Can we violate Bell inequalities by giving up CFD?

[RUTA]

The reasoning goes like this:

• If at some point, Alice knows for certain what Bob's measurement's outcome will be before the measurement takes place, then that reflects a physical fact about Bob's situation.
• Either (A) that fact was true before Alice performed her measurement (and her measurement merely revealed that fact to her), or (B) the fact became true when Alice performed her experiment.
• Choice (A) is a hidden-variables theory, of the type ruled out by Bell's inequality.
• Choice (B) implies that something taking place near Alice (her measurement) caused a change in the facts about Bob.

Nicely said and let me add the following. There is no "fact of the matter" aka "Mermin instruction set" concerning the property of the thing Alice is measuring before she actually performs her measurement, and the same is true of Bob (Choice (A) is ruled out). However, after Alice makes her measurement, there is a "fact of the matter" about what Bob will measure in that same setting. So, as stevendaryl points out, Alice's measurement "caused a change" in the facts about Bob (we're assuming he makes that particular measurement, i.e., I'm not talking about CFD because that is Choice (A) which has been ruled out). But, if the measurements are space-like related, then there is a frame in which Bob's measurement occurs before Alice's and the observers in that frame are equally justified in saying Bob's measurement "caused a change" in the facts about Alice. So, what we have to accept, apparently, is that the events are "co-causal," which means in effect they constitute "one thing." That's the mystery of entanglement -- many experimental outcomes distributed in spacetime all constituting a single, "co-causal" entity.

 

[Nick666]

If it disagrees with experiment then its wrong. In that one statement is the essence of science -

What if the Bell experiments they're doing now with closing all 3 loopholes in the same experiment will not violate the inequalities ?

 

[Ilja]

What if the Bell experiments they're doing now with closing all 3 loopholes in the same experiment will not violate the inequalities ?

This would be fine, the dream of all working theoretical physicists - they would have a chance to find an improvement for the in this case falsified quantum theory.

One could think that I could be unhappy, because this destroys one of my main arguments against standard relativity, in favour of a hidden preferred frame. But, no, I would be happy too.

But unfortunately this is not probable at all.

 

[bhobba]

What if the Bell experiments they're doing now with closing all 3 loopholes in the same experiment will not violate the inequalities ?

That would be very big news and likely be the start of a revolution in physics. But it not very likely - still one never knows.

Thanks
Bill

 

[ShayanJ]

What if the Bell experiments they're doing now with closing all 3 loopholes in the same experiment will not violate the inequalities ?

The comments in the beginning of this lecture were interesting for me. You may want to listen.

 

[RUTA]

There are number of things about your proposed model and RB interpretation in general.
First, entanglement model is not worked out. In p.154-155 setup is described and then when it would be time to introduce particular configuration of "spacetimesource elements" and show how one arrives at expected result there is some handwaving instead.
Second, there was requirement that model has to be local (factorizable, in case bhobba would read this). But as I understand, relations that are fundamental in this model are non-local, right?
Third, to me AGC seems like a cheat (read, non scientific explanation). Is there some motivation why it is reasonable to introduce AGC?
And forth, to me it seems that switching from worldlines to relations as fundamental entities is philosophically fundamental and so extremely radical change that steps out of domain of science.

Oops, I just saw this post. For some reason, I don't get notified of all posts on a watched thread. Thanks for your reply.

1. Entanglement is explained ontologically using Dowker's GHZ set-up in that paper (http://www.ijqf.org/wps/wp-content/uploads/2015/06/IJQF2015v1n3p2.pdf). You can use whatever method you like for computing the probability amplitude of the spacetimesource element associated with a particular outcome. I used the path integral approximation of Sinha, S., & Sorkin, R.: A Sum-Over-Histories Account of an EPR(B) Experiment.Foundations of Physics Letters 4, 303-335 (1991) to compute the amplitude for particular outcomes in the standard EPR-Bell experiment, for example (slides 6-9 of this talk).

