The 4-Percent Universe

by Richard Panek

  His initial paper on the temperature of the universe—Dicke had forwarded a preprint to Penzias after the phone call about the Bell Labs detection—had repeatedly bounced back from the Physical Review referee because it was duplicating earlier calculations by Alpher, Herman, Gamow, and others. Peebles finally withdrew the paper in June 1965. He managed to rectify some of those oversights in the paper on the cosmic microwave background he wrote with Dicke, Roll, and Wilkinson. Even that paper, however, referred only to Gamow's work on the primordial creation of elements, not to his work predicting the temperature of the cosmic background. Gamow sent an angry note to Penzias, listing citations of his early work and concluding, "Thus, you see, the world did not start with almighty Dicke."

  Still, the obscurity in which these documents languished was a reflection of the indifference many scientists felt toward cosmology and general relativity. No longer. By December 1965, Roll and Wilkinson had mounted their antenna on the roof of Guyot Hall and gotten the same reading as Penzias and Wilson. Within months two more experiments (one by Penzias and Wilson) had found what a sound scientific prediction demands: a duplication of results—in this case, a detection of what was already being called "the 3-K radiation."

  You could feel the shift, if you were an astronomer or physicist. Both the Steady State and Big Bang interpretations had relied not just on math and observation but on speculation. They were modern counterparts to Copernicus's attempt to save the appearances; they were theories in need of evidence. And just as Galileo, with the aid of the telescope, had detected the celestial phenomena that decided between an Earth-centered and a Sun-centered cosmos, forcing us to reconceive the universe, so radio astronomers, with the aid of a new kind of telescope, were now detecting the evidence that decided between the Steady State and Big Bang cosmologies, necessitating a further reconception of the universe.

  Seeing beyond the optical part of the electromagnetic spectrum didn't have to mean seeing more. The sky might not have harbored more information than meets the eye, even one aided by an optical telescope. The introduction of radio astronomy could have left the Newtonian conception of the universe intact. But seeing beyond the optical did mean seeing more phenomena and having to accommodate new kinds of information. This new universe would still run like clockwork; the laws that had arisen through Galileo's observations and Newton's computations would still presumably apply. But now, so would Hubble's and Einstein's, and in their universe the motions of the heavens weren't cyclical so much as linear; their cosmos corresponded not so much to a pocket watch, its hands and gears grinding and turning but always returning to the same positions, as to a calendar, its fanning pages preserving the past, recording the present, and promising the future.

  Maybe, Peebles thought, making theories of the universe wasn't so silly after all. Not that the always-cautious Peebles now embraced the Big Bang theory. But the uniformity of the microwave background that he had predicted and that Penzias and Wilson had detected would certainly correspond to a universe that looked the same on the largest scales no matter where you were in it. Einstein had posited an elephant on an incline, and that's what the universe turned out to be: homogeneous.

  "Which is an amazing thing," Peebles thought. "But there it is: The universe is simple."

  2. What's Out There

  WHAT THE UNIVERSE could be, or should be, didn't much concern her. She wasn't a theorist. She was an astronomer—an observer. The universe was what it was. And what it was, everywhere you looked, was in motion.

  Well, she wasn't an astronomer yet. She'd never actually observed, except as a child, using a telescope that her father had helped her build out of a lens she'd ordered through the mail and a cardboard linoleum tube she'd gotten free from a store in downtown Washington, D.C. And that telescope didn't even work properly; she couldn't take pictures of the stars with it, because it couldn't track their motions—or, more accurately, their apparent motions, since it's the turning of the Earth that gives stars the illusion of arcing across the night sky.

  She should have known that the camera wouldn't work. The motions of the stars were part of what got her interested in astronomy. Her second-floor bedroom window—the one right above her bed—faced north, and around the age of ten she noticed that the stars appeared to be slowly circling a point in the northern sky, and that over the seasons the stars themselves changed. Ever since, she found that she would rather track the motions of the night sky than sleep. She memorized the paths of meteors, then registered them in a notebook in the morning. Later, in high school, whenever she had to write a research paper the topic she chose was invariably something to do with astronomy—reflecting telescopes (the kind with mirrors) or refracting telescopes (the kind with lenses). At a certain point in the evening her mother might call up the stairs, "Vera, don't spend the whole night with your head out the window!" But she did, and her parents didn't seem to mind, not really.

