Local realism ruled out? (was: Photon entanglement and )

[Demystifier]

Akhmeteli, I have no objections to your last post. It's fair enough.

 

[Demystifier]

It leads me to another question.

Say, we found a mapping of our physical spacetime P and any system in it into some other (abstract) space A. There is 1:1 relationship between P and A.

If theory is nonlocal in P but local in A, would you call such theory local or not?

Example: We map surface into line, R2 into R1
Theory, which is local in R2 is non local in R1.

There is a whole thread devoted to this idea:
https://www.physicsforums.com/showthread.php?t=285019

 

[akhmeteli]

Akhmeteli, I have no objections to your last post. It's fair enough.

Thank you very much!

 

[DrChinese]

But then I may say that there are many proofs (rather than Proof) that the world is local, such as: the absence of signal nonlocality; microcausality in quantum field theory; the absence of experimental violations of the genuine Bell inequalities; holes in no-go theorems, and so on.

You might say the signal locality is evidence of locality, but the rest of what you say is wrong - again. If you want to reject evidence that goes against your personal opinion, please do not label it as science. Just call it for what it is: a quasi-religious view.

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities. There is no hole in the GHZ no-go. And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense. Please explain how photons that are not - and have never been - in each other's light cones can become entangled. According to local realism, that should not be possible. I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

 

[ThomasT]

I am pretty sure that this case should be distinguishable from true entanglement, but I don't quite see how (yet).

The first set of polarizers unentangles, but polarizes identically, the counter-propagating disturbances

I certainly agree that it is part of the definition ...

Factorability of the joint probability expression defines Bell locality.

 

[DrChinese]

But then I may say that there are many proofs (rather than Proof) that the world is local, such as: ... the absence of experimental violations of the genuine Bell inequalities...

Just to demonstrate a specific example that this makes no sense. The below reference was submitted this week by a highly respected research group. It demonstrates nonlocality, see the title. Now, according to your thinking, this is actually evidence of locality rather than non-locality as it states. Are you following any of this, or am I wasting my time? I don't expect you to change your position, rather to simply stop writing what has already been refuted here.

http://arxiv.org/abs/1003.0432

Testing nonlocality over 12.4 km of underground fiber with universal time-bin qubit analyzers

Felix Bussieres, Joshua A. Slater,Jeongwan Jin, Nicolas Godbout, and Wolfgang Tittel
(Dated: March 1, 2010)

"We experimentally demonstrate that the nonlocal nature of time-bin entangled photonic qubits persists when one or two qubits of the pair are converted to polarization qubits. This is possible by implementing a novel Universal Time-Bin Qubit Analyzer (UTBA), which, for the First time, allows analyzing time-bin qubits in any basis. We reveal the nonlocal nature of the emitted light by violating the Clauser-Horne-Shimony-Holt inequality with measurement bases exploring all the dimensions of the Bloch sphere. Moreover, we conducted experiments where one qubit is transmitted over a 12.4 km underground fiber link and demonstrate the suitability of our scheme for use in a real-world setting. The resulting entanglement can also be interpreted as hybrid entanglement between different types of degrees of freedom of two physical systems, which could prove useful in large scale, heterogeneous quantum networks. This work opens new possibilities for testing nonlocality and for implementing new quantum communication protocols with time-bin entanglement."

 

[SpectraCat]

The first set of polarizers unentangles, but polarizes identically, the counter-propagating disturbances

I don't think that is an accurate description, not without some additional qualifying statements. In fact, I am not sure it is right ... how can you be so sure that the first set of polarizers breaks the entanglement? It certainly seems logical, but is there an experimental result confirming this? I originally thought as you did for this case, but I started looking for experimental verification, and it all seemed ambiguous. As far as I can tell, the only thing that can be said for sure is that detection of one member of an entangled pair breaks the entangled state, and I don't think it has been proven that interaction with a polarizer is the same as detection. (Actually, I would be happy if the polarizer interactions were proven to be equivalent to detection, because it would drastically strengthen my position in an argument with DrChinese that I have been having in another thread!)

