This task was energized by his deep dissatisfaction with the direction of quantum theory. According to the uncertainty principle, articulated by German physicist Werner Heisenberg, there is an inherent fuzziness to the workings of nature. One time a decaying atom might spit out a particle in one direction, next time in another, seemingly at random. Even the particle's location is vague, described in probabilities rather than absolutes. Numerous experiments seemed to show that the uncertainty principle is correct, but Einstein was not impressed. In fact, he was infuriated. He was guided to relativity by his belief in ironclad determinism—and now some of the leading scientists of the day were claiming the most basic behavior of subatomic particles appears governed by statistics. “[Quantum] theory yields much, but it hardly brings us closer to the Old One's secrets. I, in any case, am convinced that He does not play dice,” Einstein wrote in a 1926 letter to Max Born, his frequent confidant. This quote later morphed into the more concise “God does not play dice with the universe.”
Einstein's search for a unified field theory also drew sustenance from his conviction that general relativity must apply everywhere in the universe. When he looked outward, this led him to his “Cosmological Considerations” and the first all-encompassing mathematical description of the universe. Whatever details he got wrong, he could rest assured that the basic approach was sound: relativity really does apply even at the largest scales. When he looked inward, however, there seemed no room for gravity. Three forces—electro-magnetism and the two nuclear forces, known only as “strong” and “weak”—dominate the atomic world. But gravity should operate there, too. If electrons behaved like planets circling the atomic nucleus, general relativity predicted that they should constantly shed tiny bits of gravitational energy. Gradually the whole system should run down. The only way to avoid this would be if gravity follows quantum rules, which forbid such energy leakages from happening. But Einstein had no quantum theory of gravity. Again, the two systems were at loggerheads.
Judging from the amount of effort Einstein expended and the meager progress he achieved, his quest to reconcile relativity and quantum theory was, if not his true greatest blunder, at least his greatest blind alley. In January of 1929, as Hubble was putting the final touches on his study of galaxy redshifts, Einstein published the first paper intended to show the world the unity in physics that, for the moment, he alone could see. Within a year, Einstein rejected his ideas as unworkable, moved from Vienna to Berlin, and began a collaboration with a young American physicist named Walther Mayer, whom he hoped would aid him in his holy quest. Many more relocations, collaborators, and false starts lay ahead. In the early 1930s Eddington joined in, following his own idiosyncratic path. Decades later, the unified field theory remains a painfully unattained goal in physics.
Sweeping changes in the scientific and political realms shifted Einstein's interest back to cosmology, for a brief while, at least. In economically depressed Germany, Hitler's support was on the rise, and Einstein had become a prominent focal point for anti-Semitic attitudes. The publication of 100 Authors Against Einstein, a torrent of cheap attacks on Einstein's ideas and character, was indicative of the changing political climate. Einstein spent much of 1930 abroad. When he returned to Berlin, he received a visit from Arthur Fleming, chairman of the board of trustees of Caltech, who invited him to take a temporary position as a research associate at the institute. Einstein, intrigued by reports of the momentous discoveries coming from Mount Wilson, which is operated by Caltech, required little persuasion. In December 1930, the Old World's champion theorist set off for a showdown with the upstart observers in the New World.
Einstein had scarcely kept up with theoretical physics over the past dozen years while he buried himself in his unified field theory. He was even less in touch with the state of deep-space astronomy. He was therefore eager to visit the California peak where, he noted, “new observations by Hubble and Humason concerning the red shift of light in distant nebulas make it appear likely that the general structure of the universe is not static.” At Mount Wilson, the always status-conscious Hubble latched on to Einstein like a bulldog. He proudly walked his famous visitor through the mechanical workings of the huge observatory, showing off the spectrographs that had detected those wondrous redshifts. Einstein insisted on the full tour, including close-up examination of the telescope mechanism, spectrographs, and photographic plates. Throughout, the camera bulbs flashed and Hubble made sure to appear within the same frame as Einstein whenever possible. In a particularly proud moment, the Hubbles had the Einsteins over for dinner. Not taking any chances, Hubble had invited Doris Kenyon, a leading actress of the day, gambling that Einstein would be charmed by the presence of a genuine Hollywood star.
