Einstein’s revolution enters second century

What Einstein did
Back in 1896, when Einstein was 16 years old, he tried to imagine what it would be like to catch up with a light wave. Would he see the light wave frozen in place as he sped alongside? Or would he see nothing at all?

That musing on the nature of light stuck with him over the decade that followed, as he studied physics in Zurich, then took up a post in the Swiss patent office while he was finishing up his doctoral thesis.

One of the crowning achievements of 19th-century physics was the determination that light was an electromagnetic wave. But there were still some nagging questions: For example, if light was a wave, exactly what medium was it waving in? And why did the waves always seem to travel at the same speed, whether you were moving toward them or away from them?

At the time, most physicists saw such questions as esoteric matters they'd resolve someday by tinkering with the existing theories. But not Einstein.

"The reason he was such a revolutionary was that he was much more aware than other people that there were still a lot of deep mysteries," Dyson says. "He asked much more penetrating questions."

Einstein's 'big year'
Rigden said Einstein's "big idea" was that light behaved not only like a wave, but like particles as well. The first of his miracle-year papers, completed in March 1905, showed how the particle theory could explain phenomena that puzzled wave theorists. The big idea has had practical consequences to this day, ranging from the rise of digital cameras to the rumblings of NASA's solar-powered Mars rovers.

In April 1905, Einstein finally completed his thesis, laying out how the properties of solutions could be used to determine the dimensions of molecules. He followed up with yet another paper claiming that the mysterious jiggling of microscopic particles, known as Brownian motion, were actually caused by molecular collisions.

Not only did that research confirm that matter was composed of atoms of a particular size, but the statistical methods that Einstein used are still being applied to fields ranging from air-quality monitoring to stock market analysis.

MIRACLE  PHYSICS Five key papers from 1905, Einstein's "annus mirabilis" or miracle year: Quantum nature of light (PDF file) Dimension of molecules (PDF file) Brownian motion (PDF file) Special relativity Mass-energy equivalence (E=mc2)

In June 1905, Einstein published a paper answering his own teenage riddle: It would be impossible to catch up with a light beam. No matter how fast you were running, the beam would flash away at its usual speed. In observing the universe, scientists could disagree about their measurements of space and time, but the laws of physics would always hold true.

That was the heart of Einstein's special theory of relativity, and it planted the seeds for a follow-up paper that September, proposing an equivalence between mass and energy expressed by the formula E=mc². Einstein's claim encouraged other researchers to plumb the secrets of the atom, eventually opening the way for nuclear power and atomic weapons.

"That was a big year," Rigden says. "It got bigger as time went on."

In 1907, Einstein had what he called the "happiest thought of my life," that a person falling freely would not sense any gravitational field. In 1916, Einstein turned that realization into his general theory of relativity, which revolutionized the concept of gravity. In 1917, he wrote yet another paper that laid the groundwork for the invention of the laser four decades later — the theoretical keystone for technologies ranging from space-based weapons programs and fiber-optic communications to DVD players and grocery-store scanners.

Einstein's final quest
By the 1920s, Einstein's theories won him international fame — but also resentment. As a Jew in Germany, he came up against the anti-Semitic sentiments that would eventually force him to find refuge in the United States.

There was a scientific falling-out as well: Other physicists focused more and more on the fuzzy, probabilistic aspects of quantum theory — a view that Einstein dismissed with the famous statement that "God does not play dice."'

Einstein took a different path, searching for a deeper theory that would unify gravity and electromagnetism. "Everyone else was doing quantum theory, and he was trying to do the unified field theory," said Nancy Thorndike Greenspan, the biographer of physicist Max Born, one of Einstein's contemporaries.

In 1947, Einstein poured out his frustrations to Born in a letter: "I am quite convinced that someone will eventually come up with a theory whose objects, connected by laws, are not probabilities but considered facts, as used to be taken for granted until quite recently. I cannot, however, base this conviction on logical reasons, but can only produce my little finger as witness."

Einstein died in 1955 without finding the theory on which he staked his reputation and his little finger. But strangely enough, the discoveries of the past decade have revived interest in his quest.

"Other physicists made fun of Einstein back in the '30s, '40s and '50, but now many of the world's outstanding physicists are trying to do what Einstein was trying to do," Rigden says. "It's no longer something to laugh at."

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