Phase-entanglement, Bell's theorem and non-locality.

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Sylvia Else

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Dec 13, 2012, 1:01:37 PM12/13/12
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The results of measurements of phase entangled particles together with
Bell's theorem provide pretty convincing evidence that the Universe
contains non-local interactions.

Yet I'm lead to wonder.

Let's imagine the usual idealised experimental scenario, where there is
an emitter of particles in a twin state and measurement devices
performing measurements in a space-like separated way, with the results
then brought together for comparison. We know that when performed
appropriately, this will show that the measurement results are
correlated in a way that, by Bell's theorem, cannot be explained by any
local interaction - the measurements are non-locally linked, and thus
the Universe is non-local.

Now step back. Consider that the above is performed in complete
isolation, except that the results of the final step - comparison of the
measurements, is transmitted to an outside observer.

Since the experiment, except for the last step, is performed in
isolation, the outside observer can regard the entire experimental
situation as a superposition of quantum states with no decoherence
except at the last step. The "measurements" are nothing but further
entanglements between the twin sate particles and the measuring
apparatus. The last step involves an interaction between particles that
represent the results of the earlier "measurements", with the sets of
particles for the two measurements for a given twin state pair of
particles being already entangled. Those particles now further interact
locally to produce the transmitted result of the comparison to the
outside observer.

So the outside observer can calculate the evolution of the system, and
the final transmitted results, without needing to assume any non-local
interactions. In particular, the outside observer cannot use Bell's
theorem to prove that the system is non-local.

From this perspective, it looks as if the appearance of non-locality in
the system results from a false assumption by observers embedded in the
system that they are somehow independent of it, and that their
measurement results are determined before they are compared.

Sylvia.

xxein

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Dec 15, 2012, 8:32:12 AM12/15/12
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> From this perspective, it looks as if the appearance of non-locality i=
n
> the system results from a false assumption by observers embedded in the
> system that they are somehow independent of it, and that their
> measurement results are determined before they are compared.
>
> Sylvia.

xxein: Is there the possibility that the the measurement apparati is
flawed and non-accountable for real interpretation?

I ask this in the wonderment of whether the aperture size it fitting
the polarization profile for the object's detection. But, mostly, it
appears that a gravity function may be detected because this could be
considered as a differential to any local measurement as a hidden
local but non-local variable. Always confusing, isn't it?

I am referring to a graph that shows the difference between quantum
measurements and the 'local real' predictions of relativity amongst
the angles of detection (the apparent cosine function that shows the
variance).

I have not thought about Bell's theorem exemplified in this way before
so I may just be wrong in my offering. At the same 'time' it may be
enlightening to some wishing to explore this further.

If we really knew the physic...

Jos Bergervoet

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Dec 15, 2012, 8:32:33 AM12/15/12
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On 12/13/2012 7:01 PM, Sylvia Else wrote:
> The results of measurements of phase entangled particles together with
> Bell's theorem provide pretty convincing evidence that the Universe
> contains non-local interactions.

But the results are never in contradiction with local quantum
field theory! So where do you see this evidence?

> Yet I'm lead to wonder.
>
> Let's imagine the usual idealised experimental scenario, where there is
> an emitter of particles in a twin state and measurement devices
> performing measurements in a space-like separated way, with the results
> then brought together for comparison. We know that when performed
> appropriately, this will show that the measurement results are
> correlated in a way that, by Bell's theorem, cannot be explained by any
> local interaction

OK, you need the global entanglement. But it is caused by
local interactions (in the emitter of the twin state) and
has spread with less than the speed of light.

> - the measurements are non-locally linked, and thus
> the Universe is non-local.

There exists non-local entanglement, but how can you prove
that this needs non-local *interactions*? (As you claimed!)

...
> So the outside observer can calculate the evolution of the system, and
> the final transmitted results, without needing to assume any non-local
> interactions.

An inside observer can do the same calculation. Or do you
see a problem there? This observer will then realize that
they are in a superposition of states. (The singular "they"
as pronoun makes sense here even without the aim of being
gender-neutral..)

