To be honest, I'm not even particularly impressed by the claim that the only mathematical universes that can exist are the self-consistent ones. I think that is

To be honest, I'm not even particularly impressed by the claim that the only mathematical universes that can exist are the self-consistent ones. I think that is mostly stipulated in these theories for post hoc reasons. So some of them aren't consistent... so what? Do the consistency police come along and strip you of your "existence"? How? Why? We humans use inconsistent logics all the time. When confronted by inconsistencies we often just fix them up, either with some other logic or just plain ad hoc new rules. Inconsistent universes can similarly each be rescued by an infinite number of "fixups", up to and including uncountably infinite functions that simply brute force resolve the inconsistencies. This renders the term "inconsistent" meaningless in this context because rather than an inconsistent universe not being able to "exist" it instead represents some infinite class of existing universes with some fixups applied. The main problem I have with this line of argumentation is that in its zeal to explain why anything exists, it actually goes all the way to the other end of the spectrum and can't explain why anything doesn't exist. But clearly there are things that don't exist, by virtue of the fact that the subjective experience of being in a universe where literally everything exists would be one of total chaos; in any given moment, the countably-infinite possible futures where the next subjective instant is "reasonable" to you is dwarfed by the uncountably infinite possible futures that contain an embedding of "you" and your next subjective instant is not reasonable to you. (And if you're objecting to my casual assertion that your next instant is at best countably infinite, I'm already erring on the side of giving grace to the argument; I'd personally characterize them as straight-up finite.) Things exist; some things also don't exist. The mathematical universe hypothesis covers the first at the cost of failing the second. Math isn't parabolas and conic sections and tiny integers getting added together; math is uncountably infinite functions of uncountably infinite structures being mapped to other uncountably infinite structures with no pattern, out of which we carve our little niches that are useful and comprehensible and mistake them as being the rule, rather than than the vanishingly tiny exception. Something isn't just causing things to exist, it is also holding back the incomprehensible chaos of total, undifferentiated existence. (The fine tuning of the physical universe is a nearly insignificant mystery next to this. How is reality reasonable to any degree at all? Forget the question of life, how does there exist any structure that has a reasonable subjective existence rather than total, utter chaos beyond any capability we have to imagine?)