Sunday, April 20, 2014

On the Einstein-Podolsky-Rosen Thought-Experiment

On the Einstein-Podolsky-Rosen Thought-Experiment
From:  E.D.
To:  Arjun Janah
Cc:  R.B.
Sent:  Sat, Apr 19, 2014 10:23 pm
Subject:  RE: Blog post of our correspondence re. probability.


<personal details, deleted by Arjun 04/20/14>
    Also,  a correction or clarification about Bell's theorem. My understanding of it at this time is that Bell's theorem does establish non-local causation in the following sense. If two particles depart from one another in different directions and then, later, the spin of one of the particles is altered, the spin of the other particle instantaneously changes also. However, this fact can not be used to communicate instantaneously (or faster than the speed of light). So in that sense, there is not non-local causation, because we at the macro level can not observe it.

    I could have it all wrong, but I think the main point is that in the end q.m. does not explain non-local causation or action-at-a-distance (such as telepathy, precognition, other mystical states of union, etc.) at the level of human consciousness. So q.m. is disappointing for people who wanted to use it for that purpose.

<See also the third section added below this one -- the e-mail I received at 6:34 pm on 04/20/14 from E.D. -- for a sharper clarification of this issue. -- Arjun 04/20/14>

    I think I mentioned this book to you before, but this is the sort of thing I'm referring to here:

    "How the Hippies Saved Physics"


From:  Arjun Janah
To:  E.D.
Cc:  R.B., blank01, P.B.,V.K
Sent:  Sun, Apr 20, 2014 12:55 am
Re:  Blog post of our correspondence re. probability.

<personal  details, deleted by Arjun 04/20/14>

    Yes, I think you have described the core quantum-entanglement situation concisely and correctly. But my knowledge of this is limited. I will try to go into some details below, which may or may not shed more light on what you have neatly summarized.

    This was (to my knowledge) first posed as a challenge to q.m. (or its emergent interpretation at the time) by Einstein, Podolsky and Rosen. It is a strange sort of instantaneous action-at-a-distance.  Bell later formulated, I am told, what had come to be known as the EPR paradox as a testable inequality.

    Electrons possess an internal or intrinsic angular momentum, called "spin", which has, in certain natural units, a value of 1/2. From quantum mechanics, the projected value of this spin, along any chosen spatial direction, can have only two observed values: +1/2 or -1/2 (in those same natural units).

    Two electrons can combine into either a total-spin = zero state (where the two electron spin-vectors are aligned oppositely: 1/2 -1/2 =0) or a total-spin = one state (where their spin-vectors are aligned in the same direction, 1/2 + 1/2 =1).  These are the only definite total-spin states allowed by the rules of q.m.

    Consider two electrons that are known to be in, say, a total-spin = zero state, but for which the individual spin directions of the two electrons are unknown.  If those two electrons move apart in space without further disturbances (caused, for example, by our further observations), then they should remain in that total-spin = 0 state.

    In the usual intepretation of q.m., the spin-values of each electron along any given direction are not only not known to us (and here's where we may strongly quibble with that interpretation) they are indeterminate in an absolute sense. This is the thing that Einstein and his colleagues could not (with good reason, in their minds) accept.

    If we now make an observation on one of the electrons and find its spin value along a certain direction is, say, +1/2, then we know that the spin value of the distant electron along the same direction will have to be -1/2.

    While it is perhaps understandable, as per the usual interpretation, that it was our act of observation (a measurement of spin value along a chosen axis) that "threw" the observed electron from an undetermined individual-spin-alignment state into the definite +1/2 state, how could we say the same of the distant electron?

    Could our measurement made on the local electron here truly have "thrown" that distant electron there into its spin -1/2 state?  Or was it already in that state before we made our local measurement on its partner?

    E, P & R had presented the instantaneous throw of the individual spin of the distant electron (following an observation of its local partner) into a definite state as a paradox, something that arose out of q.m. and its accepted interpretation, but appeared to violate the precept that the fastest way in which an event at one place could affect an event in another place was via a signal sent from the first event to the second -- which signal could not travel faster than the speed of light (or other electromagnetic waves) in a vacuum. And this speed, though large, is finite. So instantaneous causation was considered impossible.

    So E, P & R argued that either the accepted interpretation of q.m. was wrong -- i.e., the electron-spins were in fact aligned along a certain direction (in which case the observation was only a discovery of what had already existed in reality) rather than being truly indeterminate in an absolute sense -- or else one would have to accept instantaneous causation, which violated a precept that was considered sacred, one on which Einstein's theory of relativity and so also all of physics had rested.

    But after Bell had formulated this as an inequality that could in principle be tested, tests were done that showed (so it is alleged) that the accepted interpretation of q.m. is in fact correct.

    However, although instantaneous causation does apparently occur (if we swallow all of this, which is a mixture of observed fact, mathematical q.m. rules and an interpretation that was formulated by some of the most thoughtful people, including Niels Bohr) it is alleged that this cannot be used to do any true communication.  This alleged fact has been taught to physics students for some time now as the saving grace in this situation.  I am not clear in my mind, at this time, on how to understand or explain that point.

    This is my own (surely incomplete and faulty) understanding of the situation, dating back many decades to my undergraduate days in India, when I came upon EPR by chance. (I did not learn about Bell's inequality till later, and still am pretty ignorant about that.)

    As far as the relevance of any of this to paranormal phenomena, I have no understanding at all about that aspect.  That is not to rule out such phenomena, only to state the lack of any linkage that I know of.


From:  P. B.
To:  Arjun Janah
Cc:  E.D., R.B., blank01, V.K.
Re:  Blog post of our correspondence re. probability.
Sent:  Sun, Apr 20, 2014 2:31 am

Dear Arjun,

 <personal detail, deleted by Arjun 04/20/14>

  The actual description of the EPR thought experiment evades the question
of fluctuations, of electron spin for instance, which destroy coherence.

  In other words, if the electrons in the EPR paradox are in the normal
paramagnetic state, as we take for granted, then spin correlations will be
exponentially damped in space and time. In a ferromagnet, the spin states
will be correlated and will be entangled. Flipping the spin of a majority spin
will ensure that a minority spin will be promoted to the Bose condensed state.

  Verifying this entanglement hypothesis means verifying that the
Bose condensed state depends only on temperature ( in classical
critical phenomena) or on a bias (in quantum critical phenomena),
as for instance in the breaking of symmetry at different energy scales.

From: E. D.
To: Arjun Janah
Sent: Sun, Apr 20, 2014 6:34 pm
Subject: RE: More blog posts


These (things I wrote that you posted) were mostly off-the-cuff remarks made by e-mail.

You might want to add this as an addendum, in answer to your question about what parapsychology has to do with Bell's theorem.

The connection between parapsychology and Bell's theorem is that the existence of non-local causation is a necessary (though not sufficient) condition for the existence of parapsychological phenomena. Telepathy, for example, suggests that there is an immediate and instantaneous connection between minds (and the brains that embody those minds). Psychokinetic phenomena suggest that the mind has an immediate (non-local) causal power over physical objects held at a distance. If Bell's theorem proved that non-local causation exists, it would fulfill one condition for the existence of parapsychological phenomena.
Of course, parapsychological phenomena might still not exist because there might be other conditions that are necessary for them to occur that can not be fulfilled. But the impossibility of non-local causation is the most commonly cited reason to reject the possibility of parapsychological phenomena. So demonstrating the possibility of non-local causation would greatly increase the possibility that parapsychological phenomena might occur.


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