Bell Theorem and probabilty theory

[mn4j]

Actually, this loophole is testable experimentally : we just have to emit the pairs of particles one by one, so that the time window for coincidences can be extended far beyond the maximum processing time for the detection.
This way, we can count all detections, whatever the delay between them.

If the idea in the paper is right, Bell's inequality should become respected.
If the idea in the paper is wrong, Bell's inequality should still be violated.

Maybe this have been already done.

What do you mean by "emit the pair of photons one by one"?
Aren't two entagled photons emitted at the same time, by definition?

 

[Pio2001]

I mean decreasing the emission rate until pairs of photons are emitted slower (both photons being still emitted at the same time, of course).
we can then set the window of the coincidence counter very large, so that it counts the detection of two photons whatever the small time delay introduced by the authors in order to violate Bell's inequality.

If I have understood correctly their simulation, De Raedt et al.show that Bell's inequality violation in Aspect-like experiments is not necessarily caused by quantum non-local effects, but may come from an artefact caused by the coincidence counter setup.

Quantum theory predicts that as long as the two photons are from the same entangled pair, Bell's inequality will be violated.
In my understanding, De Raedt et al. simulation violates Bell's inequality introducing a delay between the photons AND setting the coincidence window narrower than this delay. So it predicts that if the coincidence window is widened enough for counting all coincidence, whatever the delay between the recording of the events, Bell's inequality will become respected.

In practice, that's exactly what happens in the real data set that they took as an example, BUT, it seems logical to assume that this is because widening the time window, we count more and more false coincidences, thus decreasing the correlations.
Decreasing the physical emission rate at the source, we should be able to widen the coincidence window without increasing the false coincidence rate at all.

This way, if Bell's inequality is still violated, the hypothesis of an artifact in the coincidence counter setup will be rejected, and the quantum non local correlations will remain the only explanation.

 

[zonde]

we just have to emit the pairs of particles one by one, so that the time window for coincidences can be extended far beyond the maximum processing time for the detection.

There is something that can be done without decreasing emission rate.
You can use two coincidence windows of different width. Say that coincidences that are in one widow but are outside other will be poorly synchronized coincidences and coincidences that are inside smaller widow are decently synchronized coincidences. Now if you calculate rate "poorly synchronized coincidences"/"decently synchronized coincidences" for different relative polarization angles you should not see any correlation between relative angle and this rate for fair sampling assumption to hold.
And if there is no such correlation there will be match less possible models for coincidence loophole if any.
Good thing is that analysis like that can be done without performing any new experiments based only on existing data from experiment where all detections are recorded with timestamps (and coincidences are found later from recorded data).

 

[DrChinese]

Maybe what you need is to spell out what evidence it will take for you to see the problem with Bell's theorem. Surely if your belief in it is rational, it must be falsifiable. What will it take to falsify it? Seriously, have you ever considered this question even?

Let's see if I get this right. The experimental evidence is X, and we are supposed to use that evidence to conclude not-X.

The thing about Bell is that it is more or less independent of whether local reality or QM is correct. It says they both cannot be correct, which was not obvious at the time. So let's get specific.

QM says the coincidence rate for entangled photon pairs at 60 degrees is 25%. Local realistic theories say the true coincidence rate is at least 33%. Raedt is saying that the true rate is [insert your guess here since he skips this step]% but that experiments will always support QM.

Now, once again, how are we supposed to conclude there is anything wrong with Bell? Clearly, the entire issue here is Raedt trying to explain why a LR theory, which makes predictions incompatible with QM, actually provides an experimental result compatible with QM. So clearly, this is not about Bell at all. You may as well say that all experiments supporting General Relativity are actually evidence of Newtonian gravity.

Now, get serious. Even Raedt ought to be able to see why the argument falls flat. It is going to take experimental evidence IN FAVOR of a local realistic theory to convince anyone of their result. If they really had a bead on anything, they would be proposing an experiment to test their ideas. Rather than writing a paper saying they are correct in the face of evidence to the contrary.

 

[kobak]

I spent some time reading de Raedt's articles and talking with him about them. Let me answer some of the mn4j's questions in the last postings ("the only two important questions", as you write).

So what?. You still did not answer the following:
1. Do you deny that they presented event-by-event simulation of EPRB?
2. Do you claim that the model of their simulations is not local realistic?

These are the only two important questions. If you agree that they have indeed presented an event-by-event simulation of EPRB, then you end up with only two options

a) Their model is not local realistic or
b) Their model is local realistic contrary to the claims of Bell.

1. Yes, they did present event-by-event simulations of the certain experiments (like Aspect's and Weihs' et al.), that often are thought to be conclusive evidences that Bell's equality is violated.

2. Yes, their models are local realistic.

But you are totally wrong about two options that I'm supposedly left with. The important thing to realize is that no conclusive test of EPRB has ever been done. Every experiment that has been conducted has certain loopholes (there's even a special wikipedia article about those). This means that all those experiments are not ideal, and it's possible to explain their results with a local realist theory. This is well-known to everybody who is interested in QM foundations, and has been known already for ages (Philip Pearle showed in the late 1970s how this can be done using one of the loopholes).

de Raedt presents yet another model of how these loopholes can be used to still "give some chance" to local realism. This is certainly not a big deal, and has no consequences to Bell's theorem. The usual hope is that in some years the conclusive experiment will be performed (I've heard people hoping that it will occur in 10-20 years).

What I find particularly confusing in de Raedt's articles is that they are totally out of context: he never mentions a word "loophole", leave alone all existing bulk of knowledge about them. This is misleading to say the least.

See http://arxiv.org/abs/quant-ph/0703120 for this critique (yes, I do know that there's a reply by de Raedt; I think that his reply misses the point).

This seems rather dismissive. Raedt's work is not an attack on QM. They have developed a local realistic hidden variable model which gives the same result as QM in EPR type experiments and explains double-slit diffraction among other phenomena.
The matter is very simple, do you claim their model is not local realistic?

This paper about double-slit (http://arxiv.org/abs/0809.0616) is a different story, but also very telling. Have you read it? Did you realize that this model works only because many photons "get lost"? If we imagine a perfect emitter that emits 1 photon per second and we let it emit 1000 photons, and then we count how many photons hit the screen and how many photons hit the double-slit screen, and then we add those two numbers together, then the result according to this model will be a lot less then 1000.

This is clearly a prediction different from that of QM. This model can be tested and falsified. I'm absolutely sure that it's just wrong.

Of course such an experiment is tremendously difficult to perform, but there's an easier test. This model works because the detectors have memory and are "learning". Now if we start to jiggle the screen back and forth (parallel to itself) sufficiently fast, then de Raedt's model predicts that the interference image will get smeared (I think it's stated in the paper). Now, here's the question for you: what is the prediction of QM?

I think that QM predicts that the interference picture will stay the same. I asked de Raedt this question, and he replied that in his opinion QM predicts nothing, because it requires the experimental apparatus to be completely fixed during the experiment and not "jiggled". Well, then I asked him what would he say if such an experiment is performed and the interference picture does not change.

He said that in that case he would (I quote here) retire.

The bottomline is that what de Raedt proposes are some local realistic explanations of the certain experiments. All his models are in principle distinguishable from QM (as Bell always told us). And personally I'm quite sure that when the tests are done, these models will be proven false.

 

[Pio2001]

QM says the coincidence rate for entangled photon pairs at 60 degrees is 25%. Local realistic theories say the true coincidence rate is at least 33%. Raedt is saying that the true rate is [insert your guess here since he skips this step]% but that experiments will always support QM.

Yes, it follows from figure 6 in the first paper that according to their simulation, the true rate, in your example, may actually be 25 %, while being measured at 33 % because of the least correlated photons being registered by the two detectors at a time interval bigger than the time window of the counter. Which leads to discarding the least correlated pairs.

 

[DrChinese]

I spent some time reading de Raedt's articles and talking with him about them. Let me answer some of the mn4j's questions in the last postings ("the only two important questions", as you write).
1. Yes, they did present event-by-event simulations of the certain experiments (like Aspect's and Weihs' et al.), that often are thought to be conclusive evidences that Bell's equality is violated.

