In 1939, Richard Feynman, a graduate of MIT, arrived in John Wheeler's Princeton office to report for duty as his teaching assistant. The soft-spoken Wheeler was a raging nonconformist full of wild ideas about the universe. The boisterous Feynman was a cautious physicist who believed only what could be tested. Yet a lifelong friendship and enormously productive collaboration was born that led to a complete rethinking of the nature of time and reality.