A pair of gamma-ray photons — one possessed of a million times the energy of the other — arrived at virtually the same instant at NASA’s orbiting Fermi Gamma-ray Space Telescope, after a 7.3-billion-year race across the universe. Some proponents of alternatives to Einstein’s theory of gravity would have predicted that the more energetic would have been much farther behind the less energetic one. They were wrong — Einstein wins this round.