Is Superdeterminism a Plausible Explanation for Quantum Mechanics?

[facenian]

After this discussion here are two conclusions:
1. The paper is not very interesting because it relies on superdeterminism
2. The authors issue a wrong statement when saying that double slit experiments can be interpreted as an statistical effect.

Thank you guys!

 

[DrChinese]

This is not correct. You may want to check Bell's "The theory of local beables ". Here he explains the concept of local causality and draws a nice picture(fig.3) where the common causes responsable for the correlations are seen to lie in the overlap region of their past light cones. This is how the correlations are supposed to be locally explained by the hidden variables.

Sorry, you are mistaken (excepting of course that all experiments on Earth can be said to exist in a common light cone.

The reason is that the experiment I cited is NOT causally constructed like most Bell tests. The cited experiment had never been performed while Bell was alive, not sure it had even been conceived at that time. There have now been many experiments in which entanglement occurs without any causal contact between the entangled particles. So it makes no sense to construct a paper around an explanation of entanglement that ignores experiments such as what I cited. They have basically ignored decades of experimental work.

 

[DrChinese]

After this discussion here are two conclusions:
1. The paper is not very interesting because it relies on superdeterminism
2. The authors issue a wrong statement when saying that double slit experiments can be interpreted as an statistical effect.

Thank you guys!

1. Assuming everyone agrees the OP article is intended as a superdeterministic explanation of Bell, I would call such a paper a scientific sham. IMHO there's no science hiding there.

 

[morrobay]

Well from this complete paper by the authors : https://arxiv.org/abs/1605.0849T3
They are intending a deterministic explanation for the correlations:" In our view non - local correlations emerge from a deterministic evolution of a shared hidden variable between two components of the ontological pair. And this also agrees with @A. Neumaier and his definition of Extended causality: *
"Joint properties of an extended object depend only on the union of the closed past light cones of their constituent parts and can influence only the union of the closed future cones of their constituent parts."
* Can this definition of Extended causality apply to space like separated experiments ?

 

[facenian]

The reason is that the experiment I cited is NOT causally constructed like most Bell tests. The cited experiment had never been performed while Bell was alive, not sure it had even been conceived at that time. There have now been many experiments in which entanglement occurs without any causal contact between the entangled particles. So it makes no sense to construct a paper around an explanation of entanglement that ignores experiments such as what I cited. They have basically ignored decades of experimental work.

Sorry but I'm suspicious about your assertion. I agree that the precicion to test Bell theorem has been increasing with time, however you are saying that the basic concept of entanglement that Einstein and Bell were talking about has become obsolete rendering Bell's proofs inaplicable.
Since I'm not an expert I can not tell but I would like hear some other opinion on this point.

 

[DrChinese]

Sorry but I'm suspicious about your assertion. I agree that the precicion to test Bell theorem has been increasing with time, however you are saying that the basic concept of entanglement that Einstein and Bell were talking about has become obsolete rendering Bell's proofs inaplicable.

Nothing about Bell's Theorem has changed or diminished in the slightest. If you think that's what I am saying, please reconsider. What you were quoting is something else written by Bell about a specific type of Bell test. Bell tests have advanced greatly since to eliminate even more "loopholes". Some of those loopholes are detection/fair sampling and locality, which are simultaneously eliminated in this test. Also, and relevant to the OP's claims:

"Our experiment already excludes all models that predict that the random inputs are determined a maximum of 690 ns before we record them..."

That is in addition to the fact that Alice and Bob are not in causal contact. So there are no shared local variables related to the particles being measured. And the measurement settings themselves are determined independently by Alice and Bob a very short time before their measurements, far too short to have been communicated from one to the other.

That's quite a lot of physics for even a superdeterministic hypothesis to overcome.

 

[stevendaryl]

Here's a question for Dr. Chinese, who is more familiar with these tests of entanglement. The usual way that a Bells-Theorem-violating twin pair is produced is something like the figure below:

There is some kind of decay process that produces an entangled particle/antiparticle. (I drew it as a photon decaying into an electron/positron pair, which actually isn't possible, but maybe you could substitute a $\pi_0$ meson to make it plausible. How the particles are produced are not important for this discussion.)

