On his road to general relativity, Einstein himself took many wrong turns. From 1907 to 1914 he struggled with what the physicist Abraham Pais called “one of the hardest problems of the century” — explaining gravity in a way that permits the laws of nature to be the same for all observers, no matter how they are moving. Einstein had to learn new math and jettison common prejudices, such as the universal belief that Euclidean geometry described reality accurately. He struggled with distractions, both in his personal life and in physics problems posed by quantum theory. And he found that nature stubbornly refused to cooperate. By 1914 he had essentially given up, believing that a partially successful attempt — a sort of general relativity lite — was the best that nature would allow.

But then somehow Einstein’s brain rebooted. His theory began to solidify, and he swiftly composed four papers, one a week, during November 1915. By the last paper he had finally found the decisive equation that launched his gravitation revolution.

Wow!

apart from its use in cosmology, general relativity was not widely applied to scientific problems in its first four decades. For the most part, general relativity languished in departments of mathematics, rarely studied in physics.

“General relativity was essentially a dead subject for a long time,” says the prominent relativity theorist Wolfgang Rindler of the University of Texas at Dallas. “People considered it a dormant science.”

Only after Einstein died in 1955 did general relativity come to life. About that time Wheeler, at Princeton University, began a program to explore its implications and train students to pursue them. By the early 1960s, new astronomical phenomena demanded explanations that Newtonian physics could not provide, and general relativity was poised for its renaissance. In the decades that followed, general relativity proved crucial for describing all sorts of celestial phenomena. At the same time, physicists devised ever more precise tests of its predictions, and Einstein passed them all. As Will has noted, “It is remarkable that this theory, born 100 years ago out of almost pure thought, has managed to survive every test.”

Even harder than finding the equations for general relativity is explaining how, out of almost pure thought, Einstein did it. Science historian Gerald Holton once remarked, while describing Einstein in the context of defining scientific genius, that “there is a mutual mapping of the mind and lifestyle of this scientist, and of the laws of nature.” Einstein himself ascribed his success to discovering the deep relationship between mathematics and the physical world.

“a more profound knowledge of the basic principles of physics is tied up with the most intricate mathematical methods.” He learned that from his pursuit of general relativity.

In the end, Einstein’s mind produced a mathematical theory so rich that it entailed unsuspected cosmic novelties. Fantastic physical phenomena were first discovered not through the lenses of telescopes, but within the squiggles Einstein had scratched out on paper to make the world make sense — to him. And now physical nature makes sense to modern science only because of Einstein’s insights.