I Do Bell Experiments Show Local Overlap of Wave Functions Before Measurement?

[Fra]

I'm not sure what you mean. Equation (2) in that paper is the locality assumption: the result $A$ does not depend on the settings $\vec{b}$ and vice versa. Other assumptions, including anything you might want to relate to "causality", are elsewhere in the paper.

Equation (2) contains the assumption of statistical independence, but it also contains more - the partition assumption. Ie. the assumption that it makes senses to partition the probability into an average over the outcome given by the hidden variable.

partition assumption
$$P(A,B |O_ {A}) = \sum_{\lambda} P(A,B|\lambda|O_ {A}) P(\lambda|O_ {A})$$

statistical independence
$$P(A,B |O_ {A}) = \sum_{\lambda} P(A|\lambda|O_ {A}) P(B|\lambda|O_ {A}) P(\lambda|O_ {A})$$
$$\sim \int_{\lambda} P(A|\lambda) P(B|\lambda) d \lambda$$

The partition assumption makes sense there the causal role of the hidden variable is of the simple "experimenter ignorance type", and compliant also to the old pool-table realism. But other causal mechanisms that still make use of hidden variables are still possible, I am thinking of those that can be thought of as subjective, but still real.

So all Bell theorem disproves is the "naive" ignorance type of HV mechanism.

/Fredrik

 

[Fra]

most probably one will have to find a way to quantum-theoretically describe the classical spacetime model as an emergent phenomenon.

Yes, I also think spacetime needs to be emergent in some sense, but one must not fool oneself and think that such an emergence can be phrased in terms of the same QM. The way it's done is to just embedd the 4D space into a larger space, or avoid curvature by embedding it into a larger space which is asymptotically flat. But you can not cheat like that and get around the core issue that the formalism depends on the very thing that is supposed to be emergent.

I think the QM formalism itself, needs to be more flexible and emergent itself, from a more general logic from QM itself also emerges.

/Fredrik

 

[PeterDonis]

partition assumption

What is $O_A$? It would help if you would use the same notation that the paper you quoted from uses.

 

[Fra]

Nothing in quantum theory explains what "force" acts on/causes distant Bob's B to change to a specific state based on a decision by distant Alice. QT does not "explain" this in a local manner, even though it predicts correctly.

I agree, this again is the key point of the discussion!

Here it's hard to avoid addressing the link between entanglement and the makeup of space I would say. Because locality can be thought of both with respect to regular 3D space and "information space". And with these thoughts, I think there are MORE possibilities to find explanations than the original "naive" forms of causal mechanisms involving HV, that are what Bell inequality describes.

/Fredrik

 

[Fra]

What is $O_A$? It would help if you would use the same notation that the paper you quoted from uses.

Sorry, $O_A$ is Observer-A (ie. Alice), $O_B$ is obsever-B (ie. Bob). I consider all probabilities conditional to the observer. Soem of the orignal notation grosses over this, this is what i decomposed the conditional probabilities to illustrated what i mean.

/Fredrik

 

[*now*]

Bell shows that the predictions of QT violate his inequalities, yes--of course that is easy to show. And therefore no "local realistic" model can reproduce the predictions of QT, since "local realistic" models will obey his inequalities.

this paper discusses a view that has been said to be “local and realistic” https://arxiv.org/pdf/1806.08150.pdf

 

[PeterDonis]

$O_A$ is Observer-A (ie. Alice), $O_B$ is obsever-B (ie. Bob).

Ok, so how does your notation match up with what's in the Bell paper you quoted? Again, it would help if you'd just use the same notation Bell does. As you state it I have no idea how what you say relates to what Bell said.

I consider all probabilities conditional to the observer. Soem of the orignal notation grosses over this, this is what i decomposed the conditional probabilities to illustrated what i mean.

This still doesn't help me to match up what you say with what Bell said.

 

[msumm21]

Explaining the Bell Inequality by expanding the particles to their full, shared wave function is not any kind of "loop hole". Quite the contrary, it demonstrates that the spatial extant of that wave function is part of the non-local "mechanism" that supports the accurate QM predictions.

I think I understand. I realize that calling the entangled pair local to one another (because the wave function overlaps) is a bit satisfying at first, but of course there's still something "nonlocal" in a sense to "spread the information around the wavefunction's spatial extent."

Local realism addresses the communication of information. In a strict (and inaccurate) sense, if we attempt to postulate that a piece of information resides solely at a point within a particle, that information could only be "presently" local to another particle if that other particle also included that point. Allowing a single copy of that information to be spatially distributed (occupying more than a point) is an immediate violation of local realism. Allowing multiple copies of that information doesn't violate local realism, but it also can't be used to explain Bells Inequality.

Since the "copies of information" would need to "spread around the spatial extent of the wave function" faster than speed of light, that's why it would still need to violate local realism, right? If so, makes sense to me, just want to ensure I understand what you said. Thanks!