> From this perspective, it looks as if the appearance of non-locality in
> the system results from a false assumption by observers embedded in the
> system that they are somehow independent of it,

The false assumption seems to be that they reject being in
a superposition (entangled with each other). And of course
the criticism only holds for those observers that make
this assumption! Prudent observers will accept that they
are entangled, and no non-local interaction is necessary.

They might still be surprised by how smoothly the decoherence
of their state of mind happens! (You don't usually observe
your own entanglement, as far as I can see..)

> and that their
> measurement results are determined before they are compared.

Here I cannot follow you.. If there is entanglement then
the different possible results are all still present as
a probability amplitude. You can look at subspaces of the
Hilbert space where you project out all but one set of
consistent results, but that doesn't mean the rest of the
Hilbert space ceases to exist! So nothing is "determined".
And the fact that decoherence (largely) suppresses the
interaction between subspaces still doesn't mean that only
one subspace remains in existence.

Just the fact that we don't observe the other subspaces
(where other sets of results were measured) cannot serve
as proof that those have collapsed from existence!

--
Jos

Jimmy Kesler

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Dec 15, 2012, 8:46:05 AM12/15/12
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On Thu, 13 Dec 2012 18:01:37 +0000, Sylvia Else alluded :

> From this perspective, it looks as if the appearance of non-locality in
> the system results from a false assumption by observers embedded in the
> system that they are somehow independent of it, and that their
> measurement results are determined before they are compared.

yes, the correlation info is transmitted faster than the speed of light

Sylvia Else

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Dec 16, 2012, 1:40:44 AM12/16/12
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On 16/12/2012 12:32 AM, Jos Bergervoet wrote:
> On 12/13/2012 7:01 PM, Sylvia Else wrote:
>> The results of measurements of phase entangled particles together with
>> Bell's theorem provide pretty convincing evidence that the Universe
>> contains non-local interactions.
>
> But the results are never in contradiction with local quantum
> field theory! So where do you see this evidence?

One needs to be clear that Bell's theorem does not in any way predict
results that differ from QM. In the early days, it might have appeared
that Bell's theorem suggested experiments (Aspect's being the first)
that would falsify QM because Bell's theorem proved that no non-local
real model could lie behind QM and locality have been taken as a given.
In the event, Aspect's result was consistent with QM, meaning that
whatever modem lies behind QM, it has to be non-local, or some other
assumtion in Bell's theorem has to be false.

Bell's theorem seems conclusive on this point. If we assume that a
measurement leads to an immediate and definite result, then the
correlation between the results of measurements on phase entangled
particles cannot be explained by a purely local model.

>
>> Yet I'm lead to wonder.
>>
>> Let's imagine the usual idealised experimental scenario, where there is
>> an emitter of particles in a twin state and measurement devices
>> performing measurements in a space-like separated way, with the results
>> then brought together for comparison. We know that when performed
>> appropriately, this will show that the measurement results are
>> correlated in a way that, by Bell's theorem, cannot be explained by any
>> local interaction
>
> OK, you need the global entanglement. But it is caused by
> local interactions (in the emitter of the twin state) and
> has spread with less than the speed of light.
>
>> - the measurements are non-locally linked, and thus
>> the Universe is non-local.
>
> There exists non-local entanglement, but how can you prove
> that this needs non-local *interactions*? (As you claimed!)

Bell's theorem can be proved without any reference to entanglement at
all, and purely in terms of decisions made during an experiment, and the
observations that result. See something I've prepared on this at

http://www.cryogenic.net/BellsTheorem.pdf

>
> ...
>> So the outside observer can calculate the evolution of the system, and
>> the final transmitted results, without needing to assume any non-local
>> interactions.
>
> An inside observer can do the same calculation. Or do you
> see a problem there? This observer will then realize that
> they are in a superposition of states. (The singular "they"
> as pronoun makes sense here even without the aim of being
> gender-neutral..)

