First Light: The Search for the Edge of the Universe

by Preston, Richard

  Inside the data room, Jim Gunn typed instructions to the computer. Maarten Schmidt sat at his desk. Schmidt said, “I cannot tell if they are going to get everything fixed. I am not as teh-nically developed as Jim.” He pronounced the word technically with a soft ch—a Dutch accent. The recent unaccountable loss of his 1950-model Eveready flashlight had touched Maarten Schmidt with a small sorrow, a fact that revealed the nature of his feelings toward electronic devices. But he knew what he wanted from the sky—quasars—and who could help him get them—Jim Gunn. Maarten leaned back and put one ankle across the other knee; he was six feet, four inches tall and did not fit well under desks. He said, “This run is radically new. We have been looking for quasars at exceedingly high redshifts. Tonight is the first time we have ever tried to do this with 4-shooter. It is the most difficult thing we have tried so far—”

  “If you do that, Jim”—Barbara Zimmerman’s voice rose above the others—“it clears the register.”

  “Should I go for it?” Gunn asked.

  “I don’t know,” she said. “Hell, yes.”

  A clatter of computer keys, and then, “Oh, Lord, now what?”

  After a slight pause, Maarten Schmidt continued. “The statistical material on these high-redshift quasars is small. We don’t know much about their properties. We barely, if at all, understand quasars. Their fate, while they live, is purely speculative.” He stood up and squared his stack of papers. He crossed and recrossed the small room while he talked. He said that quasars whose light was shifted strongly toward the red end of the color spectrum were the most distant objects that an optical telescope could resolve—some of them lived, so to speak, at the edge of the universe. Quasars were not easy to find. In all of his team’s previous searches for deeply redshifted quasars, they had not found any of this class of object at all. “This is puzzling,” he said. “We know they are out there. So why aren’t we finding any? No, I am not worried, it is probably a matter of statistics. Perhaps there are not so many of these high-redshift quasars as we had originally supposed. But when you don’t find a thing and you know it is there, then there is always the worry that you are doing something wrong.”

  Quasars are the most luminous objects in the universe. Although they shine at great distances from the earth—far, far beyond the Milky Way—they are so intrinsically brilliant that they appear in a telescope as points of light, like stars. They are not stars. Quasars are tiny objects, however. The core of a quasar may be no larger than a solar system. The energy that causes a quasar to shine is mysterious. Quasars do not “burn” in either a chemical or a nuclear sense of the word. Whatever energy powers a quasar, it is not the thermonuclear fusion that makes the sun shine.

  Most astronomers believe that quasars are a long distance away from the Local Supercluster—a long way from our neck of the woods. According to Hubble’s law, which is named after its discoverer, Edwin Hubble, the galaxies are moving away from one another. The universe, as an object, is in a state of expansion. Since the totality of human civilization occupies a stroboscopic instant in the unraveling of cosmic time, objects in the sky appear to be motionless, as if caught in a strobe flash, when, in fact, a dance is happening out there. Some galaxies are spinning on their axes, and some galaxies are circling around each other. Two galaxies can touch for a while in a pas de deux, or one galaxy can burst through another, tearing both apart. At the same time, in general, galaxies are slowly withdrawing from one another, because the universe is expanding. Astronomers can discern such movement only through measurement. Spectroscopy—the division of light into its component wavelengths—reveals not only that spiral galaxies are spinning, but also that our galaxy is receding from virtually all other galaxies; that all galaxies are receding from one another (except those bound into clusters by mutual gravity). The galaxies are scattering, somewhat like a crowd leaving a stadium. This general expansion of the universe is called the Hubble flow. The galaxies are being carried along in the Hubble flow. As a result, the light of most galaxies—as seen from earth—is stretched downward in frequency toward the lower end of the color spectrum, toward red. This is a phenomenon known as a Doppler shift. It is similar to the lengthening whistle of a departing train. According to Hubble’s law, the more distant a galaxy is, the faster it is moving away from us, and therefore the more downwardly stretched—more redshifted—the galaxy’s light appears to be. Quasars are the most redshifted objects in the universe, which to most astronomers signifies that quasars are also the most distant objects that can be seen through a telescope. They inhabit the outer reaches of the optically explored universe: the edge of the universe.

