Local realism ruled out? (was: Photon entanglement and )

[yoda jedi]

Second, what difference does it make whether he goes from locality to realism (or determinism or hidden variables or whatever) or vice versa? I think you end up at the same point either way.

absolute irrelevant, directionality it doesn't matter, the emphasis is on DETERMINISM look the word FROM not bold, but persist the word TO (my mistake).

i have to post in this way:

.....differed with Einstein about the (allegedly) fundamental nature of the Born probabilities and hence on the issue of -> determinism. Indeed, whereas Born and the others just listed after him believed the outcome of any individual quantum measurement to be unpredictable in principle, Einstein felt this unpredictability was just caused by the incompleteness of quantum mechanics (as he saw it)......


---------------------------


...Bell himself has stressed this aspect and has remarked that it is extremely difficult to eradicate this prejudice:

"My own first paper (Physics 1, 195 (1965.) on this subject starts with a summary of the EPR argument from locality to deterministic hidden variables. But the commentators have almost universally reported that it begins with deterministic hidden variables." ...

...It has to be remarked that deterministic hidden variable theories assume that the complete specification of the state of the system implies that all physical properties are actually possessed by the systems prior to any measurement process. This is equivalent to the request of realism discussed by the above mentioned authors...

Realism is not Determinism (and Determinism is not Realism)
Reality can be deterministic or not, be real is exist, determined or undertermined (defined or undefined, counterfactual definiteness or indefiniteness) contextual or non contextual, predictable or unpredictable.
be real is : "being qua being", just being.

 

[Eye_in_the_Sky]

"counterfactuality"

Back in post #477, I wrote the following:

"Counterfactual definiteness" is a weaker premise than "instruction sets".

"Counterfactual definiteness" is the assumption that there would have been definite outcomes in the counterfactual cases (without necessarily assigning specific values to those outcomes).

"Instruction sets" is the assumption in which the definite outcomes in (at least some of) the counterfactual cases are assigned specific values.

3. Sorry, to me CD = realism and yes I know that it doesn't to some people. If you can give me a specific example of a relevant difference, that would be wonderful.

Below, I give an example in which counterfactual reasoning is used to reach a certain conclusion. If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

The validity of the argument itself requires the acceptability of a certain type of 'counterfactual reasoning'. What I have in mind is a principle which asserts merely that

there would have been definite outcomes in the counterfactual cases.

Taken on its own, the principle would not permit an a priori assignment of specific values to any of the outcomes in the counterfactual cases. [... And, as far as I can tell, nowhere in the argument is such an assignment required to be made.]

Perhaps such a principle is not the same as "CFD", i.e. "counterfactual definiteness", and so I am incorrect in my post #477 characterization of "CFD" (repeated at the top of this post) [... at later time, I would like to look into this question of 'definition' in more detail]. Therefore, I will return to my earlier nomenclature of using the expression "CF" ("counterfactuality") to denote the notion of 'counterfactual reasoning' in general.

Finally, the question I wish to raise (at least, preliminarily) is the following:

What, if anything, is wrong with the type of CF employed in the argument of the example below?
_______________________________________

Example

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t₁ Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t₂ the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t₃ after t₂, with subsequent registration occurring at a time t₄.

So, we have

t₁ [Alice chooses] < t₂ [Alice gets result] < t₃ [Bob chooses] < t₄ [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t₁ and t₂, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t₃ and t₄, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Let us fix our attention to a time t, where t₂ < t < t₃. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a'.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of S_a would apply, whereas in case (2) an eigenstate of S_a' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Therefore, Quantum Mechanics is "incomplete".

 

[DrChinese]

...it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of S_a would apply, whereas in case (2) an eigenstate of S_a' would apply...Therefore, Quantum Mechanics is "incomplete".

This was the EPR argument. Local causality + HUP -> (QM is incomplete) or (Reality is observer dependent - in this case Alice).

The above statement is a shortcut way of saying this argument is no longer accepted. It was not universally accepted even when first presented in 1935. But certainly it went out of fashion after that.

Note your assumption: local causality. Hmmm. Is that valid? No, that is suspect. Also, the usual deduction is that Bob's reality is dependent on a choice made by Alice if QM is complete. I would say this is a generally accepted conclusion: that either locality does not hold, or reality is dependent on observeration.

 

[RUTA]

Below, I give an example in which counterfactual reasoning is used to reach a certain conclusion. If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

Finally, the question I wish to raise (at least, preliminarily) is the following:

What, if anything, is wrong with the type of CF employed in the argument of the example below?
_______________________________________

Example

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t₁ Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t₂ the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t₃ after t₂, with subsequent registration occurring at a time t₄.

So, we have

t₁ [Alice chooses] < t₂ [Alice gets result] < t₃ [Bob chooses] < t₄ [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t₁ and t₂, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t₃ and t₄, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Let us fix our attention to a time t, where t₂ < t < t₃. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a'.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of S_a would apply, whereas in case (2) an eigenstate of S_a' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Therefore, Quantum Mechanics is "incomplete".

Your use of the term "locality" encompasses both causal locality and separability, but otherwise it looks like the EPR argument with the same conclusion. To finish the story you've only to add QM's predicted violation of the Bell inequality with its subsequent experimental confirmation whence people believe QM is complete. Get rid of superdeterminism (keep free will) and that leaves you having to discard causal locality and/or separability, which is where the debate is centered.

