Authors: Carl Sagan
In the very beginning everything was resting in perpetual darkness: night oppressed everything like an impenetrable thicket.
—The Great Father myth of
the Aranda people of
Central Australia
All was in suspense, all calm, all in silence; all motionless and still; and the expanse of the sky was empty.
—The Popol Vuh of the
Quiché Maya
Na Arean sat alone in space as a cloud that floats in nothingness. He slept not, for there was no sleep; he hungered not, for as yet there was no hunger. So he remained for a great while, until a thought came to his mind. He said to himself, “I will make a thing.”
—A myth from Maiana,
Gilbert Islands
First there was the great cosmic egg. Inside the egg was chaos, and floating in chaos was P’an Ku, the Undeveloped, the divine Embryo. And P’an Ku burst out of the egg, four times larger than any man today, with a hammer and chisel in his hand with which he fashioned the world.
—The P’an Ku myths, China
(around third century)
Before heaven and earth had taken form all was vague and amorphous … That which was clear and light drifted up to become heaven, while that which was heavy and turbid solidified to become earth. It was very easy for the pure, fine material to come together, but extremely difficult for the heavy, turbid material to solidify. Therefore heaven was completed first and earth assumed shape after. When heaven and earth were joined in emptiness and all was unwrought simplicity, then without having been created things came into being. This was the Great Oneness. All things issued from this Oneness but all became different …
—Huai-nan Tzu, China
(around first century
B.C.)
These myths are tributes to human audacity. The chief difference between them and our modern scientific myth of the Big Bang is that science is self-questioning, and that we can perform experiments and observations to test our ideas. But those other creation stories are worthy of our deep respect.
Every human culture rejoices in the fact that there are cycles in nature. But how, it was thought, could such cycles come about unless the gods willed them? And if there are cycles in the years of humans, might there not be cycles in the aeons of the gods? The Hindu religion is the only one of the world’s great faiths dedicated to the idea that the Cosmos itself undergoes an immense, indeed an infinite, number of deaths and rebirths. It is the only religion in which the time scales correspond, no doubt by accident, to those of modern scientific cosmology. Its cycles run from our ordinary day and night to a day and night of Brahma, 8.64 billion
years long, longer than the age of the Earth or the Sun and about half the time since the Big Bang. And there are much longer time scales still.
There is the deep and appealing notion that the universe is but the dream of the god who, after a hundred Brahma years, dissolves himself into a dreamless sleep. The universe dissolves with him—until, after another Brahma century, he stirs, recomposes himself and begins again to dream the great cosmic dream. Meanwhile, elsewhere, there are an infinite number of other universes, each with its own god dreaming the cosmic dream. These great ideas are tempered by another, perhaps still greater. It is said that men may not be the dreams of the gods, but rather that the gods are the dreams of men.
In India there are many gods, and each god has many manifestations. The Chola bronzes, cast in the eleventh century, include several different incarnations of the god Shiva. The most elegant and sublime of these is a representation of the creation of the universe at the beginning of each cosmic cycle, a motif known as the cosmic dance of Shiva. The god, called in this manifestation Nataraja, the Dance King, has four hands. In the upper right hand is a drum whose sound is the sound of creation. In the upper left hand is a tongue of flame, a reminder that the universe, now newly created, will billions of years from now be utterly destroyed.
These profound and lovely images are, I like to imagine, a kind of premonition of modern astronomical ideas.
*
Very likely, the universe has been expanding since the Big Bang, but it is by no means clear that it will continue to expand forever. The expansion may gradually slow, stop and reverse itself. If there is less than a certain critical amount of matter in the universe, the gravitation of the receding galaxies will be insufficient to stop the expansion, and the universe will run away forever. But if there is more matter than we can see—hidden away in black holes, say, or in hot but invisible gas between the galaxies—then the universe will hold together gravitationally and partake of a very Indian succession of cycles, expansion followed by contraction, universe
upon universe, Cosmos without end. If we live in such an oscillating universe, then the Big Bang is not the creation of the Cosmos but merely the end of the previous cycle, the destruction of the last incarnation of the Cosmos.