  Hers was, in a way, a Newtonian view of the universe: matter in motion; predictable patterns; celestial objects (and the Earth was one, too, if you thought about it) that, for all their peregrinations, invariably wound up back where they started. But Vera Cooper was born in 1928, three years after Edwin Hubble announced that our Milky Way galaxy was hardly singular, and one year before he presented evidence that the galaxies seemed to be receding from one another—the farther apart, the faster. The only universe she'd known was full of galaxies, and those galaxies were in motion.

  And so, as a graduate student at Cornell, when she had to think about a topic for her master's thesis, she tried to update the old clockwork view of the cosmos for the new expanding universe. She reasoned that since the Earth rotated on its axis, and the solar system rotated, and the galaxy rotated, then maybe the universe had an axis too. Maybe the whole universe rotated.

  The premise seemed reasonable. Her husband, Robert Rubin, a doctoral candidate in physics at Cornell, had shown her a brief, speculative article by George Gamow in the journal Nature, "Rotating Universe?" Then she heard that Kurt Godel, at Princeton, was working on a theory of a rotating universe.

  Her approach also seemed reasonable. She gathered data on the 108 galaxies for which astronomers had managed to measure a redshift. Then she separated out the motions that were due to the expansion of the universe—what astronomers call recessional motions. Did the motions that remained—the peculiar motions—exhibit a pattern? She plotted them on a sphere and thought they did. In December 1950, at the age of twenty-two, still half a year shy of getting her master's degree, Vera Cooper Rubin presented her thesis at an American Astronomical Society meeting in Haverford, Pennsylvania.

  Rubin had never suffered from a lack of confidence. When an admissions officer at Swarthmore College told her that because astronomy was her profession of choice and painting was one of her favorite hobbies, she might want to consider a career as a painter of astronomical scenes, she laughed and applied to Vassar. When she got a scholarship to Vassar and a high school teacher told her, "As long as you stay away from science, you should do okay," she shrugged and pursued a BA in astronomy (with a heavy load of philosophy of science on the side). When a Cornell professor told her that because she had a one-month-old son he would have to take her place at the Haverford AAS meeting and present her paper in his own name, she said, "Oh, I can go," and, nursing newborn and all, she went.

  The response from the AAS crowd when she concluded her presentation was nearly unanimous: The premtse was odd, the data weak, the conclusion unconvincing. The criticism continued until the astronomer Martin Schwarzschild kindly signaled an end to the discussion by rising and saying, in a high-pitched voice, "This is a very interesting thing to have attempted." The moderator called a coffee break, and Rubin left the meeting.

  She herself hadn't thought her paper was extraordinary; it was a master's thesis, after all. Still, she thought that as master's theses went, it was fine. She had taken a pile of numbers and handled them in the most careful fashion she knew, and she thought t
he result was worth reporting. She thought that she'd given a good talk, and that she'd given it as well as she could. She reminded herself that she had never been to an AAS meeting before, and that she hadn't even met many professional astronomers. Maybe this was just how astronomers behaved. She decided she would file these criticisms in the same category as the comments from the admissions officer and her teachers. The next day her hometown paper the Washington Post ran an article under the headline "Young Mother Figures Center of Creation by Star Motions." So she could console herself that real astronomers would at least know who she was (or, because of a typo, who "Vera Hubin" was).

  Still, the experience did teach Rubin an important lesson: She was such a novice that she didn't know how far out of the mainstream her work was. She didn't know that Gamow was nearly alone among astronomers, and Godel among theorists, in finding the question of a rotating universe worthy of serious consideration. Gamow had admitted, in the Nature paper, that the idea of a rotational universe was "at first sight fantastic"—which, at first sight, it was. But what if you didn't trust first sight? First sight—the evidence of the senses, unaided by technology—tells you that the Earth is stationary, that the Sun revolves around the Earth, that Jupiter is moonless and Saturn ringless and the stars motionless, and that the stars are as far as there is. The point Gamow was trying to make was that astronomers needed to go beyond first sight, because now they had a new scale of the universe to consider.

