From: Amara Graps (Amara.Graps@mpi-hd.mpg.de)
Date: Thu Sep 14 2000 - 06:41:17 MDT
Hi extropes,
I saw this thread on sci.physics.research and since this is a topic
often discussed before, thought I'd pass it on. I think that we've
even discussed these papers too.
(Is it OK, to pass usenet threads to this mailing list?)
Amara
==================================================================
From: gregegan@netspace.zebra.net.au (Greg Egan)
Newsgroups: sci.physics.research
Subject: Re: Faster than light
Date: 11 Sep 2000 13:14:18 GMT
There's an interesting paper by David Deutsch at:
<http://xxx.lanl.gov/abs/quant-ph/9906007>
Information Flow in Entangled Quantum Systems
Authors: David Deutsch, Patrick Hayden
All information in quantum systems is, notwithstanding Bell's theorem,
localised. Measuring or otherwise interacting with a quantum system S has
no effect on distant systems from which S is dynamically isolated, even if
they are entangled with S. Using the Heisenberg picture to analyse quantum
information processing makes this locality explicit, and reveals that
under some circumstances (in particular, in Einstein-Podolski-Rosen
experiments and in quantum teleportation) quantum information is
transmitted through 'classical' (i.e. decoherent) information channels.
--
Greg Egan
Email address (remove name of animal and add standard punctuation):
gregegan netspace zebra net au
From: Hans Moravec <hpm@cmu.edu>
Newsgroups: sci.physics.research
Subject: Re: Faster than light
Date: 12 Sep 2000 10:02:57 GMT
Organization: Robotics Institute, Carnegie Mellon University
gregegan@netspace.zebra.net.au (Greg Egan):
> There's an interesting paper by David Deutsch at:
> <http://xxx.lanl.gov/abs/quant-ph/9906007>
> Information Flow in Entangled Quantum Systems
> Authors: David Deutsch, Patrick Hayden
Very interesting! Quantum mechanics is realistic
and local: Einstein, Bohr and Bell were led away
from that conclusion by an incorrect premise:
that measurement probabilities reflect
stochastic variables, when in fact they arise
from a more complex but deterministic mechanism
describable essentially by hidden variables
representable as Heisenberg matrices (and whose
local nature is confusingly obscured in the more
common Schrodinger state formulation).
It whets the appetite for the 1999 Deutsch paper
(listed as Proc. R. Soc. to appear), which promises
to explain the mystery of the Heisenberg mechanism
(I would guess in the many worlds manner).
A lighter but less filling paper with the same slant
is
<http://xxx.lanl.gov/abs/quant-ph/0003146>
Does Quantum Nonlocality Exist? Bell's Theorem
and the Many-Worlds Interpretation
Authors: Frank J. Tipler
Quantum nonlocality may be an artifact of the
assumption that observers obey the laws of classical
mechanics, while observed systems obey quantum
mechanics. I show that, at least in the case of
Bell's Theorem, locality is restored if observed
and observer are both assumed to obey quantum
mechanics, as in the Many-Worlds Interpretation.
Using the MWI, I shall show that the apparently
"non-local" expectation value for the product of
the spins of two widely separated particles --- the
"quantum" part of Bell's Theorem --- is really due
to a series of three purely local measurements. Thus,
experiments confirming "nonlocality" are actually
confirming the MWI.
From: gregegan@netspace.zebra.net.au (Greg Egan)
Newsgroups: sci.physics.research
Subject: Re: Faster than light
Date: Wed, 13 Sep 2000 07:15:22 +0800
Organization: None
In article <39BDCC7A.8EC6C2D6@cmu.edu>, Hans Moravec <hpm@cmu.edu> wrote:
> gregegan@netspace.zebra.net.au (Greg Egan):
> > There's an interesting paper by David Deutsch at:
> > <http://xxx.lanl.gov/abs/quant-ph/9906007>
> > Information Flow in Entangled Quantum Systems
> > Authors: David Deutsch, Patrick Hayden
> Very interesting! Quantum mechanics is realistic
> and local: Einstein, Bohr and Bell were led away
> from that conclusion by an incorrect premise:
> that measurement probabilities reflect
> stochastic variables, when in fact they arise
> from a more complex but deterministic mechanism
> describable essentially by hidden variables
> representable as Heisenberg matrices (and whose
> local nature is confusingly obscured in the more
> common Schrodinger state formulation).
>
> It whets the appetite for the 1999 Deutsch paper
> (listed as Proc. R. Soc. to appear), which promises
> to explain the mystery of the Heisenberg mechanism
> (I would guess in the many worlds manner).
The reference to (Deutsch, 1999) doesn't give a title or preprint number,
but I'm fairly sure it's this article, already on the preprint server:
<http://xxx.lanl.gov/abs/quant-ph/9906015>
Quantum Theory of Probability and Decisions
Authors: David Deutsch
The probabilistic predictions of quantum theory are conventionally
obtained from a special probabilistic axiom. But that is unnecessary
because all the practical consequences of such predictions follow from the
remaining, non-probabilistic, axioms of quantum theory, together with the
non-probabilistic part of classical decision theory.
There's another paper on the server that takes issue with "Quantum Theory
of Probability and Decisions", at
<http://xxx.lanl.gov/abs/quant-ph/9907024>, but as yet nothing that cites
"Information Flow in Entangled Quantum Systems".
FWIW, I found the latter extremely enlightening. Trying to see why the
MWI gives a local account of EPR & teleportation is definitely much easier
in the Heisenberg picture!
--
Greg Egan
Email address (remove name of animal and add standard punctuation):
gregegan netspace zebra net au
--
***************************************************************
Amara Graps | Max-Planck-Institut fuer Kernphysik
Interplanetary Dust Group | Saupfercheckweg 1
+49-6221-516-543 | 69117 Heidelberg, GERMANY
Amara.Graps@mpi-hd.mpg.de * http://galileo.mpi-hd.mpg.de/~graps
***************************************************************
"Never fight an inanimate object." - P. J. O'Rourke
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