Is Bell's Logic Aimed at Decoupling Correlated Outcomes in Quantum Mechanics?

[billschnieder]

Don't know about that precise inequality, but as I mentioned in an earlier post:

DId I hear ONE with a but attached?

 

[JesseM]

DId I hear ONE with a but attached?

There have been others that closed the detection loophole since, see here for example. But no experiments have been done that have closed all loopholes, though as I said it would probably require a very contrived local realist model to exploit all the loopholes simultaneously and agree perfectly with QM predictions in all cases that have been tested so far. Why do you care anyway? You don't believe that local realism implies the Bell inequalities anyway, so even if a loophole-free experiment were performed you would just return to some of your old mathematically confused arguments about the proof itself or the idea that any experiment could test it without "controlling for" the hidden variables.

 

[Maaneli]

Now come on, it's not that hard. 3 elements of reality? Really, just read the last couple of paragraphs of EPR and tell me you have no idea what this is about. I understand that you want locality to be part of the equation, and I am not debating the point since I know you won't agree, but certainly you can see that EPR is about elements of reality for ONE particle. And that does not require a locality assumption at all.

Edit - I modified the below, thanks to the clarifications by JenniT and Hurkyl of what you (probably) intended to say in your argument.

<< A single particle, Alice, has 3 elements of reality at angles 0, 120, 240 degrees. This is by assumption, the realistic assumption, and from the fact that these angles - individually - could be predicted with certainty. >>

What, precisely, is the experimental set-up you're talking about, and what do these elements of reality correspond to in the experimental set-up? Measurement settings, perhaps? But then in what sense does the "single particle" "have" these elements of reality? Is the single particle just being measured by these elements of reality fixed at these angles? Are the measurements simultaneous? Or one at a time?

<< It is obvious from the Bell program that there are NO datasets of Alice which match the QM expectation value. Ergo, the assumption is invalid. And you don't need to consider settings of Bob at all. You simply cannot construct the Alice dataset. QED. >>

Nonsense. Bell's inequality is completely contingent on a comparison of statistical correlations between two space-like separated measurement outcomes on two separate particles. Without that, you simply have no dataset to compare to the QM-predicted correlations, in a way which implies a violation of Bell's inequality.

<< The key difference is that the elements of reality are NOT referring to separate particles. >>

Again, WHAT do they refer to? If they are just the measurement settings, then this already amounts to the assumption of local beables.

<< They never were intended to! All the talk about Bob's setting affecting Alice's outcome only relates to Bell tests. >>

The whole point of your argument was, allegedly, to show that the QM violation of Bell's inequality only relies on the assumption of realism, and not locality! And you have shown nothing in this respect.

<< But it should be clear that there is no realistic Alice who can match the QM expectation value. >>

No, I don't see how this follows from anything you've said.

And there was nothing I saw in the last couple of paragraphs in the EPR paper which helped to clarify your argument.

BTW, I am still waiting for your response after reading Bell's La Nouvelle Cuisine.

 

[Hurkyl]

I would have assumed the "element of reality at angle 120 degrees" is the physical quantity that determines which result Alice will get if she sets her measuring device at 120 degrees.

 

[billschnieder]

I would have assumed the "element of reality at angle 120 degrees" is the physical quantity that determines which result Alice will get if she sets her measuring device at 120 degrees.

If the assumption is that a single particle has three such elements of reality at three different angles, then the fact that no experiment has ever been performed in which a single particle was measured at three angles, let alone 2, should be a relevant omission, shouldn't it?

 

[Gordon Watson]

I would have assumed the "element of reality at angle 120 degrees" is the physical quantity that determines which result Alice will get if she sets her measuring device at 120 degrees.

Dear Hurkyl, I am drafting a reply to an excellent post by JesseM and I would like to use the correct physical term for Bell's lambda. I would have assumed that "element of reality TESTED at angle 120 degrees" has some meaning and that "the element of reality" would be a random variable = Bell's lambda?

Would it be acceptable to a physicist to say that Bell's lambda represent spin vectors unconstrained as to length or orientation? And to add ... but correlated by the conservation of angular momentum?

And to say that the measurement interactions reduce the random variables of infinite variability to a few discrete orientations equating to the test settings of the detectors?

I hope this is clear?

Thank you.

 

[Maaneli]

I would have assumed the "element of reality at angle 120 degrees" is the physical quantity that determines which result Alice will get if she sets her measuring device at 120 degrees.

In DrC's argument, Alice is not the experimentalist setting the measuring device at some angle. Alice is just a "particle".

 

[Gordon Watson]

In DrC's argument, Alice is not the experimentalist setting the measuring device at some angle. Alice is just a "particle".

Yes, agreed, that is what I have found. A bit confusing but I always thought DrC's "slips" could be "ignored" ... and that Alice was the experimenter with setting a and outcome A.

 

[Maaneli]

Yes, agreed, that is what I have found. A bit confusing but I always thought DrC's "slips" could be ignored.

I prefer not to do his thinking for him. Besides, that's not the only slip I found in his argument.

 

[Hurkyl]

In DrC's argument, Alice is not the experimentalist setting the measuring device at some angle. Alice is just a "particle".

Fine, it's the physical quantity that would determine the result if it happened to be measured by a measuring device set to 120 degrees.

 

[Gordon Watson]

Maaneli: OK - Touché!