If the inside observer takes the view that after doing a measurement
they are in a superposition of states, then the issue goes away, because
they are no longer assuming, as Bell's Theorem requires, that the
measurement produces an immediate and definite result. The observer
accepts that nothing is definitely resolved (if it ever is), until their
results are compared with those of the other observer, at the earliest.

>
>> From this perspective, it looks as if the appearance of non-locality in
>> the system results from a false assumption by observers embedded in the
>> system that they are somehow independent of it,
>
> The false assumption seems to be that they reject being in
> a superposition (entangled with each other). And of course
> the criticism only holds for those observers that make
> this assumption! Prudent observers will accept that they
> are entangled, and no non-local interaction is necessary.

That's pretty much the idea I'm pushing. The reason I started this
discussion was an irritation about the number of experiments that seem
to be reported that purport to show the speed of some presumed influence
that travels between the measurements at multiples of the speed of
light, or even "instantaneously" (which is means little). Absent a proof
(which I believe will not be forthcoming) that the measurement results
are immediate and definite, those expreiments seem rather pointless, and
the claims of FTL influences (which nevertheless remain out of reach of
direct examination) are entirely spurious.
>
> They might still be surprised by how smoothly the decoherence
> of their state of mind happens! (You don't usually observe
> your own entanglement, as far as I can see..)
>

Indeed no.

>> and that their
>> measurement results are determined before they are compared.
>
> Here I cannot follow you.. If there is entanglement then
> the different possible results are all still present as
> a probability amplitude. You can look at subspaces of the
> Hilbert space where you project out all but one set of
> consistent results, but that doesn't mean the rest of the
> Hilbert space ceases to exist! So nothing is "determined".
> And the fact that decoherence (largely) suppresses the
> interaction between subspaces still doesn't mean that only
> one subspace remains in existence.
>
> Just the fact that we don't observe the other subspaces
> (where other sets of results were measured) cannot serve
> as proof that those have collapsed from existence!
>

I am not disagreeing with that. The truth may be that what I'm
suggesting is already accepted by a substantial part of the physics
community. Just not those who do FTL influence style experiments.

Sylvia.

Sylvia Else

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Dec 16, 2012, 3:35:44 AM12/16/12
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There are a few issues here. In real experiments the experimenter has
the problem of deciding whether two received photons are actually
members of the same pair. This has to be inferred from the fact that
they are received at nearly the same time (suitably adjusted, where
necessary for known propogation delays). However, the consquence of
counting two photons as paired when they are not should be to reduce the
observed correlation, so that should not be a problem provided that it
doesn't happen so often as to reduce the correlation below the maximum
posited by Bell's theorem for a purely local system.

Another is that in practice, because so many of the photons are not
detected, the simple limit proposed by Bell is not testable. Instead
there are rather involved mathematical extrapolations that determine a
different limit that the actual experimental situation must exceed for
it to be possible to infer that the ideal experiment would exceed Bell's
limit. These extrapolations might be subtlely flawed, despite being peer
reviewed.

Yet another is the possibility that the Universe is just outright
cheating. For example, unless the choices of orientation of the
polarisation detectors is made so close to each other in time that no
subluminal (i.e. local) message could pass between them, then the
Universe might send a message by an unknown, but subluminal means and
decide on the outcomes such that Bell's limit is exceeded even though
the mechanism is actually purely local. Various strategies have been
used to prevent this, to the point where every known loophole has been
closed, but no single experiment has closed all the loopholes at the
same time. Unless the Universe is being truely capricious in a way that
requires intelligence, it's hard to see that these loopholes can really
still compromise the result.

> I ask this in the wonderment of whether the aperture size it fitting
> the polarization profile for the object's detection. But, mostly, it
> appears that a gravity function may be detected because this could be
> considered as a differential to any local measurement as a hidden
> local but non-local variable. Always confusing, isn't it?
>
> I am referring to a graph that shows the difference between quantum
> measurements and the 'local real' predictions of relativity amongst
> the angles of detection (the apparent cosine function that shows the
> variance).
>
> I have not thought about Bell's theorem exemplified in this way before
> so I may just be wrong in my offering. At the same 'time' it may be
> enlightening to some wishing to explore this further.
>
> If we really knew the physic...
>

I have posted a link to a PDF written by me under the subject heading
"Just Bell's Theorem". In that version, I have attempted to show just
how little the actual physics impacts on the conclusion of non-locality.

