God In The Equation Read online

  The Princeton and Bell Labs teams published joint papers in the Astrophysical Journal Letters the summer of 1965. Penzias and Wilson cautiously reported their discovery of an anomalous microwave source coming from all directions in the sky. It appeared that the heavens were aglow with energy. Dicke and Peebles harbored little doubt that the mystery source was in fact energy left over from the initial expansion of the universe. Lemaitre, seventy-one years old and ailing, was comforted by the news that scientists had spotted the presumed afterglow from the fireworks of his primeval atom. Once again a major piece of cosmological research debuted in the daily papers, not in the scientific literature. The news about microwave background appeared on the front page of the May 21, 1965, New York Times, affirming the big bang theology squarely to the world. Only then did Penzias and Wilson realize the full magnitude of what they had done.

  The amount of energy in Penzias and Wilson's signal was minute. It implied that space has a temperature of about three degrees centigrade above absolute zero, or -453 degrees Fahrenheit. For comparison, Earth's atmosphere would freeze solid at a temperature of about -370 degrees Fahrenheit. But the signal cannot be denied. You see a bit of it in the snow on a TV tuned to an empty UHF channel; you hear it in the static of an FM radio set between stations. The big bang had predicted it. The steady state offered no obvious mechanism for creating such a flood of cold radiation. To this day, nobody has come up with a convincing alternative explanation for the microwave background. “Astronomy leads us to a unique event, a universe which was created out of nothing,” Penzias reflected. “Thus the observations of modern science seem to lead to the same conclusions as centuries-old intuition.” The steady state model suffered a mortal blow, somewhat reminiscent of what happened to Lambda after Hubble's discovery of the galaxy redshifts. Hoyle fundamentally wanted the same thing Einstein had originally wanted, an eternal and all-embracing description of the universe. He had used a mathematical invention much like Lambda to achieve it. And like Einstein, Hoyle fell before the powerful doctrine of falsification.

  The big bang won—for now—and the priests of sci/religion rejoiced that they had advanced another step toward sublime, ultimate truth. With the discovery of the microwave background, cosmologists had at last scored an accurate prediction. This success was to big bang cosmology what the 1919 eclipse expedition was to Einstein's general relativity. Before the event, the theory had beauty and elegance on its side, and that was enough to attract many adherents. Now the theory had observation as well. The adherents became true believers, and the public swayed again before the power of sci/religion. The discovery of the microwave background vindicated Alpher's bold talk about applying numbers and equations to the first five minutes of cosmic history. Time was on the cosmologists' side.

  During the 1960s, they continued to probe those first moments in increasing realistic detail. In 1966 Peebles performed a detailed analysis of the primordial nuclear reactions based on the latest data on the density of the universe and a brand-new estimate of the amount of energy in the universe, based directly on the recent measurement of the cosmic microwave background. His model accurately accounted for the observed cosmic abundance of helium, which makes up roughly one-quarter of the matter in every star and nebula. Studies of deuterium, a heavy version of hydrogen, provided further testimony on behalf of the big bang. There's hardly any deuterium in the universe, just one atom for every thirty thousand ordinary hydrogens. But it is peculiar that there is any deuterium at all. Deuterium is a fragile atom that is only consumed, not created, in the nuclear furnaces of stars. It therefore must have originated with the universe itself. A year after Peebles's work, Hoyle and two colleagues studied 144 different possible nuclear reactions. In the end, they quietly concluded that the heat and density of the big bang would have created just the right conditions for synthesizing deuterium, conditions that never occur in the interiors of stars. For a man engaged in a dogged intellectual fight, Hoyle was remarkably gracious to his enemies. Although it did not lead where he had hoped, he praised the knowledge gained by blending cosmology with particle physics. “I think if cosmology had to depend on astronomers, it would be in a much weaker state,” he quipped.

  By the late 1960s, most astronomers considered the debate closed. The big bang was the official creation mythology of sci/religion, and its details were inscribed in the pages of the Astrophysical Journal. The universe began in a ferociously hot cataclysm. That initial mishmash of particles and energy turned to a brew of protons and neutrons bashing into each other, which in turn transformed into a brew of hydrogen, deuterium, helium, and lithium. Stars and galaxies formed from dense regions in the debris. Aeons later, the galaxies are still flying apart, producing the redshifts recorded by Slipher and Hubble. The mix of elements looked right, the estimated age of the universe roughly matched that of the oldest stars, and the microwaves glowed from above like a heavenly blessing on the theory. Peebles reminisced about the mood of those days: “The universe is simple. It's expanding in a computable way—which is an amazing thing. I never would have anticipated it could have worked out so easily, but there it is.” Cosmology's unknowns were tumbling like dominoes. Never had the secret of the Old One seemed so close.

