i am going to speculate that high-end physics/cosmology has gone very far off the deep end. so, for example, stephen hawking has concluded on the basis - i guess? - of mathematics that "the universe has every possible history", and we're way into multiverses, infinitely many different spaces, and stuff.
Dr. Tegmark, in his new book, “Our Mathematical Universe: My Quest for the Ultimate Nature of Reality,” turns the idea on its head: The reason mathematics serves as such a forceful tool is that the universe is a mathematical structure. Going beyond Pythagoras and Plato, he sets out to show how matter, energy, space and time might emerge from numbers.
now, i'm afraid i do not understand the claim that the universe is a mathematical structure. does that mean that physical objects are abstract objects? well, you'll need to grapple with the fact that that cannot possibly be the case, given that abstract and concrete objects have extremely different sorts of properties, and hence cannot be identical. where is the number 5, bro? inside that star?
now it may sound crass to say it, but isn't whether there are other universes - whatever that means - an empirical question? (if not, i wouldn't think it's a scientific question at all.) you can stipulate universes, or invent them - but you can't discover them except in the usual human way: by actual experience. i should have said it's quite like insisting that you know the number of planets before looking at all, maybe from a biblical passage, or just by thinking about it real hard. a few decadesago we called that "the dark ages".
the piece says that they're going beyond plato and pythagoras, but maybe they're just going back to the little stage where people were worshipping abstract objects and trying to view the physical universe either as an illusionistic scrim over the numbers and concepts, or as actually being made out of them. like i say, that's not just a puzzling formulation. if you tell me a wall is made of bricks, i understand what you're saying. if you tell me it's made out of 16 and 137, or emerges from them (causally?) it's going to take a lot to convince me that you mean anything at all.
maybe, just perhaps, this stuff isn't science whatsoever. it certainly isn't science that involves things like experiments and systematic observation. perhaps we're back to the wildest metaphysical speculation. there's a lot to be said for that, i think, but that is also not the way it's being presented. indeed, hawking, for example is (a) doing philosophy all the time, (b) doing it very very badly, (c) denying that he's doing it at all. but if you want to believe whatever he says, go right ahead, because even if everyone believed that the universe has every possible history or whatever it may be, that will have no effects at all on this one.