OK Corral: Local versus non-local QM

[JesseM]

wm, would you agree that it would be impossible to violate the Bell inequalities classically if one obeyed all the conditions specified in the proof of Bell's theorem (including the condition that the state of the objects/signals emitted by the source be statistically independent of the detector settings), even if one allowed the measurements to modify the state of the objects/signals received by the two experimenters?

 

[DrChinese]

1. In that EPRB was the source of Bell (1964), and in that we both accept that the experimental results would agree with QM, if the experiment was done, I am interested in your personal derivation of the EPRB correlation.

2. Can you provide such? Because your words are (to me) so unclear and confusing that I get lost. I am much less likely to get lost when I see you derive the EPRB correlation in mathematical terms that you understand and commit to.

3. See here (again) how my wording is twisted by you: I said that Bell realism is satisfied by dirty socks and library books. THAT IS: They satisfy Bellian Inequalities. Then YOU say: Bell's theorem is not satisfied by dirty socks and library books.

4. Bellian inequalities are satisfied by the Bellian realism of dirty socks (= the realism from which it was derived) and Bellian inequalities are breached by quantum particles because they are not like dirty socks.

5. YOU ASK: Given my acceptance of QM and Bell-test results, why am I still talking about local realism? BECAUSE it is Bellian (limited, constrained) realism that we should reject; it being not valid in general. (See my recent note on this thread about the shifty (''subtle'') move by d'Espagnat regarding A+; a move endorsed by Bell and many others ... and rejected by me. Do you personally accept it for quantum particles?)

6. So let's see your derivation of the EPRB (spin-half) correlations and take it from there. OK?

I might be wrong, and my words no better than yours: BUT Maths is the best logic (so let's see yours)! wm

What EPR-B correlations are you taking about?

You need to make a specific statement and let's discuss that. I will be glad to discuss any side of Bell's Theorem you want to discuss. I have already referenced several derivations of Bell on my web pages, so I am not sure what you are asking.

To make it clear: I advocate a standard reading of EPR/Bell/Aspect. Bell realism is as limited - or not - as you care to view it. There are those who refer to it as "naive realism" but I personally reject that description (as would Einstein, who was a realist of the same vein).

The math of the Bell realism assumption is simple: assume the simultaneous existence of pre-determined values for 3 non-commuting spin operators (A, B and C). Then prepare a table which shows these 8 permutations when measured as up/down (electrons) and the relative percentages. You will find that it is not possible to create such a table AND have it agree to experiment UNLESS you put negative percentages in some spots.

If you think we should reject "Bellian realism" and accept "locality": I think that is a perfectly sensible interpretation and have no issue with it. But I doubt that most folks will conclude that local realism is still a viable option just because "Bellian realism" is too "limited". If you can come up with an acceptable alternative definition of realism, I would be interested in seeing it.

 

[DrChinese]

In my view, most quantum objects are perturbed by ''measurement'' and that is why Bellian Inequalities are breached by quantum objects! Bellian realism being of very limited validity.

So what if an observation perturbs a system under study? That in no ways explains anything, and it certainly does not explain Bell test results. This is pure hand-waving, and is just as true in the classical world.

 

[wm]

wm, would you agree that it would be impossible to violate the Bell inequalities classically if one obeyed all the conditions specified in the proof of Bell's theorem (including the condition that the state of the objects/signals emitted by the source be statistically independent of the detector settings), even if one allowed the measurements to modify the state of the objects/signals received by the two experimenters?

Hi JesseM,

Would I agree that it is impossible to violate the Bell inequalities classically if one obeyed all the conditions [see* below] specified in the proof of Bell's theorem (including the condition that the state of the objects/signals emitted by the source be independent of the detector settings), even if one allowed the measurements to modify the state of the objects/signals received by the two experimenters?

No; I would not agree.

*But (to be sure we agreeing on the question), I would surely like you to spell out all the conditions, especially any that you see relating to the move in Bell's (1964) maths which no experiment can confirm. I refer to the unnumbered equations between his (14) and (15).

PS: (1) I have not forgotten an old question of yours and have been waiting a reply from a central authoritative source.

(2) Is it not fascinating that Bell should leave unnumbered the most crucial equations in his paper? Did he have doubts? Remember (as I understand the position): He [like me] did not like his theorem!

So let's be sure of the conditions; regards, wm

 

[wm]

Epr-bohm

What EPR-B correlations are you taking about?

You need to make a specific statement and let's discuss that. I will be glad to discuss any side of Bell's Theorem you want to discuss. I have already referenced several derivations of Bell on my web pages, so I am not sure what you are asking.

To make it clear: I advocate a standard reading of EPR/Bell/Aspect. Bell realism is as limited - or not - as you care to view it. There are those who refer to it as "naive realism" but I personally reject that description (as would Einstein, who was a realist of the same vein).

The math of the Bell realism assumption is simple: assume the simultaneous existence of pre-determined values for 3 non-commuting spin operators (A, B and C). Then prepare a table which shows these 8 permutations when measured as up/down (electrons) and the relative percentages. You will find that it is not possible to create such a table AND have it agree to experiment UNLESS you put negative percentages in some spots.

If you think we should reject "Bellian realism" and accept "locality": I think that is a perfectly sensible interpretation and have no issue with it. But I doubt that most folks will conclude that local realism is still a viable option just because "Bellian realism" is too "limited". If you can come up with an acceptable alternative definition of realism, I would be interested in seeing it.

