High above the Earth, thirty-one atomic clocks tick in quiet defiance of intuition — running faster than any clock on the ground, not through error, but through the precise operation of laws Einstein described a century ago. The Global Positioning System, built to guide ships and drivers, cannot function without accounting for the warping of spacetime itself: a 38-microsecond daily drift that, left uncorrected, would scatter your location across a small country by nightfall. What began as an engineering problem became an ongoing proof that the universe behaves exactly as one man predicted it w