EPR and Non-Locality - For and Against

[RUTA]

It can be valid in a relativistic model with a hidden preferred frame. So, it is only in conflict with a particular interpretation of relativity, which forbids, for some metaphysical reasons, a hidden preferred frame. Such a conflict with relativistic metaphysics does not change QT in its minimal interpretation.

That is my understanding, too. Relativity of simultaneity in SR does not rule out a preferred frame. Nor does SR rule out superluminal causation. Indeed, some particle theorists have postulated the existence of tachyons. One reason people claim that SR is incompatible with superluminal causation is that they demand causes precede effects and subscribe to no preferred reference frame. Those two assumptions/preferences then rule out a causal connection between spacelike separated events.

 

[RUTA]

Thanks RUTA, I had read your insight article and as much as I understood it, it was very interesting, but I don't quite understand it to the level of seeing how it refutes the challenge of incompleteness.

I'm talking about a specific attribute of "anti-realist" interpretations of the mathematics, which says that the mathematics is simply a tool which makes predictions about the outcomes of experiments. If this is the case, then the mathematics does not describe the system prior to its interaction with the measurement device, which would render it an incomplete description of nature.

The argument is simply that if you believe time dilation and length contraction are "completely" explained by the light postulate (NPRF applied to the speed of light c), then you should believe that violations of the Bell inequality to the Tsirelson bound are "completely" explained by "conservation per NPRF" (NPRF applied to Planck's constant h). Both the light postulate and the Bell state correlations are based in NPRF, they just involve two different constants, c and h. So, clearly, this argument fails for those who still seek "constructive efforts" to explain time dilation and length contraction

The power of principle explanation is summed up nicely by the quote I just today added to the Insight from Pauli (reference in the Insight):

Understanding nature surely means taking a close look at its connections, being certain of its inner workings. Such knowledge cannot be gained by understanding an isolated phenomenon or a single group of phenomena, even if one discovers some order in them. It comes from the recognition that a wealth of experimental facts are interconnected and can therefore be reduced to a common principle. In that case, certainty rests precisely on this wealth of facts. The danger of making mistakes is the smaller, the richer and more complex the phenomena are, and the simpler is the common principle to which they can all be brought back. ... The ability to predict is often the consequence of understanding, of having the right concepts, but is not identical with 'understanding'.

But, this is just personal preference.

 

[Lynch101]

The argument is simply that if you believe time dilation and length contraction are "completely" explained by the light postulate (NPRF applied to the speed of light c), then you should believe that violations of the Bell inequality to the Tsirelson bound are "completely" explained by "conservation per NPRF" (NPRF applied to Planck's constant h). Both the light postulate and the Bell state correlations are based in NPRF, they just involve two different constants, c and h. So, clearly, this argument fails for those who still seek "constructive efforts" to explain time dilation and length contraction

Ah, OK. I had understood that point in the insights article then. I just wasn't sure if there was something I was missing.

Leaving relativity aside for the moment, I don't think that point addresses the fundamental issue relating to anti-realist interpretations of QFT, that if the mathematics of QFT only describe/predict the [classical level] observable outcomes of experiments then, by necessity, this would render it an incomplete description of nature because it doesn't describe the system prior to its interaction with the measurement device.

The power of principle explanation is summed up nicely by the quote I just today added to the Insight from Pauli (reference in the Insight):

Einstein's thoughts on the difference between constructivist and principled explanations are also worth noting. Emphasis is my own.

When we say that we have succeeded in understanding a group of natural processes, we invariably mean that a constructive theory has been found which covers the processes in question.
...
The advantages of the constructive theory are completeness, adaptability, and clearness, those of the principle theory are logical perfection and security of the foundations. The theory of relativity belongs to the latter class.

 

[PeterDonis]

this is true in the minimal interpretation

No, it isn't. The minimal interpretation does not say Bob's description of his particle changes when Alice makes her measurement. It only says it changes when Bob makes his measurement.

What you are calling "the minimal interpretation" is your personal preference, not the minimal interpretation.

It can be valid in a relativistic model with a hidden preferred frame.

