On 20/04/2016 3:21 pm, smitra wrote:
On 20-04-2016 03:02, Bruce Kellett wrote:
On 20/04/2016 6:56 am, smitra wrote:
The mistake made is to invoke classical reasoning after the
measurements are made. If the choice for the orientation of the
polarizers were not made in advance, then Alice and Bob cannot have
said to have made any definite choices at all.
I think you need to learn something about decoherence , and the
emergence of the 'classical' from the 'quantum'. In the final
analysis, Alice and Bob meet to compare their results. By that stage,
their results, and their relative magnet orientations, are definite
and classical (FAPP if you wish). And that is the end result we have
to explain. All else is boondoggle.
Invoking FAPP is precisely where your argument goes wrong.
Actually, I think that in order for MWI to make any sense at all, the
separation of worlds has to be absolute, not just FAPP -- but that is
another argument.
While due to decoherence the macroscopic world looks classical, in
reality (assuming MWI) it not classical. This means that when Bob
meets with Alice that the settings Alice chose are still not
determined. It is only when Alice communicates to Bob what her
polarizer settings were
If Alice's setting are not determined, how can she communicate to Bob
what they were? Decoherence works for both Alice and Bob separately, and
long before they meet. Both have definite magnet settings and definite
results by then -- that is decoherence at work.
that Bob becomes localized in that particular sector of the multiverse
where this is now fixed.
So, decoherence ensures that long before A and B meet, there are only
ffour worlds in the general case, ++, +-, -+, and --. It is the fact
these these possibilities have different probabilities that is to be
explained, and you have not explained that.
If Bob were to be imagined being located in that particular branch
were Alice had made definite choices and had made definite
observations, then that implies the existence of an observable for Bob
that only acts on himself that will yield the exact details of what
Alice has done. So, Bob could in principle have psychic powers, the
information of what Alice did would already be present in his brain
before Alice communicates these to him!
No it doesn't.
Obviously, Bob's brain does not have any information about what Alice
did until the details are communicated to him. So, Bob's mind is
identical across the many branches where Alice and, due to
decoherence, the local environment is different. So, in the experiment
the effectively classical communication is not at all trivial, in the
MWI it is a crucial step localizing the observers in the multiverse as
where the measurements of the spins.
So classical communication has quantum effects? It is the classical
communication that 'causes' the EPR correlations? What about the effect
of the entangled spins -- that is purely quantum, and that gives rise to
the quantum correlations.
What is your reactions to Maudlin's comment
(https://arxiv.org/abs/1408.1826)
"Finally, there is one big idea. Bell showed that measurements made far
apart cannot regularly display correlations that violate his inequality
if the world is local. But this requires that the measurements have
results in order that there be the requisite correlations. What if no
“measurement” ever has a unique result at all; what if all the “possible
outcomes” occur? What would it even mean to say that in such a situation
there is some correlation among the “outcomes of these measurements”?
"This is, of course, the idea of the Many Worlds interpretation. It does
not refute Bell’s analysis, but rather moots it: in this picture,
phenomena in the physical world do not, after all, display correlations
between distant experiments that violate Bell’s inequality, somehow it
just seems that they do. Indeed, the world does not actually conform to
the predictions of quantum theory at all (in particular, the prediction
that these sorts of experiments have single unique outcomes, which
correspond to eigenvalues), it just seems that way. So Bell’s result
cannot get a grip on this theory.
"That does not prove that Many Worlds is local: it just shows that
Bell’s result does not prove that it isn’t local. In order to even
address the question of the locality of Many Worlds a tremendous amount
of interpretive work has to be done. This is not the place to attempt
such a task"
Bruce
Microsoft Word - What Bell Did revised.docx
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