raised in boring conditions. I'd expect wild fowl to at least appear more intelligent, because they have to deal with a harsher world. -- JSBillings 13:41, 27 October 2007 (UTC)

Is it true that turkeys believe that they are safe from predators, provided that they cannot see the predator themselves? In other words, if they see a fox (or whatever), they'll just hide their heads behind the nearest object? --Kurt Shaped Box 18:46, 27 October 2007 (UTC)

Wouldn't evolution deal with that pretty quickly? Btw, do foxes live in North America? If not, that would not be such a good example. DirkvdM 08:10, 29 October 2007 (UTC)

New World vultures are known for having a particular good sense of smell. Pfly 07:47, 28 October 2007 (UTC)

Broken link

When I tried to ask a new question on this page a minute ago, it got added to the page about the letter C. Has somebody vandalised it? —Preceding unsigned comment added by GaryReggae (talk • contribs) 19:48, 26 October 2007 (UTC)

There was a problem in the header, which I believe has been fixed. However if you got a cached version of the page, this may explain why you still saw the problem even after it was fixed. Friday (talk) 20:19, 26 October 2007 (UTC)

Science Info

Hi all, Can anyone here provide me with some help, Im looking for interesting information about science, scientists, audios, videos, pictures, articles and etc. All I need is some useful links where I can find my need. Thanking you in advance. —Preceding unsigned comment added by 84.255.171.194 (talk) 22:04, 26 October 2007 (UTC)

Try Google.-- Flyguy649 ^talk 22:05, 26 October 2007 (UTC)

Try:

Category:Images by scientific discipline

Category:Scientists

Portal:Science

Commons Category:Science

Rockpocket 22:18, 26 October 2007 (UTC)

For scientific articles, try Google Scholar. Icek 03:05, 27 October 2007 (UTC)

gender ratios in a species

Are there any species of vertebrates for which the male-female ratio across the entire population is not close to 1:1? Sex ratio seems to be the only article on this topic, but it says pitifully little about non-humans.--M@rēino 22:55, 26 October 2007 (UTC)

Good question, this. Entire population sex ratios are impossible to measure, so scientists instead have to model them. They will often measure fetal, birth, litter or weaning sex ratios. A few interesting things have been found. Fetal sex ratios appear to slightly favor the sex that is larger in size (usually males). A 1988 study by Jaarsveld et al showed that spotted hyenas (unusual in that females are larger than males) had a 47% male fetal sex ratio, but a 55% male juvenile sex ratio. Thus birth ratios are skewed to adjust for the fact more of one sex will die during weaning. However, this doesn't really impact the overall population and the differences are not significanly different from 1:1 anyway.

More interesting, and pertinent, is the situation with certain types of lemming. Wood Lemmings produce about 3 times as many females as male offspring. This is due to an unusual genetic system where they have two different types of X chromosome, X^x and X^O. Any combination of XX is female and X^OY is male as one would expect, but X^xY is female. These unusual females are fertile but only produce X^x ova, which mean they only produce female offspring. Its not fully known the extent to which nature balances up the differences in the adult population, but sampling studies seem to suggest that males do make up as little as 25% of the population at equilibrium (Bengtsson 1977). Lemmings are strange creatures, though, and their populations tend to be cyclical. Its hypothesized that a high female sex ratio may suit this life cycle as a buffer against local mate competition and inbreeding during population low points. Rockpocket 23:59, 26 October 2007 (UTC)

Insects often have many more females than males. With ants, for example, the males are only for procreation and only appear for a short period of time. I don't know what the male/female ratio is at that time, but most of the time there aren't any males at all, so you'd have to average that out.

Btw, for mammals, wouldn't it also make more sense to have more females, for the purpose of procreation? Women carry a child for a long time, but there need only be a few males because their job is done quickly. All the genetic variation can be in the females. And they can take over the male roles by becoming stronger. So I'd like to turn the question upside down. Why is there usually a 1:1 ratio for males and females? DirkvdM 08:38, 27 October 2007 (UTC)

An answer to that can be found in evolutionary game theory: the actual rigorous analysis is somewhat complicated, but the upshot is that spending equal amounts of resources to produce offspring of either sex is an evolutionarily stable strategy: if the general population deviates from this equilibrium by favoring one sex, one can obtain higher reproductive success with less effort by producing more of the other. For species where the cost of successfully raising one offspring is roughly the same regardless of its sex, this translates to an approximately equal sex ratio. Of course, all this assumes that the genes that mainly determine the sex ratio are not sex-linked themselves: meiotic drive genes, as in Rockpocket's lemming example, can play merry hell with the whole thing, at least until some other gene evolves to counter them. —Ilmari Karonen (talk) 23:57, 27 October 2007 (UTC)

Good answer, Ilmari Karonen. Mechanistically, of course, its easy to understand why most mammalian sex ratio are around 1:1. Its because the male sex gametes typically determines the sex of the offspring. Since males are typically XY, there tends to be a 50/50 chance each sperm contains an X or Y chromosome and thus a 50/50 chance of producing offspring of either sex. To deviate from the ratio at equilibrium, you have to evolve a way of influencing this genetically (as the lemmings did) or else you influence the survival of one sex over the other. Rockpocket 01:02, 28 October 2007 (UTC)

The ratio of lions is roughly 1:1 too? --Wirbelwindヴィルヴェルヴィント (talk) 07:59, 28 October 2007 (UTC)

According to a study of hunted lions in the Selous Game Reserve, "the adult sex ratio (36–41% male) [is] ... similar to those of unhunted populations." [13] A study of lions in the Maasai Mara National Reserve found, "overall, their sex ratio was almost at parity and varied neither spatially nor seasonally. Sex ratio was even among subadults but skewed toward males and females among cubs and adults, respectively." [14] Thus it appears the variable pressures on lions during their lives adjusts for sex ratio. It would appear males are more likely to die as they increase in age (not surprising considering the pride system) so more of them are born to make up for it. However, when you add juveniles, sub-adults and adults together, the ratio is around 1:1. Rockpocket 19:45, 28 October 2007 (UTC)

Thanks, everyone! --M@rēino 13:04, 29 October 2007 (UTC)

October 27

Crude oil production

Hello,

Can anyone tell me what has been the total world production of crude oil, in trillions of tonnes, over the period 1859 to 2007?

Many thanks, Carlyon —Preceding unsigned comment added by Carlyon (talk • contribs) 00:16, 27 October 2007 (UTC)

Thats a tough one. Using this dataset from OECD, the total world production of crude oil between 1971 to 2005 was 1.107827 trillion tonnes (trillion meaning a million million). This table provides data back to 1960 in million barrels a day. Beyond that all I can find is Image:Hubbert world 2004.png, from which you could try to source the raw data back to 1900. Rockpocket 01:02, 27 October 2007 (UTC)

Calcium Gluconate Chemical Structure

I'm having trouble putting together the chemical structure of calcium gluconate. I've tried using the BKchem molecular editor or similar programs to lay it out but i've completely forgotten how to do so. If this was all still fresh in my mind from my school years, I'd have no problem. Wikipedia shows a good bit of information about calcium gluconate, but in particular I need to see in diagram form the chemical structure of said supplement. Again, I've completely forgotten how to put these things together. [15] —Preceding unsigned comment added by 76.177.150.63 (talk) 00:39, 27 October 2007 (UTC)

It's a salt of gluconic acid. The rightmost hydrogen in the structure is to be removed (and a superscripted minus sign is to be written right of the rightmost oxygen) to get gluconate. Calcium gluconate is made up of 2 of these units and 1 Ca²⁺ ion, compare with calcium acetate (I think the picture in this article is of the kind you want to have). I don't know the real spatial arrangement of calcium and gluconate ions which can be determined using X-ray crystallography. Icek 03:00, 27 October 2007 (UTC)

Let me see if I've got this straight. From the gluconic acid you've shown, remove the rightmost H and replace it with a superscripted -? How would i illustrate 2 of these units correctly? The shown unit enclosed in parentheses (or whatever the correct term would be here)? Then followed with Ca²⁺? Is this the only possible way of illustrating Calcium Gluconate? thank you very much. —Preceding unsigned comment added by 76.177.150.63 (talk) 23:25, 27 October 2007 (UTC)

You could also draw 2 gluconate molecules and a Ca²⁺ between them (with the right molecule being a rotated version of the left one - the Ca²⁺ should be close to both O^-), similar to the picture in the Wikipedia article (which is a rendering of a space-filling 3d model - the green thing is the calcium ion). Icek 09:08, 28 October 2007 (UTC)

3 dB per octave?

Is there a way of getting a 3dB per octave boost or cut over a wide frequency range? —Preceding unsigned comment added by 88.109.17.174 (talk) 00:45, 27 October 2007 (UTC)

Yes but if it's the simple answer I think it is, I suspect this is a homework problem. Hint: Single poles and zeros create 3dB/octave changes in power. --DHeyward 07:03, 27 October 2007 (UTC)

Uh, no, first-order filters are 6dB per octave.