That's certainly not the minimal interpretation either. The minimal interpretation of QFT has no preferred frame, since that would be additional structure added that does not affect any predictions and therefore gets scraped right off by Occam's razor.

 

[RUTA]

Leaving relativity aside for the moment, I don't think that point addresses the fundamental issue relating to anti-realist interpretations of QFT, that if the mathematics of QFT only describe/predict the [classical level] observable outcomes of experiments then, by necessity, this would render it an incomplete description of nature because it doesn't describe the system prior to its interaction with the measurement device.

Einstein's thoughts on the difference between constructivist and principled explanations are also worth noting. Emphasis is my own.

Yes, those who still advocate for a constructive account of SR provide many Einstein quotes showing his support for a "completion" of SR, i.e., a constructive account of SR. And, yes, there is little doubt that in the EPR paper he is advocating for a constructive account of Bell state entanglement, i.e., it is "incomplete" without a constructive account. The question is, what would Einstein say today about the situation?

Today, we know that the same principle (NPRF) accounts for time dilation and length contraction in SR and Bell state entanglement and the Tsirelson bound in QM. And, 65 years after his death, we still have no accepted constructive accounts of these "mysteries." Keep in mind he knew nothing of the Bell inequality and its experimental violation by the Bell spin states.

Personally, I advocate for the explanatory power of principle explanation only because of my view that physics is concerned with providing constraints on experience, as explained in this 2020 Entropy paper. Since that deals with consciousness studies, i.e., it's beyond physics, I don't expound on that in PF. Essentially, this redefines what it means to provide a constructive account, so it is not "anti-realist".

 

[bhobba]

No, this is true in the minimal interpretation,

What interpretation is that? I know a few I would describe as minimalist eg Bayesian and Ensemble. I would not call Copenhagen minimalist since there are various versions. I maintain discussion of issues like the papers I started this thread with is best done using a stated interpretation so it does not devolve into a quagmire of unidentified assumptions.

The minimal interpretation does not contain any notion of space,

Hmmm. How do you take a partial derivative wrt to x,y and z as per the Schrödinger's equation without the concept of space? In fact it would play havoc with Wigner's Theorem.

So, it is only in conflict with a particular interpretation of relativity, which forbids, for some metaphysical reasons, a hidden preferred frame. Such a conflict with relativistic metaphysics does not change QT in its minimal interpretation.

The modern view of relativity as space time geometry does not forbid a preferred frame - it merely says it is superfluous as far as the laws of physics are concerned. It's in the statement of the POR which is the laws of physics are the same in any inertial frame. If there was a preferred frame then its 'wind' would be frame dependent. If the POR is true, this 'wind' can not affect the laws of physics. If it has no affect on that why have it in the first place ie it is superfluous. Those that want a preferred frame seem to want it for philosophical not physical reasons.

Thanks
Bill

 

[PeterDonis]

What interpretation is that?

PF's consensus presentation of the minimal interpretation is here:

https://www.physicsforums.com/insights/the-7-basic-rules-of-quantum-mechanics/

Postulate 7 is the one most relevant to this discussion. It needs to be read carefully, particularly the phrase "successive, non-destructive projective measurements"; Alice's and Bob's spacelike separated measurements in the scenario under discussion are not "successive, non-destructive projective measurements" under this postulate.

 

[Lynch101]

The question is, what would Einstein say today about the situation?

It would certainly be interesting to find out.

65 years after his death, we still have no accepted constructive accounts of these "mysteries."

And there might be a fundamental limit on how far we can probe nature, meaning that such a complete description of nature, as explains these "mysteries", simply is not possible.

Essentially, this redefines what it means to provide a constructive account, so it is not "anti-realist".

Apologies, I keep coming back to this point but I think it is key to the question of completeness - and this only really applies to "anti-realist"/instrumentalist interpretations of QFT: if the mathematics is only a computational tool which calculates predictions for the observable outcomes of experiments then it does not, by necessity, describe the state prior to its interaction with the measurement device. If does not describe the system prior to this, then it cannot be a complete description of nature.

I may not be understanding your position, however. Are you saying that the interpretation you are advocating does not treat the mathematics purely instrumentally?