 

[yoda jedi]

Back in post #477,

(iii) QM is "complete" ,


Therefore, Quantum Mechanics is "incomplete".

the quantum state is not just incomplete, but epistemic, i.e. a representation of an
observer’s knowledge of reality rather than reality itself.

 

[Frame Dragger]

...the quantum state is not just incomplete, but epistemic.....

...And yet his was still not a particularly good way of demonstrating that.

 

[yoda jedi]

being incomplete can not propose or derive any ontological premise.

 

[Frame Dragger]

being incomplete can not propose or derive any ontological premise.

I truly look forward to RUTA's reply to this, as I suspect s/he will have something interesting on the subject.

 

[Demystifier]

If the argument is valid, then one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

I think that we can safely say that (i) is not compatible with (iii).
Namely, if QM (where by QM I mean QM in its standard form) is complete then everything about nature can be derived from QM. However, from QM one cannot derive that some macroscopic objects (e.g., humans) have ability to make a free choice. Therefore, if QM is complete, then free choice does not exist.
Similarly, if free choice exists, then it is something that is not explained by QM. Therefore, if free choice exists, then QM is not complete.

It follows that QM cannot be consistently interpreted such that only (ii) or only (iv) or even only (ii) and (iv) are relinquished. Instead, one must relinquish (i) or (iii) or both. (Which does not exclude the possibility that something else should be relinquished as well.)

 

[SpectraCat]

Let us formulate an argument from the perspective of the mutual rest frame of Alice and Bob.

Suppose that at time t₁ Alice makes a 'free-choice' to measure the spin component of her incoming particle along some axis and that at a later time t₂ the outcome has been registered. Let Bob's laboratory be situated farther from the source than Alice's laboratory such that he can invoke a 'free-choice' of his own at a time t₃ after t₂, with subsequent registration occurring at a time t₄.

So, we have

t₁ [Alice chooses] < t₂ [Alice gets result] < t₃ [Bob chooses] < t₄ [Bob gets result] .

Next, consider the spacetime region A temporally bounded by t₁ and t₂, and spatially bounded by the walls of Alice's laboratory. Similarly, consider the spacetime region B temporally bounded by t₃ and t₄, and spatially bounded by the walls of Bob's laboratory. Finally, assume that Bob's laboratory (although farther from the source than Alice's) is still close enough to the source so as to ensure a spacelike separation of the two spacetime regions A and B.

Consider now the following counterfactuals (where a and a' are nonparallel unit vectors):

(1) Alice chooses to measure the spin component along the a-axis;

(2) Alice chooses to measure the spin component along the a'-axis.

Everything up to here looks fine

Let us fix our attention to a time t, where t₂ < t < t₃. In case (1), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a as a characterization of the 'information' relevant to region B for any measurement Bob may happen to choose, whereas, in case (2), Quantum Mechanics would inform Alice that she is justified in ascribing an eigenstate of S_a'.

Here is where you run into problems IMO ... Alice in fact cannot say anything about the "information" relevant to region B at any point. She cannot know for sure if her measurement was the one that destroyed the entanglement, and thus established the eigenstates of which operator (Sa or Sa') should be measured in region B, until she hears from Bob on a normal channel. Until then, she must allow for the possibility that Bob previously made a measurement that destroyed the entanglement, and she is measuring the projection of a well-defined eigenstate at her end.

Since Alice's measurement choice as well as the registration of the associated outcome are each comprised of events which are "local" to the spacetime region A, it follows from "local causality" that the 'real factual situation' in spacetime region B must be independent of the cases (1) and (2). Yet, in case (1) an eigenstate of S_a would apply, whereas in case (2) an eigenstate of S_a' would apply.

Thus, two (actually ... infinitely many) distinct quantum states can apply to the same 'real factual situation' in region B. Since these distinct states have distinct physical implications in connection with the various possible measurements Bob has at his disposal to perform, it follows that at most one of these states (if any, at all) can provide a "complete" characterization of the relevant 'information'.

From this, we see that – in relation to the various measurements from which Bob can choose – the "quantum-mechanical state" which Alice ascribes to region B cannot in general provide a "complete" characterization of relevant 'information'.

Hopefully my comment above helps to illustrate why (I think) the above analysis is flawed. The space-like separation between Alice and Bob means that they cannot know anything about measurements performed in the each other's regions until those results are communicated somehow. Alice is of course free to *assume* whatever she likes about what is going on in region B, but she can't *know* for sure until she hears from Bob. The apparent contradiction you have raised therefore does not seem to hold for Alice, or for Bob ... it would only hold for a hypothetical omniscient observer who could "see" what was going on in both space-time regions simultaneously. Since we know from SR that such an observer cannot exist, I don't see any contradiction here. Am I missing something?

 

[Gordon Watson]

What am I missing?

If I prepare photon-pairs correlated via identical linear polarization (say, some pairs V-correlated and some pairs H-correlated) then Bell-tests show Bell's inequality to be satisfied ... with no suggestion of nonlocal influences. Right? [Let's call these photon-pairs classically correlated.]

BUT if I prepare more highly correlated photon-pairs (say, correlated via identical angular momentum) then Bell-tests show Bell's inequality to be false. [Let's call these photon-pairs quantum-mechanically correlated.]

Why should more highly correlated results (from more highly correlated photon-pairs) be attributed to nonlocal influences?