Sylvia.

FrediFizzx

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Dec 18, 2012, 12:49:14 PM12/18/12
to
"Sylvia Else" <syl...@not.at.this.address> wrote in message
news:aj4t4p...@mid.individual.net...
> On 16/12/2012 12:32 AM, Jos Bergervoet wrote:
>> On 12/13/2012 7:01 PM, Sylvia Else wrote:
>>> The results of measurements of phase entangled particles together with
>>> Bell's theorem provide pretty convincing evidence that the Universe
>>> contains non-local interactions.
>>
>> But the results are never in contradiction with local quantum
>> field theory! So where do you see this evidence?
>
> One needs to be clear that Bell's theorem does not in any way predict
> results that differ from QM. In the early days, it might have appeared
> that Bell's theorem suggested experiments (Aspect's being the first)
> that would falsify QM because Bell's theorem proved that no non-local
> real model could lie behind QM and locality have been taken as a given.
> In the event, Aspect's result was consistent with QM, meaning that
> whatever modem lies behind QM, it has to be non-local, or some other
> assumtion in Bell's theorem has to be false.

Yes, Bell made a *physical* mistake in not specifying the correct
topology for an EPR-Bohm scenario. Please see Joy Christian's "Disproof
of Bell's Theorem".

http://arxiv.org/abs/1201.0775
"On the Origins of Quantum Correlations"
http://arxiv.org/find/grp_physics/1/au:+christian_j/0/1/0/all/0/1

http://www.brownwalker.com/book.php?method=ISBN&book=1599425645
"Disproof of Bell's Theorem; Illuminating the Illusion of Entanglement"

Though Bell's theorem is mathematically proven, that doesn't mean it has
been physically proven. Dr. Christian has successfully shown that when
a parallelized 3-sphere topology is chosen for the EPR-Bohm scenario,
quantum mechanics is local and realistic. Furthermore, he has shown
generally that a parallelized 7-sphere topology can explain all quantum
correlations. For those that might be more interested in the
topological aspects please see the discussion on the FQXi blog at the
following link.

http://www.fqxi.org/community/forum/topic/1352#post_71101

> Bell's theorem seems conclusive on this point. If we assume that a
> measurement leads to an immediate and definite result, then the
> correlation between the results of measurements on phase entangled
> particles cannot be explained by a purely local model.

Yes, they can be explained by a purely local model. See the above
links.

Best,

Fred Diether


Rich L.

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Dec 18, 2012, 8:52:27 PM12/18/12
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[[Mod. note -- I have rewrapped paragraph-length lines. -- jt]]

There is a lot of confusion over these issues, and I think they all
come about because of faulty beliefs about how the world works. I
don't claim to have it figured out, but I'd like to suggest some
ideas I think have promise:

-One major problem with attributing a result at one location to a
"measurement" at another is Relativity. If we accept that Relativity
is correct then we cannot have a consistent version of physics and
still assert that the detection of a particle at A "causes" a certain
result at point B which is spacelike separated from A. Any assertion
of faster than light interactions violates Relativity, and I'm
inclined not to accept that yet.

-An underlying assumption in all talk about entangled particles is
that they somehow are emitted from the source without any knowledge
of where they are going to end up. This is certainly a very intuitive
assumption that agrees with our daily experience. Historically it
is a result of a philosophical debate in the late 1800's that ended
up rejecting action at a distance. Einstein certainly rejected
"spooky action at a distance". I'm starting to wonder if maybe
action at a distance should be reconsidered however.