 

[bhobba]

I'm talking about a specific attribute of "anti-realist" interpretations of the mathematics, which says that the mathematics is simply a tool which makes predictions about the outcomes of experiments.

I would describe that as realist. I would describe anti-realist as a view like Wittgenstein's where he thinks it is about nothing. Turing took him to task on that one - saying bridges would fall over etc if it wasn't true. But either way this is not a subject we discuss as it really is philosophy. We simply think of mathematics as part of models. It s the models that are true or false - what the math is we leave open.

Thanks
Bill

 

[bhobba]

PF's consensus presentation of the minimal interpretation is here:

I should have remembered that. Sticking to that certainly makes things easier to discuss.

Thanks
Bill

 

[Lynch101]

I would describe that as realist. I would describe anti-realist as a view like Wittgenstein's where he thinks it is about nothing. Turing took him to task on that one - saying bridges would fall over etc if it wasn't true. But either way this is not a subject we discuss as it really is philosophy. We simply think of mathematics as part of models. It s the models that are true or false - what the math is we leave open.

Thanks
Bill

Thanks Bill. I'm using the term "anti-realist" in the sense it was explained in this thread on anti-realist interpretations of QM. As it was explained there, the "anti-realist" interpretation is not anti-realist in the strict philosophical sense of being juxtaposed with realism, rather it says that the mathematical elements of the theory don't correspond to elements of reality. This might be contrasted with naiive instrumentalism which is agnostic on the question of whether or not the mathematics represents an underlying ontology.

In this sense of "anti-realism", the mathematics of QFT are taken to be nothing but a tool to calculate the predictions for the outcomes of experiments. That is, they only tell us the probability of a particle registering on a classical level measurement device. Such anti-realist interpretations would, by necessity, be incomplete descriptions of nature because they don't describe the system prior to its interaction with the measurement device.

To my untrained eye, it appears that this is where some people are talking at cross purposes in this thread. On one hand, there are those who are arguing that QM does not necessitate non-locality because QFT is a local theory, by construction. It doesn't appear as though this particular point is being disputed.

The issue appears to arise when people call for an explanation of the correlations observed in experiments. This, to my mind, appears to be a slightly different question which is being conflated with the question, does QM necessitate non-locality? A more accurate question might be, does nature necessitate non-locality?

It appears that QM doesn't necessitate non-locality because QFT is local, but QFT doesn't appear to be a complete description of nature. Any attempt at a more complete description of nature appears to necessitate non-locality.

At least, that is how I have read the arguments in this thread.

 

[PeterDonis]

It appears that QM doesn't necessitate non-locality because QFT is local

As has already been pointed out multiple times (the first time was me, way, way back in post #2 of this thread--it would be really nice if people would read it before blithely using the term "nonlocality"), this depends on what you mean by "nonlocality".

QFT says that spacelike separated measurements commute; it is "local" in this sense.

QFT also predicts violations of the Bell inequalities; it is "nonlocal" in this sense.

Any attempt at a more complete description of nature appears to necessitate non-locality.

Again, it depends on what you mean by "nonlocality". See above.

Also, both of the statements that QFT agrees with, above, are experimental facts; so any more complete description of nature must still agree with them.

 

[Lynch101]

As has already been pointed out multiple times (the first time was me, way, way back in post #2 of this thread--it would be really nice if people would read it before blithely using the term "nonlocality"), this depends on what you mean by "nonlocality".

QFT says that spacelike separated measurements commute; it is "local" in this sense.

QFT also predicts violations of the Bell inequalities; it is "nonlocal" in this sense.

Again, it depends on what you mean by "nonlocality". See above.

From my reading of it, it isn't simply the predicted violations of Bell inequalities that render the theory non-local, it is the attempted explanation of a mechanism to account for the observed correlations which appears to necessitate non-locality, in the sense that a measurement performed in one location has an instantaneous effect in a spatially separated location.

"Anti-realist" interpretations of QFT don't seem to attempt to explain how or why the observed correlations deviate from the predictions of classical physics, they simply predict that they will. But, such anti-realist interpretations appear to be incomplete descriptions of nature. The attempted explanations, as opposed to the simple predictions, of the observed correlations appear to require some form of FTL influences - but not of the sort that can be used to transmit signals.

