My private opinion, Jonah, is that the “many worlds interpretations” (MWIs) of quantum physics–there are at least three–are total crocks.

Martin Gardner is of the same mind. He skewered the MWIs in an essay in Skeptical Inquirer magazine four or five years ago. The article (and a response to critics of it) is printed in Martin’s 2003 book Are Universes Thicker than Blackberries? (NB: The book title refers to the fruit, not the gadget.) Martin’s conclusion:

The stark truth is that there is not the slightest shred of reliable evidence that there is any universe other than the one we are in. No multiverse theory has so far provided a prediction that can be tested. … Surely the conjecture that there is just one universe and its Creator is infinitely simpler and easier to believe than that there are countless billions upon billions of worlds, constantly increasing in number and created by nobody. I can only marvel at the low state to which today’s philosophy of science has fallen.