  The word redshifted is misleading in the case of quasars, for a deeply redshifted quasar is not exactly red in color. Quasars disgorge opulent, multitudinous colors all at once—gamma rays, X rays, ultraviolets, blues, greens, yellows, reds, infrareds, microwaves, and, in the case of some quasars, radio waves, all of which are forms of light at different wavelengths. The trick of recognizing a redshift in a quasar by examining its light was at one time not easy to accomplish. Maarten Schmidt invented that trick in 1963. While reading the text of light from a quasar, Schmidt discovered that quasars are not nearby stars, as everyone had supposed, but monsters—objects on the backdrop of the sky, unimaginably far beyond the local galaxies. In effect, he showed that what looked like fireflies in our backyard were beacons near the horizon.

  As a telescope looks out at quasars it looks not only toward the edge of the universe, but also toward the beginning of time. Light consists of photons, which are inseparably both waves and particles. Light moves at a speed of 186,282 miles per second through space—a snail’s pace by the measure of cosmic distance. Nothing can move faster than a photon. A photon would require about fifty thousand years to traverse the length of the Milky Way galaxy. If a star were to explode on the other side of the Milky Way, astronomers would learn about it fifty thousand years later.

  An event cannot be seen, or known, until the photons emitted by that event reach a detector, such as photographic film or the retina of the human eye. A light-year is the distance that a photon can travel through a void in one year, which happens to be about six trillion miles. Photons produced by an event happening billions of light-years away from an observer will require billions of years to stream toward the observer. When a telescope makes a photograph of deep sky, it makes an image of the past; it displays events that took place in different periods of cosmic history, depending on how far away from the earth they are.

  Astronomers refer to the depth of astronomical vision as lookback time. Seeing outward is equivalent to looking backward in time, because the telescope’s mirror is capturing primeval light. The universe—as we see it—could be imagined as a series of concentric shells centered on the earth—shells of lookback time. The shells closest to the earth contain images of galaxies near us in time and space. Farther out are shells containing images of remote galaxies—galaxies as they existed before our time. Still farther out is the shell of the early universe. Some of the photons reaching a telescope’s mirror are nearly as old as the universe itself. The quasars are brilliant pinpoints of light that seem to surround the earth on all sides, shining out of deep time. Beyond the quasars, the observable universe has a horizon, which could be imagined as the inner wall of a shell. This horizon is the limit of lookback time, which is also an image of the beginning. As a mirror looks toward the edge, it looks toward the beginning. At the end of the sky lies the beginning.

  The sky could be imagined as a palimpsest containing stories written on top of one another going back to the origin of time. A telescope looking outward into lookback time strips layers from the palimpsest; it magnifies and reimages small, faint letters in the underlayers of the manuscript. The sky could also be imagined as a book, bound into chapters that tell a story. As a telescope probes out into the sky, it reads backward through the story, from the last chapter to the first. When a mirror collects the light of a distant quasar, it co
llects photons that have streamed freely through space for most of the time the universe has existed and are now reaching the mirror. The light of a deeply redshifted quasar is a light coming out of chapter one—from somewhere in the middle of the book of Genesis.

  The light of the most remote quasars left them at a time when the universe was about ten percent of its age today, evolving rapidly and violently and probably still organizing itself into galaxies. The exact time of this epoch is uncertain, because the age of the universe is uncertain. The universe is probably somewhere between ten and twenty billion years old, which means that the earliest epoch of the quasars happened between nine and eighteen billion years ago. While the quasar’s light was traveling on its way to the earth, the quasar died out. A high-redshift quasar is a fossil image—its light exists as a trace of an extinct object. Quasars once shone (are seen shining, will be seen shining) within cosmic history—long before the sun, the earth, and perhaps even the Milky Way came into being, when the universe was young and quite obviously different from today.

