[cma]

> Also, the measurement problem is only a problem of the Copenhagen interpretation. It doesn't exist in the many worlds interpretation.

Doesn't many worlds require branching into numbers of branches that would in some cases be irrational numbers? And you have to have some kind of index on the branch to make some of them physically distinguishable enough to still maintain probability. If equivalent branches are in there it's hard to explain how a 75%/25% branch would be distinguishable as a probability to an observer without some kind of extra index like information that has them land in the 75% more often. ( https://en.wikipedia.org/wiki/Many-worlds_interpretation#Pro...)

> That has nothing to do with the measurement problem.

He refered to I think the Diósi-Penrose model, where it would:

https://en.wikipedia.org/wiki/Di%C3%B3si%E2%80%93Penrose_mod...

[GoblinSlayer]

Born rule doesn't need index, it needs statistics of a sequence of measurements, then statistics is rationalized as a result of a stochastic process.

[cma]

In that link that says that was Everett's initial attempt to solve but it has been debated and extended. I only have a podcast understanding of it, and have heard the popular proponents of many worlds like Sean Carrol say that is the biggest problem that needs more development, he has his own self-locating thing but there are many other approaches.

But on the other point, how can there be an irrational number of branches to sample these statistics from? I just can't visualize the type of structure that would have that but I'm sure it is more subtle. I've heard the branches aren't branches under MWI but instead are something more continuous and I guess I don't understand it at that point.

[GoblinSlayer]

Wikipdeia references https://arxiv.org/abs/0905.0624 and first thing I noticed in section IV the author incorrectly calculates copenhagen prediction (because probabilities are counterintuitive), but correctly everettian prediction (because marginal outcomes are obvious there) and claims this discrepancy disproves MWI, he conveniently forgets about empirical equivalence of interpretations, so that it's easier to make an error and get different predictions. Then makes incorrect claim about MWI. Any given observer will probably observe confirmation of Born rule due to the law of large numbers.

[GoblinSlayer]

The structure of superposition is given by solution of the Schrodinger equation. It's often continuous, e.g. electron's s orbital in atom is a continuum of coordinate eigenstates. In this case a discrete sum is replaced with an integral and Born rule becomes a function on this continuum, but a discrete case can be easier to understand, so I recommend to start with that. The proof follows the law of large numbers https://en.wikipedia.org/wiki/Law_of_large_numbers