Local, non-realistic description of the EPR-Bohm experiment

[ueit]

I propose for your consideration the following version of this experiment:

We have a source, S that produce pairs of spin 1/2 entangled particles and two detectors, A and B that measure the spin of those particles. The detectors are oriented on the same direction, say X and they are fixed. As expected the measurement results will always be anti-correlated.

For the purpose of this discussion I define non-realism as the belief that the neither measured values nor some other property that determines those values exist prior to the measurement. A non-realist will state that there is nothing about the measured particles that determines the measured value of the spin.

Now, I am asking those that consider themselves non-realists how do they explain the observed results in a local way.

Thank you,

Andrei

 

[PeterDonis]

I am asking those that consider themselves non-realists how do they explain the observed results in a local way.

Why do you think they have to? Why does a non-realist have to believe in locality? (Btw, you haven't defined "local", and you should if you want your question to be well-defined.)

 

[ueit]

Why do you think they have to?

I don't think that. I only want to know if a non-realist can provide a logically coherent picture of this experiment, or, if not, to state that clearly.

Why does a non-realist have to believe in locality? (Btw, you haven't defined "local", and you should if you want your question to be well-defined.)

I didn't say that one cannot hold a non-local and non-realist view, but I am not particularly interested about it. It is also simple to come up with such an interpretation. For example, one can say that once a measurement is performed at A the wave function collapses instantly everywhere "producing" the corresponding anti-correlated result at B.

By locality I mean that no physical effect should propagate instantly, but it should be limited at the speed of light. The example above, involving a real, physical collapse is an example of a non-local theory.

 

[PeterDonis]

I only want to know if a non-realist can provide a logically coherent picture of this experiment

But you didn't ask for that--you asked for all that plus a local picture, which is a more restricted requirement. What if the only logically coherent picture that a non-realist can provide is non-local?

For example, one can say that once a measurement is performed at A the wave function collapses instantly everywhere "producing" the corresponding anti-correlated result at B.

I agree that this is non-local, but it also looks realist to me; it says that something real happens--the wave function collapse--that explains the correlations. Or, to put it another way, the only reason you would need to have something like "wave function collapse" to explain the correlations is if B had some state before the collapse, which the collapse could change to the anti-correlated state. A non-realist model, on your definition, has no need to invoke wave function collapse, or anything else, to "produce" the anti-correlated result at B, because there's nothing to produce, since nothing definite about B exists prior to B's measurement.

By locality I mean that no physical effect should propagate instantly, but it should be limited at the speed of light.

This looks like a well-specified definition, but consider two different models:

(1) Bell's local realistic model, in which "locality" means the statistics of measurements on A and B must factorize; in other words, schematically, we must have P(AB|ab) = P(A|a) P(B|b), where the capital letters represent measurement results and the lower case letters represent settings of the measuring devices.

(2) Quantum field theory, in which the key requirement is that measurements at spacelike separations must commute, i.e., their results cannot depend on the order in which they occur.

Are both of these models "local" by your definition? Bell's model doesn't talk about "propagation" of anything, and QFT, while it has things called "propagators", doesn't require that "nothing propagates faster than light", and in fact the propagators don't vanish for "faster than light" propagation (spacelike separated events)--the only condition is that operators at spacelike separations commute.

 

[ueit]

What if the only logically coherent picture that a non-realist can provide is non-local?

I think that would be a severe blow to non-realism, as many choose to reject realism exactly because they want to preserve locality.

I agree that this is non-local, but it also looks realist to me; it says that something real happens--the wave function collapse--that explains the correlations. Or, to put it another way, the only reason you would need to have something like "wave function collapse" to explain the correlations is if B had some state before the collapse, which the collapse could change to the anti-correlated state. A non-realist model, on your definition, has no need to invoke wave function collapse, or anything else, to "produce" the anti-correlated result at B, because there's nothing to produce, since nothing definite about B exists prior to B's measurement.

I disagree. There is no need to invoke a pre-existing value of B that needs to be changed to some other value by the collapse. One could simply say that there is no such property as spin prior to collapse and the measurement at A is responsible for the creation of both spins, at A and B.

It is true that such a picture is realist in regards to the existence of the wave-function but is not realist according to my definition of realism as it does not ascribe any value for the spins prior to the measurement.