(Emphasis added.)

1. DrC, EPRB, EPR-B stands here for EPR-BOHM. (EPR-Bell is written for EPR-BELL; and I am not seeking a derivation of Bellian Inequalities.) So I am sincerely seeking your derivation of the related correlation:

(1) CORRELATION (EPR-Bohm; spin-half particles) = -a.b'

per terms in OP.

2. Thank you for the realisation that one can drop Bellian-realism and RETAIN LOCALITY. That exactly summarises my position.

3. That alternative definition of realism (called CLR = Common-sense local realism) is on my website (known to you). I'd welcome some critique of it before throwing it in here.

4. So: Could I see your maths for EPR-Bohm, please?

Thanks, wm

 

[wm]

So what if an observation perturbs a system under study? That in no ways explains anything, and it certainly does not explain Bell test results. This is pure hand-waving, and is just as true in the classical world.

Hand-waving?

I had the impression that Bell thought (counter-factually) that an unmeasured system had the property that would have been revealed IF that system had been measured.

That is why he endorsed ''the d'Espagnat move'' mentioned by me here earlier. Thus:

I'd like to encourage you in the view that: It surely makes more sense to get rid of pseudo-realism (= limited realism = Bellian realism) than locality.

Thus Bell once strongly endorsed a derivation of his inequalities by d'Espagnat (Sci. Am. November 1979). In it you find this move:

"These conclusions require a subtle but important extension of the meaning assigned to the notation A+. Whereas previously A+ was merely one possible outcome of a measurement made on a particle, it is converted by this argument into an attribute of the particle itself.'' (Emphasis added.)

In my view, most quantum objects are perturbed by ''measurement'' and that is why Bellian Inequalities are breached by quantum objects! Bellian realism being of very limited validity.

PS: As I recall, Bell said he could do no better than d'Espagnat!

wm

DrC, Are you saying that Bellian Inequalities are based on measurement perturbation?

Regards, wm

 

[JesseM]

Hi JesseM,

Would I agree that it is impossible to violate the Bell inequalities classically if one obeyed all the conditions [see* below] specified in the proof of Bell's theorem (including the condition that the state of the objects/signals emitted by the source be independent of the detector settings), even if one allowed the measurements to modify the state of the objects/signals received by the two experimenters?

No; I would not agree.

*But (to be sure we agreeing on the question), I would surely like you to spell out all the conditions, especially any that you see relating to the move in Bell's (1964) maths which no experiment can confirm. I refer to the unnumbered equations between his (14) and (15).

Well, on the previous thread I already attempted to spell out all the conditions I thought were relevant, in post #133:

do you agree or disagree that if we have two experimenters with a spacelike separation who have a choice of 3 possible measurements which we label A,B,C that can each return two possible answers which we label + and - (note that these could be properties of socks, downhill skiers, whatever you like), then if they always get opposite answers when they make the same measurement on any given trial, and we try to explain this in terms of some event in both their past light cone which predetermined the answer they'd get to each possible measurement with no violations of locality allowed (and also with the assumption that their choice of what to measure is independent of what the predetermined answers are on each trial, so their measurements are not having a backwards-in-time effect on the original predetermining event, as well as the assumption that the experimenters are not splitting into multiple copies as in the many-worlds interpretation), then the following inequalities must hold:

1. Probability(Experimenter #1 measures A and gets +, Experimenter #2 measures B and gets +) plus Probability(Experimenter #1 measures B and gets +, Experimenter #2 measures C and gets +) must be greater than or equal to Probability(Experimenter #1 measures A and gets +, Experimenter #2 measures C and gets +)

2. On the trials where they make different measurements, the probability of getting opposite answers must be greater than or equal to 1/3

I guess I should note that when I say "the assumption that their choice of what to measure is independent of what the predetermined answers are on each trial", this refers to the assumption that the detailed state of the objects/signals sent out by the source, a state which we assume implies a predetermined answer to every measurement (otherwise I don't see any way of explaining how both experimenters always get the same answer when they make the same measurement), is not in any way correlated with or informed by the experimenters' choice of detector settings on that trial.

Also, note that I am not making any assumption that when they make a measurement of a property, they are simply revealing a property which was already present in the state before measurement. I only assume that the state before measurement + the choice of detector setting determines the outcome of the measurement completely. For example, if the experimenter measures a particle on axis A and gets the result "spin-up", this need not imply the particle was somehow in a spin-up state on axis A before it was measured; it just implies that the state of the particle before measurement was such that it was guaranteed that if the detector was on setting A on the measurement, the result would come back "spin-up". Again, without assuming this sort of determinism, there seems to be no way that you could explain how both experimenters always get the same result when they make the same measurement, and still satisfy all the conditions I describe above. Would you agree, at least, with this necessity for determinism in the outcome given both the state of the object/signal emitted by the source on a trial and the choice of detector setting, if the experimenters do indeed get the same result on every trial where they choose the same setting, and the object/signal is a purely classical one, and all my conditions above are being obeyed?

PS: (1) I have not forgotten an old question of yours and have been waiting a reply from a central authoritative source.