-The "entangled particle" experiments can make perfect sense if you
allow action at a distance, but consistent with Relativity. That
is, in Relativity there is a concept of null lines. These are
simply points in space-time that have zero separation as calculated
via the metric. i.e. all points on a common light cone (either
past or future) have zero separation from the vertex of the light
cones. If we take this zero separation literally (and I think most
don't), then in a sense the emitter of a photon and the detector
can interact directly because they have "zero separation". If the
emitter is restricted to emitting a photon only when it has a place
to land, then at the moment of emission all requirements for
conservation of energy, polarization, etc. can be satisfied. If
two photons are being emitted by some process at the same time,
presumably both photons must have a place to go before emission,
and both must satisfy applicable conservation laws. This is a
picture that is Relativistic-ally consistent, and also consistent
with QM. I think this is a tough idea for many people to swallow,
especially when they understand its implications. I'm not convinced
myself, although I find the idea intriguing.

-This view can be consistent with QM because the emitter can randomly
choose any available receiver on its future light cone to send the
photon, provided the applicable conservation laws are satisfied.
I think the current assumption is that an atom emits its photon
into space, and the photon then moves out at the speed of light and
interacts with matter until it is destroyed. It has been observed,
however, that if an atom is in a space that cannot support the
emitted photon (e.g. a resonant cavity), the atom will not emit the
photon. This too seems consistent with the idea that the emitter
interacts with the receiver in some way prior to emission.
Wheeler?Feynman absorber theory seems to do something like this,
as does the Transactional interpretation of QM.

Just some comments...

Rich L.

JohnF

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Dec 19, 2012, 4:00:59 AM12/19/12
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Rich L. <ralivi...@sbcglobal.net> wrote:
> [...] If we accept that Relativity is correct then we cannot have
> a consistent version of physics and still assert that the detection
> of a particle at A "causes" a certain result at point B which is
> spacelike separated from A. Rich L.

Doesn't matter which "caused" the other. There's no possible problem
until information about the outcomes of both measurements eventually
becomes simultaneously available at some single point/event,
which will obviously be in the future lightcone of both measurements.
Until that happens, nobody knows nothing about any possible correlation.
Supopose you have two different observers, both in the future lightcone
of both measurements, but relatively moving so that one thinks
A caused B, and the other thinks B caused A. Doesn't matter.
Both see total spin (or whatever) zero, and each can validly/consistently
speculate whatever they like about which caused which. Either the
-1/2 measurement "caused" the +1/2 measurement, or vice versa.
Not a meaningful concept, e.g., in a causal set poset, the two separate
measurement events would be (causally) incomparable. But everything
physically meaningful, like total spin when initially prepared,
will work out consistently.

--
John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )

Sylvia Else

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Dec 20, 2012, 11:18:19 AM12/20/12
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Though both A and B can be split into pairs observers A' and A", and B'
and B", and then at a future time A' and B' meet up and compare results.
But so do A" and B", and in a space-like separated way from the meeting
between A' and B'.

So even at the meeting between A' and B', or A" and B", there is still
nothing definite that can be said about the measurements, but the
comparisons appear to have become entangled as well, because they have
to give the same results if they in turn are compared at some common
point in the further future.

Of course, that argument can be continued ad infinitum.

Sylvia.

Rich L.

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Dec 20, 2012, 11:19:25 AM12/20/12
to
[[Mod. note -- In this posting as received, every 2nd line of the quoted
text was blank. I have removed these quoted blank lines. -- jt]]