This looks like a well-specified definition, but consider two different models:

(1) Bell's local realistic model, in which "locality" means the statistics of measurements on A and B must factorize; in other words, schematically, we must have P(AB|ab) = P(A|a) P(B|b), where the capital letters represent measurement results and the lower case letters represent settings of the measuring devices.

(2) Quantum field theory, in which the key requirement is that measurements at spacelike separations must commute, i.e., their results cannot depend on the order in which they occur.

Are both of these models "local" by your definition? Bell's model doesn't talk about "propagation" of anything, and QFT, while it has things called "propagators", doesn't require that "nothing propagates faster than light", and in fact the propagators don't vanish for "faster than light" propagation (spacelike separated events)--the only condition is that operators at spacelike separations commute.

In my opinion the first example says nothing about locality as I understand it, but more about the interaction between the systems A and B. The second example, again could refer to a theory that is local, but also non-local. It depends on the specific interpretation one holds. So, in conclusion, neither example is necessarily local by my definition, but it could be if further details are provided.

 

[DrChinese]

I think that would be a severe blow to non-realism, as many choose to reject realism exactly because they want to preserve locality.

This is a severe misunderstanding of the local non-realist viewpoint. Regardless of your preferred interpretation, it should be noted that:

1. There are no non-local effects that are not traceable via diagrams where c is respected. (Such diagrams, however, will have arrows in both time directions, implying time symmetry, certainly a reasonable concept.) So locality is maintained because of experiment, not because someone prefers locality over non-locality.

2. The heart of Bell's Theorem is that pre-existing well-defined values for counterfactual measurements don't agree with theory (and experiment). That's essentially saying that we don't live in a realistic world.

The out for that, of course, is the existence of a heretofore unknown non-local mechanism that otherwise does not express itself. So do you wonder why someone would be skeptical of that?

 

[ueit]

This is a severe misunderstanding of the local non-realist viewpoint.

The line you quoted was a reply to what Peter Donis said:

What if the only logically coherent picture that a non-realist can provide is non-local?

I suppose you agree that if non-realistic theories must necessarily be non-local this would be a serious problem especialy in light of your first point:

locality is maintained because of experiment

That being said I did not claim that the non-realistic theories must be non-local and the purpose of this thread was to learn about such local and non-realistic theories. Maybe you can help me with that.

The heart of Bell's Theorem is that pre-existing well-defined values for counterfactual measurements don't agree with theory (and experiment). That's essentially saying that we don't live in a realistic world.

I have a different view of that, but, even if I grant you that we don't live in a realistic world it is still interesting to explore the remaining, non-realist theories. You are invited to present your own preferred theory and give a short description of what happens, in your opinion, in the experiment described in my OP.

 

[DrChinese]

You are invited to present your own preferred theory and give a short description of what happens, in your opinion, in the experiment described in my OP.

Since no one knows the details of a physical mechanism, anything I say will be speculative.

You are quite capable of reading about the various interpretations which are local non-realistic: MWI, Time Symmetric, Retrocausal, etc. In all of them, there is some kind of dependence on the observer's role. I.e. we live in an observer-dependent world. There is no real point in yet another debate on these, as Bell compliant interpretations are considered viable and a matter of personal preference.

 

[Demystifier]

I propose for your consideration the following version of this experiment:

We have a source, S that produce pairs of spin 1/2 entangled particles and two detectors, A and B that measure the spin of those particles. The detectors are oriented on the same direction, say X and they are fixed. As expected the measurement results will always be anti-correlated.

For the purpose of this discussion I define non-realism as the belief that the neither measured values nor some other property that determines those values exist prior to the measurement. A non-realist will state that there is nothing about the measured particles that determines the measured value of the spin.

Now, I am asking those that consider themselves non-realists how do they explain the observed results in a local way.

Thank you,

Andrei

My attempt to take local non-realism seriously led me to a sort of solipsism:
https://arxiv.org/abs/1112.2034

Another attempt, in which I wanted to make local non-realism look reasonable (which excludes solipsism), led me to a soft version of it in Sec. 2.2 of
https://arxiv.org/abs/1703.08341

For other alternatives to non-locality, see also Sec. 5.3 of the latter paper above.

 

[ueit]

Since no one knows the details of a physical mechanism, anything I say will be speculative.

If you don't know the details how do you know the theory is local?

