The idea that there are other universes than our own (perhaps an infinite number) is quite common today. It is often used to explain how our universe was able to produce and sustain such rich biodiversity that we see on Earth. The idea being that given an infinite number of chances, our ordered and balanced universe is simply eventual. Sometimes, even, this talk is used as evidence that ‘science’ shows (even ‘proves’!) that our universe, after all, is not the result of the action of any kind of Creator.
As a Theist, I want to say that the idea of other universes or other dimensions is interesting to me, but completely unnecessary. For example, the suggestion by some that other universes or other dimensions to reality could finally provide a scientific explanation for ‘where god is’, is silly to me – the most basic of all versions of classic monotheism has always been that the Creator is present in all space.
Further, I want to say that using the word ‘science’ with regard to theories about multiple universes or dimensions is to stretch the word ‘science’. As the paper ‘Multiverses and Cosmology: Philosophical Issues‘ points out, while these kinds of theories may be interesting and useful, they are firmly unscientific.
“We may, of course, postulate the existence of such a multiverse as a metaphysical assumption, but it would be a metaphysical assumption without any further justifiability – it would be untestable and unsupportable by any direct or indeed indirect evidence.” … “The point is that there is not just an issue of showing a multiverse exists. If this is a scientific proposition one needs to be able to show which specific multiverse exists; but there is no observational way to do this. Indeed if you can’t show which particular one exists, it is doubtful you have shown any one exists.” (p. 26, underlining not in original)
This objection to multiverse theory being specifically ‘scientific’ is not an attack on science or an attempt to limit it. Quite the opposite, in fact. This objection is an attempt to protect the methods inherent to science, which assumes that reality is consistent, verifiable and meaningfully testable.
Does this mean that multiverses do not exist? Of course not. It simply means that theories concerning them (however logical and rational) cannot be advanced in the realm of ‘science.’ Multiverses, like a Creator, are not proved or dis-proved by science.