For a long time, quantum mechanics could be treated as a black box. You had an atomic nucleus sitting their quietly, not really deviating from your classical intuition, and then some quantum magic would occur, and now you have several decay products flying away. The remoteness of the quantum effects themselves is what has enabled physicists to get away for so long using quantum mechanics without really understanding it. (Thereby enabling such monstrosities as the “Copenhagen interpretation” of quantum mechanics, and its unholy offspring “shut up and calculate.”) ...No, the Copenhagen interpretation. It is a lot more coherent than the Many-worlds interpretation (MWI).
The objection to Copenhagen is just that it’s completely incoherent. It imagines a distinct “classical” realm, doesn’t tell you what’s in that realm and what’s truly quantum, doesn’t explain when wave functions collapse, etc. The Born Rule isn’t “explained” at all — it’s just postulated. And the Uncertainty Principle is exactly the same in MWI as it is in Copenhagen, so I’m not sure what the distinction is there.
MWI has its own issues, certainly, as do all other known versions of QM. But at least it’s well-defined, whereas Copenhagen is kind of a joke.
Copenhagen does not postulate the Born rule, but at least it explains the probabilities. The MWI does not explain probabilities at all, and has no experimental evidence for it.
The core of the problem is that Niels Bohr was a positivist while Carroll subscribes to this view:
The basic scientific assumption is that there is exists a complete and coherent description of how the world works. ... Given what we know about the universe, there seems to be no reason to invoke God as part of this description.This view lead Carroll to believe in zillions of unobesrvable alternate universes and all sorts of other bizarre hypotheses, but he refuses to accept a scientific explanation that he regards as incomplete.
There is no reason to accept MWI.
A recent essay asks, Has Science Established that the Cosmos is Physically Comprehensible? The answer is no.
Science is all about testing hypotheses, and not leaping to unverifiable conclusions just because you pursue a more complete and coherent description of how the world works. I say Carroll has a very wrong idea of science. That is why he subscribes to string theory and other nonsense.