You are quite capable of reading about the various interpretations which are local non-realistic: MWI, Time Symmetric, Retrocausal, etc. In all of them, there is some kind of dependence on the observer's role. I.e. we live in an observer-dependent world.

Can you please pick your favorite theory and show, in a few words that it is able to provide a local description of the proposed experiment? For example the locality of MWI seems questionable to me. The first measurement creates two branches and this splitting seems to act instantaneously everywhere. The second measurement is different than the first as it will not produce another split, etc.

There is no real point in yet another debate on these, as Bell compliant interpretations are considered viable and a matter of personal preference.

I think it is, because Bell theorem only allow for the possibility of local, non-realistic theories, it does not guarantee that they actually exist. Even if they exist, one should see what their implications are, and if those implications are not worse than, say, the non-locality implied by de Broglie-Bohm interpretation. For example, while I would agree with you that non-locality seems unlikely given the experimental data we have, retrocausality doesn't seem much more likely.

 

[ueit]

Another attempt, in which I wanted to make local non-realism look reasonable (which excludes solipsism), led me to a soft version of it in Sec. 2.2 of

https://arxiv.org/abs/1703.08341

In the paper you say:

In short, “local non-reality” should mean: Reality is non-local, but physics is about the measurable, which is local.

Can you apply this idea to the proposed experiment? What are the elements which are part of physics and how do they act to produce the observed results?

 

[Demystifier]

Can you apply this idea to the proposed experiment? What are the elements which are part of physics and how do they act to produce the observed results?

According to such a view of QM (which by no means is the only possible view), it is not the aim of physics to say how the observed results are produced. Therefore your question does not have a physical answer within such a view of QM. With such a view of QM, dealing with questions like that belongs to meta-physics (which I don't mean in a derogatory sense), rather than physics.

 

[DrChinese]

If you don't know the details how do you know the theory is local?...retrocausality doesn't seem much more likely.

The likelihood is not relevant here. You asked, here is the answer: In some non-realistic local theories, the connection between elements of an experimental setup occur at light speed. Take for example entanglement-swapping setups (I can provide references upon request). In those, entanglement can be made to occur such that particles are entangled that have never coexisted. You can also alter the parameters of the same setup so that the entangled state is created after detection of the entangled particles. In all of these setups, it is easy to see that the connection between the 2 entangled particles is traced at c and is not instantaneous.

However, the connections are not clearly forward in time. What mechanism supports this, I can't and don't purport to explain. I am not trying to sell anybody on anything, just pointing out that this makes as much sense (or as little) as any other accepted interpretation. A well-defined example of a theory which describes the above in much more detail is Relational BlockWorld (which considers itself to be acausal rather than retrocausal).

In the International Journal of Quantum Foundations:
http://www.ijqf.org/wps/wp-content/uploads/2015/06/IJQF2015v1n3p2.pdf

 

[ueit]

According to such a view of QM (which by no means is the only possible view), it is not the aim of physics to say how the observed results are produced.

But it should, at the very least, be able to represent the experiment mathematically so that the experimental results can be compared with the theories' prediction. It should include the particle pair (as this is the system QM's postulates refer to), it should be able to represent the state of that system and predict what results are expected. You cannot claim for example that the quantum system does not exist (because it wasn't measured at the source) and yet claim that it has a state and evolves according to Schrödinger equation. And, by the way, the state cannot be measured either. So I'm afraid that the view you are proposing is simply unusable as a theory of physics.

 

[Demystifier]

But it should, at the very least, be able to represent the experiment mathematically so that the experimental results can be compared with the theories' prediction. It should include the particle pair (as this is the system QM's postulates refer to), it should be able to represent the state of that system and predict what results are expected. You cannot claim for example that the quantum system does not exist (because it wasn't measured at the source) and yet claim that it has a state and evolves according to Schrödinger equation. And, by the way, the state cannot be measured either. So I'm afraid that the view you are proposing is simply unusable as a theory of physics.

To see how states represent experiment mathematically, see e.g.
A. Peres, Quantum Theory: Concepts and Methods
But as stressed in this book, "Quantum phenomena do not occur in a Hilbert space, they occur in a laboratory."
In other words, in such a view of QM, the mathematical objects of QM only represent the observable stuff. Sure, I cannot say that quantum system doesn't exist because I haven't measured it. But I can say, in such a view of QM, that quantum formalism doesn't represent objects which cannot be measured. You may devise another formalism (dBB theory perhaps) which represents objects irrespective of measurement, but that's not a subject of physics (understood in a narrow positivist sense).

