Free will

Free will is the ability to choose between different possible courses of action. It is closely linked to the concepts of responsibility, praise, guilt, sin, and other judgments which apply only to actions that are freely chosen. It is also connected with the concepts of advice, persuasion, deliberation, and prohibition. Traditionally, only actions that are freely willed are seen as deserving credit or blame. There are numerous different concerns about threats to the possibility of free will, varying by how exactly it is conceived, which is a matter of some debate.

Some conceive free will to be the capacity for an agent to make choices in which the outcome has not been determined by past events. Determinism suggests that only one course of events is possible, which is inconsistent with the existence of such free will. This problem has been identified in ancient Greek philosophy, and remains a major focus of philosophical debate. This view that conceives free will to be incompatible with determinism is called incompatibilism, and encompasses both metaphysical libertarianism, the claim that determinism is false and thus free will is at least possible, and hard determinism, the claim that determinism is true and thus free will is not possible. It also encompasses hard incompatibilism, which holds not only determinism but also its negation to be incompatible with free will, and thus free will to be impossible whatever the case may be regarding determinism.

Entropy (arrow of time)

Entropy is the only quantity in the physical sciences (apart from certain rare interactions in particle physics; see below) that requires a particular direction for time, sometimes called an arrow of time. As one goes "forward" in time, the second law of thermodynamics says, the entropy of an isolated system can increase, but not decrease. Hence, from one perspective, entropy measurement is a way of distinguishing the past from the future. However in thermodynamic systems that are not closed, entropy can decrease with time: many systems, including living systems, reduce local entropy at the expense of an environmental increase, resulting in a net increase in entropy. Examples of such systems and phenomena include the formation of typical crystals, the workings of a refrigerator and living organisms.

Entropy, like temperature, is an abstract concept, yet, like temperature, everyone has an intuitive sense of the effects of entropy. Watching a movie, it is usually easy to determine whether it is being run forward or in reverse. When run in reverse, broken glasses spontaneously reassemble, smoke goes down a chimney, wood "unburns", cooling the environment and ice "unmelts" warming the environment. No physical laws are broken in the reverse movie except the second law of thermodynamics, which reflects the time-asymmetry of entropy. An intuitive understanding of the irreversibility of certain physical phenomena (and subsequent creation of entropy) allows one to make this determination.

Entropy (disambiguation)

Additional relevant articles may be found in the following categories:

Entropy, in thermodynamics, is a state function originally introduced to explain why part of a thermodynamic system's total energy is unavailable to do useful work.

Entropy may also refer to:

Thermodynamics

Introductory articles

Diversity index

A diversity index is a quantitative measure that reflects how many different types (such as species) there are in a dataset, and simultaneously takes into account how evenly the basic entities (such as individuals) are distributed among those types. The value of a diversity index increases both when the number of types increases and when evenness increases. For a given number of types, the value of a diversity index is maximized when all types are equally abundant.

When diversity indices are used in ecology, the types of interest are usually species, but they can also be other categories, such as genera, families, functional types or haplotypes. The entities of interest are usually individual plants or animals, and the measure of abundance can be, for example, number of individuals, biomass or coverage. In demography, the entities of interest can be people, and the types of interest various demographic groups. In information science, the entities can be characters and the types the different letters of the alphabet. The most commonly used diversity indices are simple transformations of the effective number of types (also known as 'true diversity'), but each diversity index can also be interpreted in its own right as a measure corresponding to some real phenomenon (but a different one for each diversity index).