He was, but Humason's photographic plates carried out the greater seduction, convincing Einstein that the redshifts were real. Cosmology had changed drastically since Einstein dismissed Lemaitre's ideas at the Solvay Conference back in 1927. Now he scrambled to catch up. On February 4, 1931, Einstein told the assembled media at the observatory that he officially rescinded his original cosmology and endorsed the expanding universe. Chastened by Humason's rapidly growing stack of galactic redshifts, Einstein renounced his static conception of the universe and pointed out that cosmic expansion fits in perfectly well with general relativity—something that had been true all along, of course. Then he glanced at his watch—he was running late, as usual—flashed another of his trademark indeterminate smiles, and darted out of the room, brushing aside the questions erupting from the dazzled swarm of reporters.
To the sci/religious faithful, this was not exactly fresh news. Hubble's measurements of galactic motions were well-known. Most of the scientists who were seriously following these developments had already recognized that the recent findings discredited the kind of universe Einstein envisioned in 1917. And by the time he visited Mount Wilson, Einstein had largely dropped out of the cosmology game anyway. He had made his one towering contribution and had remained largely silent since. To the outside world, however, his endorsement was a momentous event, like a blessing from the pope. (In fact, his word carried much greater weight than the cosmological pronouncements that Pope Pius XII attempted twenty years later.) If Einstein said the universe expands, then it must be so, and the papers reported it accordingly. Hubble was only too happy to face the media and provide any necessary quotes that Einstein, who spoke little English and who by this time had learned how to avoid the press, could not. Einstein's visit to Mount Wilson spread the gospel of the expanding universe and helped secure Hubble's place in the history books.
For Einstein, letting go of the static universe also meant freeing himself from Ernst Mach's theory of inertia, completing his drift away from the empiricist philosophy he once held so dear. Now the question was, what kind of cosmological model could reconcile the new observations with Einstein's old spiritual values? The one thing he was sure about was that it would not contain Lambda, but in every other way he was as willing as ever to fine-tune the universe for maximum beauty. His first pick was an oscillating universe that expands and contracts endlessly, so it could still be immortal. This solution, known as “the Friedmann-Einstein model,” had a couple of kinks. First, it implied the current expansion was uncomfortably young. Second, and worse from Einstein's point of view, each rebound appeared to pass through a moment of zero volume and infinite density, a state that he considered nonsensical.
Before starting work on an alternative answer, Einstein took a trip to Caltech, where he crossed paths with his old friend and sparring partner, de Sitter. For anyone interested in cosmology, the stretch from Caltech to Mount Wilson was the place to see and be seen. De Sitter, like Einstein, was pondering how to craft a description of the universe that would take into account the evident motions of the galaxies. The two teamed up on yet another solution, called—surprise—“the Einstein-de Sitter model.” This time they aimed for maximal simplicity. Not only did they jettison Lambda, they also found a way
to eliminate the overall curvature of space-time, so that the universe would be flat as a Kansas cornfield. Such a universe wouldn't be static, but it would exhibit a different kind of balance. The gravitational pull of all the matter in the universe would exactly counter the expansion. As a result, the universe is always slowing down but takes an infinite amount of time to brake completely to a halt.
The Einstein-de Sitter universe is still considered one of the simpler and more attractive conceptions of the universe. It surfaced repeatedly in other forms, and it has stuck around as an underpinning of the modern big bang theory. It satisfies the needs of general relativity. It expands forever, so there is no messy end to the universe, and there is no need for Lambda. It does, however, imply the existence of a Lemaitre-like beginning of the universe. Einstein and de Sitter simply glossed over this point. As much as Einstein wanted to know the mind of God right now, he had a powerful aversion to any discussion of origins or first causes. Any kind of discontinuity struck him as hideous. The existence of a moment of creation implies a discontinuity in the most literal sense—a break in the flow of time at the beginning. This surely explains why Einstein originally called Lemaitre's solution “abominable.” The vast majority of cosmologists since then have had no qualms about exploring back all the way to the first moments of cosmic time.