Having said that, let's assume that you are correct, and the first set of polarizers does break the entanglement. In that case, the first set of polarizers will completely block all coincidence measurements if the source is the typical choice of a type-II PDC, which generates HV-VH type entanglement (Bell state). As you can see, if the entangled state is disrupted by the first set of polarizers, only one of the counter-propagating photons will be transmitted (although we don't know which one); the other will be blocked with 100% efficiency. For HH+VV type entanglement (which is not what is used in typical Aspect-style experiments), you would get 100% transmission in both directions ... I guess this is what you are talking about?

Now, the latter case means that both photons acquire a fixed polarization angle $$\phi$$ relative to the lab frame. The detection probabilities are now dependent on the detection angles at A and B relative to the lab frame, call these $$\theta_{A}$$ and $$\theta_{B}$$. So, for any single measurement, the individual probabilities of detection events at A and B are given by Malus's law as:

$$cos^{2}\left(\phi-\theta_{A}\right)$$ and $$cos^{2}\left(\phi-\theta_{B}\right)$$

So the probability of a coincidence is given by:

$$cos^{2}\left(\phi-\theta_{A}\right)cos^{2}\left(\phi-\theta_{B}\right)=\frac{1}{4}\left\{2cos^{2}\left(\phi-\theta_{A}\right)+2cos^{2}\left(\phi-\theta_{B}\right)+cos^{2}\left(\theta_{A}-\theta_{B}\right)+cos^{2}\left(2\phi-\theta_{A}-\theta_{B}\right)-2\right\}$$

Now, I believe that your construction also had the angle $$\phi$$ as random and variable throughout the experiment, so that means that for a large sample size, Alice's observations will amount to integration of the above expression over all possible values of $$\phi$$, which yields:

$$\frac{1}{4}\int^{2\pi}_{0}\frac{d\phi}{2\pi}\left\{2cos^{2}\left(\phi-\theta_{A}\right)+2cos^{2}\left(\phi-\theta_{B}\right)+cos^{2}\left(\theta_{A}-\theta_{B}\right)+cos^{2}\left(2\phi-\theta_{A}-\theta_{B}\right)-2\right\}=\frac{\left[2cos^{2}\left(\theta_{A}-\theta_{B}\right)+1\right]}{8}$$

EDIT: I just noticed that you also give this same expression in an earlier post, so it looks like we are both approaching the problem the same way. Still, my conclusion seems different than yours ...

So, while this expression contains the cos²theta term (theta being the relative angle, or theta_A-theta_B), it is not equal to it. Most importantly, this expression never goes to zero for any choice of theta. So as I hypothesized, there will still be a measurable difference between the entangled and unentangled cases, even with your more elaborate unentangled source.

Factorability of the joint probability expression defines Bell locality.

Ok, I'll accept that if it moves things forward.

 

[akhmeteli]

What is wrong with you?

1. Bell points out about perfect correlations, which is also present in EPR. This does not require any further discussion, it is an experimental fact and accepted by all: entangled particles exhibit this, and no assumption is required.

I am not quite sure what you're trying to say and don't want to guess. Care to explain?

UE and PP are irrelevant to Bell, and I challenge you to produce a reference otherwise.

I gave you the reference. I gave you the arguments indicating you need UE and PP or something like that to obtain the QM correlations in the Bell theorem. You don't like the author of the reference. You don't want to discuss his quotes or my arguments. I certainly can live with that.

2. Do you not read anything I (or anyone else) says? I said that QM predicts the cos^2(theta) relationship for entangled particles. It does not predict otherwise.

I reject this last statement ("it does not predict otherwise"). This is what the QM theory of measurement predicts. QM unitary evolution predicts something different: according to UE, there is no irreversibility, so no measurement is ever final. Thus, QM predicts at least two different things, not one, for the same phenomenon.