2. Yes, their models are local realistic.

But you are totally wrong about two options that I'm supposedly left with. The important thing to realize is that no conclusive test of EPRB has ever been done. Every experiment that has been conducted has certain loopholes (there's even a special wikipedia article about those). This means that all those experiments are not ideal, and it's possible to explain their results with a local realist theory. This is well-known to everybody who is interested in QM foundations, and has been known already for ages (Philip Pearle showed in the late 1970s how this can be done using one of the loopholes).

de Raedt presents yet another model of how these loopholes can be used to still "give some chance" to local realism. This is certainly not a big deal, and has no consequences to Bell's theorem.

...

The bottomline is that what de Raedt proposes are some local realistic explanations of the certain experiments. All his models are in principle distinguishable from QM (as Bell always told us). And personally I'm quite sure that when the tests are done, these models will be proven false.

Welcome to PhysicForums, kobak! And thank you very much for this insight on de Raedt.

I was just looking at the papers in a bit more detail. I have been disappointed by the approach, as it obscures what is being asserted in favor of trying to prove Bell wrong (which I think is overreaching). I do not personally consider these to be counter-examples to Bell, and I seriously doubt they will sway others either.

1. Their model (at least in one paper) does not provide fair sampling (assuming I read it correctly) to deliver an explicitly biased sample. As such, it exploits the loopholes you mention and doesn't really provide anything new (as you also mention). Quote:

"The mathematical structure of Eq. (18) is the same as the one that is used in the derivation of Bell’s results and if we would go ahead in the same way, our model also cannot produce the correlation of the singlet state. However, the real factual situation in the experiment [8] is different: The events are selected using a time window W that the experimenters try to make as small as possible. ...

"In our simulation model, the time delays ti are distributed uniformly over the interval [0, Ti] where T1 = [not random]."

In other words, there is tinkering with the time window and by their choice of how the time window is chosen, combined with time delay parameter choice, they bias the sample. They have to, because otherwise the raw source data would run afoul of Bell.

2. The other paper (also Dec 2007/Feb 2008) relies on so-called DLMs (Deterministic Learning Machines). These purport to satisfy local causality and involve a form of memory from trial to trial:

"A DLM learns by processing successive events but does not store the data contained in the individual events. Connecting the input of a DLM to the output of another DLM yields a locally connected network of DLMs. A DLM within the network locally processes the data contained in an event and responds by sending a message that may be used as input for another DLM. Networks of DLMs process messages in a sequential manner and only communicate with each other by message passing: They satisfy Einstein’s criterion of local causality. For the present purpose, we only need the simplest version of the DLM [11]. The DLM that we use to simulate the operation of the Stern-Gerlach magnet is defined as follows. The internal state of the ith DLM, after the nth event, is described by one real variable un,i. Although irrelevant for what follows, this variable may be thought of as describing the fluctuations of the applied field due to the passage of an uncharged particle that carries a magnetic moment."

and

"A key ingredient of these models, not present in the textbook treatments of the EPRB gedanken experiment, is the time window W that is used to detect coincidences. We have demonstrated (see Section IIG) the importance of the choice of the time window by analyzing a data set of a real EPRB experiment with photons [32].

3. With both of these, the critique is really the same: why not point to the specific difference? They do everything humanly possible to obscure what should be a simple point: what is the difference between QM and their LR? Clearly, they could show how their data points satisfy the Inequality if all trials are considered and are fully independent, while the sub-sample within the time window is biased to yield a result consistent with QM but violating the Inequality.

Specifically: the QM prediction of entangled photon coincidences is .250 at 60 degrees. So we know their adjusted result must therefore also be .250. The LR value must be .333 or greater, so the delta is .0833. Which data items were excluded to get this result? Or why would the results be biased specifically towards that of a wrong theory (QM)? These are the lines in the sand, and they really are not addressed. I can see the hand waving in the equations, but without this simple explanation I don't see where they have anything. Quoting again:

"Extensive tests (data not shown) lead to the conclusion that for d = 3 and to first order in W, our simulation model reproduces the results of quantum theory of two S = 1/2 objects, for both Case I and Case II."

Clearly, for the algorithm to work, the delta must be .0833 at 60 degrees; delta=0 at 0 and 45 degrees; and so on. That delta function, in my opinion, should jump off the page. In reality, I don't think they have identified such a function. They should be the ones to point out the source of the delta. I have tried, but can't really follow their algorithm far enough to generate values.

My point is basically: why not make a testable prediction showing how using the algorithm, the experimental results vary in good agreement with the model but NOT according to any quantum mechanical prediction? I.e. if I change the time window and delay parameters in an actual experiment, the results match the LR model but are not explained by QM. After all, according to the LR model, it is strictly an accident of chance that QM happens to be correct in its predictions regarding how entangled photons behave (since there are no such things as entangled photons in LR, by definition).

 

[Pio2001]

I have tried, but can't really follow their algorithm far enough to generate values.

I only read the december 2007 paper with the Deterministic Learning Machines. They give two algorithms, the one with DLM (page 16 : deterministic model), and a pseudo-random one, much simpler (page 16 : pseudorandom model). The way to sort results follows (page 17 : time tags / data analysis).

They suggest a possible physical meaning for this bias : "experimental evidence that the time-of-flight of single photons passing through an electro-optic modulator fluctuates consederably can be found in ref 56"

I find this idea interesting, because it is more realistic to suppose that the time-of-flight of a photon can depend of its polarisation in an environnement sensitive to polarisation, than to suppose that the detector purposely discards detections that would comply with Bell's inequality.
This relation is explicitely proposed page 17 in the last paragraph before "5.Data Analysis" (the formula have no number). They later set d=3 in this formula (for 1/2 spin particles).

Zonde's idea to test coincidence efficiency vs relative angle seems good. We could try it on available data (after checking that it works for all possible scenarii of this kind).

 

[DrChinese]

They suggest a possible physical meaning for this bias : "experimental evidence that the time-of-flight of single photons passing through an electro-optic modulator fluctuates consederably can be found in ref 56"

I find this idea interesting, because it is more realistic to suppose that the time-of-flight of a photon can depend of its polarisation in an environnement sensitive to polarisation, than to suppose that the detector purposely discards detections that would comply with Bell's inequality.
This relation is explicitely proposed page 17 in the last paragraph before "5.Data Analysis" (the formula have no number). They later set d=3 in this formula (for 1/2 spin particles).

Thanks, I'll look again. There must be a connection between the polarization and detection probability (which is here related to the window size and delay factors) in order to get the desired results. I just couldn't figure out where, and I couldn't figure out why that wasn't highlighted.

 

[mn4j]

Let's see if I get this right. The experimental evidence is X, and we are supposed to use that evidence to conclude not-X.

The thing about Bell is that it is more or less independent of whether local reality or QM is correct. It says they both cannot be correct, which was not obvious at the time. So let's get specific.

You do realize that Bell has a definition of local reality which has not been verified experimentally don't you. If you think it has been verified, show me experimental evidence that proves Bell's definition of local reality. Have you not been reading this thread at all? The bulk of the discussion was about this point.

QM says the coincidence rate for entangled photon pairs at 60 degrees is 25%. Local realistic theories say the true coincidence rate is at least 33%. Raedt is saying that the true rate is [insert your guess here since he skips this step]% but that experiments will always support QM.

NO! Bell's local realist theories say the true coincidence rate is 33%. If you disagree, point me to a reference about a local realist theory which makes that claim. Again you will notice that only Bell makes that claim, which it turns out is a straw-man, because there is no experimental validation of it. Do you know of any local realist theory for which that claim is valid? If not, why do you state it as though it was dogmatically accepted to be the case?

So then we have:
1. What QM predicts
2. What Bell claims (and this is crucial) local realist theories should result in
3. What experiments observe

It turns out (1) agrees with (3) but disagrees with (2). If you are thinking intellectually honestly, you must realize that failure of (3) to agree with (2) can mean that Bell's claim about local realist theories is dubious. Yet, for some reason you'd rather think Bell was a god and every claim he made was dogma, which leads you to conclude that both (1) and (3) are results of non-local realist theories. Why is that, I ask? This is not rocket science.

Now, once again, how are we supposed to conclude there is anything wrong with Bell? Clearly, the entire issue here is Raedt trying to explain why a LR theory, which makes predictions incompatible with QM, actually provides an experimental result compatible with QM.

