We must move on to consider the explanations that have been offered for the expansion of the universe, Broadly speeking, the older ideas fall into two groups. One was that the universe started its life a finite time ago in a single huge explosion, and that the present expansion is a relic of the violence of this explosion. This ”big bang’ idea seemed to me to be unsatisfactory even before detailed examination showed that it leads to serious difficulties. For when we look at our own galaxy there is not the smallest sign that such an explosion ever occured, But the really seroius difficulty arises when we try to reconcile the idea of an explosion with the requirement that the galaxies have condensed out of diffuse background materials. The two concepts of explosion and condensation are obviously contradictory, and it is easy to show, if you postulate an explosion of sufficient violence to explain the expansion of the universe, that condensation, looking at all like the galaxies, could never have been formed.
I come now to the second group of theories. The ordinary idea that two particles attract each other is only accepted if their distance apart is not too great. At really large distances, so the argument goes, the two particles repel each other instead. On this basis it can be shown that if the density of the background material is sufficiently small, expansion must occur.
Leave Your Comments