Again, this is where it appears to me that people are talking past each other. While QM/QFT might not necessitate non-locality, of the sort @DrChinese appears to be advocating, nature herself might.

Lee Smolin talks about this in Time Reborn (p.142)

As long as we’re just checking the predictions of quantum mechanics at the level of statistics, we don’t have to ask how the correlations were actually established. It is only when we seek to describe how information is transmitted within each entangled pair that we need a notion of instantaneous communication. It’s only when we seek to go beyond the statistical predictions of quantum theory to a hidden-variables theory that we come into conflict with the relativity of simultaneity.

This means giving up the relativity of simultaneity and embracing its opposite: that there is a preferred global notion of time. Remarkably, this does not require overthrowing relativity theory; it turns out that a reformulation of it is enough. The heart of the resolution is a new and deeper way of understanding general relativity theory which reveals a new conception of real time.

 

[RUTA]

Apologies, I keep coming back to this point but I think it is key to the question of completeness - and this only really applies to "anti-realist"/instrumentalist interpretations of QFT: if the mathematics is only a computational tool which calculates predictions for the observable outcomes of experiments then it does not, by necessity, describe the state prior to its interaction with the measurement device. If does not describe the system prior to this, then it cannot be a complete description of nature.

I may not be understanding your position, however. Are you saying that the interpretation you are advocating does not treat the mathematics purely instrumentally?

Once you understand reality per neutral monism (as in our Entropy paper) with physics providing the constraints on experience, fundamental explanation is not rooted in causal mechanisms. Certainly some principles/constraints have corresponding causal mechanisms, e.g., Fermat's principle has Snell's law, but since causal mechanisms are not fundamental, it's perfectly ok that some principles/constraints do not have corresponding causal mechanisms. Consequently, time dilation and length contraction are explained fundamentally by NPRF, just like Bell state entanglement and the Tsirelson bound, without any corresponding causal mechanisms (no ether, no superluminal signals, etc.). Once you have the most fundamental principles/constraints on experience, you have a complete understanding of reality according to this ontology. That's not instrumentalism, because we have provided an ontology. It's just an ontology rooted in principles/constraints rather than causal mechanisms. We wrote an entire book arguing for this type of ontology (Beyond the Dynamical Universe), but the Entropy paper is a sufficient summary

 

[RUTA]

To summarize again, Bell state entanglement does not entail that QT is incomplete or inconsistent with SR. As we argue in our book, papers, and Insights, the many "mysteries" of modern physics don't indicate a need to "fix" it. While modern physics is certainly not finished, what exists of it now can be seen as beautifully comprehensive and coherent with the appropriate view of physics.

 

[PeterDonis]

it isn't simply the predicted violations of Bell inequalities that render the theory non-local

Did you even read my post? Did you go back and read post #2 in the thread?

The term "non-local" does not have a single unique meaning. It means different things to different people.

"Violates the Bell inequalities" is one of the multiple meanings this term has been used to denote. So to say that violations of the Bell inequalities don't render the theory non-local is meaningless; it could be true or false, depending on what you decide "non-local" means.

So the best thing to do is to not use the term at all in this discussion.

 

[Jimster41]

QFT says that spacelike separated measurements commute; it is "local" in this sense.

QFT also predicts violations of the Bell inequalities; it is "nonlocal" in this sense.

Do like all of them commute? If so, is it pair-wise, n-wise, all-n-wise? Or only ones Alice and Bob set up real careful?

 

[PeterDonis]

Do like all of them commute?

In QFT, any measurement operators at spacelike separated events commute.

 

[Morbert]

"Anti-realist" interpretations of QFT don't seem to attempt to explain how or why the observed correlations deviate from the predictions of classical physics, they simply predict that they will. But, such anti-realist interpretations appear to be incomplete descriptions of nature. The attempted explanations, as opposed to the simple predictions, of the observed correlations appear to require some form of FTL influences - but not of the sort that can be used to transmit signals.

Lee Smolin talks about this in Time Reborn (p.142)

It is only when we seek to describe how information is transmitted within each entangled pair that we need a notion of instantaneous communication.