So who cares how that is arrived at if you think QM is wrong (an embarassing position by the way)?

People care. Not everybody is as flexible as you with logic to "freely admit" problems with QM theory of measurements and express indignation when somebody says that standard QM is, strictly speaking, wrong. I am not the only one who wants to know exactly what is right in QM and what is wrong. When people rigorously show that QM theory of measurement is just an approximate consequence of UE, it matters, because we then know that we cannot trust QM theory of measurement 100%, as you seem to do (while "freely admitting" problems with it :-( )

Bell says QM conflicts with LR, really, how hard is that for you to understand? It is absurd to repeat the same statements over and over in post after post.

I do understand that standard QM conflicts with LR. I repeat, I do understand that. What I am trying to explain is: standard QM conflicts with itself as well, so LR does not have more problems than standard QM itself.

You don't have to agree with QM to know this is the prediction and there is no other (if so, what is it?).

I agree this is a prediction of standard QM. And I disagree, there is other prediction based on UE only. I cannot rewrite the results of Allahverdyan's articles here or rederive them for any experimental setup you may wish to "challenge" me with to tell you "what is it"- the "other" prediction.

You don't have to be a genius to figure out that LR must respect Bell's Inequality once Bell's Theorem is considered.

Again, I agree, LR must respect the (genuine) Bell inequalities.

And that is different than QM.

And I question this. You can only prove that using both UE and QM theory of measurement, which contradict each other. Therefore, you can only state that LR cannot reproduce ALL predictions of QM - this is your phrase. But as long as S(tandard) QM contains mutually contradictory elements, this inability to reproduce all predictions of an internally inconsistent theory is not a problem of LR, but a problem of SQM

3. Again, reference please.

Again, I gave you a reference. I gave you the arguments. You don't like them and don't care to discuss? Fine with me.

4. nightlight? You must be kidding, right? He never said this that I recall.

He questioned that the Bell inequalities can be violated in QM, unless you use PP, which he rejected. He quoted Kowalski's results to suggest that linear equations of UE in Hilbert space can be a disguise for nonlinear differential equations in 3+1 dimensions. So, again, I mostly follow his reasoning.

And I disagreed with almost everything he said. nightlight is a diehard local realist who ignores Bell test results and disagreed with Bell, as I recall.

I did not say you praised his posts:-)

But never did I hear a comment that QM was "wrong" because of mutually contradictory elements. But perhaps you can correct me on that point, I would welcome that.

You did not hear that from nightlight or from anybody? I am not sure about nightlight. But I gave you other references to the contradiction between UE and QM theory of measurement, and you seem to agree there are problems in this area.

5. Laughable! You completely mischaracterize the nature of Zeilinger et al's position on loopholes by quoting out of context. It is true that Zeilinger would like to see a "loophole-free" demonstration of a Bell test, but that is for significantly different reasons than you describe. Zeilinger has already ruled out local realism in numerous OTHER experiments, need I re-reference these? GHZ is a good starter, and there are plenty of others. So it is not about LR being viable or not to him!

I fully agree that Zeilinger is no fan of LR. As for my "quoting out of context"... Look, with all due respect, I am not going to learn Zeilinger's articles by heart or look for a quote confirming YOUR point of view - that would be really rich. So I gave you a quote. You want to prove that Zeilinger believes LR has been ruled out by experiments - give me a direct quote with such claim, and we'll discuss it, don't give me a reference to a dozen articles where I am supposed to find confirmation of your point of view.

Further: the measurement problem - which I acknowledge freely - is hardly a flaw in QM. May as well say GR is wrong too at a singularity because of division by zero.

Look, I know next to nothing about GR, but it is my understanding the singularity is regarded as an indication that GR will be corrected in this point by a future theory. Wouldn't it be natural to think that same logic is in order for QM?

