The Day We Found the Universe (41 page)

Georges Lemaître with Albert Einstein in 1933 at the
California Institute of Technology
(Courtesy of the Archives
,
California Institute of Technology)

The impasse held until Hubble and Humason verified that the galaxies were truly moving outward in a uniform way and Lemaître's model, circulated more prominently in the
Monthly Notices
in 1931, could at last explain it as the fabric of spacetime stretching outward, carrying the galaxies ever farther apart. Now it was no longer Einstein's universe or de Sitter's universe, but the
expanding
universe, and Lemaître became the toast of the cosmological town for being one of its primary creators. Hubble did not really discover the expanding universe in 1929, as written up in textbooks and commonly presumed these days. That realization did not actually occur until Hubble's data could be viewed with Lemaître's model firmly in mind. Lemaître, far more than Friedmann, had linked his model with ongoing astronomical ob servations. His solution was described as a “brilliant discovery.” Top mathematical theorists began to flock to the new field of relativistic cosmology, both to extend the model and to produce variations on Lemaître's original theme of a universe in bloom. In preparing a review paper for a physics journal in the early 1930s, Princeton theorist Howard P. Robertson, himself a leading expert in this new endeavor, noted, “Imagine my surprise on being able to rustle together more than 150 references on relativistic cosmology! It seems to me that some of our highlights…are going off the deep end.”

Astronomers and theorists alike were thunderstruck by this radically new picture of the universe, which was reported as breathtaking in its grandeur and terrifying in its implications. “The theory of the expanding universe is in some respects so preposterous,” said Eddington, “that we naturally hesitate before committing ourselves to it. It contains elements apparently so incredible that I feel almost an indignation that anyone should believe in it—except myself.” That's because by then he knew that it was rooted in the most powerful idea to be introduced in the world of physics since Isaac Newton—Einstein's general theory of relativity—and test after test was proving it true.

James Jeans, a prolific writer as well as theorist, employed the iconic description of the cosmic expansion used to this day. “On the face of it,” he said, “this looks as though the whole universe were uniformly expanding, like the surface of a balloon while it is being inflated, with a speed that doubles its size every 1,400 million years… If Einstein's relativity cosmology is sound, the nebulae have no alternative—the properties of the space in which they exist compel them to scatter.” Eddington first devised this picture when he introduced his colleagues to Lemaître's solution in a 1930 paper to the
Monthly Notices of the Royal Astronomical Society
. Paint dots on that balloon and, as it expands, every dot will move farther from every other dot in a regular fashion. Similarly, wrote Eddington, in the expanding universe the galaxies appear to be “embedded in the surface of a balloon which is steadily inflating.” Every galaxy in the cosmos thus sees its neighbors receding into distant space.

Though Hubble left such interpretations of the velocity-distance relationship to others, he did participate in the discussions, hoping to glean what data needed to be gathered to select between competing theories. Astronomers and theorists previously resided in separate domains, but now he got them talking. Grace Hubble recalled the commotion it created in her household, shortly after Lemaître's model got wide circulation: “About every two weeks some of the men from Mount Wilson and Cal Tech came to the house in the evening…astronomers, physicists, mathematicians. They brought a blackboard from Cal Tech and put it up on the living-room wall. In the dining-room were sandwiches, beer, whiskey and sodawater; they strolled in and helped themselves. Sitting around the fire, smoking pipes, they talked over various approaches to problems, questioned, compared and contrasted their points of view. Someone would write equations on the blackboard and talk for a bit, and a discussion would follow.”

There was much to argue about. Those still skeptical of general relativity were offering other explanations for the outward march of the galaxies. British cosmologist E. Arthur Milne, for example, posited that the expansion of spacetime was merely an illusion. Space was steady as a rock, but the spiral nebulae upon forming started moving in random directions and with different velocities. Over the eons, the nebulae with the fastest speeds naturally moved farther out, setting up the appearance of a cosmic expansion. It was a model that philosophically pleased Milne, who didn't believe space could possibly curve, bend, or move.

Caltech astronomer Fritz Zwicky proposed that light waves, as they traveled through space, could be interacting with matter, setting up a sort of gravitational drag. The more a light wave traveled, the more it lost energy, shifting its wavelength toward the red end of the spectrum. It resembled the de Sitter effect, only this time matter was doing the work. This could explain why the nebulae farthest out displayed the largest redshifts. Space wasn't expanding at all; the photons of light were simply getting weaker and weaker in their journey through a matter-filled cosmos. Hence, this model came to be known as the “tired photon” theory. There was no natural way to explain how this would happen; it required a new law of physics, but that didn't deter Zwicky at all. He was a legend among astronomers for his chutzpah. He felt his explanation might be pointing to a new physical phenomenon.

Hubble worked for a number of years with Caltech theorist Richard Tolman on how to test these competing models of the universe. They wanted to see which one was most compatible with the data arriving at the telescope. Their effort eventually came to naught. Given the state of astronomy at the time and the instruments available, there were simply too many uncertainties—too much guesswork—to reliably choose one cosmological model over another. Their initial data, though, seemed to better support some alternative theories, like Zwicky's “tired photon” scheme. But Hubble made the call that his data were too uncertain, which kept the expanding universe in play. “We cannot assume that our knowledge of physical principles is yet complete,” he wrote, “nevertheless, we should not replace a known, familiar principle, by an ad hoc explanation unless we are forced to that step by actual observations.” To back away from Einstein, the proof for Hubble had to be overwhelming. On the other hand, the uncertainty of it all likely reinforced his qualms at advocating any particular interpretation.

