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Is There a Multiverse?

Entry 957, on 2009-03-03 at 19:56:11 (Rating 1, Science)

For many years now there has been a theory that our universe might just be one of many - in fact probably one of an infinite number - of other universes. The Big Bang would be an event where our universe formed inside a multiverse and that other universes with different properties would also exist in parallel to ours.

Recently I have seen more discussion of the idea and it seems to be being taken a bit more seriously now. The latest source was an article in New Scientist: "Dark flow: Proof of another universe?" from 23 January 2009 which provided a possible way to test the idea.

If you have been following current issues in astronomy and cosmology you will no doubt have heard of dark matter and dark energy. These two have caused a lot of trouble because they constitute 95% of the mass of the universe but we really don't know what they are. Dark matter is material which only interacts gravitationally and clumps on large scales causing gravitational effects on galaxies. Dark energy is a uniform force causing the universe to expand faster as time passes.

As if those weren't enough we now have dark flow! This seems to be the observation that galaxy clusters are moving towards a specific spot in space (this is independent of the general expansion of the universe) and again, we don't know why. One possibility is that it is caused by large structures beyond the observable edge of our universe. Another is that the force is from another universe.

I must say I like the multiverse idea from a philosophical perspective because it eliminates many problems with the older Big Bang hypothesis where our universe was all there is and it, including time and space, were created from nothing in the Big Bang.

The problems were: how did the universe originate from nothing, what caused the Big Bang, why does our universe have the special physical laws and constants which make it possible for life to evolve, and what happens before and after the universe (if that even means anything).

If there is a multiverse then presumably it is infinite in time and space. Fluctuations in its material cause new universes to be created constantly. Each universe has its own laws and there are infinitely many, so having one with the exact laws and constants we have is not only possible, it is certain. And the "cosmic bubbles" which become universes continue on infinitely in the past and future so universes always exist.

As I said, its very neat from a philosophical perspective but is it science? Well, being able to test a theory is a major requirement of science. If a theory can't be tested then we just endlessly speculate on it as a possibility, like philosophers tend to do, without making any real progress. I didn't think multiverse theories were testable but now it seems that perhaps they are.

We may look back in a few years and think its amusing that we used to think that our universe was all there was. Its very much like the initial assumption that our country was the center of everything, then our planet, then our solar system, then our galaxy. All of those ideas were wrong. Now it seems that even our universe isn't special either!

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