 

[DrChinese]

What am I missing?

1. If I prepare photon-pairs correlated via identical linear polarization (say, some pairs V-correlated and some pairs H-correlated) then Bell-tests show Bell's inequality to be satisfied ... with no suggestion of nonlocal influences. Right? [Let's call these photon-pairs classically correlated.]

2. BUT if I prepare more highly correlated photon-pairs (say, correlated via identical angular momentum) then Bell-tests show Bell's inequality to be false. [Let's call these photon-pairs quantum-mechanically correlated.]

3. Why should more highly correlated results (from more highly correlated photon-pairs) be attributed to nonlocal influences?

1. These are not polarization entangled. The Bell Inequality does not really apply.

2. These are polarization entangled. The Bell Inequality should apply if you assert local realism, but experiments show the inequality is violated.

3. Because the inequality is violated, you must reject local realism. Essentially, the correlation level crosses a boundary. You shouldn't be able to have this level of correlation if locality and realism apply. So many people reject locality, and assert non-locality.

 

[Gordon Watson]

1. These are not polarization entangled. The Bell Inequality does not really apply.

2. These are polarization entangled. The Bell Inequality should apply if you assert local realism, but experiments show the inequality is violated.

3. Because the inequality is violated, you must reject local realism. Essentially, the correlation level crosses a boundary. You shouldn't be able to have this level of correlation if locality and realism apply. So many people reject locality, and assert non-locality.

Thank you DrC.

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

 

[DrChinese]

Thank you DrC.

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

1, 2: Sorry, not sure I follow what you are saying. If Bell's Inequality is respected, the photons are not polarization entangled. Entangled photons can be entangled on one or more pairs of observables.

3. Yes and no. There is no quantum of action to figure in for the realistic argument.

4. Some in fact do abandon realism. I personally lean in that direction a bit. But I am also slippery and sometimes change my mind.

5. Double slit is not a factor either way.

6. There are reasons, although they are subjective: a) It is easier to picture a non-local influence than the non-realistic alternative. I.e. thinking of a physical mechanism. b) Bohm worked out a non-local model to a sufficient level as to show it is conceptually viable.

 

[RUTA]

1, was given to show that entangled photons are not just of identical linear polarization.

2, was given to question why locality would be abandoned, in that the correlations in #1 do not require such abandonment.

3, in view of the HUP, appears to require the abandonment of EPR elements of reality. That seems to be easy, because EPR-realism neglects the quantum-of-action in any measurement.

4. So why is it not the case that EPR-realism is universally abandoned while locality (and hence relativity) is retained?

5. Does the double-slit experiment favor nonlocality?

6. There must be some strong reason for nonlocality being widely supported? As against the easy job of dropping EPR-realism: Yes?

I took the non-separable approach (aka non-EPR-realism) in my interpretation (“Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090 & “Why Quantum Mechanics Favors Adynamical and Acausal Interpretations such as Relational Blockworld over Backwardly Causal and Time-Symmetric Rivals,” Michael Silberstein, Michael Cifone & W.M. Stuckey, Studies in History & Philosophy of Modern Physics 39, No. 4, 736 – 751 (2008). http://dx.doi.org/10.1016/j.shpsb.2008.07.005 ).

I've given many presentations to experts in the foundations community and even though the formalism is textbook (irreps of spacetime symmetry group (FoP supra) or path integrals over graphs (arXiv 0908.4348)), people have a very difficult time with our brand of nonseparability, i.e., ontic structural realism. It runs contrary to the fundamental manner by which our brains construct perceptions -- things moving in space as a function of time, i.e., dynamism. In all honesty, my colleagues and I sometimes find ourselves asking questions in the wrong (dynamical) fashion and we've been working with RBW for 5 yrs.

So, I suspect we hear more about non-local solutions to EPR than non-separable ones because at least people can imagine a non-local dynamism.

 

[Gordon Watson]

I took the non-separable approach (aka non-EPR-realism) in my interpretation (“Reconciling Spacetime and the Quantum: Relational Blockworld and the Quantum Liar Paradox,” W.M. Stuckey, Michael Silberstein & Michael Cifone, Foundations of Physics 38, No. 4, 348 – 383 (2008), quant-ph/0510090 & “Why Quantum Mechanics Favors Adynamical and Acausal Interpretations such as Relational Blockworld over Backwardly Causal and Time-Symmetric Rivals,” Michael Silberstein, Michael Cifone & W.M. Stuckey, Studies in History & Philosophy of Modern Physics 39, No. 4, 736 – 751 (2008). http://dx.doi.org/10.1016/j.shpsb.2008.07.005 ).

I've given many presentations to experts in the foundations community and even though the formalism is textbook (irreps of spacetime symmetry group (FoP supra) or path integrals over graphs (arXiv 0908.4348)), people have a very difficult time with our brand of nonseparability, i.e., ontic structural realism. It runs contrary to the fundamental manner by which our brains construct perceptions -- things moving in space as a function of time, i.e., dynamism. In all honesty, my colleagues and I sometimes find ourselves asking questions in the wrong (dynamical) fashion and we've been working with RBW for 5 yrs.

So, I suspect we hear more about non-local solutions to EPR than non-separable ones because at least people can imagine a non-local dynamism.

