The Harvard psychologist Joshua Greene is an expert in “trolleyology,” the self-effacing way he describes his research into the manifold variations on the “trolley problem.” The basic form of this problem is simple: There’s a trolley barreling towards five people, who will die if they’re hit. But you could switch the trolley onto another track on which only a single person stands. Should you do it?
From this simple test of moral intuition, researchers like Greene have created an endless set of variations. By varying the conditions ever so slightly, the trolley problem can serve as an empirical probe of human minds and communities (though not everyone agrees).
For example, consider the footbridge variation: You’re standing on a footbridge above the trolley tracks with a very large person, who, if you push him or her, can stop the trolley from killing the five people. Though the number of lives saved is the same, it turns out that far more people would throw the switch than push the person.
