From: Anonymous <nobody@REPLAY.COM>
Date: Thu, 29 Jan 1998 19:06:46 +0800
To: cypherpunks@cyberpass.net
Subject: Re: EPR, Bell, and FTL Bandwidth (fwd)
Message-ID: <199801291045.LAA19417@basement.replay.com>
MIME-Version: 1.0
Content-Type: text/plain



Eric Cordian writes:

> An Entity at Replay writes:
>  
> > You agree with the foolish statement that the behavior of correlated
> > photons is no more weird than sending out two envelopes?  I thought
> > you had more sense than that.
>  
> With correlated branch systems, examination of one branch can disclose
> information about another branch which is currently distant from us.
> This is no more weird in the quantum mechanical case, than it is in
> the classical case.  The envelope analogy is perfectly appropriate.
>  
> That's not to say that quantum mechanical systems aren't "weird" in
> ways that classical systems are not.  It's just that this is not one
> of those areas of weirdness.

It's much worse than this.  The violation of Bell's inequality implies
that changes to the basis used to measure one particle cause changes in
the observed state of the remote particle.  Of course this can't be used
to transmit information; we all agree on that.  The remote particle has
a random orientation.  But the point is, Bell's theorem shows that the
remote orientation depends on how the local measurement is done.

This is not a matter of simply perceiving or deducing what the conditions
are at the remote branch, as in the envelope case.  A better analogy
would be an envelope which could be opened in two ways, from the top
or from the bottom.  If you open from the top then the remote envelope
will have the same contents as the local one, while if you open from
the bottom then the remote envelope will have the opposite contents.
In each case the contents are random; the remote observer has no
idea whether you opened from the top or the bottom.  But somehow
your decision on how to open the envelope (what basis to measure the
photon) is changing how these globally separated subsystems relate to
each other.  (This analogy isn't perfect, either, because it might seem
that magic changes to the local contents could make the envelope work.
Bell's reasoning shows that it is the remote photon's state which must
be altered by the choice of how to measure the local one.)

This is the fundamental flaw in the envelope analogy, which makes it
seriously flawed and misleading.  It gives the impression that some kind
of hidden variables (the contents within the envelope) can easily solve
the problem, when nothing could be further from the truth.  It papers
over one of the most mysterious facets of quantum mechanics, by making it
appear to be mundane.  It represents a fundamentally mistaken way to view
remote correlated particles.

> > How do you explain the violation of Bell's theorem in QM?  What is
> > your nice, cozy, friendly, un-weird explanation?  I'm curious whether
> > you are going to sacrifice locality or reality.  Somehow I think
> > you'll have to go beyond what is necessary to explain the behavior of
> > envelopes.
>  
> The wavefunction of the universe is not a physical observable.  I do
> not have to sacrifice causality for physical phemonema to have
> non-local collapse of the wavefunction when measurements are
> performed.  A satisfactory theory of quantum mechanical measurement
> does not currently exist, and it has even been conjectured that
> gravitation may be the sole force immune from quantum mechanical
> superposition, and that this may be the mechanism behind wavefunction
> collapse.  There are other hypotheses as well, and the experiments to
> distinguish amongst them have yet to be performed.
>  
> A correct theory of quantum mechanical measurement will disclose the
> mechanisms by which things like non-local wavefunction collapse,
> quantum teleporation, the quantum eraser effect, and other current
> oddities are mediated.  This will undoubtedly involve a deeper
> understanding of how quantum gravity works, and perhaps even the
> physics underlying the existence of consciousness itself.

OK, so you can't explain it.  Fine, it is indeed a mysterious phenomenon,
and no doubt you are correct that more insights will come in the future.

Now, compare this with the envelope analogy Tim May offered:

>> All that is revealed is a _correlation_, a kind of structure built
>> into the Universe. Interesting, but not so weird as it seems.  (And
>> this is not any kind of "action at one site instantaneously changing
>> the state far away." No more so than sending two envelopes out, one
>> with a "1" inside and the other with a "0" inside changes things
>> instantaneously.....)

Are you at all tempted to resort to such language in trying to understand
how the envelopes could work?  Is it puzzling how we could open one here
and find a 1 and suddenly know that there is a 0 in the remote envelope?
Do we need to learn more about how measurements of envelope contents work
before we can begin to tackle this thorny philosophical conundrum?

Of course not!  The envelope case is transparently obvious.  There are
no puzzles here, no complexities, no confusion.  The only confusion
is in the minds of those who think that correlated envelopes have
anything to do with correlated photons, or that the hidden variables
which perfectly well explain what is happening with the envelopes shed
any light whatsoever on the workings of nonlocal QM systems.

> However, none of this implies in the least that a physical effect is
> propagated non-causally across vast distances when a conscious choice
> is made to measure one of two non-commuting observables for one of a
> pair of "entangled" particles, which, I believe, is what the current
> argument is over.

No, the current argument is over how much of a jackass Tim May is.