Almost all of modern cosmology – and especially the idea of an expanding universe and a Big Bang – is based on the idea that the red shift of distant galaxies is a Doppler effect and arises from their speed of recession. But there are other kinds of red shifts in nature. There is, for example, the gravitational red shift, in which the light leaving an intense gravitational field has to do so much work to escape that it loses energy during the journey, the process perceived by a distant observer as a shift of the escaping light to longer wavelengths and redder colors. Since we think there may be massive black holes at the centers of some galaxies, this is a conceivable explanation of their red shifts. However, the particular spectral lines observed are often characteristic of very thin, diffuse gas, and not the astonishingly high density that must prevail near black holes. Or the red shift might be a Doppler effect due not to the general expansion of the universe but rather to a more modest and local galactic explosion. But then we should expect as many explosion fragments traveling toward us as away from us, as many blue shifts as red shifts. What we actually see, however, is almost exclusively red shifts no matter what distant objects beyond the Local Group we point our telescopes to.
There is nevertheless a nagging suspicion among some astronomers that all may not be right with the deduction, from the red shifts of galaxies via the Doppler effect, that the universe is expanding. The astronomer Halton Arp has found enigmatic and disturbing cases where a galaxy and a quasar, or a pair of galaxies, that are in apparent physical association have very different red shifts. Occasionally there seems to be a bridge of gas and dust and stars connecting them. If the red shift is due to the expansion of the universe, very different red shifts imply very different distances. But two galaxies that are physically connected can hardly also be greatly separated from each other – in some cases by a billion light-years. Skeptics say that the association is purely statistical: that, for example, a nearby bright galaxy and a much more distant quasar, each having very different red shifts and very different speeds of recession, are merely accidentally aligned along the line of sight; that they have no real physical association. Such statistical alignments must happen by chance every now and then. The debate centers on whether the number of coincidences is more than would be expected by chance. Arp points to other cases in which a galaxy with a small red shift is flanked by two quasars of large and almost identical red shift. He believes the quasars are not at cosmological distances but instead are being ejected, left and right, by the ‘foreground’ galaxy; and that the red shifts are the result of some as-yet-unfathomed mechanism. Skeptics argue coincidental alignment and the conventional Hubble-Humason interpretation of the red shift. If Arp is right, the exotic mechanisms proposed to explain the energy source of distant quasars – supernova chain reactions, supermassive black holes and the like – would prove unnecessary. Quasars need not then be very distant. But some other exotic mechanism will be required to explain the red shift. In either case, something very strange is going on in the depths of space.
The apparent recession of the galaxies, with the red shift interpreted through the Doppler effect, is not the only evidence for the Big Bang. Independent and quite persuasive evidence derives from the cosmic black body background radiation, the faint static of radio waves coming quite uniformly from all directions in the Cosmos at just the intensity expected in our epoch from the now substantially cooled radiation of the Big Bang. But here also there is something puzzling. Observations with a sensitive radio antenna carried near the top of the Earth’s atmosphere in a U-2 aircraft have shown that the background radiation is, to first approximation, just as intense in all directions – as if the fireball of the Big Bang expanded quite uniformly, an origin of the universe with a very precise symmetry. But the background radiation, when examined to finer precision, proves to be imperfectly symmetrical. There is a small systematic effect that could be understood if the entire Milky Way Galaxy (and presumably other members of the Local Group) were streaking toward the Virgo cluster of galaxies at more than a million miles an hour (600 kilometers per second). At such a rate, we will reach it in ten billion years, and extragalactic astronomy will then be a great deal easier. The Virgo cluster is already the richest collection of galaxies known, replete with spirals and ellipticals and irregulars, a jewel box in the sky. But why should we be rushing toward it? George Smoot and his colleagues, who made these high-altitude observations, suggest that the Milky Way is being gravitationally dragged toward the center of the Virgo cluster; that the cluster has many more galaxies than have been detected heretofore; and, most startling, that the cluster is of immense proportions, stretching across one or two billion light-years of space.
The observable universe itself is only a few tens of billions of light-years across and, if there is a vast supercluster in the Virgo group, perhaps there are other such superclusters at much greater distances, which are correspondingly more difficult to detect. In the lifetime of the universe there has apparently not been enough time for an initial gravitational nonuniformity to collect the amount of mass that seems to reside in the Virgo supercluster. Thus Smoot is tempted to conclude that the Big Bang was much less uniform than his other observations suggest, that the original distribution of matter in the universe was very lumpy. (Some little lumpiness is to be expected, and indeed even needed to understand the condensation of galaxies; but a lumpiness on this scale is a surprise.) Perhaps the paradox can be resolved by imagining two or more nearly simultaneous Big Bangs.
If the general picture of an expanding universe and a Big Bang is correct, we must then confront still more difficult questions. What were conditions like at the time of the Big Bang? What happened before that? Was there a tiny universe, devoid of all matter, and then the matter suddenly created from nothing? How does that happen? In many cultures it is customary to answer that God created the universe out of nothing. But this is mere temporizing. If we wish courageously to pursue the question, we must, of course ask next where God comes from. And if we decide this to be unanswerable, why not save a step and decide that the origin of the universe is an unanswerable question? Or, if we say that God has always existed, why not save a step and conclude that the universe has always existed?
Every culture has a myth of the world before creation, and of the creation of the world, often by the mating of the gods or the hatching of a cosmic egg. Commonly, the universe is naively imagined to follow human or animal precedent. Here, for example, are five small extracts from such myths, at different levels of sophistication, from the Pacific Basin:
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 Pan Ku, the Undeveloped, the divine Embryo. And Pan 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 . . .