You clearly like to turn back the clock hands with meaningless semantic diversions. How about a little useful science to go with your words? Noone - least of all me - claims QM answers all questions about all things. I think the same conclusion is in order where there is a c It is a model, and it is a very useful one. You have only to lay on the table a model that matches and exceeds it to get my attention. Short of that, you are nothing but HOT AIR.

If I suggested that you do a little useful science and support YOUR hot air with a loophole-less experimental demonstration of violations of the Bell inequalities, I guess you would call my suggestion "empty rhetoric", although you seem to be sure we'll live long enough to see such a demonstration. Why should not I apply this term to your suggestion?

 

[Dmitry67]

Is it possible to say that LR is ruled out experimentally and ignore all agruments about internal problems in QM?

 

[Demystifier]

Is it possible to say that LR is ruled out experimentally and ignore all agruments about internal problems in QM?

It is possible, but not with absolute certainty. This is because the detectors have a very low efficiency, so the experimental statistics refers to a very small sample of actual particles. In principle, it is possible that this small sample is not a typical sample, but a sample with very special properties, making the illusion of violation of Bell inequalities. Nobody knows a good reason why this sample would not be a typical one, yet such a possibility in principle exists.

This is like president elections. Before the actual counting of all votes, usually there is a preliminary counting of a small sample of all votes. Usually it is a good representative of all the votes, yet the victory of one president candidate over the other cannot be proclaimed before the actual counting of all (or at least of the majority of all) votes.

Akhmetely is like a president candidate who believes that he will win the elections even though all statistics on small samples say the opposite. It's true, such a president candidate may still win, but statistically it is very unlikely.

 

[ZapperZ]

It is possible, but not with absolute certainty. This is because the detectors have a very low efficiency, so the experimental statistics refers to a very small sample of actual particles. In principle, it is possible that this small sample is not a typical sample, but a sample with very special properties, making the illusion of violation of Bell inequalities. Nobody knows a good reason why this sample would not be a typical one, yet such a possibility in principle exists.

This is like president elections. Before the actual counting of all votes, usually there is a preliminary counting of a small sample of all votes. Usually it is a good representative of all the votes, yet the victory of one president candidate over the other cannot be proclaimed before the actual counting of all (or at least of the majority of all) votes.

Akhmetely is like a president candidate who believes that he will win the elections even though all statistics on small samples say the opposite. It's true, such a president candidate may still win, but statistically it is very unlikely.

Good analogy, but here's the second half of it.

Say that you DO ask all the citizens to vote, but not officially, i.e. not by casting it in a ballot on election day. For example, you got every single citizen to be at a voice caucus before the actual election. And they vote for the president. So you got the vote of every single citizen.

Yet, again, he refuses to accept the vote because this time, it is not an "official" vote because he said that between this caucus and the actual voting day, someone could change his/her mind.

This is what is going on with the EPR-type experiment using charge particles, where the detection efficiency is 100%. The only drawback here is that they still have not been able YET to close the locality loophole (and I fully expect that they will soon!). That's why I mentioned earlier that these loopholes are closed separately in different experiments. It is like you get the SAME result no matter if you only do a "sample election", or if you do a caucus of 100% of the citizen. What are the odds that if you do not win on any of those, that you will win if 100% of the citizen voted on election day? We live our lives with significantly lower odds than that!

Zz.

 

[Dmitry67]

Thank you
What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?

 

[Demystifier]

Zz, thanks for the second half. Can you give me a reference for the EPR-type experiment using charged particles with the 100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

 

[ZapperZ]

Zz, thanks for the second half. Can you give me a reference for the EPR-type experiment using charged particles with the 100% detection efficiency?
(If you already did it on some post above, you can only write the post number.)

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.

 

[Demystifier]

I've mentioned several, but it'll take too long to hunt for them on here. But here's a couple of references that I have handy:

S. Olmschenk et al., Science v.323, p.486 (2009).
D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

Zz.

Thanks! The paper is available for free:
http://www.sciencemag.org/cgi/reprint/323/5913/486.pdf?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=olmschenk&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT

However, from the title and the abstract it is not obvious that this paper closes the fair sampling loophole of nonlocality. Do you know a paper which states it more explicitly?