 

[Maaneli]

Fine, it's the physical quantity that would determine the result if it happened to be measured by a measuring device set to 120 degrees.

Bravo. But his conclusion still doesn't follow.

 

[Hurkyl]

Bravo. But his conclusion still doesn't follow.

I haven't followed the discussion. I was just hoping to accelerate things by clearing up the use of the term, allowing you to formulate another response if appropriate.

 

[Gordon Watson]

I would have assumed the "element of reality at angle 120 degrees" is the physical quantity that determines which result Alice will get if she sets her measuring device at 120 degrees.

Fine, it's the physical quantity that would determine the result if it happened to be measured by a measuring device set to 120 degrees.

Dear Hurkyl, this seems to be confusing?

"Element of reality at angle 120 degrees" is probably NOW best allocated to the orientation a of Alice's test device.

"NOW" now being added because "the" physical quantity impacting on, and interacting with the device, is a random member of an infinite set.

So to say "it's the physical quantity" seems confusing to me.

I am hoping your answer to my query re spin-vectors will clarify it all for me.

Thank you.

 

[Maaneli]

I haven't followed the discussion. I was just hoping to accelerate things by clearing up the use of the term, allowing you to formulate another response if appropriate.

Thanks ...

 

[Maaneli]

If the assumption is that a single particle has three such elements of reality at three different angles, then the fact that no experiment has ever been performed in which a single particle was measured at three angles, let alone 2, should be a relevant omission, shouldn't it?

Yes, I agree (assuming that set-up is exactly what DrC has in mind).

 

[ThomasT]

Oh really? If I have a photon polarized H>, please tell me what is varying randomly.

I thought we were talking about photons incident on the polarizers. Are you talking about photons transmitted by the polarizers?

Or if it is of unknown polarization, please tell me of ONE experiment which demonstrates that it varies randomly with time.

This is getting very confusing. If the polarization of the photons is unknown, then this would indicate that you're talking about the photons incident on the polarizer. If the polarization of the photons incident on the polarizer isn't varying randomly, then how would you account for the observed photon flux for individual setups. Isn't it the same no matter what the polarizer setting is?

 

[DrChinese]

1. I thought we were talking about photons incident on the polarizers. Are you talking about photons transmitted by the polarizers?

2. This is getting very confusing. If the polarization of the photons is unknown, then this would indicate that you're talking about the photons incident on the polarizer. If the polarization of the photons incident on the polarizer isn't varying randomly, then how would you account for the observed photon flux for individual setups. Isn't it the same no matter what the polarizer setting is?

Grrr. Photons *incident* on a polarizer can be of known polarization (such as H>) or unknown polarization.

1. Photons of known polarization do not have a "randomly varying vector" or whatever you called it. They may oscillate, but their polarization remains fixed and does not vary. We know that experimentally.

2. Photons of unknown polarization do not have a "randomly varying vector" either - as far as anyone knows. There is no test that indicates this is as you describe it. However, they do provide random results when they are measured with a polarizer. Of course, if you have a pair of entangled photons, which of course are of unknown polarization, you would deduce that they definitely do not have a "varying" polarization. "Varying" meaning changing with time. They definitely do not change with time, otherwise you would not have perfect correlations (since those correlations are time invariant).

My point is that characterization of entangled photons in the manner you describe is not warranted.

 

[DrChinese]

If the assumption is that a single particle has three such elements of reality at three different angles, then the fact that no experiment has ever been performed in which a single particle was measured at three angles, let alone 2, should be a relevant omission, shouldn't it?

Bill, please read EPR. They specifically address this point, there is no omission. And that is the crux of my argument. They say "no reasonable definition of reality can be expected" to require that all individual elements of reality be predicted at the same time. So that means that if Alice (yes the particle) has elements of reality at 0, 120 and 240 degrees, these must be ASSUMED to be simultaneously existing.

a. Yes, that there are individual elements of reality is deduced from tests of different particles.
b. No, there is no test of one particle which demonstrates that there are more that one polarization element of reality at a time (per the EPR definition).

So I am simply accepting EPR at their word. And so did Bell. So it should be obvious now that there cannot be any group of photons that have simultaneous elements of reality for 0, 120 and 240 degrees which also satisfy the QM expectation relationship of cos^2 (cos for spin 1/2 particles). There is absolutely no locality involved in this deduction.

And Bell was quite aware of this. But he was also aware that an experimental test using entangled particles might suffer from the idea that detector a might influence an outcome B (and vice versa). Enter locality.

 

[DrChinese]

<< A single particle, Alice, has 3 elements of reality at angles 0, 120, 240 degrees. This is by assumption, the realistic assumption, and from the fact that these angles - individually - could be predicted with certainty. >>

What, precisely, is the experimental set-up you're talking about, and what do these elements of reality correspond to in the experimental set-up? Measurement settings, perhaps? But then in what sense does the "single particle" "have" these elements of reality? Is the single particle just being measured by these elements of reality fixed at these angles? Are the measurements simultaneous? Or one at a time?

<< It is obvious from the Bell program that there are NO datasets of Alice which match the QM expectation value. Ergo, the assumption is invalid. And you don't need to consider settings of Bob at all. You simply cannot construct the Alice dataset. QED. >>

Nonsense. Bell's inequality is completely contingent on a comparison of statistical correlations between two space-like separated measurement outcomes on two separate particles. Without that, you simply have no dataset to compare to the QM-predicted correlations, in a way which implies a violation of Bell's inequality.

