>The lesson is just that you can’t define frequencies or proportions in infinite sets that lack natural orderings. The number line is the exception, not the rule.

In the context of multiverses, there are natural ways of ordering them. In MWI for example, you could consider universes that first differ from ours by a more recent branching event to be "closer" than ones that branched further back. Then whatever density you want can be defined in the set of universes that diverged later than time t, as t is taken to zero.

Frequency in a multiverse shouldn't really be any less intuitive than a frequency measurement in our single universe. If space is infinite, then it also contains infinite planets. But it is still obvious that most of space is empty.

(Just like it is obvious that infinite coin flips should be time-ordered when referring to their "frequency".)

To start with a little nitpick:

>Joy says that “most” universes are ones where life did not evolve, but you cannot have “most” of infinity.

You can have "most" of infinity. For example, most whole numbers are not prime, and both of those sets are (the same size of) infinite. Still, the ratio of the number of primes to the number of non-primes below a certain value is small (and tends to zero as that value tends to infinity).

Personally, I don't think Everything attempts to comment on Many Worlds in any meaningful way, because its multiverse is fundamentally unlike the one Many Worlds would predict. As you highlight, seemingly every universe in Everything contains some sort of version of the same characters, and they all have the same personalities deep down. For "every you is you" to be a meaningful statement means ruling out the vast majority of Many World universes that are populated by people a bit like you, but a bit like someone else. (And requires inserting a fundamental idea of a "person" that isn't emergent from particles.)

Fundamentally, Everything is a story about characters, not metaphysics, using wacky soft sci-fi as a backdrop. It aims to convey a message about love and relationships relevant to our single universe.

To address this:

>To me, I find the many-worlds interpretation is a way of ridding ourselves of the uncomfortable idea that the laws of physics are not deterministic. Having no answer to explain why a superposition reduces to one state and not another is disconcerting. Saying that a superposition does reduce to another state, except it occurs in a dual universe we cannot currently observe, is an easy way to remove the question altogether.

I think your take on Many Worlds is a little off. The interpretation is actually the idea that superpositions are never reduced, which naturally leads to a "multiverse". One is not invented arbitrarily. In terms of postulates it's actually the simplest way of stating quantum mechanics, because interpretations that make the wave function "collapse" require an extra rule that is mathematically ugly, not clearly defined, and doesn't even change the experimental results (to any extent that is currently measurable).

>[In MWI] We are just one sample in an infinite list of possibilities, so there is no meaning to why we happen to be in this state.

On the contrary, there is just as much or as little meaning (or "free will") in Many Worlds as in any single-universe model. (To circle back to the start:) Yes, there may be an infinite number of "you", but most of them will make the same sort of choices, derived from their biology and experiences, as you do. Only in a vanishingly small proportion of worlds will some freak quantum event have you acting counter to your own history.