Now, let's vary the experiment by producing 4 particles, as shown in this figure:

In this figure, we produce two sets of correlated pairs. The question then is: Is there something that can be done to the two particles in the box--some kind of measurement maybe--that forces the remaining two particles to be entangled? Maybe if you measure the total spin of the two particles in the box, and find them to have total spin zero, then that will force the other particles to be anti-correlated?

If an experiment like this were possible, then it would be a way to produce entangled particles that have no common past. That would seem to be an even simpler argument against local hidden variables than Bell's theorem--the correlations can't possibly be explained in terms of local hidden variables if they never met in the past to share that hidden variable.

 

[DrChinese]

And this also agrees with @A. Neumaier and his definition of Extended causality: *
"Joint properties of an extended object depend only on the union of the closed past light cones of their constituent parts and can influence only the union of the closed future cones of their constituent parts."

Entangled quantum objects need not have a common past light cone, nor a common future light cone. This can be seen by the existence of entangled pairs where the sub-components have never co-existed at any point in time.

The point to recognize here is that the technology today has advanced so far that the old ways of looking at entangled pairs is outmoded. Formerly, entangled pairs arose from a common source. That provided us an easy to picture model of entanglement which is intuitive (to some degree). Everything apparently moves forward in time:

(Future)
Alice: V :Bob
(Past)

However, entangled pairs can be created from fully independent sources as well. I.e. 2 lasers in different spatiotemporal regions. Those objects are then entangled via entanglement swapping at a third spacetime point. This is done in such a way as the spacetime cones of the swapping components is also independent. In fact this can be done after the other particles no longer exist, just to drive the point home.

Now, if you choose to define the extended object as being the region defined by ALL of its components at all times they exist, then the definition above is fine. However, the resulting causal diagram has arrows in BOTH directions of time. It looks something like (Chris would be in the middle, not labeled below):

(Future)
Alice: W :Bob
(Past)

Having those arrows going both ways in time is a problem for most people. So define it as you see fit.

 

[DrChinese]

Here's a question for Dr. Chinese, who is more familiar with these tests of entanglement. The usual way that a Bells-Theorem-violating twin pair is produced is something like the figure below:

View attachment 220547

There is some kind of decay process that produces an entangled particle/antiparticle. (I drew it as a photon decaying into an electron/positron pair, which actually isn't possible, but maybe you could substitute a $\pi_0$ meson to make it plausible. How the particles are produced are not important for this discussion.)

Now, let's vary the experiment by producing 4 particles, as shown in this figure:

View attachment 220548

In this figure, we produce two sets of correlated pairs. The question then is: Is there something that can be done to the two particles in the box--some kind of measurement maybe--that forces the remaining two particles to be entangled? Maybe if you measure the total spin of the two particles in the box, and find them to have total spin zero, then that will force the other particles to be anti-correlated?

If an experiment like this were possible, then it would be a way to produce entangled particles that have no common past. That would seem to be an even simpler argument against local hidden variables than Bell's theorem--the correlations can't possibly be explained in terms of local hidden variables if they never met in the past to share that hidden variable.

Ha, I just posted something like your diagram, except yours is much better...

 

[DrChinese]

Here's a question for Dr. Chinese, who is more familiar with these tests of entanglement. The usual way that a Bells-Theorem-violating twin pair is produced is something like the figure below:
...

In this figure, we produce two sets of correlated pairs. The question then is: Is there something that can be done to the two particles in the box--some kind of measurement maybe--that forces the remaining two particles to be entangled? Maybe if you measure the total spin of the two particles in the box, and find them to have total spin zero, then that will force the other particles to be anti-correlated?

If an experiment like this were possible, then it would be a way to produce entangled particles that have no common past. That would seem to be an even simpler argument against local hidden variables than Bell's theorem--the correlations can't possibly be explained in terms of local hidden variables if they never met in the past to share that hidden variable.

And the answer is a big YES.

