On 15/11/2017 12:44 am, smitra wrote:
On 14-11-2017 09:23, Bruce Kellett wrote:
On 14/11/2017 5:51 pm, smitra wrote:
Within this model, Bob does not decohere until that time he is told
what Alice has found.
That is simply not true. Decoherence is not subject to a particular
person's knowledge. When Alice and Bob are next to each other, they
are jointly entangled with a particular result.
I think that this needs to be discussed in more detail. Decoherence
does not cause a superposition to get reduced to either one of the two
possible outcomes. Given what Bob knows, he cannot locate himself in
either sector. If this were not true then given everything Bob is
aware of, he could get to better odds than 50-50 for guessing the
spin. But that implies information transfer to something his brain can
access.
One of the strongest arguments for MWI was that it eliminates the
concept of a conscious observer from the interpretation of quantum
mechanics. This is seen to be particularly important in quantum
cosmology, but it is relevant everywhere. You seem to be wanting to turn
the clock back and make consciousness, and conscious knowledge of
events, central to your interpretation.
The branches form under decoherence for every quantum event. Whether you
know about it or not, or know the result of the experiment, is
irrelevant. Schrödinger's cat is definitely dead in one branch, and
definitely alive in the other, whether you open the box or not.
That is MWI in standard QM. If you want to propose another theory in
which consciousness is central, then that is up to you. But you have to
show that your alternative theory reproduces all the observed results of
quantum mechanics before you can say that you are right and everyone
else is wrong.
So, it boils down to decoherence acting on a microscopic degrees of
freedom, while brains and computers must be robust systems that would
not function well if they would be affected by such effects. Thermal
noise would make computing impossible.
If you have robust bitstrings that are only going to be affected by
information present in the environment at a sufficiently coarse
grained level, then that bitstring is never going to pick up any
information about Alice's result other than via direct communication
or any leakage of information e.g. if Bob is in to cold reading, or if
there are other correlations at the macroscopic level that Bob can
exploit.
So, we have two decohered parallel worlds, but Bob is mentally
identical in the two sectors despite decoherence having split his
body. As long as he cannot access that information, he is the same
person in both sectors.
And the rock on the ground outside the laboratory is the same in both
decohered worlds. That is irrelevant to the existence of such worlds in
MWI. As I said, Bob's knowledge or lack of knowledge is irrelevant to
the fact that locality implies there are worlds in which angular
momentum is not conserved in the scenario that I have outlined.
Bruce
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