At a joint meeting of the Royal Society and the Royal Astronomical Society in 1919, Arthur Eddington announced a discovery that turned physics on its head. Eddington had measured the position of a star cluster near the limb of the sun during a total solar eclipse; the stars appeared to have moved from their normal spots in the sky. This proved that Isaac Newton’s theory of gravity was wrong, that it ought to be replaced with a new theory—the “general theory of relativity”—from another physicist, Albert Einstein.
It will be no surprise to hear that Eddington’s pronouncement was controversial. Newton was the father of modern physics—in some ways, the father of modern science. He was the patron saint of the Royal Society. And now his work was being overturned by an upstart German-Swiss Jew who made his breakthrough at a desk in the Bern patent office, where he kept his notes in a drawer he referred to as his “theoretical physics department.” Still, that’s what the data said: Einstein’s theory correctly predicted the star cluster’s position; Newton’s did not. During the century since that meeting, Einstein’s physics has been debated, dismissed, accepted, exceeded, and returned to. It has remained obscenely contentious and provoked some of the most remarkable ideas in the history of human scholarship. It changed the world, and its story is told in The Perfect Theory.
After graduating from the Polytechnic Institute of Zurich in 1900, Einstein’s lackluster grades kept him from securing a university position. Nonetheless, “over a period of just a few months,” writes Pedro Ferreira, “Einstein had written a string of papers that were . . . transforming physics.” The papers were on the behavior of light and the chaos of dust particles; one “tackled a problem that had been plaguing physicists for almost half a century: how the laws of physics seem to behave differently depending on how you look at them.” Einstein “brought them together with his principle of relativity.”
In 1907, Einstein was still working through a daily quota of patent applications, but his reputation was sufficient for an important journal, the Yearbook of Electronics and Radioactivity, to commission him to write a review of his work, “On the Relativity Principle and the Conclusions Drawn From It.” He was given two months, “and in those two months Einstein realized that his principle of relativity was incomplete. It would need a thorough overhaul if it was to be truly general.”
Einstein’s special relativity rectified inconsistencies in Newton’s mechanics and Maxwell’s electromagnetism; but it didn’t include gravity, so that’s where Einstein directed his thinking. His work on relativity had been based on inertial frames of reference, in which everything moves at a constant velocity. Whether you’re sitting in a parked car or driving at 90 miles per hour on a level road, you’re in an inertial frame of reference, and relativity says that physics will behave the same in either circumstance. That’s why when you toss your cell phone into the passenger seat while cruising at 90 mph the phone doesn’t fly backwards and crash through the rear window.
What Einstein began to consider for a more general theory of relativity was accelerating frames of reference. Ferreira provides a metaphor: Imagine getting into a ground-level elevator and hitting the button for the top floor. As your frame of reference accelerates—as the elevator begins to go up—you feel a little heavier. As the elevator descends, you feel lighter. Einstein couched this in terms of a thought experiment: “If a person falls freely he will not feel his own weight.” In physical terms, he concluded, acceleration and gravity are indistinguishable. If you’re weightless in a spaceship beyond the influence of any source of gravity, and it starts to accelerate upwards at a rate of 32.2 feet per second squared—equivalent to the force of gravity on Earth—everything would appear to behave exactly as it does on Earth’s surface.
This conclusion has substantial implications. “Imagine yourself riding in a spaceship far from any planets and stars,” writes Ferreira.