2. The spacetimesource element is local in the SR sense, i.e., no superluminal signaling. It is non-local in the geometric sense of a differentiable manifold, but it's called "disordered locality" in that context, not "non-locality." See Caravelli, F., & Markopoulou, F.: Disordered Locality and Lorentz Dispersion Relations: An Explicit Model of Quantum Foam (2012) http://arxiv.org/pdf/1201.3206v1.pdf and Prescod-Weinstein, C., & Smolin, L.: Disordered Locality as an Explanation for the Dark Energy. Physical Review D 80, 063505 (2009) http://arxiv.org/pdf/0903.5303.pdf.

3. We tried to motivate the adynamical global constraint (AGC) over dynamical alternatives in sections 1 and 2 of that paper. Essentially, since we're using ontic structural realism in a block universe, the AGC seemed the simplest way to look for new physics. The AGC is mathematically articulated in section 3 and the corresponding approach to quantum gravity and unification (“An Adynamical, Graphical Approach to Quantum Gravity and Unification,” W.M. Stuckey, Michael Silberstein & Timothy McDevitt. Forthcoming In: Licata, I (ed.) The Algebraic Way: Space, Time and Quantum Beyond Peaceful Coexistence, Imperial College Press, London (2015) http://arxiv.org/abs/0908.4348) has empirical implications (see for example: Stuckey, W.M., McDevitt, T., & Silberstein, M.: Modified Regge Calculus as an Explanation of Dark Energy. Classical and Quantum Gravity 29, 055015 (2012) http://arxiv.org/abs/1110.3973), so I consider it "scientific." That's semantics of course.

4. We chose the ontology of our spacetimesource element because reifying the computational model is typically the simplest way to generate a commensurate ontology. The payoff is a local, realist, psi-epistemic model without CFD or superdeterminism. But, of course, anyone is free to construct their own ontology for our approach, i.e., physics underdetermines metaphysics.

Thanks again for your interest.

 

[atyy]

That would be very big news and likely be the start of a revolution in physics. But it not very likely - still one never knows.

Wow, you are such a sober, serious scientist. Only "likely the start of a revolution"?

 

[Derek Potter]

The reasoning goes like this:

• If at some point, Alice knows for certain what Bob's measurement's outcome will be before the measurement takes place, then that reflects a physical fact about Bob's situation.
• Either (A) that fact was true before Alice performed her measurement (and her measurement merely revealed that fact to her), or (B) the fact became true when Alice performed her experiment.
• Choice (A) is a hidden-variables theory, of the type ruled out by Bell's inequality.
• Choice (B) implies that something taking place near Alice (her measurement) caused a change in the facts about Bob.

Sure. I've said almost exactly the same thing, using the staggered observation scenario. But I put it even more specifically: the sensitivity of Bob's detector is determined by Alice's measurement. I can't see any other way of describing it without abandoning realism. Einstein's sarcasm still stands, made more poignant by the fact it is all confirmed experimentally: there is spooky action at a distance.

 

[zonde]

The comments in the beginning of this lecture were interesting for me. You may want to listen.

The guy have build his model based on "action at a distance" and then from that perspective he is judging why detection loophole isn't likely to be violated. It does not work that way. It's called "assuming the consequent" fallacy.

 

[zonde]

What if the Bell experiments they're doing now with closing all 3 loopholes in the same experiment will not violate the inequalities ?

Nothing. Experiment failed. There are so many ways how you can spoil the experiment that you can't claim you have done it right but QM prediction is just wrong. At least I haven 't seen any proposal for experimental protocol that could in principle claim that QM prediction about violation of Bell's inequalities is falsified.

 

[atyy]

Nothing. Experiment failed. There are so many ways how you can spoil the experiment that you can't claim you have done it right but QM prediction is just wrong. At least I haven 't seen any proposal for experimental protocol that could in principle claim that QM prediction about violation of Bell's inequalities is falsified.

So you think that if the eg. the Aspect experiment had come up with results inconsistent with QM, we would believe QM is right and the experiment had been wrongly performed, like superluminal neutrinos?

 

[Derek Potter]

What means "without CFD" if the CFD is derived?

"without CFD" is what the question asks: "Can we violate Bell inequalities by giving up CFD?"
I don't know what you mean by CFD being "derived". Where is it derived? What is it derived from?

