Against "realism"

[Ilja]

If you would like to discuss the pros and cons of Norsen's paper (and I would be happy to do so), we should start another thread for that.

Ok, no problem.

My point about Norsen's paper is that IF you accepted his basic argument - as you say you do - THEN you naturally wind up with a favorable perspective on Bohmian interpretations. That is not the only way to get to that point, but I think it is natural. Because then, you essentially view Bell's Theorem as a rejection of locality - as Norsen essentially does, since he thinks that "naive realism" (his words) is not so relevant to Bell's Theorem.

That's not a problem, once I indeed favour a Bohmian interpretation.

(By the way, I laughed when Norsen attached the word "naive" to a respectable viewpoint. Apparently, no one bothered to explain to Einstein that his cherished viewpoint was in fact naive.

What he describes as naive (out of memory, once we start a new thread about it, I would have to reread it) is naive if taken as an axiom. EPR argue that this special situation follows from locality. Such an argumentation is not naive at all.

Anyway, realism - robust, healthy and meaningful - is fully present in Bell's Theorem as an assumption and there is nothing weak about it. It is difficult to imagine how Bell's famous paper can be considered absent the arguments presented in the EPR paper - in which the famous phrase "elements of reality" is defined - given the title Bell chose. I think Bell could have labeled his realism assumption more clearly, but that does not change the argument or its impact.)

It is clearly important to recognize that it is the first part of Bell's theorem (and, essentially, the EPR argumentation) that from weak realism and locality follows what is appropriately named "naive realism".

Many presentations of the violation of BI fail to recognize this, and from point of view of these presentations it looks like only the "naive realism" (which is, indeed, quite unreasonable to postulate even in classical situations), fails.

To give up weak (meatphysical) realism is quite another category. It means to give up the search for realistic explanation with only one reason: One does not like the fact that all realistic explanations require a preferred frame.

Then, giving it up does not preserve the realistic versions of Einstein causality or relativistic symmetry: Without reality, they are about nothing, thus, become meaningless anyway.
Thus, they have to be given up anyway. No reason to give up metaphysical realism.

[Dmitry67]

Without reality, they are about nothing, thus, become meaningless anyway.

The best approach to realism is MUH
But I dont know how to call it.
I like MUH, so I would rather ask you - MUH is it an ultimate realism or an ultimate denial of the one?

[DrChinese]

What he describes as naive (out of memory, once we start a new thread about it, I would have to reread it) is naive if taken as an axiom. EPR argue that this special situation follows from locality. Such an argumentation is not naive at all.


Norsen had an interesting (read: wrong) take on EPR. Locality is assumed in EPR, not really a factor per se. It is simply used as a technique to have particles interact and then separate. So the separability requirement is an experimental requirement so that we can go deeper into the central question of EPR: is there a "more complete" level of reality of a single particle.

1. The abstract of EPR reads: "In a complete theory, there is an element corresponding to each element of reality... In quantum mechanics in the case of tow physical quantities described by non-commuting operators, the knowledge of one precludes the knowledge of the other... One is led to conclude that the description of reality as given by a wave function is not complete." The paper concludes (before a final paragraph): "No reasonable definition of reality could be expected to permit this."

2. Nowhere does EPR discuss FTL influences, which they take to be sacrosanct. Of course, EPR's conclusion was wrong in the sense that they expected a "reasonable" definition of reality, one which is not observer independent. As Bell showed, that was not possible. We might get a clue as to what the paper was about from its title, "On the Einstein Podolsky Rosen Paradox." Clearly, not about locality. These papers are about the nature of reality. Is reality observer dependent, as QM seems to imply? Or is the moon round even when no one is looking, as Einstein believed?

In 1935, there was no question in the minds of EPR that their thought experiment - if performed - would demonstrate that the HUP could be beaten. On the other hand, most others (Bohr etc.) felt the opposite. But everyone could see one case which would not answer the question either way: the case of the so-called perfect correlations. This is essentially the kind of example EPR uses, where total momentum is known before 2 particles interact. EPR asked if you could learn more about a SINGLE particle (in this case) than the HUP allows. So that is the ultimate question: does an independent particle have well-defined values for non-commuting observables? If YES, well, that is realism, my friend. You can call it naive if you like but that is CERTAINLY what Einstein believed in.

3. So in the case of the perfect correlation, to switch to the entangled photon setup which was not experimentally feasible in 1935: A measurement on Alice allows you to predict, with perfect confidence, the result of an identical measurement on Bob. Now clearly, this was predicted by both QM and the local realist school led by Einstein. And Bell discussed this in his paper as well, showing in his (4) - (8) some examples in which these results could be derived by simple models (which themselves could be called naive or toy if you need to label them). Clearly, when Alice and Bob are measured at identical settings, the results should match perfectly. This is a requirement of any candidate mechanical theory, local or non-local. (In a way, it is simply a consequence of the greater requirement that any candidate theory reproduce the QM predictions.)

4. Bell introduces the requirement of realism after his (14), when he hypothesizes: "it follows that c is another unit vector". This is the leap. Previously, we had 2 particles and 2 measurement setting possibilities. Now he adds the "realistic" requirement that there must also be values at other measurement settings.

It is pretty obvious that if you don't have an a, b and c, then you can't get to Bell's inequality (15). Realism is NOT inserted as a requirement because it was previously assumed, as Norsen claims. Bell adds it here because it wasn't explicit previously, and needed to be added to obtain Bell's key result.

5. Now, you are free to disagree with my analysis, as Norsen does. But you will be hard pressed to make Norsen's argument by direct reference to EPR and Bell (not an absolute requirement, but you will see quickly that Norsen's reasoning depends on some very shaky inference). Norsen is completely wrong when he challenges:

"...anyone who claims that Bell’s Theorem is a theorem about 'local realist' theories ... needs to explain clearly what they mean by 'realism' [done, see 2. above] and show precisely where such 'realism' is assumed in the derivation of Bell’s inequalities. [done, see 4. above]"

I have refuted his argument by reference to the key articles themselves. Norsen's historical perspective is extremely skewed, and this was pointed out by Shimony himself in another one of Norsen's historical outings. I know Norsen is bright and knowledgeable, but that does not change my opinion of the interpretation of Bell's result (nor my conclusion that Norsen is wrong). And apparently, it hasn't swayed the opinions of his peers either. I could probably produce any number of recent quotes that state to the effect:

"No physical theory of local Hidden Variables [i.e. local realism] can ever reproduce all of the predictions of Quantum Mechanics."

[DrChinese]

Sorry, I realize we hadn't posted the link to Travis' article:

Norsen (2006): Against 'realism' (http://arxiv.org/abs/quant-ph/0607057)

[akhmeteli]

Norsen is completely wrong when he challenges:

"...anyone who claims that Bell’s Theorem is a theorem about 'local realist' theories ... needs to explain clearly what they mean by 'realism' [done, see 2. above] and show precisely where such 'realism' is assumed in the derivation of Bell’s inequalities. [done, see 4. above]"]

I don't know much about this topic, but I would like to understand your point of view. It looks like you define realism in "2. above" as "naive realism". On the other hand, I believe Norsen argues against using this definition with respect to the set of local realist theories allegedly banned by the Bell theorem using the following reasoning: "it was already known, prior to Bell’s Theorem and prior to any experimental tests of Bell’s inequalities, that Non-Contextual HVTs (i.e., Naive Realist theories) are wrong, are not empirically viable." So let me ask you if you disagree with the quoted Norsen's statement or you just believe that, while the statement is correct, naive realism is still what the Bell theorem is about?

I have refuted his argument by reference to the key articles themselves. Norsen's historical perspective is extremely skewed, and this was pointed out by Shimony himself in another one of Norsen's historical outings. I know Norsen is bright and knowledgeable, but that does not change my opinion of the interpretation of Bell's result (nor my conclusion that Norsen is wrong). And apparently, it hasn't swayed the opinions of his peers either. I could probably produce any number of recent quotes that state to the effect:

"No physical theory of local Hidden Variables [i.e. local realism] can ever reproduce all of the predictions of Quantum Mechanics."

One can agree or disagree with the statement in bold font, but my problem with it (and I apologise if the following may look as a distraction for this thread) is that a much stronger statement may be equally true or wrong: "No physical theory free of mutually contradictory assumptions can ever reproduce all of the predictions of Quantum Mechanics." Indeed, it seems to me that standard quantum mechanics contains mutually contradictory assumptions: while unitary evolution does not allow irreversibility, the projection postulate requires irreversibility, thus unitary evolution and the projection postulate are mutually contradictory, and the Bell theorem requires the latter or something similar as an essential assumption.

[DrChinese]

1. I don't know much about this topic, but I would like to understand your point of view. It looks like you define realism in "2. above" as "naive realism". On the other hand, I believe Norsen argues against using this definition with respect to the set of local realist theories allegedly banned by the Bell theorem using the following reasoning: "it was already known, prior to Bell’s Theorem and prior to any experimental tests of Bell’s inequalities, that Non-Contextual HVTs (i.e., Naive Realist theories) are wrong, are not empirically viable." So let me ask you if you disagree with the quoted Norsen's statement or you just believe that, while the statement is correct, naive realism is still what the Bell theorem is about?

2. One can agree or disagree with the statement in bold font, but my problem with it (and I apologise if the following may look as a distraction for this thread) is that a much stronger statement may be equally true or wrong: "No physical theory free of mutually contradictory assumptions can ever reproduce all of the predictions of Quantum Mechanics." Indeed, it seems to me that standard quantum mechanics contains mutually contradictory assumptions: while unitary evolution does not allow irreversibility, the projection postulate requires irreversibility, thus unitary evolution and the projection postulate are mutually contradictory, and the Bell theorem requires the latter or something similar as an essential assumption.

1. I completely disagree with Norsen's assertions. Notice that I quote from EPR and Bell directly to come to my point. Norsen takes a tour of things that are tangential to the issues of EPR and Bell (such as "metaphysical realism"). EPR and Bell talk about realism (elements of reality) and I don't see any reason to call it "naive" in the circumstances. You would be hard pressed to convince science historians that Einstein had abandoned realism later in life after specifically saying:

"I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it."

I really don't see how this definition is ambiguous in any way, nor do I see it as naive. Nor have I seen any historical evidence that the subject of "local realism" had simply become an issue of "locality" by the time of either the EPR or the Bell papers - as Norsen asserts. If it had, we'd all be Bohmians now (and obviously we aren't).

How can Norsen say, with a straight face, that "it was already known, prior to Bell’s Theorem and prior to any experimental tests of Bell’s inequalities, that Non-Contextual HVTs (i.e., Naive Realist theories) are wrong, are not empirically viable." I have read my share of historical papers, and that is as far from accurate as it gets. For that to be true, we'd need to believe that all scientists would have agreed that Bell tests (not yet invented, of course) would have expected the results per Aspect. Now, how exactly could that have been true, considering such experiments were not generally discussed until many years later? Yes, a few had heard of EPR-B, but not many until later.

Regarding the Kochen Specker theorem: it not only was not mainstream in 1965, it wasn't published yet. Please reference: Kochen, S. and Specker, E. (1967): "The Problem of Hidden Variables in Quantum Mechanics". Gleason's theorem was around, but I doubt you'd find too many who would call that a well-known result (even today).

Finally, there are plenty of scientists today who believe that nature is local non-realistic, in diametric opposition to Norsen's assertion. We would need to accept that scientists correctly rejected realism prior to Bell, but erroneously did not reject locality after Aspect. Show me anything that makes that sound like a mainstream history of the past 50 years.

No, Bell is about realism a la Einstein (who accepted it and thought QM was incomplete), a la Bohr (who rejected it because he saw QM as complete), a la the many other scientists who had no idea whether Einstein was right or Bohr was right. That is what Bell's Theorem is all about.


2. As to mutually contradictory assumptions: it is locality and realism that are the 2 on the table, and they are not mutually contradictory. Perhaps it is possible to tie them to ideas that become contradictions, but that would require additional debate.

[akhmeteli]

1.
How can Norsen say, with a straight face, that "it was already known, prior to Bell’s Theorem and prior to any experimental tests of Bell’s inequalities, that Non-Contextual HVTs (i.e., Naive Realist theories) are wrong, are not empirically viable.".

Thank you, this is what I wanted to understand. So you just disagree with this statement. I am not sure I have my own opinion on this matter.


2. As to mutually contradictory assumptions: it is locality and realism that are the 2 on the table, and they are not mutually contradictory. Perhaps it is possible to tie them to ideas that become contradictions, but that would require additional debate.

What I was trying to say is that predictions of standard quantum mechanics are mutually contradictory, which makes it quite difficult to reproduce all of them anyway:-).

[DrChinese]

What I was trying to say is that predictions of standard quantum mechanics are mutually contradictory, which makes it quite difficult to reproduce all of them anyway:-).

There are certainly some strange elements; spin and entanglement predictions being some. Clearly, that sets a very high bar for theory development; we can't have a new candidate theory that makes predictions which are different than reproducible experiments...

[mn4j]

EPR asked if you could learn more about a SINGLE particle (in this case) than the HUP allows. So that is the ultimate question: does an independent particle have well-defined values for non-commuting observables? If YES, well, that is realism, my friend. You can call it naive if you like but that is CERTAINLY what Einstein believed in.