NO! Your bias is clouding your judgement of Raedt's work. Raedt has developed a model which is unmistakably and convincingly LR, and he shows that it agrees with (1) and (3). Again, if you are thinking intellectually honestly, you must realize that according to Bell's definition (and this is crucial) of what LR means, this is impossible.

If you want to criticize Raedt, you have to show that either:
1) The model he has developed is not LR
2) The model he has developed does not reproduce the results of QM and real experiments
You have done neither.

Now, get serious.

No. YOU get serious!

 

[mn4j]

The important thing to realize is that no conclusive test of EPRB has ever been done.

EXACTLY! So on what basis do followers of Bell purport to have proven that local realist theories should produce a certain result?

Here is an experiment to try:
- use a separate set of apparatus for each pair of photons emitted. If you still obtain the QM result, then Raedt's model is wrong.

 

[kobak]

> The important thing to realize is that
> no conclusive test of EPRB has ever been done.

EXACTLY! So on what basis do followers of Bell purport to have proven that local realist theories should produce a certain result?

Well, I'm glad that we agree on something. However, your question doesn't relate to my statement that you quote. Let me try to clarify things a bit.

There are two things: Bell's theorem as an abstract theorem, and its experimental tests. Bell's theorem states that local realist theories can't reproduce all the predictions of QM. It doesn't need to be proven by experiment, because the proof is given on a piece of paper. The experiment has to show what is correct: QM or local realism. What I said means that no conclusive proof that QM is right and LR is wrong (i.e. no conclusive violation of Bell's inequalities) has ever been done. This has no relation to the validity of the theorem itself.

Now, you seem to claim that Bell's theorem is wrong. But even if it were wrong, de Raedt's articles about EPR wouldn't prove it wrong (because as I explained, those articles only show that the experiments done so far were not perfect).

Finally, one more point. What exactly does "local realism" mean, is a philosophical question. For his proof Bell used a particular equation (P(A|aBL) = P(A|aL) or something like that) and he gave certain "physical" arguments about why this should be true if we assume local realism.

Famous ET Jaynes (and de Raedt follows Jaynes here) wrote a paper that you cited in this discussion, where he claimed that Bell made a stupid mistake when applying rules of probability (this is not a quote, but that's how it sounds). This is absurd. Bell certainly understood the rules of probability perfectly well and he actually did give the physical arguments for his assumption (that Jaynes seemed to fail to either notice or understand).

You may still say that local realism does not necessarily entail this assumption of Bell. Since "local realism" isn't something defined by a formula, this is in principle a meaningful claim. However I never saw any local realist model that would violate Bell's assumption (in the very particular example that Bell is discussing). de Raedt's models of simulations of Aspect-Weihs experiments have no relation to this issue.

 

[mn4j]

The experiment has to show what is correct: QM or local realism. What I said means that no conclusive proof that QM is right and LR is wrong (i.e. no conclusive violation of Bell's inequalities) has ever been done. This has no relation to the validity of the theorem itself.

Why MUST LR and QM contradict each other? Just because Bell says they must? This is what you fail to realize. The issue here is not whether QM is wrong and LR is right! The issue, whether Bells understanding of LR is correct.

Now, you seem to claim that Bell's theorem is wrong. But even if it were wrong, de Raedt's articles about EPR wouldn't prove it wrong (because as I explained, those articles only show that the experiments done so far were not perfect).

If you agree that the experiments were not perfect, then how come those same experiments are still presented as proof of Bell's theorem. Bell's theorem is a negative theorem.

Bell says, "NO LR can reproduce the QM results". Now Bell better be sure that his definition of LR is such that it accounts for EVERY possible LR theory. If even 1 is found that can not be modeled by Bell's equations, Bell's theorem has to be thrown out. Do you agree with this? De Raedt's articles presents just one such models.

Finally, one more point. What exactly does "local realism" mean, is a philosophical question. For his proof Bell used a particular equation (P(A|aBL) = P(A|aL) or something like that) and he gave certain "physical" arguments about why this should be true if we assume local realism.

Famous ET Jaynes (and de Raedt follows Jaynes here) wrote a paper that you cited in this discussion, where he claimed that Bell made a stupid mistake when applying rules of probability (this is not a quote, but that's how it sounds). This is absurd. Bell certainly understood the rules of probability perfectly well and he actually did give the physical arguments for his assumption (that Jaynes seemed to fail to either notice or understand).

I'll take Jaynes over Bell any day when it comes to who understands probability better. Take a look at De Raedts recent article together with Hess (http://arxiv.org/abs/0901.2546) for a succinct explanation of Bell's error.

You may still say that local realism does not necessarily entail this assumption of Bell. Since "local realism" isn't something defined by a formula, this is in principle a meaningful claim. However I never saw any local realist model that would violate Bell's assumption (in the very particular example that Bell is discussing).

Don't you realize that the type of claim Bell is making about LR models requires that he MUST be absolutely sure that he has presented an exhaustive representation of ALL POSSIBLE LR models. I am perfectly happy to accept that Bell's theorem is true ONLY for the LR models narrowly defined by his assumptions.

de Raedt's models of simulations of Aspect-Weihs experiments have no relation to this issue.

Don't forget that you already agreed that de Raedt's model is LR. So they are relevant. Bell's equations do not apply to a deterministic learning machine model like de Raedt's. How then can Bell claim that No LR can reproduce the QM results?

You see, the problem with Bell's theorem is not that his conclusions can not be drawn from his assumptions. The problem is that those conclusions are interpreted by those who don't know better beyond the scope of the assumptions on which they are based. For someone purporting to characterize all LR models, he chose a severely narrow and handicapped subset of LR to base his calculations on.

 

[Pio2001]

What about the GHZ proof, then ?

 

[kobak]

Dear mn4j,
we are already going in circles. I will try to summarize my points as clear as possible and I would like to ask you to comment on each of them, whether you agree or not. If you still don't listen to what I'm saying, then it's better to stop this discussion.

1. All the experiments that has been done so far to test Bell's inequalities ARE. NOT. PERFECT. This is not something to agree or disagree, it's just a fact, and it's admitted by everybody, including of course the experimenters themselves. Agreed?

2. These experiments definitely can't be presented "as proof of Bell's theorem", because they are not. Please stop asking me why they are presented in such way! If anybody does so, he or she just doesn't understand anything here. Bell's theorem is a theoretical construct, it doesn't need to be proven by experiment. Experiment has to show whether Bell's inequalities are violated or if they are not. Agreed?

3. I quote you: "I am perfectly happy to accept that Bell's theorem is true ONLY for the LR models narrowly defined by his assumptions". OK, let's call all theories that Bell's theorem applies to "Bell local realistic" (BLR). Now, Bell's theorem says and proves that BLR theories should obey Bell's inequalities while QM violates them. Agreed?

4. Your main point seems to be that BLR is only a narrow subclass of LR theories. Well, I repeat: what is "local realism" is a philosophical question. I'm personally quite happy to include in my notion of local realism the assumption that the outcomes of Bob's experiments are statistically independent from Alice's choice of experimental settings (this is Bell's assumption and precise definition of BLR). You are not, right?

5. Since scientific consensus is that BLR and LR are the same thing, and you disagree, the only meaningful way to disagree is to give an example of a LR theory that is not BLR. Agreed?

6. In case you want to say that de Raedt's models are such kind of example, I repeat once again: NO, they ARE NOT. de Raedt showed (as was already known) that the experiments to test Bell's inequalities were not perfect (there are loopholes), and because of these experimental flaws their results can be explained in LR way. Agreed?

7. But (the crucial point!) de Raedt's model is obviously not only LR, but BLR as well! IF a loophole-free test of Bell's inequalities is ever done and IF Bell's inequalities are still found to be violated, then de Raedt won't be able to explain this with his model (why? because of Bell's theorem). Agreed? Please think a bit before answering.

I'm asking you think, because you wrote that "Bell's equations do not apply to a deterministic learning machine model like de Raedt's". This is just plain wrong. Of course they do apply! De Raedt's model is perfectly BLR.

