EPR and Non-Locality - For and Against

[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".

 

[Buzz Bloom]

I am not educated in QM, so this post is to ask a few questions related the the non-locality/entanglement controversy for which I am hoping for a simple answer.

As I understand an example of the entanglement part, what appears to two observers is two partcles having a combined propery that their spin directions are opposite. If there are two devices far apart, each positionsed to test spin with respect to the same axis direction. When each of these two particles arrive at its target device, its spin will be determined, and when both spins are determined it will be found that they have opposite spins.

Assume that there is a clock associated with each device, and the clock times are synchronized, so that the determination of each measured spin is associated with a specific time.

Assume the two devices are separated by a distance D, and that the two times related to the devices determining a spin value differ by a time T. Therefore this result might be interpreted as the the ealier spin determination influences the later spin determination and the influence traveled at a speed of D/T, and the configuration might well be that D/T > c.

I think I understand that the transmission of influence does not in any way permit an observer to predict the spin of the second particle before the particle arrives at its devise.

My question is the following. Does the influence from the location of one device determining a spin value and the second devise determining a spin value constitute a transmission of information? That is, is influence information? Also ,is this a controversial question?

If one defines the transmission of influence to NOT be a transmission of information, then no information has traveled faster than c. Would this mean that there is not any non-locality issue? If not, why not?

 

[PeterDonis]

Does the influence from the location of one device determining a spin value and the second devise determining a spin value constitute a transmission of information?

Not by any definition of "information" that I am aware of.

If one defines the transmission of influence to NOT be a transmission of information, then no information has traveled faster than c. Would this mean that there is not any non-locality issue?

As I have said umpteen times now in this thread, it depends on what you mean by "non-locality". There is not a single accepted meaning for that term. So questions like this do not have single well-defined answers.

 

[Dale]

Since we are going in circles this thread is closed. In the future, everyone please remember to be clear about what you mean by ambiguous terms