Re: explanation for teleportation/entanglement?

[Kevin de Laplante <***>]

Folks,

For an essay on teleportation and entanglement written by a respected
philosopher of physics, see

http://plato.stanford.edu/entries/qt-entangle/
>
> I personally am highly suspicious of whether quantum nonlocality is an
> actual phenomena. Most, if not all, experiments related to nonlocality
> measure 'spin', which, as I understand it, cannot uniquely distinguish a
> local correlation from a nonlocal correlation. Position/momentum
> measurements would be preferable, since they are complementary qualities,
> but are apparently more difficult to perform for these kinds of
experiments.
> Also, the Bell inequalities which purported to prove nonlocality have been
> called into question repeatedly over the years.

As a purely sociological observation, among philosophers of physics, the
consensus appears to be that the case for some form of nonlocality has only
grown over the years.  (See for example Michael Redhead's *Incompleteness,
Nonlocality and Realism* (1987) or Jeffrey Bub's *Interpreting the Quantum
World* (1997).  A more accessible source is Tim Maudlin's *Quantum
Non-Locality and Relativity* (2002); he's interested in working out the
implications of quantum nonlocality for Einstein's critique of the
absoluteness of simultaneity, but he's got an argument there for an
inference to nonlocal causal influences straight from the experimental
data.)  This conclusion comes not only from the experimental tests of the
Bell inequalities, but also formal analyses of the range of local hidden
variable theories that are consistent with the statistical predictions of
quantum mechanics.

I'm not sure what you mean by spin measurements being unable to distinguish
between local and nonlocal correlations.

I'm also not familiar with the sense in which the Bell inequalities have
come into question.  They're formal predictions of the statistical
distribution of experimental results, given certain realist assumptions
about quantum properties.  They are just one of a family of so-called
"no-go" theorems that have been generated over the past fourty years --
theorems that show that the predictions of quantum mechanics in conjunction
with the assumption of locality implies a contradiction (either statistical,
in the case of Bell's theorem, or algebraic, in the case of others).  One
can always question the experimental tests of the quantum predictions, but
it's worth noting that there's never been an unambiguous disconfirmation of
any prediction of quantum theory.

Philosophers have discussed the issue of to what extent we have, or can
have, an "explanation" of nonlocal quantum correlations.  All of the above
authors address the question in some form or anothere.  There's no concensus
on this issue, partly because it remains unclear what would, or should,
count as an explanation for the correlations.  The issue, ultimately, is
tied up with the broader issue of how to interpret the quantum formalism,
and there's no dearth of candidates on that topic.

Kevin


> > -----Original Message-----
> > From: ROSEN Forum [mailto:*** Behalf Of Dan
> > Fiscus
> > Sent: Monday, February 16, 2004 10:32 AM
> > To: ***
> > Subject: explanation for teleportation/entanglement?
> >
> >
> > John K. or Tim or anyone,
> >
> > What is the standard explanation for teleportation and
> > entanglement? I read a few web pages on these topics
> > at NASA and other websites, and they link the phenoms
> > to quantum computing, but I don't remember anyone
> > giving an explanation for "spooky action at a distance"
> > as Einstein called it.
> >
> > Seems like a possible arena in which some "space", medium
> > or communication of relations my help...
> >
> > Thanks for any info,
> >
> > Dan
>