 

[.Scott]

Since the "copies of information" would need to "spread around the spatial extent of the wave function" faster than speed of light, that's why it would still need to violate local realism, right? If so, makes sense to me, just want to ensure I understand what you said. Thanks!

Right!

 

[vanhees71]

I think I understand. I realize that calling the entangled pair local to one another (because the wave function overlaps) is a bit satisfying at first, but of course there's still something "nonlocal" in a sense to "spread the information around the wavefunction's spatial extent."

It doesn't make sense to say "the entangled pair [is] local to one another". Locality in the standard sense of the HEP community is what relativistic QFT builds into the description of particles, i.e., the Hamilton density of the theory commutes with any local observable for arguments of the corresponding operators that are spacelike separated. This implies that there cannot be any causal influence between events (in this case measurement events like detector clicks registering the one and the other particles at far-distant places).

There is indeed "something nonlocal", and that's the strong correlations between the outcome of measurements on entangled states at far-distant places, and this correlations are due to the preparation of the particles before (!) the measurement. Entangled states describe an "utmost quantum situation", where the two particles cannot be described as individual, separated entities, but only as the pair in -well- an entangled state. It's much more precise to call it "inseparability" (Einstein) rather than "non-locality", because locality is already a clear mathematical statement of properties of relativistic QFTs. Since the Bell tests are all describable within relativistic QFTs there's no contradiction between this sharp definition of "locality" and the "inseparability" demonstrated by these very Bell tests.

Since the "copies of information" would need to "spread around the spatial extent of the wave function" faster than speed of light, that's why it would still need to violate local realism, right? If so, makes sense to me, just want to ensure I understand what you said. Thanks!

The problem is what "realism" means here. My understanding of Bell's writings is that he defines it as the property that all observables always take determined values, which are unknown to us due to hidden variables, which we can describe only probabilistically. This together with "locality" (and I understand Bell as precisely meaning by locality the usual HEP definition; one must not forget that Bell not only did his now more famous work on the foundations of QT but also before brillant work in relativistic QFT, discovering among others the (chiral) anomaly in gauge theories) leads to the Bell inequality, which is violated by QT for entangled states and made it a scientifically testable question, whether "local realism" (EPR) or "Q(F)T" is right, and the result, maybe to the bewilderment of Bell himself, is in favor of Q(F)T, and this with an amazing significance and accuracy!

 

[Fra]

I'll try to explain...

This still doesn't help me to match up what you say with what Bell said.

My point is that I don't accept the equipartion assumption, which is rarely discussed, it's just uncritically "put in there", and it is part of the old legacy of the mechanical causal logic.

As I see it, there can be a hidden variable, $\lambda$ that is set when the entangled pair is created, and this explains the statistical correlation in without violating locality! So we have the explanation of correlations.

But howto escape the Bell inequality:

IMO (in my qbist inspired agent interpretation) it does not logically follow that the observations at say Alice detector, is a function of alice detector settings and $\lambda$. My argument is a combination of informationlocality of agent action and that an interaction is a resulting form an action and reaction. Informationlocality suggest that Alice's detectors rection to the incoming entangled particle must be independent on $\lambda$ as the entangled pair by construction is ISOLATED From everything until it hits the apparatous(which Alice has set as she wishes). So the apparatous REACTION of the incoming particle, follow the expectations - which is determined not by lambda, by by the preparation procedure where the entangled pair is created. EXACTLY how the action is determined by a systems expectations of it's environment, is technically an open question. I do not have the explicit math. But that is exactly what I expect from future research (it follows from my own interpretation and understanding of physical law and QM).

So that is in short why I think the equipartition assumption is wrong to start with. Equiparition assumption holds only for the most naive old style causal mechanisms. This is what i referred to as causal mechanisms. I guess one can also associate this with the "naive realism". As I entertain a form of "subjective HV", there is still a form of reality, but reality is relative, and this influences interactions. This type of mechanism is not ruled out by Bell.

/Fredrik

 

[DrChinese]

1. As I see it, there can be a hidden variable, $\lambda$ that is set when the entangled pair is created, and this explains the statistical correlation in without violating locality! So we have the explanation of correlations.

2. Information locality suggest that Alice's detectors rection to the incoming entangled particle must be independent on $\lambda$ as the entangled pair by construction is ISOLATED From everything until it hits the apparatous(which Alice has set as she wishes). So the apparatous REACTION of the incoming particle, follow the expectations - which is determined not by lambda, by by the preparation procedure where the entangled pair is created.

1. If correct, this is exactly what Bell demonstrates requires explicit nonlocal action. Why? Because there is no $\lambda$ dataset that yields the quantum expectation values unless you FIRST know how Alice plans to measure.

