Over four months, March through June 1905, Albert Einstein produced four papers that revolutionized science. One explained how to measure the size of molecules in a liquid, a second posited how to determine their movement, and a third described how light comes in packets called photons—the foundation of quantum physics and the idea that eventually won him the Nobel Prize. A fourth paper introduced special relativity, leading physicists to reconsider notions of space and time that had sufficed since the dawn of civilization. Then, a few months later, almost as an afterthought, Einstein pointed out in a fifth paper that matter and energy can be interchangeable at the atomic level specifically, that E=mc2, the scientific basis of nuclear energy and the most famous mathematical equation in history.
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No wonder 2005 has been designated worldwide as a celebration of all things Einstein. International physics organizations have proclaimed this centenary as the World Year of Physics, and thousands of scientific and educational institutions have followed their lead. Images of Einstein have become even more common than usual, discussions of his impact a cultural drumbeat. “His name is synonymous with science,” says Brian Schwartz, a physicist at the City University of New York Graduate Center. “If you ask kids to show you what a scientist looks like, the first thing they’ll draw is wild white hair.”
In many ways, Einstein’s “miracle year” inaugurated the modern era, with its jumpy, discordant points of view and shocks to established truths. But the time, generally, was one of great cultural and social upheaval. Also in 1905, Sigmund Freud published his essay “Jokes and their Relation to the Unconscious” and an account of one of his first psychoanalyses. Pablo Picasso switched from his Blue Period to his Rose Period. James Joyce completed his first book, Dubliners. Still, no one’s rethinking of universal assumptions was more profound than Einstein’s.
Largely for that reason, Einstein today is more myth than man, and the essence of that myth is that the workings of his mind are beyond the reach not only of most mortals but even of most physicists. As with many myths, there’s some truth to it. “I learned general relativity three times,” says Spencer Weart, director of the Center for History of Physics at the American Institute of Physics. “It’s that difficult, subtle, different.”
But there’s also a good deal of exaggeration to the myth. Right from the start, long before he was Einstein the Inscrutable, the most prescient of his fellow physicists understood what he’d accomplished and its larger significance. He’d reinvented physics, which is just another way of saying he’d reinvented the way we all—physicists and nonphysicists alike—conceive of our place in the cosmos.
Specifically, he’d reinvented relativity. In a 1632 treatise, Galileo Galilei set forth what would become the classic version of relativity. He invited you, his reader, to imagine yourself on a dock, observing a ship moving at a steady rate. If someone at the top of the ship’s mast were to drop a rock, where would it land? At the base of the mast? Or some small distance back, corresponding to the distance that the ship had covered while the rock was falling?
The intuitive answer is some small distance back. The correct answer is the base of the mast. From the point of view of the sailor who dropped the rock, the rock falls straight down. But for you on the dock, the rock would appear to fall at an angle. Both you and the sailor would have equal claim to being right—the motion of the rock is relative to whoever is observing it.
Einstein, however, had a question. It had bothered him for ten years, from the time he was a 16-year-old student in Aarau, Switzerland, until one fateful evening in May 1905. Walking home from work, Einstein fell into conversation with Michele Besso, a fellow physicist and his best friend at the patent office in Bern, Switzerland, where they were both clerks. Einstein’s question, in effect, added a complication to Galileo’s imagery: What if the object descending from the top of the mast wasn’t a rock but a beam of light?
His choice wasn’t arbitrary. Forty years earlier, the Scottish physicist James Clerk Maxwell had demonstrated that the speed of light is constant. It’s the same whether you’re moving toward the source of light or away from it, or whether it’s moving toward or away from you. (What changes isn’t the speed of the light waves, but the number of waves that reach you in a certain length of time.) Suppose you go back to the dock and look at Galileo’s ship, only now the height of its mast is 186,282 miles, or the distance that light travels in a vacuum in one second. (It’s a tall ship.) If the person at the top of the mast sends a light signal straight down while the ship is moving, where will it land? For Einstein as well as Galileo, it lands at the base of the mast. From your point of view on the dock, the base of the mast will have moved out from under the top of the mast during the descent, as it did when the rock was falling. This means that the distance the light has traveled, from your point of view, has lengthened. It’s not 186,282 miles. It’s more.
That’s where Einstein begins to depart from Galileo. The speed of light is always 186,282 miles per second. Speed is simply distance divided by, or “per,” a length of time. In the case of a beam of light, the speed is always 186,282 miles per second, so if you change the distance that the beam of light travels, you also have to change the time.