Inside the box, you perform what is referred to as a Bell State Measurement (BSM). Some of these project Alice and Bob into an entangled state. When that happens, Alice and Bob are perfectly correlated* AS IF they were the pair originally entangled. That is called entanglement swapping.

https://arxiv.org/abs/quant-ph/0201134
https://arxiv.org/abs/0809.3991

So this is what I have been referring to in some of my prior posts. Of course, "conspiracy" theories will evolve even under these scientific challenges. However, the resulting (super)deterministic quantum theories becomes (laughably ) untenable with these scenarios. If someone were to postulate a specific way they worked, it could easily be falsified.

*Or anti-correlated, depending on the result of the BSM. Note that the BSM results are themselves random.

 

[stevendaryl]

And the answer is a big YES.

Inside the box, you perform what is referred to as a Bell State Measurement (BSM). Some of these project Alice and Bob into an entangled state. When that happens, Alice and Bob are perfectly correlated* AS IF they were the pair originally entangled. That is called entanglement swapping.

https://arxiv.org/abs/quant-ph/0201134
https://arxiv.org/abs/0809.3991*Or anti-correlated, depending on the result of the BSM. Note that the BSM results are themselves random.

Good. Then as I said, in some sense, it seems that Bell's inequality is almost unnecessary to demonstrate the impossibility of a local hidden-variables theory that could explain the correlations, since is there is no way for the entangled particles to acquire a common hidden variable.

 

[rubi]

The question then is: Is there something that can be done to the two particles in the box--some kind of measurement maybe--that forces the remaining two particles to be entangled?

The Hilbert space of the full system is of the form $\mathcal H = \mathcal H_1 \otimes \mathcal H_2 \otimes \mathcal H_3 \otimes \mathcal H_4$. It can be proven mathematically that if the observables of each particles commute in spacelike separated regions (which is true in the standard model), then the reduced density matrix on $\mathcal H_1 \otimes \mathcal H_4$ is completely independent of what you do to the particles in the box ($\mathcal H_2 \otimes \mathcal H_3$). It's an easy undergrad exercise. So no physical interaction in the box can physically entangle particle 1 &4. However, what you can do is produce entangled statistics by post-selecting events based on information that is obtained from particles 2 & 3. This is what's called entanglement swapping. It's not a physical process, but rather an operation that is applied to measurement data that has already been recorded after it has been recorded.

 

[DrChinese]

So no physical interaction in the box can physically entangle particle 1 &4. However, what you can do is produce entangled statistics by post-selecting events based on information that is obtained from particles 2 & 3. This is what's called entanglement swapping. It's not a physical process, but rather an operation that is applied to measurement data that has already been recorded after it has been recorded.

I would dispute such characterization. No one can be sure that the Bell State measurement of 2 & 3 does not cause a change to 1 & 4. The experiment must be viewed as a total context, and identifying the causal agents when there is quantum nonlocality is not really possible. This is same kind of issue as you have with a quantum eraser. Does the eraser cause a non-local change?

My point is not to start an argument about this, but to say that causality cannot be identified clearly unless you start with a specific interpretation. And we know where interpretations will take us...

 

[stevendaryl]

I would absolutely dispute such characterization. No one can be sure that the Bell State measurement of 2 & 3 does not cause a change to 1 & 4.

But depending on the spacetime separation, the measurements of 2&4 can be spacelike separated from the subsequent measurements of 1&4. So I can't see how there could be a local hidden-variables explanation.

The experiment must be viewed as a total context, and identifying the causal agents when there is quantum nonlocality is not really possible. This is same kind of issue as you have with a quantum eraser. Does the eraser cause a non-local change?

I'm only saying that the experiment seems incompatible with a local realistic explanation.

 

[DrChinese]

I'm only saying that the experiment seems incompatible with a local realistic explanation.

Oh, I agree completely. These experiments are even stronger arguments against local realistic explanations than the original Bell types.

And just to be clear: when I say the the Bell State Measurement of 2 & 3 projects 1 & 4 into an entangled state, I don't mean that it is doing so in local realistic terms. This is strictly a quantum nonlocal description. This is the usual description given by authors of these papers. Note: You could also say that the measurement of 1 & 4 casts 2 & 3 into a Bell State.

 

[kurt101]

However, the resulting (super)deterministic quantum theories becomes (laughably ) untenable with these scenarios.