Anti-realists would not grant Smolin the implicit assumption he is making. He is assuming the system consists of a pair of spacelike separated divisible objects. If this is what the system really is, then quantum theory is incomplete in the sense you describe. But that is not necessarily what the system really is.

Asher Peres makes a subtle point in his book "Quantum Theory: Methods and Concepts": Quantum theory is universal insofar as it can describe the physics of any system, but it does not offer a single closed description of every system. By this, he means the application of quantum theory to any system (e.g. one the scientist wishes to observe) is only meaningful in the context of an ancillary "exophysical" system to which the theory is not applied (e.g. the scientist). If this is the character of physical descriptions of nature, then quantum theory is complete insofar as there is no physics it does not account for. If you insist on a closed ontic account of nature, then quantum theory is incomplete. But you should also justify this insistence.

 

[Lynch101]

Did you even read my post? Did you go back and read post #2 in the thread?

The term "non-local" does not have a single unique meaning. It means different things to different people.

I did, but I thought it was pretty clear which meaning @DrChinese and Lee Smolin were referring to, and therefore the meaning I was referencing.

"Violates the Bell inequalities" is one of the multiple meanings this term has been used to denote. So to say that violations of the Bell inequalities don't render the theory non-local is meaningless; it could be true or false, depending on what you decide "non-local" means.

There is a pretty obvious connection between the definition of non-local as involving instantaneous (or FTL) influences and the definition of non-local as "Violates the Bell inequalities". The former is the attempt to explain the latter and/or the latter is evidence of the former. This might lead us to suspect that there is a slight misappropriation of the term "non-local" when trying to define it as "Violates the Bell inequalities".

To try to elaborate: We have the experimental evidence of violations of Bell inequalities and know that these go against the predictions of classical physics. If we then try to explain how these violations of Bell inequalities occur and the answer we arrive at is: there must be some sort of instantaneous (or FTL) influence occurring, whereby a measurement in location A has an instantaneous effect at location B (which is spatially separated). This means that actions, such as measurements, don't simply exert influence in their locality at a maximum speed of c. This instantaneous (or FTL) influence we refer to as non-local - to contrast it with the idea that actions can only exert influence in their locality at a maximum speed of c.

To then suggest that "non-locality" is just another name for the violations of Bell inequalities seems to conflate the effect with the cause or the observed phenomenon with the attempt to explain how the observed phenomenon is possible, given that it goes against classical physics.

Do the other definitions of "non-local" share a similar connection?

So the best thing to do is to not use the term at all in this discussion.

Or, it might be worth exploring which term was first in use, which one offers the most explanatory power, and whether or not there are connections between the different definitions, as above, which can be delineated.

 

[Lynch101]

Once you understand reality per neutral monism (as in our Entropy paper) with physics providing the constraints on experience, fundamental explanation is not rooted in causal mechanisms. Certainly some principles/constraints have corresponding causal mechanisms, e.g., Fermat's principle has Snell's law, but since causal mechanisms are not fundamental, it's perfectly ok that some principles/constraints do not have corresponding causal mechanisms. Consequently, time dilation and length contraction are explained fundamentally by NPRF, just like Bell state entanglement and the Tsirelson bound, without any corresponding causal mechanisms (no ether, no superluminal signals, etc.). Once you have the most fundamental principles/constraints on experience, you have a complete understanding of reality according to this ontology. That's not instrumentalism, because we have provided an ontology. It's just an ontology rooted in principles/constraints rather than causal mechanisms. We wrote an entire book arguing for this type of ontology (Beyond the Dynamical Universe), but the Entropy paper is a sufficient summary

Thanks RUTA, I am interested in the idea of monism, so I'll certainly start by checking out the paper.

We might be talking at cross purposes here because I am only talking about anti-realist/instrumental interpretations of QM i.e. those interpretations which say that the mathematics ONLY allows us to predict the observable outcomes of experiments i.e. the probability that a particle will register at a particular measurement device. These interpretations would be incomplete descriptions of nature for the reasons mentioned, they don't describe the system prior to its interaction with the measurement device.

Does the interpretation you are proposing describe the system prior to measurement?