Dear RUTA: Your alternative approach sounds interesting, and worthy of extra study, and in line with my own thoughts, so I'd encourage you to put ALL your papers on arViv (with hot-links on PF, if that is permitted). Or open a PF IR page with hot links?

"Studies in History & Philosophy of Modern Physics" is not available at my library.

I would introduce RBW as an explicit non-EPR-realism [nEPRr] approach <full stop> on the grounds that you see clearly that EPR "elements of physical reality" are false and that (as a consequence), locality does not need to be abandoned until we have explored more realistic [i.e., nEPRr] approaches. [EPR-realism being totally unrealistic, IMO.]

In this way you can introduce strangers such as me to your "non-separable" approach without the suspicion that "non-separable" is sneaky shorthand for "non-locality". As to the difficulty of imagining your approach? Can it be more difficult than imagining that the speed of light is constant?

I'm off to study your RBW.

Is RBW the correct and universal designation of your approach?

 

[Gordon Watson]

1, 2: Sorry, not sure I follow what you are saying. If Bell's Inequality is respected, the photons are not polarization entangled. Entangled photons can be entangled on one or more pairs of observables.

3. Yes and no. There is no quantum of action to figure in for the realistic argument.

4. Some in fact do abandon realism. I personally lean in that direction a bit. But I am also slippery and sometimes change my mind.

5. Double slit is not a factor either way.

6. There are reasons, although they are subjective: a) It is easier to picture a non-local influence than the non-realistic alternative. I.e. thinking of a physical mechanism. b) Bohm worked out a non-local model to a sufficient level as to show it is conceptually viable.

Dear DrC, what I was saying in my 1 and 2 is not that important. It was not (in your words)

"If Bell's Inequality is respected, the photons are not polarization entangled"

but rather:

"Classically-correlated photons satisfy BI, quantum-correlated photons do not."

This view leads me to reject EPR-realism (which I view as so amateurish as to be not worthy of a second thought). IMO, EPR-realism neglects the measurement interaction (for I understand EPR-realism to mean that measurement outcomes reflect "one-to-one" input properties) and yet we see that (in a Bell-test) even classically-correlated photons are modified by measurement.

So my 1 and 2 were to explain why I reject EPR-realism ... and seek a new REALISM ... before I reject locality.

That is why I am interested in (and don't understand) those who take the opposite approach. And why I'm interested especially in what leads you to occasionally flip-flop?

Also, how do you view RUTA's RBW approach?

 

[RUTA]

Dear RUTA: Your alternative approach sounds interesting, and worthy of extra study, and in line with my own thoughts, so I'd encourage you to put ALL your papers on arViv (with hot-links on PF, if that is permitted). Or open a PF IR page with hot links?

"Studies in History & Philosophy of Modern Physics" is not available at my library.

You can get the RBW papers from my homepage: http://users.etown.edu/s/stuckeym/

I would introduce RBW as an explicit non-EPR-realism [nEPRr] approach <full stop> on the grounds that you see clearly that EPR "elements of physical reality" are false and that (as a consequence), locality does not need to be abandoned until we have explored more realistic [i.e., nEPRr] approaches. [EPR-realism being totally unrealistic, IMO.]

In this way you can introduce strangers such as me to your "non-separable" approach without the suspicion that "non-separable" is sneaky shorthand for "non-locality". As to the difficulty of imagining your approach? Can it be more difficult than imagining that the speed of light is constant?

I'm off to study your RBW.

Is RBW the correct and universal designation of your approach?

Thanks for the hints as to how to explain RBW :-) Yes, Relational Blockworld or RBW is the "universal designation."

 

[DrChinese]

Dear DrC, what I was saying in my 1 and 2 is not that important. It was not (in your words)

"If Bell's Inequality is respected, the photons are not polarization entangled"

but rather:

"Classically-correlated photons satisfy BI, quantum-correlated photons do not."

This view leads me to reject EPR-realism (which I view as so amateurish as to be not worthy of a second thought). IMO, EPR-realism neglects the measurement interaction (for I understand EPR-realism to mean that measurement outcomes reflect "one-to-one" input properties) and yet we see that (in a Bell-test) even classically-correlated photons are modified by measurement.

So my 1 and 2 were to explain why I reject EPR-realism ... and seek a new REALISM ... before I reject locality.

That is why I am interested in (and don't understand) those who take the opposite approach. And why I'm interested especially in what leads you to occasionally flip-flop?

Also, how do you view RUTA's RBW approach?

Flip flop! Me?

I flip flop a bit on interpretations, mainly because I am always trying to determine if any interpretation might make a subtle assumption which could lead to a test.

I really like the RBW approach. It considers future context as relevant to fundamental quantum interactions, which seems to make sense (to me).

On the other hand: I would not be so quick to reject the EPR definition of realism. It is a powerful definition, a good line in the sand.

 

[IcedEcliptic]

how do we talk about local realism without invoking EPR? "real" has too many definitions otherwise, we need somewhere to begin, yes?

 

[yoda jedi]

how do we talk about local realism without invoking EPR? "real" has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

 

[IcedEcliptic]

be real is independent of any conceptual consideration.

We need to discuss something yoda jedi, and reality is a standard we believe we experience. Contrasting with that seems sensible.

 

[RUTA]

I had just posted this reference in another thread, but maybe you should read it to if you're not aware of it.

M.D. Reid et al. Rev. Mod. Phys. v.81, p.1727 (2009).