I am having trouble coming to the same conclusion, that the experiment you cited (https://arxiv.org/abs/1508.05949) invalidates any deterministic quantum theories. Do you also mean this to invalidate deterministic quantum theories that depend on FTL (spooky action at a distance)?

 

[DrChinese]

I am having trouble coming to the same conclusion, that the experiment you cited (https://arxiv.org/abs/1508.05949) invalidates any deterministic quantum theories. Do you also mean this to invalidate deterministic quantum theories that depend on FTL (spooky action at a distance)?

I agree completely.

But there will probably be someone who holds to the superdeterministic explanation: that everything that occurs on Earth is part of the same conspiracy that makes QM look correct.

 

[rubi]

I would absolutely dispute such characterization. No one can be sure that the Bell State measurement of 2 & 3 does not cause a change to 1 & 4.

I suppose I should make the mathematics a bit more clear:
The state of the system is $\left|\psi\right> = (\left|\psi_1\right>\otimes \left|\psi_2\right> - \left|\psi_2\right> \otimes \left|\psi_1\right>) \otimes (\left|\psi_3\right>\otimes \left|\psi_4\right> - \left|\psi_4\right> \otimes \left|\psi_3\right>)$. You can now do two things:
1. Compute the reduced density matrix in $\mathcal H_1 \otimes \mathcal H_4$ and call it $\rho_\text{no measurement}$.
2. Perform the Bell state measurement on particles 2 & 3. In that case, you get 4 orthogonal projectors $P_1,\ldots P_4$ and thus 4 states $\left|\xi_i\right> = P_i \left|\psi\right>$. Now you can compute the density matrix $\rho_\text{BSM} = \sum_i \left|\xi_i\right>\left<\xi_i\right|$ and again compute the reduced density matrix in $\mathcal H_1 \otimes \mathcal H_4$ and call it $\rho_\text{measurement}$.
Of course, you have to add all the normalization constants, which I omitted for brevity. You will find that mathematically $\rho_\text{no measurement} = \rho_\text{measurement}$. This shows that the Bell state measurement on particles 2 & 3 can not influence the physical state of the composite 1 & 4 system. Of course, this does not prevent us from performing entanglement swapping on the recorded data.

The experiment must be viewed as a total context, and identifying the causal agents when there is quantum nonlocality is not really possible. This is same kind of issue as you have with a quantum eraser. Does the eraser cause a non-local change?

I did view the experiment in the total context. The question is: Can the actions on particles 2 & 3 have a causal influence on the physical state of the 1 & 4 system? For this to be true, the state of the 1 & 4 system must change depending on what one does to the 2 & 3 system, but it doesn't. Yes, the situation is very analogous to the quantum eraser. It's also an effect of post-selection, which can be understood from standard quantum theory. The experiment says nothing about causality. It's just yet another indication that the predictions of quantum mechanics are correct.

 

[DrChinese]

...The question is: Can the actions on particles 2 & 3 have a causal influence on the physical state of the 1 & 4 system? For this to be true, the state of the 1 & 4 system must change depending on what one does to the 2 & 3 system, but it doesn't. ... The experiment says nothing about causality. It's just yet another indication that the predictions of quantum mechanics are correct.

I agree with virtually everything you are saying. The part I think is unjustified is in bold (I added that emphasis). No one can really say. This is quantum nonlocality. There is no well-defined causal direction that we know of.

Yet to imply that post-selection means that everything evolves forward in time is tantamount to making a back-handed local realistic argument. And that I dispute. As far as anyone knows: measuring 2 & 3 as being in a Bell State does in fact project 1 & 4 non-locally into a fully entangled state. Or in the words of the second of the 2 papers I cited:

"A successful entanglement swapping procedure will result in photons 1 and 4 being entangled, although they never interacted with each other. This is done by performing a Bell-state measurement on particles 2 and 3, i.e. by projecting them on one of the four Bell states. Consequently, photons 1 and 4 will be projected onto the Bell state corresponding to the BSM outcome."

The mathematical language is not in question here. Just the interpretation... and clearly what I am saying is the same as the authors of the paper. And yet there are other acceptable causal interpretations too. But a local realistic one is NOT one of those.