 

[Lynch101]

Anti-realists would not grant Smolin the implicit assumption he is making. He is assuming the system consists of a pair of spacelike separated divisible objects. If this is what the system really is, then quantum theory is incomplete in the sense you describe. But that is not necessarily what the system really is.

But, if we don't grant Smolin his assumptions and we are left with the mathematical framework which only predicts the probability of a particle registering on a particular measurement device, then we are left without a description of the system prior to its interaction with the instrument, which would mean we have an incomplete description of nature.

Are there attempted explanations of the observed correlations which don't necessitate non-locality (in the FTL sense)? I've encountered the idea in multiple places that, in order to explain the violations of Bell inequalities we must give up one or more of the following:
1) Locality (in the FTL sense)
2) Realism (in the strict philsophical sense)
3) Local realism
4) Free Will

Is that accurate?

By this, he means the application of quantum theory to any system (e.g. one the scientist wishes to observe) is only meaningful in the context of an ancillary "exophysical" system to which the theory is not applied (e.g. the scientist). If this is the character of physical descriptions of nature, then quantum theory is complete insofar as there is no physics it does not account for. If you insist on a closed ontic account of nature, then quantum theory is incomplete. But you should also justify this insistence.

Apologies, there might be a nuance in there that I'm not quite picking up on because I don't quite follow how it would address the point I've been making.

I'm not sure if I'm insisting on a closed ontic account of nature, or not, genuinely. I just know that the point I am making is fairly rudimentary: if a theory [or interpretation of that theory] only makes predictions about what will be observed when a system interacts with a measurement device, then it doesn't describe the system prior to that interaction. As a result of not describing the system prior to its interaction with the measurement device, it could not be considered a complete description of nature.

To me, that would seem like a reasonable justification (well, if it were formulated to be a justification that is.)

 

[Morbert]

But, if we don't grant Smolin his assumptions and we are left with the mathematical framework which only predicts the probability of a particle registering on a particular measurement device, then we are left without a description of the system prior to its interaction with the instrument, which would mean we have an incomplete description of nature.

I'm not sure if I'm insisting on a closed ontic account of nature, or not, genuinely. I just know that the point I am making is fairly rudimentary: if a theory [or interpretation of that theory] only makes predictions about what will be observed when a system interacts with a measurement device, then it doesn't describe the system prior to that interaction. As a result of not describing the system prior to its interaction with the measurement device, it could not be considered a complete description of nature.

The anti-realist position maintains that quantum theory produces a description of the physical system both prior to measurement and after measurement, and both of these descriptions are on equal footing, physically and ontologically. The spin of a particle is equally real or not real whether or not the particle is described with the state $|\psi\rangle = |\uparrow\rangle+|\downarrow\rangle$ or with the state $|\psi\rangle = |\uparrow\rangle$, and hence the collapse of a wavefunction after measurement does not render the spin of a particle any more or less real than it was before measurement. Should these descriptions be in terms of a primitive ontology, or in terms of records that can be generated in ancillary systems that might interact with the system? Smolin would insist on the former. But it's not a very compelling insistence.

Are there attempted explanations of the observed correlations which don't necessitate non-locality (in the FTL sense)? I've encountered the idea in multiple places that, in order to explain the violations of Bell inequalities we must give up one or more of the following:
1) Locality (in the FTL sense)
2) Realism (in the strict philsophical sense)
3) Local realism
4) Free Will

Is that accurate?

If we

i) Reject the premise that a quantity refers to an element of reality if we can predict with absolute certainty the experimental outcome associated with that quantity
ii) Interpret quantities in terms of experimental records and their likelihoods/expectations, and hence do not attempt to simultaneously model complementary quantities/mutually exclusive experiments

then the correlations follow naturally from quantum theory without any violation of the principle of local causes.

[edited first paragraph to make it clearer]

 

[RUTA]

We might be talking at cross purposes here because I am only talking about anti-realist/instrumental interpretations of QM i.e. those interpretations which say that the mathematics ONLY allows us to predict the observable outcomes of experiments i.e. the probability that a particle will register at a particular measurement device. These interpretations would be incomplete descriptions of nature for the reasons mentioned, they don't describe the system prior to its interaction with the measurement device.

