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

[Eye_in_the_Sky]

6. Sure, how about this member of your "non-existent" school:

A Bell Theorem with no locality assumption (2006), C. Tresser.
http://arxiv.org/abs/quant-ph/0608008

A pint of beer says you debate the merit of the paper BEFORE you acknowledge the existence of the school... and that you are flat out incorrect on this point.


7. Well, I think we found your hot spot. See 6.

Sorry about that. I thought you meant a school which claims that 'realism' alone is a sufficient condition for a derivation of Bell's inequality. ...

But now I see it seems you mean something else. From what is said in the abstract of that paper, it looks like you are referring to a school which claims that 'realism' alone is the reason for the violation of Bell's inequality.
... Okay, this can make sense.
____________________________________

My opportunity for posting in the forum is about to expire. In a month or so I will be able to come back, but then, only infrequently.

Dr. Chinese, I have printed out a copy of your post, and I will take it with me when I go. I will also print out copies of the references you have cited. When I return, I will post back in this thread any responses I may have.

There is, however, one more thing you might be able to help me with.

Well actually I don't have to do anything to debunk Norsen. ... some have in fact already debunked his general line of thinking.

If you can post some links to references which do the debunking, then please do so. I may still have a chance to print more things out before I go.
____________________________________

BE WELL, ALL.

... "let there be light" ...

... one-we-all SHINE!

 

[DrChinese]

Sorry about that. I thought you meant a school which claims that 'realism' alone is a sufficient condition for a derivation of Bell's inequality. ...

But now I see it seems you mean something else. From what is said in the abstract of that paper, it looks like you are referring to a school which claims that 'realism' alone is the reason for the violation of Bell's inequality.
... Okay, this can make sense.
____________________________________

My opportunity for posting in the forum is about to expire. In a month or so I will be able to come back, but then, only infrequently.

Dr. Chinese, I have printed out a copy of your post, and I will take it with me when I go. I will also print out copies of the references you have cited. When I return, I will post back in this thread any responses I may have.

There is, however, one more thing you might be able to help me with.

If you can post some links to references which do the debunking, then please do so. I may still have a chance to print more things out before I go.
____________________________________

BE WELL, ALL.



... one-we-all SHINE!

Well, I am going to award you the pint of beer... although I think you are splitting a few hairs in your acknowledgment.

I am scared now that you will say this reference is not a "debunking" of Travis... as perhaps it is more of taking issue with a specific item. However, coming as it is from Shimony (and you don't see a lot of "named" critiques), I think you have to take it that it is Norsen's essential program that is coming under fire. Everyone who knows Norsen has a great respect for him, as I do, but that does not color the fact that I disagree with 2 key elements of his analyses. Specifically, I object to Norsen's historical characterization of the EPR argument; and his assertion that Bell tests prove non-locality. The below does not touch too much on either of these, so I simply provide it for your interest. Please do not respond to the merits of the actual argument as I am not trying to debate those, nor is this paper related to this thread in and of itself.

http://www.brown.edu/Departments/EEB/roberts/sawicki/sawickietal_AJP_adaircomment_reply_2005.pdf

We look forward to your return, as always...

-DrC

 

[Frame Dragger]

@Eye: Hurry back, this is all very interesting to read as it's developed! I learn so much from the struggle when people try to communicate (and then succeed) on these complex and/or weighty topics, especially on the net.

@DrChinese: I've just had a friend corner me about superdeterminism, and while my instinct was to scoff, I wanted to come here first. My understanding is that it is vanishingly unlikely, or an excuse to say "god". Does anyone really explore that as a viable loophole? It seems impossible, but I often miss the long-shot and go with the more balanced->depressive view.

From my understand, Bell's Inequalities really were about starting with many of EPR's "assumptions", and trying to work with them towards some kind of test of LR. The notion of superdeterminism just seems to be a pointless exercise IF it existed, and pointless if it doesn't. Am I really off-base here or flat out wrong?

 

[DrChinese]

@Eye: Hurry back, this is all very interesting to read as it's developed! I learn so much from the struggle when people try to communicate (and then succeed) on these complex and/or weighty topics, especially on the net.

@DrChinese: I've just had a friend corner me about superdeterminism, and while my instinct was to scoff, I wanted to come here first. My understanding is that it is vanishingly unlikely, or an excuse to say "god". Does anyone really explore that as a viable loophole? It seems impossible, but I often miss the long-shot and go with the more balanced->depressive view.

From my understand, Bell's Inequalities really were about starting with many of EPR's "assumptions", and trying to work with them towards some kind of test of LR. The notion of superdeterminism just seems to be a pointless exercise IF it existed, and pointless if it doesn't. Am I really off-base here or flat out wrong?

t' Hooft has written about superdeterminism, and I will send a reference. Others too. I say it is just another way of saying god. I will explain in a follow up post.

