On Thu, Jan 9, 2014 at 11:53 AM, John Clark <johnkcl...@gmail.com> wrote:

> On Wed, Jan 8, 2014 at 1:42 PM, Bruno Marchal <marc...@ulb.ac.be>
>
> > to me, the Bell's inequality experimental violation is a quite strong
>> evidence for MW, that is QM-without collapse.
>>
>
> To me Bell's inequality experimental violation is a quite strong evidence
> that reality is not local or not realistic or not either. MWI is not local
> so it could be correct, and emotionally it is my favorite interpretation,
> but logically I must admit that it is not the only interpretation that
> could be correct.
>

Why do you say "MWI is not local"? Many physicists who advocate the MWI
would disagree, like David Deutsch:

http://arxiv.org/abs/1109.6223
http://arxiv.org/abs/quant-ph/9906007

This paper by Mark Rubin presents another defense of locality in the MWI:

http://arxiv.org/abs/quant-ph/0103079

In it he mentions some of the history of defenses of MWI locality:

"In the Everett interpretation the nonlocal notion of reduction of the
wavefunction is eliminated, suggesting that questions of the locality of
quantum mechanics might indeed be more easily addressed. On the other hand,
while wavefunctions do not suffer reduction in the Everett interpretation,
nonlocality nevertheless remains present in many accounts of this
formulation. In DeWitt’s (1970) often-quoted description, for example,
“every quantum transition taking place on every star, in every galaxy, in
every remote corner of the universe is splitting our local world on earth
into myriads of copies of itself.” Contrary to this viewpoint, others argue
(Page, 1982; Tipler, 1986, 2000; Albert and Loewer, 1988; Albert, 1992;
Vaidman, 1994, 1998, 1999; Price, 1995; Lockwood, 1996; Deutsch, 1996;
Deutsch and Hayden, 2000) that the Everett interpretation can in fact
resolve the apparent contradiction between locality and quantum mechanics.
In particular, Deutsch and Hayden (2000) apply the Everett interpretation
to quantum mechanics in the Heisenberg picture, and show that in EPRB
experiments,1 information regarding the correlations between systems is
encoded in the Heisenberg-picture operators corresponding to the
observables of the systems, and is carried from system to system and from
place to place in a local manner. The picture which emerges is not one of
measurement-type interactions “splitting the universe” but, rather,
producing copies of the observers and observed physical systems which have
interacted during the (local) measurement process (Tipler, 1986)."

Two more by Rubin:
http://arxiv.org/abs/quant-ph/0204024
http://arxiv.org/abs/0909.2673

Conceptually it's not that hard to see how the MWI offers a loophole in
Bell's proof--Bell assumed that each spin measurement yielded a single
definite outcome, but if you instead imagine that each spin measurement
causes the experimenter to split into copies who observe different outcomes
and aren't aware of one another, then the universe doesn't have to decide
which version of experimenter #1 gets matched up to which version of
experimenter #2 until there's been time for signals moving at the speed of
light to travel from each experimenter to someone in the middle who can be
aware of the results at both locations. If that isn't clear, in post #11 at
http://www.physicsforums.com/showthread.php?t=206291 I gave a sort of toy
model of how duplicating the experimenters at different locations and
matching them up later can allow for each of the matched pairs to observe
Bell inequality violations without any need for nonlocality.

Jesse




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