9. THE EVOLUTION OF THE UNIVERSE

by Patrick Moore

One of the first men to draw up a modern-type theory of creation of the universe was a Belgian priest, George Lema�tre. He supposed that originally all the material was contained in a very dense "primeval atom", which exploded, sending its material outward in all directions. Expansion began, and continued for thousands of millions of years. Two forces were acting against each other: gravitation on the one hand, and the so-called "cosmical repulsion" on the other. According to Lema�tre, cosmical repulsion became dominant, so that the expansion of the universe is still going on. Various modifications of this theory have been made, but in any case it assumes that the universe began at a definite moment in the past. The universe is evolving, and must eventually die, so that it may be compared with a clock which is running down. We can understand why the whole conception has been nicknamed the "big bang" hypothesis.

Then a little over a decade ago, Professors Hoyle, Bondi, and Gold, working at Cambridge, proposed an entirely different scheme. They suggested that there never was a definite moment of creation, so that the universe has always existed - and will moreover exist for ever. As old galaxies die, new matter is created, and the universe may be likened to a clock which is being continually re-wound.

The practicable test appeared to be obtainable from studies of very distant galaxies. It must be remembered that, on the evolutionary theory, the density of material in the universe used to be much greater than it is now, so that many thousands of millions of years ago the galaxies were closer together than is at present the case. If the steady-state theory is correct, the universe has always had much the same aspect as it has now, since galaxies which pass beyond the observable horizon will be replaced by new galaxies formed from the continually created matter. Consequently, we could decide the rival hypotheses if we could look backward in time to see the universe as it used to be thousands of millions of years ago.

In effect, this is precisely what can be done. Take, for instance, the galaxy 3C-295, recently studied by Minkowski in the United States. Its distance is about 5,000,000,000 light-years; we are therefore looking at it as it used to be 5,000,000,000 years ago, before the Earth came into existence as a separate body. We are looking through time as well as through space.

By the methods of radio astronomy it should be possible to study galaxies still more remote than this, and a positive test may be made. On the evolutionary theory, the galaxies were relatively crowded together in past ages - say 8,000,000,000 or 9,000,000,000 years ago; on the steady-state theory, they were not. If, then, galaxies at a distance of 8,000,000,000 or 9,000,000,000 light-years are seen to be closer packed than those in our own region of space, then the evolutionary idea is valid. If not, then the steady-state theory is vindicated.

At Cambridge, Professor Ryle and his colleagues have carried out exhaustive studies of very weak radio sources, which are regarded as associated with remote galaxies. It is maintained that some of these lie at least 8,000,000,000 light-years from us, which should be far enough for any increase in "crowding" to become noticeable. The crux of the matter is, therefore: are these weak, distant sources more numerous than they should be on the steady-state theory? The answer, according to Ryle, is a definite "yes". If so, then the steady-state theory must be either modified or else abandoned.

It is hardly necessary to add that Professor Ryle's work has been carried out with the greatest care, and is a magnificent technical achievement. Every possible source of error has been taken into account, and the whole research programme has already taken years. Yet it is certainly premature to say that the problem has been definitely solved in favour of the "big bang" idea, and it is still essential to keep an open mind.

Further research will probably enable us to decide between the two theories, but this is not the same thing as solving what is often termed "the mystery of the creation". We still have no idea how the material of the universe came into being, whether it did so at one particular moment or as a continuing process, and in this respect we are as yet completely in the dark.

There are so many unknown and uncertain factors that it would be most unwise to jump to conclusions, and studies carried out in the near future may well cause the pendulum of scientific opinion to swing once more.

(from The Listener, 9th March, 1961)