The day before the experiment began, researchers converted a corridor in Stanford's psychology building into a mock prison. Small cells were arranged to hold three prisoners each. A closet became solitary confinement. A larger room across the corridor housed the guards and warden. Guards received khaki uniforms from a military surplus store, wooden batons, and mirrored sunglasses designed to prevent eye contact and create anonymity. Prisoners were confined around the clock. The US Office of Naval Research funded the study to understand conflict between military guards and prisoners. What happened next exceeded anyone's expectations for a simulation.

The transformation happened faster than the researchers anticipated. Guards began asserting dominance. Prisoners, stripped of their names and given numbers, grew passive and depressed. Some asked to leave but were initially told they could not, despite having signed consent forms that supposedly guaranteed their right to withdraw. The experiment was perceived by many to involve questionable ethics, the most serious concern being that it continued even after participants expressed their desire to leave. Digitized recordings released decades later revealed that warden David Jaffe explicitly encouraged one guard to be more "tough" for the benefit of the experiment's conclusions.

The Stanford Prison Experiment became one of psychology's most famous studies, cited in textbooks and referenced whenever abuse scandals like Abu Ghraib emerged. But critics have questioned whether it was science at all. French historian Thibault Le Texier established that guards were given explicit direction about how to behave, and that Zimbardo's conclusions were largely written before the experiment concluded. Participants interviewed for the National Geographic documentary "The Stanford Prison Experiment: Unlocking the Truth" confirmed many of Le Texier's claims. A 2007 study found that people who responded to advertisements mentioning "prison life" scored higher on measures of aggressiveness, authoritarianism, and narcissism than those who saw neutral ads, suggesting the participants themselves may have been self-selected for abusive tendencies.

Four years before the Stanford experiment, another unsettling study unfolded just miles away. In 1967, high school teacher Ron Jones conducted The Third Wave experiment in Palo Alto, demonstrating how quickly authoritarian group dynamics could take hold in a classroom. Jones used methods similar to Nazi Party techniques to show his students how ordinary Germans could have participated in the Holocaust. Both experiments examined how readily people conform to assigned roles and authority structures. Both suggested that personality mattered less than situation. And both left participants uncertain about what had been real and what had been performance.

The Stanford Prison Experiment's most lasting impact may be on research ethics rather than psychology. The harm inflicted on participants prompted American universities to strengthen requirements for institutional review boards and ethical oversight of human experiments. Today, studies must receive approval before they begin, and participants must be able to withdraw without obstruction. The experiment also spawned multiple films, television episodes, and books exploring its implications. Whether the Stanford Prison Experiment revealed something true about human nature or merely demonstrated what happens when an authority figure encourages cruelty remains contested. The basement of Jordan Hall returned to ordinary academic use, but the questions raised there about power, conformity, and the thin veneer of civilization continue to resonate.