18 Experiments That Crossed Every Line, Ranked By Cruelty

In 1971, psychologist Philip Zimbardo created a simulated prison in Stanford University’s basement with 24 student volunteers assigned as guards or prisoners. The experiment was meant to last two weeks but ended after six days when some guards started to act increasingly abusive. Graduate student Christina Maslach raised concerns about what she witnessed. Although influential, the study later faced criticism over its methods and remains one of psychology’s most debated experiments.