 

[ueit]

The likelihood is not relevant here. You asked, here is the answer: In some non-realistic local theories, the connection between elements of an experimental setup occur at light speed. Take for example entanglement-swapping setups (I can provide references upon request). In those, entanglement can be made to occur such that particles are entangled that have never coexisted. You can also alter the parameters of the same setup so that the entangled state is created after detection of the entangled particles. In all of these setups, it is easy to see that the connection between the 2 entangled particles is traced at c and is not instantaneous.

However, the connections are not clearly forward in time. What mechanism supports this, I can't and don't purport to explain. I am not trying to sell anybody on anything, just pointing out that this makes as much sense (or as little) as any other accepted interpretation. A well-defined example of a theory which describes the above in much more detail is Relational BlockWorld (which considers itself to be acausal rather than retrocausal).

In the International Journal of Quantum Foundations:
http://www.ijqf.org/wps/wp-content/uploads/2015/06/IJQF2015v1n3p2.pdf

It seems to me that the Relational BlockWorld interpretation is a strict deterministic and realistic theory. True, the particles do not exist as fundamental entities but they are a manifestation of spacetime geometry. It looks like a realistic hidden-variable theory. It also seems to have some implications you vigorously denied, like the non-existence of free-choice. Could you please elaborate on that?

I would also appreciate if you could explain how is this theory explaining the experiment proposed in the OP.

 

[ueit]

To see how states represent experiment mathematically, see e.g.
A. Peres, Quantum Theory: Concepts and Methods
But as stressed in this book, "Quantum phenomena do not occur in a Hilbert space, they occur in a laboratory."
In other words, in such a view of QM, the mathematical objects of QM only represent the observable stuff. Sure, I cannot say that quantum system doesn't exist because I haven't measured it. But I can say, in such a view of QM, that quantum formalism doesn't represent objects which cannot be measured. You may devise another formalism (dBB theory perhaps) which represents objects irrespective of measurement, but that's not a subject of physics (understood in a narrow positivist sense).

Let me try to sketch an argument so that my question becomes better defined.

The experiment I proposed reveals that there is a perfect anti correlation between the measurements at A and B. There are in my opinion three possible ways to make sense of this:

1. There is no cause for the correlations. They have to be taken as brute-facts.

I consider that such a view shouldn't be taken seriously. It implies the same amount of fine-tuning just like the naive view of superdeterminism. The only difference is that the fine-tunning of the initial conditions is replaced to a perpetual fine-tuning of the present.

2. The measurment at A determines the result at B.

This implies non-locality

3. There is a common cause in the past that determines both the results at A and B.

This is the hidden-variable approach. Probably MWI can also be included here, as the wave-function itself produces all possible results in a deterministic way. The randomness is just a result of our inability "see" the big picture.

I am interested if you agree with this argument and, if you do, where is the place of local-non-realistic theories.

Thanks!

 

[DrChinese]

It seems to me that the Relational BlockWorld interpretation is a strict deterministic and realistic theory. True, the particles do not exist as fundamental entities but they are a manifestation of spacetime geometry. It looks like a realistic hidden-variable theory. It also seems to have some implications you vigorously denied, like the non-existence of free-choice. Could you please elaborate on that?

I wouldn't agree with your assessment as deterministic. Try looking at this link, maybe it is more clear:

http://philsci-archive.pitt.edu/3247/1/RBW_FPP_2007.pdf

 

[ueit]

I wouldn't agree with your assessment as deterministic. Try looking at this link, maybe it is more clear:

http://philsci-archive.pitt.edu/3247/1/RBW_FPP_2007.pdf

At page 9 of that document it says:

the entire experimental EPR set-up, its past, present and future, and the spacetime symmetries of that set-up are all just ‘there’—no one could really perform some alternative measurement on the other wing of the experiment without changing the entire spatiotemporal description of the experiment.

It is not deterministic in the classical sense, as the "state" at a future moment cannot be computed from the present state (the authors consider their theory acausal) but the future is still predetermined. There is no choice, no randomness. So, I wouldn't call such a theory non-deterministic either.

But the main issue is not determinism, but realism. This theory is a hidden-variable theory, so it is not a valid example of a non-realistic local one. This is made clear at page 8:

According to the account developed here, we offer a deflation of the measurement problem with a novel form of a hidden-variables “statistical interpretation.”