If you think that none of the violation of EPR/Bell, GHZ, CHSH, Leggett, etc. inequalities constitutes a violation of local realism, then you ARE proposing something that is not already established. This means that you need to back this up with a published work to support that you are not proposing your own personal theory.

Zz.

Do you have a title for that reference? The title is required for my interlibrary loan request.

 

[yoda jedi]

We need to discuss something yoda jedi, and reality is a standard we believe we experience. Contrasting with that seems sensible.

Reality does not need you, to exist.

 

[IcedEcliptic]

Reality does not need you, to exist.

Cute, but metaphysics and philosophy, and not helpful when discussing non-locality.

 

[yoda jedi]

Cute, but metaphysics and philosophy, and not helpful when discussing non-locality.

i am not discussing NON LOCALITY.

"real" has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

We need to discuss something yoda jedi, and reality is a standard we believe we experience.

Reality does not need you.

 

[Frame Dragger]

Ahh, it's good to be back. I see this thread has not changed much.

@Yoda Jedi: what kind of reality are you talking about in a local realism thread? I'm not getting what you're driving at, and I've been reading this thread for a while. The title is photon entanglment, so, I'm genuinely not getting your drift here.

 

[IcedEcliptic]

i am not discussing NON LOCALITY.

You are not discussing the topic of the thread? I'm completely confused, perhaps if you spoke in more than single sentences I could learn more from you.

 

[yoda jedi]

You are not discussing the topic of the thread? I'm completely confused, perhaps if you spoke in more than single sentences I could learn more from you.

Discussing:

"real"has too many definitions otherwise, we need somewhere to begin, yes?

be real is independent of any conceptual consideration.

reality is a standard we believe we experience.

Reality does not need you.

 

[DrChinese]

Ahh, it's good to be back. I see this thread has not changed much.

 

[Eye_in_the_Sky]

say NO to "local realism" – say YES to 'nonlocal' 'reality'

I think it is true to say that Quantum Mechanics implies 'nonlocality'.

This 'nonlocality' is either in a sense of 'causation' or in a sense of 'existence' or (say maybe) 'identity'.

 

[Eye_in_the_Sky]

Your use of the term "locality" encompasses both causal locality and separability, but otherwise it looks like the EPR argument with the same conclusion. To finish the story you've only to add QM's predicted violation of the Bell inequality with its subsequent experimental confirmation whence people believe QM is complete. Get rid of superdeterminism (keep free will) and that leaves you having to discard causal locality and/or separability, which is where the debate is centered.

______________

As a matter orientation with regard to perspective, here are three (takes on) takes on "separability" I have come across:

State Separability: The "state" 'assigned' to a "compound physical system" at any time is supervenient on the "states" then 'assigned' to its "component subsystems".

... that which we conceive as 'existing' ('real') should somehow be localized in time and space. That is, the 'real' in one part of space, A, should (in theory) somehow 'exist' independently of that which is thought of as 'real' in another part of space, B. If a physical system stretches over the parts of space A and B, then what is 'present' in B should somehow have an 'existence' independent of what is 'present' in A.

SEPARABILITY: mutually independent 'existence' of spatially distant 'things'.
______________

In connection with the scenario of Alice and Bob, I am trying to imagine a 'reality' in which the "microsystem" 'exists' in a 'manner' which is not "existentially separable", whereas, on the other hand, the "macro-instruments" (of Alice and Bob) do 'exist' in a 'manner' which is "existentially separable".
______

So, for example – as applied to the "macro-instruments" (of Alice and Bob) – by "existentially separable" I mean (something like):

The 'real' "state of Alice's instrument" and the 'real' "state of Bob's instrument" 'exist' independently of one another.

That is ... in any theory in which a notion of "state" is 'assigned' to the "instruments" of Alice and Bob, the following two conditions will hold:

1) The "state of Alice's instrument" and the "state of Bob's instrument" can be 'specified' independently of one another;

and

2) A 'specification' of the "joint state of Alice's instrument and Bob's instrument" is equivalent to a joint 'specification' of the "state of Alice's instrument" and the "state of Bob's instrument".
______

So, to repeat:

I am trying to imagine a 'reality' in which:

the "microsystem" (i.e. "singlet state") 'exists' in a 'manner' which is not "existentially separable",

whereas, on the other hand,

the "macro-instruments" (of Alice and Bob) do 'exist' in a 'manner' which is "existentially separable" [... except(,) perhaps(?) possibly(??) where/when their mutual "instruments" happen to be 'linked' via a common, "existentially nonseparable" 'onething' (such as, a "singlet state")].


... I seem to be getting stuck at this spot.

 

[Eye_in_the_Sky]

This was the EPR argument. Local causality + HUP -> (QM is incomplete) or (Reality is observer dependent - in this case Alice).

Yes. The only essential difference between the argument I have given and that of original EPR lies in the "completeness" condition.

I agree. Even if the argument I have posed can go through, its 'lesson' can be no different from that of original EPR.

So ... I see then ... as far as original EPR is concerned, you have no objection to the type of CF used. Okay. That helps clarify for me your position on CF. Good.

So, we are left with the question of which notion(s) ought to be relinquished:

... one of the following must be relinquished:

(i) 'free-choice' ,

(ii) QM is "local" ,

(iii) QM is "complete" ,

(iv) some other (implicit, currently unidentified) assumption .