On Wednesday, December 19, 2012 3:00:59 AM UTC-6, JohnF wrote:
> Rich L. <ralivi...@sbcglobal.net> wrote:
> > [...] If we accept that Relativity is correct then we cannot have
> > a consistent version of physics and still assert that the detection
> > of a particle at A "causes" a certain result at point B which is
> > spacelike separated from A. Rich L.
>
> Doesn't matter which "caused" the other. There's no possible problem
> until information about the outcomes of both measurements eventually
> becomes simultaneously available at some single point/event,
> which will obviously be in the future lightcone of both measurements.
> Until that happens, nobody knows nothing about any possible correlation.
> Supopose you have two different observers, both in the future lightcone
> of both measurements, but relatively moving so that one thinks
> A caused B, and the other thinks B caused A. Doesn't matter.
> Both see total spin (or whatever) zero, and each can validly/consistently
> speculate whatever they like about which caused which. Either the
> -1/2 measurement "caused" the +1/2 measurement, or vice versa.
> Not a meaningful concept, e.g., in a causal set poset, the two separate
> measurement events would be (causally) incomparable. But everything
> physically meaningful, like total spin when initially prepared,
> will work out consistently.
>
> --
> John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )

This response, I think, shows another confusion we have. Some interpret QM to mean that an event hasn't really happened until some person perceives it. In other words, there is no issue about the correlation between what happens at A and B until some person is able to examine both events and wonder about the correlation. There is good reason for this idea, even though I question it myself. There are situations, such as a "photon" reflecting off a diffraction grating, that strongly imply that the photon simultaneously reflected off of each of the facets of the grating at the same time. This raises the questions about the reality of simultaneous alternate paths the photon (or other particle) can take, and what constitutes a measurement (where the wave function "collapses" into a definite single state.

I would like to think that the world does its thing independent of any intelligent being perceiving or wondering about what is happening. That the events at A and B happen, and show what ever correlation they show without any dependence on who observes those events. I realize that this is contrary to some interpretations of QM, and brings us to the difficult question of "What is a measurement?". I am trying to come up with an interpretation of QM that would make all this clearer. I think that reconsidering action at a distance might do that, but I can't claim to have that answered yet. My opinions on all this are probably a bit out of the mainstream.

Rich L.

JohnF

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Dec 27, 2012, 2:29:25 AM12/27/12
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Below are two followups I submitted, twice, to spr
but which never appeared, and no email comments from
moderator, either. So I've posted them here, and
emailed RichL and SylviaE where to find them.

------------------------------------------------------------------------
followup to Rich L
------------------------------------------------------------------------
Rich L. <ralivi...@sbcglobal.net> wrote:
> [[Mod. note -- removed quoted blank lines. -- jt]]
> JohnF wrote:
>> Rich L. <ralivi...@sbcglobal.net> wrote:
>> > [...] If we accept that Relativity is correct then we cannot have
>> > a consistent version of physics and still assert that the detection
>> > of a particle at A "causes" a certain result at point B which is
>> > spacelike separated from A. Rich L.
>>
>> Doesn't matter which "caused" the other. There's no possible problem
>> until information about the outcomes of both measurements eventually
>> becomes simultaneously available at some single point/event,
>> which will obviously be in the future lightcone of both measurements.
>> Until that happens, nobody knows nothing about any possible correlation.
>> Supopose you have two different observers, both in the future lightcone
>> of both measurements, but relatively moving so that one thinks
>> A caused B, and the other thinks B caused A. Doesn't matter.
>> Both see total spin (or whatever) zero, and each can validly/consistently
>> speculate whatever they like about which caused which. Either the
>> -1/2 measurement "caused" the +1/2 measurement, or vice versa.
>> Not a meaningful concept, e.g., in a causal set poset, the two separate
>> measurement events would be (causally) incomparable. But everything
>> physically meaningful, like total spin when initially prepared,
>> will work out consistently.
>> John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )
>
> This response, I think, shows another confusion we have.
> Some interpret QM to mean that an event hasn't really happened
> until some person perceives it. In other words, there is no issue
> about the correlation between what happens at A and B until some person
> is able to examine both events and wonder about the correlation.
> There is good reason for this idea, even though I question it myself.
> [snip]
> Rich L.
>
My reason for it is as follows. It's not so much a person perceiving it,
but rather an apparatus registering it. That is, if you want to say that
"correlation" is an actual physical observable, then you'd better
be able to build a device that blinks once for "yes" or twice for "no"
(or anything like that). And that device necessarily needs the outcomes
of both measurements available to it. Until that becomes possible,
in the future lightcone of both measurements, there can be no such
apparatus, and hence no such physical observable.
John Forkosh ( mailto: j...@f.com where j=john and f=forkosh )