  Saying that all the billions of stars we see are part of our galaxy and that billions of galaxies lie beyond our own doesn't do justice to the scale of the universe. Just as our eyes didn't need to evolve to see radio waves in order for us to survive, maybe our minds didn't need to evolve to understand the numbers that astronomers were now trying to incorporate into their thinking. Like cultures that count "One, two, three, more," we tend to regard the scale of the universe—to the extent that we regard it at all—as "Earth, planets, Sun, far."

  Consider: How long would it take you to count to a million at the "one Mississippi" rate of one second per number? Eleven days—or, to be exact, 11 days, 13 hours, 46 minutes, and 40 seconds. How long would it take you to count to a billion at the same rate? A billion is a thousand million—that is, a million one thousand times over. So you would have to count a million Mississippis—eleven days of counting—a thousand times. That's 31 years, 8% months. To reach a trillion, you'd have to count to a billion a thousand times—31 years a thousand times, or 31,000 years. A light-year—the distance light travels in a year—is about six trillion miles. To count to six trillion, you would need six sets of 31,000 years, or 186,000 years.

  Earlier generations of astronomers had to learn to adjust their thinking to accommodate successive discoveries about new scales of the universe: that the Sun is 93 million miles distant; that the nearest star after the Sun is 4.3 light-years, or 25 trillion miles, away (that's 186,000 years of Mississippis 4.3 times, or about 800,000 years); that our "island universe" consists of billions of stars at similar distances from one another; and that the diameter of this island universe, from one end of its spiral disk to the other, is about 100,000 light-years (186,000 years of Mississippis a hundred thousand times, or more than eighteen billion years of counting, a number you couldn't appreciate without first appreciating the meaning of "billion").

  In this context, however unfathomable and even ludicrous, the term "billions of galaxies" at least begins to suggest the difference in scale between the island universe Hubble inherited and the universe he bequeathed to the next generation. His universe was saturated with galaxies as far as the "eye" could see—whether the "eye" was the one he used, the behemoth 100-inch Hooker telescope atop Mount Wilson, or its successor, the 200-inch Hale telescope atop Mount Palomar, which saw first light in 1949, promising astronomers access to galaxies at greater and greater redshifts. Who knew where this emerging reconception of the universe might lead? Astronomers of the mid-twentieth century who wanted to work in Hubble's universe would have to engage with its hist ory and structure on the grandest scale imaginable. They'd have to do cosmology.

  Not that Rubin thought of herself as a cosmologist. She didn't even think of herself as an astronomer, and not just because she'd never looked through a professional telescope. Six months after that AAS meeting, she had her master's degree and her husband had his doctorate, and they had moved to the D.C. area to be near his job. Their son wasn't yet one, and they were planning to have another child, and even though her husband kept encouraging her to pursue her doctorate, she felt that life was complicated enough at the moment. So it was her choice not to become an astronomer just yet, and to wonder every day whether she would ever become one. Even so, she felt that nothing had prepared her for this life: living in a suburb, staying home with her son while her husband went to work, crying whenever an issue of the Astrophysical Journal —she'd kept the subscription—came into the house.

  Then one day the phone rang. It was George Gamow.

  She was standing at the window in her apartment. The phone rested on a table. The sofa was elsewhere. There was no place to sit. Did the cord stretch? No matter. It was the kind of conversation you wanted to have while standing. So she stood and stared out the window and listened as George Gamow asked Vera Rubin about her research.

  Her husband shared an office with Ralph Alpher at Johns Hopkins University's Applied Physics Laboratory in Silver Spring, Maryland. Robert Herman had an office down the hall. Gamow did some consulting work for the laboratory, and Alpher and Herman often collaborated with him. From them Gamow had heard about her thesis. He told her that he wanted to know about her work on the rotation of the universe for a talk he was giving at the lab. (She wouldn't be able to attend: No wives allowed.)