 

[Mentz114]

I suppose I should make the mathematics a bit more clear:
The state of the system is $\left|\psi\right> = (\left|\psi_1\right>\otimes \left|\psi_2\right> - \left|\psi_2\right> \otimes \left|\psi_1\right>) \otimes (\left|\psi_3\right>\otimes \left|\psi_4\right> - \left|\psi_4\right> \otimes \left|\psi_3\right>)$. You can now do two things:
1. Compute the reduced density matrix in $\mathcal H_1 \otimes \mathcal H_4$ and call it $\rho_\text{no measurement}$.
2. Perform the Bell state measurement on particles 2 & 3. In that case, you get 4 orthogonal projectors $P_1,\ldots P_4$ and thus 4 states $\left|\xi_i\right> = P_i \left|\psi\right>$. Now you can compute the density matrix $\rho_\text{BSM} = \sum_i \left|\xi_i\right>\left<\xi_i\right|$ and again compute the reduced density matrix in $\mathcal H_1 \otimes \mathcal H_4$ and call it $\rho_\text{measurement}$.
Of course, you have to add all the normalization constants, which I omitted for brevity. You will find that mathematically $\rho_\text{no measurement} = \rho_\text{measurement}$. This shows that the Bell state measurement on particles 2 & 3 can not influence the physical state of the composite 1 & 4 system. Of course, this does not prevent us from performing entanglement swapping on the recorded data.I did view the experiment in the total context. The question is: Can the actions on particles 2 & 3 have a causal influence on the physical state of the 1 & 4 system? For this to be true, the state of the 1 & 4 system must change depending on what one does to the 2 & 3 system, but it doesn't. Yes, the situation is very analogous to the quantum eraser. It's also an effect of post-selection, which can be understood from standard quantum theory. The experiment says nothing about causality. It's just yet another indication that the predictions of quantum mechanics are correct.

What about phase changes ? They are ignored in your analysis. Can the BSM affect amplitudes so that no probabilities change but a correlation is changed.

 

[kurt101]

I agree completely.

Sorry to be pedantic, but what do you mean by "I agree completely"? Are you saying that the experiment (https://arxiv.org/abs/1508.05949) invalidates deterministic quantum theories that depend on FTL (spooky action at a distance)?

 

[rubi]

I agree with virtually everything you are saying. The part I think is unjustified is in bold (I added that emphasis). No one can really say. This is quantum nonlocality. There is no well-defined causal direction that we know of.

Yet to imply that post-selection means that everything evolves forward in time is tantamount to making a back-handed local realistic argument. And that I dispute. As far as anyone knows: measuring 2 & 3 as being in a Bell State does in fact project 1 & 4 non-locally into a fully entangled state. Or in the words of the second of the 2 papers I cited:

"A successful entanglement swapping procedure will result in photons 1 and 4 being entangled, although they never interacted with each other. This is done by performing a Bell-state measurement on particles 2 and 3, i.e. by projecting them on one of the four Bell states. Consequently, photons 1 and 4 will be projected onto the Bell state corresponding to the BSM outcome."

The mathematical language is not in question here. Just the interpretation... and clearly what I am saying is the same as the authors of the paper. And yet there are other acceptable causal interpretations too. But a local realistic one is NOT one of those.

Of course, I'm not disputing the fact that local realism is experimentally excluded. Maybe we just have a disagreement about definitions. The state of the composite system 1 & 4 is defined to be the density matrix that contains all information about the statistics of the composite system 1 & 4. And this density matrix is unaffected. However, the state of the composite 1 & 2 & 3 & 4 system is clearly affected by the measurement on particles 2 & 3. But in order to detect this change, one needs to perform measurements on the full system. Measurements on the 1 & 4 system can't detect a change of the global state. The state of the composite 1 & 4 system meets the mathematical criterion of an unentangled state, i.e. it is described by a separable density matrix, but the state of the composite 1 & 2 & 3 & 4 system becomes (even more) entangled through the BSM.

What about phase changes ? They are ignored in your analysis. Can the BSM affect amplitudes so that no probabilities change but a correlation is changed.

Phase changes are also included in the analysis. Everything is contained in the projectors $P_1,\ldots,P_4$, whose form is restricted by the commutation relations in such a way that the density matrix of the composite 1 & 4 system is unaffected.

