Astronomy is no exception. A famous case is a prediction of cosmic proportions that first appeared in a 1948 scientific paper almost as an afterthought—and was soon forgotten. Decades passed before the dismissed conjecture turned into cosmology’s greatest tool.
By the late 1940s, scientists had been grappling for several years with a tough question: how did the universe come to manufacture its vast array of elements? Until the end of the nineteenth century, everyone had just assumed that matter always was and would always be, but revelations coming out of atomic physics laboratories in the first half of the twentieth century—ranging from radioactivity to nuclear transformations—overturned that notion. The elements obviously came from somewhere. The most plausible factory was inside a star, but no physicist in that era could get stellar models to build an atom heavier than helium. Anything more weighty quickly disintegrated within their theoretical computations.
What to do? In 1942 the Russian-American physicist George Gamow simply looked around for another locale for cooking up the elements, and he found one in Georges Lemaître’s “primeval atom.” The idea, a relatively new one, was that the universe had emerged and expanded from an initial hot plasma. (The term “Big Bang” didn’t arrive until 1949.)
As Gamow’s graduate student at George Washington University in the mid-1940s, Ralph Alpher took on the challenge for his doctoral thesis and demonstrated theoretically how it could be done. Like some skilled astrophysical chef, he started with a highly compressed stew of neutrons that Gamow had nicknamed “ylem,” after Aristotle’s name for the basic substance out of which all matter was supposedly derived. As the temperature of the cosmos began to plunge, some of those particles decayed into protons, which promptly began to stick to remaining neutrons. Step by step, each element was built up from the one before it—from helium to lithium, lithium to beryllium, beryllium to boron, and so on through the periodic table. In less than half an hour, when the last of the free neutrons decayed away, the cosmic meal was complete, with Alpher and Gamow concocting the full complement of universal “flavors,” all the way up to uranium.
Their first report on this mathematical recipe, a one-page synopsis published in Physical Review, is more famous for its byline than its content. Gamow, a merry prankster, listed the paper’s authors as Alpher, Bethe, and Gamow, even though noted physicist Hans Bethe never participated in the work. Gamow couldn’t resist the pun on the first three letters of the Greek alphabet: alpha, beta, gamma. That the 1948 paper chanced to be published on April Fool’s Day only added to the fun.
While earning his master’s and Ph.D., Alpher had also been working at the Applied Physics Laboratory of Johns Hopkins University. There, after getting his doctorate, he continued to collaborate on Gamow’s campaign to study the physics of the Big Bang model. He was joined by fellow lab employee Robert Herman. The two young scientists went on to develop a detailed account of the evolution of the newborn universe, work described in 1977 by physicist Steven Weinberg in his book The First Three Minutes as “the first thoroughly modern analysis of the early history of the universe.”
Early in their investigations, the pair came to realize that Alpher’s original scheme for elemental cooking had an insurmountable flaw: while the newborn universe could make a few light elements, the cosmic expansion both dispersed and cooled the primordial plasma before the heavier elements had any chance of forming. With better stellar models, others would later prove that stars could do the job after all (see chapter 15). But no matter: in the course of their investigations, Alpher and Herman were still able to make a historic calculation that has stood the test of time.
In 1949 a composite picture was constructed with Robert Herman on the left, Ralph Alpher on the right, and George Gamow in the center as a genie coming out of a bottle of “ylem,” the proposed mixture of elementary particles out of which the elements formed.
(American Institute of Physics, Center for History of Physics)
This result was revealed in an unusual manner. On October 30, 1948, Gamow published an article in the British journal Nature titled “The Evolution of the Universe.” But in checking over Gamow’s reported results, Alpher and Herman found some errors. They soon dashed off a correction, a brief letter to the editor barely four paragraphs long that was published within two weeks. With their more accurate figures, Alpher and Herman showed how the density of matter and the density of radiation changed as the universe evolved. In doing so, they curtly noted at the end of their letter that “the temperature in the universe at the present time is found to be about 5° Kelvin.” That’s only 5 Kelvin above absolute zero, the point at which all motion ceases. (On the Fahrenheit scale, that’s 9 degrees above absolute zero, which is –459.67 F.)
