On 6/7/2016 1:57 AM, Bruno Marchal wrote:
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.
I don't think that's true. When part of the necessary information is
carried away at the speed of light it's impossible (according to current
theory) to erase it.
In practice that is quickly impossible, but reason of BIG numbers, but
the wave, or the unitary evolution, is always reversible.
That's slightly different. It assumes there is a "wave function of the
multiverse" which is highly non-local (it includes other universes).
Since everything is inside it, there's no way to arrange its reversal.
To say it's reversible just means putting -t for t and -p for p is still
a solution.
Brent
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