Buch lesen: «The Invisible Century: Einstein, Freud and the Search for Hidden Universes»

ONE MORE THINGS IN HEAVEN

Look.

And so the boy looked. His father had something to show him. It was small and round like a miniature clock, the boy saw, but instead of two hands pointing outward from the center of the face it had one iron needle. As the boy continued to look, his father rotated the object. He turned it first one way, then the other, and as he did so the most amazing thing happened. No matter how the boy’s father moved the object, the needle continued pointing in the same direction—not the same direction relative to the rest of the device, as the boy might have expected, but the same direction relative to … something else. Something out there, outside the device, that the boy couldn’t see. The needle was shaking now. It trembled with the effort. Some six decades later, when Albert Einstein recalled this scene, he couldn’t remember whether he had been four or five at the time, but the lesson he’d learned that day he could still summon and summarize crisply: “Something deeply hidden had to be behind things.”

Some things deeply hidden, actually. As the boy grew older, he learned what a few of those deeply hidden somethings were: magnetism, the subject of his father’s demonstration on that memorable day; electricity; and the relationship between the two. He learned that the existence of a relationship between magnetism and electricity was still so recent a discovery that nobody yet understood how it worked, and then he learned that within his lifetime physicists had demonstrated that this relationship manifested itself to our eyes as light. And he learned that even though nobody yet understood how light worked, what everybody did know was that it traveled along the biggest deeply hidden something of them all, one that had so far eluded the greatest minds of the age but one that was now, as a prominent physicist of the era proclaimed, “all but in our grasp.”

That something was the ether. Einstein himself sought it, in a paper he wrote in 1895, “Über die Untersuchung des Ätherzustandes im magnetischen Felde” (“On the Investigation of the State of the Ether in a Magnetic Field”). This contribution to the literature, however, wasn’t so much original scholarship as a five-finger exercise that wound up pretty much reiterating current thinking, since Einstein was only sixteen at the time and, as he cautioned prospective readers (such as the doting uncle to whom he sent the paper), “I was completely lacking in materials that would have enabled me to delve into the subject more deeply than by merely meditating on it.”

Still, it was a start. Over the following decade, Einstein would graduate from self-consciously precocious adolescent, speculating beyond his abilities, to willfully arrogant student at the Swiss Polytechnic in Zurich, to humble (if not quite humbled) clerk at the Swiss Office for Intellectual 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 from the conclusion which it seemed to prove may be found in a brilliant suggestion made independently by FitzGerald, and by Lorentz of Leiden.” Kelvin was referring to the physicists George Francis FitzGerald of Dublin, who had submitted a brief conjecture regarding the ether to the American journal Science in 1889, and Hendrik Antoon Lorentz, who in an 1892 paper and then in an 1895 book-length treatise had elaborated an entire argument along nearly identical lines: The ether compresses the molecules of the interferometer—as well as those of the Earth, for that matter—to the exact degree necessary to render a null result. In which case, the two beams of light in Cleveland actually did travel at two separate speeds, as the measurements of their multiple-mirror-deflected journeys would have shown, if only the machinery hadn’t contracted just enough to make up the difference. “Thus,” Lorentz concluded, “one would have to imagine that the motion of a solid body (such as a brass rod or the stone disc employed in the later experiments) through the resting ether exerts upon the dimensions of that body an influence which varies according to the orientation of the body with respect to the direction of motion.”

“An explanation was necessary, and was forthcoming; they always are,” the French mathematician and philosopher Henri Poincaré wrote of Lorentz in 1902 in his Science and Hypothesis; “hypotheses are what we lack the least.” Lorentz himself conceded as much. Two years later he proposed a mathematical basis for his argument while virtually sighing at the futility of the whole enterprise: “Surely this course of inventing special hypotheses for each new experimental result is somewhat artificial.”