EDIT: Now I've noticed that you added a PRL reference. It is more explicit. This is exactly what I needed. Thanks again.

 

[zonde]

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities. There is no hole in the GHZ no-go.

There is exactly the same fair sampling hole in GHZ.
Basically Bell theorem says you can't get different correlations predicted by QM using the same pairs. That is exactly the same with GHZ. Only in GHZ this is purer as you have group of four correlations where one of them falls out if you assume the same detected pairs for all correlations.

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.

That's right. Failure of disproof is a failure. It can't be proof of something else.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled. According to local realism, that should not be possible. I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

 

[DrChinese]

1. There is exactly the same fair sampling hole in GHZ.


2. Your implied reference to the experiment you quoted earlier is quite poor.
If you read this article you can easily find out that it's claim is seriously biased. While if you somehow imagine that photons appear from nowhere you might claim that but in that case you are very far off not only from local realism but from SQM too.
To confirm that you just have to note that tuning condition for experiment is observation of Hong–Ou–Mandel dip.

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

 

[zonde]

D.N. Matsukevich et al., PRL v.100, p.150404 (2008).

http://arxiv.org/abs/0801.2184"
"We observe violation of a Bell inequality between the quantum states of two remote Yb+ ions separated by a distance of about one meter with the detection loophole closed. The heralded entanglement of two ions is established via interference and joint detection of two emitted photons, whose polarization is entangled with each ion. The entanglement of remote qubits is also characterized by full quantum state tomography."
As I understand it states that emitted photons of two ions interact and as a result two ions become entangled (entanglement teleportation) and as a result the same photons that where used to entangle ions instantaneously show signs of ion entanglement (result of entanglement is telported back to photons). And then these photons are detected. Right?

Interesting but it is quite unclear what it has to do with local realism.

 

[Demystifier]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

Do the authors of the paper reporting the actual GHZ experiment explicitly claim that this disproof of LR does not contain any experimental loopholes?

 

[SpectraCat]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

Zonde's criticism is actually a reasonable one, and is not really addressed in the paper. The fact is that the pump photons for this experiment come from the same source, and an interferometer is actually part of the experimental scheme upstream of the two independent PDC's. Therefore, I think any claim that the two initial entangled pairs in this experiment are "independent" needs to be very carefully examined. I have been thinking about this since zonde first mentioned this criticism a few weeks ago, and I have not been able to disprove or rectify it. I definitely don't think it can be dismissed out of hand.

I would like to see a version of this experiment that uses two independent pump lasers ... but that is quite technically challenging from a synchronization point of view. There are also non-trivial issues concerning how "identical" the pump pulses are in such a case, because distinguishability of the B & C photons could (would?) disrupt the entanglement swapping. That last point in particular is why I think zonde's criticism is deserving of very careful analysis.

 

[zonde]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

Theoretically LR was ruled out by Bell theorem.
And no you can't do that with sample size of 1. You need 4 experiments (with sample size of 1):
- one channel H/V, other L/R, third L/R
- one channel L/R, other H/V, third L/R
- one channel L/R, other L/R, third H/V
- one channel H/V, other H/V, third H/V
or if we can't do H/V and L/R simultaneously then even 8 experiments.

2. Zeilinger? Are you serious? If that doesn't work, I am not sure who I would need to present.

No, not Zeilinger. See post #219 where I gave the quote (and link to paper):
https://www.physicsforums.com/showthread.php?p=2590786#post2590786"
That is the same paper you discussed in other thread.

 

[zonde]

What also puzzles me is the motivation of that group of "diehard localists". There are no people who deny SR and other modern theories seriously, except few crackpots.

The only 2 exceptions I know are: MOND and LR. Why locality is so important for these people that they won' accept the nonlocality no matter what?

Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

 

[Dmitry67]

Oh, that is somewhat irrational feelings toward consistent overall picture.
I believe that this consistency it is a requirement to use intuition fully.

And SR is consistent - there are no contradictions with more intuitive neo-Lorentzian interpretation.

well, yes, but:
* there is no alternative suggested by local realists. there are no neo-LR interpretations to compare with. Even MOND curvefitting, no matter how naive is it, is better: at least, it is something.
* Why intuition insists on locality? Mine does not.

 

[Demystifier]

* Why intuition insists on locality? Mine does not.

Mine too. For example, the Newton law of gravity is quite intuitive to me. Also, when I was a little child, I thought that light and sound come to me from their source instantaneously.

 

[DrChinese]

Zonde's criticism is actually a reasonable one, and is not really addressed in the paper. The fact is that the pump photons for this experiment come from the same source, and an interferometer is actually part of the experimental scheme upstream of the two independent PDC's. Therefore, I think any claim that the two initial entangled pairs in this experiment are "independent" needs to be very carefully examined. I have been thinking about this since zonde first mentioned this criticism a few weeks ago, and I have not been able to disprove or rectify it. I definitely don't think it can be dismissed out of hand.

I would like to see a version of this experiment that uses two independent pump lasers ... but that is quite technically challenging from a synchronization point of view. There are also non-trivial issues concerning how "identical" the pump pulses are in such a case, because distinguishability of the B & C photons could (would?) disrupt the entanglement swapping. That last point in particular is why I think zonde's criticism is deserving of very careful analysis.

It is true that the same pump is being used in the referenced experiment. But subseqently, Zeilinger has put together a method of synchronizing separate lasers. Nothing changes when the proper setup is used and the photons are indistinguishable - as would be expected from QM. I think it is only a matter of time before all of the separate elements can be assembled into a single experiment. I would agree that it is always desirable to run the experiment with all the refinements together, where possible and practical.

http://arxiv.org/abs/0809.3991

In the above, there is entanglement swapping but there is no attempt (as I recall) to also perform delayed choice.

 

[DrChinese]

Theoretically LR was ruled out by Bell theorem.
And no you can't do that with sample size of 1. You need 4 experiments (with sample size of 1):
- one channel H/V, other L/R, third L/R
- one channel L/R, other H/V, third L/R
- one channel L/R, other L/R, third H/V
- one channel H/V, other H/V, third H/V
or if we can't do H/V and L/R simultaneously then even 8 experiments.


No, not Zeilinger. See post #219 where I gave the quote (and link to paper):
https://www.physicsforums.com/showthread.php?p=2590786#post2590786"
That is the same paper you discussed in other thread.

OK, Tittel & Gisin et al. I guess I am missing what you are saying, because you cannot be questioning these folks' conclusions.

 

[akhmeteli]

You might say the signal locality is evidence of locality, but the rest of what you say is wrong - again. If you want to reject evidence that goes against your personal opinion, please do not label it as science. Just call it for what it is: a quasi-religious view.

With all due respect, if you declare something wrong, it does not necessarily mean it is indeed wrong. I discuss your specific arguments below.

There are in fact hundreds of experimental violations of "genuine" Bell Inequalities.

There are none. Nil. Gimme a break, or a reference to experimental violations without loopholes.

There is no hole in the GHZ no-go.

Does not it use the QM theory of measurement?

And how can a hole in a no-go theorem be evidence for locality anyway? That doesn't even make sense.

If you think that a no-go theorem with a hole is a proof of nonlocality, then a hole in that theorem is certainly a proof of locality. I could agree that a hole is not a proof of locality, but not before you agree that a theorem with a hole is not a proof of nonlocality. This is a zero-sum game, and I believe the rules should be the same for proponents of both views.

Please explain how photons that are not - and have never been - in each other's light cones can become entangled.