Einstein tried to present his abandonment of Lambda in the best possible light. He wrote that Hubble's redshifts “can be interpreted. . . as an expansive motion of the system of stars in the large—as required, according to Friedmann, by the field equations of gravitation.” The expanding universe is thus “to some extent a confirmation of the theory,” he claimed. Note that in the current understanding, galaxies are not zooming through space; it is the space between them that expands. Therefore, the reddening of the galaxies described by Hubble really isn't due to the Doppler shift. The change is properly known as a cosmological redshift. As the space between us and a distant galaxy expands, so does the light moving through that space. The stretched light appears shifted to the red end of the spectrum, just like a Doppler shift. But every galaxy, every possible observer, can feel motionless because the movement takes place in space itself. This utterly counterintuitive phenomenon makes sense (to the extent that it can make sense) in the framework of general relativity. Conversely, general relativity leads naturally to this kind of expansion. If only Einstein could have resisted his distaste for beginnings he could have predicted the expanding universe rather than reluctantly embracing it after the miraculous evidence was set before him.
Lambda is visible evidence of a flaw in Einstein's cosmological thinking. Viewed against the backdrop of his legendary brilliance, Lambda has therefore gained considerable notoriety as Einstein's “biggest blunder.” This description comes not from Einstein but from the physicist George Gamow, the former student of Friedmann's who was instrumental in developing the big bang model of the origin of the universe. “When I was discussing cosmological problems with Einstein, he remarked that the introduction of the cosmological term was the biggest blunder he ever made in his life,” Gamow wrote in his autobiography, My World Line. Pundits rarely quote the next sentence, which casts Lambda in a different light: “But this 'blunder,' rejected by Einstein, is still sometimes used by cosmologists even today, and the cosmological constant denoted by the Greek letter Lambda rears its ugly head again and again and again.”
Lambda has survived because it is a prime tool for reconciling theory and observation, just as scriptural commentary or midrash does for the traditional religions. Lambda is the leap of faith that reconciles the Word and the world. For instance, there was the pesky problem of the age of the universe. Hubble's recorded velocities, combined with his erroneous estimates of galactic distances, seemed to indicate a universe no more than two billion years old. Lemaitre manipulated Lambda so that he could allow as much as hundred billion years of time, which he still worried might be inadequate. These seeming age discrepancies persisted for decades, and Lambda kept popping up as a possible solution. In the 1950s, Lambda took on a new guise in order to create a model of the universe that expands but has no beginning. In the 1980s, another form of Lambda appeared to explain what happened to the universe during the first 10“35 seconds of its existence. Four years ago, Lambda adopted its latest disguise. Now it accounts for the accelerating pace of the big bang. In an irony that Einstein would surely appreciate, it is also invoked these days to make the geometry of space flat—just as space was supposed to be in the Lambda-free Einstein-de Sitter universe.
THE MORE THAT cosmology became a real theory of the world, the more it mattered to get all the numbers right and make sure they all fit together. As the models grew more detailed and precise, the high priests of cosmology focused on smaller and smaller details of the big creation story. They began to ask not just whether the universe had a beginning, but when, why it started to expand, how quickly it happened, what the exact temperature and density were at a given moment. Each step forward was impelled by a wildly uncertain hypothesis that lingered until shot down and replaced by another one.
