LITMIR.BIZ

Скачать книгу

Property in Bern, where he wound up in part because his professors had refused to write letters of recommendation for someone so dismissive of their authority. As Einstein reported in a letter in May 1901, “From what I have been told, I am not in the good books of any of my former teachers.” Yet even as a patent clerk, Einstein continued to seek the ether, for the same reason that physicists everywhere were seeking the ether. When electromagnetic waves of light departed from a star that was there and hadn’t yet arrived here, they had to be traveling along something. So: What was it? Find that something, as physicists understood, and maybe electricity and magnetism and the relationship between the two wouldn’t seem so deeply hidden after all.

      Among the seekers of the ether, one was without equal: the Scottish physicist William Thomson, eventually Baron Kelvin of Largs. As one of the most prominent and illustrious physicists of the century, Lord Kelvin had made the pursuit of the ether the primary focus of his scientific investigations for literally the entire length of his long career. He’d first thought he found it on November 28, 1846, during his initial term as a professor of natural history at the University of Glasgow. He was mistaken. As he wrote a friend in 1896, on the occasion of the golden jubilee of his service to the university, a three-day celebration that attracted two thousand representatives of scientific societies and academies of higher learning from around the world, “I have not had a moment’s peace or happiness in respect to electromagnetic theory since Nov. 28, 1846.”

      Part of the problem with the ether was how to picture it. “I never satisfy myself unless I can make a mechanical model of a thing,” Kelvin once told a group of students. “If I can make a mechanical model, I can understand it.” In one such demonstration that was a perennial favorite of his students, he would draw geometrical shapes on a piece of india rubber, stretch the rubber across the ten-inch mouth of a long brass funnel, and, having hung the funnel upside down over a tub, direct water from a supply pipe into the thin tube at the top. As the water collected in the mouth of the funnel, the india rubber bulged, and it drooped, and it gradually assumed the shape of a globule. Soon the blob had expanded to a width nearly double the diameter of the mouth from which it appeared to be emerging, and just when the rubber seemed unable to stretch any thinner, it did anyway. All the while Kelvin continued to lecture, calmly commenting on the subject of surface tension as well as on the transformations the simple Euclidean shapes on the rubber were now undergoing. Then, at precisely the moment Kelvin calculated that neither india rubber nor the ten benches of physics students could endure any greater tension, he would raise his pointer, poke the gelatinous mass hanging before him, and, turning to the class, announce, “The trembling of the dewdrop, gentlemen!”

      The trembling of the dewdrop, the angling of the gas molecule, the orbiting of a planet: the least matter in the universe to the greatest, and all operating according to the same unifying laws. Here was the whole of modern science, in one easy lesson. More than two hundred years earlier, René Descartes had expressed the philosophical hope that a full description of the material universe would require nothing but matter and motion, and several decades after that Isaac Newton had expressed the physical principles that described the motion of matter. The rest, in a way, had been a process of simply filling in the blanks—plugging measurements of matter into equations for motions, and watching the universe tumble out piecemeal yet unmistakably all of a single great mechanistic piece. The lecture hall where for half a century Kelvin demonstrated his models was a monument of sorts to this vision: the triple-spiral spring vibrator he’d hung from one end of the blackboard; the thirty-foot pendulum, consisting of a steel wire and a twelve-pound cannonball, that he’d suspended from the apex of the dome roof; two clocks, those universal symbols of the workings of the universe. Matter and motion, motion and matter, one acting upon the other; causes leading inexorably to effects that, by dint of more and more rigorous and precise examination, were equally predictable and verifiable to whatever degree of accuracy anyone might care to name: Here was a cosmos complete, almost.

      The exception was the ether. When numerous experiments in the early nineteenth century began showing that light travels in waves, physicists naturally tried to describe a substance capable of carrying those waves. The consensus: an absolutely incompressible, or elastic, solid. For Cambridge physicist George Gabriel Stokes, that description suggested a combination of glue and water that would act as a conduit for rapid vibrations of waves and also allow the passage of slowly moving bodies. For British physicist Charles Wheatstone, it meant white beads, which he used in his Wheatstone wave machine of the early 1840s—a visual aid that vividly demonstrated how ether particles might move at right angles to a wave coursing through their midst and an inspiration for numerous similar teaching aids of the era.

      And for Kelvin, “the nearest analogy I can give you,” as he once said during a lecture, “is this jelly which you see.” On other occasions, he might begin his demonstration with Scotch shoemakers’ wax. If he shaped the wax into a tuning fork or bell and struck it, a sound emanated. Then he would take that same sound-wave-conveying wax and suspend it in a glass jar filled with water. If he first placed corks under the substance, then laid bullets across the top of it, in time the positions of the objects would reverse themselves. The bullets would sink through the wax to the bottom while the corks would pop out the top. “The application of this to the luminiferous ether is immediate,” he concluded: a substance rigid enough to conduct waves traveling at fixed speeds in straight lines from one end of the universe to the other, if need be, yet porous enough not to block the passage of bullets, corks, or even—by the same application of scale that rendered minuscule dewdrops and giant rubber globules analogous—planets.

      Not to block—but surely to impede? Surely at least to slow the passage of a planet? An elastic solid occupying all of space would have to present a degree of resistance to a (in the parlance of the day) “ponderable body” such as Earth. But to what degree precisely? In an effort to determine the exact extent of the luminiferous (or light-bearing) ether’s drag on Earth, the American physicist Albert A. Michelson devised an experiment that he first conducted in Berlin in 1881. His idea was to send two beams of light along paths at 90-degree angles to each other. Presumably the beam following one path would be fighting against the current as Earth plowed through the ether, while the beam on the other path would be swimming with the current. Michelson designed an ingenious instrument, which he called an interferometer, that he hoped would allow him to make measurements that, through a series of calculations, would determine the velocity of the Earth through the ether. The Berlin reading, however, suffered from the vibrations of the horse cabs passing outside the Physical Institute. So he moved his apparatus to the relative isolation of the Astrophysical Observatory in Potsdam, where he repeated the experiment. The reading, to his surprise, indicated nothing.

      Which was impossible. An interaction between a massive planet and even the most elastic of solids surely couldn’t pass undetected or remain undetectable. “One thing we are sure of,” Kelvin told an audience in Philadelphia three years later, while on his way to lecture at Johns Hopkins University in Baltimore, “and that is the reality and substantiality of the luminiferous ether.” And if experiments of unprecedented refinement and sophistication failed to detect it, there was only one reasonable alternative course of action. As Kelvin wrote in his preface to the published volume of those Baltimore Lectures, “It is to be hoped that farther experiments will be made.”

      They were. In 1887 Michelson tried again, this time with the help of the chemist Edward W. Morley. Together they constructed an interferometer far more elaborate and sensitive than the ones Michelson had used in Germany, secured it in an essentially tremor-free basement at the Case School of Applied Science in Cleveland, and set it floating on a bed of mercury for, literally, good measure. Michelson had in mind a specific number for the wavelength displacement he expected the ether would produce, and he further decided that a reading 10 percent of that number would conclusively indicate a null result. What he got was a reading of 5 percent of the displacement he thought the ether might produce—a blip attributable to observational error, if anything. Michelson found himself forced to reach the same conclusion he’d previously reported: “that the luminiferous ether is entirely unaffected by the motion of the matter which it permeates.”

      “I cannot see any flaw,” said Kelvin of this experiment, in a lecture he delivered in the summer of 1900. “But a possibility of escaping

Скачать книгу