Re: HARDY and Mathematical versus Physical Reality

From: Joao Leao <>
Date: Wed, 29 Oct 2003 10:24:33 -0500

scerir wrote:

> Bruno Marchal:
> > In Bohm's theory there is no collapse of the wave.
> No collapse of the wave-function takes place upon measurement.
> One must obtain, nevertheless, the "reduced" wave-function of the
> system. Once a specific result has been obtained in a measurement,
> only that term (of the global, universal superposition) counts.
> This is a sort of "effective" or, better, "pragmatic" collapse.

This not quite the case. In the Bohmian interpretation the "collapse"
is, in fact, determined by the non-local quantum potential pretty
much as the outcome of a critical phase transition which suppresses
all the branches of the superposition but the one that matches the
measured outcome. This is indeed "effective" but hardly pragramatic.

> > So it is indeed as deterministic as Everett formulation of QM.
> Are they both non-local, at least in principle? I'm asking this
> because, usually, I read that MWI is local, and that seems to me
> very very strange, just because of the "split". I also read that
> the Bohmian theory is non-local (though this original non-locality
> is almost, but not entirely, suppressed by the general quantum
> "equilibrium" condition).

The Bohmian Int. (in the post-51 version) is decidedly non-local and
amounts to an alternative (hidden variable) theory with the same
phenomenology as QM. The Everett Interpretation is just as non-local
as QM with the peculiar distinction that it accommodates non-locality
in its peculiar way, where the unconnected "locales" are made relative
to the different branches of the wave function.

It should perhaps be pointed out that a good number of advocates of
Everett (David Albert anong them) are keen in not using the
"Many-Worlds" ontology and insist on Everett's original "Relative
Interpretation of the Wave Function" which makes a lot more sense
in my opinion, as an interpretation of entanglement.

> Regards,
> s.



Joao Pedro Leao  :::
Harvard-Smithsonian Center for Astrophysics
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Received on Wed Oct 29 2003 - 10:26:32 PST

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