From my understanding of the EPR paper, the above seems to be not quite accurate. The EPR paper says:

If, without in any was 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. (pp 777)

It appears to me they are saying, position and momentum can not both be simultaneously real parameters of particle. In other words, not being able to simultaneously predict or measure both values with certainty indicates that they are not both simultaneously real quantities. This is subtly different from saying a real particle is one in which both position and momentum are simultaneously well defined.

Clearly they indicate this to be the issue because on the next page they say:

From this follow 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.

Their definition of real quantities also did not indicate that the two observables be non-commuting. They go on to explain that no reasonable definition of reality should permit the reality of the position and momentum of one system to be dependent on the process of measurement carried out on a different system which does not disturb the first system in any way.

[DrChinese]

DrC said: "EPR asked if you could learn more about a SINGLE particle (in this case) than the HUP allows. So that is the ultimate question: does an independent particle have well-defined values for non-commuting observables? If YES, well, that is realism, my friend. You can call it naive if you like but that is CERTAINLY what Einstein believed in."

1. From my understanding of the EPR paper, the above seems to be not quite accurate. The EPR paper says:

"If, without in any was 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. (pp 777)"

2. It appears to me they are saying, position and momentum can not both be simultaneously real parameters of particle. In other words, not being able to simultaneously predict or measure both values with certainty indicates that they are not both simultaneously real quantities. This is subtly different from saying a real particle is one in which both position and momentum are simultaneously well defined.

3. Clearly they indicate this to be the issue because on the next page they say:

"From this follow 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."

Their definition of real quantities also did not indicate that the two observables be non-commuting. They go on to explain that no reasonable definition of reality should permit the reality of the position and momentum of one system to be dependent on the process of measurement carried out on a different system which does not disturb the first system in any way.

1. There is no difference in what I say and what you quote. Realism = elements of reality are simultaneous for non-commuting (or commuting, for that matter) observables. This exactly matches the words and intent of EPR. They flat out say that there are elements of reality to Alice and Bob BECAUSE they can be predicted in advance. And that is an excellent argument, one that makes perfect sense. But Bell demonstrated it was simply wrong - but not 'til later!

Let's use a specific example, going back to photons. According to EPR, Alice's photon is measured at any angle X. If Bob's photon is measured at X, the outcome can be predicted with certainty. Therefore, there is an element of reality associated with X. Now, we know if we measure Alice and Bob at Y instead where X<>Y, we can still predict the results. So if we do the same at every angle and circle 360 degrees, we will convince ourselves that there was an element of reality associated with every possible position. Because when Alice and Bob are measured at the same angle, the results are perfectly correlated.

So, EPR asserts that hidden variables (or realism, or elements of reality) make sense as an explanation for the phenomena. The problem was, the essential flaw in the EPR argument does not show up in the particular example used - which QM also predicts the same results. Their basic concept of reality was fine, but it took Bell to see the additional requirement that makes local realism untenable. We will come back to this in 3.

2. It is QM, not EPR, that says p and q are not simultaneously well-defined. EPR denies this because they are asserting realism. And it is not the particle's reality that is in question, it is the simultaneous realism of well-defined values for non-commuting observables of that particle.

3. EPR's conclusion, as listed here, is technically correct. The issue is that EPR thought they proved (1), when actually it is (2) that is true.

Repeating the question EPR asks (my words): "does an independent particle have well-defined values for non-commuting observables?" Translated (their words, which are identical in essence to mine): "when the operators corresponding to two physical quantities do not commute, do the two quantities have simultaneous reality? EPR's correct conclusion was "(2) when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality".

Now, why not (1) which is what EPR thought they had proved (that QM was incomplete)? Because EPR ruled out (2) because they felt it was "unreasonable". That is the only mistake in the paper, as Bell later showed that they did not use a sufficiently strong mathematical requirement for realism. If they had, they would have seen that it is their viewpoint that was not "complete", as it yields predictions at odds with experiment.

In their view of their paper's result, they "proved" that you could beat the HUP. But we know now that you cannot. I doubt you disagree with that point.

[mn4j]

1. There is no difference in what I say and what you quote. Realism = elements of reality are simultaneous for non-commuting (or commuting, for that matter) observables.
This exactly matches the words and intent of EPR. They flat out say that there are elements of reality to Alice and Bob BECAUSE they can be predicted in advance.

If that were the case, a real system could be made unreal by describing it with non-commuting observables. That is why I said the difference is subtle. The reality in question was that of the physical quantities in the theory and not of the underlying system being studied.

Let's use a specific example, going back to photons. According to EPR, Alice's photon is measured at any angle X. If Bob's photon is measured at X, the outcome can be predicted with certainty. Therefore, there is an element of reality associated with X. Now, we know if we measure Alice and Bob at Y instead where X<>Y, we can still predict the results. So if we do the same at every angle and circle 360 degrees, we will convince ourselves that there was an element of reality associated with every possible position. Because when Alice and Bob are measured at the same angle, the results are perfectly correlated.
Again you are confusing the reality of the quantities in the theory with that of the system.

The problem was, the essential flaw in the EPR argument does not show up in the particular example used - which QM also predicts the same results.
I think maybe you misunderstood their example.

2. It is QM, not EPR, that says p and q are not simultaneously well-defined. EPR denies this because they are asserting realism. And it is not the particle's reality that is in question, it is the simultaneous realism of well-defined values for non-commuting observables of that particle.
This is not accurate. No where in that article does EPR deny the fact that p and q are not simultaneously well-defined. In fact it is a central aspect of their proof that QM must not be complete.

3. EPR's conclusion, as listed here, is technically correct. The issue is that EPR thought they proved (1), when actually it is (2) that is true.

Repeating the question EPR asks (my words): "does an independent particle have well-defined values for non-commuting observables?" Translated (their words, which are identical in essence to mine): "when the operators corresponding to two physical quantities do not commute, do the two quantities have simultaneous reality? EPR's correct conclusion was "(2) when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality".

Now, why not (1) which is what EPR thought they had proved (that QM was incomplete)? Because EPR ruled out (2) because they felt it was "unreasonable". That is the only mistake in the paper, as Bell later showed that they did not use a sufficiently strong mathematical requirement for realism. If they had, they would have seen that it is their viewpoint that was not "complete", as it yields predictions at odds with experiment.

In their view of their paper's result, they "proved" that you could beat the HUP. But we know now that you cannot. I doubt you disagree with that point.

I think maybe you misunderstood their conclusion. EPR proved that there were two alternatives:
(1) The QM description of reality given by the wave function is not complete
(2) When the operators corresponding to two physical quantities do not commute, they cannot have simultaneous reality.

This derivation of both alternatives IS the main conclusion of the EPR paper.

They then go on to show that if you ASSUME (1) to be false (as Bohr was arguing then), you end up contradicting (2) as well which they have already proven is the only other valid alternative to (1).

In essence they were forcing the hand of those who claimed QM was complete by showing that if they believed that, they must also accept that position and momentum are both simultaneously real physical quantities (see their defintion of complete earlier in the paper). But if they accept that, then they find themselves in a situation in which the reality of the position AND momentum of the SECOND particle which has not been disturbed in any way was dependent on a measurement carried out on the FIRST particle with which the SECOND particle is not interacting.

The issue was not an attempt to defeat HUP for a single particle as you seem to be saying, but to show that if QM is complete, a reasonable definition of reality should not permit what the QM wave function permitted.

[DrChinese]

1. If that were the case, a real system could be made unreal by describing it with non-commuting observables. That is why I said the difference is subtle. The reality in question was that of the physical quantities in the theory and not of the underlying system being studied... Again you are confusing the reality of the quantities in the theory with that of the system...I think maybe you misunderstood their example.

2. This is not accurate. No where in that article does EPR deny the fact that p and q are not simultaneously well-defined. In fact it is a central aspect of their proof that QM must not be complete.

3. I think maybe you misunderstood their conclusion. EPR proved that there were two alternatives:
(1) The QM description of reality given by the wave function is not complete
(2) When the operators corresponding to two physical quantities do not commute, they cannot have simultaneous reality.

This derivation of both alternatives IS the main conclusion of the EPR paper.

They then go on to show that if you ASSUME (1) to be false (as Bohr was arguing then), you end up contradicting (2) as well which they have already proven is the only other valid alternative to (1).

In essence they were forcing the hand of those who claimed QM was complete by showing that if they believed that, they must also accept that position and momentum are both simultaneously real physical quantities (see their defintion of complete earlier in the paper). But if they accept that, then they find themselves in a situation in which the reality of the position AND momentum of the SECOND particle which has not been disturbed in any way was dependent on a measurement carried out on the FIRST particle with which the SECOND particle is not interacting.

The issue was not an attempt to defeat HUP for a single particle as you seem to be saying, but to show that if QM is complete, a reasonable definition of reality should not permit what the QM wave function permitted.

I guess we can argue all day as to who doesn't understand and who does. So I will skip that part.

1. I do not assert that the system is unreal or real, etc. What we are discussing is whether there are well-defined values for non-commuting observables at points in time where those observables are not being measured. So it is the values of p and q we are discussing. Not sure what subtlety you refer to. Could you reference a specific relevant point if this is still an issue? Otherwise we can move on.

2. Again, it is QM that asserts that p and q are not simultaneously well-defined. Obviously, if you read the final sentence, EPR doubt that is so: "We, however, believe such a [more complete] theory is possible." Do you really question their viewpoint on the HUP at that point?

3. I completely agree with your assessment of what their proper conclusion is, which is that either (1) or (2) is true. So we agree here.

I agree that Bohr would argue that (1) is false, ergo (2) is true. So we agree here too.

EPR assumes (2) is false - which makes (1) true by their logic - because of 2 different reasoning components:

a) In their words, "no reasonable definition of reality could be expected to permit this." They had previously included their "reasonable definition of reality" in their argument that leads to the negation of (2) above. Thus, the negation of (2) that they claimed is dependent on their assumptions.

b) And what were those assumptions? They were: p is an element of reality, and q is an element of reality, and they could both be measured to any degree of accuracy, thereby beating the HUP. Of course, we now know this assumption has been experimentally falsified via Aspect et al. So here is the quote from EPR which backs up my description of their assumption, from the first paragraph after their (18): "In the first case we must consider the quantity P as being an element of reality, in the second case the quantity Q is an element of reality." They then say that this conclusion could be objected to if you insist on simultaneous requirement of measurement or prediction (which we would in an experiment).

So what we are left we is that their deduction of either (1) or (2) being true is a good and proper conclusion. But their ruling out (2) was erroneous, because they based their contradiction on an unwarranted assumption. That assumption being the result of a thought experiment (given their view of a reasonable definition of reality) when, in fact, the true result of that experiment was the opposite of their assumption when it was actually performed nearly 50 years later.

Now, what does this say about Norsen?

I. Clearly, the definition of elements of reality are not naive or trivial and I hope we can drop usage of these words.
II. Clearly, locality is not the main issue either. For if it were, EPR would have needed to add a third part to their main conclusion of (1) and (2), and that would be (3) that the process of measurement on one system disturbs the second system in some way. Gosh, how did they forget that if EPR was all about locality and realism had already been shown to be false? So Norsen is completely wrong about his point that EPR and Bell assume realism is false. Realism is the main point.
III. Clearly, the HUP is an issue and one could derive the result, as EPR did, that belief in the HUP leads to the assertion that there cannot be simultaneous reality for P and Q. We certainly know now, after Aspect, that EPR realism is false...
IV. Unless, of course, the process of measurement on one system disturbs the second system in some way. I.e. non-locality is true. Which is exactly what every book says about Bell, that either realism is false or non-locality is true. In complete contradiction to Norsen's conclusion.

[mysearch]

As a newcomer to QM, I am simply trying to get a handle on some of the key issues and do not want to get in the way of a very interesting discussion. However, I have posted some questions about HUP in the following thread and was interested in comments linked to this topic: http://www.physicsforums.com/showthread.php?t=306829

It appears to me they are saying, position and momentum can not both be simultaneously real parameters of particle. In other words, not being able to simultaneously predict or measure both values with certainty indicates that they are not both simultaneously real quantities.

2. Again, it is QM that asserts that p and q are not simultaneously well-defined. Obviously, if you read the final sentence, EPR doubt that is so: "We, however, believe such a [more complete] theory is possible."

In the thread above, I was trying to get a clarification of the QM position that appears to state that uncertainty is intrinsic, at least, at the quantum level and not just as issue of measurement. However, my question in this thread is whether the extent of `realism` you are discussing has to be qualified by the scale of the particles in question, i.e. is there a point where [p] and [q] cease being simultaneously ambiguous and classical reality returns?

[mn4j]

1. I do not assert that the system is unreal or real, etc. What we are discussing is whether there are well-defined values for non-commuting observables at points in time where those observables are not being measured. So it is the values of p and q we are discussing. Not sure what subtlety you refer to. Could you reference a specific relevant point if this is still an issue? Otherwise we can move on.

The non-existence of well-defined values for non-commuting observables at points in time where those observables are not being measured is not at issue. EPR proved this aspect from QM. They never question it. Your statement seems to imply that they questioned it. They didn't.

2. Again, it is QM that asserts that p and q are not simultaneously well-defined.
Agreed. This is never in question in the EPR paper. (2) in their conclusion is derived from that fact.