 

[stevendaryl]

I'm not

Sorry to be pedantic, but what do you mean by "I agree completely"? Are you saying that the experiment (https://arxiv.org/abs/1508.05949) invalidates deterministic quantum theories that depend on FTL (spooky action at a distance)?

As far as I know, the nonlocal rule of thumb (I consider it too imprecise to count as an "interpretation") that measurement collapses the wave function is consistent with every quantum experiment performed so far.

 

[stevendaryl]

What about phase changes ? They are ignored in your analysis. Can the BSM affect amplitudes so that no probabilities change but a correlation is changed.

What do you mean by "correlation"? I thought correlation was defined in terms of probabilities. So if you don't change any probabilities, you don't change the correlation.

Do you mean changes of two-particle probabilities without changing single-particle probabilities?

 

[DrChinese]

Sorry to be pedantic, but what do you mean by "I agree completely"? Are you saying that the experiment (https://arxiv.org/abs/1508.05949) invalidates deterministic quantum theories that depend on FTL (spooky action at a distance)?

No, just that local realistic ones are ruled out. At this point, it is "generally" agreed that nonlocal theories such as Bohmian Mechanics are viable.

 

[DrChinese]

Of course, I'm not disputing the fact that local realism is experimentally excluded. Maybe we just have a disagreement about definitions. The state of the composite system 1 & 4 is defined to be the density matrix that contains all information about the statistics of the composite system 1 & 4. And this density matrix is unaffected. However, the state of the composite 1 & 2 & 3 & 4 system is clearly affected by the measurement on particles 2 & 3. But in order to detect this change, one needs to perform measurements on the full system. Measurements on the 1 & 4 system can't detect a change of the global state. The state of the composite 1 & 4 system meets the mathematical criterion of an unentangled state, i.e. it is described by a separable density matrix, but the state of the composite 1 & 2 & 3 & 4 system becomes (even more) entangled through the BSM.

I don't disagree really with any of this, and I don't think you disagree with the following:

We do the BSM on 2 & 3 and see we have an entangled pair in 1 & 4. 1 & 4 have never interacted on any local realistic basic. They did not have a common origin either, and no local causal agent ever impacted the pair. Clearly, if one were trying to explain their entanglement using some desperate form of local realism: about the only thing left is to say that these entangled particles were created on the same planet and everything on the planet shares a common light cone. Of course, that explanation fails in one critical manner: why aren't any and all pairs of particles - anywhere on Earth regardless of origin - also entangled? Why just these few special ones that had the successful BSM? That is, if the "Earth as common light cone" idea is to be considered? (Obviously, that idea seems ridiculous to me. )

I am relating the above scenario to the OP article, which is constructing its premise on a flawed concept: that all entanglement arises from a common entanglement source. It doesn't, as the experiments I cited indicate.

 

[Mentz114]

What do you mean by "correlation"? I thought correlation was defined in terms of probabilities. So if you don't change any probabilities, you don't change the correlation.

Do you mean changes of two-particle probabilities without changing single-particle probabilities?

I mean two particle correlations are not independent of phase. But I have to be satisfied with @rubi s answer. I'm struggling with the idea that the NV's can be entangled already before the interaction at C.

 

[rubi]

We do the BSM on 2 & 3 and see we have an entangled pair in 1 & 4.

We need a clear definition of the terms here in order to agree or disagree. As I said, with the standard definition of the state of a (sub-)system that I have given (a state is defined to be a density matrix in the Hilbert space of the (sub-)system), the state of the 1 & 4 subsystem is separable (a quick calculation shows $\rho^{1,4}_\text{measurement} = \rho^{1,4}_\text{no measurement} = \left|\psi_1\right>\left<\psi_1\right|\otimes\left|\psi_4\right>\left<\psi_4\right|$), rather than entangled, while the state of the 1 & 2 & 3 & 4 system is entangled, i.e. non-separable.