------------------------------------------------------------------------
followup to Sylvia E
------------------------------------------------------------------------
Sylvia Else <syl...@not.at.this.address> wrote:
> JohnF wrote:
>> Rich L. <ralivi...@sbcglobal.net> wrote:
>>> [...] If we accept that Relativity is correct then we cannot have
>>> a consistent version of physics and still assert that the detection
>>> of a particle at A "causes" a certain result at point B which is
>>> spacelike separated from A. Rich L.
>>
>> Doesn't matter which "caused" the other. There's no possible problem
>> until information about the outcomes of both measurements eventually
>> becomes simultaneously available at some single point/event,
>> which will obviously be in the future lightcone of both measurements.
>> Until that happens, nobody knows nothing about any possible correlation.
>> Supopose you have two different observers, both in the future lightcone
>> of both measurements, but relatively moving so that one thinks
>> A caused B, and the other thinks B caused A. Doesn't matter.
>> Both see total spin (or whatever) zero, and each can validly/consistently
>> speculate whatever they like about which caused which. Either the
>> -1/2 measurement "caused" the +1/2 measurement, or vice versa.
>> Not a meaningful concept, e.g., in a causal set poset, the two separate
>> measurement events would be (causally) incomparable. But everything
>> physically meaningful, like total spin when initially prepared,
>> will work out consistently.
>>
> Though both A and B can be split into pairs observers A' and A", and B'
> and B", and then at a future time A' and B' meet up and compare results.
> But so do A" and B", and in a space-like separated way from the meeting
> between A' and B'.
>
> So even at the meeting between A' and B', or A" and B", there is still
> nothing definite that can be said about the measurements, but the
> comparisons appear to have become entangled as well, because they have
> to give the same results if they in turn are compared at some common
> point in the further future.
> Sylvia.

The key fact of your example is, I believe, when you correctly
say that that "they [both] have to give the same results".
And that fact effectively means there's no entanglement,
at least not in the usual "quantum mystery" kind of way...
Consider the following analogous situation. We usually prepare
an entangled pair of electrons in a total spin 0 state to
illustrate the "quantum mystery". But suppose instead that we
have a preparation device that prepares the pair in a total
spin 1 state. Are they still entangled now? Let's see: they've
been prepared entangledly because the preparation device
prepared them as a pair, not as two distinguishbale particles.
On the other hand, we already know their measurement outcomes:
it's |+1/2> for both. That is, "they [both] have to give the
same result", exactly like your remark above.
The elucidation is, I believe, as follows. When prepared in
a total spin 0 state, each electron is in a (mysterious quantum)
superposition state, |+1/2> + |-1/2> (properly normalized).
But when prepared in a total spin 1 state, each electron winds
up in the same (less mysterious) |+1/2> state, no superposition
necessary. And your example above is of that "less mysterious"
no-superposition variety.

Jos Bergervoet

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Dec 28, 2012, 4:07:17 AM12/28/12
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On 12/20/2012 5:19 PM, Rich L. wrote:
...
> I would like to think that the world does its thing
> independent of any intelligent being perceiving or
> wondering about what is happening. That the events
> at A and B happen, and show what ever correlation
> they show without any dependence on who observes
> those events. I realize that this is contrary to
> some interpretations of QM,

Then why don't you stick to the basic equations of
QM? With a Hamiltonian that gives unitary evolution
of a solution vector describing the experiment and
the observers you get everything you ask for in the
above!

> and brings us to the difficult question of "What
> is a measurement?". I am trying to come up with
> an interpretation of QM that would make all this
> clearer.

What exactly do you find unclear about a Hamiltonian
that gives unitary evolution of a solution vector
describing the experiment and the observers?

> I think that reconsidering action at a distance
> might do that,

Might do what?! Why shouldn't we use the existing
mathematical description?

--
Jos
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