You suggest:

... Bob's reality is dependent on a choice made by Alice if QM is complete. I would say this is a generally accepted conclusion: that either locality does not hold, or reality is dependent on observeration.

Okay. Let us write this as:

(QM is complete) Λ (local causality) → Bob's 'reality' depends on Alice's choice ,

where the 'reality'-dependence is "non-causal".
_________

For clarity, let us consider an example.

Suppose Alice measures S_x and gets the result "+". Then Bob's 'reality' is such that

if Bob measures S_x then he cannot obtain the result "+".

On the other hand, if Alice had measured S_y (instead of S_x), then Bob's 'reality' would have been such that

if Bob measures S_x then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

Only now is it beginning to become clearer to me (although, not yet quite 'altogether') what is going on here.

First, let me explain the two motivations I had for my having posed the argument in the manner I did:

motivation 1: Somehow, vaguely, I felt that by stripping the microsystem of all 'reality', then (as a consequence) the "nonseparability" issue would – simply – disappear; [... Now, however, I see it seems that the issue has not just disappeared, but rather, it has been transferred over to the macroscopic experimental arrangement;]

and

motivation 2: Since Bell's "local causality" criterion is about 'probability' 'assignments' made on the basis of "complete" 'information', I suspected that by couching the quantum state in terms of 'information', then somehow, a previously hidden insight would emerge. [... And indeed (... I think)... I see it now.]

Bell's "local causality" criterion goes like this ["types" of emphasis added] (diagram[/color]):

A ["complete" stochastic] theory will be said to be "locally causal" if:

The 'probabilities' 'attached' to 'values' of "local beables" in a spacetime region 1 are unaltered by 'specification' of 'values' of "local beables" in a spacelike separated region 2, when what happens in the backward light cone of 1 is already sufficiently 'specified', for example by a full 'specification' of ['values' of] "local beables" in a spacetime region 3.

Now here comes the 'catch':

... what sort of 'existence' do these "local" 'beables' have?

These "local beables" belong to a 'realm' regarding which the principle of "separability" applies.
________

For example, the following four quantities are all construed (by Bell) as being "local beables":

a ≡ Alice's setting ,
b ≡ Bob's setting ,
A ≡ Alice's outcome ,
B ≡ Bob's outcome .
________

So ... "separability" as applied to (these) "local beables" (in this context of Alice and Bob) would (seem to) mean (among other things (something like this)):

The 'real' "state of Alice's instrument" and the 'real' "state of Bob's instrument" 'exist' independently of one another.

This then is (supposed) to imply that in any theory in which a notion of "state" is 'assigned' to the "instruments" of Alice and Bob, the following two conditions will hold:

1) The "state of Alice's instrument" and the "state of Bob's instrument" can be 'specified' independently of one another;

and

2) A 'specification' of the "joint state of Alice's instrument and Bob's instrument" is equivalent to a joint 'specification' of the "state of Alice's instrument" and the "state of Bob's instrument".
_____________________

I believe it is correct to see the conjunction of assumptions in Bell: locality + realism.

In connection with "stage 2" of Bell's argument, I agree with you. But in connection with "stage 1" I do not see it.

Okay, now I see it. That is, what I am now seeing regarding "stage 1" (in terms of a conjunction of assumptions) in Bell is very much along the lines of what you had put as:

locality + realism .

(After quite some thought ... I think) I would (like to) put it like this:

Bell's "local causality" criterion ↔

"causally local" 'reality' Λ "existentially separable" 'macro-apparatus-world' .


... Does this make sense to you?

 

[DrChinese]

Y

For clarity, let us consider an example.

Suppose Alice measures S_x and gets the result "+". Then Bob's 'reality' is such that

if Bob measures S_x then he cannot obtain the result "+".

On the other hand, if Alice had measured S_y (instead of S_x), then Bob's 'reality' would have been such that

if Bob measures S_x then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

Yes, that pretty well sums it up. By the EPR reasoning, Bob's reality is determined by a choice of measurement by Alice. This is required by the HUP.

 

[RUTA]

I think it is true to say that Quantum Mechanics implies 'nonlocality'.

This 'nonlocality' is either in a sense of 'causation' or in a sense of 'existence' or (say maybe) 'identity'.

Or both.

 

[RUTA]

motivation 1: Somehow, vaguely, I felt that by stripping the microsystem of all 'reality', then (as a consequence) the "nonseparability" issue would – simply – disappear; [... Now, however, I see it seems that the issue has not just disappeared, but rather, it has been transferred over to the macroscopic experimental arrangement;]

Correct. This is the basis for the Relational Blockworld interpretation, i.e., no microsystem plus nonseparable experimental equipment.

 

[DevilsAvocado]

Suppose Alice measures S_x and gets the result "+". Then Bob's 'reality' is such that

if Bob measures S_x then he cannot obtain the result "+".

And if we add http://en.wikipedia.org/wiki/Relativity_of_simultaneity" to that – I say Bob can do whatever he likes = free-choice.

 

[jambaugh]

For clarity, let us consider an example.

Suppose Alice measures S_x and gets the result "+". Then Bob's 'reality' is such that

if Bob measures S_x then he cannot obtain the result "+".

On the other hand, if Alice had measured S_y (instead of S_x), then Bob's 'reality' would have been such that

if Bob measures S_x then he can obtain the result "+".

