Trolley problem

The trolley problem is a thought experiment in ethics. The general form of the problem is this: There is a runaway trolley barreling down the railway tracks. Ahead, on the tracks, there are five people tied up and unable to move. The trolley is headed straight for them. You are standing some distance off in the train yard, next to a lever. If you pull this lever, the trolley will switch to a different set of tracks. However, you notice that there is one person on the side track. You have two options: (1) Do nothing, and the trolley kills the five people on the main track. (2) Pull the lever, diverting the trolley onto the side track where it will kill one person. Which is the correct choice?

The problem was first introduced by Philippa Foot in 1967, but also extensively analysed by Judith Thomson,Peter Unger, and Frances Kamm as recently as 1996, and has also been revisited in 2015 (Larman and Oates). The German Hans Welzel discussed a similar problem as early as 1951. Outside of the domain of traditional philosophical discussion, the trolley problem has been a significant feature in the fields of cognitive science and, more recently, of neuroethics. It has also been a topic in popular books dealing with human psychology.