8. You mentioned the recent de Raedt's article with Hess (http://arxiv.org/abs/0901.2546). I've seen it and I took a brief look, but I didn't read it carefully and I failed to understand the crux of it. I just don't want to investigate 40+ pages of formulas, when I already know that de Raedt's reasoning is often confusing and misleading, and that Hess is well-known for fighting will Bell's theorem, though his claims were long ago shown wrong by people, whose opinion I respect in this issue (see http://arxiv.org/abs/quant-ph/0208187).

If you have read and understood this 40+ pages article, everybody here will be grateful if you give us the arguments in a concise and clear way.

9. For some reason you completely ignored my point about double-slit paper of de Raedt. You were first to mention it! Did you read it? If you did, could you please comment on what I said earlier? If you didn't, how come you use it in the arguments?


dk

 

[DrChinese]

8. You mentioned the recent de Raedt's article with Hess (http://arxiv.org/abs/0901.2546). I've seen it and I took a brief look, but I didn't read it carefully and I failed to understand the crux of it. I just don't want to investigate 40+ pages of formulas, when I already know that de Raedt's reasoning is often confusing and misleading, and that Hess is well-known for fighting will Bell's theorem, though his claims were long ago shown wrong by people, whose opinion I respect in this issue (see http://arxiv.org/abs/quant-ph/0208187).

If you have read and understood this 40+ pages article, everybody here will be grateful if you give us the arguments in a concise and clear way.

Good post. I tried to find the meat in the argument and couldn't either. If anyone had a good counter-argument, they would put their proof up front rather than hide it. Meanwhile, we have the following history of experimental teams seeing violation of Bell Inequalities:

Aspect, 1982: 5 standard deviations.
Kwiat, 1995: 102 standard deviations.
Kurtsiefer, 2002: 204 standard deviations.
Barbieri, 2003: 213 standard deviations.

And since entanglement doesn't even exist in any local realistic theory (by definition), it is interesting to note that last year, Vallone et al were observing hyper-entanglement on photons in 3 independent degrees of freedom. Further, there have been numerous experiments involving time-bin entanglement, including with photons that have never interacted in the past. Just the loophole de Raedt thought to exploit in his later paper (you would think experiments like this would finally end the search for an LR theory).

None of this could be predicted by any local realistic theory. On the other hand, all are predicted by QM. This is why looking for LR theories is a waste of time. It made sense up until the 1970's or so, but not since.

 

[kobak]

Meanwhile, we have the following history of experimental teams seeing violation of Bell Inequalities

Sorry, DrChinese, are you saying that some of these experiments were loophole-free? As far as I know, this has so far never been achieved.

If it is true, then exactly how many standard deviations is observed -- doesn't really matter. A strict believer in local realism still can say: there are this and that loopholes, and so the results can be explained in a sophisticated enough local realistic way. It can be 100000 standard deviations, or whatever. What is important (in the sense of putting a full stop in this discussion) is to conduct an experiment, completely free of any loopholes.

 

[DrChinese]

Sorry, DrChinese, are you saying that some of these experiments were loophole-free? As far as I know, this has so far never been achieved.

If it is true, then exactly how many standard deviations is observed -- doesn't really matter. A strict believer in local realism still can say: there are this and that loopholes, and so the results can be explained in a sophisticated enough local realistic way. It can be 100000 standard deviations, or whatever.

I disagree. What is being asserted is anti-scientific because in a sense, no experiment is loophole free. As you are undoubtedly aware, there are still experiments going on to test General Relativity. At least there, the competing theories (or versions of GR as you may call them) have key elements in common.

On the other hand, there is no existing candidate LR theory on the table to compare to QM at this time. Stochastic Mechanics (Marshall, Santos) is an example of a field of research in that regard, but every candidate SM model is found to have problems and is quickly modified again. And since such models do not predict anything useful, there is no incentive to study them further. We already have a very useful model - QM - and the experiments supporting it are in the thousands. Something useful from the field of study would go a long way towards convincing the scientific community.

So yes, I think quantity does matter, and I think utility matters. And I think the history of the area does matter as well, including when a theory (QM) is supported by improving technology. That doesn't mean that conventional thinking is right always. I just mean to say that science evolves towards ever more useful theories. I do not see how LR theories can ever hope to fall into that category (useful) since they deny the known phenomena of entanglement. I mean, we are at the point now of entangling particles with no common history. Why don't the local realists acknowledge the obvious hurdle such experiments place on LR theories?

And as a practical matter, I disagree that loophole-free experiments have not been performed. In my opinion, the fair-sampling loophole has been closed (Rowe et al, 2001). In my opinion, the strict locality loophole has been closed (Weihs et al, 1998). Etc. Why should you need to close every loophole simultaneously if you can close each separately? If a prisoner cannot escape from the first lock by itself, and cannot escape from the second lock by itself, how can he escape when both locks are present? I don't disagree with a desire to close all loopholes simultaneously; but I think that is a standard that is being applied to Bell tests which is applied nowhere else in science. Surely you must have noticed this as well.

 

[kobak]

I disagree. What is being asserted is anti-scientific because in a sense, no experiment is loophole free. As you are undoubtedly aware, there are still experiments going on to test General Relativity. ... And as a practical matter, I disagree that loophole-free experiments have not been performed. In my opinion, the fair-sampling loophole has been closed (Rowe et al, 2001). In my opinion, the strict locality loophole has been closed (Weihs et al, 1998). Etc. Why should you need to close every loophole simultaneously if you can close each separately? ... I don't disagree with a desire to close all loopholes simultaneously; but I think that is a standard that is being applied to Bell tests which is applied nowhere else in science. Surely you must have noticed this as well.

Three points. First. I'm not an expert in Bell tests and loopholes issue, so can't really comment on that on the detailed level. I know that there's for example "time-coincidence" loophole (http://arxiv.org/abs/quant-ph/0312035), which is apparently exactly the loophole de Raedt is exploiting (http://arxiv.org/abs/quant-ph/0703120, the link I already gave). I'm not sure that all known loopholes were already closed even separately, though this might be true. In particular, I just don't know any details about this "entanglement" studies that you cite (and don't have time at the moment to start reading them). Do they test Bell inequalities after this entanglement "swapping"? Or how else these findings prove LR false?

Second. I guess that I slightly disagree with you about different standards of tests. Of course there are super-precise tests of GR still being done. But to test GR you need to observe something that is predicted by GR, like light deflection or whatnot. When this is observed, nobody claims that there's a "loophole" in this experiment, and the results can be interpreted such that light is not deflected. It's evident: nobody heard of any loopholes in GR tests. On the other hand, to test QM versus LR one needs to show that the Bell's inequalities are violated. And all the attempts to show it still have some loopholes that allow alternative explanations.

Third. Nobody in his right mind claims that QM is "wrong". For de Raedt, QM is a correct mathematical model working well on the ensemble level only, without saying anything about single events. He is not trying to show that QM is wrong, he is trying to show that it can be completed in a LR way. Well, we know that it's impossible due to Bell. But de Raedt obviously disagrees. And it doesn't make a lot of sense for me to defend de Raedt, but he is most definitely not a crackpot (he has done a huge amount of "real" work in computer simulations of different physical models, including decoherence etc.). I believe (as you do) that his reasoning about Bell is flawed, but he certainly does not try to obscure anything on purpose: I'm quite sure that he is honest.

 

[mn4j]

1. All the experiments that has been done so far to test Bell's inequalities ARE. NOT. PERFECT. This is not something to agree or disagree, it's just a fact, and it's admitted by everybody, including of course the experimenters themselves. Agreed?

Agreed! This is a fact. Not a single loophole-free experiment has ever been performed.

2. These experiments definitely can't be presented "as proof of Bell's theorem", because they are not. Please stop asking me why they are presented in such way! If anybody does so, he or she just doesn't understand anything here.

Agreed!

Bell's theorem is a theoretical construct, it doesn't need to be proven by experiment. Experiment has to show whether Bell's inequalities are violated or if they are not. Agreed?

No. I disagree. So long as Bell's inequalities purport to make claims about reality, the correspondence between those inequalities and reality MUST be independently validated by experiments before any claims they make about reality can be said to be proven.

3. I quote you: "I am perfectly happy to accept that Bell's theorem is true ONLY for the LR models narrowly defined by his assumptions". OK, let's call all theories that Bell's theorem applies to "Bell local realistic" (BLR). Now, Bell's theorem says and proves that BLR theories should obey Bell's inequalities while QM violates them. Agreed?