Bell definitely was responding to EPR specifically. He wanted to address Einstein's idea that a form of local realism - more complete and to be discovered in the future - could be compatible with the predictions of QM.

 

[Frame Dragger]

t' Hooft has written about superdeterminism, and I will send a reference. Others too. I say it is just another way of saying god. I will explain in a follow up post.

Bell definitely was responding to EPR specifically. He wanted to address Einstein's idea that a form of local realism - more complete and to be discovered in the future - could be compatible with the predictions of QM.

Thank you very much DrChinese! I look forward to the reference, but to be fair I believe as you do, that it's the "Creationism" of LR et al.

EDIT: Not to mention the whole idea is so terribly... bleak. It says something about the lengths people will go to when resolving cognitive dissonance.

 

[ThomasT]

Well... Let's look at this as a boundary. Bell assumed that the LRT would need to match the predictions of QM. So if you follow that approach, there is no boundary. LR is simply ruled out, and that is the end of it. Of course, you must prove that the predictions of QM are supported to get this result.

Next, there is the boundary you describe. This comes from a relaxed assumption. The relaxed assumption is that the perfect correlations of EPR are in effect, but the Local Realistic Theory does not match QM. This yields the Bell Inequality, which is essentially the "closest" any LR can come to the predictions of QM. Of course it still wouldn't match the predictions of QM. But it would not violate Bell's Theorem/Inequality.

So the boundary condition is a result of Bell pointing out that QM and LR are incompatible as to their predictions. It really has nothing to say about assumptions within those theories OTHER than the LR being realistic/separable. And there is certainly no requirement that the LR have the linear relationship you mention. The function could be anything, since it doesn't match QM (or experiment).

What I'm asking is:

How is, eg., (1-P(|a-b|)) + (1-P(|a-b|)) => 1-P(2|a-b|) , the simplest and archetypal Bell inequality, derived?

The assumption of a local common cause wrt the relationship between entangled photons isn't enough to warrant the assumption that the above inequality literally represents. So, I'm guessing that the derivation of this inequality depends on the assumption of realism wherein the term realism means attributing definite values to the relevant property (or properties) of polarizer-incident optical disturbances in optical Bell tests.

As I see it, the assumption of local common cause, without realism, justifies the application of Malus Law in Bell tests. Would you agree with this?

Considering this, and from Tresser's and others' formulations of inequalities without an explicit locality condition, it appears that not only can nonlocality in Nature not be inferred but also that the applicability of Malus Law supports the continued assumption that Nature is exclusively locally causal in line with the requirements of SR.

So, it seems to me at this time (and of course I'm still somewhat confused by it all ) that LR models ARE ruled out -- but due to the realism part (not the localism part).

P(A,B) = cos²|a-b| can therefore be considered as a local nonrealistic understanding of optical Bell test correlations.
-------------------------------------
Wrt superdeterminism, hasn't it already been agreed that this term just means determinism applied to everything in our universe -- and doesn't determinism already mean that?

I do hope that if this thread continues it doesn't digress to include discussions of superdeterminism and free will, again.

 

[Frame Dragger]

@ThomasT: As DrChinese and I were just discussing, and as he's been saying OVER and OVER... Realism as defined by EPR!

 

[ThomasT]

@ThomasT: As DrChinese and I were just discussing, and as he's been saying OVER and OVER... Realism as defined by EPR!

What's your point?

 

[yoda jedi]

Well, you could be into that whole "let there be light" bit, but really I like your explanation much better.

of course, clarity as of water.

real or realistic is the term to distinguish, simply, what exists from what does not exist.
come from the latin realis.
and ontology is the philosophical study of the existence or reality in general.

"the science of being qua being", 'Qua' means 'in the capacity of'.

 

[Frame Dragger]

Again, the WORD "Realism" does not matter. The term Realism in this context is the realism as defined by EPR. Call it butternut squash if that helps... the name doesn't matter, the understanding of the principle does.

