Big Bang versus Einstein

As we look further and further out into space we see that the stars are more and more red-shifted in colour. The simplest explanation is that the universe is expanding in every direction. It is this expansion that produces a Doppler red-shift in the wavelength of light from distant stars..

Measurements are only approximate, but the rate of expansion, called the Hubble constant, or H, is normally taken to be about 50 to 100 kilometres/second per MegaParsec. A Parsec is 3.26 million light-years, so the constant may also be expressed as 2.4E^-18 meters/second per meter of distance.

It is one thing to know that the universe is expanding, another to work out why. Here are two possible answers...

1. By inference from explosions on Earth, we might surmise that the universe started with a Big Bang and the expansion is the aftermath of that explosion; as the universe expands the rate of expansion slows from the effects of gravitational attraction. This is the most popular theory. There is inferential proof of the Big Bang in the background microwave radiation that can be detected by suitable equipment as coming from every region of the universe. The explosion would have caused radiation that can be seen today as being incredibly red-shifted and weakened in the microwave part of the spectrum. For this to be the case the universe must be closed so that no radiation leaks away - it does not work in a universe where the universe is bounded by an infinite void - and this is far from being proven and is likely to remain unprovable for the foreseeable future. Even if it were closed, more precise measurements of the spectrum are needed before it can be proved to be an aftermath of the Big Bang. So the jury is still out on the background radiation.
2. Einstein’s equations on Relativity show as an obvious solution that the universe is expanding. At the time he worked out these equations no-one was aware of the expansion of the universe, so he arbitrarily added a Cosmological Constant to his equations to eliminate the expansion they predicted; after the physical discovery of the expansion of the Universe he felt he should have trusted his equations more, and regretted ever adding the Constant. His equations demonstrated that the universe is expanding for no other reason than to satisfy its own equations for existence. This Relativistic Expansion is not associated with an impelling force such as an explosion, but is the very nature of our present electromagnetic universe. This means the universe may be infinite in time - we just happen to live in a corner of it and at a time that is currently condensing from gas into galaxies and solar systems.

The main difficulty with the Big Bang is that there is no way it could have happened within the present rules of our universe. So if you want the big bang theory to work you have to make up a special set of rules and assume they applied just for the duration of the big bang at the start of everything. After that the rules changed to what we know today. In some ways it is a “Creation Story” because these early rules can never be replicated, duplicated, or tested - you take one solid piece of evidence (the perceived expansion of the universe), throw away the current rules of the universe, including the conservation of mass/energy, then make up new rules for the start of the universe, just to make the Big Bang work. You can make the equations work, but there is just no way of testing whether they model a real event. The real “Creation” problems, however, occur in the first creation event, the actual formation of first bubble of the space-time Universe, before the Big Bang started.

The main difficulty with Relativistic Expansion is that it is counter-intuitive; how can the Universe “just expand” without anything driving that expansion. In fact, it is inherent in the nature of a relativistic universe. The universe is always expanding, but the rules always remain the same. That means that it takes the same time to double in size. So in maybe eight billion years it will be double its present size, in 16 billion years it will have doubled again to four times its present size, and so on. In a relativistic universe the rate of expansion is always increasing.

The key difference between the two models is that the rate of expansion in the Big Bang model must slow down as gravity pulls on all the matter, while in the relativistic model it must speed up. This we can measure! Most interesting is the recent work that shows that the rate of expansion of the universe is accelerating, which would support the Relativistic Expansion model.

So there you have it. A Big Bang, whose predictions do not match actual measurements; or Einstein’s equations, whose predictions are everywhere in accord with practical measurements; or perhaps something else altogether. Looks like Einstein wins, with the Eternal Universe that is infinite in time going backwards as well as forwards, having no beginning and no end.