Agreed without prejudice. Note that every loop-hole found to date is a hidden assumption in Bell's proof. I do not claim by agreeing to the above that all loop-holes have been found.

4. Your main point seems to be that BLR is only a narrow subclass of LR theories. Well, I repeat: what is "local realism" is a philosophical question. I'm personally quite happy to include in my notion of local realism the assumption that the outcomes of Bob's experiments are statistically independent from Alice's choice of experimental settings (this is Bell's assumption and precise definition of BLR). You are not, right?

Again remember that every loop-hole is a hidden assumption of Bell's proof. The fact that there are loop holes tells you that BLR is not exhaustive of all LR.

5. Since scientific consensus is that BLR and LR are the same thing, and you disagree, the only meaningful way to disagree is to give an example of a LR theory that is not BLR. Agreed?

No. If you think scientific consensus is that BLR and LR are the same thing, then you have not been paying attention, and this thread does not exist, and the loop-holes do not exist.

6. In case you want to say that de Raedt's models are such kind of example, I repeat once again: NO, they ARE NOT.

If you say Raedt's modes are not examples of LR which are not accounted for by Bell's LR, I repeat once again: YES THEY ARE. You see this kind of discussions takes us no where. Explain why they are not.

de Raedt showed (as was already known) that the experiments to test Bell's inequalities were not perfect (there are loopholes), and because of these experimental flaws their results can be explained in LR way. Agreed?

That is a very narrow reading of de Raedt's work. Did you completely fail to understand the importance of the Deterministic Learning Machine model of de Raedt's?

7. But (the crucial point!) de Raedt's model is obviously not only LR, but BLR as well!

If de Raedt's model is BLR then how do you explain the fact that the model violates the inequality, when according to Bell it is impossible. Think before you answer. If you want to say that only under certain conditions will violate the inequality, then you still face the question of answering how come some BLR will violate the inequality under certain conditions. There is no escaping here.

IF a loophole-free test of Bell's inequalities is ever done and IF Bell's inequalities are still found to be violated, then de Raedt won't be able to explain this with his model (why? because of Bell's theorem). Agreed? Please think a bit before answering.

This is circular reasoning. A loop-hole free test of Bell's inequality is required to be able to validate the inequality in the first place. Violation of Bell's inequality in any experiment has two possible explanations, not just one.
1) That Bell's inequality is a correct representation of local reality and the experiment is either not real or not local or both
2) That Bell's inequality is not a correct representation of local reality.

Now for some reason, Bell's followers ALWAYS gravitate towards (1). Do you agree that (2) is also a possibility and MUST be considered together with (1) when interpreting the results of these experiments? Please, I need a specific answer to this question.

I'm asking you think, because you wrote that "Bell's equations do not apply to a deterministic learning machine model like de Raedt's". This is just plain wrong. Of course they do apply! De Raedt's model is perfectly BLR.

You have no idea what you are talking about. Even ardent Bell believers have shown that not all LR are accounted for in BLR. See http://arxiv.org/abs/quant-ph/0205016 for one example. Bell's starting equation is the following:
$$P(AB) = \sum_i P(A|a_i)P(B|b_i )P(\lambda_i)$$
This experiment does not apply in situations in which $$\lambda_{i+1}$$ is dependent on $$\lambda_{i}$$, like is the case in de Raedt's model. The reason is simple. If case (i) and case (i+1) are not mutually exclusive, you can integrate or as in this case perform a sum the way Bell did.

8. You mentioned the recent de Raedt's article with Hess (http://arxiv.org/abs/0901.2546). I've seen it and I took a brief look, but I didn't read it carefully and I failed to understand the crux of it. I just don't want to investigate 40+ pages of formulas, when I already know that de Raedt's reasoning is often confusing and misleading, and that Hess is well-known for fighting will Bell's theorem, though his claims were long ago shown wrong by people, whose opinion I respect in this issue (see http://arxiv.org/abs/quant-ph/0208187).

This explains why you will never understand him. Apparently, as soon as you see Hess or de Raedt, you put on green goggles. The article you posted as disproving Hess is nothing short of a joke. (See http://arxiv.org/abs/quant-ph/0307092).

If you have read and understood this 40+ pages article, everybody here will be grateful if you give us the arguments in a concise and clear way.

If you are interested in understanding the opposing position, you will make the effort to read and understand their arguments before purporting to refute it. Since it appears you have access to de Raedt personally, why don't you ask him to explain to you concisely what the article is talking about. That will be much better than any of my efforts to explain his work to a hostile audience.

9. For some reason you completely ignored my point about double-slit paper of de Raedt. You were first to mention it! Did you read it? If you did, could you please comment on what I said earlier? If you didn't, how come you use it in the arguments?

You claimed that some photons were lost in their double slit simulation. This is wrong! All photons reach the detector and affect the outcome of the experiment. Maybe what you were trying to say is that in their model, not all photons result in a click. In any case, do you have experimental evidence proving that all photons leaving the source MUST result in a click at the detector in a double slit experiment?

 

[mn4j]

On the other hand, there is no existing candidate LR theory on the table to compare to QM at this time.

You are mischaracterizing the debate as one between LR and QM. It is NOT.

Stochastic Mechanics (Marshall, Santos) is an example of a field of research in that regard, but every candidate SM model is found to have problems and is quickly modified again. And since such models do not predict anything useful, there is no incentive to study them further. We already have a very useful model - QM - and the experiments supporting it are in the thousands. Something useful from the field of study would go a long way towards convincing the scientific community.

So yes, I think quantity does matter, and I think utility matters. And I think the history of the area does matter as well, including when a theory (QM) is supported by improving technology.

The utility of a theory says nothing about it's correctness. The system of epicycles was very useful in the dark ages but you won't claim it as a correct theory. Technology always precedes theoretical understanding.

Why should you need to close every loophole simultaneously if you can close each separately? If a prisoner cannot escape from the first lock by itself, and cannot escape from the second lock by itself, how can he escape when both locks are present?

You answer your own question. The papers you mentioned are just prisoners claiming to have escaped because they were able to open one of seven locks. Unless you can open all seven locks you can't reasonably claim to have escaped, even if you change your name to Houdini.

I don't disagree with a desire to close all loopholes simultaneously; but I think that is a standard that is being applied to Bell tests which is applied nowhere else in science. Surely you must have noticed this as well.

It is common sense. The standard is demanded by the claims made by Bell. Extraordinary claims require extraordinary evidence. If you claim there is no green stone on Jupiter, you better get your ducks together and be sure you have combed every micrometer of the planet before you can say your experiment proves the claim. Yet if you claim there is a white stone in Alabama, all you have to do is find one white stone anywhere in Alabama to prove your claim. Bell says NO LR can violate his inequality.

 

[DrChinese]

Three points. First. I'm not an expert in Bell tests and loopholes issue, so can't really comment on that on the detailed level. I know that there's for example "time-coincidence" loophole (http://arxiv.org/abs/quant-ph/0312035), which is apparently exactly the loophole de Raedt is exploiting (http://arxiv.org/abs/quant-ph/0703120, the link I already gave). I'm not sure that all known loopholes were already closed even separately, though this might be true. In particular, I just don't know any details about this "entanglement" studies that you cite (and don't have time at the moment to start reading them). Do they test Bell inequalities after this entanglement "swapping"? Or how else these findings prove LR false?

Second. I guess that I slightly disagree with you about different standards of tests. Of course there are super-precise tests of GR still being done. But to test GR you need to observe something that is predicted by GR, like light deflection or whatnot. When this is observed, nobody claims that there's a "loophole" in this experiment, and the results can be interpreted such that light is not deflected. It's evident: nobody heard of any loopholes in GR tests. On the other hand, to test QM versus LR one needs to show that the Bell's inequalities are violated. And all the attempts to show it still have some loopholes that allow alternative explanations.