Neither of these modern cosmologies may be altogether to our liking. In one, the universe is created, somehow, ten or twenty billion years ago and expands forever, the galaxies mutually receding until the last one disappears over our cosmic horizon. Then the galactic astronomers are out of business, the stars cool and die, matter itself decays and the universe becomes a thin cold haze of elementary particles. In the other, the oscillating universe, the Cosmos has no beginning and no end, and we are in the midst of an infinite cycle of cosmic deaths and rebirths with no information trickling through the cusps of the oscillation. Nothing of the galaxies, stars, planets, life forms or civilizations evolved in the previous incarnation of the universe oozes into the cusp, flutters past the Big Bang, to be known in our present universe. The fate of the universe in either cosmology may seem a little depressing, but we may take solace in the time scales involved. These events will occupy tens of billions of years, or more. Human beings and our descendants, whoever they might be, can accomplish a great deal in tens of billions of years, before the Cosmos dies.
If the universe truly oscillates, still stranger questions arise. Some scientists think that when expansion is followed by contraction, when the spectra of distant galaxies are all blue-shifted, causality will be inverted and effects will precede causes. First the ripples spread from a point on the water’s surface, then I throw a stone into the pond. First the torch bursts into flame and then I light it. We cannot pretend to understand what such causality inversion means. Will people at such a time be born in the grave and die in the womb? Will time flow backwards? Do these questions have any meaning?
Scientists wonder about what happens in an oscillating universe at the cusps, at the transition from contraction to expansion. Some think that the laws of nature are then randomly reshuffled, that the kind of physics and chemistry that orders this universe represent only one of an infinite range of possible natural laws. It is easy to see that only a very restricted range of laws of nature are consistent with galaxies and stars, planets, life and intelligence. If the laws of nature are unpredictably reassorted at the cusps, then it is only by the most extraordinary coincidence that the
cosmic slot machine has this time come up with a universe consistent with us.
*
Do we live in a universe that expands forever or in one in which there is an infinite set of cycles? There are ways to find out: by making an accurate census of the total amount of matter in the universe, or by seeing to the edge of the Cosmos.
Radio telescopes can detect very faint, very distant objects. As we look deep into space we also look far back into time. The nearest quasar is perhaps half a billion light-years away. The farthest may be ten or twelve or more billions. But if we see an object twelve billion light-years away, we are seeing it as it was twelve billion years ago in time. By looking far out into space we are also looking far back into time, back toward the horizon of the universe, back toward the epoch of the Big Bang.
The Very Large Array (VLA) is a collection of twenty-seven separate radio telescopes in a remote region of New Mexico. It is a phased array, the individual telescopes electronically connected, as if it were a single telescope of the same size as its remotest elements, as if it were a radio telescope tens of kilometers across. The VLA is able to resolve or discriminate fine detail in the radio regions of the spectrum comparable to what the largest ground-based telescopes can do in the optical region of the spectrum.
Sometimes such radio telescopes are connected with telescopes on the other side of the Earth, forming a baseline comparable to the Earth’s diameter—in a certain sense, a telescope as large as the planet. In the future we may have telescopes in the Earth’s orbit, around toward the other side of the Sun, in effect a radio telescope as large as the inner solar system. Such telescopes may reveal the internal structure and nature of quasars. Perhaps a quasar standard candle will be found, and the distances to the quasars determined independent of their red shifts. By understanding the structure and the red shift of the most distant quasars it may be
possible to see whether the expansion of the universe was faster billions of years ago, whether the expansion is slowing down, whether the universe will one day collapse.
Modern radio telescopes are exquisitely sensitive; a distant quasar is so faint that its detected radiation amounts perhaps to a quadrillionth of a watt. The total amount of energy from outside the solar system ever received by all the radio telescopes on the planet Earth is less than the energy of a single snowflake striking the ground. In detecting the cosmic background radiation, in counting quasars, in searching for intelligent signals from space, radio astronomers are dealing with amounts of energy that are barely there at all.
