New books mount aggressive but ultimately unpersuasive defenses of multiverses

Upvoted your unpopular but sensible post.

One thing I've wondered about is the assumption that every possible universe exists independently, with an infinity of entire universes splitting at every fork (n states per picosecond per particle, compounding!); it seems to me that shared state(s) and a long-tail of micro-diffs (like git / Merkle trees / etc) could model the same phenomenon more efficiently/parsimoniously (disclaimer: not even slightly a theoretical physicist). This could potentially allow sufficiently overlapping states to merge, or exactly opposing states to cancel, yielding an equilibrium amongst the sea of micro-probabilities, converging either to a singular universe, or a much smaller patchwork of stable universes (either separate, or intertwined).

This parsimony question also overlaps the Simulation Hypothesis: the fact that most physical laws resolve at macro-scale, by aggregating probabilities, and only break down into odd behavior (where a particle seems to care whether or not you're looking), smells to this programmer like an optimization hack. :)

Just started reading Donald Hoffman's "The Case Against Reality", which posits some very bold answers to this question, theorizing that there is no reason to assume that base reality is anything like our perceptions (subjective or scientific), any more than there's a reason to assume the perception of a desktop icon has a direct relationship with its filesystem implementation. The implications of a "consciousness-first" rather than "matter-first" explanation of existence are staggering, and it isn't hard to set up a model in which that explanation is more parsimonious than Multiple Worlds.

The thing missing is an explanation for why we find ourselves in a particular branch. Insisting that this doesn’t require an explanation is never going to be satisfying for some people.

I’ll try to explain why, using your random variable sampling analogy, which is telling. In the case of say, sampling from a coin toss random variable, there is indeed a more primitive explanation for why the coin comes up heads or tails, it’s just that it would be a much more complicated explanation involving knowledge of huge amounts of detail about the exact force applied to the coin, maybe air currents in the area where coin is being flipped, etc. But in principle that is all explainable.

With quantum measurement, there is no such explanation available, even in principle. We are told only that we will find ourselves in one of the possibilities admitted by the distribution predicted by QM. We have no further explanation for which one it will be. The QM multiverse folks then expect us to be okay with this as the end of the explanation. But notice this is a choice to adopt something as axiomatic. We could have done that at other points in the history of physics but didn’t.

I agree that the multiverse is a bit over-hyped. However, some of the author's statements just rub me the wrong way:

Science cannot resolve the existence of either God or the multiverse, making agnosticism the only sensible position.

Science also can't refute me being a brain in the vat, or the universe having been created last thursday with the appearance of age. It's not only ok to commit to beliefs that cannot be proven scientifically, it is necessary.

Moreover, at a time when our world, the real world, faces serious problems, dwelling on multiverses strikes me as escapism—akin to billionaires fantasizing about colonizing Mars. Shouldn’t scientists do something more productive with their time?

Why stop at the natural sciences? Let's get rid of all the useless parts of mathematics - or art and music, for that matter...

If you restricted human endeavours to the utilitarian, the world would be poorer for it.

No, science isn't pure philosophy; the default position should be what we have evidence to support, that's what empiricism is all about. Many things can be logical that aren't true.