Third. Nobody in his right mind claims that QM is "wrong". For de Raedt, QM is a correct mathematical model working well on the ensemble level only, without saying anything about single events. He is not trying to show that QM is wrong, he is trying to show that it can be completed in a LR way. Well, we know that it's impossible due to Bell. But de Raedt obviously disagrees. And it doesn't make a lot of sense for me to defend de Raedt, but he is most definitely not a crackpot (he has done a huge amount of "real" work in computer simulations of different physical models, including decoherence etc.). I believe (as you do) that his reasoning about Bell is flawed, but he certainly does not try to obscure anything on purpose: I'm quite sure that he is honest.

A couple of comments, and by the way I doubt our positions are very different overall.

Any theory, including GR, can be attacked as lacking loophole free experimental support by a sufficiently motivated scientist. The concept would be to deny an essential element of the theory, and then try to show that somehow the experiment "could" be wrong even if the evidence is convincing by normal scientific standards. What if GR readings are not a fair sample? Maybe Newtonian physics is correct instead because there is a built-in sample bias. (I am only kidding of course.)

The entanglement swapping issue is really just another aspect of the hurdles any LR theory must explain. Two independently created photon pairs A1/A2 and B1/B2 are created. By performing a suitable partial Bell State Measurement (BSM) on one of each pair (A1 & B1), their partners A2 and B2 are now partially entangled (as to time bin). (So in this particular case, polarization is not swapped but that has been done as well by Pan, Zeilinger et al.) So the question is: how do the local hidden variables guiding A2 and B2 - which have never been in causal contact - manage to be correlated? That's not even a process that a non-local Bohmian (dBB) type theory has an easy time with.

As to intellectual honesty: no assertion being made to the negative. I just ask why someone in that position wouldn't make the source of the delta between LR model and QM be obvious? That is the first thing we all look for. And yet I always find myself reading a lecture on the wrongs of Bell while looking for that little detail I know is there somewhere. The author, I would think, would know what that detail is.

I always ask myself: what would Einstein have thought about Bell or Aspect? If he were alive today, I think he would be well convinced and would cede the essential point.

 

[DrChinese]

The utility of a theory says nothing about it's correctness. The system of epicycles was very useful in the dark ages but you won't claim it as a correct theory. Technology always precedes theoretical understanding.

That's wrong: how are theories judged correct? There is no such standard. Theories can have experimental support, and theories can make predictions that can be tested. And that is how they are judged. Correctness implies black and white, right or wrong. Theories can be better or worse depending on their application. But I cannot meaningfully say a theory is correct.

As to technology preceding theory: that makes no sense at all. Sometimes it does, sometimes it doesn't. There is no historical absolute on this. So again, meaningless.

 

[kobak]

Thanks for replying. In the beginning I started answering and addressing all the points where we disagree, but this is getting too huge and difficult to handle (so I'll concentrate on the main issue). But let me first say one thing. I'm not a "hostile audience", because I sincerely try to understand what de Raedt is saying. But it's extremely difficult to talk with you because you're constantly being very sloppy. Here's an example:

If you say Raedt's modes are not examples of LR, I repeat once again: YES THEY ARE. You see this kind of discussions takes us no where. Explain why they are not.

Are you joking? I have been saying all the way that I think that de Raedt's models are LR. Well, I think that you just miswrote something here, but it's quite difficult to try to decipher you sometimes. Another example:

2) That Bell's inequality is not a correct representation of local reality.
Now for some reason, Bell's followers ALWAYS gravitate towards (1). Do you agree that (2) is also a possibility

What on Earth is this second option supposed to mean at all? "Bell's inequality is not a representation of local reality"? Eh? I guess that what you mean here is that BLR is not LR. But it's really a pain to guess what you meant all the time.

Now, it's clear that the *MAIN POINT* is that you think there are LR theories that are not BLR. And you think that de Raedt's model is an example. I don't see why it's not BLR, I think it's absolutely BLR, and I think that I never saw any LR-but-not-BLR suggestion. And without an example I won't believe that that's possible. Here's your objection:

If de Raedt's model is BLR then how do you explain the fact that the model violates the inequality, when according to Bell it is impossible.

Well, my answer is simple: it does not violate the inequality. The inequality "seems" to be violated in the particular experimental setup because the certain post-selection procedure is applied. It's possible to create correlation by post-selecting, that's what this whole coincidence loophole is about!

You have no idea what you are talking about. Even ardent Bell believers have shown that not all LR are accounted for in BLR. See http://arxiv.org/abs/quant-ph/0205016 for one example.

Thanks for giving this link, it's actually interesting. I don't see though how it proves your point. Authors clearly write that "memory loophole" that they're describing can be avoided in experiment. If it's avoided along with other loopholes -- goodbye LR.

You claimed that some photons were lost in their double slit simulation. This is wrong! All photons reach the detector and affect the outcome of the experiment. Maybe what you were trying to say is that in t heir model, not all photons result in a click. In any case, do you have experimental evidence proving that all photons leaving the source MUST result in a click at the detector in a double slit experiment?

Yes, I meant exactly this: not all photons result in a click. I don't have an evidence, but it could be obtained. I described two experiments that could check this model. Take a look at the second. De Raedt says that if the screen is moved back and forth, the interference picture will get smeared. If this experiment is done and interference is NOT smeared, then de Raedt himself said that he would "retire", which I guess means that he will admit that his models are totally wrong and give up. And what would you say in this case?

 

[kobak]

DrChinese, yes, I think that our position regarding the main points here is the same. And I must say that I myself have also wondered many times about what "would Einstein have thought about Bell or Aspect"...

 

[Pio2001]

No. I disagree. So long as Bell's inequalities purport to make claims about reality, the correspondence between those inequalities and reality MUST be independently validated by experiments before any claims they make about reality can be said to be proven.

In photons' polarisation experiments, the correspondance between Bell's inequality and reality are that a detection is noted 1 and an absence of detection is noted 0, and also that nothing that is done outside the past light-cone of an event has any observable consequence on this event, which corresponds to the fact that in Bell's theorem, A does not depend on beta and that B does not depend on alpha.

The second correspondance is validated by experiments that show that nothing can go faster than light.
The first correspondance has not to be experimentally validated. You don't have to prove that you set 1 for a detection and 0 otherwise. We believe you !

Agreed without prejudice. Note that every loop-hole found to date is a hidden assumption in Bell's proof. I do not claim by agreeing to the above that all loop-holes have been found.

Action of the detector on the source, disproven by Aspect with ultra-fast switch, was not a hidden assumption, it was the explicit assumption that A did not depend on beta and conversely.
Fair sampling loophole was not either. Bell's theorem applies to the means of all measurments, not only some of them.
Statistics loophole have been filled with the GHZ evidence.

I've not studied all this, but not all loopholes were hidden assumptions in Bell's theorem. Actually, it seems to me that most loopholes claimed to be found in Bell's theorem rather than in experiments were unfounded. The CHSH generalisation of Bell's theorem makes things more clear : it takes into account anything that can happen around the measurment as hidden variable.

If you say Raedt's modes are not examples of LR which are not accounted for by Bell's LR, I repeat once again: YES THEY ARE. You see this kind of discussions takes us no where. Explain why they are not.

They violate Bell's inequality because Cxy depends on both t(n,1) and t(n,2) (equation 3), which is not the case in Bell's theorem. In Bell's theorem, Cxy depends only on the product of the measurments results (the Kronecker deltas in equation 3).

The role of t(n,1) and t(n,2) is to introduce a measurable individual dependence on the measurment angles, while they have no effect on the individual spin results.

Technically, it makes Cxy not being Bell's coincidence rate anymore. It has more to do with "what we measure" than with "what is locality".

That is a very narrow reading of de Raedt's work. Did you completely fail to understand the importance of the Deterministic Learning Machine model of de Raedt's?

De Raedt's pseudorandom model works without any Deterministic Learning Machine, and perfectly predicts Bell's inequality violation ! DLM are not involved in this step.
DLM are there to restore determinism, after the prevous step has restored locality.

Moreover, I'm not sure of it, but it seems to me that DLM would be accounted for as hidden variables in the general CHSH proof of Bell's theorem of 1969 :
This generalisation attributes hidden variables not only to the particles, but also to the measurment devices. For this purpose, the result A, function of the hidden variable lambda, and of the angle alpha, with the value -1 or +1, is replaced by the average value of A, function of alpha and lambda, on all hidden variables of the measurment device, and we start with
|average of A| <= 1. (respectively for B...)

