Science: Inconstant Constant?

A feature of the relativity theory . . . is the absoluteness of the velocity of light. —Sir Arthur Stanley Eddington. The speed of light is perhaps the most fundamental of all the constants of nature. —Dr. Arthur Holly Compton. Speed-of-light . . . that most fundamental constant.—Dr. Robert Andrews Millikan. In a universe torn to metaphysical shreds by conflicting theories as to its nature and origin, with the calm old laws of cause &; effect pushed aside by principles of indeterminance and inanimate free will, with time no longer the placid ticking of a clock but a fourth dimension, the speed of light has remained a faithful standby. Ready to doubt almost everything else, 20th Century scientists have not doubted that light always travels at the same speed through a vacuum. Last week from a sunny California valley came shocking news that “that most fundamental constant” is apparently a variable. Nineteenth Century theorists supposed that light was propagated through space by an all-pervading ether. The late great Albert Abraham Michelson, first U. S. Nobel Prizewinner in Science, reasoned that if this ether existed, then the motion of the earth through it should affect the velocity of light. In 1887 he and Edward W. Morley rigged up an interferometer, raced two beams of light against each other, one parallel to the earth’s motion, the other perpendicular. The two beams arrived at their common destination at the same instant. This historic experiment discredited the ether-concept. Eighteen years later Albert Einstein posited the central feature of the “special theory of relativity”—that there was no such thing as the motion of bodies through a stationary ether, that bodies could move only in relation to one another. Meanwhile Michelson had begun a lifetime task of determining it down to the last fraction of a mile per second. Seven years ago he flashed a beam of light between Mt. Wilson and Mt. San Antonio, 22 mi. away, clocked it over &; over, finally announced that light’s speed was 186.284 mi. per sec., with a probable error of less than 2 mi. per sec. But while Dr. Michelson never doubted that light’s speed was constant in vacua, the air even between lofty mountain peaks is no vacuum. In a valley near Pasadena he had built a mile-long tube of corrugated iron (TIME, Nov. 24, 1930). Powerful pumps sucked out all but a few stray molecules of air. The U. S. Coast &; Geodetic Survey measured the tube to within .063 of an inch. Then Dr. Michelson measured it. At one end of the tube was a 32-sided mirror which could be spun as fast as a bacteriologist’s centrifuge. Light from this end raced down the tube, back from a reflector at the other end. The mirror was turned just fast enough for succeeding facets to catch the returning light, send it on repeated journeys down the tube and back. The essential calculation was simple, involved only the speed of the rotating mirror, the number of facets, the length of the tube. But Dr. Michelson. insisting on precision, working feverishly against the paralysis creeping upon him, died before his tests were complete (TIME, May 18, 1931). Dr. Francis Gladheim Pease of Mt. Wilson Observatory and Fred Pearson, longtime and loyal Michelson assistant, went on spinning the mirror, looking through the eyepiece, making charts.

Last spring they issued a terse, tight-lipped announcement that they had completed actual measurements, would need six months to check their data, iron out some unaccountable variations. In the Pease-Pearson report last week the variations, up to 12 mi. per sec., were stunningly unaccounted for, were apparently real fluctuations in the speed of light. Worse, they were not irregular but seemed to occur in well-defined rhythms. There was one cycle of 14¾ days, another of about a year, another apparently following the tides of the ocean. And at 9 p. m. every night something happened which threw the tests entirely askew. Dr. Pease and Assistant Pearson did not say flatly that the speed of light could no longer be regarded as a constant. “The observed irregularities,” they said, “are unexplained and their elucidation apparently will require more sensitive apparatus.” Albert Einstein, at Princeton’s Insti tute for Advanced Study, foresaw no need of revising his relativity theory, spoke of deformations in the earth’s surface, said the Pease-Pearson results should be “most interesting from a geophysics standpoint.” Harvard Observatory’s Director Harlow Shapley thought the results were due entirely to the relationship of earth, sun and moon movements, pointed out that the 14¾-day fluctuation was roughly equal to half a lunar cycle and the annual fluctuation to the earth’s revolution round the sun. From nearby Caltech, Dr. Robert Andrews Millikan suggested that there may have been something wrong with the apparatus.