Obviously, if you read the final sentence, EPR doubt that is so: "We, however, believe such a [more complete] theory is possible." Do you really question their viewpoint on the HUP at that point?
That is not how I understand the final sentence. They are not here saying, they believe it is possible to have a more complete theory in which non-commuting observables will be simultaneously real. The bold part is the crucial part, they have already previously proven that to be impossible! I understand them to be saying that it is possible to have a more complete theory in which the physical quantities describing the system each have simultaneous reality (note the absence of non-commuting observables in this sentence). Your characterization of their final sentence implies they claim it it is possible to have a a theory in which non-commuting observables will have simultaneous reality. They already proved that this is not possible (alternative (2)). Again the crucial phrase is the one in bold.

I agree that Bohr would argue that (1) is false, ergo (2) is true. So we agree here too.
Not quite. EPR showed that according to if you assume QM to be complete, you arrive at the conclusion that non-commuting observables can have simultaneous reality which as they proved in the paper is not possible since (1) and (2) can not both be false. Therefore, your ergo above leads to a contradiction. Therefore the assumption that QM is complete must be false.

EPR assumes (2) is false - which makes (1) true by their logic - because of 2 different reasoning
components:

a) In their words, "no reasonable definition of reality could be expected to permit this." They had previously included their "reasonable definition of reality" in their argument that leads to the negation of (2) above. Thus, the negation of (2) that they claimed is dependent on their assumptions.

b) And what were those assumptions? They were: p is an element of reality, and q is an element of reality, and they could both be measured to any degree of accuracy, thereby beating the HUP. Of course, we now know this assumption has been experimentally falsified via Aspect et al. So here is the quote from EPR which backs up my description of their assumption, from the first paragraph after their (18): "In the first case we must consider the quantity P as being an element of reality, in the second case the quantity Q is an element of reality." They then say that this conclusion could be objected to if you insist on simultaneous requirement of measurement or prediction (which we would in an experiment).


Note that the assertions were either:
(1) QM is not complete, OR
(2) non-commuting observables do not have simultaneous reality

So it is not clear to me how you can say they claim (2) is false. What negates (2) is the when the assumption that QM is complete is taken to it's logical conclusion. This is what they set out to show:

"In QM it is usually assumed that the wave function does contain a complete description of the physical reality of the system in the state to which it corresponds. At first sight this assumption is entirely reasonable, for the information obtainable from a wave function seems to correspond exactly to what can be measured without altering the state of the system. We shall show, however, that this assumption, together with the criterion of reality given above, leads to a contradiction"

[b]So what we are left we is that their deduction of either (1) or (2) being true is a good and proper conclusion. But their ruling out (2) was erroneous, because they based their contradiction on an unwarranted assumption.
They never ruled out (2). Rather, they showed that assuming that QM as complete leads naturally to the elimination of (2) which is the only other possible alternative, thus a contradiction -- therefore the assumption that QM is complete is faulty. So clearly this is affirming (2) rather than ruling it out.

As to the relevance of their thought experiment, they explained that no reasonable definition of reality should permit the reality of an observable at a distant non-interacting system to be dependent on a measurement done on a different distant system which is not interacting with the first system or disturbed it in any way. If you take issue with this, suggest a reasonable definition of reality which permits this.

I believe I have shown elsewhere on this forum the faults of Bell's theorem and interpretations of Aspect-type experiments. So I would not rehash those arguments here.

[DrChinese]

1. The non-existence of well-defined values for non-commuting observables at points in time where those observables are not being measured is not at issue. EPR proved this aspect from QM. They never question it. Your statement seems to imply that they questioned it. They didn't.

Note that the assertions were either:
(1) QM is not complete, OR
(2) non-commuting observables do not have simultaneous reality

So it is not clear to me how you can say they claim (2) is false. What negates (2) is the when the assumption that QM is complete is taken to it's logical conclusion... They never ruled out (2). Rather, they showed that assuming that QM as complete leads naturally to the elimination of (2) which is the only other possible alternative, thus a contradiction -- therefore the assumption that QM is complete is faulty. So clearly this is affirming (2) rather than ruling it out.

2. As to the relevance of their thought experiment, they explained that no reasonable definition of reality should permit the reality of an observable at a distant non-interacting system to be dependent on a measurement done on a different distant system which has not interacted with the first system or disturbed the first system in any way. If you take issue with this, suggest a reasonable definition of reality which permits this.

3. I believe I have shown elsewhere on this forum the faults of Bell's theorem and interpretations of Aspect-type experiments. So I would not rehash those arguments here.

To keep things straight:

(1) QM is not complete.
(2) non-commuting observables do NOT have simultaneous reality.
(3) either (1) is true, or (2) is true, this is an uncontested conclusion of EPR.
(4) according to EPR: if QM is complete, i.e. (1) is false, then non-commuting observables DO have simultaneous reality.
(5) since (4) negates (2), then by (3) we must accept (1).
(6) conclusion (4) was contested by Bohr and many others QM proponents at the time, and they rejected (1) and (4) and of course (5).

Hopefully we can agree on the above. If you don't accept these, there is really no point because EPR was NOT generally accepted at that time as proving QM was not complete.

1. EPR says that QM implies (2). Then they prove (4), which negates (2) making (1) true. So of course they reject (2). Not sure how anyone can walk away with any other conclusion. They say that QM is incomplete! So obviously they deny (2). They repeat this at the end and I quoted it.

2. Of course I take issue with this, and so does virtually the entire physics community!! That is because Bell's Theorem is generally accepted. Reality does NOT need to match the definition provided by EPR, and it certainly doesn't need to be reasonable. That is the whole point!!!

3. I am just now realizing that you deny Bell, which means that you also disagree with Norsen. So what stake do you have in this thread? I thought we were discussing Norsen's paper, and now I realize you have ignored Norsen's paper altogether. We can talk about Bell on another thread.

[mn4j]

Not sure how anyone can walk away with any other conclusion. They say that QM is incomplete! So obviously they deny (2). They repeat this at the end and I quoted it.
The fact that both (1) and (2) can not both be simultaneously false, does not mean both (1) and (2) can not both be simultaneously true. That is your error in interpreting their conclusion.

2. Of course I take issue with this, and so does virtually the entire physics community!! That is because Bell's Theorem is generally accepted. Reality does NOT need to match the definition provided by EPR, and it certainly doesn't need to be reasonable. That is the whole point!!!
So then if you disagree with Norsen, what defintion of reality would you provide? In as much as I disagree with Norsen about Bell, I do agree with him that most of the time when people talk of "local reality" they themselves do not know what reality means.

Also Norsen's definition of "naive realism" does not apply to EPR. Unless you misunderstand EPR to be claiming a real system must have simultaneous values for "non-commuting observables". However, that is not what EPR claimed at all.

[DrChinese]

1. The fact that both (1) and (2) can not both be simultaneously false, does not mean both (1) and (2) can not both be simultaneously true. That is your error in interpreting their conclusion.

2. So then if you disagree with Norsen, what defintion of reality would you provide? In as much as I disagree with Norsen about Bell, I do agree with him that most of the time when people talk of "local reality" they themselves do not know what reality means.

Also Norsen's definition of "naive realism" does not apply to EPR. Unless you misunderstand EPR to be claiming a real system must have simultaneous values for "non-commuting observables". However, that is not what EPR claimed at all.

1. Now you are really going off the deep end with rabbit trails. The question at hand is whether realism, simultaneous well-defined values for non-commuting operators, is a subject of discussion in EPR and Bell. The question is NOT whether realism is supported or not by these papers, or even if both (1) and (2) can both be true (which of course EPR argues that they cannot). The fact is that EPR's (1) is akin to saying QM makes correct predictions. EPR's (2) is akin to saying realism does not hold. Essentially, EPR says that is QM is correct, then realism does not hold. It also says, by contranegative, that if reality holds then QM is not correct. See where this is going? It's about realism, i.e. FOR 'REALISM'.

2. Definition has been provided above already, of course is the same one used by EPR and Bell. Glad to hear that you and Norsen have a lock on your own private definition of local realism and the rest of us don't have access to same. For what purpose is that? Use the language the rest of us use.

If you want to discuss the role of realism and locality in Bell's Theorem, as Norsen actually does, let's continue. Otherwise I would prefer to discuss with those who are interested in this topic.

[mn4j]

The question at hand is whether realism, simultaneous well-defined values for non-commuting operators, is a subject of discussion in EPR and Bell.
That of course seems to be a private definition of realism. It is certainly contrary to the EPR definition of realism and that is what I have been trying to show you. Norsen does not mention that definition anywhere. So how can that be the question?

2. Definition has been provided above already, of course is the same one used by EPR and Bell.
As I have alreay pointed out to you, the definition you keep repeating is totally contrary to the definition from EPR. If by "local realism" you are understand realism to mean what you defined above, then such "local realism" will have nothing to do with EPR as I've already explained and can explain again if you wish.

Glad to hear that you and Norsen have a lock on your own private definition of local realism and the rest of us don't have access to same. For what purpose is that? Use the language the rest of us use.
The definitions used by Norsen in his paper are not new. He did not create them. The have been known and discussed in philosophical circles for centuries. You can not voluntarily ban the use of the term "Naive realism" just because you don't like it. It has a specific widely accepted meaning.

[DrChinese]

As I have alreay pointed out to you, the definition you keep repeating is totally contrary to the definition from EPR. If by "local realism" you are understand realism to mean what you defined above, then such "local realism" will have nothing to do with EPR as I've already explained and can explain again if you wish.


Definition of realism (actually non-realism) per EPR: "...when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality."

I just don't see how it gets any simpler than this. I will pass on further debate with you on the matter, as it seems to have no purpose. If anyone else wants to discuss the Norsen paper, I would be happy to oblige.

[Ilja]

The best approach to realism is MUH
But I dont know how to call it.
I like MUH, so I would rather ask you - MUH is it an ultimate realism or an ultimate denial of the one?

I don't take is seriously. It's more the ultimate denial of realism, by making the notion meaningless.

[Ilja]

Norsen had an interesting (read: wrong) take on EPR. Locality is assumed in EPR, not really a factor per se. It is simply used as a technique to have particles interact and then separate. So the separability requirement is an experimental requirement so that we can go deeper into the central question of EPR: is there a "more complete" level of reality of a single particle.

Of course locality is assumed in EPR. That is Norson's reading as well: EPR is an argument from pure locality to deterministic (naive) realism about the spin components.

2. Nowhere does EPR discuss FTL influences, which they take to be sacrosanct. Of course, EPR's conclusion was wrong in the sense that they expected a "reasonable" definition of reality, one which is not observer independent. As Bell showed, that was not possible. We might get a clue as to what the paper was about from its title, "On the Einstein Podolsky Rosen Paradox." Clearly, not about locality. These papers are about the nature of reality. Is reality observer dependent, as QM seems to imply? Or is the moon round even when no one is looking, as Einstein believed?

It does not discuss FTL influences and does not have to, once it is an argument from locality to naive realism about the spin components. To conclude that the EPR conclusion (QM incomplete) is wrong is one thing, that their argument (locality -> naive realism) is wrong another one. Pilot wave theory proves that they may be wrong about the reality of the spin components (assuming for simplicity Bohms version of the experiment) without being wrong in their argument (because it is locality that fails).

Once their conclusion was that QM is incomplete, I see no reason to say that they were wrong in this point.

In 1935, there was no question in the minds of EPR that their thought experiment - if performed - would demonstrate that the HUP could be beaten. On the other hand, most others (Bohr etc.) felt the opposite.

Let's not speculate about states of mind. We have facts. One fact is that EPR give an argument from locality to naive realism. Not? If yes, the next question is if the argument is valid. (To be distinguished from the question if the conclusion is valid or the assumption false.)

So that is the ultimate question: does an independent particle have well-defined values for non-commuting observables? If YES, well, that is realism, my friend. You can call it naive if you like but that is CERTAINLY what Einstein believed in.

I CERTAINLY do not have to care, in this question, about what Einstein believed in. (What I believe is that Einstein, knowing about Bell's theorem, would have claimed that this theorem gives the ultimate test between QM and relativity: Or QM, or relativity should be simply wrong. This is what I believe as well. And, given the results of the BI tests, the conclusion is that relativity is wrong. (I resist to speculate about the question if the founder of relativity would have accepted this or tried to save his child in some way. The latter would have been an excusable human weakness.)


4. Bell introduces the requirement of realism after his (14), when he hypothesizes: "it follows that c is another unit vector". This is the leap. Previously, we had 2 particles and 2 measurement setting possibilities. Now he adds the "realistic" requirement that there must also be values at other measurement settings.

Without having Bell at hand, I remember that all we need from realism is already applied in his formula (2). If we hypothesize something, and we do not try to cheat about this, we do not use an expression of type "it follows".

It is pretty obvious that if you don't have an a, b and c, then you can't get to Bell's inequality (15). Realism is NOT inserted as a requirement because it was previously assumed, as Norsen claims. Bell adds it here because it wasn't explicit previously, and needed to be added to obtain Bell's key result.

Correct. But that we have a, b, and c follows from locality (and the weak, non-naive version of realism used explicitly in formula (2)).

5. Now, you are free to disagree with my analysis, as Norsen does. But you will be hard pressed to make Norsen's argument by direct reference to EPR and Bell (not an absolute requirement, but you will see quickly that Norsen's reasoning depends on some very shaky inference).

The inference is an inference following from the EPR argument. It seems, you have not understood the crucial difference between the two notions of realism involved here:

1. The naive realism that any measurement reveals some predefined property of the measured object, say, a spin component.

2. The much weaker metaphysical realism, which allows as well that "measurement results" are results of complex interactions between "measurement device" and "measured object", which makes the use of measurement terminology in these cases inadequate.

