Hal Finney wrote:

> Joao Leao writes:
> > I don't believe that there is ANY question that QM is non-local! This is
> > the outcome of 30 years of experiments with entangled multiparticle
> > states.  I also think that non-locality is pretty well defined in this
> > context (the way Bell put it) and we know what implications it has
> > in the laboratory and elsewhere.
>
> Philosophically the real question is not why QM is non-local, because
> there is no a priori reason the universe should be local.  The question
> is why the universe is so nearly local; why it appears to be local
> for all practical purposes, if it is built on non-local underpinnings;
> why the non-local connections are unable to affect causality.

I agree up to the last point. It is quite clear why the non-locality does
not have nastier bearing on causal connections: the reason is that the
statistical nature of quantum mechanical predictions wipes out most
of the correlations that could carry supraluminal influences. The best
descriptions of this effect are due to Abner Shimony, under his own
characterization of "Passion-at-a-distance", (vs. Action).

On the other hand we don't know whether other aspects of, say, early universe

cosmology were not influenced by the non-locality of, say, Quantum Gravity...

> In the all universe hypothesis, all theories of physics are instantiated.
> Only in some universes will life and consciousness evolve.  Perhaps it is
> plausible that locality, or something like it, is a necessary precondition
> for the kinds of mechanisms that allow computation.  And we believe that
> computation is necessary for consciousness.

Correction: you believe the last item! I am entirely unsure of it. Your
speculation
is quite interesting, though. I would spell it a little different
though: Maybe
locality or something like it is a necessary ingredient for the one or more
of
the mechanisms that allow anthropic selection...

> So it is reasonable that the universe will be at least superficially
> or approximately local.  It still seems surprising that this property
> can be built on a non-local foundation, with the non-localities somehow
> cancelling themselves out or becoming insignificant at certain scales.

It could also be that a lot of the "dark energy" that fills the universe and
is
fully non-localized (or localized everywhere if you prefer) is a leftover of
less local days...

>
> I suspect that it will turn out that this paradoxical physics is actually
> one of the simplest models that both provides for a sufficiently complex
> and varied universe to allow spontaneous evolution; and a sufficiently
> stable and local one that computation can exist.  QM gives us ~100 kinds
> of atoms that can form an infinite variety of molecules; gravity gives
> us stars that synthesize sufficient quantities of a substantial variety
> of these atoms, and planets which concentrate the intermediately sized
> atoms together.  It might well be difficult to reproduce such combinations
> of properties if we had different physical laws.

Right! That is basically my point above.

>
>
> Hal Finney

-Joao

--

Joao Pedro Leao  :::  [EMAIL PROTECTED]
Harvard-Smithsonian Center for Astrophysics
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