What did Einstein ever do for us?
Published: 03 Jun 2005 12:00 BST
"The outstanding problems in physics now are in some respects harder than the outstanding problems in physics 100 years ago," said Rice University physics professor Doug Natelson. That doesn't mean Einstein had it easy, though. If Einstein hadn't existed, he said, "I doubt it would have been one individual who would have figured out all these things in such a short space of time."
Quantum physics
Einstein's first paper, submitted in March, concerned quantum physics, the peculiar realm of the ultra-tiny in which certainties are replaced by fuzzy clouds of probability. Max Planck started the quantum physics ball rolling in 1900, but Einstein gave it major impetus when he showed that 19th-century physicists' view of light as electromagnetic wave was incomplete.
The word "quantum" refers to energy in discrete packets, or quanta. In the case of light, these particles are called photons. Einstein's work helped show that light behaved both as particle and a wave.
Light's wavelike nature could be seen in phenomena such as interference patterns that also appear with waves in water. For example, with both light and water, peaks of two waves can combine into a taller peak, or a trough of one wave can cancel out the peak of another.
But some phenomena don't take well to the wave description. One was the photoelectric effect, in which light shining on metal causes it to emit electrons. Einstein's first 1905 paper relied on the quantum description of light to explain how an increase in the light intensity caused more electrons to be emitted — but not higher-energy electrons, as the wave theory predicts.
"This was revolutionary. Neither classical mechanics nor classical electromagnetic theory could survive in the face of quantum phenomena," said John Stachel, editor of Einstein's Miraculous Year: Five Papers That Changed the Face of Physics.
Quantum physics didn't even sit well with Einstein himself. "No longer did tiny particles have a definite position and speed... Einstein was horrified by this random, unpredictable element in the basic laws and never fully accepted quantum mechanics," said Stephen Hawking, a cosmologist at the University of Cambridge, in an essay in Robinson's book.
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