But yes, it’s certainly possible to design a filter that only changes by 3 dB per octave. Perhaps the easiest way to design such filter is to use a digital filter. Just do an Fast Fourier Transform, manipulate the spectrum to have the desired frequency response, and convert back to the time domain.

It'd be a lot more complicated to design if you have to do it as an analog filter, but it'd still be possible. It'd have to be a high-order filter, that combines an equal number or almost equal number of high-pass and low-pass first-order filters within one circuit. To see that it’s possible to design such an analog filter, you could always split the signal into an arbitrarily large number of bands using a bunch of band pass filters, amplify each band separately by an appropriate amount, and then join the signals together in one output. MrRedact 08:09, 27 October 2007 (UTC)

Actually, I thought of a much easier way to design such an analog filter. Just combine a first-order filter with an analog multiplier in a feedback circuit such that the multiplier is doing a square root. MrRedact 08:20, 27 October 2007 (UTC)

Oops, wait, I think DHeyward may have hit the nail on the head. Are you talking about 3dB voltage per octave, or 3dB power per octave? I assumed you meant voltage. If you meant power, then the answer is a trivial first-order low pass filter or high pass filter. MrRedact 10:06, 27 October 2007 (UTC)

It was 3 dB per octave in voltage i wanted (power is dead easy). —Preceding unsigned comment added by 88.111.67.141 (talk) 15:44, 27 October 2007 (UTC)

OK, then did you understand my idea for the analog version of the filter? The input of the whole filter would be the input of a first-order filter. The output of the first-order filter would go to the + input of an op amp. The output of the op amp, which is the output of the whole filter, would also go to both inputs of a four quadrant analog multiplier. The output of the multiplier would go to the – input of the op amp. You might need a resistor or two in there to tweak the gain or bias, but that’s the basic idea. MrRedact 20:39, 27 October 2007 (UTC)

Yes I understand: a 6dB/octave roll off, when square rooted will give a 3dB/oct roll off? This is one way i thought of, but I want it to work very fast, so the analog mult idea may not be capable of the speed. (the accuracy is not that important- 5% will do)

A mosfet has a square law relationship between voltage and current. You should be able to turn 6 dB/octave in input voltgage to 3db/octave in output current pretty easily. You can use it directly or in the feedback of an op amp. --DHeyward 21:34, 27 October 2007 (UTC)

This idea of using a mosfet (insted of an anlog mult) as the squaring element in MrR's topology is interesting. How would I setup a mosfet circuit to give me a true square of the input voltage (including the dc level)? Also could it be a JFET?

I just googled "mosfet square root circuit". here is one. The middle opamp has the mosfet in the feedback with the drain as the output. This is what I was thinking. JFETs are square law as well though they may require different biasing to stay in saturation. But now that I think about it, you may need square function to get you to "power" and then "power" is 3 db/Octave. --DHeyward 02:22, 28 October 2007 (UTC)

Interesting circuit, tho Im not keen on the necessary inversion and the active offsetting circuit. But thanks for finding it!

stop watch hardware

I want to know the harware of a stop watch(just stop watch) whose accuracy is 0.1 second. —Preceding unsigned comment added by Gangt (talk • contribs) 07:24, 27 October 2007 (UTC)

See stopwatch. The rate of a mechanical stopwatch is controlled by the balance wheel while an electronic stopwatch uses a crystal oscillator. --Justanother 19:14, 27 October 2007 (UTC)

Shock in AC and DC

Why do we get sucked in and pushed out while receiving shocks?..Is it due to ac and dc shock?..What is the shock difference in these two and which one is more fatal?.. —Preceding unsigned comment added by 122.164.49.85 (talk) 08:56, 27 October 2007 (UTC)

See Electric shock#Issues affecting lethality which discusses this. 84.64.123.72 11:33, 27 October 2007 (UTC)

The shock causes your muscles to contract. This can mean that your hand is immediately, and involuntarily pulled away from the cause of the shock - but if you have a grip around the live object then your grip may tighten and you'll be unable to let go no matter what. SteveBaker 02:44, 28 October 2007 (UTC)

German Weinstein: Potassium tartrate or Potassium bitartrate?

Hi, the German article de:Weinstein links to Potassium bitartrate aka cream of tartar etc. and vice versa. Dictionaries say so, too. (See also de:Wikipedia:Auskunft#Weinstein. But Potassium tartrate claims that that is the main ingredient of "Weinstein", though easily confused with the other. Can someone clear that up, please? T.a.k. 10:06, 27 October 2007 (UTC)

Granular layer - cerebellum

Granular layer redirects to cerebellum. Why is this and is this correct? Lova Falk 10:32, 27 October 2007 (UTC)

Did you see the granular layer section? Here's a link with some other definitions. JMiall₰ 11:48, 27 October 2007 (UTC)

Granular layers also occur outside of the cerebellum (most notably, in the cerebral cortex), so this redirection is not really appropriate I think. EelkeSpaak 15:32, 27 October 2007 (UTC)

Cost of heat

A man lives in a place where the temperature is below freezing all year round. His house is heated with electricity, and he has an electric water heater. He keeps his house at a constant 20C, except for the "cold room", in which the thermostat is set at 5C. The water heater is located in an area where the temperature is 20C. He decides to move the water heater to the "cold room", to gain more living space. (This does not significantly change the distance from the water heater to where the hot water is used.) The man notices that the temperature in the "cold room" remains at 5C, even though the water heater feels warm. Would the total monthly electric bill change because of the move? GarthGarth 13:31, 27 October 2007 (UTC)Garth

If I understand the assumptions correctly, no. Electric heaters are 100% efficient in the sense that they produce one kWh of heat per kWh of electricity. Since (by assumption) nothing else changed in the move, the total power consumed by the water and space heaters must be the same as before, although it may be differently distributed between them. -- BenRG 14:19, 27 October 2007 (UTC)

I can't see how that can be right. The hot water is loosing heat by means of radiation and conduction the rate of both are affected by the temperature difference between the hot water and the room temperature. Conduction is proportional to temperature difference and radiation goes as the 4th power.Theresa Knott | The otter sank 14:38, 27 October 2007 (UTC)

The water heater will have to work a little more to keep the water hot, compared to the 20C room, since more heat is being lost to the colder room. At the same time, the heater in the house has to work less to keep the 5C room at 5C, so the house heater will use less energy. So the monthly energy bill is probably going to change. Whether its up or down depends on more specific info such as efficiencies, volume/area of the rooms, etc, and a bit of calculus. Arakunem^Talk 15:26, 27 October 2007 (UTC)

The water heater will use more electricity due to the greater temperature differential between the hot water and the room. However, the wasted heat from the water heater will contribute to the heating of the room. So the room's heaters will work a little less, and the water heater will work a little more. Probably won't see much change in electrical usage.

Obviously, this assumes the rooms are heated year round, and moving the water heater doesn't change the temperature of any of the rooms, and the new plumbing doesn't snake outside, and so on...--Duk 17:08, 27 October 2007 (UTC)

No, no change at all. Forget the details. The temperatures stay the same, so the same amount of heat is generated. The only problem might be efficiency, but since heat is the ultimate energy waste product, but also the goal here, efficiency will be 100%, no matter what. So unless more or less warmth leaks out of the house, for example because the heater is moved to or from an outer wall, energy consumption will remain the same. DirkvdM 17:52, 27 October 2007 (UTC)

That assumes that none of the heat from the water heater (and the water in it) is lost to the room. Arakunem^Talk 23:03, 27 October 2007 (UTC)

Actually, it's the opposite. It assumes the water heater is just another heating element in the room. There are 3. One for the 20C rooms, one for the 5C room and the water heater. The temperature doesn't change in the rooms. The heating elements were just rearranged. The details of the percentage of heat from each element is not asked, just the overall heat. It doesn't change because there are no changes in the temperatures of the rooms. The sum of the heat is the same in each case so the energy added is the same. --DHeyward 06:46, 28 October 2007 (UTC)

If the electricity is being turned to heat in both cases, there will be no difference. If the water heater works that way, but the heater from the room moves heat in from outside, which is more likely the case, the less efficient water heater will be doing proportionally more of the heating, and the electricity bill will go up. — Daniel 20:18, 27 October 2007 (UTC)

Hang on, hang on, hang on.

If the water heater loses some heat to the room, we can think of it as being less than 100% efficient at heating water, but it is guaranteed to be 100% efficient at heating the water+room system.

If the other furnace is outside, and if it is less than 100% efficient, it might well lose some heat to the outside, which would then be lost forever.

So, paradoxically, if the other heater is outside, the less efficient the water heater is, the lower the overall electricity bill will be...

(The only exception would be the case where the grossly inefficient water heater in the "cold room" ended up heating it above the requisite 5°C.)

