On 6/06/2016 7:39 am, Brent Meeker wrote:
On 6/4/2016 11:39 PM, Bruce Kellett wrote:
I think you are trying to move the goal posts here.... The original
argument about non-locality in MWI was the contention by people like
Price, Tipler, Brown, and Christian that Bell made certain
assumptions that were not true in the Everetttian approach. Their
conclusion was that his theorem was not applicable to the MWI,
rendering the argument that local hidden variables were ruled out
inapplicable in that case. (Though Joy Christian tries to go further
and argues that Bell made a trivial mistake that rendered his
'theorem' invalid in all interpretations.) I have rebutted the
various claims of these papers in other posts: Bell does not depend
on such ill-defined things as counterfactual definiteness, and
certainly does not assume that experiments have only single outcomes.
My conclusion is that Bell's theorem is valid universally -- merely
changing the interpretation does not alter that, and thus
non-locality has been shown to be intrinsic to quantum mechanics.
You are now attempting to change the argument: you appear now to
accept that individual experimenters will see the quantum world as
non-local, but that this is merely an observer-dependent effect,
arising from self-location in the multiverse: another instance of
FPI. I think that you have to do a bit more work on this changed
approach to non-locality: I think you will find that the argument
does not work like the FPI account of apparent indeterminism in a
deterministic universe. Bell's theorem applies to every set of
correlations obtained by experimenters in every branch of the
universal wave function -- there is no 'external' perspective from
which Bell' s theorem does not apply. If there were, there would have
to be a local account available from the 'bird' perspective, and
there is no such account. If you claim that there is, then the onus
is on you to produce that account. The singlet state
|psi> = (|+>|-> - |->|+>)/sqrt(2)
is the wave function from the 'bird' perspective, and particles 1 and
2 are separated in the 'bird' perspective as much as in any 'frog'
perspective. Going outside the perspective of the individual
experimenters does not actually gain you anything in this instance.
I don't think anyone (except Joy Christian) argues that Bell's theorem
does not apply in MWI - I certainly don't think that.
That was the central argument that sought to establish that MWI was
local -- MWIers claim that Bell assumed something in his proof that
does not hold in MWI, so the theorem does not apply to MWI. The
conclusion they want to draw is that since the Bell inequalities are
inapplicable in MWI, observation of violations of the inequalities can
not be interpreted as evidence of non-locality. I think that argument is
dead -- Bell did not assume counterfactual definiteness, and even if he
did, that would not have affected his proof. Also, he did not need to
assume that experiments had only one result -- the theorem applies to
correlations between decohered experimental results, and thus applies
equally to all branches of the wave function (if you want to think in
MWI terms).
But I think that "which universe" is a non-local hidden variable in
MWI and so explains the correlation without violating Bell's theorem.
I have difficulty in working out what this means. The quantum
correlations do not violate Bell's theorem, Bell's theorem simply states
that the quantum correlations cannot be explained by any local
interactions, visible or hidden. The question of "which universe" in the
many worlds approach might be considered to be a non-local hidden
variable, but that does not take you any distance towards an explanation
of the correlations. As you point out elsewhere, all that is required is
the wave function itself -- the wave function predicts the observed
correlations, and because it refers to both of the separated particles
simultaneously, it is, in itself, non-local. No further explanation is
required.
Bruce
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