 

[zonde]

So you think that if the eg. the Aspect experiment had come up with results inconsistent with QM, we would believe QM is right and the experiment had been wrongly performed, like superluminal neutrinos?

No, result can be consistent with QM. You just can have poor visibility of correlations so that they do not violate BI.

 

[atyy]

No, result can be consistent with QM. You just can have poor visibility of correlations so that they do not violate BI.

What if you could still show 100% correlation at certain angles?

 

[zonde]

What if you could still show 100% correlation at certain angles?

What do you mean by that? If you have poor visibility you don't have 100% correlation at certain angles. You have 100% correlation modulus visibility at these angles.

 

[Derek Potter]

What do you mean by that? If you have poor visibility you don't have 100% correlation at certain angles. You have 100% correlation modulus visibility at these angles.

To suppress the [+ -] and [- +] cases, which are half of the total, the [+ +] and [- -] rates would have to be doubled. Otherwise the experimenters would notice that the coincidence rate was being depressed. I believe that single detector rates can now exceed 80% so the coincidence detection rate should be more than 50% making it a bit hard for the Conspiracy Fairies to double it for the desired outcomes. So they must resort to making the detectors register wrongly - a [+ -] as a [+ +] for instance. They would still need to collude superluminally (edit - or alter the recorded data - who cares?).

 

[atyy]

What do you mean by that? If you have poor visibility you don't have 100% correlation at certain angles. You have 100% correlation modulus visibility at these angles.

Let's say they can get the EPR result of 100% correlation at certain angles.

But at other angles the prediction of QM is violated, so there is no Bell inequality violation.

Perhaps we could still model that using QM - maybe we just got the Hamiltonian is wrong - rather amazingly at such a low energy.

 

[Derek Potter]

Let's say they can get the EPR result of 100% correlation at certain angles.
But at other angles the prediction of QM is violated, so there is no Bell inequality violation.
Perhaps we could still model that using QM - maybe we just got the Hamiltonian is wrong - rather amazingly at such a low energy.

And if we could it would be a cute model of something that does not exist.

 

[Ilja]

"without CFD" is what the question asks: "Can we violate Bell inequalities by giving up CFD?"
I don't know what you mean by CFD being "derived". Where is it derived? What is it derived from?

In Bell's proof it is derived, in the very beginning, using the EPR argument.

That means, it is derived from:
1.) The EPR criterion: I we can, without in any way disturbing a system, predict with certainty the result of an experiment, then there exists an element of reality which defines this measurement result.
2.) The experimental fact about the 100% anticorrelation in this particular experiment if Alice and Bob measure in the same direction,
3.) Einstein causality, which makes sure that nothing measured by Bob can influence the system measured by Alice, and reverse.
and this derivation works only for this particular experiment - for other experiments, it is far away from clear if one can derive such a thing. So, there is no CFD assumption to be given up.

 

[atyy]

And if we could it would be a cute model of something that does not exist.

We should all definitely say QM will never be falsified, since historically that's the surest way to get something falsified.

OK, to be fair to Thomson, he only really got aeroplanes wrong. He actually was pretty prescient about relativity and quantum mechanics.

For an argument against QM, here is http://arxiv.org/abs/hep-th/0106109. It's a sophisticated form of the argument that the only widely agreed on interpretation of QM is Copenhagen, which needs a classical observer who presumably has a lab in classical spacetime, contrary to quantum gravity where spacetime is quantum.

 

[zonde]

To suppress the [+ -] and [- +] cases, which are half of the total, the [+ +] and [- -] rates would have to be doubled. Otherwise the experimenters would notice that the coincidence rate was being depressed. I believe that single detector rates can now exceed 80% so the coincidence detection rate should be more than 50% making it a bit hard for the Conspiracy Fairies to double it for the desired outcomes. So they must resort to making the detectors register wrongly - a [+ -] as a [+ +] for instance. They would still need to collude superluminally (edit - or alter the recorded data - who cares?).