Norsen is completely wrong when he challenges:

"...anyone who claims that Bell’s Theorem is a theorem about 'local realist' theories ... needs to explain clearly what they mean by 'realism' [done, see 2. above] and show precisely where such 'realism' is assumed in the derivation of Bell’s inequalities. [done, see 4. above]"

I have refuted his argument by reference to the key articles themselves.

Which I have refuted ;-)

Norsen's historical perspective is extremely skewed, and this was pointed out by Shimony himself in another one of Norsen's historical outings. I know Norsen is bright and knowledgeable, but that does not change my opinion of the interpretation of Bell's result (nor my conclusion that Norsen is wrong). And apparently, it hasn't swayed the opinions of his peers either.

I prefer not to argue about majorities (of peers or whatever group you like to care). Even in politics I'm not a democrat.

I could probably produce any number of recent quotes that state to the effect:

"No physical theory of local Hidden Variables [i.e. local realism] can ever reproduce all of the predictions of Quantum Mechanics."

I can easily write something similar without contradicting Norsen: I have fulfilled his requirement to define what I mean with realism (ilja-schmelzer.de/realism/definition.php (http://ilja-schmelzer.de/realism/definition.php)) and where this definition is used (formula (2) of Bell). So you have to try harder. As well as Bell was not against measurements, Norsen is not against realism, as long as if it is a well-defined notion.

[DrChinese]

1. Of course locality is assumed in EPR. That is Norson's reading as well: EPR is an argument from pure locality to deterministic (naive) realism about the spin components.

2. Without having Bell at hand, I remember that all we need from realism is already applied in his formula (2). If we hypothesize something, and we do not try to cheat about this, we do not use an expression of type "it follows".

Correct. But that we have a, b, and c follows from locality (and the weak, non-naive version of realism used explicitly in formula (2)).

The inference is an inference following from the EPR argument. It seems, you have not understood the crucial difference between the two notions of realism involved here:

3. The naive realism that any measurement reveals some predefined property of the measured object, say, a spin component...

1. I agree that locality is assumed. "...no real change can take place in the second system as a consequence of anything that may be done to the first system." But that hardly makes this an argument of locality to determinism. Reality is defined and mentioned any number of times, and is obviously the prime point EPR makes. They never even question that the result of an actual experiment will be that there is no apparently non-local effect.

2. You have trouble with this idea: the simultaneous realism of a and b is discussed in EPR. In Bell, the simultaneous realism of a, b and c is discussed. If you do not assume the simultaneous realism of a, b and c, you cannot get Bell's result. Assuming the separability requirement (Bell's (2) is not enough). Realism is NOT assumed within (2). Because (2) discussed just a and b. QM does not assert that there is a simultaneous a, b and c because it is complete as is.

3. ...is called an "element of reality" according to EPR. Call it naive if you want, that is what EPR and Bell are about.

[Ilja]

EPR and Bell talk about realism (elements of reality) and I don't see any reason to call it "naive" in the circumstances....
I really don't see how this definition is ambiguous in any way, nor do I see it as naive.

If I (following Norsen) use the term "naive realism", I do not mean as well that Einstein has been a naive realist.

His criterion of reality is clearly not one of naive realism. What is classified as "naive realism" is only the conclusion derived by EPR (and reused by Bell) from non-naive realism and locality to naive realism about spin directions (or, in the original, about momentum together with coordinates)

Nor have I seen any historical evidence that the subject of "local realism" had simply become an issue of "locality" by the time of either the EPR or the Bell papers - as Norsen asserts. If it had, we'd all be Bohmians now (and obviously we aren't).

That's your problem of not appreciating the arguments. The facts are one thing, the beliefs of people another one. Even if you prefer one of the popular religions, you should see that most of the religious people on Earth believe into the wrong deities. In a similar way, even if Norsen is right, it does not follow that everybody has to become a Bohmian.

How can Norsen say, with a straight face, that "it was already known, prior to Bell’s Theorem and prior to any experimental tests of Bell’s inequalities, that Non-Contextual HVTs (i.e., Naive Realist theories) are wrong, are not empirically viable."

Very simple, by comparing the dates of impossibility theorems for non-contextual HVT's with Bell's paper. I do not care much about history and have not done it, but at least von Neumann's theorem was well-known. Moreover, "it is known" in science always means only "known by specialists in this domain", and not "known by democratic majorities" in whatever sense.

I have read my share of historical papers, and that is as far from accurate as it gets. For that to be true, we'd need to believe that all scientists would have agreed that Bell tests (not yet invented, of course) would have expected the results per Aspect.

There have been lot's of experiments before Aspect. What was new in Aspect's experiment was how the speed of light was involved. (But I'm not firm enough in history, so I would prefer in my papers a weaker formulation which makes the same point, say, by replacing "empirically not viable" with "in conflict with quantum predictions".)

Now, how exactly could that have been true, considering such experiments were not generally discussed until many years later? Yes, a few had heard of EPR-B, but not many until later.

Very simple "is known" in science does not mean "is known by some majority". All those who have not cared about the particular question do not count.

Finally, there are plenty of scientists today who believe that nature is local non-realistic, in diametric opposition to Norsen's assertion. We would need to accept that scientists correctly rejected realism prior to Bell, but erroneously did not reject locality after Aspect. Show me anything that makes that sound like a mainstream history of the past 50 years.

Please a quote of this diametric opposition. As I see it, Norsen's conclusions are not mainstream, but this clearly does not make them wrong. Again, correctness has nothing to do with majorities. And why it should have been correct to reject realism before Aspect is beyond my understanding.


No, Bell is about realism a la Einstein (who accepted it and thought QM was incomplete), a la Bohr (who rejected it because he saw QM as complete), a la the many other scientists who had no idea whether Einstein was right or Bohr was right. That is what Bell's Theorem is all about.


I agree. And Norsen is about realism a la Einstein. Even if his paper is named "against realism".

2. As to mutually contradictory assumptions: it is locality and realism that are the 2 on the table, and they are not mutually contradictory. Perhaps it is possible to tie them to ideas that become contradictions, but that would require additional debate.

I disagree. They have to be specified, of course (Norsen's requirement). But for the most reasonable specifications they are contradictory.

[Ilja]

1. There is no difference in what I say and what you quote. Realism = elements of reality are simultaneous for non-commuting (or commuting, for that matter) observables. This exactly matches the words and intent of EPR. They flat out say that there are elements of reality to Alice and Bob BECAUSE they can be predicted in advance. And that is an excellent argument, one that makes perfect sense. But Bell demonstrated it was simply wrong - but not 'til later!

Certainly not. The argument (which differs from the conclusion) remains valid. Bell proves that the conclusion is wrong, thus, the assumption is wrong. The assumption is localitiy
(and an extremely weak version of realism named "metaphysical realism" by Norsen).

2. It is QM, not EPR, that says p and q are not simultaneously well-defined. EPR denies this because they are asserting realism. And it is not the particle's reality that is in question, it is the simultaneous realism of well-defined values for non-commuting observables of that particle.

Realism and locality.

That is the only mistake in the paper, as Bell later showed that they did not use a sufficiently strong mathematical requirement for realism. If they had, they would have seen that it is their viewpoint that was not "complete", as it yields predictions at odds with experiment.

This has nothing to do with the difference between EPR and Bell. The requirements of EPR and Bell regarding realism as well as locality are essentially identical, and the first part of Bell's proof is (see Norsen) simply a repetition of the EPR argument.

In their view of their paper's result, they "proved" that you could beat the HUP. But we know now that you cannot. I doubt you disagree with that point.

There is no need. EPR clearly stated their assumptions. In particular, locality. Locality is wrong, as we know today. Thus, the EPR argument from locality remains valid and correct.

[Dmitry67]

Definition of realism (actually non-realism) per EPR: "...when the operators corresponding to two physical quantities do not commute the two quantities cannot have simultaneous reality."


This is why I like MUH. Words are too slippery and fuzzy.
What quantity is physical? How can we tell physical quantity from non-physical one? Well, physical quantity is real :)

So, I can rewrite the sentence above as

"...when the operators corresponding to two physical quantities do not commute the two quantities cannot be simultaneously physical"

or, if you prefer it this way:

"...when the operators corresponding to two real quantities do not commute the two quantities cannot be simultaneously real"

[Dmitry67]

2 Ilja
What is really funny is that Demystifier, who is trying to protect the Bohmian realism, still can not tell real entities from the non real ones!

It is not completely clear to me whether the sea particles in hadrons are real or virtual. But in both cases, the Bohmian interpretation makes a clear interpretation of them. So let us discuss both possibilities.

WOW.
Yes, WOW.
How can't one become a MUH proponent after that?

[Ilja]

b) And what were those assumptions? They were: p is an element of reality, and q is an element of reality, and they could both be measured to any degree of accuracy, thereby beating the HUP. Of course, we now know this assumption has been experimentally falsified via Aspect et al. So here is the quote from EPR which backs up my description of their assumption, from the first paragraph after their (18): "In the first case we must consider the quantity P as being an element of reality, in the second case the quantity Q is an element of reality."

This is not an assumption, but a conclusion, which follows only if we use locality. Without locality, the choice of the measurement at A can influence the result at B, thus, the result at B may be created by the measurement at A and not be an element of reality, even if the EPR criterion of reality is true.

I. Clearly, the definition of elements of reality are not naive or trivial and I hope we can drop usage of these words.

You misunderstand Norsen's use of "naive realism" if you assume that he classifies Einstein's realism as naive realism.


II. Clearly, locality is not the main issue either. For if it were, EPR would have needed to add a third part to their main conclusion of (1) and (2), and that would be (3) that the process of measurement on one system disturbs the second system in some way. Gosh, how did they forget that if EPR was all about locality and realism had already been shown to be false? So Norsen is completely wrong about his point that EPR and Bell assume realism is false. Realism is the main point.

Sounds confused. The EPR criterion of reality is all about locality. The word "predict" already contains an ordering in time and the consequential causal ordering, "without disturbing in any way" is clearly about causal influences. Where do you read that "EPR and Bell assume realism is false"?

BTW, it was non-contextual (naive) realism which was known to be false.

III. Clearly, the HUP is an issue and one could derive the result, as EPR did, that belief in the HUP leads to the assertion that there cannot be simultaneous reality for P and Q. We certainly know now, after Aspect, that EPR realism is false...

Clearly we do not. Pilot wave theory is EPR-realistic but not falsified by Aspect.

IV. Unless, of course, the process of measurement on one system disturbs the second system in some way. I.e. non-locality is true. Which is exactly what every book says about Bell, that either realism is false or non-locality is true. In complete contradiction to Norsen's conclusion.

No. Norsen criticises the use of "realism" in many descriptions. They suggest that it is naive realism which is in conflict with relativity, and in this case it looks reasonable to reject naive realism.

But EPR realism, or metaphysical realism, is not naive realism, but much weaker, much more fundamental, much more difficult and unreasonable to reject. As unreasonable that it is reasonable to omit this assumption, as well as we usually omit classical logic and probability theory from the list of the assumptions we use.

The confusion between naive realism (a quite nonsensical theory) and metaphysical realism (a foundation of the scientific method) is what is criticized in "against realism".

[Ilja]

1. I agree that locality is assumed. "...no real change can take place in the second system as a consequence of anything that may be done to the first system." But that hardly makes this an argument of locality to determinism. Reality is defined and mentioned any number of times, and is obviously the prime point EPR makes. They never even question that the result of an actual experiment will be that there is no apparently non-local effect.

2. You have trouble with this idea: the simultaneous realism of a and b is discussed in EPR. In Bell, the simultaneous realism of a, b and c is discussed. If you do not assume the simultaneous realism of a, b and c, you cannot get Bell's result. Assuming the separability requirement (Bell's (2) is not enough). Realism is NOT assumed within (2). Because (2) discussed just a and b. QM does not assert that there is a simultaneous a, b and c because it is complete as is.

3. ...is called an "element of reality" according to EPR. Call it naive if you want, that is what EPR and Bell are about.

First, I can get Bell's result without assuming the simultaneous realism of a, b and c, because I can apply the EPR argument to prove the simultaneous realism of a, b and c, assuming only weak realism (which allows the values of a, b, c to be created in case of measurement and transferred to the other part, thus, does not assume the simultaneous realism of a, b and c) and locality (which closes this possibility).

What is called naive is to postulate the simultaneous realism of a, b and c. This is not what EPR or Bell do. They derive this, based on locality.

[Dmitry67]

Can I ask:

1 The meaning of realism vs non-reliasm in EPR/Bell discussions
2 And the meaning of realism in 'are virtual particles real?' discussions
are they the same or not???

[mn4j]

Can I ask:

1 The meaning of realism vs non-reliasm in EPR/Bell discussions

The primary focus of EPR was not realism but completeness of QM. Their argument that QM is not complete was based on a sufficient but not exclusive definition of the reality of physical quantities in the sense of how well they correspond to the attributes of the underlying system being studied. The reality of the underlying system has never been in question; not in QM, not in any physical theory as physics is by the way the study of reality and real phenomena.

