The Day We Found the Universe (40 page)

Your Calculations Are Correct,
but Your Physical Insight Is Abominable

F
ifty-four years after its founding in 1820, the Royal Astronomical Society began to hold its monthly meetings at new headquarters in the west wing of Burlington House, a former private Palladian mansion that houses a number of British learned societies off Piccadilly in the heart of London. At the society's gathering on January 10, 1930, after a report on the current performance of two clocks at the Royal Observatory in Greenwich, the chairman called upon Willem de Sitter, then visiting England, to give an account of his latest research. De Sitter rose and spoke that evening about his own attempts to link the velocity of a galaxy to its distance. Just as Hubble had demonstrated the previous year, de Sitter too graphed a straight line through his points, making use of data obtained by Hubble, Lundmark, and Shapley. But could he explain this orderly recession of the galaxies? “I am not sure that I can,” de Sitter told his audience. The Dutch astronomer was coming to appreciate that his cosmological model was inadequate, not a good approximation of the observed universe at all. His solution depended on the cosmos being empty, but the universe was undoubtedly chock-full of matter.

In the ensuing discussion, Arthur Eddington casually wondered aloud why only two cosmological models—Einstein's and de Sitter's—had so far come out of general relativity to describe the universe. Were other solutions possible, ready for plucking within Einstein's equations? A number of respected mathematicians had been sporadically tinkering with the models, offering up modifications, but none generated wide interest. Was that the end of the road?

Einstein and de Sitter had each started with different simplifying assumptions and so arrived at different solutions. But they did have one thing in common: Both took for granted that the overall structure of spacetime was static—fixed and rigid. “I suppose the trouble is that people look [only] for static solutions,” noted Eddington at the meeting. From one perspective, de Sitter's solution could be viewed as nonstatic, if you considered any matter in it as immediately flying off, “but as there isn't any matter in it that does not matter,” argued Eddington.

Much more was at stake in Eddington's question. It was easy to imagine a massive object like a star indenting spacetime in a very local and specific location, but could the entire fabric of the cosmos, across the span of the universe, be changing as the eons passed? Could the universe itself be dynamic? It seemed more realistic and plausible to imagine the galaxies traveling
through
space rather than spacetime itself varying, so everyone insisted on a cosmic space that did not move. “From the point of view of cosmologists in the 1920s,” writes science historian Helge Kragh, a dynamic universe “was a concept outside their mental framework, something not to be considered, or, if it was considered, to be resisted.” But, just in case, Eddington already had a research assistant looking into such a formulation.

What Eddington forgot was that this additional cosmological model had already been conceived and presented to him. This solution had been around for years and meshed nicely with Hubble's observations. It wasn't Einstein's universe, and it wasn't de Sitter's. Like Goldilocks and her chairs, this new cosmic model was something in between—and just right.

The novel solution was the brainchild of Eddington's former pupil, Abbé Georges Lemaître, both a physicist and Jesuit priest. A member of the faculty at the Catholic University of Louvain in Belgium, Lemaître soon read the remarks Eddington made at the London meeting, published in the latest issue of the
Observatory
, and quickly sent off a letter reminding Eddington of a paper he had written three years earlier, which provided the answer Eddington craved. Few had seen the article, titled “A Homogeneous Universe of Constant Mass and Increasing Radius Accounting for the Radial Velocities of ExtraGalactic Nebulae,” because for some unknown reason Lemaître had published it in an obscure Belgian journal,
Annales de la Société Scientifique de Bruxelles (Annals of the Brussels Scientific Society)
rather than a publication on every astronomer's must-read list. Eddington had either put Lemaître's paper aside, never getting around to reading it, or simply didn't comprehend its importance at the time. In any case, all memory of it had vanished from his mind. After receiving Lemaître's message, he was a bit shamefaced at the lapse. Looking back over the 1927 paper, he at last recognized its significance and with great enthusiasm made up for his blunder. He speedily sent de Sitter a copy of Lemaître's article, writing at the top, “This seems a complete answer to the problem we were discussing.” De Sitter as well grasped the brilliance of Lemaître's approach, calling it “ingenious” and immediately abandoning his own solution. Eddington soon arranged for Lemaître's paper to be translated and reprinted in the March 1931 issue of the
Monthly Notices of the Royal Astronomical Society
, where it could at last be given a proper showcase.