  Yet the spirit of Lambda persisted. The priests of sci/religion hungered for more complete knowledge and deeper explanations. All of the telescopes and all of the equations still did not indicate why or how the big bang took place. They told nothing of whether the universe would expand forever or someday reverse course and start over again. They did not explain how order emerged from chaos. They did not explain why everything looks so simple: the smooth scattering of galaxies across the sky, the smooth glow of cosmic microwaves, the smooth expansion of space. And they did not speak to the most fundamental puzzles. Why this universe rather than any other? Why is there something rather than nothing?

  The big bang needed something more—not just Lambda, but a whole new family of Lambdas.

  7. HISSES FROM THE MICROWAVES

  THAT THE POPE COULD NOT do with his rhetoric, King Carl XVI Gustaf of Sweden accomplished with a handshake, a gold medal, and a piece of paper. On December 10, 1978, the king stood onstage at the Stockholm Concert Hall and handed Arno Penzias and Robert Wilson their shared the Nobel Prize in physics for detecting the pervasive microwave hiss left over from the time of cosmic birth, publicly endorsing the big bang as the modern world's official story of creation. The blessing went both ways. The notoriously conservative Nobel Committee had now officially converted to the faith of sci/religion.

  The key elements of Einstein's 1917 prophecy were fulfilled. He had envisioned a universe uniformly populated with galaxies, so that the equations of general relativity could describe all of space. And so it was. He had hoped for a static universe but reconciled himself to an expanding universe in which the density of matter provides just enough gravity to counter the outward motion. And so it could be—the data were not yet conclusive, but such a balance at least seemed possible. He had claimed that physical law holds steady across time. And so it did, by all appearances. Nuclear simulations by Alpher, Herman, and others yielded increasingly detailed and convincing descriptions of the light elements that formed during the first few minutes of the cosmic fireball. Penzias and Wilson's detection of the afterglow of the big bang was the final proof of the power of sci/religion across billions of years of time. The latest cosmological models didn't even need Einstein's rejected Lambda. Astronomers had expanded their inferred age of the universe to about fifteen billion years, leaving plenty of time for the formation of the Earth and the evolution of the oldest known stars.

  Yet the high priests of sci/religion were not satisfied. The big philosophical question—Why is the universe the way it is?—continued to nag at them. And as astronomers took better measure of the universe, the question took on increasingly concrete forms. The cosmos appeared to have been built to very exact specifications, and nobody could account for it. Imagine walking into a forest a
nd noticing that the trees are arranged in neat rows and the streams cut geometrically perfect lines. Your map of the region tells you this is virgin forest, where everything should have been shaped only by nature, yet the pattern of the landscape looks very organized. Surely you would be surprised and would want to know the reason for this unexpected arrangement. Cosmologists found themselves in an analogous situation. Once again it was clear that something was missing from the models—some intangible that would make all the pieces fit together.

  One sign of trouble, called “the flatness problem,” came disguised as good news. A flat universe is one in which the density of matter and the curvature of space-time exactly balance out, so that parallel beams of light neither converge nor diverge as they move. This is the form that Einstein had favored: in the simplest formulations, a flat universe is the same thing as a universe in which the gravitational pull of the galaxies exactly offsets the cosmic expansion. By the late 1960s, astronomers had found that the total mass of the universe is in fact close to that critical density. But Peebles and Dicke, the Princeton University cosmologists who had provided the theoretical interpretation of the ubiquitous microwaves as the afterglow of the big bang, were puzzled. Einstein had never given a reason why the universe should be flat. He just thought it would be simpler and more attractive if God had made the universe that way. If the big bang occurred in a random way, however, the universe presumably could have formed with any density, ranging from zero to nearly infinite. Why should it have almost exactly the critical density, the one that just happens to produce a flat universe that follows the rules of classical Euclidian geometry? Why not a density a million times greater or a trillion times less?

  The mystery grew deeper when Peebles and Dicke thought back to the earliest stages of the universe. When the universe was smaller and younger, the effect of any deviation from critical density would have been magnified. For the density to be anywhere near critical today, it had to be astonishingly close at the time of the big bang. To be precise, at the earliest moment that physicists could analyze, the density needed to be within one part in 1060 of the critical value. Surely that could not have happened by chance, but no cosmological model could explain why the geometry of the universe is so flat and why its mass so close to the balance point between gravity and expansion, an equilibrium weirdly reminiscent of what Newton had requested of God to keep His universe from tottering. “How did the universe arrange these initial conditions?” Peebles wondered.

  As with the rows of trees in the forest, the odds of a beautiful balance in the universe happening through random good luck seemed exceedingly small. Alternately, there might be some as yet undiscovered reason why the universe must have the critical density. Cosmologists thought back to Einstein's philosophical query: “What really interests me is whether God could have created the world any differently; in other words, whether the demand for logical simplicity leaves any freedom at all.” As the great telescopes and new satellite observatories revealed more about the kind of universe we live in, the question grew increasingly acute.

