On 31-08-2023 06:08, Bruce Kellett wrote:
On Thu, Aug 31, 2023 at 12:27 PM smitra <smi...@zonnet.nl> wrote:
There is no problem here because in practice MWI is nothing more
than
the usual QM formalism to compute the outcome of experiments where
you
then assume that the ensemble of all possible outcomes really
exists.
Locality then follows from the fact hat the dynamics of the theory
is
manifestly local. The Hamiltonian only includes local interactions
and
observers are part of this dynamics. Although observer are not
explicitly treated as being part of the wavefunction that describes
the
entire system, the assumption is that in principle, this is the
case. In
practice, one can then proceed according to the usual QM formalism.
That is all very well, but it is not a local account of violations of
the Bell inequalities. You merely claim that the local theory is such
an account, but you do not spell it out.
John has addressed this in a subsequent reply where he cites an old
reply giving the detailed account involving polarizers.
Thing is that in conventional QM we only have the dynamics only involves
the Schrödinger equation and collapse. The time evolution according to
the Schrödinger equation is manifestly local, while the collapse is the
only non-local part. So, any version of QM in which there is no collapse
is guaranteed to be local.
Another important thing to note here is that Bell's theorem only applies
to hidden variable theories, it does not apply to QM in general. The MWI
is not a hidden variables theory, so Bell's theorem has nothing
whatsoever to say about this.
We have had this discussion before, and you couldn't give the detailed
local account then either.
You disputed the well established fact that all known interactions are
local. You would not take a formal answer like
psi(x, t) = Exp(-i H/hbar t) psi(x,0)
where H is the a local Hamiltonian that describes the dynamics for an
answer. You wanted me two explicitly write out H for a Bell-type
experiment for H a manifestly local Hamiltonian, and then to compute the
time evolution. Me not doing that was your argument that something
non-local was going on here.
Bell'e theorem applies in Everettian
quantum mechanics in exactly the same way as it applies in one-world
accounts. Bell's theorem proves that the effect is non-local, so no
local account is possible in any interpretation of QM.
Bell's theorem only applies to hidden variable theories, MWI is not a
hidden variables theory. Bell's theorem does not even prove that
Bell-type correlations are non-local in one-world interpretations of QM.
Until that time one postulates hidden variables, Bell's theorem has
nothing whatsoever to say about this.
Saibal
John points out the thought experiments by Deutsch makes it clear
that
the usual QM formalism will not work in certain cases, that will
then
falsify the ad hoc collapse postulate. If you then believe that MWI
cannot account for violation of Bell's inequalities while ordinary
QM
can, then that begs the question of how removing the FAPP
unobservable
sectors where all other outcomes are realized, could matter at all.
The other sectors are not just FAPP unoservable, they are not
observable in principle. How could the presence of unobservable fairy
tales affect anything at all? The standard account of violations of
the Bell inequalities in quantum mechanics relies on the notion of
non-locality. And since the effect is non-local, no local account is
possible.
Bruce
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