Violation of Bell's inequality in any experiment has two possible explanations, not just one.
1) That Bell's inequality is a correct representation of local reality and the experiment is either not real or not local or both
2) That Bell's inequality is not a correct representation of local reality.

Now for some reason, Bell's followers ALWAYS gravitate towards (1). Do you agree that (2) is also a possibility and MUST be considered together with (1) when interpreting the results of these experiments? Please, I need a specific answer to this question.

I myself agree, but case 2 deals with what we do, while case 1 deals with what we get.

In De Raedt's simulation, Cxy is not the coincidence rate defined in Bell's theorem. That's how Bell's inequality does not represents what's going on in the simulation.
If the simulation is a good representation of reality, then the experiment can be modified so as to make W big enough compared to |t(n,1) - t(n,2)| in equation 3, so that the Heaviside function is always equal to 1, and Cxy tends to Bell's definition of the measurments product.
This way, we get back the experiment in adequation with Bell's theorem (case 2 is discarded), and we can test local determinism.

Another, sad, example : Joy Christian's use of Clifford algebra to prove Bell wrong ( http://arxiv.org/abs/quant-ph/0703179 ). Christian uses the half spin model, where Bell's theorem is applied setting spin down = -1, and spin up = +1.
He starts from the hypothesis that spin down and spin up are not real numbers, but numbers from Clifford algebra. He then shows that S can be equal to more than 2.

Since Bell's theorem says nothing else than if the possible results are -1 or 1, then S<=2, Christian's result is trivial and useless !

 

[mn4j]

That's wrong: how are theories judged correct? There is no such standard. Theories can have experimental support, and theories can make predictions that can be tested. And that is how they are judged. Correctness implies black and white, right or wrong. Theories can be better or worse depending on their application. But I cannot meaningfully say a theory is correct.

As to technology preceding theory: that makes no sense at all. Sometimes it does, sometimes it doesn't. There is no historical absolute on this. So again, meaningless.

I guess then you believe the system of epicycles is an accurate representation of the solar system and the motion of the planets!

 

[mn4j]

What on Earth is this second option supposed to mean at all? "Bell's inequality is not a representation of local reality"? Eh? I guess that what you mean here is that BLR is not LR. But it's really a pain to guess what you meant all the time.

If you have thought it through clearly enough you will know what the second option means. Let me put it to you in layman terms.

A man was depressed to the point he believed he was dead. No matter the efforts of his family he kept saying he was dead. A smart doctor tried to convince him that dead men do not bleed. After a significant effort he accepted. But at that moment, the doctor pierced him with a needle and he started bleeding. Can you guess what his next statement was? The doctor had hoped he would say "I am alive". Instead he said "Oops, I guess dead men bleed afterall".

The violation of Bell's inequality only proves that that the assumptions used in deriving the inequality do not apply to the experiment in question. Do you agree? Please give me a specific answer to this.

Those assumptions include assumptions about the way probabilities of local realist variables are supposed to be calculated. So in effect, Bell has an untested presentation of how local realist theories are supposed to behave. Yet when the inequalities are violated, instead of re-evaluating those assumptions, Bell proponents screem "I guess dead mean bleed after all".

Now, it's clear that the *MAIN POINT* is that you think there are LR theories that are not BLR. And you think that de Raedt's model is an example. I don't see why it's not BLR, I think it's absolutely BLR, and I think that I never saw any LR-but-not-BLR suggestion. And without an example I won't believe that that's possible.

I already mentioned why this is not a constructive criticism. I also explained in my previous post to you why de Raedt's mode is not accounted for by Bell. The article I presented by a pro-Bellist clearly states that Bell's model does not account for models like de Raedt's which have memory effects, notwithstanding the conclusion of that paper. Also your claim that you never saw any suggestion that Bell's representation of LR was not exhaustive is surprising because it is numerous in the literature. This thread was started by one such, Hess has presented a few, Joy Christian has presented a few. Are you serious?

Well, my answer is simple: it does not violate the inequality. The inequality "seems" to be violated in the particular experimental setup because the certain post-selection procedure is applied. It's possible to create correlation by post-selecting, that's what this whole coincidence loophole is about!

What experiment setup, it is a simulation. What aspect of the simulation do you claim deviates from how real experiments are actually performed.

Thanks for giving this link, it's actually interesting. I don't see though how it proves your point.

Do you agree that according to this article, Bell's theory does not account for models with memory effects. The authors state as much even though they end up dismissing it's importance. At least they were honest to admit that Bell's theory does not account for such local realist theories, which you apparently are still unwilling to do.

Authors clearly write that "memory loophole" that they're describing can be avoided in experiment. If it's avoided along with other loopholes -- goodbye LR.

That is beside the point. Do they or do they not state that Bell's model of LR does not apply to situations in which there are memory effects? Please answer this question.

Yes, I meant exactly this: not all photons result in a click. I don't have an evidence, but it could be obtained. I described two experiments that could check this model.

You don't have evidence, yet you are ready and willing to proclaim proudly that de Raedt's model is wrong on this basis? Isn't it more prudent to wait until you have obtained such evidence before you make such claims?

Take a look at the second. De Raedt says that if the screen is moved back and forth, the interference picture will get smeared. If this experiment is done and interference is NOT smeared, then de Raedt himself said that he would "retire", which I guess means that he will admit that his models are totally wrong and give up. And what would you say in this case?

Do you believe, the interference will get smeared if the slits are moved back and forth? What about the source?

 

[DrChinese]

I guess then you believe the system of epicycles is an accurate representation of the solar system and the motion of the planets!

The map is not the territory, my friend. Theory is always a model (map). And some are better than others.

 

[kobak]

Hello again, mn4j,
I suggest that if we continue this discussion at all, let's try to concentrate on the most important points only and also try avoid nitpicking each other (like what "scientific consensus" really means etc.). I'm quite sure that we won't reach an agreement, but we can at least pinpoint our disagreements.

The violation of Bell's inequality only proves that that the assumptions used in deriving the inequality do not apply to the experiment in question. Do you agree? Please give me a specific answer to this.

Yes, certainly.

Those assumptions include assumptions about the way probabilities of local realist variables are supposed to be calculated. So in effect, Bell has an untested presentation of how local realist theories are supposed to behave.

Well, let me put it a bit differently. I've been always repeating here that "local realism" is not a well-defined term. So strictly speaking you're right: it might not be fully correct to say (without any additional clarifications) that Bell's theorem proves that all LR theories should obey Bell's inequality. I hope you'll be happy that I agree with you here.

However, here's my main point: Bell derives his technical assumption about probabilities distribution by providing some particular *physical* intuition. This technical assumption that he uses is certainly always true and absolutely uncontroversial in all areas of classical (meaning non-quantum) physics. It's just the plain fact, that in all classical physics the outcome of Bob's experiment can never be statistically dependent on Alice's choice of experimental setup etc., so Bell's assumption holds. So let me drop the issue of "local realism" and make the following claim instead: Bell's theorem shows that *assuming "classicality"* -- his inequality has to be true.

Do you agree to such a statement? Note, that even if de Raedt model turns out to (a) be not BLR, (b) violate Bell's inequalities, (c) be just right (I still strongly disagree that it's possible, but even if it's like that), -- then this is certainly not a "classical" model. In classical physics apparata do not learn. The same goes for Christian's models: if they are right, then ok, spin measurements form a Clifford algebra (whatever this means), and this is again certainly not a "classical" model.

So, to recapitulate: do you agree that Bell's technical assumptions about correlations are completely well motivated, if we change the assumption of "local realism" to assumption of "classicality"? I very much hope that you will agree to that.

---------

Now, except of this, I see two main issues. First: I claim that de Raedt's model is BLR (and hence has to obey Bell's inequalities, and hence will not be able to hold anymore, after a loophole-free violation of inequalities is observed). You're saying that his model is not BLR, and your argument is that it's even stated in the Darrett-Popescu article. Well, I have to read it more carefully to answer you here. I will try to find the time for that and get back then, that's important.

