If a runaway trolley is destined to hit a group of five people but can be diverted onto a track where it will hit only one, is it right to divert it? What if it can only be stopped by throwing somebody in front of it?
The Trolley Problem
Developed by MIT Philosopher Judith Jarvis Thomson, now emerita, the famous "trolley problem" has been debated for more than 30 years, as philosophers the world over struggle to understand what principle underlies the different responses elicited by the two scenarios. In each case, one person is sacrificed to save five. Yet people overwhelmingly support diverting the train and object to throwing a person into its path. Why?
Today this question has crossed disciplines, taken up by researchers in the rapidly growing field of moral psychology, which aims to investigate moral responses empirically. Psychology Professor Marc Hauser of Harvard, for example, is investigating the theory that some basic moral sense is hard-wired in the human brain—an idea analogous to MIT Professor Noam Chomsky's theory of universal grammar.
Hauser has incorporated variations on the trolley problem into his "Moral Sense Test," an online survey that initially posed moral questions to 5,000 subjects in 120 countries (the test has since been taken by upwards of 150,000 people). Responses have proved remarkably consistent across gender, age, educational level, ethnicity, religion and national affiliation.
Professor Thomson nevertheless sees polls as irrelevant to the ethical question. In a recent paper re-examining the trolley problem, she writes that despite popular opinion, it is impermissible to kill one person by diverting the train to save five — the bystander may choose to do nothing. There is a major moral difference between killing five people and letting five die, Thomson says. Why remains a subject for debate.