Ultimately it is not really important whether any given physicist remembered to include the condition I mentioned in their statements of Bell's theorem or not (although I've shown that several do in their papers); all that's really important is my claim that if you include that condition, along with others I mention, then it is impossible to violate any Bell inequalities classically, but possible to violate them in quantum physics (we are, I hope, debating the physical question of whether quantum results are compatible with local realism, not the historical question of whether Bell or any other particular physicist remembered to state all the relevant conditions in their proofs). If you disagree, then you should be able to come up with a classical experiment where this condition and the other ones I mentioned are all obeyed, yet some Bell inequality is violated; your previous example involving classical polarized light and the source being "yoked" to Alice's detector setting obviously does not obey all my conditions.

 

[DrChinese]

DrC, Are you saying that Bellian Inequalities are based on measurement perturbation?

I am saying that perturbation from measurement has nothing to do with explaining why quantum systems violate Bell Inequalities. It is either because a) realism is a bad assumption; or b) locality is a bad assumption.

Your statement about A+ has nothing to do with this. What Bell thought about his theorem in later years does not prove anything anyway.

 

[DrChinese]

1. DrC, EPRB, EPR-B stands here for EPR-BOHM. (EPR-Bell is written for EPR-BELL; and I am not seeking a derivation of Bellian Inequalities.) So I am sincerely seeking your derivation of the related correlation:

(1) CORRELATION (EPR-Bohm; spin-half particles) = -a.b'

per terms in OP.

2. Thank you for the realisation that one can drop Bellian-realism and RETAIN LOCALITY. That exactly summarises my position.

3. That alternative definition of realism (called CLR = Common-sense local realism) is on my website (known to you). I'd welcome some critique of it before throwing it in here.

4. So: Could I see your maths for EPR-Bohm, please?

Thanks, wm

1. I know what EPR-B stands for. I have no idea of the context.

2. Good.

3. I do not know what common sense realism is. Bell's Realism is pretty common sense to most people.

4. What math are you talking about? Are you talking about the predictions of QM for spin 1/2 particles?

 

[vanesch]

I only assume that the state before measurement + the choice of detector setting determines the outcome of the measurement completely. For example, if the experimenter measures a particle on axis A and gets the result "spin-up", this need not imply the particle was somehow in a spin-up state on axis A before it was measured; it just implies that the state of the particle before measurement was such that it was guaranteed that if the detector was on setting A on the measurement, the result would come back "spin-up". Again, without assuming this sort of determinism, there seems to be no way that you could explain how both experimenters always get the same result when they make the same measurement, and still satisfy all the conditions I describe above.

Indeed. One could illustrate this with the following observation:
Imagine two people, Alice in New York, and Bob in Tokyo, throwing each 1000 times a dice in the following way. They can choose, for each of their 1000 trials, to use a red, a blue or a green box at there disposal ; then they throw the dice in the box of their choice, and write down the outcome and the color of the box they chose.

Note that, if Bob picks the red box for his 52th throw, then he will never know what he would have gotten if instead he'd have picked the green one. And if he next picks the green one, that will not be his 52th, but his 53th throw.

The funny thing now, is when Bob and Alice come together, that they find out that each time that, by coincidence, they picked the same color, well, they also got the same outcome ! Of course, in advance, they cannot know for which throws they will pick the same color, and they cannot determine the outcome. But they simply see that in those particular cases WHEN they pick the same color, then they ALWAYS obtain the same outcomes.

Now, this funny correlation would be totally incomprehensible if there were not some "common origin" or "some action at a distance" between the dice, right ? And if we exclude the last possibility, then we would be looking at some very funny phenomenon. It would be black magic, until we proposed some MECHANISM by which both dice would somehow, in advance, know what to set as a result as a function of the color of the box. One would go and look at the producer of the dice: maybe he put some very complicated mechanism inside each of them.

People who dismiss any "a priori" determinism of the outcomes in an EPR experiment, ought to feel totally comfortable with the above situation, under the motto: "correlations happen".

 

[wm]

1. I know what EPR-B stands for. I have no idea of the context.

2. Good.

3. I do not know what common sense realism is. Bell's Realism is pretty common sense to most people.

4. What math are you talking about? Are you talking about the predictions of QM for spin 1/2 particles?

In reply, by number:

1. EPR-Bohm has two spin-half particles in the singlet state; correlation as previously given here.

2. Good.

3. I told you where to find a definition of CLR (= common-sense local realism) but you do not look? Bell's realism is common-sense? Particles unperturbed ... that A+ ''d'Espagnat move'' again? Are you saying that this Bell-endorsed move is of no consequence?

I say: Drop such ''nonsense'' and such ''fiddles'' and retain LOCALITY?

4. I am talking about you deriving the EPR-Bohm correlation of -a.b' (per terms in OP) so that I can better understand the realism that you hold to; or the locality that you reject; and the terminology that you support mathematically.

If you do the maths, I am presuming we might agree re the terms and come to some agreement about the validity (or otherwise) of LQM (Local QM).

Was it Feynman who said: Do the maths, or risk parrotting the errors of others?

wm

 

[Demystifier]

Wm was right: This really is OK corral.

 

[DrChinese]

3. I told you where to find a definition of CLR (= common-sense local realism) but you do not look? Bell's realism is common-sense? Particles unperturbed ... that A+ ''d'Espagnat move'' again? Are you saying that this Bell-endorsed move is of no consequence?

