June 1, 2005 4:00 AM PDT
A century later, Einstein's first ideas still hold power
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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 classic 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 England, in an essay in Robinson's book.
Molecules and atoms
The next two papers were easier for the physics community to swallow. They validated the idea that matter was composed of atoms and of groups of atoms called molecules.
Though most scientists accepted the concept, there were significant holdouts. "At that time, there were people who doubted the existence of molecules," Stachel said.
The first of these papers, a doctoral thesis submitted in April, was Einstein's prediction that the size of molecules could be gauged by the effects of dissolving sugar in a liquid. Einstein argued that "the effect of the dissolution of sugar molecules would change the viscosity of fluid; you can measure the viscosity, and from that estimate the size of the molecules," Stachel said. His prediction proved to be not far from reality.
Second was a description of the mechanism underlying Brownian motion--a particle's small random movements named after botanist named Robert Brown who observed pollen grains jiggling in water. Einstein derived a theory that predicted how far a particle will move over time, given such buffeting--a theory that was confirmed a few years later and which demonstrated that properties such as temperature and pressure were reflections of the average behavior of huge numbers of molecules.
Einstein's final two 1905 papers concerned relativity, the mind-bending idea about the ticking of clocks and the speed of light that most people associate with Einstein.
In June came the first paper, describing special relativity. In it, Einstein proposed a solution to a problem that had plagued physicists concerned with the spread of light waves. The prevailing belief was that light waves traveled in a fixed medium called the ether, analogous to how water waves travel in the medium of the ocean and sound waves travel in the medium of the air.
Under that belief, the speed of light would vary according to how fast an observer was traveling compared with the ether. Physicists Albert Michelson and Edward Morley famously failed to find that difference in an experiment to measure changes in the speed of light as the Earth moved in different directions compared with this theoretical ether.
Einstein's June paper simply did away with the idea of the ether and said light moves at the same speed--about 186,000 miles per second--
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