So then, in their seminal paper, EPR argued that if the value of a physical quantity can be predicted without measurement or disturbing the system in any way, the quantity corresponds to a real property of the underlying system. They then proceeded to show that for non-commuting observables as defined in QM, this does not hold. Which means the theory (QM) purporting to be complete and yet using non-commuting observables as though they had independent reality can not be complete. Their argument was never to claim that in order for "realism" to be true, non-commuting observables must have simultaneously precise values. In fact, they proved that non-commuting observables CAN NOT have simultaneously precise values and thus can not be simultaneously real. So it is mind boggling why Dr Chinese keeps insisting that the EPR definition of so called "realism" is "simultaneous values of non-commuting observables".

Therefore, their conclusion was that the wavefunction can not be a complete description the system in question. Note that this conclusion was anchored on the fact that in QM, the wavefunction is considered to be a complete description of the state of the system to which it corresponds. But as they proved, if you accept QM to be complete, you MUST also accept that the reality of a physical quantity describing particle 2, can depend on the an experiment performed on particle 1 which is so far away that no interaction is possible. The implication therefore was that, accepting QM to be complete led the "believer" to an unreasonable definition of reality (ie FTL).

Note the following:
1) admitting that QM is not complete does not in any way mean QM is wrong.
2) EPR NEVER questioned any of the correlations predicted by QM. So experimental support of the QM correlations does not refute the EPR argument.

So then, to refute EPR, there is only one option
- Insist that QM is complete and then also insist that FTL is possible (some prefer to say reality is non-local which is exactly the same thing as FTL)

- Bell's inequality ONLY proved that the mathematical model of probability used by Bell to derive the inequalities, does not apply to the systems modeled by QM
- Aspect type experiments ONLY prove that
1) QM is a much better theory for modelling real systems than Bell's inequalities.
2) the mathematical model of probability used by Bell to derive the inequalities, does not apply to real systems

Now unto the issue of "Naive realism", consider an example, color. Is the color of an object a real property of the object. Not according to EPR because then it will be possible to instantaneously change the color of the sun by wearing green goggles. However, EPR does not deny that color is a real experience of the person making the observation, only that it can not be a real property of the sun. A "Naive realist" on the other hand believes everything we observe is directly carried around by the objects as properties.

Now how does FTL tie up with this. Let's use the color analogy. Note that although color is not a real property of the sun, it is a real property of the system composed of sun AND observer. However, any attempt to separate the system and attribute some of the properties to different parts is bound to result in paradoxes. The similarity with the QM wavefunction is inescapable. The EPR conclusion was essentially saying, a theory which only deals with colors as real attributes of objects can not be complete because no reasonable definition of reality should permit the reality of the sun's color (if it were real) to be changed by FTL communication. Therefore there must be some underlying real physical property of the sun which a more complete theory will more directly handle.

[Dmitry67]

So then, in their seminal paper, EPR argued that if the value of a physical quantity can be predicted without measurement or disturbing the system in any way, the quantity corresponds to a real property of the underlying system.

So then, to refute EPR, there is only one option


Wait, wait, the very first assumption was wrong...

[Ilja]

In fact, they proved that non-commuting observables CAN NOT have simultaneously precise values and thus can not be simultaneously real. So it is mind boggling why Dr Chinese keeps insisting that the EPR definition of so called "realism" is "simultaneous values of non-commuting observables".


You must have read another EPR paper. This is not what EPR prove. This is what Bell was able to prove with his inequalities.

- Bell's inequality ONLY proved that the mathematical model of probability used by Bell to derive the inequalities, does not apply to the systems modeled by QM
- Aspect type experiments ONLY prove that
1) QM is a much better theory for modelling real systems than Bell's inequalities.
2) the mathematical model of probability used by Bell to derive the inequalities, does not apply to real systems


I disagree. The mathematical model of probability used by Bell is fine and compatible with observation. It has to be combined with locality to give the inequalities.

[mn4j]

You must have read another EPR paper. This is not what EPR prove. This is what Bell was able to prove with his inequalities.



I disagree. The mathematical model of probability used by Bell is fine and compatible with observation. It has to be combined with locality to give the inequalities.
I'm afraid you too have misunderstood EPR. EPR never admitted or suggested that it was possible for non-commuting observables to be simultaneously real. The only way you come to that point, is if YOU insist contrary to EPR that QM is complete.

Bell's prove was based on naive hidden variables not non-commuting ones. So if any thing, it only proves the non-validity of a theory based only on non-contextual variables.

Are you claiming that Bell's inequality are more accurate description of reality than experiments? Isn't it obvious that the violation of Bell's inequalities by real experiments implies Bell's model of reality used in deriving the inequalities must be wrong? Or do you consider the experiments unreal?

[DrChinese]

First, I can get Bell's result without assuming the simultaneous realism of a, b and c, because I can apply the EPR argument to prove the simultaneous realism of a, b and c, assuming only weak realism (which allows the values of a, b, c to be created in case of measurement and transferred to the other part, thus, does not assume the simultaneous realism of a, b and c) and locality (which closes this possibility).

What is called naive is to postulate the simultaneous realism of a, b and c. This is not what EPR or Bell do. They derive this, based on locality.

This is completely wrong. You might consider referencing materials or providing proofs rather than just making things up (as you have in prior posts as well).

First, EPR is about a and b (i.e. 2 operators, actually p and q), not a, b and c. There is a difference, as Bell needed a, b and c to obtain his result.

Second: EPR is about realism, not locality. They define and mention reality, elements of reality and the like perhaps a dozen times in their paper. Locality is mentioned once in passing. They also assume a particular result in their reasoning regarding the outcome of a hypothetical experiment. The question is whether you can measure, say p, on Alice and then obtain additional information about Alice from a measurement on Bob (which had previously interacted with Alice). However, we now know that their assumed result - more information than QM allows per the HUP - would not be born out. In other words, if Bell's Theorem had never been discovered we would still know that EPR was wrong. That is because entangled particles do not provide more information than the HUP permits.

Lastly, you cannot derive Bell without reference to a, b and c existing simultaneously. Instead of making unsubstantiated claims, do it and show us! Even Norsen has never answered that challenge and believe me, I have made it. All he ever does is say that separability is all you need (Bell's (2)). Yet: how many versions of Bell's Inequality have you seen with just 2 measurement settings? You need 3, which requires that you assume the simultaneous realism of something not observed!! If you assume local hidden variables, you cannot construct result sets that are consistent with QM at all variations of 3 settings. But you can with just 2.

Now, if there was not the possibility that the measurement apparati might be able to communicate non-locally, then there would be no need to consider the locality question at all. But as it is, non-locality is a "loophole" if you will. As a result, Bell's Theorem must allow for either a non-realistic theory AND/OR a non-local theory. QED.

[SDetection]

I'm not getting it, why the position and momentum of a particle are necessarily non-commuting observables:
I mean for example, a photon's position in a laser beam is always observed/measured all the time by other particles (I meant photons), yet this doesn't alter its momentum.
Am I missing something?. And please be easy on me, I represent the public audience!.

[Dmitry67]

Other particles? If you are talking about the air/glass, then yes, light interacts with these particles. But what is important that such interaction does not leave any traces, it is absolutely reversible. So it is not considered a measurement (details may vary in different interpretations)

[SDetection]

Other particles? If you are talking about the air/glass, then yes, light interacts with these particles. But what is important that such interaction does not leave any traces, it is absolutely reversible. So it is not considered a measurement (details may vary in different interpretations)

But that means that the uncertainty is because the fault of the measurement process, while Heisenberg clearly stated that this is not the case. He said that it's just how the real world works.

[DrChinese]

This really doesn't have anything to do with this thread. This is a general question about the HUP. I really think this should be asked elsewhere...

And yes, there are plenty of times that particles interact with other particles and fields and still act according to the HUP and "as if" they had not been measured/observed. Examples include: light through a lens, off a mirror, changing from one medium to another. :smile: In each of these cases, if the photon is an entangled photon, the entanglement can be maintained.

[mn4j]

First, EPR is about a and b (i.e. 2 operators, actually p and q), not a, b and c. There is a difference, as Bell needed a, b and c to obtain his result.

Actually EPR is about prediction of 2 different physical quantities ((q1, p2) or (p1, q2) ie 2 values from a set of pairs). Bell's analysis of course missed the mark because he treated pairs of values from a set of triples as though they were being selected from a set of pairs. In other words, he naively thought you could select pairs of values from a set of triplets and they would be equivalent to selecting pairs of values from a set of pairs. That is why it is not possible to derive the inequalities without introducing the error of using 3-stations. (See Hans De Raedt, Karl Hess, Kristel Michielsen (2009) Extended Boole-Bell inequalities applicable to quantum theory http://arxiv.org/abs/0901.2546)

Second: EPR is about realism, not locality.
Actually it is both, because their main conclusion is based on their claim that FTL is unreasonable. I take it you believe FTL is reasonable.

The question is whether you can measure, say p, on Alice and then obtain additional information about Alice from a measurement on Bob (which had previously interacted with Alice).
Actually, that was not exactly their issue. The issue was that according to QM, by choosing to measure p1, you can know q2 exactly but not p2, however for exactly the same system, you can choose to measure q1 and end up knowing p2 exactly but not q2. Therefore according to their definition of reality, q2 will be real in the first experiment, and unreal in the second experiment. However, particle two is so far away that interaction is not possible (read non-local, except FTL), therefore it is unreasonable to expect a theory, which claims to completely model reality, to permit the reality of a physical quantity of a very distant particle (so far away that no iteraction is possible) to be changed instantaneously based on which measurement we choose to perform on particle 1. The key is not about being able to obtain additional information but being able to change the reality of a quantity at particle 2 by deciding which measurement you are going to do on particle 1.

So clearly, both locality and reality are at issue:
1- If you contest their definition of reality, provide an alternative
2- If you accept their definition of reality, and also accept that QM is complete, then you must also admit that FTL is possible.
3- If the QM state vector is not complete then a more complete state vector must exist


However, we now know that their assumed result - more information than QM allows per the HUP - would
not be born out.
EPR was not about HUP. Just because the incomplete description of QM involves p and q with an uncertainty relationship does not mean the more complete description of the underlying system needs or relies on p and q or even other non-commuting observables. EPR did not make any suggestion that p and q must be part of this more complete state vector. The only requirement was that a more complete description existed, not that the specific description must include non-commuting observables.

Now, if there was not the possibility that the measurement apparati might be able to communicate non-locally, then there would be no need to consider the locality question at all. But as it is, non-locality is a "loophole" if you will. As a result, Bell's Theorem must allow for either a non-realistic theory AND/OR a non-local theory. QED.

Seems to me you are admitting that you believe superluminal communication or psychokinesis is reasonable.

[DrChinese]

1. Actually, that was not exactly their issue. The issue was that according to QM, by choosing to measure p1, you can know q2 exactly but not p2, however for exactly the same system, you can choose to measure q1 and end up knowing p2 exactly but not q2.

2. Seems to me you are admitting that you believe superluminal communication or psychokinesis is reasonable.

1. QM does NOT say that you can measure p1, and know q2 exactly. It says the exact opposite, that entangled p1 and q2 are non-commuting just like p1 and q1 are. This is supported by experiment.

(By the way, we have previously discussed that the papers of the De Raedts do not follow Bell. They obviously have a local realist agenda, as do you. If you want to debate Bell, this is not the thread. This thread is about Bell and realism.)

2. Per Bell. yes. However, I would stipulate that if superluminal, it is instantaneous.

[Ilja]

I'm afraid you too have misunderstood EPR. EPR never admitted or suggested that it was possible for non-commuting observables to be simultaneously real. The only way you come to that point, is if YOU insist contrary to EPR that QM is complete.

Bell's prove was based on naive hidden variables not non-commuting ones. So if any thing, it only proves the non-validity of a theory based only on non-contextual variables.

Are you claiming that Bell's inequality are more accurate description of reality than experiments? Isn't it obvious that the violation of Bell's inequalities by real experiments implies Bell's model of reality used in deriving the inequalities must be wrong? Or do you consider the experiments unreal?

First, I disagree with your reading of EPR. As I already said, you must have read another EPR paper. I even see no starting point to argue.

It appears you have also read a different Bell paper, because in the Bell paper I have read there was nothing naive in the assumptions he has used. Non-contextuality is certainly not among the assumptions used by Bell.

The important assumption used by Bell is Einstein causality.

Last but not least, I fully agree with the experiments, as well as I fully agree with the notion of realism used in Bell's theorem. There is no contradiction, because Bell has used in his theorem also another assumption, namely a realistic version of Einstein causality. Thus, the experiments simply prove that this version of Einstein causality is wrong.

[Ilja]

This is completely wrong. You might consider referencing materials or providing proofs rather than just making things up (as you have in prior posts as well).

Just to clarify: This is not a scientific paper, but a simple posting in a discussion forum. To write a paper about it I see no reason because there would be nothing new in it - all this is well-known.

First, EPR is about a and b (i.e. 2 operators, actually p and q), not a, b and c. There is a difference, as Bell needed a, b and c to obtain his result.


That's nothing to object. I know that only Bohm improved the thought experiment by replacing p and q by spins.

Second: EPR is about realism, not locality. They define and mention reality, elements of reality and the like perhaps a dozen times in their paper. Locality is mentioned once in passing.

How often they mention realism in comparison with causality is completely irrelevant. Their argument requires locality. As well, it requires a weak form of realism (the EPR criterion of reality). And, combining these two, they obtain something which Norsen calls naive realism about the relevant observables.

They also assume a particular result in their reasoning regarding the outcome of a hypothetical experiment. The question is whether you can measure, say p, on Alice and then obtain additional information about Alice from a measurement on Bob (which had previously interacted with Alice). However, we now know that their assumed result - more information than QM allows per the HUP - would not be born out. In other words, if Bell's Theorem had never been discovered we would still know that EPR was wrong. That is because entangled particles do not provide more information than the HUP permits.