Read EPR!

EPR is not talking about whether Alice and Bob have simultaneous elements of reality, they are talking about Alice only. Bob is used to prove there is an element of reality to Alice because, by their definition: if an Alice outcome can be predicted in advance with certainty. then it is real. They observe Bob to accomplish this, that is all Bob is for.

Now, it should be clear that I can choose to measure Bob any way I like, let's say 0, 120 or 240 degrees. So if I measure Alice the same way, I can demostrate an element of reality for those settings. The EPR conclusion was that it is unreasonable to require that all of those settings be predictable at once!

I don't happen to agree with that conclusion, but there it is. Realism is defined a la EPR. And if you don't think Bell used that exactly, read Bell again. I will be glad to supply the reference quotes (which can then be suitably ignored in favor of something else). But I am operating nearly verbatim at this point, both for EPR and Bell.

 

[DrChinese]

Dear Hurkyl, this seems to be confusing?

"Element of reality at angle 120 degrees" is probably NOW best allocated to the orientation a of Alice's test device.

"NOW" now being added because "the" physical quantity impacting on, and interacting with the device, is a random member of an infinite set.

So to say "it's the physical quantity" seems confusing to me.

I am hoping your answer to my query re spin-vectors will clarify it all for me.

Thank you.

JenniT, you should read EPR yourself. As I keep telling you, this is assumed by Bell.

The 2nd to last paragraph of EPR:

"One could object to this conclusion on the grounds that our criterion of reality is not sufficiently restrictive. Indeed, one would not arrive at our conclusion if one insisted that two or more physical quantities can be regarded as simultaneous elements of reality only when they can be simultaneously measured or predicted. On this point of view, since either one or the other, but not both simultaneously, of the quantities P and Q can be predicted, they are not simulataneously real. This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."

It takes a minute to parse that out, but it say that it is unreasonable to require the spin elements of reality at 0, 120 and 240 degrees (my angle settings not theirs) to be simultaneously proven.

That is for a single particle and you can call it anything you like. Alice, a, A, particle 1, or whatever. According to the EPR result (which is wrong because of Bell): QM is incomplete because there exist elements of reality which QM does not provide values for.

 

[DrChinese]

Bravo. But his conclusion still doesn't follow.

My conclusion being exactly: That both EPR's definition of reality AND the QM expectation values (cos^2) cannot both be accurate for a group of photons. This deduction is completely independent of any kind of experimental proof. In fact, this is simply the Bell result before you imagine trying to put together an experimental version. When you put together an experimental version, then locality comes into play.

So yes, it follows from EPR and Bell. In fact, this is what my_wan and several others are alluding to when they say that Malus implies violation of BIs.

 

[billschnieder]

It takes a minute to parse that out, but it say that it is unreasonable to require the spin elements of reality at 0, 120 and 240 degrees (my angle settings not theirs) to be simultaneously proven.

That is for a single particle and you can call it anything you like. Alice, a, A, particle 1, or whatever. According to the EPR result (which is wrong because of Bell): QM is incomplete because there exist elements of reality which QM does not provide values for.

DrC,
Your interpretation of EPR is not correct.

The paragraph before the one you quoted says:

"Previously we have proved that either (1) the quantum-mechanical description of reality given by the wave function is not complete or (2) when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality. Starting then with the assumption that the wave function does give a complete description of the physical reality, we arrived at the conclusion that the two physical quantities with noncommuting operators can have simultaneous reality. Thus the negation of (1) leads to the negation of the only other alternative (2). We are forced thus to conclude that the quantum-mechanical description of physical reality given by wave functions is not complete.

This is the main conclusion of the paper. The part you quoted is merely pre-empting how someone might object to their main conclusion. You are trying to parse that final paragraph in a way which contradicts their main conclusion.

"One could object to this conclusion on the grounds that our criterion of reality is not sufficiently restrictive. Indeed, one would not arrive at our conclusion if one insisted that two or more physical quantities can be regarded as simultaneous elements of reality only when they can be simultaneously measured or predicted. On this point of view, since either one or the other, but not both simultaneously, of the quantities P and Q can be predicted, they are not simultaneously real. This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."

Note they are saying here that, if you assume that QM is complete, then as they have just proven above, according to QM, both the the local P and the remote Q are simultaneously real, but then such a reality in which measurement of local P automatically changes the reality of a remote Q, is unreasonable. Therefore it does not matter for their argument whether you choose to restrict the definition of "simultaneous reality" to "only when they can be simultaneously measured or predicted".

In short, they are saying either QM is not complete, or if you insist that QM is complete, you must adhere to an unreasonable reality in which FTL is possible.
Therefore your statement underlined above is not remotely similar to what EPR wrote.

 

[DrChinese]

DrC,
Your interpretation of EPR is not correct.

I can't make you read it my way. You'll have to do that on your own.

But they say it. True, one might object to their conclusion regarding the completeness of QM on the ground mentioned - elements of reality must be simultaneously predictable. And that would negate their conclusion, as you mention. But they still say that, in their opinion, their definition should stand - the less restrictive one. And their definition is (paraphrased):

"Two or more physical quantities can be regarded as simultaneous elements of reality when they can be predicted with certainty without disturbing the particle in any way - regardless of whether those elements can be simultaneously predicted."

