On 06 Jun 2016, at 03:20, 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.
Come on. It was not an argument in logic, but in quantum mechanics. It
is a consequence of the linearity of both the evolution and the tensor
product. Once you define a world by a set closed for interaction (or
possible interaction), space-like separations orthogonalize the
realities. It just makes no sense to singularize Alice and Bob in one
world/relative-branch when they are entangled with the singlet state.
Separate branches arise only from decohered quantum interactions.
Not in the MWI. If you decide to fix some base, you can consider that
the branches are separated at the start. It is the differentiation
view of Deutsch, which works also for the universal machine's "many-
dreams" interpretation of arithmetic. The Y = ll rule. IN QM it is
just that
a(b + c) = ab + ac if a is an observer, he does not need to look at
the particle state b/c to be multiplied.
Of course, from the digital mechanist view, all this talk is
premature. It is just that I don't see any spooky action at a distance
in the MW.
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.
Somehow that would please a digital mechanist, as this would make the
physical even less real. But I am not convinced by your argument.
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.
I think we might disagree about what we mean by "physical world".
Space-like-separated world can interfere probabilistically without any
possible interactions in between. Quantum non separability can exist
between space-like separated worlds, but as we can hope, without any
need of physical interaction or causation between them.
Bruno
Bruce
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