... DrC, is this example included in what you mean by "Bob's reality is dependent on a choice made by Alice"? ... or is it not?
__________________________

There is a critical distinction I would make here. When you speak of what might happen from Bob's end you are not describing an Objective Reality (what is) but rather as you've presented it the actuality of what may happen.

If you further interpret the "Why" of this actualization then you may invoke an objective reality, i.e. the state of Bob's system is in the subset of states which exclude those where property S_x has value "+". In so doing you will run into the Bell type inequalities which are violated by QM because the presumption that the system and its environment is in a set of states implies the probabilities of outcomes defines a probability measure over that set.

It is this transition from "what happens" actuality to a "what is" reality that we non-realists object to. But note that you can avoid this, still speak of what happens in an objective way (which is why in CI you need the measuring devices to be classical level, you need objective reality of your measurement record) and avoid the need to invoke non-local causation.

That's I believe the heart of classic Copenhagen interpretation.

You needn't invoke CI if you prefer another interpretation (though I think you'd be incorrect) but you should be careful to distinguish when you are describing a reality=objective state of existence vs. actuality=behavior.

It is hard to recognize this distinction at first since we grow up thinking classically where all that happens can be equivalently described in terms of what is.

 

[Count Iblis]

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

 

[jambaugh]

And if we add http://en.wikipedia.org/wiki/Relativity_of_simultaneity" to that – I say Bob can do whatever he likes = free-choice.

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time. Space/time was a http://en.wikipedia.org/wiki/Fiber_bundle" with time as the base and each slice of space (and the state of all within it) is a fiber indexed by this time base. Very much the continuum analogue of a movie with each frame a reality snapshot.

Relativity of simultaneity already begins to sand away at our old concept of objective reality. To preserve it in classical SR we invoke the frozen history of all past and future in a composite space-time. This of course doesn't allow choice or change except by selecting a whole new space-time universe.

In order to still speak of possibilities and probabilities and choices in a deterministic setting we invoke typically a classical field theory, again a fiber-bundle (space-time base with fibers the possible configurations of local reality and typically also some gauge degrees of freedom).

Now any time we see fiber-bundles we can be sure there is a relativity principle which may unify base with fiber and with is a group deformation of actions where the one-way dependence of fiber action on base coordinate becomes a two-way interaction. In this case matter affects the space-time just as space-time affects the matter and we get GR.

Well I'm getting off track... the point is that we already have good reason to soften up our traditional "objective reality" mindset and begin thinking in terms closer to the epistemological basis of science, the actuality of what we observe instead of the imagined state of reality with which we modeled it in past.

 

[jambaugh]

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

This is exactly the process of transitioning to the classical scale. We look at the necessary conditions for a system of events to behave classically, e.g. commutativity of observables on the scale to which we make distinctions. When the pointer on a particle counter is set to large units so that the momentum of that pointer can be similarly refined, we don't care about the hbar's worth or error. The device has amplified the microscopic observable (of say a particle's spin) to one which is classical in scale (say the loud clicks of one of two particle detectors). (and this amplification is an irreversible thermodynamic process b.t.w.)

The critical question is "does a classical reality-model work adequately for the system?" if so then we have no problem treating the system classically. But we can also embed this classical system inside a large quantum one (the classical variables are a commuting subset of the larger class of quantum observables.) This is what we must do in order to see that classical measuring devices in a quantum universe is perfectly consistent and not dualistic.

Think of it in terms of the actuality of people living in the US and the construct of "Government" and "Law" which has a more objective behavior (ideally) than the actual people but which none-the-less is a function of and embedded within the world of people doing what people do. Note we also see in this analogy that when pushed to cases the idealized law breaks down (corruption,miscarriages of justice, civil disobedience, et al) because at the fundamental level the people are not just clockwork objects and thus their implementation of law is not perfect according to how the law itself defines "what ought to be". And yet to function as a society we must work with an objective system of government and laws, recognizing them as not the fundamental nature of us but a useful and necessary construct.

EDIT: So too I say is "reality" a useful and necessary construct but not fundamental.

 

[RUTA]

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time. Space/time was a http://en.wikipedia.org/wiki/Fiber_bundle" with time as the base and each slice of space (and the state of all within it) is a fiber indexed by this time base. Very much the continuum analogue of a movie with each frame a reality snapshot.

Relativity of simultaneity already begins to sand away at our old concept of objective reality. To preserve it in classical SR we invoke the frozen history of all past and future in a composite space-time. This of course doesn't allow choice or change except by selecting a whole new space-time universe.

In order to still speak of possibilities and probabilities and choices in a deterministic setting we invoke typically a classical field theory, again a fiber-bundle (space-time base with fibers the possible configurations of local reality and typically also some gauge degrees of freedom).

Now any time we see fiber-bundles we can be sure there is a relativity principle which may unify base with fiber and with is a group deformation of actions where the one-way dependence of fiber action on base coordinate becomes a two-way interaction. In this case matter affects the space-time just as space-time affects the matter and we get GR.

Well I'm getting off track... the point is that we already have good reason to soften up our traditional "objective reality" mindset and begin thinking in terms closer to the epistemological basis of science, the actuality of what we observe instead of the imagined state of reality with which we modeled it in past.

