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On that day in May, two scientific expeditions were finally putting his theory of general relativity to the test. In Sobral, Brazil, and on Príncipe Island, off the western coast of Africa, two teams were viewing a total solar eclipse; in measuring the deflection of starlight by the sun’s gravitational field, they proved Einstein right.

“His equations allowed cosmology to become a science,” John Barrow, the cosmologist, wrote in an email. “Before him, cosmology was like a branch of art history. You could imagine any type, shape or form of universe you liked.”

But Einstein’s equations, he added, “are more sophisticated than any others in science. They describe whole universes. Every solution of Einstein’s equations describes an entire possible universe that is consistent with the laws of physics.” Since 1916, Dr. Barrow noted, Einstein’s equations — matched to astronomical observations — have revealed static universes, expanding universes, accelerating universes, and universes that are rotating, oscillating, cyclic, distorted, irregular, chaotic, inflationary, and eternal.