In Chapter 10 we wonder whether there is enough matter in the universe eventually to stop the recession of distant galaxies, and whether the universe is infinitely old and therefore uncreated. Some light on both these questions may since have been cast in experiments by Frederick Reines, of the University of California, who believes he has discovered a that neutrinos exist in three different states, only one of which could be detected by neutrino telescopes studying the Sun; and b that neutrinos - unlike light - have mass, so that the gravity of all the neutrinos in space may help to close the Cosmos and prevent it from expanding forever.
Future experiments will show whether these ideas are correct. But they illustrate the continuing and vigorous reassessment of received wisdom which is fundamental to the scientific enterprise. On a project of this magnitude it is impossible to thank everyone who has made a contribution. However, I would like to acknowledge, especially, B. Others who helped in clarifying matters of fact or approach are listed at the back of the book.
The final responsibility for the content of the book is, however, of course mine. I thank the staff at Random House, particularly my editor, Anne Freedgood, and the book designer, Robert Aulicino, for their capable work and their patience when the deadlines for the television series and the book seemed to be in conflict. I owe a special debt of gratitude to Shirley Arden, my Executive Assistant, for typing the early drafts of this book and ushering the later drafts through all stages of production with her usual cheerful competence.
This is only one of many ways in which the Cosmos project is deeply indebted to her. I am more grateful than I can say to the administration of Cornell University for granting me a two-year leave of absence to pursue this project, to my colleagues and students there, and to my colleagues at NASA, JPL and on the Voyager Imaging Team. My greatest debt for the writing of Cosmos is owed to Ann Druyan and Steven Soter, my co-writers in the television series. They made fundamental and frequent contributions to the basic ideas and their connections, to the overall intellectual structure of the episodes, and to the felicity of style.
I am deeply grateful for their vigorous critical readings of early versions of this book, their constructive and creative suggestions for revision through many drafts, and their major contributions to the television script which in many ways influenced the content of this book.
The delight I found in our many discussions is one of my chief rewards from the Cosmos project. They were endowed with intelligence, they succeeded in knowing all that there is in the world. When they looked, instantly they saw all that is around them, and they contemplated in turn the arc of heaven and the round face of the earth.
Let their sight reach only to that which is near; let them see only a little of the face of the earth! Are they not by nature simple creatures of our making? Must they also be gods? Where is the way to the dwelling of light, And where is the place of darkness. I shall have no more if I possess worlds.
By space the universe encompasses and swallows me up like an atom; by thought I comprehend the world. Our business in every generation is to reclaim a little more land. Huxley, The Cosmos is all that is or ever was or ever will be. Our feeblest contemplations of the Cosmos stir us - there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, of falling from a height.
We know we are approaching the greatest of mysteries. The size and age of the Cosmos are beyond ordinary human understanding. Lost somewhere between immensity and eternity is our tiny planetary home. In a cosmic perspective, most human concerns seem insignificant, even petty. And yet our species is young and curious and brave and shows much promise. In the last few millennia we have made the most astonishing and unexpected discoveries about the Cosmos and our place within it, explorations that are exhilarating to consider.
They remind us that humans have evolved to wonder, that understanding is a joy, that knowledge is prerequisite to survival. I believe our future depends on how well we know this Cosmos in which we float like a mote of dust in the morning sky. Those explorations required skepticism and imagination both.
Imagination will often carry us to worlds that never were. But without it, we go nowhere. Skepticism enables us to distinguish fancy from fact, to test our speculations. The Cosmos is rich beyond measure - in elegant facts, in exquisite interrelationships, in the subtle machinery of awe. The surface of the Earth is the shore of the cosmic ocean. From it we have learned most of what we know. Recently, we have waded a little out to sea, enough to dampen our toes or, at most, wet our ankles. The water seems inviting.
The ocean calls. Some part of our being knows this is from where we came. We long to return. These aspirations are not, I think, irreverent, although they may trouble whatever gods may be. The dimensions of the Cosmos are so large that using familiar units of distance, such as meters or miles, chosen for their utility on Earth, would make little sense. Instead, we measure distance with the speed of light. In one second a beam of light travels , miles, nearly , kilometers or seven times around the Earth.
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In eight minutes it will travel from the Sun to the Earth. We can say the Sun is eight light-minutes away. In a year, it crosses nearly ten trillion kilometers, about six trillion miles, of intervening space. That unit of length, the distance light goes in a year, is called a light-year. It measures not time but distances - enormous distances. The Earth is a place.
It is by no means the only place. It is not even a typical place.
The inner meaning of outer space: Human nature and the celestial realm
No planet or star or galaxy can be typical, because the Cosmos is mostly empty. The only typical place is within the vast, cold, universal vacuum, the everlasting night of intergalactic space, a place so strange and desolate that, by comparison, planets and stars and galaxies seem achingly rare and lovely. In everyday life such odds are called compelling.
Worlds are precious.
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The exponent counts the number of zeroes after the one. From an intergalactic vantage point we would see, strewn like sea froth on the waves of space, innumerable faint, wispy tendrils of light. These are the galaxies. Some are solitary wanderers; most inhabit communal clusters, huddling together, drifting endlessly in the great cosmic dark. Before us is the Cosmos on the grandest scale we know.
We are in the realm of the nebulae, eight billion light-years from Earth, halfway to the edge of the known universe. A galaxy is composed of gas and dust and stars billions upon billions of stars. Every star may be a sun to someone. Within a galaxy are stars and worlds and, it may be, a proliferation of living things and intelligent beings and spacefaring civilizations. But from afar, a galaxy reminds me more of a collection of lovely found objects - seashells, perhaps, or corals, the productions of Nature laboring for aeons in the cosmic ocean.
There are some hundred billion 10 11 galaxies, each with, on the average, a hundred billion stars. In the face of such overpowering numbers, what is the likelihood that only one ordinary star, the Sun, is accompanied by an inhabited planet? Why should we, tucked away in some forgotten corner of the Cosmos, be so fortunate? To me, it seems far more likely that the universe is brimming over with life.
But we humans do not yet know. We are just beginning our explorations. From eight billion light-years away we are hard pressed to find even the cluster in which our Milky Way Galaxy is embedded, much less the Sun or the Earth. The only planet we are sure is inhabited is a tiny speck of rock and metal, shining feebly by reflected sunlight, and at this distance utterly lost.
But presently our journey takes us to what astronomers on Earth like to call the Local Group of galaxies. Several million light-years across, it is composed of some twenty constituent galaxies. It is a sparse and obscure and unpretentious cluster. One of these galaxies is M31, seen from the Earth in the constellation Andromeda. Like other spiral galaxies, it is a huge pinwheel of stars, gas and dust. M3 1 has two small satellites, dwarf elliptical galaxies bound to it by gravity, by the identical law of physics that tends to keep me in my chair.
The laws of nature are the same throughout the Cosmos. We are now two million light-years from home. Beyond M3 1 is another, very similar galaxy, our own, its spiral arms turning slowly, once every quarter billion years.