In the August 2011 edition of Scientific American, famed cosmologist, George Ellis, wrote an article titled “Does the Multiverse Really Exist?”  Here are some great excerpts from that article:

“Similar claims [about a multiverse] have been made since antiquity by many cultures.  What is new is the assertion that the multiverse is a scientific theory, with all that implies about being mathematically rigorous and experimentally testable.  I am skeptical about this claim.  I do not believe the existence of those other universes has been proved—or ever could be.  Proponents of the multiverse, as well as greatly enlarging our conception of physical reality, are implicitly redefining what is meant by ‘science.’”—pg 39

“For a cosmologist, the basic problem with all multiverse proposals is the presence of a cosmic visual horizon.  The horizon is the limit to how far away we can see, because signals traveling toward us at the speed of light (which is finite) have not had time since the beginning of the universe to reach us from farther out.  All the parallel universes lie outside our horizon and remain beyond our capacity to see, now or ever, no matter how technology evolves.  In fact, they are to far away to have had any influence on our universe whatsoever.  That is why none of the claims made by multiverse enthusiasts can be directly substantiated.”—pg 40-41

It’s interesting that many scientists want to call the multiverse “science,” but then want to say Intelligent Design theory is not science because it trades on unobserved entities and/or cannot be tested.  You cannot have your cake and eat it to.  At least Ellis is trying to be consistent in his definition of science.

Ellis on how shaky the foundation is on which multiverse speculations rest:

“Known physics predicts other domains.  Proposed unified theories predict entities such as scalar fields, a hypothesized relative of other space-filling fields such as the magnetic field.  Such fields should drive cosmic inflation and create universes ad infinitum.  These theories are well grounded theoretically, but the nature of the hypothesized fields is unknown, and experimentalists have yet to demonstrate their existence, let alone measure their supposed properties.  Crucially, physicists have not substantiated that the dynamics of these fields would cause different laws of physics to operate in different bubble universes.”—pg 41

Here’s what Ellis has to say about how the multiverse is the only real scientific (read, “materialistic”) theory that can solve the problem of the fine-tuning “problem,” and yet he admits that it is not testable:

“A remarkable fact about our universe is that physical constants have just the right values needed to allow for complex structures, including living things.  Steven Weinberg, Martin Rees, Leonard Susskind and others contend that an exotic multiverse provides a tidy explanation for this apparent coincidence: if all possible values occur in a large enough collection of universes, then viable ones for life will surely be found somewhere.  This reasoning has been applied, in particular, to explanation the density of the dark energy that is speeding up the expansion of the universe today.  I agree that the multiverse is a possible valid explanation for the value of this density; arguably, it is the only scientifically based option we have right now.  But we have no hope of testing it observationally.”—pg 42

Ellis on string theory:

“String theory has moved from being a theory that explains everything to a theory where almost anything is possible. … But string theory is not a tried-and-tested theory; it is not even a complete theory.  If we had proof that string theory is correct, its theoretical predication could be a legitimate, experimentally based argument for a multiverse.  We do not have such proof.”—pg 42

Remember that when atheists want to undermine our argument for God’s existence based on the beginning of the universe by appealing to cosmological models based on string theory.  Not only is there no proof that string theory is true, but the theory itself isn’t even complete.  It’s a bit premature to be building cosmological models based on string theory.  And surely, appealing to string cosmologies as a defeater to the kalam cosmological argument is not epistemically justified.

Ellis’ conclusion is grand:

“All in all, the case for the multiverse is inconclusive.  The basic reason is the extreme flexibility of the proposal: it is more a concept than well-defined theory.  Most proposals involve a patchwork of different ideas rather than a coherent whole.  The basic mechanism for eternal inflation does not itself cause physics to be different in each domain in a multiverse; for that, it needs to be coupled to another speculative theory.  Although they can be fitted together, there is nothing inevitable about it. … Nothing is wrong with scientifically based philosophical speculation, which is what multiverse proposals are.  But we should name it for what it is.”—pg 43