I say: Drop such ''nonsense'' and such ''fiddles'' and retain LOCALITY?

If you want to push a new definition of realism, bring it out where we can discuss it. But I don't see the purpose of a new definition when the current one is so well accepted. After all, it is exactly what Einstein would have expected.

Bell's realism is common sense, that is why Bell's Theorem is so important. If it did not match up to something most people can understand, it would not be as important.

I don't know why you are making a point about some "move" you are saying Bell endorsed. For all I know, he endorsed Richard Nixon (this is a joke, because he was not an American). The point is that Bell's Theorem stands as written and is generally accepted as such. There has been much debate about whether "hidden variables" exist or not, and if so, whether they are intrinsic particle attributes. If you deny Bell realism (as I am prone to do), none of that matters.

1. As to the math of the realism requirement, the usual presentation is essentially as follows:

1 >= P(A, B, C) >= 0

where A, B and C are 3 simultaneously "real" hidden variables (or attributes, or measurement setting outcomes).

2. As to the correlation in an EPR-B setup with electrons, the usual formula for matches (both up, or both down) is:

p(Match) = sin^2(\Theta/2)

The only significant difference for electrons versus photons being that there is the factor of 1/2 applied to electrons to adjust for being a spin 1/2 particle, while photons have a factor of 1 being a spin 1 particle. Also, entangled photons pairs are usually created by either Type I or Type II PDC. Type II gets a sin^2 function for matches while Type I has the cos^2 function.

 

[complexPHILOSOPHY]

Allow me to interject for a moment to pose a question for philosophical clarity. If the term 'common sense realism' is being used in the context that I suppose it might, are you referencing Thomas Reid?

That is the only 'common sense realism' that I am familiar with.

EDIT: Now that I read through some of the posts, I don't think you are referencing the philosopher. However, when I search for "Common Sense Local Realism" on google, I get returned back to physicsforums.

This leads me to believe that you should just tell me what it is, since google directed me here MY FRIEND! <3333

PAYCEEEE HOMIES.

 

[wm]

Clarifications

Well, on the previous thread I already attempted to spell out all the conditions I thought were relevant, in post #133: I guess I should note that when I say "the assumption that their choice of what to measure is independent of what the predetermined answers are on each trial", this refers to the assumption that the detailed state of the objects/signals sent out by the source, a state which we assume implies a predetermined answer to every measurement (otherwise I don't see any way of explaining how both experimenters always get the same answer when they make the same measurement), is not in any way correlated with or informed by the experimenters' choice of detector settings on that trial.

Also, note that I am not making any assumption that when they make a measurement of a property, they are simply revealing a property which was already present in the state before measurement. I only assume that the state before measurement + the choice of detector setting determines the outcome of the measurement completely. For example, if the experimenter measures a particle on axis A and gets the result "spin-up", this need not imply the particle was somehow in a spin-up state on axis A before it was measured; it just implies that the state of the particle before measurement was such that it was guaranteed that if the detector was on setting A on the measurement, the result would come back "spin-up". Again, without assuming this sort of determinism, there seems to be no way that you could explain how both experimenters always get the same result when they make the same measurement, and still satisfy all the conditions I describe above. Would you agree, at least, with this necessity for determinism in the outcome given both the state of the object/signal emitted by the source on a trial and the choice of detector setting, if the experimenters do indeed get the same result on every trial where they choose the same setting, and the object/signal is a purely classical one, and all my conditions above are being obeyed?

Ultimately it is not really important whether any given physicist remembered to include the condition I mentioned in their statements of Bell's theorem or not (although I've shown that several do in their papers); all that's really important is my claim that if you include that condition, along with others I mention, then it is impossible to violate any Bell inequalities classically, but possible to violate them in quantum physics (we are, I hope, debating the physical question of whether quantum results are compatible with local realism, not the historical question of whether Bell or any other particular physicist remembered to state all the relevant conditions in their proofs).

If you disagree, then you should be able to come up with a classical experiment where this condition and the other ones I mentioned are all obeyed, yet some Bell inequality is violated; your previous example involving classical polarized light and the source being "yoked" to Alice's detector setting obviously does not obey all my conditions.

Dear JesseM,

1. It seems to me that some of your parenthetic comments (''otherwise I don't see any way of explaining how both experimenters always get the same answer when they make the same measurement'') would be helped by your doing the maths in detail so that you understand every step.

2. This is not to say that my maths will always be correct; nor that your words are unintelligible. But more and more I find that those who offer ''almost non-intelligible maths'' (or none at all) are those whose words I struggle most to comprehend.

3. As for determinism: I am most certainly that way inclined! Take any anti-parallel detector settings in EPRB and the detectors punch out identical (++) XOR (--) results till kingdom come.

4. You have completely missed the question that I await an answer on. Let me answer it now, without the external input that I was hoping for: It is my view that Bell (dissatisfied with his own theorem) was open to any hidden-variable theory; local or non-local. However, in my view, non-local hidden-variables are so trivial as to be unworthy of the great man. For (it seems to me) one postulates that a measurement reveals a non-local hidden-variable in one wing of the experiment AND THEN that revelation is non-locally transmitted to the other wing. UGH!

5. Please recall that my earlier CLASSICAL experiment classically refuted Bellian Inequalities, not Bell's theorem. That is, that CLASSICAL experiment complied with the (plus/minus one) conditions used to derive the CHSH etc Inequalities.

