On 07 Jun 2016, at 20:06, Brent Meeker wrote:
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.
See Saibal Mitra's answer.
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).
Then arithmetic is even more non-local. it includes all the dreams of
all the dreamable universes. And if the number zero disappears, all
numbers disappears at once. That makes non-locality into a metaphor.
The point was that some people, despite understanding that we cannot
do quicker than light signaling with an EPR channel, still believe
that the violation of Bell's inequality show that there is still a
physical influence at a distance responsible for that violation. And
that *must* be the case, if there is only one physical universe. The
point is that in the MWI, the violation of Bell's inequality does no
more bring any physical influence at a distance. They are
phenomenologically explained by the "subjective probability" from the
view from inside the many terms available in the universal wave.
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.
OK.
Bruno
Brent
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