 

[yoda jedi]

Again, the WORD "Realism" does not matter. The term Realism in this context is the realism as defined by EPR. Call it butternut squash if that helps... the name doesn't matter, the understanding of the principle does.

oh sorry, then EPR is the owner of reality
consecuently,

http://physicsworld.com/cws/article/news/27640
"Quantum physics says goodbye to reality"

...giving the uneasy consequence that reality does not exist when we are not observing it...


then nothing exist, of course ! who care about names, words, concepts ! if nothing exist !

or if i or you wish name CAT to BUILDINGS or BUILDINGS to CATS who cares ?
and cats does not exist, is just semantics, all depend of the context, you live in some context (wait, you not exist if nobody measure you) and myself live in other context (if somebody measure observe me ! or EPR save me)

REALITY goes beyond contextuality or non-contextuality, counterfactual definiteness or indefiniteness, determinism or indeterminism, with unitary evolution or not.

the misundertanding goes back to:


http://arxiv.org/ftp/quant-ph/papers/0402/0402001.pdf

...Quantum Mechanics is not complete. And this is why such additional properties are referred to as « supplementary parameters », or « hiddenvariables.-----Einstein actually did not speak of « hidden variables » or « supplementary parameters », but rather of
« elements of the physical reality ». Accordingly, many authors refer to « realistic theories » rather than to « hidden variable theories », or to « supplementary variable theories »...

 

[Frame Dragger]

No, but to have a discussion about something we have to first agree on what it is we're talking about. It happens to be that in the case of BELL the standard for reality that was "agreed" on WAS EPR, so yes... EPR owns reality as far as Bell's Theorems are concerned. That's the whole damned point. If you don't get that, you're missing everything that follows.

 

[DrChinese]

1. What I'm asking is:

How is, eg., (1-P(|a-b|)) + (1-P(|a-b|)) => 1-P(2|a-b|) , the simplest and archetypal Bell inequality, derived?

2. The assumption of a local common cause wrt the relationship between entangled photons isn't enough to warrant the assumption that the above inequality literally represents. So, I'm guessing that the derivation of this inequality depends on the assumption of realism wherein the term realism means attributing definite values to the relevant property (or properties) of polarizer-incident optical disturbances in optical Bell tests.

As I see it, the assumption of local common cause, without realism, justifies the application of Malus Law in Bell tests. Would you agree with this?

3. Considering this, and from Tresser's and others' formulations of inequalities without an explicit locality condition, it appears that not only can nonlocality in Nature not be inferred but also that the applicability of Malus Law supports the continued assumption that Nature is exclusively locally causal in line with the requirements of SR.

So, it seems to me at this time (and of course I'm still somewhat confused by it all ) that LR models ARE ruled out -- but due to the realism part (not the localism part).

1. This is essentially a restatement of the realism requirement for ANY 2 pairs of "somethings" that take binary values. It could be sock colors, coin sides, or pretty much anything. This is not the "proper" form but I follow what you mean. This requirement has nothing at all to do with quantum mechanics. It follows some the probability ideas of Kolgomorov.


2. What you call a common cause is expressed a little differently usually. This comes from EPR originally, and I would say it is the idea that there are elements of reality. Those elements of reality would be what you would get from this idea:

A experiments measuring any observable attribute of Alice would allow you to predict the same attribute on Bob.

Keep in mind: these particles do NOT need to be entangled to demonstrate this effect. So it is not an assumption. It will be a demonstrated fact.


3. I happen to agree with this, although as I say it is not from a rigorous perspective. If you take a single photon - not part of an entangled pair but just one lone photon - you will eventually realize that Malus does not provide a self-consistent description of its spin either. So whatever the issue is, it does not seem to me to relate to separability/locality.


And I completely agree that if we are going to discuss/debate suprerdeterminism, we should start a new thread. Frame Dragger? Although it would probably make sense to skip it for a while if you want to follow some references first.

 

[DrChinese]

No, but to have a discussion about something we have to first agree on what it is we're talking about. It happens to be that in the case of BELL the standard for reality that was "agreed" on WAS EPR, so yes... EPR owns reality as far as Bell's Theorems are concerned. That's the whole damned point. If you don't get that, you're missing everything that follows.

You are SOOOOOO right about this. It makes it hard to discuss local realism when you change definitions away from the EPR/Bell concepts. Bell knew that his idea of realism would be immediately obvious to those who knew the EPR paper (his audience). He didn't really bother with explanations and definitions, thinking that the result he had would speak for itself.

Bell/Einstein realism = EPR elements of reality, including counterfactuals, since Einstein insisted on this.

Bell/Einstein locality = No spooky action at a distance, for similar reasons.

At the time of Bell's paper, there was a standoff: it was generally believed that QM was correct in all particulars, but might be a subset of a greater theory yet to be discovered. Much like Special Relativity was a subset of General Relativity. So the importance of Bell was to show that Einstein's realism was incompatible with Einstein's locality.

Now, the question many ask is: Does Bell locality = Einstein locality? In other words, is Bell's separability the same thing as Einsteinian locality? I am not really into debating that, because I think you just go around in circles.