2. This is not a requirement of a Bell test. Bell tests do not require that entangled particles ever interact with each other, and they do not need to have ever existed in the same spacetime cone. They can be created from fully independent sources sufficiently distant that no signal can propagate between them.

https://arxiv.org/abs/0809.3991
Abstract: "Entanglement swapping allows to establish entanglement between independent particles that never interacted nor share any common past. ..."

Consequently, there are no hidden variables from a common source as you imagine, since there is no common source, nor point of contact between the particles that Alice and Bob observe.

 

[PeterDonis]

My point is that I don't accept the equipartion assumption, which is rarely discussed,

What is the "equipartition assumption"?

 

[vanhees71]

1. If correct, this is exactly what Bell demonstrates requires explicit nonlocal action. Why? Because there is no $\lambda$ dataset that yields the quantum expectation values unless you FIRST know how Alice plans to measure.

2. This is not a requirement of a Bell test. Bell tests do not require that entangled particles ever interact with each other, and they do not need to have ever existed in the same spacetime cone. They can be created from fully independent sources sufficiently distant that no signal can propagate between them.

https://arxiv.org/abs/0809.3991
Abstract: "Entanglement swapping allows to establish entanglement between independent particles that never interacted nor share any common past. ..."

Consequently, there are no hidden variables from a common source as you imagine, since there is no common source, nor point of contact between the particles that Alice and Bob observe.

Nevertheless all the interactions involved in the preparation are of course local. What's needed are the two entangled photon pairs, photons 1 and 2 as well as potons 3 and 4, both of which are created by parametric down conversion, i.e., local interactions of laser photons with the BBO crystals. The next perparation step is the filter measurement done with photons 2 and 3, which also are based on local interactions of the photons with the beam splitter BS and the polarizing beam splitters PBS. The resulting entanglement of photons 1 and 4 after selection based on the measurement on photons 2 and 3 are all due to local interactions of photons with the "equipment" needed to prepare the entanglement of photons 1 and 4 via entanglement swapping. Of course, indeed, the photons 1 and 4 themselves never interacted ever locally. Nevertheless that does not imply that the interactions used to prepare them were in any way contradicting the locality of interactions in standard QED.

 

[DrChinese]

Nevertheless all the interactions involved in the preparation are of course local. What's needed are the two entangled photon pairs, photons 1 and 2 as well as potons 3 and 4, both of which are created by parametric down conversion, i.e., local interactions of laser photons with the BBO crystals. The next perparation step is the filter measurement done with photons 2 and 3, which also are based on local interactions of the photons with the beam splitter BS and the polarizing beam splitters PBS. The resulting entanglement of photons 1 and 4 after selection based on the measurement on photons 2 and 3 are all due to local interactions of photons with the "equipment" needed to prepare the entanglement of photons 1 and 4 via entanglement swapping. Of course, indeed, the photons 1 and 4 themselves never interacted ever locally. Nevertheless that does not imply that the interactions used to prepare them were in any way contradicting the locality of interactions in standard QED.

I wish you would stop contradicting mainstream science on this subject, as we have discussed many times. I have provided may quotes in recent years from top scientists indicating the nonlocal nature of swapping - you are the lone voice contrary to them. Again I ask for a verbatim quote from a suitable reference that says swapping is merely local, and nothing nonlocal is occurring (contradicting the below quote).

Zeilinger et al: "Quantum teleportation strikingly underlines the peculiar features of the quantum world. We present an experimental proof of its quantum nature, teleporting [nonlocally] an entangled photon with such high quality that the nonlocal quantum correlations with its original partner photon are preserved. This procedure is also known as entanglement swapping. The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons that never interacted our results directly confirm the quantum nature of teleportation."

The entanglement swap can be performed anywhere at any time. The Bell test particles can be measured by Alice and Bob anywhere and at any time. (Those particles need not have ever co-existed! And they can even be entangled AFTER they are observed!)

There can be no local description of the entire experiment with these options, since Alice and Bob were never local to each other. So we could have:

1. Alice created at T=1 and observed at T=1.5.
2. Bob created at T=2.
3. Distant Bob observed at T=3 to have perfect correlations with Alice at any desired measurement setting.
4. At a later time, the entanglement of Bob with Alice is created (yes, this seems impossible but see my reference).

 

[martinbn]

2. This is not a requirement of a Bell test. Bell tests do not require that entangled particles ever interact with each other, and they do not need to have ever existed in the same spacetime cone. They can be created from fully independent sources sufficiently distant that no signal can propagate between them.

Not very important, but they are in common light cones.

 

[martinbn]

I wish you would stop contradicting mainstream science on this subject, as we have discussed many times.

He does not contradict the science. He only objects to the use of the term nonlocal.

 

[Fra]

1. If correct, this is exactly what Bell demonstrates requires explicit nonlocal action. Why? Because there is no $\lambda$ dataset that yields the quantum expectation values unless you FIRST know how Alice plans to measure.