 

[DrChinese]

It is not deterministic in the classical sense, as the "state" at a future moment cannot be computed from the present state (the authors consider their theory acausal) but the future is still predetermined. There is no choice, no randomness. So, I wouldn't call such a theory non-deterministic either.

But the main issue is not determinism, but realism. This theory is a hidden-variable theory, so it is not a valid example of a non-realistic local one. This is made clear at page 8:

Your concept of "realistic" is flawed, to start with. A realistic theory is one in which the observer does NOT participate in the outcome, i.e. reality is not shaped by the observer. It is also one in which counterfactual measurements have as much relevance/definition as ones actually performed.

In RBW, there are no hidden variables that determine the outcome in individual quantum events. It is still based on a density matrix. RBW is an example of a non-realistic ("acausal") local interpretation of QM in which past, present and future all participate in determination of the quantum context. There are no non-local effects in this view, and really the authors of the theory can say it better than I. Stuckey et al, 2007:

... We introduce a purely geometric (acausal and adynamical) account of non-relativistic quantum mechanics (QM) called Relational Blockworld. The ontology of this interpretation is one in which constructive objects (entities such as particles or waves with worldlines in spacetime) are not fundamental constituents of reality. Rather, constructive objects are composed of spatiotemporal relations and physical phenomena are described by the distribution of spatiotemporal relations throughout space and time as a whole, i.e., in the blockworld. This represents a radical departure from physics per the dynamical perspective, e.g., particles of force exchanged by particles of matter to explain phenomena.

We justify this new worldview by outlining a result obtained independently by Kaiser [2], Bohr & Ulfbeck [3] and Anandan [4] which shows the Heisenberg commutation relations of QM follow from the relativity of simultaneity in the limit of the Poincaré group. We believe this legitimizes the use of a blockworld for the ontology of non-relativisitic quantum mechanics. That relations, rather than objects/substances with world lines, are fundamental in the blockworld is justified by the work of Bohr, Mottleson & Ulfbeck [5] who showed that the QM density matrix can be obtained from the spacetime symmetry group of the experimental configuration alone. We also outline their result herein. In order to emphasize that no thing propagates through the space between source and detector to cause an experimental “click,” we relate QM to relativistic quantum field theory (RQFT) per RBW and explain the twin-slit experiment. Per our ontology, the continuous distribution of oscillators in space (the field) per RQFT is replaced by a discrete, rarified distribution of RQFT “sources” alone (one at the experimental source, one at each slit, and one at the detector in the twin-slit experiment). The transition amplitude relating these discretely distributed RQFT sources and oscillators then provides QM’s familiar wave function giving rise to the twin-slit interference pattern per the Born rule.

We conclude by using RBW to resolve the standard conceptual problems of QM, i.e., entanglement, non-locality and the measurement problem. An important consequence of this resolution is that we do not have to compromise relativity theory. Quite the contrary, per RBW the most vexingimplication of special relativity – the lack of a moving Now due to the relativity of simultaneity (to which Einstein was“painfully resigned” [6]) – is also responsible for QM’s “only mystery” (per Feynman [7]), i.e., quantum interference. The trick is to appreciate that everything resides in a4D spacetime and nowhere else, and quantum phenomena cannot be modeled with worldlines if one is to do justice to its non-commutativestructure. Thus while clicks indetectors are perfectly classical events, the clicks are not evidence of constructivequantum entities such as particles or wave s with worldlines. Rather, the clicks are manifestations of spacetime relationsdistributed among the elements of the experimental configuration per the space time symmetries. Such acausal, globaldetermination relations do not respect any common cause principle. This fact shouldnot bother anyone who has truly transcended the idea that the dynamical or causalperspective is the most fundamental one.

 

[Demystifier]

Let me try to sketch an argument so that my question becomes better defined.

The experiment I proposed reveals that there is a perfect anti correlation between the measurements at A and B. There are in my opinion three possible ways to make sense of this:

1. There is no cause for the correlations. They have to be taken as brute-facts.

I consider that such a view shouldn't be taken seriously. It implies the same amount of fine-tuning just like the naive view of superdeterminism. The only difference is that the fine-tunning of the initial conditions is replaced to a perpetual fine-tuning of the present.