As to realism, I think there is no doubt that Bell intended a definition as close to EPR as possible. He specifically talks at length about the idea that the perfect correlations are consistent between some local realistic theories and QM. Which was where the standoff was at that time. Again, the standoff being between those who followed Einstein's tenets versus those that saw QM as complete already. ANd by complete, I mean in the sense of EPR.

 

[Frame Dragger]

@DrChinese: I found some good references and am reading through them, I won't derail the subject! Pinky swear.

Edit: I see your second post... hmmm... First thank you. Second... I really don't know. Circles, as you say. It makes me wonder if we're really capable of formulating this "theory of everything" in terms that will make sense to us as humans. It may provide guidance as to the future of technology, but so many of these issues still come down to the fact that we're brains in a box so to speak.

I agree that Bell and EPR Realism are the same; as you say it was CLEARLY Bell's intent.

I hope we all live long enough to see something like answers to these questions... they're so captivating.

 

[yoda jedi]

No, but to have a discussion about something we have to first agree on what it is we're talking about. It happens to be that in the case of BELL the standard for reality that was "agreed" on WAS EPR, so yes... EPR owns reality as far as Bell's Theorems are concerned. That's the whole damned point. If you don't get that, you're missing everything that follows.

agreement on ? on misunderstandings ? (from whoever)

and agreement ? ...where ?
here, there are only claims, opinions, if you (or whoever) wish name cat to reality or reality to cats that is your (their) misinterpretation (oh sorry !, you do not exist !, you are not real ! ).

 

[Frame Dragger]

agreement on ? on misunderstandings ? (from whoever)

and agreement ? where ?
here, there are only claims, opinions, if you (or whoever) wish name cat to reality or reality to cats that is your (their) misinterpretation (oh sorry, you do not exist, you are not real ).

*sigh* Just because your nickname is Yoda, doesn't mean you have to start rambling like him...

 

[ThomasT]

1. This is essentially a restatement of the realism requirement for ANY 2 pairs of "somethings" that take binary values. It could be sock colors, coin sides, or pretty much anything. This is not the "proper" form but I follow what you mean. This requirement has nothing at all to do with quantum mechanics. It follows some the probability ideas of Kolgomorov.


2. What you call a common cause is expressed a little differently usually. This comes from EPR originally, and I would say it is the idea that there are elements of reality. Those elements of reality would be what you would get from this idea:

A experiments measuring any observable attribute of Alice would allow you to predict the same attribute on Bob.

Keep in mind: these particles do NOT need to be entangled to demonstrate this effect. So it is not an assumption. It will be a demonstrated fact.


3. I happen to agree with this, although as I say it is not from a rigorous perspective. If you take a single photon - not part of an entangled pair but just one lone photon - you will eventually realize that Malus does not provide a self-consistent description of its spin either. So whatever the issue is, it does not seem to me to relate to separability/locality.


4. And I completely agree that if we are going to discuss/debate suprerdeterminism, we should start a new thread. Frame Dragger? Although it would probably make sense to skip it for a while if you want to follow some references first.

1. Ok, and its connection to Nature is via the faulty assumption that we can attribute definite values to the property or properties being jointly analyzed in Bell tests.

2. Ok, what I meant by common cause doesn't imply that we can attribute definite values (vis EPR elements of reality) to the locally imparted common property or properties. The only assumption necessary to justify the application of Malus Law in optical Bell tests is that whatever property or properties are being jointly analyzed, and whatever values they might have wrt some specific value of the global measurement parameter, they are the same for each of the counter-propagating disturbances incident on a and b during any given emission-coincidence interval.

It also follows from this assumption that if the angular difference of the joint polarizer settings |a-b| = 0, then the results at A and B for this setting should be identical -- and we can deduce A given B, and vice versa.

3. I think that many useful explanatory schemes don't start out very rigorously. The application of Malus Law in Bell tests follows from its application in previous (to Bell tests) similar setups (or setups with similar features). The considerations and assumptions leading to its application are all grounded in the assumption that Nature is exclusively locally causal in line with SR.

The assumption of nonlocality wrt entangled photons is just a bit too convenient, imho -- and, it creates other problems while still not really explaining entanglement.

4. As far as I'm concerned there's nothing to discuss/debate wrt superdeterminism. I agree with you that it's a completely superfluous consideration.

 

[yoda jedi]

.....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...

 

[DrChinese]

...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...

Yes, this is a bit of a tricky area. First, Bell did write about his paper after the fact... and in some cases those words can be different than the original paper. So which is the proper reference? What do you make of an author's subsequent comments to an important paper like this?

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.

Lastly, I think Bell should be looked at like a road map. Once you can see where Bell journeyed, the path becomes so much clearer for those who follow. Once you see the internal inconsistency of a local realistic approach, you realize that something has to give.

 

[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?