Originally trained in engineering, Lemaître had switched to mathematics for graduate work and upon receiving his doctorate enrolled in a seminary and was ordained a priest in 1923. Becoming fascinated with the mathematical beauty of general relativity, he went to Cambridge University for postdoctoral studies to broaden his understanding of Einstein's equations under the guidance of the eminent Eddington, who soon noticed Lemaître's talents. With his dark hair combed straight back and a cherubic face framed by round glasses, Lemaître could easily be spotted on campus because of his attire, either a black suit or an ankle-length cassock, set off by a stiff white clerical collar. Others could find him just by pursuing the sound of his full, loud laugh, which was readily aroused. Eddington told Shapley that the young Belgian, then turning thirty, was “exceptionally brilliant… quite remarkable both for his insight into physical significance of problems, and for his manipulation of intractable formulae.”

After a year in England, Lemaître traveled to the United States for further study and soon became aware of—and very interested in—the application of general relativity to cosmological questions. He made sure to attend the 1925 Washington meeting of the American Astronomical Society and was in the audience when Russell read Hubble's paper on the existence of other galaxies. While others in the room were focused on Hubble having ended the “Great Debate,” Lemaître was two jumps ahead. Though new to astronomy, he quickly realized that Hubble's discovery could also be applied to fashioning models of the universe. The newfound galaxies could be used as markers to test the condition of the universe as predicted by general relativity. Later that year, while at MIT to complete an additional PhD, he began modifying de Sitter's cosmological model. Before returning to Belgium, he visited Slipher at the Lowell Observatory, in Arizona, and also journeyed to sunny California, in order to meet Hubble and learn of the latest distance measurements of the spiral nebulae.

What Lemaître did not know during this interlude was that another researcher had already completed a similar modification. The Russian mathematician Aleksandr Friedmann had done this while Lemaître was still preparing for the priesthood. Trained in pure and applied mathematics, Friedmann specialized in the physics of the atmosphere, working at an aerological observatory and applying his expertise at the Russian front during World War I. After the war he returned to St. Petersburg to work at a geophysics observatory. There, among his diverse interests, he began investigating new solutions to Einstein's general theory of relativity, which had not been known to Russian scientists until after the war and the ensuing Russian civil strife.

The rival theories of Einstein and de Sitter were, in a way, complementary rather than competitive. In de Sitter's universe there was no matter to provide a gravitational attraction, but the cosmological repulsion allowed for movement. Einstein's universe, on the other hand, included matter, which provided enough of a gravitational force to oppose the repulsion. With enough matter, all was in perfect balance. Einstein's universe remained motionless. Friedmann blended the best aspects of these universes. He brought the two extremes under one mathematical roof, providing a model that better described the universe as we observe it: containing matter and yet also moving.

What Friedmann did most of all was introduce
time
into the deliberations. In papers written in 1922 and 1924 Friedmann began to play, in a sense, with Einstein's cosmological model. He wanted to see how curvatures in spacetime might change over time—to “demonstrate the possibility,” as he put it. To Friedmann, this was purely a mathematical enterprise, not astronomy at all. His sole goal was to try out possible solutions to Einstein's equations when applied to the entire cosmos. Like Einstein, he too filled his model universe with matter, but this time had it rapidly moving as the eons passed. Moreover, depending on the amount of matter, this movement of spacetime could be an expansion, a contraction, or even an oscillation between the two states. “We shall call this universe the
periodic world,”
he wrote in his report to the
Zeitschrift für Physik
. Friedmann even computed an age for the universe, a first in the annals of astronomy. He arrived at a figure of ten billion years, not far from today's consensus of nearly fourteen billion years, although Friedmann considered his estimate more a curiosity. He made sure to note the age could also be infinite. But, all in all, his paper was predominantly an exercise in relativistic mathematics rather than cosmology, which is why it received so little attention at the time. Friedmann made no mention of nebulae, radiation, or redshifts, nor did he promote a cosmic expansion over a contraction. The journal in fact had indexed his article under relativity theory, making no reference that it dealt with cosmology, which is why it was easily overlooked.