But on the other hand, if the other heater is inside, and if it's less than 100% efficient, any heat it loses is lost to the room, so hey presto, it's 100% efficient after all. —Steve Summit (talk) 23:17, 27 October 2007 (UTC)

And then there's how leaky the windows might be... *shifty* —Preceding unsigned comment added by Arakunem (talk • contribs) 23:23, 27 October 2007 (UTC)

Makes no difference. There has to be some heat loss to the outside, otherwise waste heat from the water heater would heat the "cold room" above 5°, and for that matter the rest of the house above 20°. Whether that loss to the outside is slight or extreme is immaterial to the rest of the problem. —Steve Summit (talk) 01:03, 28 October 2007 (UTC)

...wait a minute. Did we just do someone's homework for him? —Steve Summit (talk) 01:04, 28 October 2007 (UTC)

It's okay. I think after reading this they'll be more confused, and have to resort to thinking through what their textbook says...Skittle 15:07, 28 October 2007 (UTC)

Ah - a homework question. Ok, just draw a box with a arrows for energy_in and energy_out. Since all the temperatures and house insulation stay the same, energy_out stays the same, and therefore electricity_in must stay the same. Forget everything else! --Duk 16:25, 28 October 2007 (UTC)

I don't think a water heater can ever be 100% efficient. It's heating water in copper tank which is connected via nice metal pipes off into the outside world. Being metal, those pipes are going to conduct heat away out of the tank - and out of the room too. The answer to this question depends on the relative efficiency of the room heater and the water heater. If the water heater is more efficient then your bills should go down - if it's less efficient then they'll go up. SteveBaker 02:42, 28 October 2007 (UTC)

Not so. See my "paradoxically" argument above. It'd be very hard for an electric water heater to lose heat directly to the outside world, without heating some part of the house up first. (But similarly for a resistive electric space heater, located inside the house.) —Steve Summit (talk) 03:44, 28 October 2007 (UTC)

Yes but thats the point. The heater has been moved to a colder room, therefore is losing more heat faster than it was in the warmer room. Thus, the heater's heater will be running more frequently to keep the water at its desired temp. Thus more power is used by the water heater simply because it is running more often. The second consideration is then, that the heat lost from the heater to the room means the room's heater will not need to work as hard to keep that room at 5C, so it will use less energy. So the total house energy bill will change, but without more info you cant say for sure which way it will change, and by how much. Arakunem^Talk 15:16, 28 October 2007 (UTC)

Explain to me again why it will cost more (or less) to heat a room with waste heat from an electric water heater, versus with heat from an electric heater. —Steve Summit (talk) 16:40, 28 October 2007 (UTC)

Yes, you are quite correct! I was looking at the components and not the system as a whole. *Awards one pie* :) Arakunem^Talk 18:21, 28 October 2007 (UTC)

I don't see the location making any difference in energy use in the specified, somewhat atypical, conditions. The 5 degree room is already electrically heated, so any heat lost from the hot water heater from the insulated tank or the water pipes or even the electrical wiring to the air in the cold room will displace heat which would otherwise have been consumed by the heater in the cold room which maintained it 5 degrees warmer than the outside. The heat from the water heater which would otherwise have helped heat the warm rooms will be replaced by additional heat from the electric heaters there. Zero net effect. If it were a real world home, and the water heater were moved from living space to an unheated garage or unheated basement, the electric bill might go up, since most homes do not have a room thermostatically maintained five degrees warmer than a constant temperature outside. The devil is in the details. Edison 21:10, 28 October 2007 (UTC)

Yeah, but the assumption was that the temperature in the rooms is thermostatically maintained.

I said it 'forget the details', Duk said that energy in = energy out and Arakunem said to look at the system as a whole. Same idea, the wording just improved gradually. If the energy in the system (the house) remains the same and the energy going out of the system (heat leakage from the house as a whole) remains the same, then the energy going in is the same. And all that energy would be in the form of heat, since heat is the ultimate energy waste product. It would have to be a very stupid heater if it didn't convert all the energy into heat - what else would it convert it into? DirkvdM 08:59, 29 October 2007 (UTC)

Why is hot water better for washing dishes?

Why is it that hot water is better when washing dishes? Why does it seem to remove more dirt/grease/debris than cold? Is it purely from the thermal effect? or does the sometimes higher pressure of a hot water tap jet also have an effect? 84.64.123.72 13:38, 27 October 2007 (UTC)

The main factor is that things dissolve more readily in hot water. For instance, a cup hot water can hold more sugar than a cup of cold water. This takes care of the dirt that dissolves in water. Most of the dirt (like fat) does not dissolve in water, so we add detergent to the water so these dissolve a well. Finally, some amount of mechanical force is necessary to speed the process along, which is where the brush comes in. This also means that if the hot water has greater pressure (not sure if that's true) it may have a slight effect. 14:14, 27 October 2007 (UTC) —Preceding unsigned comment added by Risk one (talk • contribs)

In addition hot water softens fat and allows emulsification with a soap or detergent more rapidly than at lower temeratures. Hey, it also makes doing the dishes more comfortable Richard Avery 15:13, 27 October 2007 (UTC)

"also makes doing the dishes more comfortable" - depends on how hot the hot water is. --Psud 00:53, 28 October 2007 (UTC)

Softening/melting fats is the primary reason. The liquid fat is emulsified by the detergent, this would take a lot long if the fat was still solid. Shniken1 17:19, 27 October 2007 (UTC)

Anyone else here use boiling water to clean out their frying pans? You don't even need soap if the water is hot enough - just pour it in from the kettle, let the fat melt and float to the top, pour it out, wipe the pan out with a cloth. --Kurt Shaped Box 18:54, 27 October 2007 (UTC)

Yep, also doing that avoids getting the pan too clean or something, according to my mother. And who am I to question her wisdom? Then you rub a tiny amount of oil into the pan's surface before storing it. And Dirk, I think you could only wash up with cold water if a) you didn't eat or cook any of the more interesting things I eat or b) didn't mind a thin film of rancid fat/grease on everything and c) didn't need to get things washed quickly and d) didn't have to concern yourself with germs. Skittle 15:02, 28 October 2007 (UTC)

Now that we've changed the subject into dishwashing tips, I could add one my husband sometimes applies: boil water and washing powder in a pan. The inside of the pan has never been so clean before! Lova Falk 19:06, 27 October 2007 (UTC)

A very slight effect, if any. Several years ago I started using cold water and I didn't notice a difference. Mind you, I do the dishes in two goes. I first apply the dishwater (with just a little washing up liquid, a fraction of what people in the US use), let that soak for 10 minutes while I do some other household task and then finish it off with ease. Mind you, I do this on the counter, not in the sink, with the dishwater in one of the pans, and then I dip the brush in that. Works perfectly. And then I have a good excuse to clean the counter when I'm ready. Win-win-win. :) DirkvdM 18:06, 27 October 2007 (UTC)

A side effect of using very hot water (at least for the final rinse) is that your dishes and glasses dry faster, with fewer water spots. —Steve Summit (talk) 18:30, 27 October 2007 (UTC)

If the water is sufficiently hot, it will also kill some bacteria. This may not be very relevant at home, but it becomes important if you're, say, running a summer camp where keeping the dishwashing water hot enough can mean the difference between one kid with diarrhea and 30 kids with diarrhea (and one outhouse). The problem is that the water needs to be actually uncomfortably, if not quite scaldingly, hot (at least around 50°C / 120°F or so; see e.g. [16], keeping in mind that chemical sanitizers are rarely available under camp conditions). Merely lukewarm water just makes the bugs grow faster. —Ilmari Karonen (talk) 23:27, 27 October 2007 (UTC)

You all seem to forget to rinse properly. Cold dishwater will just as easily dissolve all fat if given enough time. A brush (before and after the soak) will help this process. After that, rinse with a lot of water. Assuming any food stuff is soluble in either water or fat, this will remove everything and the pan should be as clean as the water. Right? Just try it with a very greasy pan. It would be nice if someone who has a petri dish at hand would try this. Btw, there is no need to remove/kill all bacteria. Actually, the rise of allergies in the last few decades has shown that it is actually a very bad idea. And in a normal life you're exposed to all sorts of sources of bacteria, so why become all clinical here? DirkvdM 09:09, 29 October 2007 (UTC)

electron transfer

what makes an electrin to be transfered from an atom to the other(e.g metal to non metal )in ionic bonding? —Preceding unsigned comment added by 195.225.63.210 (talk) 14:06, 27 October 2007 (UTC)

Electron configurations of lithium and fluorine. Lithium has one electron in its outer shell, held rather loosely because the ionization energy is low. Fluorine carries 7 electrons in its outer shell. When one electron moves from lithium to fluorine, each ion acquires the noble gas configuration. The bonding energy from the electrostatic attraction of the two oppositely-charged ions has a large enough negative value that the overall bonded state energy is lower than the unbonded state

Systems of atoms like to be in the lowest possible energy state. When the electron moves from the metal to the non metal the total energy of the sytem goes down.

