A few hands go up, but most of the students just erupt in giggles.

And that's exactly why, some scientists argue, this well-known "trolley dilemma," shouldn't be used for psychology experiments as much as it is.

Number of Studies Discussing the Trolley Problem

Over the past few decades, the trolley dilemma has been at the center of dozens of experiments designed to gauge subjects' moral compasses. Some people think it can help answer Big Questions about everything from the use of drones to self-driving cars.

One recent paper by Harvard's Joshua Greene and others, which involved MRI scans of people contemplating the trolley, has been cited more than 2,000 times. In 2007, the psychologists Fiery Cushman and Liane Young and the biologist Marc Hauser administered the test to thousands of web users and found that while 89 percent would flip the track switch, only about 11 percent would push the fat man.

That contradiction—that people find giving the man a fatal prod just too disturbing, even though the end result would be the same—is supposed to show how emotions can sometimes color our ethical judgments.

But one group of researchers thinks it might be time to retire the trolley. In an upcoming paper that will be published in Social and Personality Psychology Compass, Christopher Bauman of the University of California, Irvine, Peter McGraw of the University of Colorado, Boulder, and others argue that the dilemma is too silly and unrealistic to be applicable to real-life moral problems. Therefore, they contend, it doesn't tell us as much about the human condition as we might hope.

In a survey of undergraduates, Bauman and McGraw found that 63 percent laughed "at least a little bit" in the fat-man scenario and 33 percent did so in the track-switching scenario. And that's an issue, because "humor may alter the decision-making processes people normally use to evaluate moral situations," they note. "A large body of research shows how positivity is less motivating than negativity."

"If you study moral judgement and people are laughing about the experimental materials you're giving them, that might be a problem," McGraw, who also studies humor, told me in an interview.

McGraw also says the trolley problem isn't a realistic representation of actual crises of conscience. (When's the last time you even rode in a trolley?)

The dilemma was originally devised not by psychologists, after all, but by philosophers. In the 1960s, Philippa Foot and Judith Jarvis Thomson used it as a thought experiment; a way of laying bare the difference between peoples' convictions and their justifications.

In another survey, McGraw and his co-authors found that people "rated the trolley problems to be much less realistic than short scenarios about contemporary social issues."