This month, one hundred years ago, Einstein completed his theory that would forever change physics. Not just physics but his astonishing ideas revolutionized philosophy, art, and culture. A commemorative issue of Scientific American is unambiguous on his impact: “How Einstein reinvented reality.”
Before Einstein, gravity was thought to be a force that pulled coffee cups to the floor. I remember the terse graffiti written on a washroom wall that summarized this notion: “gravity sucks.”
Einstein was sitting in a Swiss patent office in 1907 when a thought “startled” him. He recalled: “If a person falls freely, he will not feel his own weight.” We all have fanciful thoughts but this one had serious implications.
In his thought experiment, Einstein imagined a person falling in an elevator. Our office worker only wanted to get off on the third floor and now he’s falling, weightless, to certain doom.
But no, Einstein now imagines our hapless worker, in his elevator, floating in space. Unless the clerk was told, he would be unable to tell the difference because in both cases he is weightless. While floating in space, free as stardust, is a better choice, he’ll still have some explaining to do.
Einstein’s genius was equating the two and called it “the equivalence principle”; both merely manifestations of the same phenomena.
Einstein then turned to another thought experiment. Now he imagined our worried wanderer accelerating upward through space, the floor pushing up on his feet. By the equivalence principle, our reluctant spaceman could easily imagine himself safely back on earth waiting in his elevator stopped between floors. But he is not.
Through a pinhole in the wall, he sees beam of sunlight. To his astonishment, the beam doesn’t hit a point exactly opposite the wall but slightly lower. Because he is being accelerated, by the time the beam hits the opposite wall the elevator has moved up.
Fine, but what could possibly cause that to happen back on earth? It turns out that space itself is curved and that light beams follow those curvatures, as does everything else. Massive objects create dents in space somewhat like a bowling boll dents a trampoline. Rather than “fall,” objects follow those indentations in space.
Great ideas, but what about the math? Einstein’s brainwaves remained in the realm of speculation until 1912 when Einstein finally applied himself to the equations that would tie acceleration and gravity together. For four years he struggled with the math, often leading to dead ends. He told a fellow genius, David Hilbert, about his problem and Hilbert went to work on it too.
Einstein was under pressure. He promised a solution to be delivered to the Prussian Academy in November, 1915. Not only was he in a race to beat Hilbert to a solution but the clock was ticking down to the lecture.
After a month of whirlwind calculations and frenzied corrections, he arrived on November 4 still wrestling with his theory. “For the last four years,” he candidly told the assembled academy, “I have tried to establish a general theory of relativity.”
It was a long gestation and a difficult delivery but one which forever changed history. Meanwhile, our office clerk has some amazing stories to tell the kids.