Nobel Prize-winning physicist Frank Wilczek explores the secrets of the cosmos. Since the dawn of recognizably modern physics in the late 17th century, our understanding of nature’s basic operating system has undergone major expansions and renovations. We brought in electromagnetic fields, space-time curvature and the quantum revolution. Through all that growth and tumult, a simple and weirdly beautiful, yet enigmatic and seemingly gratuitous, feature of the laws remained intact. Time reversal symmetry—or T for short—says that if you take a movie of events in the physical world and run it backward, what you see will obey the same basic laws.

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