I don't think that definition is hard to take away from EPR. Seriously, you do see that much, don't you? Well, assuming you can stop being craggly long enough to agree to something... that is the definition Bell uses. As I keep saying, you don't have to agree with the definition. You merely accept that is what Bell was working with. Along with most everyone after...

 

[billschnieder]

I can't make you read it my way. You'll have to do that on your own.

But they say it. True, one might object to their conclusion regarding the completeness of QM on the ground mentioned - elements of reality must be simultaneously predictable. And that would negate their conclusion, as you mention. But they still say that, in their opinion, their definition should stand - the less restrictive one. And their definition is (paraphrased):

"Two or more physical quantities can be regarded as simultaneous elements of reality when they can be predicted with certainty without disturbing the particle in any way - regardless of whether those elements can be simultaneously predicted."

I don't think that definition is hard to take away from EPR. Seriously, you do see that much, don't you? Well, assuming you can stop being craggly long enough to agree to something... that is the definition Bell uses. As I keep saying, you don't have to agree with the definition. You merely accept that is what Bell was working with. Along with most everyone after...

Again you are putting words in the "mouth" of EPR. They never provided a definition reality like the one you are suggesting. They said:

A comprehensive definition of reality is, however, unnecessary for our purpose. We shall be satisfied with the following criterion, which we regard as reasonable. 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. It seems to us that this criterion, while far from exhausting all possible ways of recognizing a physical reality, at least provides us with one such way, whenever the conditions set down in it occur. Regarded not as a necessary, but merely as a sufficient, condition of reality, this criterion is in agreement with classical as well as quantum-mechanical ideas of reality.

Note that they do not say the physical quantity being predicted, is itself an element of reality, just that it corresponds to one.

Secondly, Bell is squarely focused on locality and causality as has been pointed out to you on this thread before. Specifically, in Bell's own words, he says:

The paradox of Einstein, Podolsky and Rosen [1] was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality [2]. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty.

So this idea that there is something out-there such as the EPR definition of reality which Bell was supposedly working from is just not accurate. The words of the authors themselves confirm that to be the case.

 

[DrChinese]

Again you are putting words in the "mouth" of EPR. They never provided a definition reality like the one you are suggesting. They said:... [snip]

...Note that they do not say the physical quantity being predicted, is itself an element of reality, just that it corresponds to one.

"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. It seems to us that this criterion, while far from exhausting all possible ways of recognizing a physical reality, at least provides us with one such way, whenever the conditions set down in it occur. Regarded not as a necessary, but merely as a sufficient, condition of reality, this criterion is in agreement with classical as well as quantum-mechanical ideas of reality..."

"One could object to this conclusion on the grounds that our criterion of reality is not sufficiently restrictive. Indeed, one would not arrive at our conclusion if one insisted that two or more physical quantities can be regarded as simultaneous elements of reality only when they can be simultaneously measured or predicted. On this point of view, since either one or the other, but not both simultaneously, of the quantities P and Q can be predicted, they are not simultaneously real. This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does not disturb the second system in any way. No reasonable definition of reality could be expected to permit this."

Funny. That sounds pretty, pretty, pretty, pretty, pretty close to:

"Two or more physical quantities can be regarded as simultaneous elements of reality when they can be predicted with certainty without disturbing the particle in any way - regardless of whether those elements can be simultaneously predicted."

Yes, I do agree that the phrase "corresponding to" is much much different from "regarded as". Oh gosh now, they actually said both didn't they...

And please, don't chop up poor ol' Bell any more than you already have. You're the one who thinks his work is "fatally flawed" or whatever you called it. As I have said many times, you're the local realist - why don't you define realism and then we can move on. Either your definition will agree with EPR or it won't. Obviously, if you are in the group that thinks the EPR is not sufficiently restrictive, then you don't agree with the EPR conclusion. If you do agree with their definition, then you should agree with the Bell conclusion. Go for it!

 

[DrChinese]

I'm just curious to see how DrC will manage to distort EPR and Bell this time.

I like to distort them by using verbatim, in context quotes. Insidious!

 

[Maaneli]

And please, don't chop up poor ol' Bell any more than you already have.

Actually, you're the one who consistently misrepresents Bell's argument, regardless of all the contrary evidence right in front of your face.

 

[Maaneli]

I like to distort them by using verbatim, in context quotes. Insidious!

Actually, you have not quoted Bell on anything.

 

[Maaneli]

Realism is defined a la EPR. And if you don't think Bell used that exactly, read Bell again. I will be glad to supply the reference quotes (which can then be suitably ignored in favor of something else). But I am operating nearly verbatim at this point, both for EPR and Bell.

In my post #25, I showed you exactly how Bell defined realism, in relation to his local causality criterion. *You* are the one who has refused to acknowledge Bell's own definitions, instead saying some dismissive nonsense like "Bell said many things in many different ways" or something like that.

 

[DrChinese]

Actually, you have not quoted Bell on anything.

I'm stung!

Well, how about these:

ON THE EINSTEIN PODOLSKY ROSEN PARADOX
==================================
"In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote."

That pretty much is a direct contradiction to the conclusion of EPR. And yet based on their very definition of realism.

 

[nismaratwork]

I'm stung!

Well, how about these:

ON THE EINSTEIN PODOLSKY ROSEN PARADOX
==================================
"In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote."

That pretty much is a direct contradiction to the conclusion of EPR. And yet based on their very definition of realism.

