Mind & Body

The Trolley Problem Is a 50-Year-Old Moral Dilemma

A runaway trolley is hurtling toward five unsuspecting rail workers. If it hits them, it will surely kill them. You happen to be standing next to a switch that could divert the train onto a separate track, where only one rail worker is standing. If you flip the switch, the five workers will be spared and the single worker will be killed. Would you flip the switch? This is the classic trolley problem, and though it's 50 years old, it's becoming even more important with the spread of artificial intelligence.

I Think I Can, I Think I Can

The trolley problem was first posed in 1967 by "grand dame of philosophy" Philippa Foot as a way to illustrate the conundrums of the abortion debate. Foot mentioned the problem as just one of a series of ethical dilemmas, however, and it wasn't until a few years later when MIT philosopher Judith Thomson took up the issue that the problem got its name. Thomson devised two alternative versions, including the "switch" version we posed above. That led to a flurry of variations on this thought experiment.

See if these small adjustments change your answer:

  1. You're the driver of a runaway trolley that's hurtling toward five unsuspecting rail workers. To the left is a track where one rail worker is standing. If you do nothing, the five workers will die. If you steer to the left, one worker will die. What do you do?
  2. You're standing on a footbridge above a railroad track, where a runaway trolley is about to hit five rail workers. There's a large stranger next to you — large enough to stop the trolley if it hit him. If you pushed him onto the tracks, he would die, but the five workers would be spared. Do you push him?
  3. You're standing on a footbridge above a railroad track, where a runaway trolley is about to hit five rail workers. The large, evil man who cut the brakes on the trolley is standing next to you. If you pushed him onto the tracks, he would die, but the five workers would be spared. Do you push him?
  4. A runaway trolley is hurtling toward five unsuspecting rail workers. If it hits them, it will surely kill them. There's a separate track that loops back onto the main track, so that the entire system looks like a lowercase b. If you hit a switch, the train will follow the separate track so it loops around and comes back on the path to kill the five workers. However, there's also a large rail worker on this separate track who would stop the train if it hit him, killing him, but saving the five workers. Do you flip the switch?

Each of these scenarios make a slight change to the original, even though the choice is the same in every one: five people's lives versus one person's life. Still, these slight changes end up being very, very important: whereas you're an impartial observer in the classic version, #1 makes you a passenger on the train.

While the classic version has you flip a switch, the two footbridge variants have you physically push another human being. In one footbridge version, you're pushing a stranger who appears to be innocent; in the other, you're pushing the villain who caused this whole mess in the first place.

Dilemma #4 is even stranger: as with the classic version, you're still flipping a switch to choose whether to kill one person or five, but it's the killing of the one person, not the flip of the switch, that directly saves the five people.

Logic says that these scenarios are all the same. Your brain, however, says something very different.

Trains on the Brain

Around the turn of the 21st century, philosopher Joshua Greene decided to put a modern spin on the old problem: he put people in an fMRI machine to measure their brain activity while they pondered various trolley-problem scenarios. The results he published in 2001 showed that a person's answer correlated with their level of emotional engagement in the scenario, and that varied based on whether the decision was impersonal (flipping a switch) or personal (pushing a human being).

When participants were deciding whether or not to flip a switch, there was increased activity in the prefrontal cortex, which is associated with logic, reason, and problem-solving. When deciding whether or not to push the large stranger, conversely, there was increased activity in the amygdala, which plays an important role in fear and the fight-or-flight response, among other emotional processes. It's clear that while the decision to flip a switch was cool and rational for most people, the decision to push a person was fraught with emotion, and far more people choose to flip the switch than to push the person.

Further studies found that there are two groups of people who don't have an emotional response to the trolley problem. Those groups? Psychopaths and Buddhist monks. A Harvard undergraduate named Xin Xiang posed the footbridge variation to practicing Buddhist monks. When he compared their answers to those of average Han Chinese and American people, he found that the monks were much more likely to decide to push the stranger off the footbridge. That's probably because the monks were able to cooly analyze what benefitted the greater good. Psychopaths, however, also have no issue pushing the man off of the bridge, but that's because a defining trait of psychopaths is a lack of empathy for others.

Most people will never have to make a decision like the one in the trolley problem. But self-driving cars will. When faced with a lethal crash, do we want them to make the cool, calculated decision to kill fewer people in every scenario — even if that includes you, the driver — or do we want them to take other elements into account? In fact, you may be able to choose who survives in the crash of a self-driving car. The life-or-death issue is a conundrum engineers face today, and it's not clear that we'll ever have the right answer.

Can You Solve This Dilemma?

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Key Facts In This Video

  1. The trolley problem asks if you would pull a switch to redirect a train from hitting five people to hitting one person. 00:09

  2. Researchers have found that the brain responds differently to impersonal and personal dilemmas. 02:35

  3. Psychopaths seem to respond the same way to personal and impersonal dilemmas. 03:57

Written by Ashley Hamer November 29, 2017