Imagine you’re watching a runaway trolley barreling down the tracks, straight towards five workers. You happen to be standing next to a switch that will divert the trolley onto a second track. Here’s the problem: that track has a worker on it, too – but just one. What do you do? Do you sacrifice one person to save five? Eleanor Nelsen details the ethical dilemma that is the trolley problem.

By: Eleanor Nelson. Directed By: Eoin Duffy. Narrated By: Addison Anderson. Sound By: David Kamp.

This video is shared under a Creative Commons license (BY-NC-ND 4.0). Please visit Ted.com. This TED Talk originally appeared on TED-Ed in January 2017.