Another way of looking at it is thinking about the forces involved. Some atoms attract electrons more strongly than others. Metals tend to attract thier outer electrons less strongly than a non metal. See electronegativity for more detals. So although the electron is pupped towards the metal atom it is pulled more towards the non metal one and so hops over to it making an ionic bond Theresa Knott | The otter sank 14:29, 27 October 2007 (UTC)

After which they would each go on their own merry way, were it not that the metal is now positively charged and the non-metal positively charged, so they are attracted to each other. A bit like free sex - the exchange precedes the attraction. :) DirkvdM 18:12, 27 October 2007 (UTC)

plants

Why are some leaves spickey —Preceding unsigned comment added by 213.122.27.220 (talk) 18:22, 27 October 2007 (UTC)

A reason that comes quickly to mind is that the spiky leaves provide an adaptive advantage in protecting the plant against predation (being eaten) by animals. So, it basically acts as a self-defense mechanism in plants like holly for example. Azi Like a Fox 19:24, 27 October 2007 (UTC)

In other cases, and depending on how spiky you meant, water storage may also be a factor "Cacti have never lost their leaves completely; they have only reduced the size so that they reduce the surface area through which water can be lost by transpiration.". Our article on Leaves, specifically leaves#Adaptations, suggests that "A transformation into spines protects the plants" so my water storage comment may be a misnomer.--VectorPotential^Talk 12:33, 28 October 2007 (UTC)

What leaves are spiky? Be specific. Malamockq —Preceding comment was added at 17:17, 28 October 2007 (UTC)

The ventral posteromedial nucleus!

Here's another one of my detail questions!
On this picture the VPL borders the pulvinar, while the VPM is more in the middle. However, our own beloved Wikipedia has this picture, that puts the VPL in the middle and the VPM bordering the pulvinar. My guess is that the VPM should be in the middle (because it is called medial), and that the Wikipicture has got the VPM and the VPL mixed up.
Is my guess right or not? Lova Falk 18:53, 27 October 2007 (UTC)

Here is an actual brain section for Macaque showing the VPM medial to the VPL. This diagram also shows the VPM in a medial position. I don't think the Wikipedia diagram is meant to be very accurate....it smashes a 3D structure into a flat diagram. --JWSchmidt 04:36, 28 October 2007 (UTC)

Thank you! Lova Falk 13:48, 28 October 2007 (UTC)

Plant Absorbtion

I was wondering if plants could absorb anything besides water (ie milk, or perhaps coffee?). Would such liquids have a negative impact on plant growth or would their roots just absorb only the water part of the liquid? Thanks, Valens Impérial Császár 93 19:17, 27 October 2007 (UTC)

If a plant absorbed only water, it would die of malnutrition. Luckily for it, the water it's getting is generally dirty. Literally. I remember something about putting cellery in water dyed red with food coloring and watching the vain-like things that bring in the water turn red. — Daniel 19:51, 27 October 2007 (UTC)

You can do the same thing with flowers. Put a red rose's stem in water colored with blue ink, and you get a blue rose (according to my old biology textbook anyway). Most plants probably have a very narrow range of acidity that they can survive in. I know that mixing up used coffee grounds in soil for tomatoes helps them grow, but the caffeine in fresh coffee will kill them (so maybe decaf?). I expect that the fat content is important, which means that milk would be difficult. Most of this information (optimal acidity, hardness, etc) should be well documented for the soil, so it shouldn't be difficult to find a drink that suits a plant, or a plant that can grow in a given drink. risk 03:50, 28 October 2007 (UTC)

These are two different phenomena. Plants absorb the water and nutrients they need through their roots. When you cut the stem of a plant and immerse it in dye you are bypassing the roots, the liquid flows up through the plant by cappilary action. -- Diletante 20:48, 28 October 2007 (UTC)

How to kill Mad Cow prions?

I've heard that they're incredibly resiliant to heat, cold, UV light, pressure, chemicals and radiation. What's the best way of sterilizing something that's been contaminated with Mad Cow prions? —Preceding unsigned comment added by 84.71.69.70 (talk) 22:53, 27 October 2007 (UTC)

Our Prion#sterilization section suggets autoclaving at temperatures of 134 degrees Celsius for 18 minutes, which will pretty much denature any protein. If you want it utterly destroyed, incinerate it at even higher temperatures. If you're asking whether you can sterilize contaminated beef to an edible state, the answer is a flat no, as any method of destroying or deactivating the prion will destroy the beef. Someguy1221 22:59, 27 October 2007 (UTC)

A few years ago, I remember reading that heating contaminated medical instruments (to give an example) in concentrated sodium hydroxide or hydrofluoric acid at insanely high temperatures and pressures was the only sure-fire way of eradicating the infectious agents completely. I guess that technology has progressed somewhat since then. --Kurt Shaped Box 23:04, 27 October 2007 (UTC)

Minor point, but you can't kill a protein at all, it's not alive. If you denature a protein it can still, in most cases, be refolded under ideal conditions. See Protein denaturation, Protein folding, and of course Prion.--VectorPotential^Talk 12:26, 28 October 2007 (UTC)

Rather than temperature alone, please discuss the possibility of chemical neutralization of mad cow prions. Would bleach or diluted bleach neutralize prions? If someone fed the cat using one of the cereal bowls, and I want to make sure that prions which might have been in the "meat byproducts" part of the catfood do not remain on the dish when I eat my cereal from the same bowl sometime in the future, would a soak in bleach solution inactivate the prions? Would any other household chemical be more effective? Edison 21:01, 28 October 2007 (UTC)

You might find this paper and the references it contains useful. Of note:

"Conventional hospital disinfectants including ethylene oxide, propriolactone, hydrogen peroxide, iodophors, peracetic acid, chaotropes, and phenolics have little effect on prion infectivity.... In addition, prions are resistant to inactivation by UV irradiation, aldehyde fixation, boiling, standard gravity autoclaving at 121°C, and detergent solubilization."

As well,

"Currently recommended protocols for prion decontamination include either (i) >2% available chlorine of sodium hypochlorite for 2 h, (ii) 2 M NaOH for 1 h, or (iii) autoclaving at 134°C for 4.5 h. Each of these protocols has important limitations: sodium hypochlorite and NaOH are corrosive at the concentrations required to inactivate prions; NaOH did not inactivate CJD prions completely in some reports; and extended autoclaving at high temperature is deleterious to many materials. Currently, some high-risk surgical instruments are soaked in 2 N NaOH for 1 h, rinsed with water, and autoclaved at 134°C for 1 h, while many other such instruments are discarded."

The paper also presents a 'combined' protocol that employs an acidic SDS solution (1% sodium dodecyl sulfate plus 0.5% acetic acid) followed by 121°C that does seem to fully inactivate prions. Again, I urge you to read the full paper, and to look up the references it cites. TenOfAllTrades(talk) 21:26, 28 October 2007 (UTC)

As far as anyone knows, a human eating the meat will keep it from spreading. There's no proof humans can get infected from eating meat from a cow with mad cow disease. — Daniel 00:29, 29 October 2007 (UTC)

Dropping uncertainties

When dividing two numbers with uncertainties, the end result should have a greater uncertainty right? However, when I am doing the following:

• [(2.91 ± 0.01g) / (2.55 ± 0.01g)]

I end up with:

• 1.14 ± 0.008g

which is lower than the two original uncertainties I had. Could this be correct?

Thanks. Acceptable 23:15, 27 October 2007 (UTC)

When dividing two numbers with uncertainties, the end result should have a greater relative uncertainty, which your answer indeed does. However, I get 1.141 ± 0.006 for the answer. Did you make an arithmetic error? —Keenan Pepper 23:30, 27 October 2007 (UTC)

Ah yes, a greater relative uncertainty makes more sense. I did the calculation several times and I'm almost certain that 0.008 is correct. Much thanks. Acceptable 23:42, 27 October 2007 (UTC)

I actually get something a bit higher than 0.008:

Max value = 2.92/2.54 = 1.1496

Min value = 2.90/2.56 = 1.1328

Median value = (1.1496 + 1.1328)/2 = 1.1412 ± .0084. StuRat 18:50, 28 October 2007 (UTC)

But unfortunately Stu that is not how errors are calculated, although it seems logical. The errors in science are not upper and lower absolute bounds but probabilities basd on assumed normal distributions. Our page on error propagation gives the general formula for calculating errors. Under the specific examples you can see that for a ratio, the fractional errors combine in quadrature. I get 1.1412 +- 0.0068. Cyta 21:16, 28 October 2007 (UTC)

Which, if rounded to 2 decimal places (the error, that is), would give 1.1412 ± .007. -- JackofOz 00:14, 29 October 2007 (UTC)

the problem here is that the conventional nomenclature fro uncertainty (x±y) appears to be unambiguous, but actually is not.