1 & 4 have never interacted on any local realistic basic. They did not have a common origin either, and no local causal agent ever impacted the pair. Clearly, if one were trying to explain their entanglement using some desperate form of local realism: about the only thing left is to say that these entangled particles were created on the same planet and everything on the planet shares a common light cone. Of course, that explanation fails in one critical manner: why aren't any and all pairs of particles - anywhere on Earth regardless of origin - also entangled? Why just these few special ones that had the successful BSM? That is, if the "Earth as common light cone" idea is to be considered? (Obviously, that idea seems ridiculous to me. )

I agree with all of this.

 

[kurt101]

No, just that local realistic ones are ruled out. At this point, it is "generally" agreed that nonlocal theories such as Bohmian Mechanics are viable.

Thanks for the clarification! I think I am on the same page now.

 

[kurt101]

I mean two particle correlations are not independent of phase. But I have to be satisfied with @rubi s answer. I'm struggling with the idea that the NV's can be entangled already before the interaction at C.

I agree and maybe it is just my misunderstanding of the term entanglement, but I don't like saying that NV's can be entangled before the interaction at C.

 

[DrChinese]

I mean two particle correlations are not independent of phase. But I have to be satisfied with @rubi s answer. I'm struggling with the idea that the NV's can be entangled already before the interaction at C.

Look at the photon entanglement experiments and it is clear that photons 1 & 4 can be entangled either before or after the Bell State Measurement of 2 & 3. Ordering of the measurements is not significant to the results in any way. You can interpret that in several different ways.

 

[Mentz114]

Look at the photon entanglement experiments and it is clear that photons 1 & 4 can be entangled either before or after the Bell State Measurement of 2 & 3. Ordering of the measurements is not significant to the results in any way. You can interpret that in several different ways.

I will interpret this by assuming that all the 'events' happen at the same time. As you say, ordering and precedence have no significance.

 

[facenian]

.....
If an experiment like this were possible, then it would be a way to produce entangled particles that have no common past. That would seem to be an even simpler argument against local hidden variables than Bell's theorem--the correlations can't possibly be explained in terms of local hidden variables if they never met in the past to share that hidden variable.

Good. Then as I said, in some sense, it seems that Bell's inequality is almost unnecessary to demonstrate the impossibility of a local hidden-variables theory that could explain the correlations, since is there is no way for the entangled particles to acquire a common hidden variable.

Then I withdraw my previous suspicion about @DrChinese's assetions but I was right when I said that for these new tests hidden variables models are irrelevant rendering Bell's original arguments inaplicable

 

[DrChinese]

but I was right when I said that for these new tests hidden variables models are irrelevant rendering Bell's original arguments inaplicable

You are looking at things in reverse. Bell tests are tests of local realism (local hidden vaiables). The local realistic boundary is usually expressed as a Bell inequality. These tests have that attribute too. Certain elements are 100% identical.

However, some of these tests have been constructed specifically to address issues that some groups of "die-hard" local realists have expressed. Most of these issues are unreasonable (for reasons I won't get into here), but scientists have found ways to address them anyway and rule those issues out. That way they are not lingering in the background. The experiment of Hanson et al is indeed a Bell test, as are the entanglement swapping tests I cited. The original Bell test did indeed conceive of a single common source of entangled pairs. But that should not be seen as a restriction. There are literally hundreds (if not thousands) of Bell tests that have been performed to demonstrate limits on local realistic theories.

For some reason, you have it in your head that Bell has said something that this test invalidates or seems to contradict. That is far from the case. First, Bell said many things. That does not mean they all are to be taken as of equal weight. Second, Bell died before many key discoveries in this area were made. Bell would have loved these experiments. He would have loved GHZ and PBR, as well as the entanglement swapping I cite. All of these shed light on entanglement and the nature of reality. Which was the entire purpose of the Bell program in the first place. Consider that Bell's Theorem was not the only "no-go" theorem he came up with. He worked on others in the 60's too, they too are groundbreaking even though less well known. Such as BKS:

https://en.wikipedia.org/wiki/Kochen–Specker_theorem
https://arxiv.org/abs/quant-ph/9709047

 

[facenian]

For some reason, you have it in your head that Bell has said something that this test invalidates or seems to contradict.

I did not mean that. What I said is that the cases considered by Bell and EPR do not apply to these new cases of entanglement. This in no way means that this new cases invalidate what Bell and EPR have said.