Lick astronomer C. Donald Shane, in talks with Hubble in the 1930s, actually got the impression that Hubble had “a desire to show that the red shift was not an expansion…because he seemed always to be seeking some other explanation for it.” Perusing Hubble's writings on the idea of an expanding universe, you immediately detect that he was uncomfortable with it. He acceded that theorists were “fully justified” in interpreting the galaxy redshifts as a movement outward; it was the most reasonable explanation that required no new laws of physics. But then he would invariably sneak an “on the other hand” into his script. He deemed a static and infinite universe more “plausible” and “familiar,” like a pair of old shoes he found difficult to throw out. In his Rhodes Memorial Lectures, delivered at Oxford in the autumn of 1936, Hubble reaffirmed his vacillation over the interpretation of the redshifts. Their “significance is still uncertain,” he stated. With the recent introduction of both quantum mechanics and relativity, which demonstrated quite explicitly that scientists' understanding of nature can change abruptly and in surprising ways, perhaps Hubble's caution was understandable. In his lecture Hubble went on to describe the expanding universe as a “dubious world,” though still conceding it was the more likely interpretation of the redshifts. But with alternate explanations still in play, he concluded that astronomers were in “a dilemma [whose] resolution must await improved observations or improved theory or both.”

What seemed to disturb Hubble most were the enormous velocities. The farther he and Humason extended their searches into space, the faster and faster the galaxies were retreating. Near the absolute limit of Humason's spectrograph, he recorded velocities of about 25,000 miles per second, “around the earth in a second, out to the moon in 10 seconds, out to the sun in just over an hour…the notion is rather startling,” noted Hubble.

As late as 1950, responding to a Kansas professor's written inquiry about redshifts, Hubble asserted that they “represent either actual recession (expanding universe) or some hitherto unknown principle of nature. I believe that the choice of these alternatives will be determined with the 200-inch [telescope on California's Palomar Mountain] within a few years.” Maintaining his lawyerly ways, Hubble covered all the bases when making a public statement.

Others, such as Eddington, were confounded by such equivocation. “I just don't understand this eagerness to find some other theory than the expanding universe,” he wrote in a letter to a colleague. “It arose out of difficulties … in Einstein's theory. If you do away with it, you throw back relativity theory into the infantile diseases of 25 years ago. And why the fact that the solution then found has received remarkable confirmation by observation should lead people to seek desperately for ways to avoid it, I cannot imagine.”

While Hubble remained overly cautious, Shapley came to embrace the idea of an expansion lock, stock, and cosmic barrel. It's as if the two astronomers were magnets with the same polarity, always repulsing each other to opposite sides of a question. The ultimate imprimatur, though, was provided when Einstein arrived in Pasadena in 1931 in order to consult with the high priests of cosmology at both Caltech and Mount Wilson.

Started Off with a Bang

O
n November 30, 1930, Einstein, his wife, Elsa, his secretary, and a scientific assistant left Berlin for Antwerp, where they embarked on the steamer
Belgenland
. It was Einstein's second visit to the United States but his first journey to America's West Coast. Before leaving, Frau Einstein made a last-minute shopping trip to purchase a raincoat for the father of relativity. “Would it not be more practical to have the herr professor come here so we can give him an exact fit?” said the clothing store salesman. “If you knew how hard it was even to persuade my husband he needed a new coat, you wouldn't expect me to fetch him here. I wish you had my worries,” she replied. It was teasingly said that Einstein was going to Pasadena to hunt for the sole twelve men in the world who could understand him.

The revered physicist arrived in New York on December 11, where he and Elsa were greeted by a barrage of journalists, photographers, and newsreel men, a chaotic scene that greatly discomfited Einstein. “This reminds me of a Punch and Judy show, all of you standing there watching us so intently,” he remarked in German. The press described him that day as small, bright-eyed, his almost white hair trained back in a bushy pompadour, and “his face … as smooth as a girl's except for the tiny wrinkles about his eyes.” Out on the deck, a cold damp wind soon blew through his locks, swiftly turning the carefully groomed pompadour into his well-known disheveled hairstyle. After a four-day stay in New York, he and his party continued their voyage on the
Belgenland
for California, by way of the Panama Canal.

Arthur Fleming, a member of the California Institute of Technology's executive council, first extended the invitation to visit, extolling his town's summery climate and rich scientific atmosphere. Einstein, then looking for a good rest among men who spoke the language of mathematics, eagerly accepted. For one, it was an opportunity for him to meet Albert A. Michelson, the physicist whose inexplicable failure to measure a predicted change in the speed of light due to Earth's motion through an “ether” permeating space was at last explained by Einstein's special theory of relativity, which did away with the ether altogether.

Aware of Einstein's dislike for publicity, his California hosts tried to dispense with an official welcome, as in New York, but to no avail. Upon docking in San Diego on New Year's Eve, the German visitors had to endure four hours of speeches, presentations, tours, and a radio talk. Only after all the hoopla had ceased were Einstein and Elsa finally taken northward by car, eventually settling into a small Pasadena bungalow specially renovated and furnished for their stay. While shunning many public events over their two-month visit, the Einsteins enjoyed a steady round of private engagements. Over the ensuing weeks, they hosted a dinner for the director of the Los Angeles Philharmonic (with Einstein briefly playing the violin for his guest), visited a Hollywood studio, had dinner at the home of film comedian Charlie Chaplin, and motored out to Palm Springs for a four-day holiday. They did put up with the glare of the celebrity spotlight on one special occasion. The couple, he decked out in tuxedo and she in full-length evening gown, attended the premiere of Chaplin's latest movie,
City Lights
, where Einstein laughed like a little boy. There was a simple reason for this exceptional night on the town: Chaplin, instantly recognizable throughout the world, was Elsa's matinee idol. “They cheer me because they all understand me, and they cheer you because no one understands you,” Chaplin told Einstein as they walked into the theater to shouts and clapping that night.