Their argument remains valid. From the EPR criterion of reality, Einstein causality, and the observable correlations it follows that the observables considered have predefined values. We know that they cannot have them, thus, one of the assumptions used in this argument should be wrong. The only reasonable candidate is Einstein causality.

Lastly, you cannot derive Bell without reference to a, b and c existing simultaneously. Instead of making unsubstantiated claims, do it and show us! Even Norsen has never answered that challenge and believe me, I have made it.

I observe that, whenever the same direction (a,b,resp,c) is measured at A and B, the results agree. I apply the EPR criterion of reality and Einstein causality. This gives that
local values for a,b, and c have to be elements of reality.

Thus, I don't have to assume them, once I can derive this from other assumptions.

All he ever does is say that separability is all you need (Bell's (2)). Yet: how many versions of Bell's Inequality have you seen with just 2 measurement settings? You need 3, which requires that you assume the simultaneous realism of something not observed!!

Of course, as I acknowledge without any hesitation, I assume some weak form of realism. This form of realism is, of course, about what really exists, not about what is observed.

And I do not think that Norsen thinks he can do the proof without some assumption of realism. He discusses favourously two notions of realism - perceptual realism and metaphysical realism - more or less as prerequisites for doing science. Rejecting them you cannot do science at all. Thus, he has any right to assume them.

If you assume local hidden variables, you cannot construct result sets that are consistent with QM at all variations of 3 settings. But you can with just 2.
Now, if there was not the possibility that the measurement apparati might be able to communicate non-locally, then there would be no need to consider the locality question at all. But as it is, non-locality is a "loophole" if you will. As a result, Bell's Theorem must allow for either a non-realistic theory AND/OR a non-local theory. QED.

Your point being? I clearly favour the non-local version - pilot wave theory. There is absolutely no reason to give up the weak, metaphysical version of realism on needs in this proof. Therefore one can as well omit mentioning "realism", as one does omit mentioning "logic" and "mathematics" and "probability theory".

[Ilja]

1. QM does NOT say that you can measure p1, and know q2 exactly. It says the exact opposite, that entangled p1 and q2 are non-commuting just like p1 and q1 are. This is supported by experiment.


False. For standard QM, observables of different particles commute. Thus, p1 commutes with q2 and p2 commutes with q1.

[p_i, q^j] = -i hbar delta^j_i

[DrChinese]

False. For standard QM, observables of different particles commute. Thus, p1 commutes with q2 and p2 commutes with q1.


Not for entangled particles. Otherwise: you could measure p1 and q2, and q2 would tell you what q1 was to any desired precision. You would then know both p1 and q1. And we know that is wrong. You cannot learn more about the entangled system than the HUP permits. Now, please, don't confuse that with being able to measure p1 and q2 as that point is not in question. The question is whether p1 and q2 are non-commuting where particles 1 and 2 are entangled in p and q.

[p764rds]

Not for entangled particles. Otherwise: you could measure p1 and q2, and q2 would tell you what q1 was to any desired precision. You would then know both p1 and q1. And we know that is wrong. You cannot learn more about the entangled system than the HUP permits. Now, please, don't confuse that with being able to measure p1 and q2 as that point is not in question. The question is whether p1 and q2 are non-commuting where particles 1 and 2 are entangled in p and q.
Why would entanglement affect the non-commutability?

[mn4j]

From my reading of this thread, it is obvious that DrChinese clearly understands reality as defined by EPR to be what Norsen calls "naive realism". So my understanding is that both Ilja and DrChinese agree on this point that realism ala EPR is "naive realism".

Just to be clear, using the photon polarization example at three different angles (A, B and C), "naive realism" would mean the photon has simultaneously three different internal physical quantities corresponding to polarization at those angles, and that those quantities belong to the photon. So the claim then is that this is what EPR meant by realism.

If this is your claim, then both of you could not be further from the truth for the following reason. Imagine that rather than having three different internal physical quantities the photon only had one quantity that could be said to belong to the photon. Now consider that on interacting with the polarizer, the interaction reveals a result based on the angle of the polarizer or other device settings such that the observed polarizations are just three different manifestations of the same underlying quantity. In other words, it is not so much a property of the photon but of the combined "photon+polarizer" system. Clearly this scenario is NOT "naive realism" as defined by Norsen. However, this scenario is clearly real as defined by EPR. This is why I keep insisting that both of you have misunderstood EPR.

The EPR definition of reality did not mandate that the reality of one quantity be independent from the reality of another quantity. If you disagree, point to the sentence in the paper where they made the requirement. Within their definition, it is perfectly acceptable to have two quantities describing the same underlying reality so long as the two descriptions are not contradictory. Non-commuting observables get in the picture because they can not be simultaneously real and thus lead to contradictory descriptions (ie, being able to instantaneously change the reality of a remote quantity by deciding which measurement to perform locally).

Therefore it is not true that EPR realism is "naive realism".

[mn4j]

Yet: how many versions of Bell's Inequality have you seen with just 2 measurement settings? You need 3, which requires that you assume the simultaneous realism of something not observed!!
This is why I explained that you can not expect correlations of pairs of values from a system consisting of 2 photons and three settings be equivalent to those from a system consisting of 2 photons and 2 measurement settings. Its apples and oranges! The only way you can be consistent to the EPR definition is if you consider the "system" as composed of particles PLUS measuring device, and the quantities as being properties of this "system". But then you run in to the delimma that it is an unrealizable and thus unverifiable experiment. It is impossible to measure two photons using three devices. No experiment has ever been or ever will be performed using three stations to measure 2 particles. How then can anyone ever say with a straight face that Bell's inequalities have been verified experimentally?

The only thing that has happened is that the QM correlations have been confirmed by experiment, without saying anything about the validity of Bell.

[DrChinese]

Why would entanglement affect the non-commutability?

Because non-entangled particles have separate wave functions, and you could obtain a good p1 and q2 in that case.

[DrChinese]

1. From my reading of this thread, it is obvious that DrChinese clearly understands reality as defined by EPR to be what Norsen calls "naive realism". So my understanding is that both Ilja and DrChinese agree on this point that realism ala EPR is "naive realism".

Just to be clear, using the photon polarization example at three different angles (A, B and C), "naive realism" would mean the photon has simultaneously three different internal physical quantities corresponding to polarization at those angles, and that those quantities belong to the photon. So the claim then is that this is what EPR meant by realism.


Pretty much, this is the standard hidden variable (a/k/a realistic) interpretation. The requirement stems from the fact that we have "perfect" correlations at matching angle settings for entangled pairs. I separated your definition from the rest of your post so we could see that I do agree with this idea as being the basis for realism, either naive or otherwise.

I do not agree with the portion that requires there to be underlying attributes for every possible angle setting. I.e. if you divided a circle into 360 degrees and made each one an atrribute, there would be 360 attributes to describe spin. I do not believe realism asserts that there are 360 (or 360 million, or infinity, etc.) such attributes. Realism is merely the expression of the idea that there is a definite real outcome to a measurement of a specific observation, regardless of whether or not such observation is made. The mapping to an underlying physical attribute, operator, etc. is optional.

[DrChinese]

If this is your claim, then both of you could not be further from the truth for the following reason. Imagine that rather than having three different internal physical quantities the photon only had one quantity that could be said to belong to the photon. Now consider that on interacting with the polarizer, the interaction reveals a result based on the angle of the polarizer or other device settings such that the observed polarizations are just three different manifestations of the same underlying quantity. In other words, it is not so much a property of the photon but of the combined "photon+polarizer" system. Clearly this scenario is NOT "naive realism" as defined by Norsen. However, this scenario is clearly real as defined by EPR. This is why I keep insisting that both of you have misunderstood EPR.

The EPR definition of reality did not mandate that the reality of one quantity be independent from the reality of another quantity...

It really doesn't matter to Bell whether or not this version of realism is somehow different than the previously agreed version (per above post). And I don't think it matters to EPR either. But let's review the facts before we go much further. What DO we need to have? It is not 1 attribute for photon spin, it is at least 2!

The reason is that across 360 degrees, there are completely independent results at 0 and 45 degrees (and all multiple thereof) that have no value overlaps. But the strange thing is, it doesn't matter how you orient the 0 degrees direction, there are still at least 2. There could be more, but maybe not. So I certainly do not assert that realism requires there be some large number of independent attributes - I only think there are 2 to begin with (using spin of linear polarized photons as the example). But we need to allow for the facts, which definitely point to at least 2.

I believe the QM description is essentially correct or complete or whatever you want to call it. So, it would not make sense for me to think the debate about realism - which might be needed in a theory or might not - would not fit my notion of what there is to be "real" in the first place. After Bell, the question is whether a correct QM is non-local or non-realistic (or possibly both).

Now, if you are a realist, and believe there is a reasonable alternative and physical explanatory mechanism that fits the facts: please come forward with a potential model. You will see quickly that you must still postulate real definite results for n>2 measurement settings. Clearly, you could postulate n<=2 and that would match the QM view of internal degrees of freedom. (Of course, it doesn't explain the HUP but that is a separate issue.) That is what separated Bell from everything else.

Bell gave us the leap to n=3 and the realization that consistent resultsets could not be constructed by a (local) realist. There is not internal consistency because the results at settings between 0 and 45 degrees are a mixture of 0 and 45 degrees, but the mix is not a linear combination as it would need to be fit the realistic view. Of course, this description is for entangled linear polarized photons, but the analogy is the same for electrons (used in Bell). If you would like me to further explain this logic, I can provide specific examples.

[mn4j]

Pretty much, this is the standard hidden variable (a/k/a realistic) interpretation. The requirement stems from the fact that we have "perfect" correlations at matching angle settings for entangled pairs. I separated your definition from the rest of your post so we could see that I do agree with this idea as being the basis for realism, either naive or otherwise.


If this is the definition of realism at issue in Bell, then it is obvious why Bell and his proponents have missed the mark. Using my previous analogy of the sun and it's "color", you would be saying realism means the sun has a color when nobody is looking. You can see this by having two people wear different colored goggles. If you believe the realism means the sun has a color when nobody is looking, then you must also admit that the realism of the sun can be changed instantaneously by changing the color of goggles you put on (ie FTL). It is obvious to see how such a person would conclude that local hidden variable theorems are forbidden -- because in fact no local hidden variable theorem can explain being able to change the color of the sun superluminally. But as I hope is getting obvious already, the error was made by attributing to the sun only, properties that belong to the combined "sun + observer system". Correctly recognizing that the appropriate system must include the observer, you then realize that it becomes possible to use a hidden variable theorem to explain the results. The local hidden variable theorem in this case being along the lines that the sun produces a spectrum of electromagnetic radiation which when combined with the goggles results in absorption of some regions and not others resulting in different perceived colors.

I do not agree with the portion that requires there to be underlying attributes for every possible angle setting. I.e. if you divided a circle into 360 degrees and made each one an atrribute, there would be 360 attributes to describe spin. I do not believe realism asserts that there are 360 (or 360 million, or infinity, etc.) such attributes. Realism is merely the expression of the idea that there is a definite real outcome to a measurement of a specific observation, regardless of whether or not such observation is made. The mapping to an underlying physical attribute, operator, etc. is optional.

It may seem reasonable until you realize that the concept of "polarization" includes the measuring device in this particular case. You can't have it both ways. So then it is inconsistent to talk of the photon having a polarization even when no measurement has been made.

Note that to say the sun does not have a color when nobody is looking is not the same thing as saying the moon does not exist when nobody is looking. We are merely saying "color" by definition includes the object, observer and medium in the system.
Therefore
1) it doesnot even make sense to talk of "measuring" the color of the sun, because the sun does not have a color
2) it does not make sense to talk of the "sun+goggles+observer" system having a color when no measurement has been made because, the "color" of the "sun+goggles+observer" system is by definition, the result of a measurement.

Therefore I would modify your definition of realism to: Realism is merely the expression of the idea that there are objective facts about a system, whether or not observers know them (or can know them) and Local causality is therefore merely the expression of the idea that FTL or psychokinesis is unreasonable. This is the only definition of "realist local causality" that is exhaustive and consistent with EPR.

Naive realism is limited to the concept that all observations are passive revelations of properties owned by the objects being observed. But as we have seen, even if the objects own objective properties, their revelation need not be passive, in which case the revealed outcomes will be properties of the combined object/observer system. So naive realism is unreasonable. Any attempt to limit the EPR definition of reality to naive realism for the purpose of arguing against it is a straw-man argument.

In order to argue against all local realist theories therefore, you MUST prove that either:
1) No objective facts can exist about a system OR
2) argue why FTL or psychokinesis is reasonable.

Arguing against (1) is self defeating because the validity of any argument against (1) depends on the validity of (1). In other words, in order for the statement "No objective facts can exist about a system" to be valid, it must be an objective fact about all systems. So then we are left with (2). Has (2) been proven?

[mn4j]

It really doesn't matter to Bell whether or not this version of realism is somehow different than the previously agreed version (per above post). And I don't think it matters to EPR either. But let's review the facts before we go much further. What DO we need to have? It is not 1 attribute for photon spin, it is at least 2!

You contradict yourself, Why MUST you have at least 2. Clearly that means Bell's treatment does not apply to situations in which you have only one. Why can it not be just one. You also have admitted that Bell's inequalities can not be derived from less than 3. So it seems you are saying there must be at least 3 not 2.

