  Speculations and theories about the existence of other worlds have a long
history. In recent times, the arguments have shifted away from their typical
philosophical and theological character to supposedly become more objective
thanks to their scientific underpinnings. A prime example of this is the
current parallel universes or multiverse theory, which has the support of a
number of famous cosmologists. In this article, we contend that the claim for
the existence of those parallel universes, as presented in Max Tegmark's book
"Our Mathematical Universe", rests crucially on some questionable probability
arguments involving infinity. As a result, a doubt is cast over the multiverse
hypothesis: Is it more credible than the counterarguments based on
philosophical and metaphysical considerations?