2. The measurment at A determines the result at B.

This implies non-locality

3. There is a common cause in the past that determines both the results at A and B.

This is the hidden-variable approach. Probably MWI can also be included here, as the wave-function itself produces all possible results in a deterministic way. The randomness is just a result of our inability "see" the big picture.

I am interested if you agree with this argument and, if you do, where is the place of local-non-realistic theories.

Thanks!

You probably think that the above possibilities are all possibilities that exist. But in making such a conclusion you make several tacit assumptions. For instance, you tacitly assume that nature must be either local or non-local as if there is no third possibility, that backward causation is excluded, that standard logic is valid and that solipsism is excluded. Yet all these assumptions can be relaxed, which leads to various alternatives to non-locality as discussed in Sec. 5.3 of https://arxiv.org/abs/1703.08341.

Anyway, concerning local non-reality, there is a place for it within your option 1 (whether you take it seriously or not), as well as within a solipsistic approach mentioned in the reference above.

 

[DrChinese]

There are in my opinion three possible ways to make sense of this:

1. There is no cause for the correlations. They have to be taken as brute-facts.

I consider that such a view shouldn't be taken seriously. It implies the same amount of fine-tuning just like the naive view of superdeterminism. The only difference is that the fine-tunning of the initial conditions is replaced to a perpetual fine-tuning of the present.

2. The measurment at A determines the result at B.

This implies non-locality

3. There is a common cause in the past that determines both the results at A and B.

This is the hidden-variable approach.

Number 3. is ruled out by Bell's Theorem. Number 1 would not explain why quantum predictions are accurate. And the one you are asking about in the OP, local non-realistic, is omitted. As I have mentioned, in that one the observer is a participant in the quantum context (the totality of the interaction).

 

[morrobay]

https://www.physicsforums.com/threa...entanglement-and-nonlocality-comments.864726/

See post @ # 12 by @vanhees71 It seems this could qualify for a local non realistic model :
Non realistic since particles at A or B, in superposition, do not have definite spin values until measured.

 

[ueit]

Your concept of "realistic" is flawed, to start with.

The title of the first paper you linked reads:

"Relational blockworld: Providing a realist psi-epistemic account of quantum mechanics"

So, it seems, even the inventors of the theory didn't get realism right. Anyway, I have defined what I mean by realism and you didn't complain till now.

A realistic theory is one in which the observer does NOT participate in the outcome, i.e. reality is not shaped by the observer.

Can you point out where in those papers it is shown that "reality is shaped by the observer? Or better, just describe the OP experiment in terms of this theory so I can get a better feeling of what the explanation of the observed correlations is.

It is also one in which counterfactual measurements have as much relevance/definition as ones actually performed.

I disagree. No deterministic theory allows for counterfactuals because the future is completely determined. Any alternative future is meaningless.

In RBW, there are no hidden variables that determine the outcome in individual quantum events. It is still based on a density matrix.

It seems to me that the spacetime geometry does play the role of a hidden variable. But if not, can you explain what is the source of the correlations?

 

[ueit]

You probably think that the above possibilities are all possibilities that exist. But in making such a conclusion you make several tacit assumptions. For instance, you tacitly assume that nature must be either local or non-local as if there is no third possibility

Given my definition of locality:

"no physical effect should propagate instantly, but it should be limited at the speed of light"

I don't see what other possibility remains. An effect can either propagate slower than or equal to the speed of light, or at some higher speed. The law of the excluded middle precludes any other option.

[QUOTE...that backward causation is excluded[/QUOTE]

As far as I know backward causation is no different than non-locality. If A sends a signal back in time at T0 and B receives the signal also at T0 from the past it means that A sent an instant signal to B.

[QUOTE...that standard logic is valid[/QUOTE]

Standard logic is necessary for any meaningful discussion. If I say that X is not the same as X or that the truth of X implies X is false what can you understand?

[QUOTE...and that solipsism is excluded.[/QUOTE]

I tend to see solipsism just like the computer-simulation world hypothesis as being a kind of hidden-variable approach. Both results, at A and B are caused by a past event (a process in the mind or in the computer). Depending on the details of the theory one can still place it in the local or non-local camp.

Yet all these assumptions can be relaxed, which leads to various alternatives to non-locality as discussed in Sec. 5.3 of https://arxiv.org/abs/1703.08341.