The reason is that across 360 degrees, there are completely independent results at 0 and 45 degrees (and all multiple thereof) that have no value overlaps. But the strange thing is, it doesn't matter how you orient the 0 degrees direction, there are still at least 2. There could be more, but maybe not. So I certainly do not assert that realism requires there be some large number of independent attributes - I only think there are 2 to begin with (using spin of linear polarized photons as the example). But we need to allow for the facts, which definitely point to at least 2.
The issue is not merely the number of attributes but the mechanism of revelation of the outcome. Passive or not.

I believe the QM description is essentially correct or complete or whatever you want to call it.
I believe the QM description is correct but incomplete, and so did EPR. The correctness of QM has never been in question.

After Bell, the question is whether a correct QM is non-local or non-realistic (or possibly both).
QM can not be correct and non-realistic because QM is a theory about real systems. As I have shown in my previous post, the argument against realism is self-defeating. It is like saying "reality" is not realistic. I would say the real issue is what the nature of "reality" is. In otherwords, is reality local or non-local, or in yet other words, is FTL reasonable or not. You believe it is reasonable so maybe you can convince me that it is.

Now, if you are a realist, and believe there is a reasonable alternative and physical explanatory mechanism that fits the facts: please come forward with a potential model.
I don't need to have such a model in order to appreciate that FTL is unreasonable because to believe FTL will require that I simultaneously hold contradictory beliefs which would be intellectually dishonest.

In any case, an alternative explanation has been provided. See
Event-by-Event Simulation of Einstein-Podolsky-Rosen-Bohm Experiments
Shuang Zhao · Hans De Raedt · Kristel Michielsen
Found Phys (2008) 38: 322–347

Read it and we can discuss it in a separate thread.
All that this boils down to is the question: Is a deterministic local hidden variable explanation for Malus Law possible? This question has been answered in the affirmative.

[DrChinese]

1. If this is the definition of realism at issue in Bell, then it is obvious why Bell and his proponents have missed the mark. ... But as I hope is getting obvious already, the error was made by attributing to the sun only, properties that belong to the combined "sun + observer system".

2. It may seem reasonable until you realize that the concept of "polarization" includes the measuring device in this particular case. You can't have it both ways. So then it is inconsistent to talk of the photon having a polarization even when no measurement has been made.

3. Naive realism is limited to the concept that all observations are passive revelations of properties owned by the objects being observed. But as we have seen, even if the objects own objective properties, their revelation need not be passive, in which case the revealed outcomes will be properties of the combined object/observer system. ...

You are arguing pro or con realism here, yet the question is whether realism is an assumption of EPR/Bell. And NOT whether it is valid or not.

1. The issue is whether the observer determines reality. In this case, there are 2 observers, Alice and Bob. Does Alice determine Bob's reality? EPR argues NO.

As to whether the choice of pink or blue goggles determines anything: no one is arguing against your point. But a local realist requires the result for Bob to be independent of the choice of goggles made by Alice. Further, what if Alice instead chooses yellow goggles? Bell showed that the results were incompatible with your idea.

2. Of course, once Alice has made a measurement, Bob does have a definite polarization.

3. Essentially, it is passive but only in the sense that the interaction of the particle and the apparatus reveals a value that, due to whatever rules were in place, would always be revealed by a measurement of that type (per EPR). Now, if there were elements being introduced from the observer, and that is your idea, then it is incumbent that the observer's choice be communicated from Alice to Bob (per Bell).

[DrChinese]

1. You contradict yourself, Why MUST you have at least 2. Clearly that means Bell's treatment does not apply to situations in which you have only one. Why can it not be just one. You also have admitted that Bell's inequalities can not be derived from less than 3. So it seems you are saying there must be at least 3 not 2.

2. I believe the QM description is correct but incomplete, and so did EPR. The correctness of QM has never been in question.

QM can not be correct and non-realistic because QM is a theory about real systems. As I have shown in my previous post, the argument against realism is self-defeating. It is like saying "reality" is not realistic. I would say the real issue is what the nature of "reality" is. In otherwords, is reality local or non-local, or in yet other words, is FTL reasonable or not. You believe it is reasonable so maybe you can convince me that it is.

3. In any case, an alternative explanation has been provided. See
Event-by-Event Simulation of Einstein-Podolsky-Rosen-Bohm Experiments
Shuang Zhao · Hans De Raedt · Kristel Michielsen
Found Phys (2008) 38: 322–347

Read it and we can discuss it in a separate thread.
All that this boils down to is the question: Is a deterministic local hidden variable explanation for Malus Law possible? This question has been answered in the affirmative.


1. Why must you have at least 2? Because you can do an experiment on 2 (although the experiment does not prove conclusively that local realism cannot be correct). Why can't you have 3, as local realism requires? Because Bell shows that 3 are incompatible with the predictions of QM.

2. EPR did vary from QM. They were wrong in their assumption that p1 and q2 could be determined, violating the HUP. We now know that for entangled particles, you cannot learn anything additional about Alice by measuring Bob.

3. I won't discuss local realistic papers as they are a complete waste of my time. Of course, you cannot have a local realistic theory that postulates Malus and gets past Bell. So go ahead and start the thread, I just won't be there.

[DrChinese]

In the words of Zeilinger (1999), on EPR and Bell:

In 1935 Einstein, Podolsky, and Rosen (EPR) studied entangled states of the general type used in the twophoton experiment discussed above. They realized that in many such states, when measuring either linear momentum or position of one of the two particles, one can infer precisely either momentum or position of the other. As the two particles might be widely separated, it is natural to assume validity of the locality condition suggested by EPR: ‘‘Since at the time of measurement the two systems no longer interact, no real change can take place in the second system in consequence of anything that may be done to the first system.’’ Then, whether or not momentum or position can be assigned to particle (system) 2 must be independent of what measurement is performed on particle 1 or even whether any measurement is performed on it at all. The question therefore arises whether the specific results obtained for either particle can be understood without reference to which measurement is actually performed on the other particle. Such a picture would imply a theory, underlying quantum physics, which provides a more detailed account of individual measurements.

... A most important development was due to John Bell (1964) who continued the EPR line of reasoning and demonstrated that a contradiction arises between the EPR assumptions and quantum physics. The most essential assumptions are realism and locality. This contradiction is called Bell’s theorem.


As can be seen from the above (and there are no shortage of similar comments from others), the general view matches what I am saying: Norsen is ignoring the arguments that have been made, and addressed experimentally, with his presumed objective being to recast the local realistic debate in a different form than was made originally (i.e. to make it about locality alone). OK, fine, but we are missing the support for this point of view! Clearly, there is substantial support for the traditional view.

If Norsen - or any reader - thinks realism is superfluous to the debate about Bell, there is a simple solution: write it up without realism and see if it is accepted by your peers. I do not see that as possible, but maybe someone smarter that me could do it.

On the other hand: there are quite a number of arguments to the effect that realism is not only central to Bell, but that locality itself is not an issue. Examples: Kochen Specker, GHZ, etc. These demonstrate that realism must be rejected in ANY physical theory. I am not personally arguing that position, but there is certainly strong support for it. Again, from Zeilinger:

...It was initially argued by Specker (1960) for Hibbert spaces of dimension larger than two that quantum mechanics cannot be supplemented by additional variables. Later it was shown by Kochen and Specker (1967) and by Bell (1966; for a review see Mermin, 1993), that for the specific case of a spin-1 particle, it is not possible to assign in a consistent way measurement values to the squares of any three orthogonal spin projections, despite the fact that the three measurements commute with each other. This is a purely geometric argument which only makes use of some very basic geometric considerations. The conclusion here is very important. The quantum system cannot be assigned properties independent of the context of the complete experimental arrangement. This is just in the spirit of Bohr’s interpretation. This so-called contextuality of quantum physics is another central and subtle feature of quantum mechanics.

(Contextuality being essentially equivalent to the non-realistic position.)

[p764rds]

Non-commuting observables get in the picture because they can not be simultaneously real and thus lead to contradictory descriptions (ie, being able to instantaneously change the reality of a remote quantity by deciding which measurement to perform locally).


When a measurement is performed locally -for two entangled particles - nothing changes remotely apart from the local and remote states that are no longer correlated.
So, in my view there is no physical-like communication needed between the two particles. Its just that what was once correlated is no longer correlated (after local observation). Its a 'negative' logic-wise which is different from a positive logic-wise.

I can't see how a Bohmian pilot wave comes in here - its not needed - and its different from a particle arriving at its destination and reporting back (through time) to its initial position (which I see might possibly be the case) in the normal preparation and observation of one particle. Entanglement correlations is different and IMO requires that both particles refer to the same data point in information space wherever they are in spacetime - after local observation (or remote) that data point is no longer flagged as belonging to the particles.

[Ilja]

Not for entangled particles. Otherwise: you could measure p1 and q2, and q2 would tell you what q1 was to any desired precision. You would then know both p1 and q1. And we know that is wrong. You cannot learn more about the entangled system than the HUP permits. Now, please, don't confuse that with being able to measure p1 and q2 as that point is not in question. The question is whether p1 and q2 are non-commuting where particles 1 and 2 are entangled in p and q.

Yep. And if the operators p1 and q2 commute or not depends only on the operators, but in no way on the particular state (however entangled or not). And the operators q2 and -i\hbar\partial_1 commute.

What we, by measuring q2, obtain a previously existing value q1 is a consequence of the EPR argument, and needs locality. Quantum theory is nonlocal, therefore this is not essential.

[Ilja]

From my reading of this thread, it is obvious that DrChinese clearly understands reality as defined by EPR to be what Norsen calls "naive realism". So my understanding is that both Ilja and DrChinese agree on this point that realism ala EPR is "naive realism".

There are two different meanings of "realism a la EPR": What EPR use as their assumptions (the EPR criterion of reality), and what EPR obtain as a consequence of this assumption, locality, and the QM correlations. It is only the last which, in case one starts with it, could be (and has been by Norsen) named "naive realism".

Just to be clear, using the photon polarization example at three different angles (A, B and C), "naive realism" would mean the photon has simultaneously three different internal physical quantities corresponding to polarization at those angles, and that those quantities belong to the photon. So the claim then is that this is what EPR meant by realism.

No, this is only what follows, after the EPR argument (including locality) from the EPR criterion, which does not make such an assumption.

If this is your claim, then both of you could not be further from the truth for the following reason.

It has never been my claim.

[Ilja]

In the words of Zeilinger (1999), on EPR and Bell:

... A most important development was due to John Bell (1964) who continued the EPR line of reasoning and demonstrated that a contradiction arises between the EPR assumptions and quantum physics. The most essential assumptions are realism and locality. This contradiction is called Bell’s theorem.


As can be seen from the above (and there are no shortage of similar comments from others), the general view matches what I am saying: Norsen is ignoring the arguments that have been made, and addressed experimentally, with his presumed objective being to recast the local realistic debate in a different form than was made originally (i.e. to make it about locality alone). OK, fine, but we are missing the support for this point of view! Clearly, there is substantial support for the traditional view.

First, referencing Zeilinger as an authority is not very impressive. Second, Norsen quotes AFAIR himself a lot of such references to locality and realism as the assumptions, thus, you prove nothing against him with this quote. He has provided arguments against this mainstream position. If ignoring his arguments and quoting the questioned mainstream position as the mainstream position is the new way of solving scientific problems, we have
finally reached the state of democratic science, where majority decides about truth without
hearing any arguments. That's the end of science as science.

If Norsen - or any reader - thinks realism is superfluous to the debate about Bell, there is a simple solution: write it up without realism and see if it is accepted by your peers. I do not see that as possible, but maybe someone smarter that me could do it.


How often I have to repeat that realism is not superfluous, but has to be precisely defined. And once this is done, it appears that the used version of realism is so weak that to reject it becomes nonsensical, and to mention it as a nontrivial assumption unnecessary.

On the other hand: there are quite a number of arguments to the effect that realism is not only central to Bell, but that locality itself is not an issue. Examples: Kochen Specker, GHZ, etc. These demonstrate that realism must be rejected in ANY physical theory.

Not at all. These demonstrate that the rather nonsensical restriction of non-contextuality is incompatible with quantum predictions. This has nothing to do with realism.

(Contextuality being essentially equivalent to the non-realistic position.)

LOL. Contextuality has something to do with naive realism, but not with the metaphysical notion of realism Norsen and I defend. In particular, pilot wave theory is a quite nice, realistic theory, but contextual. Thus, in your words pilot wave defenders would be antirealists. Which is complete nonsense.

[DrChinese]

1. First, referencing Zeilinger as an authority is not very impressive. Second, Norsen quotes AFAIR himself a lot of such references to locality and realism as the assumptions, thus, you prove nothing against him with this quote. He has provided arguments against this mainstream position. If ignoring his arguments and quoting the questioned mainstream position as the mainstream position is the new way of solving scientific problems, we have
finally reached the state of democratic science, where majority decides about truth without
hearing any arguments. That's the end of science as science.

2. LOL. Contextuality has something to do with naive realism, but not with the metaphysical notion of realism Norsen and I defend. In particular, pilot wave theory is a quite nice, realistic theory, but contextual. Thus, in your words pilot wave defenders would be antirealists. Which is complete nonsense.