To violate BI you need around 75% efficiency. That is about the efficiency experimenters get in experiments that close fair sampling loophole (but efficiency is marginally enough to violate BI in these experiments).
But considering present experimental results, for loophole free experiment to fail nature would have to exploit both loopholes - fair sampling loophole and communication loophole (or I would rather say feedback loophole to sound less "conspiracy").

Otherwise the experimenters would notice that the coincidence rate was being depressed.

Coincidence rate is not depressed if you have poor visibility. You just have "wrong" pairs of detections.
And in real experiments there are plenty of reasons why visibility can go down. To notice that at one moment visibility starts to correlate with efficiency might be nearly impossible if you don't have clear protocol at what things you have to look and what things you have to notice.

Anyways hypothetical falsification of prediction can not relay on things like "experimenters would notice".

 

[Derek Potter]

In Bell's proof it is derived, in the very beginning, using the EPR argument.
That means, it is derived from:
1.) The EPR criterion: I we can, without in any way disturbing a system, predict with certainty the result of an experiment, then there exists an element of reality which defines this measurement result.
2.) The experimental fact about the 100% anticorrelation in this particular experiment if Alice and Bob measure in the same direction,
3.) Einstein causality, which makes sure that nothing measured by Bob can influence the system measured by Alice, and reverse.
and this derivation works only for this particular experiment - for other experiments, it is far away from clear if one can derive such a thing. So, there is no CFD assumption to be given up.

In that case I don't understand why you need to ask: "What means "without CFD" if the CFD is derived?" Given that CFD is a corollary of the EPR criterion, "without CFD" simply means "without assuming the EPR criterion".

 

[Derek Potter]

To violate BI you need around 75% efficiency. That is about the efficiency experimenters get in experiments that close fair sampling loophole (but efficiency is marginally enough to violate BI in these experiments).
But considering present experimental results, for loophole free experiment to fail nature would have to exploit both loopholes - fair sampling loophole and communication loophole (or I would rather say feedback loophole to sound less "conspiracy").

Coincidence rate is not depressed if you have poor visibility. You just have "wrong" pairs of detections.
And in real experiments there are plenty of reasons why visibility can go down. To notice that at one moment visibility starts to correlate with efficiency might be nearly impossible if you don't have clear protocol at what things you have to look and what things you have to notice.

Anyways hypothetical falsification of prediction can not relay on things like "experimenters would notice".

Most of that is precisely what I said but I have no idea why you say we can't rely on experimenters to notice the very things they know have to be checked.

 

[zonde]

In that case I don't understand why you need to ask: "What means "without CFD" if the CFD is derived?" Given that CFD is a corollary of the EPR criterion, "without CFD" simply means "without assuming the EPR criterion".

When I asked I had no idea that we can view CFD as derived. And to be honest I'm still not sure that CFD, in a particular sense that say individual photons have a property - polarization, unequivocally follows from EPR argument about elements of reality in conjunction with QM prediction about perfect correlations.

 

[zonde]

Most of that is precisely what I said but I have no idea why you say we can't rely on experimenters to notice the very things they know have to be checked.

What exactly are they going to write in a paper about experimental results? "We failed to perform the experiment but there is something fishy about how it failed."
That is job of theoreticians to point out how to know when the experiment is successful but it fails to confirm prediction, no?

 

[Derek Potter]

When I asked I had no idea that we can view CFD as derived. And to be honest I'm still not sure that CFD, in a particular sense that say individual photons have a property - polarization, unequivocally follows from EPR argument about elements of reality in conjunction with QM prediction about perfect correlations.

It doesn't. The state of the entangled pair is an element of EPR reality, the individual photons do not have states.

 

[Derek Potter]

What exactly are they going to write in a paper about experimental results? "We failed to perform the experiment but there is something fishy about how it failed."

In what sense is discovering a rate suppression that was specifically looked for a failure?

That is job of theoreticians to point out how to know when the experiment is successful but it fails to confirm prediction, no?

I am not a Trade Unionist, but I understand the job of theoreticians is to split hairs rather than design experimental protocols.

 

[andrewkirk]

In Bell's proof [CFD] is derived, in the very beginning, using the EPR argument.