I'll place the alternatives to non-locality you give at page 8-9 as follows:

1.Copenhagen local non-reality - no cause for the correlations - my option 1 (fine tuning).
2.Many worlds - I disagree that this theory cannot be described as local or non-local. Depending on how the branching is supposed to occur it might be local or non-local.
3.Super-determinism - I disagree it implies fine-tuning, but I think it's better not to discuss it here.
4.Backward causation - I think it is just non-locality with a different name.
5.Consistent histories - I think this is the most interesting approach. I disagree that it denies logic. It just does not let you to mix propositions that are not part of the same framework. I'll try to re-read Omnès' book to get a better understanding.
6.Solipsistic hidden variables - we agree on this, but the theory is realistic.

Anyway, concerning local non-reality, there is a place for it within your option 1 (whether you take it seriously or not), as well as within a solipsistic approach mentioned in the reference above.

This is also my opinion, but I am not sure that solipsism = non-realism.

 

[DrChinese]

1. Can you point out where in those papers it is shown that "reality is shaped by the observer? Or better, just describe the OP experiment in terms of this theory so I can get a better feeling of what the explanation of the observed correlations is.

2. I disagree. No deterministic theory allows for counterfactuals because the future is completely determined. Any alternative future is meaningless.

3. It seems to me that the spacetime geometry does play the role of a hidden variable. But if not, can you explain what is the source of the correlations?

You sit outside the mainstream in your use of language.

1. In a non-realistic interpretation, Alice and Bob shape the reality we experience, even if located far apart in spacetime. In the EPR paper, this corresponds to the statement: "...This makes the reality of P and Q depend upon the process of measurement carried out on the first system, which does not disturb the second system in any way. No reasonable definition of reality could be expected to permit this." Of course, they rejected the non-realistic viewpoint out of hand.

In Relational BlockWorld, for instance, the "block" includes the observer(s) in the future. In a sense, the block describes a spacetime "slice" that can interact. The speed of light c restricts the spacio-temporal extent of that slice. Because the observer is part of the block, the observer shapes the results - but not single-handed.

2. This is a complete fail on your description of "deterministic". For example: Relativity is deterministic, and yet counterfactual measurements are well-defined (and compatible with actual measurements). Not so in QM, as Bell's Theorem showed us.

3. The correlations are a result of a quantum context. For your setup, that context includes: the source, the intervening apparatus, and both observers. Due to Bell's Theorem, this context is essentially required in pretty much any interpretation. The difference between interpretations is how those components fit together and interact.

 

[ueit]

Number 3. is ruled out by Bell's Theorem. Number 1 would not explain why quantum predictions are accurate. And the one you are asking about in the OP, local non-realistic, is omitted. As I have mentioned, in that one the observer is a participant in the quantum context (the totality of the interaction).

I didn't omit local-non-realism. The argument covers in my opinion all logical possibilities. If local non-realism does not fit anywhere it means that no such a theory exist. If you thing the argument is not valid just point out the flaw.

 

[DrChinese]

I didn't omit local-non-realism. The argument covers in my opinion all logical possibilities. If local non-realism does not fit anywhere it means that no such a theory exist. If you thin[k] the argument is not valid just point out the flaw.

Demystifier and I have been pointing out the flaws from the moment this thread was started. You ignore them.

Your above comments confirm what I have been suspecting: you started this thread to advance your personal opinions. You and I and others have debated these endlessly in the past. You lay out your opinions and ask folks to knock them down. You know that's not how it works here. The focus is discussion of mainstream science.

I have provided references to a published local non-realistic theory. I have repeatedly described how such interpretations work in broad terms (a subjective/contextual reality dependent on participation of the observer). This answers your question in the OP. So I am bowing out of further discussion as it is pointless. The thread has played itself out, and is now going in circles.

 

[zonde]

I didn't omit local-non-realism. The argument covers in my opinion all logical possibilities. If local non-realism does not fit anywhere it means that no such a theory exist. If you thing the argument is not valid just point out the flaw.

Your argument does not cover all logical possibilities, just all the scientific ones (the first one is called "coincidence").
There is possibility that measurement records are not factual i.e. they are somehow subjective. That's on the side of non scientific possibilities.

 

[ueit]

Demystifier and I have been pointing out the flaws from the moment this thread was started. You ignore them.

That's not true. Demystifier had some well-defined objections to my argument and I did try to address them all in the post #25. These are not very simple issues and, of course, I might be wrong, but to say that I "ignore" the counterarguments is a lie.

