PCW Davies a British physicist describes“If we extrapolate this prediction to its extreme, we reach a point when all distances in the universe have shrunk to zero. An initial cosmological singularity therefore forms a past temporal extremity to the universe. We cannot continue physical reasoning, or even the concept of space and time, through such an extremity. For this reason, most cosmologists think of the initial singularity as the beginning of the universe. On this view, the Big Bang represents the creation event; the creation not only of all the matter and energy in the universe, but also of space and time itself.”P. C. W. Davies, “Space & time Singularities in Cosmology,” in The Study of Time III, ed. J. T. Fraser (Berlin: Springer Verlag, 1978), pp. 78?79.
A second discovery firmly cemented the fact that the universe began to exist, the CMB ‘cosmic microwave background’. In 1967, two radio engineers Arno Penzias and Robert Wilson, stumbled across radiation coming from space which was identified as the relic of the big bang. If the universe was once very dense, it should also have been very hot, since matter heats up when compressed. Hot matter emits thermal radiation so we can expect the heat left over from the birth of the universe to be bathing the universe today, in a faint glow of radiation. This was confirmed by the discovery of CMB.
Some have tried to undermine the beginning of the Universe by suggesting the the oscillating universe model. Advocates of this model envisioned a universe that would expand, gradually decelerate, shrink back under the force of its own gravitation, and then, by some unknown mechanism, re- initiate its expansion, on and on, ad infinitum.
However evidence for a finite universe comes from the second law of thermodynamics. This is a fundamental law which states that in any system the processes always tend towards an equilibrium. Energy runs down and ‘entropy’ increases. Our universe is heading for what is called ‘heat death’. It is what happens when your cup of hot coffee, if not drunk, reaches the same temperature as the room. Now when we observe our universe we know that it has not run down yet. Entropy is not at a maximum. This means that it is in the process of reaching that state. Such a process is time limited and had to start at some point with a state of low entropy. This means there must have been a start. Further, recent measurements suggest that the universe has only a fraction about one-fifth of the mass required to create a gravitational contraction in the first place (Peebles 1993: 475-83; Coles & Ellis 1994: 609-13; Sawyer 1992: A5; Ross 1993: 58).
Yet another evidence for a finite Universe is Einstein’s theory of general relativity. Three astrophysicists, Hawking, George Ellis, and Roger Penrose, published a series of papers that explicated the implications of Einstein s theory of general relativity for space and time as well as matter and energy (Hawking & Penrose 1970). Previously, physicists like Friedmann showed that the density of the universe would approach an infinite value as one extrapolated the state of the universe back in time. In a series of papers written between 1966-70, Hawking and his colleagues showed that as one extrapolated back in time the curvature of space also approached infinity. But an infinitely curved space corresponds to a radius (within a sphere, for example) of zero and thus to no spatial volume. Further, since in general relativity space and time are inextricably linked, the absence of space implies the absence of time. Moreover, neither matter nor energy can exist in the absence of space. Thus, Hawking s result suggested that general relativity implies that the universe sprang into existence a finite time ago from literally nothing, at least nothing physical. In brief, general relativity implies an absolute beginning of time, before which neither time and space, nor matter and energy, would have existed.
The space-time theorem of general relativity was, of course, conditional. It stated that, if general relativity obtains for the universe, then space and time themselves must have originated in the same initial explosion that created matter and energy. In a series of experiments, beginning just two years after Einstein published his results and continuing on to the present, the probable error of general relativity (estimated quantitatively) has shrunk from 10 to 1 to .05 percent, to a confirmation out to the fifth decimal place. Increasingly accurate tests conducted by NASA, such as the hydrogen maser detector carried by a NASA rocket in 1980 and 1994, have continued to shrink the probable error associated with the theory (Ross 1993: 66-67; Vessor 1980: 2081-84). Thus, general relativity now stands as one of the best confirmed theories of modern science. Yet its philosophical implications, and those of the Big Bang theory, are staggering. Taken jointly, general relativity and the Big Bang theory provide a compelling evidence for the origin of Universe from nothing (again, nothing physical).
These theories place a heavy demand on any proposed causal explanation of the universe, since the cause of the beginning of the universe must transcend time, space, matter, and energy.
Therefore we conclude that the Universe had a beginning. So we can summarize the argument as follows
1. Whatever begins to exist has a cause.
2. The universe began to exist.
3. Therefore, the universe has a cause.