Home › Forums › 2015 International Workshop on Quantum Foundations › Everett’s theory › Consistency of the Everett ‘world branching’ › Reply To: Consistency of the Everett ‘world branching’
After rereading the reference emphasized in your posts, I can re-emphasize my impression that, at certain point, I do agree with you.
The argument of my previous posts can be re-stated as follows: ‘world branching’ cannot be physically objective [except perhaps in a sense completely strange to me]. In your words: “Nothing ever ‘branches’ objectively in any definition.”.
[To me, this means that the phrases as ‘[dynamically] autonomous worlds’ etc are just a matter of, say, narrative aesthetics—which, according to your ‘moderating remarks’, we have agreed to avoid.]
Then, what might be new/relevant in our cited references?
Two things. First, I think that your position [that I find consistent] is not typical for the Everett MWI community; for this reason we had to go toward ‘emergent worlds’. To this end, our paper addressed the majority of the Everettians  and non-Everettians. Second, even in the context of our common view of non-objectivity of ‘world branching’, the findings referenced in my first post imply some fresh and probably interesting observations. Let me briefly focus on the latter.
Consider two bipartitions, 1+2 and A+B, of a closed composite system (the Universe) C; 1+2=C=A+B. Those bipartitions (the DISs from my previous letters) determine the pair of tensor-product-structures (TPSs) of the C’s Hilbert space. Now a universal state (in an instant of the universal time), some Psi [which has never branched], can be decomposed according to these two TPSs (DISs). Our point is that the closed composite system C (the Universe) hosts the mutually independent and autonomous, simultaneously dynamically evolving quasiclassical Worlds pertaining to the 1+2 and A+B DISs; needless to say, those worlds have nothing to do with ‘Everett worlds’. That is, instead of “Appearance of a Classical World in Quantum Theory”, we learn about “Appearance of THE Classical WORLDS in Quantum Theory”. Those non-branching/non-branched, equally (non)objective worlds [as in our QBM-model-analysis] may be mutually irreducible, i.e. not capable of defining any effective, emergent single quasiclassical world in the single Universe C. To the extent the measurement problem has been solved for the 1+2 world, it must have been equally solved also for the alternative A+B world, and vice versa.
Now the Everett world branching should be assumed for the both quasiclassical worlds, 1+2 and A+B, separately, and on the equal footing. In other words: instead of one Everett Multiverse, there are (at least) two mutually independent and irreducible Everett Multiverses. Certainly, this is a new and not yet explored picture of the quantum Universe (though initiated in http://arxiv.org/abs/1004.0148 ).
 Many Worlds? Everett, Quantum Theory, and Reality,
Eds. S. Saunders, J. Barrett, A. Kent, and D. Wallace, Oxford 2010.
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