I don't see how you can distinguish base from fibers in the case of GR as you can with Newtonian space/time, since the local configurations are given by the stress-energy tensor (SET), the components of which require the notions of space and time (can define SET via variation of matter-energy Lagrangian with respect to the spacetime metric). The so-called "interaction" between base and fiber here is not a relation between distinguishable concepts. Therefore, I would say GR is rather a self-consistency criterion for the co-construction of the two.

 

[GeorgCantor]

It is not clear to me how you can get an "objective reality" at all from a theory in which it doesn't exist at the fundamental level.

Yes that seems to be true, at least in the perspective of quantum entities in time and space. There can be no 1 electron, if there was a universe with exactly one electron, then that electron has NO objective reality, i.e. it doesn't exist. It doesn't matter if you believe in decoherence, measurement-causes-collapse, MWI, BM or some other stuff. All these interpretations require a CONTEXT, i.e. they require relationships with other quantum entities. No interpretation that i know of can restore the objective reality of objects in time and space existing in and of themselves, without a context. In this view, local realism is not ruled out but dead as a complete picture of reality.

 

[DevilsAvocado]

Speaking of Relativity of Simultaneity, our heritage of thinking in terms of objective realty goes back to the fiber-bundle structure of pre-Einstein space /time.

All I wanted to say is that there is no way to tell if Alice or Bob does the measurement first – therefore they both have absolute non-deterministic "QM-probability-freedom" to do any measurement they like.

 

[zonde]

Relativity of simultaneity already begins to sand away at our old concept of objective reality.

It's not so much about concept of objective reality as about concept of rigidity of our measurements.
So we have good reason to soften up our traditional "rigid measurements" mindset.

 

[Geigerclick]

It's not so much about concept of objective reality as about concept of rigidity of our measurements.
So we have good reason to soften up our traditional "rigid measurements" mindset.

What do you mean?

 

[zonde]

What do you mean?

I mean that relativity of simultaneity applies to both measured object and measurement equipment. So we can't have non-contextual (rigid) measurement.
And I think that the same applies to QM measurements i.e. they are contextual.

Objective reality however means that we can fit it all together when we take into account contextuality of measurements. That is easily demonstrated is SR - all measurements fit together when using Lorentz transformations.

 

[filegraphy]

"There may be a measurement problem, but I doubt it is the problem you think it is. It is kind of like the problem of why there is more matter in the universe than anti-matter. Something it would be nice to understand, but not something that is actually in contradiction to theory." Dr. Chinese
In the book Antimatter by Frank Close, there is a process when matter and antimatter form that allows more matter to remain than antimatter.

 

[jambaugh]

I don't see how you can distinguish base from fibers in the case of GR as you can with Newtonian space/time, since the local configurations are given by the stress-energy tensor (SET), the components of which require the notions of space and time (can define SET via variation of matter-energy Lagrangian with respect to the spacetime metric). The so-called "interaction" between base and fiber here is not a relation between distinguishable concepts. Therefore, I would say GR is rather a self-consistency criterion for the co-construction of the two.

The point I inferred was that GR is less separated into fiber/base than field theory in SR. But still the definition of locality makes a distinction. One localizes with regard to the base space-time manifold and not with regard to to the fiber matter fields. (But note asymptotic freedom seems to localize in the momentum domain as well) We also --of course-- have the the fiber bundle structure of the tangent bundle on the manifold, but we may view this as our linearization of the description. Kaluza-Klein type theories show how the field/space-time may be unified into a space-time-gauge manifold. We then better see the tangent bundle structure as one of convention and not essence.

I presume then that brane theories attempt to quantize from this point. I'm inclined to think the objectification of space-time is a "wrong tract" and that a more Eulerian than Lagrangian description is "the way to go". But I haven't much in the way of example theories to suggest in that direction.

We can also view the classical probability description as a fiber-bundle with base, the state manifold and fibers of probability density. This is the heart of the Bell inequality derivation which is equivalent to the assumption that probabilities form a measure over a manifold of objective states of reality. No locality issues need apply. (And "rigidity" or its lack in measurement is not the issue.)

 

[jambaugh]

I mean that relativity of simultaneity applies to both measured object and measurement equipment. So we can't have non-contextual (rigid) measurement.
And I think that the same applies to QM measurements i.e. they are contextual.

This is true I believe but the QM case goes beyond that. With the classical SR case you get mappings from each observer's measurements, which we then see as perspectives on an objective whole. i.e. the length of an object is, in the whole, seen as one observer's cross-section of the object's world-volume (the locus of all space-time events associated directly to that object.) One still has an objective reality-history.

The contextual nature of quantum systems is in the objective reality (or reality-history) itself. We may have the objective reality of anyone set of commuting measurements. But one does not map given measurements to given measurements in the unitary transformations (in the sense of outcomes=values of observables). One rather maps certainty of measurements to probabilities of measurements, or in the more general case, map amplitudes to amplitudes some of which may take on the value of certainty. One has thereby abstracted from the objective (though relative) description of the system itself to the statistical description of our knowledge about how the system might behave.

Yes the math parallels but the "thing" upon which the relativity group acts is no longer the system state. It is the "state vector" or "mode of preparation" vector identifying a class of actual systems. One cannot narrow this class to the point of all systems acting identically under any possible measurement and thus one cannot speak of a instantiation of the class as being in an objective state of reality in that this state determines the outcome of all measurements exactly. Contextuality is an important feature of understanding the quantum description but there is more than that going on here.