With little fanfare, Alpher and Herman were telling the world that the present-day universe is bathed in a uniform wash of radiation left over from the flood of highly energetic photons released in the fury of the Big Bang. Cooled down over the eons with the expansion of the cosmos, the waning fire now surrounds us as centimeters-long radio waves. Today it is known as the cosmic microwave background radiation (CMBR).
When their note was published, the primeval atom theory was still highly controversial. Many astronomers preferred the steady-state model of the universe, a theory that postulated that space-time had neither a beginning nor an end. But Alpher and Herman’s calculation was a clear-cut means of deciding between the two opposing theories of the universe’s behavior.
Yet no one followed up. Looking back, it’s hard to fathom why astronomers in the 1950s didn’t jump at the chance to point their instruments at the sky and capture this primordial whisper of creation. But some thought radio telescopes weren’t yet sensitive enough for the task; and when a few astronomers did peg an overall temperature of interstellar space at around 3 K, they didn’t link it to cosmology at all. Some of them thought it was an error in their instruments.
Radio astronomers may have been unresponsive because their field was just establishing itself after World War II, and cosmological tests were not yet taken seriously. As Weinberg noted, they “did not know that they ought to try” to detect the background radiation. The radio sky was all so new. There were too many objects—radio stars, radio nebulae, radio galaxies—grabbing their attention. Amid such distractions, Alpher and Herman’s prediction was either dismissed or utterly overlooked. And since both men later went into industrial research, the two didn’t have the opportunity to keep pushing astronomers to take a look, although they did try—at one point even holding a press conference to generate attention, but to no avail.
The idea didn’t resurface until the mid-1960s, when a team of astrophysicists at Princeton University (and some Soviet cosmologists independently) again reasoned that the Big Bang’s residual heat must be permeating the universe. At the same time, two Bell Lab researchers in New Jersey, Arno Penzias and Robert Wilson, accidentally detected what proved to be the primeval microwaves. They were trying to eliminate excess noise in a horn antenna they were calibrating for astronomical work, but a stubborn residue always remained. Once Penzias and Wilson learned of the Princeton team’s work, they at last understood that their radio interference was cosmic. In 1965 the two groups published papers simultaneously in the Astrophysical Journal. Neither paper mentioned Alpher and Herman’s earlier contribution. For detecting the cosmic microwave background radiation, Penzias and Wilson received the 1978 Nobel Prize in Physics.
Herman died in 1997, Alpher ten years later. Both were deeply pained that the career rewards for making their momentous prediction never came to pass for them—such as election to prestigious academies, sizable research grants, prized promotions. The honors that were bestowed arrived late (Alpher received the National Medal of Science in 2007, when he was hospitalized with his final illness). “But we should not indulge in sermonizing about the nature of science,” the two noted in a scientific memoir of their work published in 2001. “On to more about the CMBR,” they proclaimed. And so it sho
uld be.
Over the past two decades, detectors in space have measured the cosmic microwave background, now pegged at 2.7 K, in exquisite detail. By mapping the barely perceptible ups and downs of this signal across the breadth of the celestial sky, astronomers have revealed a wealth of cosmological information. They’ve viewed the quantum jiggles that led to galaxy formation, tallied the exact amount of ordinary matter contained in the universe, verified that there is five times more cosmic stuff of an unknown nature (called dark matter), and confirmed that space-time is permeated with a dark energy that is causing the universe not just to steadily expand, but to accelerate outward like a runaway drag racer. And to think that all this knowledge was gleaned from a radio murmur, a faint heat first mentioned unceremoniously in a brief note tucked away in a scientific journal around seven decades ago.