6. I'd hoped that DrC would have detailed his maths for the EPRB-correlations. Then my proposed more general CLASSICAL refutation of Bell's Theorem (meeting the more general conditions that you point to, and responding thereto) could have been posted as a counter-point. The hope was that we could see and discuss where DrC needed non-locality and where I thought that I did not!

PS: Is there a simple spot on PF where I can pick up on LaTeX? (My search revealed too much.) Though I'll probably post in a simpler but wholly adequate fashion.

7. So (to be clear): That earlier classical experiment of mine was directed at Bellian Inequalities only. The next is also wholly classical, but seeks to meet the more general Bellian conditions and establish the EPRB correlation -a.b' (per OP) in response to our discussion.

Thanks, and cheers, wm

 

[wm]

Clarification

If you want to push a new definition of realism, bring it out where we can discuss it. But I don't see the purpose of a new definition when the current one is so well accepted. After all, it is exactly what Einstein would have expected.

Bell's realism is common sense, that is why Bell's Theorem is so important. If it did not match up to something most people can understand, it would not be as important.

I don't know why you are making a point about some "move" you are saying Bell endorsed. For all I know, he endorsed Richard Nixon (this is a joke, because he was not an American). The point is that Bell's Theorem stands as written and is generally accepted as such. There has been much debate about whether "hidden variables" exist or not, and if so, whether they are intrinsic particle attributes. If you deny Bell realism (as I am prone to do), none of that matters.

1. As to the math of the realism requirement, the usual presentation is essentially as follows:

1 >= P(A, B, C) >= 0

where A, B and C are 3 simultaneously "real" hidden variables (or attributes, or measurement setting outcomes).

2. As to the correlation in an EPR-B setup with electrons, the usual formula for matches (both up, or both down) is:

p(Match) = sin^2(\Theta/2)

The only significant difference for electrons versus photons being that there is the factor of 1/2 applied to electrons to adjust for being a spin 1/2 particle, while photons have a factor of 1 being a spin 1 particle. Also, entangled photons pairs are usually created by either Type I or Type II PDC. Type II gets a sin^2 function for matches while Type I has the cos^2 function.

1. I'll advance my definition of CLR (common-sense local realism) in the hope that you (and Einstein) will find it agreeable.

2. I'm heartened in this regard, noting with some cameraderie that you too are ''prone to deny Bell realism''. Let me add (from my perspective) you are moving in the direction of a growing band.

3. Thus: In my opinion: If you study the Bell-endorsed d'Espagnat move (re the subtle change re A+ -- see earlier posts), then you'll see more clearly what Bellian realism entails. I think it involves a clear denial of measurement perturbation; and I'm not sure that I know where Bell moved away from that position.

4. I'm not too happy with your maths here; though I too am not a mathematician. I'll post my maths ideas (based on my view of common-sense) to see if I can move you further in that direction.

wm

 

[DrChinese]

Dear JesseM,

1. ... would be helped by your doing the maths in detail so that you understand every step.

6. I'd hoped that DrC would have detailed his maths for the EPRB-correlations...

We already understand the math of Bell. If you have something to say, say it. It is getting old wondering when you are going to drill into a specific point. I have presented standard treatments of Bell, and so far there is no point of disagreement other than you don't seem to like Bell's realism assumption. If you want to replace his with your own, you will need to make a convincing argument of the benefit of doing so because otherwise there will be no interest in pursuing the matter.

 

[DrChinese]

1. I'll advance my definition of CLR (common-sense local realism) in the hope that you (and Einstein) will find it agreeable.

2. I'm heartened in this regard, noting with some cameraderie that you too are ''prone to deny Bell realism''. Let me add (from my perspective) you are moving in the direction of a growing band.

3. Thus: In my opinion: If you study the Bell-endorsed d'Espagnat move (re the subtle change re A+ -- see earlier posts), then you'll see more clearly what Bellian realism entails. I think it involves a clear denial of measurement perturbation; and I'm not sure that I know where Bell moved away from that position.

4. I'm not too happy with your maths here; though I too am not a mathematician. I'll post my maths ideas (based on my view of common-sense) to see if I can move you further in that direction.

wm

1. Einstein said of realism: "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." That is Bell realism to a tee, and I don't see how you are going to do Bell & Einstein one better. I can tell you for sure that I am not interested in a semantics debate on realism. There needs to be a connection to the physics.

2. I haven't moved anywhere on this subject.

3. This has nothing to do with anything. I assume there is measurement perturbation, the question is what is the significance of it? Is it physical? Does it have non-local impact? etc.

4. Sorry professor! You are always welcome to add your improvements.

-DrC

 

[DrChinese]

3. Re: ''no point of disagreement other than you don't seem to like Bell's realism assumption''. I just wanted to check that you ALSO are moderately sympathetic to this point of disagreement? Yes?

No, not in the least. Bell's realism is well-defined, and it is reasonable to reject it as an assumption (while keeping locality as an assumption). That does NOT mean it is a poor definition - it is a good one and that is a big part of why Bell's Theorem is so strong!

A lot of people reject realism as an assumption, and I am hardly the first. Don't confuse the "assumption" with the "definition of the assumption" - they are entirely different.

 

[vanesch]

That is the only 'common sense realism' that I am familiar with.