Einstein was certainly aware of the Russian's paper, though. He promptly dismissed the solution, thinking it had no physical significance whatsoever. In a letter to the
Zeitschrift
, sent off right before he went on tour in Japan, he wrote that Friedmann's results “appear to me suspicious.” Friedmann, unfortunately, had little chance to either defend or champion his intriguing idea. In 1925, he became ill with typhoid, just a month after conducting a record-breaking balloon ascent (an altitude of 4.6 miles) to make meteorological and medical observations. He soon died at the age of thirty-seven. In a way, Friedmann had offered his solution too early. At this stage, most general relativists weren't terribly interested in astronomy, and astronomers who had more at stake in this quest didn't yet make the connection, believing that such models of the universe were more like mathematical toys, fun to fiddle with but hardly attached to the real world. They didn't take them seriously.

Lemaître was the exception. From the very start of his independent calculations in the mid-1920s, he kept astronomy foremost in his mind, unlike Friedmann. De Sitter's universe could explain the redshifted nebulae but required the universe be nearly empty (which it was not). Einstein's universe could be filled with matter but couldn't account for the fleeing nebulae. Lemaître declared that his aim was to “combine the advantages of both.” Returning to Belgium and a professorship at Louvain, Lemaître continued working on the problem, at last publishing his final result in 1927. Two full years before Hubble provided the definitive observational proof, Lemaître unveiled a cosmological model in which the radius of the universe increases and galaxies surf outward on the wave. The receding galaxies, as Lemaître described it in his paper, “are a cosmical effect of the expansion of the universe.”

From our perspective, it appears that all the galaxies in the universe are rushing away from
us
—that we are somehow situated at the very center of the cosmic action—but in reality you would observe the same dash outward from any other galaxy in the universe. Lemaître was the first to say directly that the galaxies are fleeing from us because spacetime at each and every point throughout the cosmos is continually stretching. The galaxies are not rushing
through
space but instead are being carried along as spacetime inflates without end. The embedded galaxies are simply going along for the ride. That's why the recession occurs in a specific way: A galaxy twice as far from us recedes twice as fast; a galaxy three times farther travels three times faster, and so on. Lemaître even estimated a rate of cosmic expansion (625 kilometers per second per megaparsec, based on the galactic velocity and distance data then available) that was close to the figure of 500 that Hubble would later calculate.

This was a tremendous accomplishment and offered an astounding vision of how the universe operates. But no one noticed—no one at all. Lemaître's paper, like Friedmann's earlier, was completely ignored. It was as if the article had never been published. Lemaître traveled in Europe and the United States afterward but inexplicably did not widely discuss this latest idea with his colleagues, either in person or in letters. Throughout his deliberations, he had been in contact with astronomers who would have been tremendously interested in his new take on the universe, such as Shapley, Slipher, and Hubble. Yet he apparently kept silent. Either he still had doubts about his new cosmic model or his ardor was dampened by encounters he had with the architects of the leading cosmological models. Though outwardly an extrovert, Lemaître was still quite sensitive to the smallest slight. In October 1927, just six months after his paper came out in the Belgian journal, he met with Einstein during the Fifth Solvay Congress in Brussels, a triennial meeting of the world's top physicists, and the two had a brief chat about Lemaître's breakthrough in the city's Leopold Park. It was at this time that Lemaître first heard from Einstein about Friedmann's similar solution. By then Einstein no longer had any objection to the mathematics in either man's model (his initial rejection of Friedmann's work had been based on an error in his own calculations), but he was still repelled by the image of the cosmos that the models of both Friedmann and Lemaître conveyed. “Your calculations are correct, but your physical insight is abominable,” asserted Einstein, who could not (and would not) imagine a universe in motion. Later, while accompanying Einstein on a university lab tour, the Belgian cleric continued to press his case, talking about the latest evidence on the galaxies' speeding away from Earth. But in the end he came away from the meeting with the impression that Einstein was “not current with the astronomical facts.” Nine months later at the 1928 General Assembly of the International Astronomical Union, de Sitter was equally dismissive of the little-known priest. As one commentator noted, de Sitter seemingly had “no time for an unassuming theorist without proper international credentials.”