CHAPTER TWENTY-EIGHT
It’s Now Einstein’s Universe
His theories explain the universe we observe today
ON January 29, 1931, the world’s premier physicist, Albert Einstein, and its foremost astronomer, Edwin Hubble, settled into the plush leather seats of a sleek Pierce-Arrow touring car for a visit to Mount Wilson in southern California. They were chauffeured up the long, zigzagging dirt road to the observatory complex on the summit, nearly a mile above Pasadena. Home to the largest telescope of its day, Mount Wilson was the site of Hubble’s astronomical triumphs. In 1923–24 he had used the telescope’s then colossal 100-inch mirror to confirm that our galaxy is just one of countless “island universes” inhabiting the vastness of space. Five years later, after tracking the movements of these spiraling disks, Hubble and his assistant, Milton Humason, had confirmed something even more astounding: The universe is swiftly expanding, carrying the galaxies outward.
On the peak that bright day in January, the fifty-one-year-old Einstein delighted in the telescope’s instruments. Like a child at play, he scrambled about the framework, to the consternation of his hosts. Nearby was Einstein’s wife, Elsa. Told that the giant reflector was used to determine the universe’s shape, she reportedly replied, “Well, my husband does that on the back of an old envelope.”
That wasn’t just wifely pride. Years before Hubble verified cosmic expansion, Einstein had fashioned a theory, general relativity, that could explain it. In studies of the cosmos, it all goes back to Einstein.
Just about anywhere astronomers’ observations take them—from the nearby Sun to the black holes in distant galaxies—they enter Einstein’s realm, where time is relative, mass and energy are interchangeable, and space can stretch and warp. His footprints are deepest in cosmology, the study of the universe’s history and fate. General relativity “describes how our universe was born, how it expands, and what its future will be,” says Alan Dressler of the Carnegie Observatories. Beginning, middle, and end—“all are connected to this grand idea.”
At the turn of the twentieth century, thirty years before Einstein and Hubble’s rendezvous at Mount Wilson, physics was in turmoil. X-rays, electrons, and radioactivity were just being discovered, and physicists were realizing that their trusted laws of motion, dating back more than two hundred years to Isaac Newton, could not explain how these strange new particles flit through space. It took a rebel, a cocky kid who spurned rote learning and had an unshakable faith in his own abilities, to blaze a trail through this baffling new territory. This was not the iconic Einstein—the sockless, rumpled character with baggy sweater and fright-wig coiffure—but a younger, more romantic figure with alluring brown eyes and wavy hair. He was at the height of his prowess.
Albert Einstein with Edwin Hubble (behind Einstein, second from left) and others from Caltech and the observatory outside the dome of the 100-inch telescope during Einstein’s visit to Mount Wilson on January 29, 1931.
(Courtesy of the Archives, California Institute of Technology)
Among his gifts was a powerful physical instinct, almost a sixth sense for knowing how nature should work. Einstein thought in images, such as one that began haunting him as a teenager: If a man could keep pace with a beam of light, what would he see? Would he see the electromagnetic wave frozen in place like some glacial swell? “It does not seem that something like that can exist!” Einstein later recalled thinking.
He came to realize that since all the laws of physics remain the same whether you’re at rest or in steady motion, the speed of light has to be constant as well. No one can catch up with a light beam. But if the speed of light is identical for all observers, something else has to give: absolute time and space. Einstein concluded that the cosmos has no universal clock or common reference frame. Space and time are “relative,” flowing differently for each of us depending on our motion.
Einstein’s special theory of relativity, published in 1905, also revealed that energy and mass are two sides of the same coin, forever linked in his famed equation E = mc2. (E stands for energy, m for mass, and c for the speed of light.) “The idea is amusing and enticing,” wrote Einstein, “but whether the Almighty is . . . leading me up the garden path—that I cannot know.” He was too modest. The idea that mass could be transformed into pure energy later helped astronomers understand the enduring power of the Sun. It also gave birth to nuclear weapons.