On the other hand your objection, that "I left out local non-realism" shows that in fact you didn't understand the argument.

Your above comments confirm what I have been suspecting: you started this thread to advance your personal opinions. You and I and others have debated these endlessly in the past. You lay out your opinions and ask folks to knock them down. You know that's not how it works here. The focus is discussion of mainstream science.

I don't know about you, but this is the first time I bring into discussion local non-realism. Presumably, local non-realism is the mainstream position on QM so I find your objection completely unjustified.

I have provided references to a published local non-realistic theory.

No, you did not. You have provide references to a theory that is described by their authors as a realist, hidden-variables approach. Let me quote again, this time from the abstract:

Abstract:
We update our Relational Blockworld (RBW) explanation of quantum physics and argue that it provides a realist psi-epistemic account of quantum mechanics as called for by Leifer. RBW accomplishes this by employing discrete graphical amalgams of space, time and sources (“spacetimesource elements”) and an adynamical global constraint as „hidden variables‟ that avoid the need for counterfactual definiteness in a realist account.

Your personal view of this theory goes against those papers so I advice you to first write to the authors, explain them the mistakes, and convince them to re-publish their work in a language more suited to your interests.

I have repeatedly described how such interpretations work in broad terms (a subjective/contextual reality dependent on participation of the observer). This answers your question in the OP.

My question was for you to show how the correlations in the EPR-Bohm experiment arise in this theory, not to explain in "broad-terms" your personal view of non-realism. It is quite obvious that you are unable to do that.

So I am bowing out of further discussion as it is pointless. The thread has played itself out, and is now going in circles.

Thanks for your contribution anyway!

 

[ueit]

https://www.physicsforums.com/threa...entanglement-and-nonlocality-comments.864726/

See post @ # 12 by @vanhees71 It seems this could qualify for a local non realistic model :
Non realistic since particles at A or B, in superposition, do not have definite spin values until measured.

I agree this account is non-realistic but it is not local (or at least not obviously so) according to the way I defined the term. That post explains that no faster-than light communication is possible, but this is also true in Bohm's interpretation even if the theory is non-local.

In the post you linked it is accepted that A and B will get anti-correlated results but no cause is given for this fact. So, either vanhees believes there is no cause (in which case the theory is indeed local, but fine-tuned) - my option 1 or, if there is a cause, we are not told about it.

 

[ueit]

Your argument does not cover all logical possibilities, just all the scientific ones (the first one is called "coincidence").
There is possibility that measurement records are not factual i.e. they are somehow subjective. That's on the side of non scientific possibilities.

I think that most non-realists would disagree with you that this subjectivity is non-scientiffic. Some claim that this is in fact the deep implication of QM. Sure, I disagree with this.

But even if we accept this subjectivity, a theory still has to provide some sort of explanation (why some observer experiences a result and not some other result). So far I have not seen such a well-defined account.

 

[morrobay]

I agree this account is non-realistic but it is not local (or at least not obviously so) according to the way I defined the term. That post explains that no faster-than light communication is possible, but this is also true in Bohm's interpretation even if the theory is non-local.

In the post you linked it is accepted that A and B will get anti-correlated results but no cause is given for this fact. So, either vanhees believes there is no cause (in which case the theory is indeed local, but fine-tuned) - my option 1 or, if there is a cause, we are not told about it.

The cause is given in post #9 same reference, again by @vanhees71 partial quote:

There is no action at a distance related to entanglement, but it's described by states of systems that are not localized and thus observations of far distant parts of the system can be correlated, but this correlation is due to the preparation of the state long before any measurement on the partial systems is done." ...
https://www.physicsforums.com/threa...entanglement-and-nonlocality-comments.864726/

 

[ueit]

The cause is given in post #9 same reference, again by @vanhees71 partial quote:

There is no action at a distance related to entanglement, but it's described by states of systems that are not localized and thus observations of far distant parts of the system can be correlated, but this correlation is due to the preparation of the state long before any measurement on the partial systems is done." ...
https://www.physicsforums.com/threa...entanglement-and-nonlocality-comments.864726/

It seems to me that the system preparation being the cause of the correlations is just postulated. The theory does not provide any link between the system preparation and the actual results. The non-localized state does not contain enough information to determine the results. And if you cannot determine the results how can you determine a correlation between them?