On 6/06/2016 3:18 pm, Brent Meeker wrote:
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.
That seems unexceptionable. Only measurement results as predicted by the
wave function can actually be observed. But this has little direct
bearing on the locality issue. The correlations could be local only if
the wave function for the separated observers were factorizable, and
this is not the case for the singlet wave function. Hence the
observation of non-local correlations.
Bruce
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