On 07 Jun 2016, at 04:24, Bruce Kellett wrote:
On 7/06/2016 2:00 am, Bruno Marchal wrote:
On 06 Jun 2016, at 03:20, Bruce Kellett wrote:
On 5/06/2016 9:44 pm, Bruno Marchal wrote:
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.
Spacelike separations do not orthogonalize anything. A world is
closed for interaction, but that is not the best defining
characteristic of a world. In MWI, worlds are produced by
decoherence following an interaction (be it a measurement or some
other interaction). Decoherence into the environment inevitably
results in the production of soft IR photons that escape from the
region. These photons are not recoverable, so once decoherence has
progressed to reasonable degree, the situation is not reversible:
the IR photons can never be retrieved and put back into the
interaction region, so once the possibilities have decohered, the
process is irreversible in principle, not just FAPP. It is this
irreversibility that precludes further interference or interaction
between the worlds. So irreversibility is the defining
characteristic of separate worlds, not just lack of interaction.
Given this, Alice and Bob separate into different branches/worlds
only following an interaction -- only when they measure their part
of the singlet state. It makes no sense to claim that this happens
before such interaction with the state because before any
measurement has been made, the situation is completely reversible
and there is only one world.
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.
That is just playing with words, and Deutsch's approach reduces the
concept of "separate worlds" to meaninglessness -- the concept
becomes so fluid as to become useless. One is very much better
advised to limit the idea of separate worlds to the irreversibility
following a decohered interaction.
That does not exist. In principle quantum erasure is always possible.
In practice that is quickly impossible, but reason of BIG numbers, but
the wave, or the unitary evolution, is always reversible.
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.
My logic is secure. You haven't refuted my basic arguments as yet.
I have and others too.
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.
That sounds like you actually do accept the standard concept of non-
locality in quantum mechanics! Spacelike separated particles can
interfere probabilistically without any possible interactions
(mechanistic force-field exchanges) between them: that is precisely
what is meant by non-locality in this context.
I think you have been too tied up with a mechanistic interpretation
of non-locality -- you appear to think that it necessarily involves
FTL exchange of some particle or other mechanistic influence. But
this is not necessarily the case -- we don't actually postulate non-
local hidden variables of this type because that would represent an
attempt to give a "local" account of "non-locality". All that is
involved is that the singlet state is a unity, even though the
entangled particles might be widely separated. This is reflected in
the fact that the wave function itself is intrinsically non-local --
it is local and deterministic only in configuration space, not in 3-
dimensional physical space.
You are the one who seem to accept that such a non-locality is not
physical, but due to the internal relative FPI. If you agree there is
no FTL action in any physical realities, I guess we agree, then.
Bruno
Bruce
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