You must explicitly define what you mean when you use the "x±y" Nomenclature. For example, if "(x±y)" means "x, with an assumption of a normal distribution with an SD of y" then "(x±y)/(z±w)" has a defined meaning. If "(x±y)" has a different meaning, then "(x±y)/(z±w)" has a different meaning. Note that you need to understand both the statistics of the numerator and the statistics of the denominator before you can have any confidence in the statistics of the result.-Arch dude 03:21, 29 October 2007 (UTC)

October 28

Red Onion Skinn cells

In Biology class, we observed a piece of red onion skin under a 40X objective lens and probably a 10X eye piece. A drop of salt water was added to the skin under the microscope, the red part of the cell shrunk. Is the red part the vacuole or cytoplasm of the cell? Acceptable 01:46, 28 October 2007 (UTC)

Usually, plant dyes (and other secondary metabolites and end products) are stuffed into vacuoles by the plant cell. They would wreak havoc with usual plant metabolism taking place in the cytoplasm. --85.179.20.169 08:36, 28 October 2007 (UTC)

Fall question

I got to wondering why tree leaves aren't all the same shape. You would think there'd be an ideal leaf shape that all trees would have settled down to, but the variety is practically infinite. Are there evolutionary pressures on tree leaf shape by species, or is it accidental? In other words, are certain characteristics of an organism of no importance for suvival, and do these characteristics thus more or less reflect some underlying symmetry or other order that is merely a manifestation of their peculiar origins or mechanisms? I hope that made sense. --Milkbreath 02:23, 28 October 2007 (UTC)

Few (if any) things are accidental when it comes to evolution, although there is always some 'noise', to allow a species to find a new optimum when the environment changes. On a large scale you can look at the difference between pine needles and leaves. Pine needles allow trees to survive very cold climates, whereas regular leaves allow trees to get the maximum amount of photosynthesis in more temperate climates. I expect it works the same way for differences between leaves. The shape of the leaf is the ideal solution for the area where the tree lives in terms of getting the most sunlight, surviving the cold, the heat, and so on. If two trees live in the exact same area, they may have different survival strategies. One tree may get the optimal amount of nutrition from the location, whereas the other may reproduce faster, expand it's habitat faster, or be better at surviving changes in the environment. I'm not an evolutionary biologist, but I figure that's how it works. And there is always the possibility that everything else being equal, there are several optimal solutions, and two trees arrive at different ones. risk 03:41, 28 October 2007 (UTC)

As Risk says, there's lots of different things that a tree needs to deal with: snow, wind, sun, heat, cold, rain, storms. Some need leaves that shed snow, others need leaves that aren't destroyed by cyclones, others need leaves that won't loose too much water in dry weather. Lots of variables means lots of different leaf shapes make lots of different "ideals". What about two trees in the same forest? Well they may also grow in disparate areas, and they may survive or thrive in different situations differently. (oh, and it's spring here - all our imported trees are starting to sprout their myriad leaves in myriad shapes. All our local trees kept their leaves over winter, so we here think it's funny to call that season "fall") --Psud 09:07, 28 October 2007 (UTC)

Most of the factors which affect leaf growth have been mentioned, but let me add disease, insects, and animals which eat or damage leaves. Unless the animal provides some benefit to the plant, like spreading seeds for it, the plant will want to minimize leaf damage. Having many small leaves may help here, as large animals won't bother with small leaves, and the leaves can be easily dropped if they become diseased. Small leaves would also fare better in strong winds, but wouldn't do as much photosynthesis, due to all the gaps between the leaves for sunlight to pass through. StuRat 18:26, 28 October 2007 (UTC)

Leaves are a critical weapon the the war between the trees and the grasses. Grasses and trees try to poison each other, and deciduous trees try to kill grass by annually blanketing the grass with leaves. The leaf shape and size is of critical importance in the success of this strategy. it is deeply involved with the activities of herbivores, so the evolutionary response times will ensure a large range of leaf shapes and sizes. The suburban ecosystem with Maple trees andblue grass is profoundly unnatural-Arch dude 03:06, 29 October 2007 (UTC)

An additional thought is that it is a mistake to assume that everything about a plant (or other organism) has been determined by evolution. Natural selection will only affect those traits that change the survival rate of the species. Sometimes that differential survival critically hinges on leaf shape (needles in evergreen trees with longer winters, waxy, pointy-tipped leaves in plants with areas of high rainfall, etc), but sometimes it does not. For example, a maple leaf and an oak leaf are quite distinct to our eyes, but are probably not all that different in terms of practical survival rates for the individual plants and their offspring. Matt Deres 16:29, 29 October 2007 (UTC)

Butterflies and the fate of the universe

A flap of the wings of a butterfly in India will, given enough time, alter the course of a tornado in the US. Not to put too fine a point on it, but it will inevitably change everything about the world. Will it do the same for the universe? Sappysap 03:54, 28 October 2007 (UTC)

• The way I understand it, that's not actually true. Rather than being taken literally, I think that statement is supposed to be a refernce to the fact that the causes of something like a tornado are so complex that minute events (eg the butterfly) that might not otherwise be associated with the outcome are related. 68.18.209.108 04:42, 28 October 2007 (UTC)

The butterfly effect is a vey specific illustration of the fact that the Earth's atmosphere is a complex and interconnected system in which small changes are quickly magnified. So attempts at predicting weather patterns more than a few days ahead are doomed to failure because we cannot practically collect enough starting data with enough precision to produce accurate estimates. By extension, it has become a metaphor for any natural system that exhibits sensitive dependence on initial conditions. It does not mean that the flap of the butterfly's wings will change everything about the world. Although the butterfly's wings could (in theory) change the course of a torndao, we know of no physical mechanism by which they could (even in theory) cause an earthquake, significantly affect the path of an asteroid, or change the temperature of the Sun. A belief in mysterious and undiscovered mechanisms which intimately link every feature of the universe is more akin to astrology than to science. Gandalf61 07:28, 28 October 2007 (UTC)

Let's put it in perspective. Here's the closest thing to affecting the Universe. Our Indian butterfly flaps it's wings, that causes a tiny (but important in our chaotic weather system) change in the course of a storm in Sydney. A lightning strike happens in one place rather than another and sends a radio pulse out into space. That pulse of radio probably doesn't go very far into the universe, and on the few occasions where it does encounter something, it has practically no effect. Then you consider that the lightning probably would have happened anyway, just somewhere a little way away from where it did happen, and that lightning flash would have been effectively identical from even a fraction of a lightyear away (if it was even detectable at that distance) --Psud 08:58, 28 October 2007 (UTC)

Alternatively, that new lightning strike hits the person who would later have discovered a viable way to extract energy from fusion on a small scale, which would lead on to globe-spanning revolutions in virtually every field of engineering. The technology would've allowed the human race to construct interplanetary and eventually interstellar transportation, and ultimately lead to the colonisation of the galaxy. Which would have an observable effect from that distance. "For want of a nail" and all that. GeeJo ^(t)⁄_(c) • 11:02, 28 October 2007 (UTC)

I feel I should point out that one needs a very strange view of the world for this question to even make sense. In order to pin the tornado on the butterfly you have to suppose that the butterfly's action could have been otherwise, but that everything after that just snowballs according to deterministic (if chaotic) laws. Future choices by other butterflies would presumably dilute the long-term meteorological influence of this one butterfly to the point where it didn't matter whether it flapped its wings or not. The analogy does make mathematical sense as a statement about initial conditions of chaotic systems, but it doesn't make physical sense unless you subscribe to some form of last Thursdayism. -- BenRG 14:39, 28 October 2007 (UTC)

That's a switch—pinning something on a butterfly. --Milkbreath 15:27, 28 October 2007 (UTC)

The problem here lies in one misstated word in the question: A flap of the wings of a butterfly in India will, given enough time, alter the course of a tornado in the US. - not will but could (with a very low probability). There are a bazillion butterflies and a bazillion wing beats - and many, many other sources of atmospheric turbulance - any and all of which are having some effect. It is the net effect of all of them that causes unpredictability. So had that butterfly not flapped at that exact moment, then perhaps the tornado halfway around the world and a decade off in time might not have happened. It's definitely possible - in a chaotic system such as our atmosphere, there is infinite sensitivity to these kinds of events. But for any specific wing beat of any specific butterfly, the odds are truly astronomically small. As to whether the event could cause universe-wide changes - yes, sure. I like GeeJo explanation as to how this could come about. It's definitely possible for a butterfly wing flap to deeply affect something over the other side of the universe a very long time into the future. Again - it's very unlikely - but for sure it can happen. SteveBaker 16:34, 28 October 2007 (UTC)

There are limits to the extent of the effect of a butterfly’s actions. Some parts of the universe can’t possibly ever be affected by a flap of a butterfly’s wings. Due to the inflation of the universe, most of the universe is beyond what can ever be reached by a photon leaving our galaxy now. MrRedact 19:09, 28 October 2007 (UTC)

And, depending on how you look at all this, you can even say "very likely" instead of "very unlikely". In a chaotic system, anything can affect anything; everything affects everything. So the likelihood is very high that "event X" (whatever it is) is caused (in part) by some ridiculously distant cause that you can't even imagine. What's very unlikely, of course, is that event X was caused by a particular ridiculously distant alleged cause Y. —Steve Summit (talk) 16:51, 28 October 2007 (UTC)

The answer is YES. Here is a fun homework problem from graduate statistical mechanics. Imagine that you knew the initial position and velocity of every particle in the universe, except that you misplaced one electron 4 light years away by 1 cm. How long does it take before that simple error, by virtue of the electron's gravity, gives rise to sufficient chaos that you can no longer predict the position of gas particles in front of you? It's an extremely small error, but it is magnified by each of umpteen interactions between the gazillion particles in any given air parcel so that appreciable chaos sets in after only a few minutes (if my memory serves). So yes, that damned butterfly will introduce chaotic effects in sensitive systems throughout the rest of the observable universe. Dragons flight 09:43, 29 October 2007 (UTC)