I don't think it is a technical term. Look at my post #42. The "common sense realism" is the idea that these correlations between dice throws of Alice and Bob "just cannot be" if there is no common causal origin.
It comes down to the idea that, when correlations occur where they are not a priori expected for some logical reason, there must be some causal link (by common origin, or by influence), and that this causal link must be found in some ontologically existing mechanism.
The reason to adhere to it, is that it is our main (and only) technique of inference and empirical enquiry.

Indeed, if you throw a switch, and a light goes on, and you throw it again, and the light goes out, and you do this 20 times, you expect there to be some kind of ontological mechanism to exist which explains this. It doesn't necessarily mean that the switch causes the light to go on. A technician might observe you through a camera, and steer the light as you throw a non-connected switch. Or worse, he might switch on and off a light, and "send you some brain waves" which make you throw the switch. Or even better, when you walked into the room, a scanner might have found out the exact state of your brain, and calculated at what moments you will throw the switch. One extravagant explanation even worse than the other. But you prefer that, over: well, correlations happen. There's no relationship. This desire of explaining correlations is, I think, what is meant by "common sense realism": there must be something real, which is the mechanism which explains the correlations.

 

[wm]

I don't think it is a technical term. Look at my post #42. The "common sense realism" is the idea that these correlations between dice throws of Alice and Bob "just cannot be" if there is no common causal origin.
It comes down to the idea that, when correlations occur where they are not a priori expected for some logical reason, there must be some causal link (by common origin, or by influence), and that this causal link must be found in some ontologically existing mechanism.
The reason to adhere to it, is that it is our main (and only) technique of inference and empirical enquiry.

Indeed, if you throw a switch, and a light goes on, and you throw it again, and the light goes out, and you do this 20 times, you expect there to be some kind of ontological mechanism to exist which explains this. It doesn't necessarily mean that the switch causes the light to go on. A technician might observe you through a camera, and steer the light as you throw a non-connected switch. Or worse, he might switch on and off a light, and "send you some brain waves" which make you throw the switch. Or even better, when you walked into the room, a scanner might have found out the exact state of your brain, and calculated at what moments you will throw the switch. One extravagant explanation even worse than the other. But you prefer that, over: well, correlations happen. There's no relationship. This desire of explaining correlations is, I think, what is meant by "common sense realism": there must be something real, which is the mechanism which explains the correlations.

(Emphasis added.)

YES! And going one step deeper: We expect there to be something real which accounts for the correlata.

Such is enlightened human nature, perhaps?

Recalling that the preparation of the highly-correlated singlet state (with its spherical symmetry), produces one of the most highly correlated states (= highly correlated correlata) that we know of.

wm

 

[wm]

No, not in the least. Bell's realism is well-defined, and it is reasonable to reject it as an assumption (while keeping locality as an assumption). That does NOT mean it is a poor definition - it is a good one and that is a big part of why Bell's Theorem is so strong!

A lot of people reject realism as an assumption, and I am hardly the first. Don't confuse the "assumption" with the "definition of the assumption" - they are entirely different.

Sorry Doc, but I'm lost and confused again. Beyond belief!

<<<Here is my assumption: LEFT BLANK.

Please, dear Professor, Do not confuse my assumption with the definition of my assumption.

Ah (light dawns): perhaps you DrC are relying on non-local transmission of my assumption.>>>

My problem! But to say ''a lot of people reject realism'' without in any way qualifying the realism of which you speak ... well that continues to be beyond me.

For now, I think it best that I find my old maths ... and maybe become (with hard study) a mathematician.

Believing, as I do, that: Maths is the best logic; and I've much to learn = comprehend.

Respectfully, wm

 

[DrChinese]

DrC,

1. Interesting: I see no mention of perturbation in your citation?

But it is specifically addressed in my definition of ''common-sense local realism'': <link removed> Would you (Einstein, Bell) disapprove? (PS: AND NB: I'm sure it can be improved!)

2. To quote my erstwhile friend: ''If you deny Bell realism (as I DrChinese am prone to do), none of that matters.''
Sorry; English is not my first language. Your proneness (= lying horizontal?) I misunderstood.

3. Non-local impact? What would that be? Peres and many others poo-poo any physicality with non-locality (I seem to recall). I am with them re physicality, since (as I before wrote to you?): How can an abstract non-physical wave not in space-time influence a concrete object in space-time?

1. The issue of perturbation by the measurement apparatus can be looked at any way you want to. It really does not affect the mathematical description of realism, which is:

1 >= P(A, B, C) >= 0

The reason is that A, B and C individually are elements of reality, because they can be predicted in advance in a Bell test. The issue is not whether the measurement somehow distorts the results, it is whether these elements of reality (EPR) exist simultaneously independently of the ACT of observation.

2. There are 2 primary assumptions in Bell's Theorem, and Bell test results lead us to deny at least one of them. You are fully justified in rejecting either one, it is simply a matter of personal preference. My preference happens to be to accept locality and deny realism, but the reverse is an acceptable position. The unjustified conclusion is to reject neither.

3. Non-locality is an issue of vital relevance. It is one of the 2 primary assumptions in Bell's Theorem, and cannot be dismissed lightly.

 

[DrChinese]

My problem! But to say ''a lot of people reject realism'' without in any way qualifying the realism of which you speak ... well that continues to be beyond me.