Oh Maaneli, I hate to add fuel to the fire that is consuming you, but one of the best treatment of this very subject is on a website named (and I presume owned) by Dr. Chinese. It seems very rigorous to me.

http://www.drchinese.com/David/EPR_Bell_Aspect.htm

I might add, I didn't look for it, this was the #3 result when I googled: "bell definition of reality epr quote"

 

[nismaratwork]

Oh, and this: http://www.springerlink.com/content/j17l7457p2357154/

 

[morrobay]

If the assumption is that a single particle has three such elements of reality at three different angles, then the fact that no experiment has ever been performed in which a single particle was measured at three angles, let alone 2, should be a relevant omission, shouldn't it?

billshnieder, instead of waiting for a perfect experiment, could you derive an inequality
as simple as the original Bell inequality.
That is based on and comports with the existing experiments.

 

[Maaneli]

I'm stung!

Well, how about these:

ON THE EINSTEIN PODOLSKY ROSEN PARADOX
==================================
"In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote."

That pretty much is a direct contradiction to the conclusion of EPR. And yet based on their very definition of realism.

That quote does nothing to support your claim, and once again you fail to recognize that the EPR argument is an argument FROM locality TO outcome determining hidden-variables. In other words, the notion of realism that EPR propose already includes a notion of locality and causality. What Bell did was to make mathematically precise these notions in the EPR argument, via his use of a theory of local beables satisfying his principle of local causality (as I explained in post #25). Bell *himself* also explains this in the quote that Bill posted. And for your information, Bill's quote of Bell is not taken out of context. You would see that if you read the paper (from which the quote was taken) in full.

By the way, I am still waiting for you to read Bell's La Nouvelle Cuisine and to get back to me, as you promised that you would.

 

[DrChinese]

By the way, I am still waiting for you to read Bell's La Nouvelle Cuisine and to get back to me, as you promised that you would.

I read it long ago, just want to refresh so I can properly mangle some context.

I think it is fairly funny that you think EPR is about locality. That relativity was to be respected was assumed.

 

[Maaneli]

I read it long ago, just want to refresh so I can properly mangle some context.

OK, so did you understand Bell's reasoning? Do you now see how he uses the assumptions of locality and causality in the derivation of his inequality?

I think it is fairly funny that you think EPR is about locality. That relativity was to be respected was assumed.

I'm sure you do, but that's because you haven't understood the EPR argument.

 

[ThomasT]

Maaneli, I understand that you're PhD physicist. Is this correct? What is your primary field? What is your motivation for being interested in the Bell stuff?

I'm asking this because you seem to be qualified to evaluate the statements presented in this thread, and also because I still don't understand what DrC is talking about. So, is it just me (I am an ignorant layperson -- with a riduculously high IQ and a knowledge of Fourier analysis), or is he, so far as you can ascertain, not making any sense wrt his requirement(s) for LR models of entanglement?

 

[Maaneli]

Maaneli, I understand that you're PhD physicist. Is this correct? What is your primary field? What is your motivation for being interested in the Bell stuff?

I'm asking this because you seem to be qualified to evaluate the statements presented in this thread, and also because I still don't understand what DrC is talking about. So, is it just me (I am an ignorant layperson -- with a riduculously high IQ and a knowledge of Fourier analysis), or is he, so far as you can ascertain, not making any sense wrt his requirement(s) for LR models of entanglement?

ThomasT,

I don't yet have a PhD. Only a BS in physics in 2008. But I will begin my graduate studies at Clemson this upcoming year, with the intent to be advised by Dr. Antony Valentini for my PhD. My 'primary field' centers around a few areas, namely, the foundations of quantum mechanics, stochastic quantization theories, the de Broglie-Bohm theory and its variants, and designing experimental tests of hidden-variables theories. Recently, I've also developed hidden-variable versions of semiclassical gravity and quantum gravity. I'm interested in Bell stuff because as an undergraduate, I was enamored with the possibility of local and nonlocal hidden variable theories underlying QM, and it was important for me to understand Bell's theorem in order to evaluate the physical possibility of said hidden variable theories.

As for evaluating statements in this thread, I haven't been following your exchange with DrC, so I can't comment on that. But my exchange with DrC has been over his misunderstanding of the assumptions used in Bell's theorem, his faith in the authority of Aspect and Zeilinger quotes, and what the implications are of experimental Bell inequality violations. DrC thinks (as, admittedly, do most people in physics) that Bell assumed something like "Local Realism", and that Bell's theorem shows that QM is inconsistent with either the assumption of Realism or Locality (though DrC says his own preference is to conclude that QM is inconsistent with Realism). By contrast, I am trying to point out to him that not only is the phrase Local Realism vague and misleading (it gives the impression that Locality and Realism are two separated assumptions of Bell's theorem, and it is unclear what Realism is intended to mean (independently of Bell's definition of Locality) in Bell's theorem), but Bell himself never used such a phrase to characterize the assumptions in his own theorem - rather, Bell spoke of Local Causality, and showed clearly how his definition of Locality relies on a specific notion of realism involving 'beables', the implication being that it makes no sense to claim that the QM violation of Bell's inequality implies that QM is inconsistent with Realism (as Bell defined it) but consistent with Locality (as Bell defined it). Also, I think that DrC has misinterpreted the EPR argument, both on its own terms, and as it relates to Bell's theorem.

