"For example, the theory of multiple universes...is sometimes drudged up as a refutation of the fine-tuning of physical constants to support life in the universe. Such a theory is put forth by no less eminent a physicist that Professor Stephen Weinberg, who cites this theory specifically as a refutation of the fine-tuning in the essay A Designer Universe? (Science and Religion: Are They Compatible?, edited by Paul Kurtz). That there cannot be any scientific verification of "other universes" is a fact which is conveniently and even studiously ignored by the defenders of these theories, since if any information can flow from one universe to the other, then the two are not really separate universes."
Let's expand on this comment a bit. First, there are two broad theories of "multiple universes": one in which these are sequential universes--as in a "Big Bounce"--and the other in which our universe is but one of many universes which exist in parallel, more-or-less simultaneously (whatever that means in relation to several things which by definition exist in their own spacetime). The second is what Professor Weinberg cites in his essay . Now, it's an interesting idea, but is it a scientific idea? I would say that it is not, but rather that it is a philosophical (metaphysical) idea dressed up in physics, expressed perhaps in the language of mathematics, but ultimately not a scientifically verifiable idea.
|Mirror universes: cool--and great for Spock!--but unverifiable.|
Suppose for the sake of argument that there really are multiple universes (whether or not we can receive any information from them and thereby actually verify their existence). Does this actually disprove theism? I answer that it does not. For one thing, there is the problem mentioned above concerning sequential universes: that there is more than one universe does not prove that there is more than one set of physical laws. Moreover, even if there are infinitely many sets of laws, there is not a guarantee that the precise set of laws needed for life as we know it will exist in any one of those universes . An infinitely large number of possible combinations may occur without exhausting all possible combinations: so the multiverse theory provides a possible answer, but not a guaranteed refutation, of the "fine tuning" argument. Moreover (and indeed, more importantly), if these universes arise from the "quantum foam" (which encompasses any of the various competing theories as to where these parallel universes come from), it still leaves unexplained where the quantum foam comes from, that is, why it exists. Indeed, it seems to me that the existence of multiple other universes is no more proof against (nor for) theism  than is the existence of many other stars and planets within our own universe .
I think that Fr James Wiseman is basically right when he says that theists should not wed ourselves to any one scientific theory (be it the Big Bang theory or the idea of one unique and uniquely designed vs many universes) as a proof of God's existence; but on the flip side, scientific theories can't really disprove that God exists, either. Moreover, unless it can actually be verified that other universes actually do exist, the theory of a "multiverse" is not so much a scientific conjecture as an idle speculation, one which provides a possible (though not a necessary) if unobservable answer for atheists against the theist's argument from the "fine-tuning" of nature. But absent that observability and thus that verifiability, it is only a conjecture, one which replaces a single supposedly silent God with a multitude of more-so unobserved universes.
 That essay purported to disprove that the universe had a Creator, and began with this supposedly scientific evidence, but ended with a veritable screed against religion which hinges on the existence of evil, the denial of free will, and the explicit claim that only religion can make a good person behave badly: hardly a scientific tract.
 Life as we know it: why does life need to exist as we know it? True, there are certain things which must necessarily occur for life to develop, so certain physical constants must be fine-tunes, e.g. so that atoms and molecules can form. Other constants are not quite so important.
 It seems to me that there are some theistic religions which would actually be vindicated by proving that other universes exist. It would certainly help make sense out of some points of Mormon eschatology.
 In his essay Religion and Rocketry, C.S. Lewis notes that one generation of atheists cited the lifelessness of the universe as proof that the universe is a cruel place, and that therefore God does not exist.The next generation of atheists stated that the overabundance of life throughout the universe proved that we were not unique, and therefore God does not exist.
Update: welcome to Mr Stuart James' eChurch Blog readers!