That means, it is derived from:
1.) The EPR criterion: I we can, without in any way disturbing a system, predict with certainty the result of an experiment, then there exists an element of reality which defines this measurement result.
2.) The experimental fact about the 100% anticorrelation in this particular experiment if Alice and Bob measure in the same direction,
3.) Einstein causality, which makes sure that nothing measured by Bob can influence the system measured by Alice, and reverse.
and this derivation works only for this particular experiment - for other experiments, it is far away from clear if one can derive such a thing. So, there is no CFD assumption to be given up.

This is not a derivation. Try writing it out as a formal logical deduction and you will see that it has fatal gaps.

I agree that Bell hypothesises your (3), which he calls 'hypothesis [2]'. He also hypothesises your (2), in the 4th and 5th lines of the first paragraph under heading 'II. Formulation'. Note however that that is not an 'experimental fact' but a hypothesis (see Popper again - it is impossible to experimentally prove that there will always be a 100% anticorrelation). Bell accurately describes this as 'according to quantum mechanics', not an 'experimental fact'.

I don't know where you get your (1) from though. What Bell wrote is 'Since we can predict in advance the result of measuring any chosen component of $\vec{\sigma}_2$, by previously measuring the same component of $\vec{\sigma}_1$, it follows that the result of any such measurement must actually be predetermined'. There is no mention of 'reality' in that part of his paper. Further, one way that the result of the second measurement could be predetermined is if it was predetermined at the time of entanglement, or earlier, what measurements, and at what spacetime locations, would be performed on the two particles, as well as their results. In that case CFD is rejected because it is impossible that any other measurements could be performed instead.

 

[Ilja]

In that case I don't understand why you need to ask: "What means "without CFD" if the CFD is derived?" Given that CFD is a corollary of the EPR criterion, "without CFD" simply means "without assuming the EPR criterion".

If one means "giving up the EPR criterion" one should say so.

First of all, because the derivation of CFD from the EPR argument has a much better candidate for rejection than the EPR criterion, namely the assumption (3) that the "measurement" made by Bob does not influence the system of Alice.

If one says, instead, "giving up CFD", one creates a very false impression of what is given up. Because CFD is a very strong assumption, and it is easy to have theories completely compatible with common sense and completely realistic which don't have CFD: all one needs is to reinterpret the "measurement" as an "interaction". The idea that unperformed interactions should have predetermined results is nonsensical. To give up such a strong and unnecessary assumption would be, therefore, a natural solution for the "problem" which is created by the (misleading) presentation of Bell's theorem as "CFD + Einstein causality => contradiction with QM", which seems to preserve Einstein causality. In fact, it does't, given that we have this first part "EPRC + Einstein causality + QM => CFD".

To give up the EPR criterion is, instead, much harder. It is essentially equivalent to Reichenbach's common cause: On starts with a correlation, in this case one "with certainty", between the prediction and the measurement result, then excludes one direct causal explanation directly by "without in any way disturbing the system", the other one implicitly by naming this a prediction, thus, assuming a temporal order, and what remains is the common cause - the element of reality - which has to predict the result, because everything else would not be sufficient as an explanation for a 100% correlation.

 

[zonde]

In what sense is discovering a rate suppression that was specifically looked for a failure?

What rate do you have on mind? If you mean that there is rate suppression for coincidences then no that was not what I was talking about. Poor visibility means poor quality of entanglement (decoherence, polarization drift). Coincidence rate at the same time can be very good.

 

[Ilja]

This is not a derivation. Try writing it out as a formal logical deduction and you will see that it has fatal gaps.

Not more gaps than usual and acceptable in an informal forum posting with verbal formulation.

I agree that Bell hypothesises your (3), which he calls 'hypothesis [2]'. He also hypothesises your (2), in the 4th and 5th lines of the first paragraph under heading 'II. Formulation'. Note however that that is not an 'experimental fact' but a hypothesis (see Popper again - it is impossible to experimentally prove that there will always be a 100% anticorrelation). Bell accurately describes this as 'according to quantum mechanics', not an 'experimental fact'.

Minor differences, which are relevant for experimenters and experimental-loophole-hopers, but not for the issue which I want to emphasize - the important difference between CFD and the EPR-CR.