  The problem of mapping the sky’s structure troubles modern astronomers. A photograph taken with a powerful telescope projects the sky onto a two-dimensional surface littered with dots. Some might be asteroids. Many are stars. Even more are galaxies. Some might be comets. A few are quasars. Quasars resemble faint bluish or yellowish stars in a photograph. In appearance, quasars too nearly resemble stars to be winnowed easily from clouds of foreground stars within the Milky Way. For much of his professional career, working step by step outward into space and backward into time, Maarten Schmidt had sought to make a map of quasars in depth—to understand their evolution through time as a class of objects. He had confronted a series of related questions. When were the quasars born? When did they die out, as a species? How did their brightness and their population change while they lived? He wanted to know how the quasars had fared en masse. He wanted to understand the birth, life, and death of the quasars over the range of cosmic time; he wanted to know the natural history of the species.

  Quasars seem to be exclusively distant objects. They are rare enough in our neighborhood so that the Local Supercluster, for example, does not contain any quasars. Nearby superclusters do not contain any quasars, either, but if one looks outward through perhaps twenty or thirty superclusters, one begins to notice quasars. The farther out in space (or back in time) a telescope probes, the more quasars it finds. This implies that the quasars gleamed and then gradually died out—and are now dark or dim objects. If quasars still existed today they would be scattered among nearby galaxies. To focus quasar light with a mirror is to reimage the past, since the only optical trace of the quasars today is a memory transported in antique light. The region of quasars begins about two billion light-years away from us, or rather, before our time, and where it all ends, or rather, begins, is what Maarten Schmidt was trying to find out.

  Schmidt and other astronomers had noticed that as they looked deeper into the universe and back into the past, the number of distant quasars rose steeply for a while and then seemed to drop off, as if the realm of quasars had an outer surface. At extreme distances, quasars were rare. Astronomers looked through a veil of quasars into apparent darkness. They had reached what seemed to be the edge of the optically known universe. They had touched a kind of membrane beyond which they were unable to see anything in any wavelength of light, apart from the radio hiss of the Big Bang. The astronomers had arrived at a dark time. Beyond the realm of the quasars stretched the visible darkness of the early universe, out of which came no detectable light. Astronomers called this the redshift cutoff. It was the horizon of the quasars. The early universe, before the age of quasars, seemed to be a dim shell surrounding the quasars, beyond the redshift cutoff. The cutoff corresponded to the time at which quasars had first appeared. How and when the quasars had popped on remained a mystery. Quasars seemed to have appeared without precursors or any kind of warning signal. “I suspect that the rise of quasars may have signaled the birth of galaxies,” Maarten said. The earliest quasars seemed to be associated with cataclysmic events that had occurred as clouds of hydrogen that had filled the early universe had condensed into galaxies full of stars—a time when the universe had been compact, turbulent, undergoing strong, rapid evolution. Maarten Schmidt felt that if his team could map the rise of quasars over time, they might get a glimpse of the architecture of the creation.

  The theorists babbled on at conferences about the nature of the early universe. Maarten Schmidt found something amusing in all this talk. “The theoreticians”—he smiled—“the theoreticians are so clever. Once we have found something, they can find four ways to explain it.” In the case of quasars, the theoreticians had already found at least four ways to explain the redshift cutoff before it had been mapped. “In all these discussions,” Maarten said, “you find that you need hard numbers. How many quasars of this redshift? How many of that redshift? How many quasars of a particular luminosity? It seemed that the bullet had to be bitten.”

  Exploring the edge of the universe was a dirty job, but somebody had to do it. Somebody had to look. Somebody had to commit quite a few years of a scientific career toward the goal of mapping the realm of the earliest quasars—a gamble that so far had not shown signs of a big payoff. Schmidt and his people had already fed plenty of nickels into the slot machine. Schmidt guessed that years of work lay ahead of him before he might see the structure of the redshift cutoff—if ever. Astronomers learned not to count on results. “This exercise,” he said, “is to gather in the facts. You cannot, of course, solve all the questions in the field. Sometimes you get answers to questions you didn’t ask.”

