On April 6, 1922, Einstein met a man he would never forget. He was one of the most celebrated philosophers of the century, widely known for espousing a theory of time that explained what clocks did not: memories, premonitions, expectations, and anticipations. Thanks to him, we now know that to act on the future one needs to start by changing the past. Why does one thing not always lead to the next? The meeting had been planned as a cordial and scholarly event. It was anything but that. The physicist and the philosopher clashed, each defending opposing, even irreconcilable, ways of understanding time. At the Socit franaise de philosophieone of the most venerable institutions in Francethey confronted each other under the eyes of a select group of intellectuals. The dialogue between the greatest philosopher and the greatest physicist of the 20th century was dutifully written down.1 It was a script fit for the theater. The meeting, and the words they uttered, would be discussed for the rest of the century.