Again, the definition is as follows:

1 >= P(A, B, C) >= 0

This is what Bell realism is, and it remains an accepted standard definition.

 

[wm]

Preliminary classical maths for EPR-Bohm correlations

Sorry Doc, but I'm lost and confused again. Beyond belief!

<<<Here is my assumption: LEFT BLANK.

Please, dear Professor, Do not confuse my assumption with the definition of my assumption.

Ah (light dawns): perhaps you DrC are relying on non-local transmission of my assumption.>>>

My problem! But to say ''a lot of people reject realism'' without in any way qualifying the realism of which you speak ... well that continues to be beyond me.

For now, I think it best that I find my old maths ... and maybe become (with hard study) a mathematician.

Believing, as I do, that: Maths is the best logic; and I've much to learn = comprehend.

Respectfully, [B]wm

This is a preliminary draft from wm, for critical comment, please. It responds to various requests for a classical derivation of the EPR-Bohm correlations which would nullify Bell's theorem. It's off the top of my head; and a more complex denouement might be required (and can be provided) to satisfy mathematical rigour:

(Figure 1) D(a) -<- w(s) [Source] w'(s') ->- D'(b')Two objects fly-apart [w with property s (a unit-vector); w' with property s' (a unit-vector)] to respectively interact with detectors D (oriented a, an arbitrary unit vector) and D' (oriented b', an arbitrary unit vector). The detectors D (D') respectively project s (s') onto the axis of detector-orientation a (b').

Let w and w' be created in a state such that

(1) s + s' = 0; say, zero total angular momentum. That is:

(2) s' = -s.

Then the left-hand result is a.s and the right-hand result is s'.b'; each a dot-product.

To derive the related correlation, we require (using a recognised notation http://en.wikipedia.org/wiki/Column_vector ), with < ... > denoting an average:

(3) <(a.s) (s'.b')>

(4) = - <(a.s) (s.b')>

(5) = - <[(ax ay az) (sx, sy, sz)] [(sx sy sz) (bx', by', bz')]>

(6) = - (ax ay az) <(sx, sy, sz) (sx sy sz)> (bx', by', bz')

(7) = - (ax ay az) <s.s> (bx', by', bz')

(8) = - (ax ay az) <1> (bx', by', bz')

(9) = - a.b'

(10) = - cos (a, b').

Let s and s' be classical angular-momenta. Then (to the extent that we meet all the Bell-theorem criteria) the result is a wholly classical refutation of Bell's theorem. [It is Bell's constrained realism that we reject; thereby maintaining the common-sense locality clearly evident above.)

E and OE! QED?

Critical comments most welcome, (though I'll be away for a day or so),wm

 

[JesseM]

1. It seems to me that some of your parenthetic comments (''otherwise I don't see any way of explaining how both experimenters always get the same answer when they make the same measurement'') would be helped by your doing the maths in detail so that you understand every step.

I don't agree this would help, there is very little in the way of "math" here, and trying to write this in a more formal way would provide no conceptual illumination. But maybe it would help if I spelled out the reasoning and assumptions a little more clearly.

1. Do you disagree that in a classical world, if the results of two measurements exhibit a 100% correlation, this must be either because one measurement determined the other, or because the results of both measurements were determined by some other event or events?

2. Do you disagree if you have a 100% probability that two measurements using the same settings always give the same results as one another on repeated trials, and the two measurements have a spacelike separation and we assume no possibility of FTL signals, then the only way to explain the perfect 100% correlation in a classical world is to assume that on each trial the results were predetermined by some event or events (presumably the emission of both signals/objects from a common origin at the source) which lie in the past light cone of both measurement-events? (if you disagree, can you suggest an alternative explanation?)

3. Do you disagree that if there was any random element to the results of either experimenter's measurement on a given trial where they both use the same settings (and I'm only talking about randomness in the outcome an experimenter will get if we know both his detector setting and the precise state of the signal/object they're measuring--the original event or events which determined the state of both object/signals at the source may still have a random element), then the probability they both get the same answer could not be 100%?

If you agree that the answers must have been predetermined on the trials where they both picked the same detector setting, then if we also add the assumption that this predetermining event or events could not in any way be affected by information about what detector settings each experimenter will choose (note that this condition can be assured in a classical universe obeying locality if each experimenter chooses their setting randomly shortly before the measurement, so that a signal moving at the speed of light would not have time to travel from the event of an experimenter picking a setting to the event of the other experimenter making their measurement), then this means the answers must have been predetermined on *every* trial, even the ones where they pick different settings.

2. This is not to say that my maths will always be correct; nor that your words are unintelligible. But more and more I find that those who offer ''almost non-intelligible maths'' (or none at all) are those whose words I struggle most to comprehend.

If you have difficulty comprehending anything, could you try to explain what point is confusing you?

3. As for determinism: I am most certainly that way inclined! Take any anti-parallel detector settings in EPRB and the detectors punch out identical (++) XOR (--) results till kingdom come.

But I wasn't just asking if you were "inclined" this way, I was asking if you agreed it would be impossible to explain the results any other way in a classical universe obeying locality where there is no way for one measurement to causally affect the other. If you disagree or are not sure, please go through my various questions about the need for determinism above to see if you disagree with any individually.