Some matter, particularly the matter in the stars, glows in visible light and is easy to see. Other matter, gas and dust in the outskirts of galaxies, for example, is not so readily detected. It does not give off visible light, although it seems to give off radio waves. This is one reason that the unlocking of the cosmological mysteries requires us to use exotic instruments and frequencies different from the visible light to which our eyes are sensitive. Observatories in Earth orbit have found an intense X-ray glow between the galaxies. It was first thought to be hot intergalactic hydrogen, an immense amount of it never before seen, perhaps enough to close the Cosmos and to guarantee that we are trapped in an oscillating universe. But more recent observations by Ricardo Giacconi may have resolved the X-ray glow into individual points, perhaps an immense horde of distant quasars. They contribute previously unknown mass to the universe as well. When the cosmic inventory is completed, and the mass of all the galaxies, quasars, black holes, intergalactic hydrogen, gravitational waves and still more exotic denizens of space is summed up, we will know what kind of universe we inhabit.
In discussing the large-scale structure of the Cosmos, astronomers are fond of saying that space is curved, or that there is no center to the Cosmos, or that the universe is finite but unbounded. Whatever are they talking about? Let us imagine we inhabit a strange country where everyone is perfectly flat. Following Edwin Abbott, a Shakespearean scholar who lived in Victorian England, we call it Flatland. Some of us are squares; some are triangles; some have more complex shapes. We scurry about, in and out of our flat buildings, occupied with our flat businesses and dalliances. Everyone in Flatland has width and length, but no height whatever. We know about left-right and forward-back, but have no hint, not a trace of comprehension, about up-down—except for flat mathematicians.
They say, “Listen, it’s really very easy. Imagine left-right. Imagine forward-back. Okay, so far? Now imagine another dimension, at right angles to the other two.” And we say, “What are you talking about? ‘At right angles to the other two’! There
are
only two dimensions. Point to that third dimension. Where is it?” So the mathematicians, disheartened, amble off. Nobody listens to mathematicians.
Every square creature in Flatland sees another square as merely a short line segment, the side of the square nearest to him. He can see the other side of the square only by taking a short walk. But the
inside
of a square is forever mysterious, unless some terrible accident or autopsy breaches the sides and exposes the interior parts.
One day a three-dimensional creature—shaped like an apple, say—comes upon Flatland, hovering above it. Observing a particularly attractive and congenial-looking square entering its flat house, the apple decides, in a gesture of interdimensional amity, to say hello. “How are you?” asks the visitor from the third dimension. “I am a visitor from the third dimension.” The wretched square looks about his closed house and sees no one. What is worse, to him it appears that the greeting, entering from above, is emanating from his own flat body, a voice from within. A little insanity, he perhaps reminds himself gamely, runs in the family.
Exasperated at being judged a psychological aberration, the apple descends into Flatland. Now a three-dimensional creature can exist, in Flatland, only partially; only a cross section can be seen, only the points of contact with the plane surface of Flatland. An apple slithering through Flatland would appear first as a point and then as progressively larger, roughly circular slices. The square sees a point appearing in a closed room in his two-dimensional world and slowly growing into a near circle. A creature of strange and changing shape has appeared from nowhere.
Rebuffed, unhappy at the obtuseness of the very flat, the apple bumps the square and sends him aloft, fluttering and spinning into that mysterious third dimension. At first the square can make no sense of what is happening; it is utterly outside his experience. But eventually he realizes that he is viewing Flatland from a peculiar vantage point: “above.” He can see into closed rooms. He can see into his flat fellows. He is viewing his universe from a unique and devastating perspective. Traveling through another dimension provides, as an incidental benefit, a kind of X-ray vision. Eventually, like a falling leaf, our square slowly descends to the surface. From the point of view of his fellow Flatlanders,
he has unaccountably disappeared from a closed room and then distressingly materialized from nowhere. “For heaven’s sake,” they say, “what’s happened to you?” “I think,” he finds himself replying, “I was ‘up.’ ” They pat him on his sides and comfort him. Delusions always ran in his family.