How does that chaos set in before the electron's misplacement can propagate (at the speed of light) to the origin? You might mean that the area around the electron becomes chaotic, but then what's the "4 light years away" about? Or perhaps you mean that the electron's entire electromagnetic field is appropriate to its actual position (as opposed to it, at $t=0$, suddenly being magically shifted by that centimeter), but I have a hard time seeing how you could have that field interact with everything else and yet have the wrong idea about its source's location. It's an interesting question — with what shape and speed does the "wave" of chaos from a disturbance propagate? — but I'm not sure how to get a quantitative answer from what you've said. --Tardis 16:08, 29 October 2007 (UTC)

Anyway, how come it's always tornadoes? I want a butterfly to flap its wings in India, and a beautiful long-legged nymphomaniac to make a wrong turn and end up in my living room. —Steve Summit (talk) 16:54, 28 October 2007 (UTC)

Well, the actions of a butterfly could cause a long-legged nymph to turn up, but that's another story... Laïka 20:24, 28 October 2007 (UTC)

If you find it comforting that the likelyhood of either nymph or nymphomaniac (that's someone who is really enthusiastic about immature insects - right?) turning up in your living room is influenced by such things - then I strongly recommend butterfly collecting. SteveBaker 22:00, 28 October 2007 (UTC)

I think astronomical systems are still chaotic, but not nearly as much as terrestrial ones. For example, if two meteors pass close by each other, a tiny difference in there original position will make a much larger difference in there final path. Unlike terrestrial systems, however, these are incredibly rare and it will take a huge amount of time for the gravitational effect of a change in the earth's weather patterns to make a noticeable difference. Also, the result of a butterfly effect is the difference between one thing that doesn't seem out of the ordinary and something else that also doesn't seem out of the ordinary. A butterfly flapping its wings will change the weather forever, but the climate will remain the same. — Daniel 23:12, 28 October 2007 (UTC)

The Butterfly effect is an example of Chaos theory. Some physical phenomena can affect "initial conditions" in ways that are unpredictable even in theory. It is possible to construct a sequence wherein the fate of the universe depends on the indertimanite state of a subatomic particle that affects, via a cascade of events, the movement of a butterfly's wing. In practice, this will not happen in this universe. -Arch dude 02:49, 29 October 2007 (UTC)

Tartaric Acid

Do you know the boiling point of Tartaric acid? The melting point is 168°C - 170°C, but I cannot find the boiling point. All of the information that I could find is on this page: http://en.wikipedia.org/wiki/Tartaric_acid Thank-you for your help. 203.113.233.115 07:31, 28 October 2007 (UTC)

This site (bottom of page) lists the boiling point at 275°C: [17]. However, many other sites don't list a BP because most of the acid will decompose before it reaches that temp. StuRat 18:14, 28 October 2007 (UTC)

definition of orthologous , paralogous, analogous,homologous

definition of orthologous , paralogous, analogous,homologous —Preceding unsigned comment added by Sujbhaskar (talk • contribs) 11:35, 28 October 2007 (UTC)

See wiktionary:orthologous, wiktionary:paralogous, wiktionary:analogous and wiktionary:homologous. Algebraist 12:18, 28 October 2007 (UTC)

And Homology (biology) at wikipedia. Algebraist 12:20, 28 October 2007 (UTC)

Mushrooms

Is a mushrooms considered a decomposer or what? —Preceding unsigned comment added by 209.244.30.199 (talk) 17:12, 28 October 2007 (UTC)

The mushroom itself is not a decomposer... the mushroom is only the spore-producing fruit-like part of a fungus. The fungus decomposes organic matter. Sancho 20:34, 28 October 2007 (UTC)

If I understand right, not all fungi are decomposers. A decomposer, according to that page, consumes dead organisms. Certainly a lot of mushroom type fungi grow on dead plants, logs, etc, but aren't there also a huge number of mushroom type fungi that are symbiotic with plants? I'm thinking of Mycorrhiza type relationships. My (admittedly vague) understanding is that most land plants depend upon mycorrhizal fungi for their very survival. When you see mushrooms growing near a tree, are they getting their food from some dead organism underground or are they symbiotic with the tree, each helping the other? My guess is quite often it is the latter. Pfly 02:01, 29 October 2007 (UTC)

From the respective articles: "Decomposers are organisms that consume dead organisms, and, in doing so, carry out the natural process of decomposition." and "Decomposition (or spoilage) refers to the reduction of the body of a formerly living organism into simpler forms of matter." We eat dead things and reduce them to simpler forms of matter so we can use them for our own bodies. So aren't we (and all living things) decomposers? Actually, doesn't dead nature do that too? I'll ask that in a new thread. DirkvdM 09:40, 29 October 2007 (UTC)

fibrous and synovial joints

Are there two types of joints between the radius and ulna? I was lead to believe they are joined by a fibrous joint. Another article tells me they have a synovial joint to allow supination and pronation. Can anyone clarify please? kramnahtal —Preceding unsigned comment added by Kramnahtal (talk • contribs) 19:07, 28 October 2007 (UTC)

Pinhole cameras

How does a pinhole camera project an image? I thought you needed a lens of mirror to focus light. I read pinhole camera but couldn't find the answer. 72.155.207.79 19:47, 28 October 2007 (UTC)

The pinhole itself acts as the lens. The second sentence of the article states this clearly: "An extremely small hole in a very thin material can focus light by confining all rays from a scene through a single point." I assume you mean "glass" instead of "mirror"; there is no mirror needed in any camera. --24.147.86.187 20:25, 28 October 2007 (UTC)

I understand that. I'm asking how air focusses light. And a curved mirror can focus light, and mirrors are most certainly used in cameras. 72.155.207.79 20:37, 28 October 2007 (UTC)

A mirror is not needed in cameras. Yes, you can set up Newtonian-telescope style lenses but that's hardly standard. Maybe you meant "lens or mirror" up above, I now see. --24.147.86.187 21:13, 28 October 2007 (UTC)

There is no real focusing of an image in a pinhole camera. It would work even in a vacuum. This is because, if you pretend for a moment that the pinhole is only large enough for one photon to make it through, each position on the film could only have been illuminated by light coming from a single direction through the pinhole. Thus, if you place an illuminated 2D picture on the outside of the pinhole camera, each position on the film corresponds to only one position on the picture outside. So inside the camera you get a nice, clear image of what's outside. Someguy1221 20:56, 28 October 2007 (UTC)

The air doesn't focus anything. The pinhole acts as a sort of collimator, if you will. Take a pinhole camera with the front off, and aim it at the calendar page for October. Consider a point on the back of the camera where the image will be. Let's locate the point about halfway between the center and a side at three o'clock. Now shrink your eye down to microscopic size and put it on that point facing the front of the camera. You will see the whole calendar page. Now put a front on the camera that has a round hole in the middle about an inch across. You'll only be able to see a few dates off to the other side. Put a front on with a smaller hole, and you'll see only one day. Make the hole very small, and the only light ray that will be hitting your eye will be coming from a tiny spot. The same goes for all the other microscopic eyes stuck to the back of the camera, but each will see a different spot on the calendar page. Voila! You've got an image, upside down and backwards. --Milkbreath 21:09, 28 October 2007 (UTC)

Do this for me (don't just think about doing it - actually DO it!). Take a piece of paper and draw on the left a stick-figure to be the subject of our photograph. On the right of the page, draw a vertical line representing the photographic negative inside the camera.

Now (without the pinhole) consider light rays coming from the subject onto the negative. Light is emitted pretty much equally in all directions from every part of the subject. So you can draw straight lines representing rays of light radiating out from our stick-figure's head and going out in all directions - lots of them hit the photographic negative - and they hit it all over it's surface. Similarly, you can draw rays radiating out from the stick figure's feet reaching any point on the negative. In fact, light from everywhere in the scene can reach every place on the negative - so all you get when you develop the plate is the average of all of the light from the whole scene hitting every point on the negative. A big white blur in fact.

OK - so let's add a pinhole "lens" to our camera. Start again with another diagram) - put the subject on the left and the negative on the right just as before - but this time, draw a vertical line down the middle of the paper with a tiny gap halfway up - this represents the front of the camera with a pinprick-sized hole in it.

Now, lets draw those lightrays coming from the stick-figure's head. They still shoot out in all directions - but most of them hit the line going down the middle of the page and are stopped. Only a few rays make it through the gap in the middle of that centerline (the 'pinhole') and onto the negative. Notice that rays from the top of the stick-figure only hit the bottom of the photographic plate over to the right of your diagram. Now do the same thing with rays from the stick figure's feet - notice that ones that go through the pinhole only hit the top of the photographic plate. Do this with rays of light from all over the stick figure and you find that each point on the original subject emits light in all directions - but the pinhole shuts all of it out except for a teeny tiny amount - so light from each point on the subject ends up at a different place on the negative. When you develop the plate - you get a nice, sharp image because the light isn't all mixed up like it was without the pinhole.

