On 26/04/2016 5:12 pm, Jesse Mazer wrote:
On Mon, Apr 25, 2016 at 10:16 PM, Bruce Kellett
<[email protected] <mailto:[email protected]>> wrote:
On 26/04/2016 5:52 am, Jesse Mazer wrote:
If the latter, I wonder how you can be so confident that Mark
Rubin's paper at http://arxiv.org/abs/quant-ph/0103079
doesn't qualify as just this sort of "local theory of copies
and matching which generally reproduces the correct quantum
predictions for arbitrary experiments", given that you said
you hadn't actually read through the paper.
I have looked more closely at the paper now, and Rubin makes a
number of elementary mistakes, and his argument certainly does not
support the conclusion you wish to draw.
I quote:
"Measurement-type interactions (20) transform the operators for
the states of awareness of observers into sums of operators, each
corresponding to a distinct state of awareness of the observer,
and each labelled with factors corresponding to the system which
the observer measured, as well as to other systems with which
/that/ system has previously interacted. These labels control the
subsequent results of measurement involving the labelled
operators, including in particular measurements of correlations
between the states of awareness of observers who have measured
particles which have previously interacted with each other."
And also:
"When one of the observers performing, say, an EPRB experiment
with both analyzer magnets oriented in the same direction
measures the spin of one of the paired particles, that observer
splits into noninteracting copies, each copy labeled with
information corresponding to the state of the observed particle as
well as to the state of the other particle."
I think the trouble here is that the particle each observer
measures may have interacted with the other, but only /before/ the
other particle's interaction with a measuring magnet. So that
operator cannot carry information about that /other/ interaction.
The second quote seems to suggest that after A's measurement, A's
state carries information about the state of the particle that
went to B for subsequent measurement.
These words don't clearly indicate the interpretation you suggest, I
would guess that "the state of the other particle" refers to the
quantum state that would be assigned to B given only knowledge of the
state of A (as well as knowledge of how they were entangled
originally). Anyway, if you want to confidently accuse him of an
"elementary mistake", I think you should have something a little more
solid than just a speculation about what his ambiguous verbal summary
"seems to suggest" to you (and keep in mind this paper did end up
making it through peer review, see
http://link.springer.com/article/10.1023%2FA%3A1020477902039 ).
A lot of dubious papers get through peer review -- nobody can ever claim
that that system is perfect.
But I think there is a more serious problem here. You have cut the
central part of my analysis of what Rubin actually says. In full, I said:
I think the trouble here is that the particle each observer measures may
have interacted with the other, but only /before/ the other particle's
interaction with a measuring magnet. So that operator cannot carry
information about that /other/ interaction. The second quote seems to
suggest that after A's measurement, A's state carries information about
the state of the particle that went to B for subsequent measurement.
That might well be the case -- if A measures
|psi> = (|+>|-> -|->|+>)/sqrt(2)
and gets |+>, it follows that only the |-> part remains for B to measure
(|-> in A's orientation, that is). But that is not sufficient. B
measures at some arbitrary angle at a spacelike separation from A's
measurement, so no matter what piece of the singlet state is left after
A's measurement, that cannot get to B at sub-light speeds before B makes
his measurement at some independent angle. So simply knowing from A's
measurement that |-> went to B is of no help in determining the joint
probabilities. Spacelike separations are the reason this experiment is
said to demonstrate non-locality, after all. And Rubin's argument
appears to have simply overlooked this crucial fact.
You think that "the state of the other particle" refers to the quantum
state that would be assigned to B given only knowledge of the state of A
(as well as knowledge of how they were entangled originally). Actually,
that is the interpretation I gave the words, except I teased out what
that actually meant. From the entangled state, given A's state (result,
say |+>), you would assign a state |-> to B. But this is wrong for
spacelike separations -- the state B actually measures is exactly the
same as the state A measured: |psi> = (|+>|-> - |->|+>)/sqrt(2).
So the measurement on A does not give any additional information about
the state B measures, all one knows is that B also measures a singlet
state.This is the problem of non-locality in a nutshell, and Rubin has
not solved it. Going into the detail of his mathematical analysis is not
necessary, because his mathematics is accurately summarized in this
section of the discussion. That is clearly wrong, so the details are
irrelevant. If you think like a physicist, rather than as a
mathematician, you look for the physics of what a paper is saying. If
the paper gets the physics wrong, it does not matter what the
mathematics says, it will necessarily be wrong also. That is the case here.
Bruce
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