  Robert Rubin had taken the job at the Applied Physics Laboratory because the proximity to Washington might give his wife educational or professional options in astronomy—options she hadn't yet explored. After the phone call from Gamow, she started taking ApJ to the sandbox, and by February 1952, pregnant with her second child, she was attending classes at Georgetown University, the only school in the D.C. area to offer a doctorate in astronomy. There, by special arrangement with George Washington University, she would be working under the supervision of Professor Gamow.

  That spring she met Gamow for the first time. He had suggested they meet in the library at the Carnegie Institution's Department of Terrestrial Magnetism, a modest campus on a hilly, wooded outskirt of Rock Creek Park in northwest Washington. DTM was an unassuming brick building in an unlikely setting. At the top of a hill at the end of a long, curving driveway in a residential neighborhood, it could have been a hospital or a retirement home. Instead, beginning in the first decade of the century, it had been the headquarters of worldwide expeditions to chart the Earth's magnetic field; once that mission was completed, in 1929, DTM had adopted a looser interpretation of investigating the nature of our planet, and began research on nuclear physics and the geology of other planets.

  Rubin had visited the sylvan setting on one earlier occasion—a talk of some sort, probably. Now she found herself returning just about every month. The entrance to the library was to the right of the stairs on the second floor. To get from the door of the library to the reading room you had to squeeze through a narrow passage between two sets of bookshelves. Every time she visited she had to hesitate on the threshold, assessing one more challenge to becoming an astronomer. The passage was, perhaps, two feet wide. Pregnant with her second child, she was, perhaps, wider.

  George Gamow turned out not to be the sort of person she might have hoped. When they didn't meet at the quiet, wood-paneled DTM library, they met at his home in Chevy Chase, Maryland. There he would invariably be shouting abuse at his wife in some distant part of the house. Where were his papers? What had she done with his papers? Why was she always going through his papers? Whether Gamow's wife was ever actually there, Rubin couldn't be sure. In the summer of 1953, Rubin and her husband paid their own way to
an astronomy workshop in Michigan; Gamow was there too, and his behavior embarrassed her. He dozed during talks, and when he woke up he asked questions that had already been answered. During afternoon discussions, just her and him and the great Mount Wilson astronomer Walter Baade, Gamow would down half a bottle of liquor. During his own lecture, he perspired alcohol.

  Rubin was beginning to realize that there are two kinds of geniuses. There's the kind we would all be if we were extremely smart and knew what we were doing. And then there's the kind you can only watch, knowing that your mind could never work that way. That's the kind of genius Gamow was. He may have dozed during lectures and asked redundant questions, but he also answered questions that nobody else could answer. Whatever Gamow's personal failings, when he spoke, you listened.

  "Is there a scale length in the distribution of galaxies?" he said to her at one of their first meetings. He was suggesting that she think not just about the overall motions of galaxies, as she had in her master's thesis, but instead about the overall result of those motions: the arrangement of galaxies.

  Was the distribution of galaxies throughout the universe random and uniform, as most astronomers assumed? Hubble himself had thought so. "On a large scale the distribution is approximately uniform," he had written in his highly influential 1936 book, The Realm of the Nebulae. "Everywhere and in all directions, the observable region is much the same." In a sense, he was simply reiterating the two assumptions of modern cosmology, homogeneity and isotropy, in layman's terms. But the way he was framing the issue was also reminiscent of the premodern island-universe thinking—emphasis on "island." In Hubble's view, and therefore the view of a generation of astronomers, the galaxy clusters that astronomers had observed would be accidents of nature, or perhaps a sort of cosmic optical illusion arising from multiple galaxies falling along our line of sight. But Gamow was thinking on a different scale. Maybe the peculiar motions of galaxies—the motions that were separate from a straightforward outward expansion—weren't random, as most astronomers assumed. Maybe the gravitational interactions among galaxies, even across previously unthinkable distances, were sometimes strong enough to counteract the expansion on a local level. Maybe no—or at least not every—galaxy is an island.