You can deduce some other things with this kind of simple diagram: If the pinhole is too big, lightrays from several close-by points on the subject can end up on the negative in the exact same place. This results in a blurry (but perhaps still recognisable) image. But if you make the pinhole too small, almost all of the light rays from the subject will hit the line down the middle of your piece of paper - hardly any make it through that teeny-tiny gap in the middle. This means that the image on the photographic plate is rather dim (because not much light hits each point)...so you need either a more sensitive film or a much longer exposure (which in turn results in a blurry image if anything in the scene is moving or the camera is shaking).

The point is that the pinhole forces all of the light in the scene to pass through a single point - and blocks all of the light that was heading off in the wrong direction. A more conventional lens focusses light through a single point (the 'focal point') - which has the same effect as the pinhole. The benefit of the lens is that it gathers light over a larger area - so you can get more light onto the film without ending up with a blurry picture. The bigger the lens, the better the quality. This is why cellphone cameras are so crap compared to big SLR cameras. Pinhole cameras do have one HUGE advantage though - they keep the image in focus no matter the distance of the subject from the camera - lenses can't do that. Everything in photography is about these kinds of trade-off.

SteveBaker 21:13, 28 October 2007 (UTC)

Incidentally, this is the same mechanism by which squinting your eyes sharpens an image—you're effectively forcing light through a smaller pinhole. TenOfAllTrades(talk) 21:30, 28 October 2007 (UTC)

There's an episode of Home Improvement in which Wilson has Mark fashion a pair of glasses out of a piece of paper with two pinholes in it. Sancho 22:31, 28 October 2007 (UTC)

Thank you very much for your clear and helpful comments, and sorry for the misunderstanding, 24.147.86.187; I did mean or. 72.155.207.79 22:33, 28 October 2007 (UTC)

Incidentally there was a BBC show called "Genius of Photography" on the other night (Uk), it made a camera obscura out of a room. They went in covered it till it was pitch-black and cut a small hole. Projected onto the wall upside-down (and reversed?) was the view from out of the window. It was very impressive - possibly available on You-tube or that bbc-download thing. ny156uk 23:18, 28 October 2007 (UTC)

The very first response to this question began, "The pinhole itself acts as the lens." That's wrong.

For convenience let's talk about a specific use of a lens or pinhole: the use where you have an object and you're projecting an image of it onto a wall. In order to make the image, you must arrange the rays of light in such a way that each point of the object corresponds to one point of the wall.

By making the light pass through a pinhole, you achieve exactly that correspondence by simple geometry: from each point on the object, there is a line of sight through the pinhole to exactly one point of the wall. That's all there is to it! If the pinhole is point O, then point A of the object corresponds to point A' on the wall were AOA' is a straight line. Point B of the object corresponds to B' on the wall, where BOB' is a straight line.

But the downside is, the whole image is formed from the few rays of light that happen to be pointed at the pinhole. That's okay if the object is very bright, like the Sun, but otherwise you need the wall to be in darkness (a camera obscura), and even so the image is not all that bright.

The purpose of using a lens is to overcome that downside. With a lens, instead of using the few rays of light that come off the object and aim at a little pinhole, we can use all the rays that come off the object and land anywhere on the lens. By choosing the correct lens and placing it correctly, we can arrange to have light paths like APA', AQA', ARA', where P, Q, R are different points on the lens. And similarly BPB', BQB', and BRB'. And so on for all the other points on the object and all the points on the lens. These paths are not all straight lines, but the lens is curved in such a way that the light follows them anyway. That's what focusing means -- this bringing back together of the rays AP, AQ, and AR to a single point A'. And you need a lens (or a curved mirror) to do it. It gives you a much brighter image, the total brightness corresponding to the area of the lens.

But with a pinhole, you don't need to focus in the first place. The pinhole sets up the correspondence between points on the object and points on the wall by geometry alone. It doens't act as a lens because in this setup there is no need to focus.

(In all this I am pretending that the size of the pinhole is negligible. In real life it can't be zero size, and this limits how sharp an image it can form. This is another advantage of a lens.)

--Anonymous, 10:00 UTC, October 29, 2007.

Esophageal Temperature Monitoring During Surgery

It is fairly common practice to monitor a patient's body temperature during a surgical procedure with the use of an esophageal stethoscope with a temperature wire inside of it. Does the temperature wire hook up to a machine that reads the data and then displays a readout? Or how does that work? Also, is it possible to lose the esophageal stethoscope in the esophagus? Thanks, Lilly Upstairs —Preceding unsigned comment added by 24.19.72.81 (talk) 22:03, 28 October 2007 (UTC)

Effective Projected Luminous Lens Area

This term is found in Federal Motor Vehicle Safety Standards for testing of lights for motor vehicles. I am trying to understand this term (EPLLA) in the context of a motorcycle turn light. I want to know how to measure this EPLLA and determine whether or not my turn lights are over the required 3.5 square inches required by the regulation. Can someone explain to me in somewhat laymen's terms what Effective Project Luminous Lens Area is and how to measure it? Thank-you 154.20.86.223 22:50, 28 October 2007 (UTC) Ray Kwan

Ray, EPLLA means the area of the effective light-emitting surface of a lamp, measured by determining the area of the 2-dimensional graphic representation of the lamp's lit lens area on a plane perpendicular to the lamp's reference axis and touching the most exterior point of the lens. "Reference axis" means the H–V axis used for photometric requirements, i.e., the effective centre of the lamp's beam pattern as produced at the lamp.

To simplify this and bring it into the realm of practical application outside of a compliance laboratory setting: The reference axis of most automotive and motorcycle lighting devices is reasonably easy to determine; it is "straight back" from the device with the device oriented in space exactly as it is oriented when installed on the vehicle. if you will place a sheet of fine-grid graph paper such that it forms a vertical plane at 90° to the lamp's reference axis, move the paper such that it just barely touches whatever part(s) of the lens protrude closest to the paper, illuminate the lamp, trace the blob(s) of light on the side of the paper opposite the lamp, and then calculate the area enclosed by your trace, you will have a close enough approximation of the device's EPLLA for most purposes. The thing you will have to be most careful of is accurately tracing the blob(s) of light. If your device uses multiple light sources, such as a cluster or array of LED emitters, you must trace each individual spot of light, omitting the dark areas in between, then total up the areas of each trace to arrive at your EPLLA.

It sounds like you've modified your motorcycle's directional indicator system in some fashion and are trying to determine if the modified or handmade indicators meet the EPLLA requirements. Good for you, most people don't bother, but be aware there are other safety performance requirements for vehicle lighting devices, as well. Intensity through various vertical and horizontal angles, intensity ratio between bright and dim modes of a park/turn or brake/tail lamp, etc.

For additional explanation, you may want to read this technical bulletin as well as this one and this one, keeping in mind that they primarily make reference to the 7¾ in² and 11⅝ in² EPLLA requirements for passenger car and large-vehicle brake lamps, respectively. Also, you may want to read through this NHTSA rulemaking discussion which goes into detail on the meaning, intent, and methods behind EPLLA requirements. If you wish to discuss vehicular lighting with more specificity, feel free to contact me via my talk page. --Scheinwerfermann 03:35, 29 October 2007 (UTC)

October 29

Batch experiment for denitrification endpoint in wastewater treatment

I am told the endpoint for denitrification in biological wastewater treatment can be determined by a batch experiment. What is the step-by-step procedure for conducting such an experiment and are there electronic sensing techniques for obtaining the same information in a continuous fashion? Thanks Thinkaboutlife 03:43, 29 October 2007 (UTC)

Gas formation at extreme low pressure and temperature

This question about wind at the miscellaneous desk spinned off into extreme planetary circumstances, with the planet so far from its star (if any) that it receives no heat (well, of course there is no absolute zero for anything). So I looked up the freezing point of helium, which is 1.15 K at 66 atm. Which would mean that even at extreme low temperatures, there would still be an atmosphere (however thin) of helium because of the vacuum surrounding it. But what about other gases? I guess I'm asking about the bottom left corner of the phase diagram (now why didn't I learn about that at school?), so extreme low pressures or a vacuum. But the article doesn't deal with that extreme. Let me start with one extreme:

• Would uranium be gaseous in outer space?
• And on above planet, at, say, an extremely low 1 Pa, what would be the boiling points of the various elements? The graph at the article doesn't go below 0.1 atm (= 10,000 Pa). And then at 10 Pa, 100 Pa, etc?