But Einstein was not satisfied. Special relativity was just that—special. It could not fully describe all types of motion, such as objects in the grip of gravity, the large-scale force that shapes the universe. Ten years later, in 1915, Einstein made up for the omission with his general theory of relativity, which amended Newton’s laws by redefining gravity.
General relativity revealed that space and time are linked in a flexible four-dimensional fabric that is bent and indented by matter. In this picture, Earth orbits the Sun because it is caught in the space-time hollow carved by the Sun’s mass, much as a rolling marble would circle around a bowling ball sitting in a trampoline. The pull of gravity is just matter sliding along the curvatures of space-time.
Einstein shot to the pinnacle of celebrity in 1919, when British astronomers actually measured this warping. Monitoring a solar eclipse, they saw streams of starlight bending around the darkened Sun. With this new insight into gravity, physicists at last were able to make actual predictions about the universe’s behavior, turning cosmology into a science.
Einstein was the first to try, an episode that showed that even he was a fallible genius. A misconception about the nature of the universe led him to propose a mysterious new gravitational effect (a notion he soon rejected.) But we now know he may have been right all along, and his “mistake” may yet turn out to be one of his deepest insights.
For Newton, space was eternally at rest, merely an inert stage on which objects moved. But with general relativity, the stage itself became an active player. The amount of matter within the universe sculpts its overall curvature. And his equations show that space-time itself can be either expanding or contracting.
When Einstein announced general relativity in 1915, he could have taken the next step and declared that the universe was in motion, more than a decade before Hubble directly measured cosmic expansion. But at the time, astronomers conceived of the universe as a large collection of stars fixed forever in the void. Einstein accepted this picture of an immutable cosmos. Truth be told, he liked it. Einstein was often leery of the most radical consequences of his ideas.
But because even a static universe would eventually collapse under its own gravity, he had to slip a fudge factor into the equations of general relativity—a cosmological constant. While gravity pulled celestial objects inward, this extra gravitational effect—a kind of antigravity—pushed them apart. It was just what was needed to keep the universe immobile, “as required by the fact of the small velocities of the stars,” Einstein wrote in 1917.
Twelve years later, Hubble’s verification that other galaxies were racing away from ours, their light waves stretched and reddened by the expansion of space-time, vanquished the static universe. It also eliminated any need for a c
osmological constant to hold the galaxies steady. During his 1931 California visit, Einstein acknowledged as much. “The red shift of distant nebulae has smashed my old construction like a hammer blow,” he declared. He reputedly told a colleague that the cosmological constant was his biggest blunder.
With or without that extra ingredient, the basic recipe for the expanding universe was Einstein’s. But it was left to others to identify one revolutionary implication: a moment of cosmic creation. In 1931 the Belgian priest and astrophysicist Georges Lemaître put the fleeing galaxies into reverse and imagined them eons ago merged in a fireball of dazzling brilliance. “The evolution of the world can be compared to a display of fireworks that has just ended: some few red wisps, ashes and smoke,” wrote Lemaître. From this poetic scenario arose today’s Big Bang.
Many were appalled by this concept. “The notion of a beginning . . . is repugnant to me,” said British astrophysicist Arthur Eddington in 1931. But evidence in its favor slowly gathered, climaxing in 1964, when scientists at Bell Telephone Laboratories discovered that the cosmos is awash in a sea of microwave radiation, the remnant glow of the universe’s thunderous launch.
The high priests of astronomy have continued the cosmological quest initiated by Einstein and Hubble, first at Mount Wilson, then at the 200-inch telescope on California’s Palomar Mountain, ninety miles (145 kilometers) to the south. How fast is the universe ballooning outward? they asked. How old is it? “Answering those questions,” says Wendy Freedman, former director of the Carnegie Observatories, “turned out to be more difficult than anyone anticipated.”
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