Bruno Marchal wrote:
On 01 Nov 2014, at 23:55, Bruce Kellett wrote:
Bruno Marchal wrote:
This I find hard to buy. I like the MW notably because it restores
determinacy and locality in the 3p big "physical" picture. In the MW
theory, we can explain the violation of Bells inequality, without
using anything non local, or instantaneous. I took Aspect experiment
as a confirmation of the MW idea.
This is not so obvious. MWI struggles to explain the violations of
Bell's inequality. It can do so only in a very strained way, and that
at the price of counterfactual definiteness. It seems to me that this
price might be too high.
One argument for this is perhaps too simple: the SWE is local and linear
all by itself, so in the Hilbert space of the "universal wave", there is
no "action at a distance". This can be used, I think, to reduce the
question of counterfactual definiteness to the question of the
definiteness of the worlds themselves, and this is not yet clear to me.
Eventually we have to find the MW view of the Kochen & Specker theorem,
well, you may be right that this is not obvious.
I will try to do this by myself, and get back if I succeed. I am
currently explaining (trying to explain to be sure) to a group of
students how to "reduce" all weirdness of quantum mechanics to only one:
"the parallel universes", but sometimes I do have a problem with the
very notion of "universe", which is rarely well defined, if define at
all. I have always the need to take into account that we have a
brain-base prejudice on the picture of the "whole", and I think that
counterfactual definiteness might be in that category.
Coming from computationalism, with the mind-body problem as motivation,
I am somehow prepared to stop believing in "universe". Coherent sheaf of
dreams, or first person plural sharable computations, like the one with
computationalism, does not have to converge on well defined "universe(s)
independent of us", so I am not sure if the abandon of counterfactual
definiteness would be a so high price to me. Eventually it might even be
welcome, as computationalism might also forbid it, so ... well, I don't
know.
If I succeed in explaining (to me and my students) Bell's inequality in
a purely local way (with many worlds, or better many relative states
(capable of perhaps NOT defining worlds, but only coherent sharable
experience), I will try to sum up the idea here.
Have you read Deutsch and Hayden paper on this? I know that is well
debated, but I have not yet found the time to read/understand the critics.
I had not read this paper, but I do not find the proposal convincing.
Deutsch seems merely to point to the fact that one observes the
correlation in a Bell-type experiment only after the classical transfer
of information, just as in any other quantum-teleportation situation.
This might be true, but it is not really an explanation of the correlations.
Bruce
Bruno
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