So Einstein was wrong—not for invoking Lambda, but for unequivocally denouncing it. Lambda is often called a “fudge factor,” but it is much more than that. It carries the charge of Einstein's cosmic spirit. It stands for the unknown, spiritual element that the scientist desperately hopes will make each cosmological model more beautiful, more complete, more true. It stands for the insane optimism that the world is knowable. It stands for Einstein's inspiring belief that science and reason can edge ever close to true, divine reality, the mystical secrets of the Old One. By the time Einstein abandoned Lambda, many of his disciples were lining up to devote themselves to that belief.
6. THE ERA WHEN THE UNIVERSE CAME FORTH FROM THE HANDS OF THE CREATOR
ON SEPTEMBER 29, 1931, the British Association organized a session devoted solely to the topic of “the evolution of the universe.” This boisterous sci/religion revival meeting drew a Who's Who in the newly intersecting fields of relativity and astronomy, including Arthur Eddington, Willem de Sitter, and Georges Lemaitre. George Gale and John Urani, philosophers of science at the University of Missouri, call this meeting “the birthday of modern cosmology.” So many people showed up to hear about the astonishing new theories that the meeting organizers had to open a second hall and amplify the presentations through a set of buzzy loudspeakers. One man was notably absent amid the commotion: the prophet himself, Albert Einstein, who was preoccupied with his search for a unified field theory that would fix quantum theory and banish his nightmare of a God that makes decisions by rolling a pair of dice.
With Einstein out of the game, cosmology erupted into a free-for-all. The great man had shown the way for science to venture into times and dimensions previously considered out of bounds. Now came the question of how to continue down this path, continuing to extend the reach of cosmology while distinguishing it from the old-time religions and philosophies that had resided here before. It was a time like Christianity after Jesus or Islam after Mohammed, as the disciples fought to see who would carry forward the Einsteinian legacy. Which model would advance toward that scientific sublime, the one true, global description of our universe? Lemaitre, Eddington, and de Sitter now represented the orthodoxy. They accepted that Hubble's redshifts indicate an expansion of the universe, and they accepted that Einstein's general relativity describes the overall cosmic framework. But there were also heretics in the midst.
The most extreme attack on the expanding universe came from the Swiss-born physicist Fritz Zwicky, Caltech's resident gadfly. He was the perfect person to take on the role of the unbeliever. Fueled equally by inventiveness and indignation, Zwicky relished denouncing his enemies as “spherical bastards”—in other words, no matter how you approach them, they still look like bastards. He was a constant source of brilliant, off-the-wall ideas about midget galaxies and dark matter, many of which fell into obscurity mainly because he so thoroughly alienated his colleagues
with knee-jerk reactions against their opinions. Now that everyone had agreed that Hubble's redshifts indicated that galaxies are moving away from us at high velocities, Zwicky naturally decided the whole interpretation had to be wrong. What's more, he believed the whole program of cosmology was off track. A strange observation such as Hubble's redshift law should prompt researchers to consider new scientific principles that they might have missed before, he insisted. Interpreting the redshifts in terms of the well-established descriptions of expanding space guided by general relativity was just a recipe for stagnation. Zwicky was the kind of man who would invent his own faith just to avoid having to go to church.
Working in his accustomed contrarian mode, Zwicky argued that Hubble's redshifts indicated a previously unknown physical process that stretches and reddens light, and he thought he knew what that process was. The cumulative gravitational field of all the mass floating about in space would exert a small drag on light waves, he believed, slowly draining them of energy. In this way, light would grow steadily redder with distance but, as in de Sitter's universe, would not denote actual movement of the galaxies. It was a clever and in some ways constructive proposal. It forced Hubble to be even more careful in his interpretation of the galactic red-shifts. If they were not real motions, then the universe might be static after all, and the new interpretations of general relativity would have to be revised yet again. Physicists could not at the time rule out the possibility of gravitational drag, but neither could they find any evidence for it. Zwicky, who had been unable to get observing time on the one-hundred-inch Hooker telescope and see for himself, railed against his enemies. “Hubble. . . and the sycophants among their young assistants were thus in a position to doctor their observational data, to hide their shortcomings,” he fumed.
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