 

[ThomasT]

Thanks Maaneli, I'll sit back and read the exchanges between you and DrC and I'm sure I'll learn something -- probably a lot that I haven't already considered. I hope that others as qualified as you will contribute to these threads on Bell's theorem, nonlocality, etc. I certainly appreciate DrC's contributions, but I just don't understand what he's saying sometimes.

I'm fascinated by the possible implications of Bell's work, but I don't want to jump on the 'nonlocality bandwagon', so to speak, until I'm satisfied that I've investigated, and understand, it thoroughly.

 

[DrChinese]

I certainly appreciate DrC's contributions, but I just don't understand what he's saying sometimes.

Neither do I!

 

[DrChinese]

... his faith in the authority of Aspect and Zeilinger quotes, and what the implications are of experimental Bell inequality violations. DrC thinks (as, admittedly, do most people in physics) that Bell assumed something like "Local Realism", and that Bell's theorem shows that QM is inconsistent with either the assumption of Realism or Locality (though DrC says his own preference is to conclude that QM is inconsistent with Realism)...

First, I think it is awesome that you will be studying with Valentini. I wish you the best, and am looking forward to seeing some papers from you in a few years.

Second, I don't rely at all on secondary quotes or work. I do all of my analytical work against primary sources. Secondary sources, such as the quotes by Zeilinger, are not authoritative in my book. The only reason I quote them - ever - is just to provide some background which supports ideas that are better expressed in the original but may be long and involved. So something like the Aspect/Zeilinger quotes from summary type articles often cut to the chase and indicate the standard view of the community at large.

Which I why I usually resist discussing Bell's book "Speakable and Unspeakable in Quantum Mechanics", although I am interested in discussing this with you.

 

[Maaneli]

First, I think it is awesome that you will be studying with Valentini. I wish you the best,

Thanks, that's kind of you.

and am looking forward to seeing some papers from you in a few years.

Hopefully sooner than that! :)

Second, I don't rely at all on secondary quotes or work. I do all of my analytical work against primary sources.

Oh, I don't doubt that your work involves primary sources from certain authors. But in this thread, I have only seen you post quotes of Zeilinger and Aspect.

Edit: And sections of EPR as well.

Secondary sources, such as the quotes by Zeilinger, are not authoritative in my book. The only reason I quote them - ever - is just to provide some background which supports ideas that are better expressed in the original but may be long and involved. So something like the Aspect/Zeilinger quotes from summary type articles often cut to the chase and indicate the standard view of the community at large.

That's fair enough. But if someone asks you (as I did previously) for a primary source which discusses in detail a claim of the standard view (such as what constitutes the Realism assumption in the Bell inequality derivation), it helps if you can also post the primary source.

Which I why I usually resist discussing Bell's book "Speakable and Unspeakable in Quantum Mechanics", although I am interested in discussing this with you.

But if you say that your analytical work involves primary sources, then, as far as primary sources go, it is indispensable to study the papers in Bell's book! After all, many of the papers include his (exceptionally clear) elaborations on the mathematical and physical assumptions that went into his own theorem! And at the very least, I think it is a good idea to study those papers, so that you can compare Bell's understanding of his own theorem against the understandings of other people.

With that said, I'm glad that you're interested in discussing this with me. I hope we can follow through.

 

[Maaneli]

Thanks Maaneli, I'll sit back and read the exchanges between you and DrC and I'm sure I'll learn something -- probably a lot that I haven't already considered. I hope that others as qualified as you will contribute to these threads on Bell's theorem, nonlocality, etc. I certainly appreciate DrC's contributions, but I just don't understand what he's saying sometimes.

You're welcome, Thomas. Let me know if you have any questions or comments about the exchange.

I'm fascinated by the possible implications of Bell's work, but I don't want to jump on the 'nonlocality bandwagon', so to speak, until I'm satisfied that I've investigated, and understand, it thoroughly.

Edit: Let me start over.

An unavoidable conclusion of Bell's theorem is that standard QM is a nonlocal theory. Now, you might wonder whether by rejecting other (non locality) assumptions in Bell's theorem, one can construct a local hidden variables theory which can also violate the Bell inequalities, and perhaps be empirically equivalent to standard QM. For example, one might consider rejecting Bell's assumption that detector settings and measurement outcomes are "free variables" (in the sense that they only have physical implications on their future light cones). Typically, proposals which attempt to implement this possibility make use of some form of "backwards causation" along the past light cones of detectors. Local hidden variables theories and toy models along these lines have been extensively developed by the likes of Aharonov and Vaidman, O. Costa de Beauregard, Huw Price, Roderick Sutherland, Ken Wharton, and Steven Weinstein, just to name a few. At the moment, this backwards causation approach seems to be the only viable alternative to nonlocality. But even so, it should be emphasized that it is still considerably less developed than nonlocal theories such as standard QM and deBB theory.

 

[billschnieder]

There is a strong argument to be made though that nonlocality is by far the most theoretically plausible, but it's certainly not yet a done deal.

Jaynes wrote the following concerning this "nonlocality" (http://bayes.wustl.edu/etj/articles/cmystery.pdf):
Jaynes, E. T., 1989, `Clearing up Mysteries - The Original Goal, ' in Maximum-Entropy and Bayesian Methods, J. Skilling (ed.), Kluwer, Dordrecht, p. 1

The spooky superluminal stuff [...] disappears as soon as we recognize, with Jeffreys and Bohr, that what is traveling faster than light is not a physical causal influence, but only a logical inference. Here is Bohr's quoted statement:
"Of course there is in a case like that just considered no question of a mechanical disturbance of the system under investigation during the last critical phase of the measuring procedure. But even at this stage there is essentially the question of an influence on the very conditions which define the possible types of predictions regarding the future behavior of the system."

