On 6/5/2016 6:20 PM, Bruce Kellett wrote:
On 5/06/2016 9:44 pm, Bruno Marchal wrote:
On 05 Jun 2016, at 08:39, Bruce Kellett wrote:
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,
But that exists: the Schroedinger wave equation.
As has been pointed out, that itself refers to two separated
locations, so is intrinsically non-local.
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.
But it makes no sense to say that particles 1 and 2, when separated,
belongs to the same branches. Bell can say that because it assumes
only one branch (so to speak) in which case there is a mysterious
spooky action at a distance. But if they are space-like separated, we
get the non-locality appearances only for those Alice and Bob wich
will be able to meet at some points, and the math shows that this
linearly and locally implied such appearances, despite the wave
evolved locally at all time in the phase space. There should be no
problem as you seem to accept the definition of worlds by set of
events/objects close for interaction. If Alice and Bob are space like
separated, they just cannot belong to the same woirld: it makes no
sense.
That claim makes no sense. You are making an elementary logical
blunder -- Separate worlds do not interact, objects with spacelike
separation do not interact, therefore spacelike separation implies
separate worlds. That argument is equivalent to: all As are Bs,
therefore this B is an A.
Separate branches arise only from decohered quantum interactions.
Preparing a singlet state and sending the particles off in separate
directions does not create separate worlds -- particles 1 and 2 are in
the same world until the spin measurements are made. Then multiple
worlds are generated, which eventually pair up so that worlds in which
correlations can be defined appear. For the singlet state under
consideration, these correlations violate the Bell inequalities in all
branches. The wave function evolves locally and linearly in
configuration space -- that is seen as non-locality in physical space.
There is no "outside view" of configurations space, so the
non-locality is intrinsic to the "bird" view of the wave function in
physical space, just as it is to the "frog" view from within a
particular branch. No local account of this physics exists.
Bruce
I think what Bruno is arguing is that decoherence is a local process, so
that although Bob and Alice's results are locally decohered, so they can
observe and record them, that only the results in which Alice and Bob's
measurements are as predicted by the wave function will be
non-orthogonal and can interact in the future where their light cones
overlap.
Brent
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