  In 1969, Charles Misner, a physicist at the University of Maryland, pointed out another kind of unexplained cosmic regularity. He was eager to take cosmology beyond its sci/religious roots based on broad extrapolations from the initial big bang and start exploring the detailed physical structure and evolution of the universe—in essence, moving out of the sketchy story of Genesis into the complicated unfolding of history that followed. During a summer seminar at Cornell University in 1965, Misner heard Peebles talking about the seeming uniformity of the cosmic microwave background, not what one would expect from the chaotic fireworks of the big bang. From the moment they discovered this radiation, before they even understood its cosmological significance, Arno Penzias and Robert Wilson had noticed that the signal in their primitive antenna was roughly the same strength in all directions. “The Earth had made a complete cycle around the sun and nothing had changed in what we were measuring.” Wilson reported. Follow-up studies showed that the cosmic microwaves are not just somewhat uniform; they are almost perfectly uniform.

  By the late 1960s, better measurements showed the intensity and effective temperature of the microwaves appeared identical in all directions to within 1 percent; on fine scales the irregularities were smaller still. Misner sensed trouble. “Things you don't understand can be constant to 10 or 20 percent, but 1 percent requires an explanation,” he said. The radiation is so smooth that for years no radio telescope on Earth could find any irregularity at all. In 1989, NASA launched the Cosmic Background Explorer (COBE) satellite to perform the kind of exacting study that could be done only from space. The results from COBE explained why studies from the ground kept turning up empty-handed. The microwave variations are there, but they are minuscule, about one part in one hundred thousand. Such rigorous sameness is practically unheard of in nature, where lumpiness and disorder is the rule. It means that the temperature and density of the early universe, which determined the frequency of the background radiation, must have been nearly identical in all locations.

  Again, such consistency might seem like good news. After all, Einstein's cosmological principle assumes that the universe should look generally the same at all places and in all directions. But as Misner reported in 1968, there is something odd about the smoothness of the microwave background. Temperature variations disappear when objects are left in prolonged contact with one another. A hot bowl of soup or a freezing scoop of ice cream will gradually match the temperature of the surrounding room, for instance. Moments after the big bang, however, the universe was expanding at close to the speed of light. Two bits of universe expanding in opposite directions could never have touched each other, nor could they have in any way communicated with each other. Somehow, though, they ended up at almost the exact same temperature. The soup takes hours to reach room temperature. The universe had no time at all—so how did it get so uniform? “I was trying to change the goals of scientific cosmology from describing the universe to explaining it,” Misner said in 1990. But the universe was not cooperating.

  One could simply give up and assume that whatever process triggered the big bang just happened to produce an exceedingly uniform explosion. Confronted with unexpected order, however, scientists prefer to hypothesize novel mechanisms that might account for it. Eudoxus put together his spheres to reproduce the regular but complicated motions of the planets. Einstein invoked Lambda to produce the kind of balance that occurred in his ideal universe. Now it was becoming clear that Gamow's picture of the big bang needed some additional feature to give it a deeper sci/religious description of how the universe began. Misner called the strange smoothness of the microwave background “the horizon problem,” because it seemed as if each part of the universe could look over its horizon, like neighbors peeking over a supposedly private fence, to see what invisible neighboring regions were doing.

  The horizon problem leads to yet another puzzle. The smoothness of the cosmic microwave background demonstrates that there were no large deviations from uniformity in the early universe. On the very largest scales, that is still true. Hubble's deep-sky surveys of the 1930s showed that the global distribution of galaxies is uniform, again just as Einstein had assumed. But on every smaller scale the universe is awash with irregularities: the planets, stars, clusters of stars, galaxies, and clusters of galaxies that punctuate the night sky. The cosmos therefore must have started out with some small lumps artfully mixed into the overall smoothness. Once again, the properties at the time of the big bang seem finely tuned. A little less of that primordial lumpiness and the universe today would be nothing but a formless void of cool gas. A little more and all the matter would have collapsed violently in on itself, birthing a hoard of menacing black holes. Either way, we would not be here to contemplate this conundrum.

  Even if the models simply assumed a smidgen of lumpiness from the start, for reasons unknown, they still had problems. We know from the microwaves that the early universe was
quite uniform even at galaxy-cluster scales. Gravity would amplify any irregularities in the hot gas, but only slowly. Cosmologists had a hard time constructing plausible models that would transform a nearly featureless early universe into the galaxy-riddled one of today. Their models worked a lot better if they added certain kinds of unseen material, or “dark matter,” into the mix. Dark matter could provide the extra gravitational pull needed to build galaxies and flatten out the universe, and if its properties were just right, it might not interfere with the uniformity of the microwave background. This mystery material was yet another fudge factor, sort of a Lambda in reverse, designed to amplify rather than counteract the pull of gravity. Each new mystery factor in big bang cosmology pointed to an unfulfilled spiritual element in the new sci/religion.