I don’t think that people in different inertial reference frames have to agree about how many worlds there are, indeed I don’t even think people in the same inertial reference frame have to agree about how many worlds there are.
At this point I have nothing to say, because there’s no coherent concept of ‘world’ left to debate.
I think one version is “if the complex amplitude for me having a certain brain state approaches zero, then the probability that I will find myself experiencing having that brain state also approaches zero”
This could become a version of ‘many-minds interpretation’. But now you need to make ‘mind’ a rigorous concept. There has to be something exact in the ontology that corresponds to the specificity of what we see! - whether it’s a whole ‘world’, or just an ‘observer experience’. If everything other than the universal wavefunction is fuzzy and vague and a matter of convention, you no longer have a theory corresponding to observed reality.
Why can’t something be both ontologically primitive and reference frame dependent? Like velocity, to take an everyday example
The 4-velocity (considered as an invariant geometric object, rather than in terms of covariant components) is the fundamental entity.
there’s no coherent concept of ‘world’ left to debate.
Good! Maybe we’re on the same page there. “World” is not part of the theory and is not a well-defined concept, in my opinion.
now you need to make ‘mind’ a rigorous concept
Hmm, I guess I would propose something like “the complete history of exactly which neurons in a brain fire at which times, to 1μs accuracy, is a mind, for present purposes”. Then I would argue that different “minds” don’t exhibit measurable quantum interference with each other, or we can say “different minds are in different worlds / branches” as a casual shorthand for that, if we want. And there is a well-defined (albeit complicated) way to project the universal wavefunction into the subspace of one “mind”, in order to calculate its quantum amplitude, and then you can apply the Born rule for the indexical calculation of how likely you are to find yourself in that mind. Something like that, I guess. I haven’t thought it through very carefully, I just think something vaguely like that could work, with a bit more effort to iron out the details. I’m not sure what’s in the literature, maybe there’s a better approach...
At this point I have nothing to say, because there’s no coherent concept of ‘world’ left to debate.
This could become a version of ‘many-minds interpretation’. But now you need to make ‘mind’ a rigorous concept. There has to be something exact in the ontology that corresponds to the specificity of what we see! - whether it’s a whole ‘world’, or just an ‘observer experience’. If everything other than the universal wavefunction is fuzzy and vague and a matter of convention, you no longer have a theory corresponding to observed reality.
The 4-velocity (considered as an invariant geometric object, rather than in terms of covariant components) is the fundamental entity.
Good! Maybe we’re on the same page there. “World” is not part of the theory and is not a well-defined concept, in my opinion.
Hmm, I guess I would propose something like “the complete history of exactly which neurons in a brain fire at which times, to 1μs accuracy, is a mind, for present purposes”. Then I would argue that different “minds” don’t exhibit measurable quantum interference with each other, or we can say “different minds are in different worlds / branches” as a casual shorthand for that, if we want. And there is a well-defined (albeit complicated) way to project the universal wavefunction into the subspace of one “mind”, in order to calculate its quantum amplitude, and then you can apply the Born rule for the indexical calculation of how likely you are to find yourself in that mind. Something like that, I guess. I haven’t thought it through very carefully, I just think something vaguely like that could work, with a bit more effort to iron out the details. I’m not sure what’s in the literature, maybe there’s a better approach...