On 09 May 2016, at 04:12, Bruce Kellett wrote:
On 9/05/2016 1:39 am, Bruno Marchal wrote:
Thanks Scerir. Very interesting.
On 08 May 2016, at 09:58, 'scerir' via Everything List wrote:
https://arxiv.org/abs/1501.03521
'Bell on Bell's theorem: The changing face of nonlocality'
Authors: Harvey R. Brown, Christopher G. Timpson
there are several interesting points here
ch. 9 - Locality in the Everett picture
ch. 9.1 EPR and Bell correlations in the Everettian setting
Nice.
I think that what we are trying to explain to Bruce is well summed
up in their section 9.1.2 (the Everett description of the singlet
state, case of non-align polarizer).
I have already discussed this in my reply to Saibal. The basic point
I would make again is that the splitting of the universal wave
function into separate "worlds" is an interpretive gloss that does
not actually alter anything in the theory.
As long as you don't separate them too much, as the wave describe a
pure state remaining pure all the time, the "world" are the
phenomenological views as seen by each doppelgangers involved. If not,
you lose the possible interferences in principle possible by quantum
memory erasure.
Furthermore, 'who knows what about whatever' is also an irrelevance
as far as the universal wave function is concerned. If you are going
to work in the many worlds paradigm, then everything ultimately
stems from the unitary evolution of the universal wave function --
all else is just interpretive gloss, of no fundamental significance.
This is the case for the discussion in section 9.1.2 of the paper by
Brown and Timpson. Their equation (9) contains all the relevant
results that set the universal wave function -- the additional third
measurement (or measurement-like interaction) leading to equation
(10) is, therefore, irrelevant. All that happens in eq. (10) is an
exchange of information -- but it is an exchange of information that
is already present in the universal wave function, no new
information is created at this point. Just like opening the box on
Schrödinger's cat, which is either alive or dead long before,
looking changes nothing. Eq. (10) is, similarly, just an
interpretive gloss of no fundamental significance. The important
point here is that everything is set in the universal wave function
before Alice and Bob meet. The relative angle of the respective
polarizers is set in the wave function long before the light cones
of Alice and Bob overlap, so that relative angle is determined non-
locally.
The universal wave function is not a local object --
I am not sure what does this mean. The SWE is linear which is a case
of extreme locality I would say.
the unitary evolution does not have any implicit notion of locality.
?
Locality is a human convention, and the universal wave function is
under no compulsion to take any notice of human conventions or
preferences.
The question is only: does Alice's measurement change something
instantaneously and physically at a distance? Obviously, this is not a
question of convention.
I see clearly that such action at a distance has to occur in all QM
with a physical collapse assumption, as Einstein saw already in 1927
at the Solvay Congress, and EPR-BELL-Bohm made testable. But if the
collapse is a first person view entangled with the particle in the
singlet state, I don't see any action at a distance occurring, even if
it looks like that for the person involved. I don't get your critic
of Brown and Timpson (9.1.2 in https://arxiv.org/abs/1501.03521 ).
Brown and Simpson are close to my feeling (say), which is that Bell's
inequality violation testing does not test locality, but the MWI itself.
Bruno
Bruce
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