In other words, "nonlocality" is not a strange concept in epistemology, it is only strange in ontology. The following analogy illustrates this (from http://arxiv.org/abs/0812.4506):

suppose that a demon rolls a pair of dice in a distant planet around Betelgeuse and that the outcome is a double-six. This nice result is immediately true on the Earth. Nevertheless, in accordance with Lorentz covariance, we will have to wait for at least 427 years before we could learn this good news. Therefore, on the one hand, we may consider that the instantaneous event is purely fictitious on the Earth. But on the other hand, the same instantaneous event may be considered as real since afterwards, we will be able to derive exactly its date and its location. In other words, the score of the demon may be considered as instantaneously valid at a distance.

The problem is, those suffering from the "Mind Projection Fallacy" do not appreciate the difference between epistemology and ontology. Jaynes describes it as follows:
Jaynes, E. T., 1990, `Probability in Quantum Theory,' in Complexity, Entropy, and the Physics of Information, W. H. Zurek (ed.), Addison-Wesley, Redwood City, CA, p. 381 (http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf)

The failure of quantum theorists to distinguish in calculations between several quite different meanings of 'probability', between expectation values and actual values, makes us do things that don't need to be done; and to fail to do things that do need to be done. We fail to distinguish in our verbiage between prediction and measurement. For example, the famous vague phrases: 'It is impossible to specify ... '; or 'It is impossible to define ... ' can be interpreted equally well as statements about prediction or statements about measurement. Thus the demonstrably correct statement that the present formalism cannot predict something becomes perverted into the logically unjustified and almost certainly false claim that the experimentalist cannot measure it!
We routinely commit the Mind Projection Fallacy: supposing that creations of our own imagination are real properties of Nature, or that our own ignorance signifies some indecision on the part of Nature. It is then impossible to agree on the proper place of information in physics. This muddying up of the distinction between reality and our knowledge of reality is carried to the point where we find some otherwise rational physicists, on the basis of the Bell inequality experiments, asserting the objective reality of probabilities, while denying the objective reality of atoms! These sloppy habits of language have tricked us into mystical, pre scientific standards of logic, and leave the meaning of any QM result ambiguous. Yet from decades of trial and error we have managed to learn how to calculate with enough art and tact so that we come out with the right numbers!

 

[Maaneli]

Jaynes wrote the following concerning this "nonlocality" (http://bayes.wustl.edu/etj/articles/cmystery.pdf):
Jaynes, E. T., 1989, `Clearing up Mysteries - The Original Goal, ' in Maximum-Entropy and Bayesian Methods, J. Skilling (ed.), Kluwer, Dordrecht, p. 1

In other words, "nonlocality" is not a strange concept in epistemology, it is only strange in ontology. The following analogy illustrates this (from http://arxiv.org/abs/0812.4506):

The problem is, those suffering from the "Mind Projection Fallacy" do not appreciate the difference between epistemology and ontology. Jaynes describes it as follows:
Jaynes, E. T., 1990, `Probability in Quantum Theory,' in Complexity, Entropy, and the Physics of Information, W. H. Zurek (ed.), Addison-Wesley, Redwood City, CA, p. 381 (http://bayes.wustl.edu/etj/articles/prob.in.qm.pdf)

Thanks, Bill. I've always found Jaynes' writings on the foundations of probability to be ground-breaking for its time.

Nonlocality is certainly "strange" (in the sense of being counter-intuitive to classical relativistic intuitions) with respect to ontology, but it should be emphasized that it is not a logically inconsistent part of the construction of certain versions of quantum theory, namely, ontological quantum theories such as de Broglie-Bohm, stochastic mechanics, and GRW collapse, where the ontology explicitly has a nonlocal dynamics.

 

[billschnieder]

Thanks, Bill. I've always found Jaynes' writings on the foundations of probability to be ground-breaking for its time.

Nonlocality is certainly "strange" (in the sense of being counter-intuitive to classical relativistic intuitions) with respect to ontology, but it should be emphasized that it is not a logically inconsistent part of the construction of certain versions of quantum theory, namely, ontological quantum theories such as de Broglie-Bohm, stochastic mechanics, and GRW collapse, where the ontology explicitly has a nonlocal dynamics.

But that is the thing, those theories are not ontological just because they are called that. For example dBB starts off by assigning ontology to a configuration. A configuration, is just a collection of information about a physical system. The configuration itself is not physical but epistemic. The so called "nonlocality" of dBB comes from the fact that this configuration contains information about the whole universe at once. It is not an ontological nonlocality but an epistemic one, even though the dBB theory also has clearer ontic components.

One thing that dBB theory shows clearly is the fact that QM is a mixture of both ontological and epistemological aspects, the problem is nobody has been able to clearly disentangle them yet. dBB came closest to doing that.

Many in the field seem to believe that quantum events have no physical causes, only probabilistic laws, but
"instantaneous action at a distance" or nonlocality, if it is ontological as is also often claimed, will qualify as physical cause. What gives?