1. Don't get this, you are essentially saying Norsen should be considered more of an authority than Zeilinger? Zeilinger is one of the pre-eminient authorities in the area, and entanglement is his specialty. Certainly this is relevant. Norsen is primarily a theorist as best I know, although I thought he was doing some experimental work more recently. I would certainly like to see something from him that delved into some new areas more at the forefront of the field, as Zeilinger is doing. Just last week, Zeilinger was co-author on a Bell experiment with entanglement on 2 degrees of freedom (finding a Bell Inequality violated by 24 SD).

Now anyone can be wrong, and anyone can be right, regardless of their prior background or reputation. But what we are discussing is not the outcome of an experiment, but rather the relevance of that outcome. So certainly, we *should* consider the opinion of the scientific community in this case.

Also: Travis frequently interprets sections of standard texts and comes up with his own views on their meaning and context - against standard opinion. OK, sometimes that can be good too. But he often ignores any text or argument which goes against his opinion. Example: Norsen says EPR is about locality and not realism. Yet EPR references locality only ONCE, versus over a dozen times for realism. He never addresses this obvious flaw in his reasoning. In addition, EPR provides the standard definition of realism ("elements of reality"). Yet Norsen seeks his own definition, changing the character of the paper in the process. It has been my hope to learn if there is any "meat" to Travis' argument that I am missing in his work. Thus, I was hoping you could enlighten me on this in some fashion. If the best anyone can do is quote Norsen over EPR, quote Norsen over Bell, and quote Norsen over Zeilinger, given the huge gaps I have just mentioned... well, that fails on every level.

2. I'm laughing... There are plenty who believe that a Bohmian interpretation is deterministic and therefore realistic. And additionally ruled out by contextual no-go proofs. I don't happen to fall in that camp. But clearly, there is something odd about asserting that a theory has hidden variables, is deterministic, and yet is also contextual. Essentially, that viewpoint agrees with the EPR conclusion that a more complete specification of the system IS possible. And I reject that.

[Ilja]

1. Don't get this, you are essentially saying Norsen should be considered more of an authority than Zeilinger? Zeilinger is one of the pre-eminient authorities in the area, and entanglement is his specialty. Certainly this is relevant.

He is a good experimenter, but I don't value his theoretical considerations. The issue we are talking about is a theoretical, almost philosophical. In this domain, Zeilinger is no authority for me.

Norsen is primarily a theorist as best I know, although I thought he was doing some experimental work more recently. I would certainly like to see something from him that delved into some new areas more at the forefront of the field, as Zeilinger is doing.

If your position is that experimenters are more on some imaginary "forefront" than theoreticians, I disagree.

Now anyone can be wrong, and anyone can be right, regardless of their prior background. But what we are discussing is not the outcome of an experiment, but rather the relevance of that outcome. So certainly, we *should* consider the opinion of the scientific community in this case.

The point is that the opinion of the scientific community has been referenced by Norsen and there is no disagreement about this opinion. Thus, for the discussion of Norsen's arguments against this opinion the facts about this opinion are irrelevant.

Also: Travis frequently interprets sections of standard texts and comes up with his own views on their meaning and context - against standard opinion. OK, sometimes that can be good too. But he often ignores any text or argument which goes against his opinion. Example: Norsen says EPR is about locality and not realism. Yet EPR references locality only ONCE, versus over a dozen times for realism.

This is something I would count as "minor objections". The word-count of "realism" and "locality" in the EPR paper is clearly not relevant for any interesting philosophical or physical question.

He never addresses this obvious flaw in his reasoning. In addition, EPR provides the standard definition of realism ("elements of reality"). Yet Norsen seeks his own definition, changing the character of the paper in the process. It has been my hope to learn if there is any "meat" to Travis' argument that I am missing in his work. Thus, I was hoping you could enlighten me on this in some fashion. If the best anyone can do is quote Norsen over EPR, quote Norsen over Bell, and quote Norsen over Zeilinger, given the huge gaps I have just mentioned... well, that fails on every level.

I don't consider Norsen as a historian of science and have not evaluated if historical claims in his paper are correct. The argumentation he gives about realism is what interests me. And these arguments are quite nice.

2. I'm laughing... There are plenty who believe that a Bohmian interpretation is deterministic and therefore realistic. And additionally ruled out by contextual no-go proofs. I don't happen to fall in that camp. But clearly, there is something odd about asserting that a theory has hidden variables, is deterministic, and yet is also contextual. Essentially, that viewpoint agrees with the EPR conclusion that a more complete specification of the system IS possible. And I reject that.

Of course, a more complete specification is possible, and there is an explicit example of such a more complete specification, pilot wave theory.

About the reasoning "deterministic and therefore realistic" - hm, one can imagine superdeterministic theories, and I would not consider them as realistic in the EPR-Bell sense, because they do not give any realistic explanations. Thus, better omit the "therefore". Pilot wave theory is deterministic and realistic.

But that pilot wave theory is contextual is correct, it is simply a fact. There is no disagreement in the scientific community about it, as far as I know. Contextuality is not in conflict with common sense realism.

[p764rds]

excuse me if I am a little off the current dispute/argument)

Norsen's paper Quote:
"We have carefully surveyed Bell’s concept of local causality, emphasizing several points which are often misunderstood:
........
• A theory’s violation of the criterion means that it
posits non-local causation, not mere non-local correlations.
• A theory’s violation of the criterion does not necessarily" End Quote
from:
http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.0401v1.pdf

My point is this:
As far as SR goes, then Lorentz Invariance must apply to strong causal phenomology. But this does not mean that weak causal structures such as entangled correlations need obey Lorentz. ALternatively (my personal preference) is that the so-called physical distance is not in fact a real distance but a metric - indentifiers for the particles (or indeed waves if QFT considered). So the particles are not actually separated as far as correlation of states is concerned at all - indeed IMO that is how they behave and why I said in an early post that I thought the correlation effect is instantaneous (or very nearly!) - and as experiment has shown too.
Particles not physically separated (only by a metric), is equivalent, to both having simultaneous access to the same 'correlation data'. (Don't forget a 'mechanism' is still helpful to explain correlation IMO)
Lorentz Invariance would not need to be invoked because there is no strong cause and effect violation with correlation.

[DrChinese]

1. If your position is that experimenters are more on some imaginary "forefront" than theoreticians, I disagree.

2. The point is that the opinion of the scientific community has been referenced by Norsen and there is no disagreement about this opinion. Thus, for the discussion of Norsen's arguments against this opinion the facts about this opinion are irrelevant.

3. This is something I would count as "minor objections". The word-count of "realism" and "locality" in the EPR paper is clearly not relevant for any interesting philosophical or physical question.

4. Of course, a more complete specification is possible, and there is an explicit example of such a more complete specification, pilot wave theory.

... But that pilot wave theory is contextual is correct, it is simply a fact. There is no disagreement in the scientific community about it, as far as I know.

1. If your opinion is that Norsen is more on some imaginary theoretical forefront than Zeilinger, I respectfully disagree. Perhaps you recall GHZ? I cannot comprehend how you could dismiss Zeilinger's theoretical work, which has opened important new areas. I am not trying to defend Zeilinger, but come on! Get your facts straight before you blow people off.

2. There is almost universal opinion that Norsen is wrong. Not sure your point here. What you were arguing a few posts back that numbers didn't matter, now you are claiming that Norsen is in the majority.

3. If the words of the author count for nothing, I guess I could claim that EPR is about tea leaves. My point, as always, is that EPR and Bell frame the conclusion, well documented, that:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

EPR set the stage, and you can see from Bell's title - "On the EPR Paradox" - what Bell's paper is about. And it is NOT about locality (as an assumption) alone.

4. Spoken in the words of a true believer. You might want to consider labeling your opinions next. There is a big difference between saying "a more complete specification is possible" and saying "it is possible to construct a candidate theory in which a more complete specification is possible". These are not the same at all, are they?

My summary: Norsen has missed the mark and overstepped in his conclusion. I welcome a reformulation of Bell which does not require realism a la EPR as a part of the proof. If Norsen would provide that, then he would have something of substance. Until then, I don't expect much to come from this piece except as references by others with the same opinion. If you have any new insights on Norsen's arguments, I welcome those. Otherwise, I will leave you to the last word on this subject.

[DrChinese]

excuse me if I am a little off the current dispute/argument)

Norsen's paper Quote:
"We have carefully surveyed Bell’s concept of local causality, emphasizing several points which are often misunderstood:
........
• A theory’s violation of the criterion means that it
posits non-local causation, not mere non-local correlations.
• A theory’s violation of the criterion does not necessarily" End Quote
from:
http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.0401v1.pdf

My point is this:
As far as SR goes, then Lorentz Invariance must apply to strong causal phenomology. But this does not mean that weak causal structures such as entangled correlations need obey Lorentz. ALternatively (my personal preference) is that the so-called physical distance is not in fact a real distance but a metric - indentifiers for the particles (or indeed waves if QFT considered). So the particles are not actually separated as far as correlation of states is concerned at all - indeed IMO that is how they behave and why I said in an early post that I thought the correlation effect is instantaneous (or very nearly!) - and as experiment has shown too.
Particles not physically separated (only by a metric), is equivalent, to both having simultaneous access to the same 'correlation data'. (Don't forget a 'mechanism' is still helpful to explain correlation IMO)
Lorentz Invariance would not need to be invoked because there is no strong cause and effect violation with correlation.

I don't think it is clear either way that Lorentz invariance need apply to wave state collapse. In fact, as I understand Demystifier's position, there may or may not be preferred frames; and key elements of the theory might or might not be Lorentz Invariant. In other words, this is not a per se requirement of the pilot wave theory either way.

Personally, I try to picture that in 4D spacetime, 2 points may be separated. But in higher dimensions, perhaps there is a shorter path between those same 2 points. That would give a non-local character. Of course, that is just a mental picture. In other words, there could be a number of non-local mechanisms out there, and Demystifier is exploring those.

[Ilja]

1. If your opinion is that Norsen is more on some imaginary theoretical forefront than Zeilinger, I respectfully disagree. Perhaps you recall GHZ? I cannot comprehend how you could dismiss Zeilinger's theoretical work, which has opened important new areas. I am not trying to defend Zeilinger, but come on! Get your facts straight before you blow people off.

I simply state as a fact that Zeilinger is no authority for me, whatever his credentials. This is not a blow, because there are simply very few people I accept as authorities, but even these are not beyond critical examination and can loose this status easily for a single nonsensical claim.

But let's simply compare not people but arguments.

2. There is almost universal opinion that Norsen is wrong. Not sure your point here. What you were arguing a few posts back that numbers didn't matter, now you are claiming that Norsen is in the majority.


You have misunderstood me. Norsen has quoted opinions of the majority he disagrees with. This is certainly not a claim that Norsen is in majority, but that he has clarified the situation, and in particular the mainstream opinion about the question he is discussing. And this simply shows that you have no point if you quote the same majority which Norsen has already quoted.

3. If the words of the author count for nothing, I guess I could claim that EPR is about tea leaves. My point, as always, is that EPR and Bell frame the conclusion, well documented, that:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

EPR set the stage, and you can see from Bell's title - "On the EPR Paradox" - what Bell's paper is about. And it is NOT about locality (as an assumption) alone.

Let's repeat: Of course, EPR and Bell use other assumptions as well: classical logic, elementary probability theory, and also some minimal assumptions about realism and causality which are necessary to do science. These are assumptions which are implicitly used in almost every scientific paper and in this sense it is not necessary to mention them explicitly. One can as well omit realism from the list of explicit assumptions and put it into the standard list of implicit ones, and, reversely, put logic into the list of explicit assumptions. If one does this, one can show that local logic is incompatible with quantum theory, which is as meaningful and correct as to say the same about local realism. It would be even better, because there is only one logic, standard classical mathematical logic, thus, this does not invite confusion between minimal metaphysical EPR-Bell realism and plainly wrong naive realism.

I do not object that one makes these assumptions explicit, but Norsen clearly has a point here.

4. Spoken in the words of a true believer. You might want to consider labeling your opinions next. There is a big difference between saying "a more complete specification is possible" and saying "it is possible to construct a candidate theory in which a more complete specification is possible". These are not the same at all, are they?

In principle, yes, but in this case "a more complete specification is possible" becomes unprovable, because all we can do is to construct candidates for such a more complete specification. To prove that a given candidate is the true completion is impossible. Therefore, with "a more complete specification is possible" one usually means that such candidate theories can be constructed.

My summary: Norsen has missed the mark and overstepped in his conclusion. I welcome a reformulation of Bell which does not require realism a la EPR as a part of the proof. If Norsen would provide that, then he would have something of substance.

I summarize that you have simply not understood his point.

Until then, I don't expect much to come from this piece except as references by others with the same opinion. If you have any new insights on Norsen's arguments, I welcome those. Otherwise, I will leave you to the last word on this subject.

I don't claim to have any new insights, I simply have understood his point, which is a simple and valid one: Using "realism" without specification in the list of assumptions invites confusion between the extremely weak notion of EPR-Bell-realism, which cannot be given up in a reasonable way, and naive realism (or the requirement for non-contextuality), which is simply wrong. And to require realism to be mentioned in the list of assumptions is inconsistent, because then one has to mention equally well logic and probability theory.

About references by others: I already don't expect anything at all from the mainstream. The mainstream works in a "publish or perish" world with short time jobs where one has to follow the authorities to get published and to get future grants. For a mainstream scientist, alternative approaches are simply too dangerous. He has to care for future jobs and grants.