First Light: The Search for the Edge of the Universe by Richard Preston Read Free Book Online

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 collects 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 lightexists 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