Like other physicists at the time, Einstein thought about ways to describe the ether, as in the precocious paper he had sent to his uncle in 1895. Also like other physicists, Einstein thought about ways to detect the ether. During his second year at college, 1897–98, he proposed an experiment: “I predicted that if light from a source is reflected by a mirror,” he later recalled, “it should have different energies depending on whether it is propagated parallel or antiparallel to the direction of motion of the Earth.” In other words: the Michelson-Morley experiment, more or less—though news of that effort, a decade earlier, had reached Einstein only indirectly if at all, and then only as a passing reference in a paper he read. In any case, the particular professor he’d approached with this proposal treated it in “a stepmotherly fashion,” as Einstein reported bitterly in a letter. Then, during a brief but busy job-hunting period in 1901, after he’d left school but hadn’t yet secured a position at the patent office, Einstein proposed to a more receptive professor at the University of Zurich, “a very much simpler method of investigating the relative motion of matter against the luminiferous ether.” On this occasion it was Einstein who didn’t deliver. As he wrote to a friend, “If only relentless fate would give me the necessary time and peace!”

Like a few other physicists at the time, Einstein was even beginning to wonder just what purpose the ether served. What purpose it was supposed to serve was clear enough. Physicists had inferred the ether’s existence in order to make the discovery of light waves conform to the laws of mechanics. If the universe operated only through matter moving immediately adjacent matter in an endless succession of cause-and-effect ricochet shots—like balls on a billiard table, in the popular analogy of the day—then the ether would serve as the necessary matter facilitating the motion of waves of light across the vast and otherwise empty reaches of space. But to say that the ether is the substance along which electromagnetic waves must be moving because electromagnetic waves must be moving along something was as unsatisfactory a definition as it was circular. As Einstein concluded during this period in a letter to the fellow physics student who later became his first wife, Mileva Maric, “The introduction of the term ‘ether’ into the theories of electricity led to the notion of a medium of whose motion one can speak without being able, I believe, to associate a physical meaning with this statement.”

The problem of the ether was starting to seem more than a little familiar. It was, in a way, the same problem that had been haunting physics since the inception of the modern era three centuries earlier: space. To be precise, it was absolute space—a frame of reference against which, in theory, you could measure the motion of any matter in the universe.

For most of human history, such a concept would have been more or less meaningless, or at least superfluous. As long as Earth was standing still at the center of the universe, the center of the Earth was the rightful place toward which terrestrial objects must fall. After all, as Aristotle pointed out in establishing a comprehensive physics, that’s precisely what terrestrial objects did. An Earth in motion, however, presented another set of circumstances altogether, one that—as Galileo appreciated—required a whole other set of explanations.

Nicolaus Copernicus wasn’t the first to suggest that the Earth goes around the sun, not vice versa, but the mathematics in his 1543 treatise De revolutionibus orbium coelestium (On the Revolutions of Celstial Orbs) had the advantage of being comprehensive and even useful—for instance, in instituting the calendar reform of 1582. Still, for many natural philosophers its heliocentric thesis remained difficult, or at least politically unwise, to believe. Galileo, however, not only found it easy to believe but, in time, learned it had to be true because he had seen the evidence for himself, through a new instrument that made distant objects appear near. His evidence was not the mountains on the moon that he first observed in the autumn of 1609, though they did challenge one ancient belief, the physical perfection of heavenly bodies; nor the sight of far more stars than were visible with the naked eye, though they did hint that the two-dimensional celestial vault of old might possess a third dimension; not even his January 1610 discovery around Jupiter of “four wandering stars, known or observed by no one before us,” because all they proved was that Earth wasn’t unique as a host of moons or, therefore, as a center of rotation. Instead, what finally decided the matter for Galileo was the phases of Venus. From October to December 1610, Galileo mounted a nightly vigil to observe Venus as it mutated from “a round shape, and very small,” to “a semicircle” and much larger, to “sickle-shaped” and very large—exactly the set of appearances the planet would manifest if it were circling around, from behind the sun to in front of the sun, while also drawing nearer to Earth.