Does the interpretation you are proposing describe the system prior to measurement?

Ah, yes, I see where what I've said so far does not answer your question per se. You need to read Section 3 of the Entropy paper, specifically Section 3.2.1. Quantum-Classical Contextuality. Therein you will see that the only objects of physical reality that exist are those that are interacting with everything else in physical reality. Since the QM systems you are talking about are not interacting with anything until they are measured (they're "screened off"), there is nothing in physical reality corresponding to them and consequently nothing to describe prior to interaction with the measurement device.

 

[PeterDonis]

I thought it was pretty clear which meaning @DrChinese and Lee Smolin were referring to, and therefore the meaning I was referencing.

Nobody is arguing about whether QM/QFT "requires nonlocality" in the specific sense of violating the Bell inequalities. Everybody agrees that it does. So a statement like this...

It appears that QM doesn't necessitate non-locality because QFT is local, but QFT doesn't appear to be a complete description of nature. Any attempt at a more complete description of nature appears to necessitate non-locality.

...is nonsense if by "non-locality" you meant "violation of Bell inequalities". You don't need a "more complete description of nature" to predict violations of the Bell inequalities. QM/QFT already do that just fine. So you could not possibly have been clear in your own mind about what you meant by "non-locality", since if you had been you would never have made this nonsensical statement.

You see why I keep saying it would be better if people would just not use the term "non-locality" at all? People confuse not just others, but even themselves, with it.

 

[PeterDonis]

There is a pretty obvious connection between the definition of non-local as involving instantaneous (or FTL) influences and the definition of non-local as "Violates the Bell inequalities". The former is the attempt to explain the latter and/or the latter is evidence of the former. This might lead us to suspect that there is a slight misappropriation of the term "non-local" when trying to define it as "Violates the Bell inequalities".

To try to elaborate: We have the experimental evidence of violations of Bell inequalities and know that these go against the predictions of classical physics. If we then try to explain how these violations of Bell inequalities occur and the answer we arrive at is: there must be some sort of instantaneous (or FTL) influence occurring, whereby a measurement in location A has an instantaneous effect at location B (which is spatially separated). This means that actions, such as measurements, don't simply exert influence in their locality at a maximum speed of c. This instantaneous (or FTL) influence we refer to as non-local - to contrast it with the idea that actions can only exert influence in their locality at a maximum speed of c.

To then suggest that "non-locality" is just another name for the violations of Bell inequalities seems to conflate the effect with the cause or the observed phenomenon with the attempt to explain how the observed phenomenon is possible, given that it goes against classical physics.

Now you're contradicting yourself. First you say that you are using "non-locality" the way @DrChinese and Lee Smolin meant it. The way they meant it is "violations of the Bell inequalities".

Then you argue that that very same meaning of "non-locality" doesn't make sense and shouldn't be used.

Wouldn't it be better to just drop the term "non-locality" altogether? All it's doing is confusing you and making you contradict yourself.

 

[PeterDonis]

it might be worth exploring which term was first in use, which one offers the most explanatory power, and whether or not there are connections between the different definitions, as above, which can be delineated.

Or we could just drop the term "non-locality" altogether, since it is not helping the situation, and just talk about, for example, what connections there might be between, say, violations of the Bell inequalities and the fact that spacelike separated measurements commute. Wouldn't that be clearer and less confusing?

 

[Lynch101]

Or we could just drop the term "non-locality" altogether, since it is not helping the situation, and just talk about, for example, what connections there might be between, say, violations of the Bell inequalities and the fact that spacelike separated measurements commute. Wouldn't that be clearer and less confusing?

I'm inclined to think that simply dropping the redundant definition of the term would be easier.

EDIT: It would also clear up the confusion that it creates.

 

[PeterDonis]

I'm inclined to think that simply dropping the redundant definition of the term would be easier.

Good luck with that, since there is not general agreement on which definition is "redundant".

 

[PeterDonis]

simply dropping the redundant definition

Also, as I pointed out in post #146, you're using the term yourself in contradictory ways, so it's not clear what definition you think is "redundant".