On Fri, Nov 22, 2024 at 3:23 PM smitra <[email protected]> wrote:

>
> Bell's theorem says that no local deterministic hidden variable theory
> can explain the correlations that QM predicts. So, Bell's theorem
> doesn't say anything about QM itself, it says something about hidden
> variable theories that seek to explain the correlations observed in QM
> experiments. So, you modify QM and assume that QM is explained by a
> classical deterministic hidden variable theory and then you obliged to
> take non-locality on board, or else your hidden variable theory will
> fail to reproduce at least some of the correlations predicted by QM.
>
> Nothing in here implies that QM is non-local.
>

The results of Bell's theorem imply exactly that. Bell assumes that the
theory is local, and shows that the QM results violate particular
inequalities. The theorem is NOT about non-local theories since Bell does
not assume a non-local theory.


> Everett introduces the splits as an effective description appropriate
> for describing macroscopic observers. He introduces density matrices so
> it should be clear that this isnt an exact qjuantum emchancial
> description and it will certainly fail to correctly describe subtle
> effects due to entanglement.
>

Density matrices are not an approximate form of QM.

There are no independent branches.
>

That is what decoherence is supposed to give you.


> > That is not the case. Everettian quantum mechanics says that they both
> > split on to two branches, and there is no clear way in the formalism
> > to see how the branches for the two individuals are related. In any
> > model, in which both outcomes are necessarily realized for every
> > measurement, there is no way to relate the outcomes.
> >
>
> Everettian QM says that this is what effectively happens, but it's
> obviously not an exact description and will fail to take into account
> subtle effects due to entanglement.
>

In other words, Everettian QM, or many-worlds, is not able to give an
account of the correlations. You are saying that that is because it is not
an exact theory. This is a pretty extreme way of getting out of the
difficulty that I have pointed out. If Everett is not just a version of
exact QM, it is of no use for anything. My claim is that it cannot
reproduce the observed correlations, therefore it is not a version of
standard QM, and is of no use for anything.

Bruce

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