My point was that I question the whole ansatz of that $\lambda$ determines the interaction statistics. IMHO I think the anzats is flawed so is no need for nonlocal actions. The detector is "informed" about the preparation (~$\psi$) only - not about $\lambda$, so at least in my interpretation the total interaction must account for the uncertatiny from preparation. So in my interpretation it's inconsistent that $\lambda$ alone can explain the interaction. The idea that lambda can explain this is built on the old ideas of how interactions work, and it's that THIS does not work that Bell IMO proves. But I supposed this is an interpretation as well.

/Fredrik

 

[PeterDonis]

I question the whole ansatz of that $\lambda$ determines the interaction statistics.

That ansatz was made by Bell for the very reason you yourself state:

The idea that lambda can explain this is built on the old ideas of how interactions work

Exactly. And:

it's that THIS does not work that Bell IMO proves.

Yes: Bell's Theorem proves that no model of the type Bell constructs using his ansatz can reproduce the predictions of QM, and also the experimental results, since those are consistent with the predictions of QM. You aren't proposing any alternative to Bell; you are simply agreeing with the implications of his theorem. What particular words you want to use to describe the class of models his ansatz covers is irrelevant.

 

[vanhees71]

I wish you would stop contradicting mainstream science on this subject, as we have discussed many times. I have provided may quotes in recent years from top scientists indicating the nonlocal nature of swapping - you are the lone voice contrary to them. Again I ask for a verbatim quote from a suitable reference that says swapping is merely local, and nothing nonlocal is occurring (contradicting the below quote).

Zeilinger et al: "Quantum teleportation strikingly underlines the peculiar features of the quantum world. We present an experimental proof of its quantum nature, teleporting [nonlocally] an entangled photon with such high quality that the nonlocal quantum correlations with its original partner photon are preserved. This procedure is also known as entanglement swapping. The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons that never interacted our results directly confirm the quantum nature of teleportation."

The entanglement swap can be performed anywhere at any time. The Bell test particles can be measured by Alice and Bob anywhere and at any time. (Those particles need not have ever co-existed! And they can even be entangled AFTER they are observed!)

There can be no local description of the entire experiment with these options, since Alice and Bob were never local to each other. So we could have:

1. Alice created at T=1 and observed at T=1.5.
2. Bob created at T=2.
3. Distant Bob observed at T=3 to have perfect correlations with Alice at any desired measurement setting.
4. At a later time, the entanglement of Bob with Alice is created (yes, this seems impossible but see my reference).

Nothing I said, contradicts, what's said by Zeilinger above. There are of course nonlocal correlations, described by entanglement, but there are nowhere nonlocal interactions needed to explain entanglement swapping or teleportation.

My view is very mainstream physics: According to relativistic QFT all the Bell-test experiments can be described correctly using a theory based on the assumption that there are no faster-than-light causal influences, which is achieved by making the interactions described by this class of QFTs strictly local (i.e., the Hamilton density is commuting with all local observables at space-like differences of their arguments).

I don't understand, what you describe by 1.-4. To which experimental setup do you refer and what are the time (?) stamps T?

 

[DrChinese]

1. Nothing I said, contradicts, what's said by Zeilinger above. There are of course nonlocal correlations, described by entanglement, but there are nowhere nonlocal interactions needed to explain entanglement swapping or teleportation.

My view is very mainstream physics: According to relativistic QFT all the Bell-test experiments can be described correctly using a theory based on the assumption that there are no faster-than-light causal influences, which is achieved by making the interactions described by this class of QFTs strictly local (i.e., the Hamilton density is commuting with all local observables at space-like differences of their arguments).

2. I don't understand, what you describe by 1.-4. To which experimental setup do you refer and what are the time (?) stamps T?

1. And for the Nth time: you quote yourself when addressing the fact that your view is not mainstream. Where is that quote? And please, something verbatim is called for - not one of your "read any book" references. If you are mainstream, why haven't I seen anything like that in the last 100+ recent papers I have read? I won't respond further to you until you supply a suitable quote supporting your position.

There *is* "something" occurring (quantum) nonlocally. No one knows the mechanism. If it was simply a matter of correlations, as you say, then everyone would agree and we wouldn't be discussing. However, teleportation is a nonlocal effect from start to finish.2. Bell test with entanglement swapping to create the entangled pair. Read my reference, post #62 for example. You know this perfectly well, but deny its significance. You cannot entangle particles that have never existed in a common spacetime cone without a nonlocal effect of some type.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

Update: Thread will remain closed as the OP question has been addressed and there is no point in wrangling over what the word "locality" means when there does not appear to be any dispute over the actual physics--what is actually observed in experiments and the theoretical, mathematical machinery that predicts it.