4. You have completely missed the question that I await an answer on. Let me answer it now, without the external input that I was hoping for: It is my view that Bell (dissatisfied with his own theorem) was open to any hidden-variable theory; local or non-local. However, in my view, non-local hidden-variables are so trivial as to be unworthy of the great man. For (it seems to me) one postulates that a measurement reveals a non-local hidden-variable in one wing of the experiment AND THEN that revelation is non-locally transmitted to the other wing. UGH!

You say "you have completely missed the question that I await an answer on", but you didn't actually say what this question was. And again, I am not really interested in historical questions about Bell's opinions; I am interested in trying to show that it is possible to prove that quantum results absolutely rule out local hidden variables, which you disagreed with earlier when I asked you about it.

5. Please recall that my earlier CLASSICAL experiment classically refuted Bellian Inequalities, not Bell's theorem.

OK, but why do you think this is relevant? I'm not aware of any physicist in history who denied that it's trivial to violate the inequalities classically if you are allowed to violate the conditions of Bell's theorem; on the other thread I showed you a very simple way of doing this in a question-and-answer game where I get to hear both questions before answering "yes" or "no".

PS: Is there a simple spot on PF where I can pick up on LaTeX? (My search revealed too much.) Though I'll probably post in a simpler but wholly adequate fashion.

Yes, see the sticky thread Introducing LaTeX Math Typesetting at the top of the "Math & Science Tutorials" forum.

7. So (to be clear): That earlier classical experiment of mine was directed at Bellian Inequalities only. The next is also wholly classical, but seeks to meet the more general Bellian conditions and establish the EPRB correlation -a.b' (per OP) in response to our discussion.

When you say "the more general Bellian conditions", do you mean the conditions of Bell's theorem, including the one I mentioned that there can be no correlation between the state of the signals/objects emitted by the source and the experimenters' choice of detector settings on each trial? If so, please present it--I'm quite confident you are either missing one of the conditions of Bell's theorem, or that your example does not actually violate any of the inequalities.

 

[vanesch]

Then the left-hand result is a.s and the right-hand result is s'.b'; each a dot-product.

The problem is: the outcome is not a continuous quantity! It is a discrete quantity, with PROBABILITY equal to the numbers you give, with a shift. You only give the expectation values of the outcomes, but the trick is that each individual outcome is a +1 or a -1, and not a continuous value in between both (although their expectation is of course).

So the correlation is not found by taking the expectation of the product of their expectation values, but rather by taking the product of the outcomes (the +1 or -1 for each), and weighting that with the relative probabilities for this to happen ASSUMING that, whatever probability distribution is given on the A-side (as a function of the local setting and the local unit vector) for the +1 and the -1, it is INDEPENDENT of the probability distribution on the B-side (as a function of the local setting and the local unit vector there).

 

[DrChinese]

Let s and s' be classical angular-momenta. Then (to the extent that we meet all the Bell-theorem criteria) the result is a wholly classical refutation of Bell's theorem.

wm,

1. This is basicly akin to saying "let's assume Bell's Theorem is wrong", which is hand-waving. You have to provide us something that yields results consistent with QM AND is local AND meets the realism requirement. You can't just say you have accomplished this because s and s' are classical.

2. Specifically, what are the expected probabilities for the 8 permutations:

A+B+C+
A+B+C-
...
A-B-C-

You will find that you cannot fill in such a table with non-negative numbers and still match QM. In other words, you have ignored the realism requirement entirely.

-DrC

 

[JesseM]

Yeah, what Vanesch said. If the value a.s represents the probability of the left detector getting result +1, and (1 - a.s) is the probability of the left detector a getting -1, and s'.b' is the probability of the right detector getting +1, and (1 - s'.b') is the probability of the right detector getting -1, then presumably the expectation value for the correlation would be:

(a.s)*(s'.b') + (1 - a.s)*(1 - s'.b') - (a.s)*(1 - s'.b') - (1 - a.s)*(s'.b')

or

4*(a.s)*(s'.b') - 2*(a.s + s'.b') + 1

 

[wm]

The problem is: the outcome is not a continuous quantity! It is a discrete quantity, with PROBABILITY equal to the numbers you give, with a shift. You only give the expectation values of the outcomes, but the trick is that each individual outcome is a +1 or a -1, and not a continuous value in between both (although their expectation is of course).

So the correlation is not found by taking the expectation of the product of their expectation values, but rather by taking the product of the outcomes (the +1 or -1 for each), and weighting that with the relative probabilities for this to happen ASSUMING that, whatever probability distribution is given on the A-side (as a function of the local setting and the local unit vector) for the +1 and the -1, it is INDEPENDENT of the probability distribution on the B-side (as a function of the local setting and the local unit vector there).

Thanks for this comment.

1. Could you let me see how you would do the QM derivation, please?

2. Here's what I was thinking with my classical maths: In the double-peaked output from an S-G magnet, we allocate +1 xor -1 in accord with the direction of the output. Say: +1 = UP; -1 = DOWN.

That is, we do not allocate a different number to those particles which arrive (say) at the bottom of the UP distribution as opposed to those which have emerged at the up-side of the UP distribution. All the UPs get +1, etc.

Thus, the number (+1 xor -1) being allocated in line with the direction (UP xor DOWN) irrespective of the position in either distribution: I thought that +1 xor -1 could equally be allocated (equally arbitrarily) in accord with the sign of the dot-product in my classical example.

?

Thanks again, wm