Re: quantum entanglement and violation of light-speed barrier

From: bernard.chaverondier (bernard.chaverondier_at_wanadoo.fr)
Date: 09/21/04 

Date: Tue, 21 Sep 2004 14:18:27 +0200

"Bill Hobba" <bhobba@rubbish.net.au> a écrit dans le message de
news:E9I3d.37477$D7.36521@news-server.bigpond.net.au...

> "Bilge" <dubious@radioactivex.lebesque-al.net> wrote in message
> news:slrncktc77.fep.dubious@radioactivex.lebesque-al.net...

Aidan Smoker:
> > >I found this discussion on Fermilab's web pages about the quantum
> > >action-at-a-distance phenomena. Even as a scientist I find it an
> > >unsatisfying explanation or resolution of the EPR paradox.

Bilge
> > Think about what's happening. You measure a photon polarization.
> > In doing so, what have you discovered? Nothing apart from the
> > polarization you just measured. Nothing about that measurement
> > involves a signal propagating faster than light.

Bill Hobba
> Exactly. As one article I read on it said
> (http://quantum.phys.cmu.edu/quest.html); say we put a black card in an
> envelope and a white card in another. We send each to a physicist
> who does not know which one they receive. When say physicist A
> opens the envelope and sees say a white card does this send an
> instantaneous message to the envelope with the black card - of course not.
> Same with EPR

Chaverondier
No. This explanation is a local Hidden variable
interpretation which has been discarded by the
violation of Bell's inequalities.

To better understand this point
  * Let us consider a polarizer which is oriented at an angle alpha
  * Let us label the measured polarisation +1 if the measured
polarization of a photon by this polarizer is alpha.
  * Lets us label the measured polarisation -1
if the measured polarization is alpha+pi/2

Then, the probability to measure a polarization +1 on the
"far" side (if a -1 polarization has been observed on the
"local" side) depends on the orientation of the _"local"_
polarizer (with regard to orientation of the far one).

This probability is 100% only if the "far" polarizer
has same orientation than the "local" one.

So, the "far" photon behaviour depends on the orientation
of the "local" polarizer when the "local" photon polarization
is measured (with regard to the orientation of the "far"
polarizer when the far measurment is performed)

However, if quantum indeterminacy is assumed to
be fundamental, then the local observer cannot bias
quantum measurement statistics (Born rule) and
consequently cannot influence the statistics of the far
photons measurements. Hence, quantum indeterminacy
is a sufficient hypothesis to preserve the compatibility
of relativist locality with quantum no-locality.

An even better understanding of quantum non locality can
be achieved if you study the Greenberg, Horn and Zeilinger
thought experiment with three particules A, B and C
of spin 1/2 in maximal intrication state

ie |psi> = (|+++>+|--->)/2^(1/2)
where + and - denote spin along the z direction

In this experiment, there no inequalities are involved.
There are only equalities that prove a local spin
measurement to depend on the orientation of the
"far" polarizers.

Bill Hobba
> Just for the record I side with the primary state diffusion interpretation
> of QM (http://arxiv.org/abs/quant-ph/9508021) because it is experimentally
> distinguishable from others - which is something I always find appealing.
> It may have been experimentally refuted by now -in which case my support
> goes down the drain - but such is life

Chaverondier
This proves your scientific curiosity to exeed
other motivations. I share this way of mind.

Bernard Chaverondier
http://perso.wanadoo.fr/lebigbang/epr.htm
Quantum determinacy or relativist locality.

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