Theory of Relativity
The second of the two most fruitful physical theories of the 20th century is the theory of relativity, which to scien~ tists and laymen alike is synonymous with the name of Einstein. Once again, there is a common misconception concerning the origin of this theory, namely, that Einstein advanced it in 1905 to "explain" the famous MichelsonMorley experiment (1887), which failed to detect a relative motion of the earth with respect to the ether, the medium' through which light was assumed to propagate. In fact, it is not even certain that Einstein was aware of this experiment in 1905; nor was he familiar with H.A. Lorentz's elegant 1904 paper in which Lorentz applied the transformation equations which bear his name to electrodynamic phenomena. Rather, Einstein consciously searched for a general principle of nature that would hold the key to the explanation of a paradox that had occurred to him when he was 16: if, on the one hand, one runs at, say, 4 miles per hour alongside a train moving at 4 miles per hour, the train appears to be at rest; if, on the other hand, it were possible to run alongside a ray of light, neither experiment nor theory suggests that the ray of light-an oscillating electromagnetic wave-would appear to be at rest. Einstein eventually saw that he could postulate that no matter what the velocityof the observer, he must always observe the same velocity c for the velocity of light: roughly 186,000 miles per second. He also saw that this postulate was consistent with a second postulate: if an observer at rest and an observer moving at constant velocity carry out the same kind of experiment, they must get the same result. These are Einstein's twO postulates of his special theory of relativity. Also in 1905 Einstein proved that his theory predicted that energy E and mass m are entirely interconvertible according to his famous equation, E= me',
For observational confirmation of his general theory 0 . relativity, Einstein boldly predicted the gravitational red shift and the deflection of starlight (an amended value), as" well as the quantitative explanation of U. J. J. Leverrier'srlong-unexplained observation that the perihelion of the. planet Mercury precesses about the sun at the rate of 43' seconds of arc per century. In addition, Einstein in 1916; predicted the existence of gravitational waves, which have only recently been detected. Turning to cosmological problems the following year, Einstein found a solution to his field equations consistent with the picture (the Einstein universe) that the universe is static, approximately uniformly filled with a finite amount of matter, and finite but unbounded (in the same sense that the surface area of a smooth globe is finite but has no beginning or end).
The Man and His Philosophy
Fellow physicists were always struck with Einstein's uncanny ability to penetrate to the heart of a complex problem, to instantly see the physical significance of a complex mathematical result. Both in his scientific and in his personal life, he was utterly independent, a trait that manifested itself in his approach to scientific problems, in his unconventional dress, in his relationships with family and friends, and in his aloofness from university and governmental politics (in spite of his intense social consciousness). Einstein loved to discuss scientific problems with friends, but he was, fundamentally a "horse for single harness."
Einstein's belief in strict causality was closely related to his profound belief in the harmony of nature. That nature can be understood rationally, in mathematical terms, never ceased to evoke a deep-one might say, religious-feeling of admiration in him. "The most incomprehensible thing about the world," he once wrote, "is that it is comprehensible." How do we discover the basic laws and concepts of nature? Einstein argued that while we learn certain features of the world from experience, the free inventive capacity of the human mind is required to formulate physical theories. There is no logical link between the world of experience and the world of theory. Once a theory has been formulated, however, it must be "simple" (or, perhaps, "esthetically pleasing") and agree with experiment. One such esthetically pleasing and fully confirmed theory is the 'special theory of relativity. When Einstein was informed of D.C. Miller's experiments, which seemed to contradict the -special theory by demanding the reinstatement of the ether, he expressed his belief in the spuriousness of Miller's re. suits-and therefore in the harmoniousness of nature-with another of his famous aphorisms, "God is subtle, but he is " not malicious."
Continued
