How do humans understand each other, cooperate, and build civilizations? Brian Greene sits down with Harvard cognitive scientist Steven Pinker — author of the newly released When Everyone Knows That Everybody Knows — for a deep dive into the psychology of common knowledge, the evolution of language, and the invisible rules that make society possible.They explore why we laugh, cry, and signal emotions, how shared understanding and social norms hold civilization together, and what happens when those norms break down. The conversation also tackles AI vs human intelligence, misinformation, and whether shared truth can survive in a fragmented digital world. This program is part of the Big Ideas series, supported by the John Templeton Foundation.Learn More