Second point is that you also say that de Raedt model is not BLR because it violates Bell's inequalities. Here I disagree strongly, and I think that this shows that you don't really understand what a "coincidence loophole" is. Here's again, how I see it: 1. de Raedt's simulation does not deviate from real experiment of Weihs et al (you asked me, how it deviated; well, it doesn't). 2. The coincidence loophole (which this experiment did not avoid) means that it's possible to explain the apparent Bell's inequality violation by the fact that events are post-selected, and because of this post-selection the correlation is created out of nothing. 3. This is exactly what de Raedt is exploiting. 4. Bottomline of this analysis: de Raedt's model is BLR, it obeys Bell's inequalities, but in the non-perfect loopholed experiment it can LOOK like it violates them. This is the view expressed here: http://arxiv.org/abs/quant-ph/0703120 (see also http://arxiv.org/abs/quant-ph/0312035 about coincidence loophole). Do you understand this argumentation? You may disagree (please tell where exactly), but do you understand it?

Let me also ask for a clarification of your point of view. Do you think that Bell's inequalities are in reality NOT violated (and all experimental violations are only due to loopholes)? Or do you think that his inequalities in reality ARE violated (so that even ideal perfect experiment will find violations), but these violations can be explained by some LR theory which is not accounted by Bell's theorem? I guess that yours is the latter opinion. Which means that even a perfect loophole-free experiment will not prove anything to you, right? Why are you then arguing about loopholes and this "prisoners who can get out in different ways" at all?

---------

Finally, about double-slit paper.

You don't have evidence, yet you are ready and willing to proclaim proudly that de Raedt's model is wrong on this basis? Isn't it more prudent to wait until you have obtained such evidence before you make such claims?

It is. I don't proclaim that his model is wrong on this basis, I'm proposing a bet (let's put it that way). Imagine this experiment is done exactly as de Raedt himself proposed it (screen is jittered from left to right parallel to itself). Question: what will happen? My bet: interference pattern doesn't change. "de Raedt's" bet: interference pattern gets smeared, because "detectors" on the screen won't have enough time to "learn". Your bet?

And additionally: imagine that experiment is made and I win. What would that mean? I think that de Raedt thinks that it will prove his model false, and he certainly does not believe that this outcome is possible AT ALL. What do you think?

Please don't ask questions about different experimental setups, I'm interested only in this one, that is defined absolutely precisely.

 

[sirchasm]

A comment on "the map is not the territory".
I believe this implies we can only simulate "territory" as in QM simulations, fliud-dynamics on supercomputers. supernova and nuclear weapons simulations etc.

So the question has to be: when is a simulation 'exact'? And can we simulate the territory = construct a map, that is indistinguishable = identical to "the territory"?

 

[mn4j]

The map is not the territory, my friend. Theory is always a model (map). And some are better than others.

Yes you are right, all theories are valid , everything is relative, the map of China is a valid map of the US, just worse than the US map and the Earth is the center of the solar system, depending on your perspective.

 

[DrChinese]

So the question has to be: when is a simulation 'exact'? And can we simulate the territory = construct a map, that is indistinguishable = identical to "the territory"?

It is impossible, in principle, for any map to precisely model a territory other than for a limited (by assumption) scope. (The only way is if the map *IS* the territory, in which case it really doesn't qualify as a map anymore.) The reason I bring this up is that our natural desire is to use a map (i.e. a model) as a convenience. When you use a map, you assume it is accurate enough to be useful for your purposes. But most people know a map is a model; yet they have trouble seeing a theory as a model of reality too. Yet it is, and this is not merely a philosophical issue. As you can see from the discussion, some people think their model is "true" or "correct". Well, a map can be more useful or less useful (as in a relative way) but I don't see how any map can be absolutely and finally "true".

Take gravity, as an example: the acceleration due to gravity on Earth is about 9.8 meters per second. And yet there are only a few objects on the planet that are actually accelerating (relative to the earth) at that rate. Most are at rest or moving according to other forces acting on the object. So obviously, no theory of gravity can describe the movement of objects on earth. You must instead expand your description to include numerous other variables on a case by case basis.

...Which defeats the point of our original map, and shows it to be absolutely wrong - if we insist on calling the map itself absolutely correct. If we acknowledge it as only a useful tool, the problem disappears. That is why I believe it is unfair to criticize QM as a tool. Because as a tool, it is useful and fulfills the reasonable demands we place on it. Only when someone tries to ask if it is "correct" does a problem arise. Instead, I think we need only ask if a better tool can be found. EPR asked if a more complete specification of a quantum system was possible, and they believed it was. But the subsequent evidence (Bell+Aspect et al) is that it is not. But I do not believe that makes QM true, it just means it is a good - or perhaps best - map.

 

[DrChinese]

Yes you are right, all theories are valid , everything is relative, the map of China is a valid map of the US, just worse than the US map and the Earth is the center of the solar system, depending on your perspective.

Sorry, didn't mean to divert you from your distinctly more interesting discussion with kobak. But I think your statement pretty well proves my point of what happens when people think their model IS reality. They freak out because they find out they are not in Kansas any more. I will bow out for a while on this thread and let you continue. Later,

 

[mn4j]

Well, let me put it a bit differently. I've been always repeating here that "local realism" is not a well-defined term. So strictly speaking you're right: it might not be fully correct to say (without any additional clarifications) that Bell's theorem proves that all LR theories should obey Bell's inequality. I hope you'll be happy that I agree with you here.

Yes I'm happy, thank you.

However, here's my main point: Bell derives his technical assumption about probabilities distribution by providing some particular *physical* intuition. This technical assumption that he uses is certainly always true and absolutely uncontroversial in all areas of classical (meaning non-quantum) physics.

And here is my main point: The above statement is False for the following reasons:
1) Bell's particular *physical* intuition does not account for the most interesting class of local hidden variables, the types Einstein and Schrödinger would have liked to see.
2) The technical assumptions he uses are not always true, for reasons I have explained here. The effect is that this introduces further hidden assumptions -- at the very least, the assumption that those technical assumptions are always true for local hidden variables. Without independent validation of this assumption, the possibility that this assumption is false will never go away, even if 99% of the scientists believe it.
3) Those technical assumptions are not uncontroversial in all areas of classical physics. In fact violation of Bell's inequalities is not limited to quantum systems. Take a look at de Raedt's recent paper for an example in which there is violation of Bell's inequality for a voting game with three human players.

It's just the plain fact, that in all classical physics the outcome of Bob's experiment can never be statistically dependent on Alice's choice of experimental setup etc., so Bell's assumption holds. So let me drop the issue of "local realism" and make the following claim instead: Bell's theorem shows that *assuming "classicality"* -- his inequality has to be true.

This is false. I have already explained in this thread that any two time varying harmonic systems are correlated and as such their probabilities are not disjoint. Unless you want to claim that two pendulums or clocks on opposite sites of the globe are not classical.

Note, that even if de Raedt model turns out to (a) be not BLR, (b) violate Bell's inequalities, (c) be just right (I still strongly disagree that it's possible, but even if it's like that), -- then this is certainly not a "classical" model. In classical physics apparata do not learn.

This is false. Let's take two classical systems
1) Heat transfer in a gas: How does the heat go from one end to another? The molecules learn the velocity of the "hotter" molecules they collide with, and transfer this "knowledge" to other molecules they themselves collide with. This is exactly what a DLM is.
2) A billiard ball. The stationary ball, on collision with the moving ball, learns the momentum of the on-coming ball. That is a DLM.

DLMs are classical!

So, to recapitulate: do you agree that Bell's technical assumptions about correlations are completely well motivated, if we change the assumption of "local realism" to assumption of "classicality"? I very much hope that you will agree to that.

Sorry, I can not agree that. Because as I have explained repeatedly, I know of systems for which Bell's inequality does not apply, which can not be classified as non-classical. But also because I am not quite sure what you mean by classical.

Now, except of this, I see two main issues. First: I claim that de Raedt's model is BLR (and hence has to obey Bell's inequalities, and hence will not be able to hold anymore, after a loophole-free violation of inequalities is observed).

So then, even if you believe it is BLR, since de Raedt's model is also a simulation, not much different from a theoretical derivation, the fact that it violates Bell's inequalities either means Bell's mathematics is wrong, or de Raedt's mathematics is wrong. So again the issue boils down to whether "a bleeding man is alive" or "dead men bleed".

I will reply to your second point in a separate post as this is getting too long.