I suppose the atmosphere (which has no wind - the point of the original question) would be built up in layers consisting of the various elements with Helium sitting at the top. DirkvdM 07:18, 29 October 2007 (UTC)

On a phase diagram, you will notice that water is liquid at 1 atmosphere and room temperature. However, we also observe that water will evaporate from lakes and puddles. This is because even though the substance is naturally a liquid under those conditions, some fraction will spontaneously change into a gas through a process described by the vapor pressure. This is true for all substances. Uranium, like most metals, is naturally a solid in the limit of zero temperature and zero pressure. However, at all temperatures above 0, some small fraction of atoms will spontaneously turn into a gas and escape since there is zero ambient pressure. For most solids, the rate at which this occurs is neglible not only compared to human experience, but also compared to the age of the universe. In other words, the amount of time before satellites "boil" away in the vacuum of outer space is truly astronomically large. Dragons flight 11:52, 29 October 2007 (UTC)

Another way to think about that is that the concept of 'temperature' is really only a statistical average of the speeds of all of the molecules in the material. Even at fairly low temperatures, some molecules will be moving quite quickly (although the majority are not). Those few fast moving molecules may have enough kinetic energy to escape the surface no matter what. So all things with temperatures above absolute zero (which is to say: "all things" since absolute zero is unattainable) will lose molecules at some rate. But the statistics of the thing mean that the rate will be exceedingly slow at low temperatures because the probability of molecules having enough energy to escape becomes very low indeed. At higher temperatures that probability increases and evaporation will happen to a much greater degree - and finally, at the boiling point of the material, all of the molecules have enough kinetic energy to shake themselves loose and escape to form a gas. SteveBaker 14:06, 29 October 2007 (UTC)

Broad spectrum antibiotics

I know that Penicillin is a broad spectrum antibiotic, but was wondering if all antibiotics ending in cillin are broad spectrum. I couldn't find the answer here on Wikipedia or online, so thought I would ask here. Thanks. Jeffpw 08:52, 29 October 2007 (UTC)

Penicillin is not a broad spectrum antibiotic. It covers a relatively narrow spectrum of organisms, and is useless in Gram negative infections. In fact, most of the "-cillin" drugs were developed in order to find drugs with a broader spectrum than penicillin. You will find more details in the penicillin article, which lists narrow, moderate, and extended spectrum penicillins. - Nunh-huh 13:13, 29 October 2007 (UTC)

Drop dead on the Moon

If you'd drop a dead body on the Moon, what would happen to it? Would it decompose? DirkvdM 09:43, 29 October 2007 (UTC)

It depends on where you drop it on the moon. If you drop it in the dark side, it'll freeze and if you drop it on the sunny side, it will fried. 58.109.93.128 10:23, 29 October 2007 (UTC)

Hmmm .. I assume "dark side" means the far side of the Moon, i.e. the side facing away from Earth, which gets just as much sunlight (two weeks on, two weeks off) as the side facing Earth. I blame Pink Floyd. Anyway, a similar question has appeared on the RD in Nov 2004 here> There is also a response on Ask Yahoo here. General consensus seems to be that there would be some decomposition due to the presence of anaerobic bacteria, as well as dessication and slow weathering as a result of temperature changes. Gandalf61 10:39, 29 October 2007 (UTC)

Actually, on the album someone says "There's no dark side of the Moon, really." but then goes on to say "As a matter of fact, it's all dark.". Which is another bit of nonsense. DirkvdM 11:48, 29 October 2007 (UTC)

Not at all; it is dark. With an albedo of .12, it's only as bright as worn asphalt. We probably think of it as bright because there are no clouds or atmosphere to shade it from the direct sunlight. Matt Deres 16:40, 29 October 2007 (UTC)

Over eons, the top several meters of the lunar regolith are stirred up via the action of micrometeorites, through a process known as lunar gardening (wow, a red link). Since there is no appreciable atmosphere on the moon, even dust flecks the size of sand grains will leave tiny impact craters (since they are moving at several km/s). Over the very long term (i.e. many tens of millions of years) such micro impacts would ultimately grind the body down to nothingness. Dragons flight 10:50, 29 October 2007 (UTC)

Ok, looks like it's a race between the bacteria in the body, dessication and being bombarded to bits. I suppose the lunar gardening is the slowest process. How much will the bacteria consume before the body is dried out and the bacteria die too (or become dormant at best)? Also, which bacteria would do this? By far most bacteria in our bodies are benevolent, but would they start decomposing the body after it dies? DirkvdM 11:48, 29 October 2007 (UTC)

Oh boy, there are some confused answers here! Let's try to clarify things a bit...

• The term "dark side of the moon" refers to the side of the moon that is never seen from earth. In this context, the word "dark" is as in "Darkest Africa" - it means "unknown", not "lacking sunlight". The far side of the moon is just as sunny as the near side (and it's not even unknown anymore - we have lots of photographs of it). However, there are places in some craters on the moon that never see sunlight where things stay perpetually frozen. The length of a 'day' on the moon is what we'd call a "lunar month" - about four weeks.
• Since either freezing or baking to the point where it would kill bacteria would be unlikely to take more than a few hours (the temperature in the sunlight is enough to melt lead). I'm pretty sure that bacterial action is a non-problem in something as thermally conductive as a corpse.
• So unless this body is tucked away on the edge of one of those very steep-rimmed craters, it would alternately freeze for two weeks then cook for two weeks. I'd say that dessication/mummification would be the most immediate effect (that's what happens to bodies left on cold/dry mountaintops) - but it's hard to know for sure. There is no oxygen - so the body wouldn't combust in the heat - but it would drive out all of the water.
• As for being bombarded by meteors - that could happen eventually - but it would be a very improbable event. There are no more meteors (per square mile) hitting the moon than there are entering the earths atmosphere. The reason the earth isn't pockmarked like the moon is because the air burns up the smaller meteors and the craters created by the larger ones get eroded by wind & rain and subducted by continental drift - where on the moon they stay intact indefinitely. Look up into the sky on a dark night - how many meteor streaks do you see? Do you think one of them would hit you if it didn't burn up? Well, the odds are about the same on the moon...a little less actually because the earth's stronger gravity is going to pull them more towards the earth than the moon.

SteveBaker 13:52, 29 October 2007 (UTC)

• "... the temperature in the sunlight is enough to melt lead" - huh? This page says the moon gets up to 123°C, and our article says lead melts at 327°C. How would lead melt on the moon? --Sean 14:34, 29 October 2007 (UTC)

I was about to make the same point as TotoBaggins - sunlight on the Moon is definitely not hot enough to melt lead. Granted that 123^oC is still too hot for most bacteria to survive, but for hyperthermophiles such as Strain 121 it is just right. I agree that bacterial decay won't be a significant factor for our Moon corpse, but I don't think we can rule it out completely. Gandalf61 14:40, 29 October 2007 (UTC)

Steve, seriously, it's not an issue of "maybe it will be hit by micrometeorites", but a certainty. Objects below about 1 cm in size never get hot enough to leave visible streaks in the sky, but the population mass density of space debris peaks at about 100 microns, and the rate is about one micrometeorite impact per km^2 per second. The Earth aquires some 50,000 tons of space dust per year. And yes, as astronauts discovered, the entirety of the lunar surface is well-mixed to a depth of several meters by the action of meteorite impacts over tens and hundreds of millions of years. Dragons flight 15:32, 29 October 2007 (UTC)

Peak Coal

What is peak coal? 58.109.93.128 13:24, 29 October 2007 (UTC)

Peak coal is detailed in the article on Hubbert peak theory. Lanfear's Bane | t 13:32, 29 October 2007 (UTC)

Jehovah's Witnesses & Marriage

Do Jehovah's Witnesses believe and or support marriage to other religions. The reason I ask this question is I am not a Jehovah's Witness and am engaged to one and her father isn't in support at all of us. The rest of his children are married to a Jehovah's Witness. His brother isn't one and is married to one. Any help would be appreciated.

Thanks,

(email removed per instructions at top of page) —Preceding unsigned comment added by Timfreidag (talk • contribs) 14:47, 29 October 2007 (UTC)

• In most religions, getting the blessing of your fiancee's preacher, and then getting the preacher to perform the ceremony, is a sure-fire way to overcome this obstacle. Of course, you and your fiancee should be prepared for the possibility that the preacher is also intolerant of interfaith marriages. --M@rēino 16:33, 29 October 2007 (UTC)

Surely not! Surely religion is all about tolerance? If his brother is married to a JW, surely it would be possible for you? He may be using his faith as an excuse if he is not happy with his daughters choice of partner. (That's not that I am saying there is anything wrong with you, I am just hazarding a motive for his actions). Lanfear's Bane | t 16:54, 29 October 2007 (UTC)

Alcohol - on the verge of anaebriation!

If I have a few glasses of wine and start feeling light headed, what is happening in my brain to make me feel like that? Thanks. —Preceding unsigned comment added by 88.144.1.100 (talk) 16:04, 29 October 2007 (UTC)

We have an article specifically on the topic of Effects of alcohol on the body. Friday (talk) 16:05, 29 October 2007 (UTC)

Twin prop aircraft

after flicking through the "What is the name for this kind of aircraft, and why don't we make them?" post, I was thinking. Everyone dismissed the tail rotor on a transverse twin prop aircraft as pointless, but if you did have both props spinning in the same direction and a tail rotor to counteract any net rotation, would rotational manoeuvrability not dramatically increase with charge over the speed and hence thrust from the tail rotor, possibly allowing extremely sharp turns to be made, even at low speeds? ΦΙΛ Κ 16:28, 29 October 2007 (UTC)