  Edwin Hubble had showed that the redshift of a galaxy depended on its distance from earth: the more redshifted the galaxy, the farther away it was. Much to their regret, astronomers had not yet been able to link this redshift scale to an absolute measure of distance. Thus they could not tell precisely how far away from earth any galaxy or quasar was, except within a relative range. But even if he could not know exactly how far away the quasars were, Maarten Schmidt felt that if he could collect a sample of quasars of the highest redshifts and plot their redshifts on a graph, then he could learn things about the birth of quasars. He wanted to see the distribution of quasars through time in the vicinity of the redshift cutoff.

  He had urged Gunn to try to jury-rig 4-shooter, so that the camera would scan long ribbons of sky. To gather a tapestry of stars and then to search the tapestry for quasars might be a good way to find a lot of quasars. The strips of sky would be recorded on magnetic tape. When enough tapes had piled up, from a variety of scans, then Don Schneider, the team’s image-processing expert, would analyze the tapes, searching for stabs of quasar light. They could sweep the Hale Telescope across the sky, of course, but it seemed easier to stop the motion of the telescope and let the turning of the earth move the sky past the mouth of the telescope. This was a technique known as a transit. To put a telescope in transit, you shut down the telescope’s drive motors, clamp the bearings, and let stars drift past the mouth of the telescope as the earth turns. Instead of scanning the telescope across the sky, Maarten thought that he would let the earth do the work.

  The telephone rang in the data room.

  Don Schneider picked up the receiver. “Big Eye,” he said, and then, after a pause, “It’s going to be just unbelievable. Amateur night at the Big Eye—”

  “Don’t say that, Donz!” Gunn barked.

  Don stretched the cord to get out of Gunn’s hearing. He lowered his voice and said, “We’ve been working for three days and we still haven’t been able to get the experiment to work. We were just lucky it snowed last night—we couldn’t have started, anyway.”

  Maarten Schmidt, the Principal Investigator, crossed the room and looked over Jim Gunn’s shoulder while Jim clacked at the keyboard of the computer.

  Jim muttered, “I don’t know what will happen tonight, Maarten.”

  “That’s an exciting way to
start,” Maarten said pleasantly.

  “Juan, we need to slew,” Jim said. He wanted to move the telescope rapidly (slew it), to point it at a bright star in order to calibrate the sensors.

  The night assistant hit a switch. Nothing happened.

  Maarten said, “Is there a problem, Juan?”

  “No,” Juan said, running out of the room.

  Maarten laughed. “The telescope has rusted!”

  Juan returned. Somebody had left the stairs under the telescope—the telescope always refused to move until the stairs were rolled away. Hitting toggle switches, Juan slewed the telescope across the sky and centered it on a bright star. Jim Gunn typed a command to 4-shooter on his computer keyboard: EXPOSE.

  4-shooter responded on the computer screen: OK. But nothing happened.

  Gunn peered into the main video screen, which displayed whatever the camera saw. “Black!” he said. “I don’t see any stars!” Everyone talked at once.

  “4-shooter is real unhappy.”

  “Something’s getting in the way.”

  “Maybe we’re pointed at the ceiling.”

  There was a pause, and then, “Naw, that’s not the problem!”

  “Well, where is the dome pointed?”

  “We’re looking east.”

  “Is the mirror open?”

  “The mirror is open.”

  “Yeah, but I don’t see any stars!” Gunn groaned. “Where’s my calculator?” He tore through a pile of papers.

  Maarten paced back and forth. He began to whistle “The March of the Wooden Soldiers,” from The Nutcracker—whistling in the dark, so to speak.

  Juan said, “The mirror is open. The dome is open. The stars are out—”

  “We’re getting no light!” complained Jim Gunn.

  “No evidence of light?” Maarten asked.

  “Absolutely none at all.”

  By now they understood that 4-shooter had gone dead.