I don't know where you get your (1) from though. ... There is no mention of 'reality' in that part of his paper.

From my poor memory about the EPR argument. The argument itself is mentioned in the title of Bell's paper as well as in the text by "With the example advocated by Bohm and Aharonov, the EPR argument is the following." The exact quote of the EPR Criterion of Reality from Einstein, Podolsky, Rosen, Can quantum-mechanical description of physical reality be considered complete, Phys.Rev. 47, p.777 (1935), is the following:

If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of physical reality corresponding to this physical quantity.

Further, one way that the result of the second measurement could be predetermined is if it was predetermined at the time of entanglement, or earlier, what measurements, and at what spacetime locations, would be performed on the two particles, as well as their results. In that case CFD is rejected because it is impossible that any other measurements could be performed instead.

Yes, the superdeterminism loophole. You have forgotten to mention the Matrix loophole - that reality is, in one formulation I like, "only a boring advanture game, but the graphics are cool". Above loopholes could be easily considered as variants of giving up causality, because in above worlds causality would be meaningless. Anyway, they would be interesting only for people who would not give up relativity even if a working FTL phone would be presented to them.

 

[harrylin]

[..] The idea that unperformed interactions should have predetermined results is nonsensical. [..]

That "nonsensical idea" is exactly what Bell argues to be logically necessary - and at first sight his reasoning looks sound to me and most others.
He argues as follows:

"We are assuming that particles
have properties which dictate their ability to pass certain tests - whether or
not these tests are in fact made. To account for the perfect anticorrelation
when identical tests (parallel Stern-Gerlach magnets) are applied to the two members
of a pair, we have to admit that the pairing is a generalized à la
Bertlmann - when one has the ability to pass a certain test, the other has not."
- Bertlmans's socks, Bell

I think that for those angles the reasoning is indisputable and I'm curious if you can point out an error in that reasoning.

For me a somewhat tricky part (which he claims to be "trivial") is the expanded reasoning that follows for other angles.

 

[Derek Potter]

If one means "giving up the EPR criterion" one should say so.

Yes and if you mean "one particular case" then one should say so. The derivation you have kindly unpacked for me ("EPRC + Einstein causality + QM => CFD") only derives CFD in one special case, not "QM". A special case where BI is not even violated. As zonde's question is about BI violation you cannot claim that CFD is derived. (edit i.e. for zonde's purposes.)

 

[Ilja]

That "nonsensical idea" is exactly what Bell argues to be logically necessary - and at first sight his reasoning looks sound to me and most others.
He argues as follows:
"...To account for the perfect anticorrelation when identical tests (parallel Stern-Gerlach magnets) are applied to the two members of a pair, we have to admit that ..."
I think that for those angles the reasoning is indisputable and I'm curious if you can point out an error in that reasoning.

(emphasis and ... mine)
I don't even want to do this, because I agree with this reasoning.

My point is that assuming CFD, as a general principle, does not make such arguments, but simply assumes that all unperformed measuerements have outcomes - this is, last but not least, what is implicitly presupposed if one names something a measurement - that means, something existing is measured. But this naive presupposition would disappear if one remains "measurement" into "interaction". If I interact with paper using a pencil, the resulting picture will not be the measurement of some property of the paper, and nobody would suspect that this picture existing as part of the paper before I started my interaction.

Instead, Bell does not make such a presupposition. He proves that, in this particular situation, it follows from the perfect anticorrelation (and, of course, Einstein causality).

 

[Ilja]

Yes and if you mean "one particular case" then one should say so. The derivation you have kindly unpacked for me ("EPRC + Einstein causality + QM => CFD") only derives CFD in one special case, not "QM". A special case where BI is not even violated. As zonde's question is about BI violation you cannot claim that CFD is derived.

Why do you think that BI is not violated in this special case?

The question is, of course, what exactly is the "special case" here. It is defined by the preparation of that special superpositional state - which makes it special - but for all possible measurements of spin components by Alice and Bob. Because for every particular such spin measurement, we can apply the EPR reasoning and conclude that for this particular outcome CFD holds.

And this is already enough CFD to prove the BI.