 

[Maaneli]

But that is the thing, those theories are not ontological just because they are called that. For example dBB starts off by assigning ontology to a configuration. A configuration, is just a collection of information about a physical system. The configuration itself is not physical but epistemic. The so called "nonlocality" of dBB comes from the fact that this configuration contains information about the whole universe at once. It is not an ontological nonlocality but an epistemic one, even though the dBB theory also has clearer ontic components.

One thing that dBB theory shows clearly is the fact that QM is a mixture of both ontological and epistemological aspects, the problem is nobody has been able to clearly disentangle them yet. dBB came closest to doing that.

Many in the field seem to believe that quantum events have no physical causes, only probabilistic laws, but
"instantaneous action at a distance" or nonlocality, if it is ontological as is also often claimed, will qualify as physical cause. What gives?

I think I should clarify what is meant when it is said that deBB theory is an "ontological" theory. Roughly speaking, it means simply that the theory gives an observer-independent account of what fundamental objects *might* compose the real physical world. In other words, the ontology of deBB theory is a *hypothesis* of the ontology of the real physical world.

And to state it more accurately, the proposed ontology in deBB theory is not just a configuration of point particles, but rather a configuration of point particles whose dynamics supervenes on an ontological causal agent in configuration space, namely, the quantum wavefunction; and all the empirical predictions of the deBB theory (in other words, the epistemic aspect of the deBB theory) supervene on the dynamics of the particle configuration. So there is in fact both an ontological and epistemic aspect to the deBB theory, and the distinction and relation between the two is clear.

Regarding how nonlocality arises in deBB theory, what you said is not correct. The nonlocality in (standard) deBB theory is in fact ontological (as well as epistemic in the sense of how the nonlocality manifests in the empirical predictions of the deBB theory), because it is a consequence of the fact that the ontological quantum wavefunction (on which the dynamics of the particle configuration supervenes) is a field that lives on a 3N-dimensional configuration space, and which is in general not factorizable into tensor products of wavefunctions in 3-space.

Now, I should say that there do exist other ontological theories to which the standard deBB dynamics is an approximation. Examples of such theories are Nelson's stochastic mechanics, and Norsen's Theory of Exclusively Local Beables - in both of these theories, the quantum wavefunction in configuration space is neither ontological nor fundamental; rather, the wavefunction in configuration space plays a very specific epistemic role in encoding the (hypothesized) ontological fields that determine the dynamics of the particle configuration in those theories. But again, these are *different* theories from standard deBB, and the latter certainly has its own self-consistent interpretation involving both ontological and epistemic aspects.

As for why "many in the field seem to believe that quantum events have no physical causes, only probabilistic laws, but 'instantaneous action at a distance' or nonlocality, if it is ontological as is also often claimed, will qualify as physical cause", I quite agree with you that the physicists in the field who think that way are simply being inconsistent. And I think the reason for the inconsistency is a failure to fully grasp the implications of EPR and Bell's theorem.

 

[billschnieder]

And to state it more accurately, the proposed ontology in deBB theory is not just a configuration of point particles, but rather a configuration of point particles whose dynamics supervenes on an ontological causal agent in configuration space, namely, the quantum wavefunction;
...
Regarding how nonlocality arises in deBB theory, what you said is not correct. The nonlocality in (standard) deBB theory is in fact ontological (as well as epistemic in the sense of how the nonlocality manifests in the empirical predictions of the deBB theory), because it is a consequence of the fact that the ontological quantum wavefunction (on which the dynamics of the particle configuration supervenes) is a field that lives on a 3N-dimensional configuration space and which is in general not factorizable into tensor products of wavefunctions in 3-space.

I won't say I have an thorough understanding of deBB, but I'm not convinced that the wavefunction defined in configuration space, is necessarily ontological. The fact that the number of dimensions increases with number of particles is suggestive that at least for more than 1 particle, the wavefunction is not entirely ontological but includes epistemic aspects. So I do not doubt the fact that the wavefunction is nonlocal, just the idea that it is ontological.

EDIT:
David Bohm seemed to agree when he said the following:

While our theory can be extended formally in a logically consistent way by introducing the concept of a wave in a 3N-dimensional space, it is evident that this procedure is not really acceptable in a physical theory.
* Bohm, David (1957), Causality and Chance in Modern Physics. London: Routledge & Kegan Paul.

 

[Maaneli]

I won't say I have an thorough understanding of deBB, but I'm not convinced that the wavefunction defined in configuration space, is necessarily ontological. The fact that the number of dimensions increases with number of particles is suggestive that at least for more than 1 particle, the wavefunction is not entirely ontological but includes epistemic aspects. So I do not doubt the fact that the wavefunction is nonlocal, just the idea that it is ontological.

But my point is that in the *standard* deBB theory, all that there is is this nonlocal wavefunction and particle configuration, and the dynamical laws relating the two. And if the standard deBB theory is to be understood consistently on its own terms, the wavefunction can only be understood as ontological. (Maybe I should qualify this by mentioning that there are some Bohmians who think that the wavefunction can be understood as nomological (in other words, as something like a physical law); but I think there is overwhelming evidence which shows that such a view is untenable). Now, you may (reasonably) think that the standard deBB view of the nonlocal wavefunction being ontological is physically implausible, such as for the reason you just gave. But if you take that route, then you're implying a different theory than the standard deBB theory. And again, examples of theories along the lines of what you probably have in mind are those of Nelson and Norsen, where the nonlocal wavefunction is just epistemic, and the standard deBB theory is in some sense an approximation.