First of all, I said several times that entanglement per se does not spell nonlocality (if you disagree, and you seem to disagree, the burden of proof is on you - I reject your "by definition" argument - indeed, if, for example the entangled particles are not spatially separated, they are no problem for locality, so don't tell me about definitions), so I don't need to explain anything. You can only declare nonlocality if the Bell inequalities are violated, and there is no evidence of violations of the genuine Bell inequalities. If you deny that, this is just your personal theory.

Ok, so, as I said, I am under no obligation to explain entanglement. However, I can repeat the following: "QFT-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post https://www.physicsforums.com/showpost.php?p=1825523&postcount=90." So we have nonlinear differential equations in 3+1 dimensions, which are local, as input, use the referenced mathematical trick, and get something looking very much like quantum field theory, but equivalent to the input local equations on the set of solutions of those local equations. But now you have linear evolution equations in the Fock space, so there could be at least an appearance of entanglement. Again, I did not explore this much further as a local explanation of entanglement, but this does look like a possibility.

According to local realism, that should not be possible.

Sez who? See above.

I notice that no matter where this thread goes, you avoid these difficult questions, and resort to the weakest references as part of your hand waving.

Look, in this post I had to pretty much repeat myself, that means I did not "avoid these difficult questions" previously.

 

[akhmeteli]

Ok, so I think I finally understand why it has been to hard to understand your point of view here, at least in my case. You are actually challenging the foundations of the standard formulation of quantum mechanics, by attacking one of the core postulates. This is of course fine, but it would have been helpful if you constructed your arguments in that context from the beginning, rather than focusing on the Bell theorem, which is actually just collateral damage from your primary attack.

I regret that I was not able to make my posts easier to understand.

In truth, there is nothing wrong with Bell's theorem, because he simply takes for granted the postulates that are part and parcel of SQM ... that is what one is *supposed* to do with postulates, when working within a theoretical framework. On the other hand, you refuse to accept one of those postulates, as you have stated consistently from the beginning, and of course this is the really the only logical grounds on which to challenge an otherwise correct mathematical proof/derivation.

I agree on these points.

EDIT: As I said above, this is fine, but it is hardly mainstream in this case. While the "measurement problem" has been debated long and hard in quantum mechanics, I think most people would still concede that this has not so far proved to be a practical problem for either measurements, or for theoretical predictions derived from the accepted postulates.

I'd say it is not the mainstream in the sense that few people care about it. On the other hand, not many people deny there is a problem. For example, DrChinese does not deny this. So in this sense you may perhaps say it is the mainstream. You may also wish to look at the Schlosshauer quote at the end of my post 41 in this thread.

So, while I tend to view your challenge to SQM as rather quixotic, who is to say that I am correct?

Quixotic? I don't know. Well, sometimes even I think that there should be less painful ways to make friends:-) On the other hand, I think my arguments are pretty straightforward, so many people do understand them, like you understood them. You did not become a local realist, you still think Nature is nonlocal, we still disagree, but you just understood my arguments, and I think this is good for both of us. You see, I am not even sure I can call myself a local realist: indeed, if tomorrow experiments prove me wrong, so be it, I'll have to change my views.

Actually, I guess you would say nightlight is quixotic as well, but I am grateful to him, as he made clear some things that looked totally mysterious.

All I can say is that the postulates of SQM have served us rather well to this point, and there are no clear-cut cases where they have been found to be false. Perhaps there is a point to be made that they are somehow self-contradictory, but so far that is not a widely held view. I have no problem "rationalizing away" the seeming contradiction that you raise, because the unitary evolution postulate pertains to the microscopic quantum system, whereas the measurement postulate pertains to the interaction of the quantum system with a macroscopic detector. Thus the apparent irreversibility that seems to be the focus of your concerns could in my view just be an "effective irreversibility" resulting from entropic effects as the quantum system interacts with the (effectively) continuous distribution of states represented in the macroscopic detector. I think that if this is correct (and I am not claiming that it is), it would be provide a nice symmetry with classical physics, where temporal irreversibility is also just an "effective" phenomenon resulting from the tendency of natural systems to seek states of high entropy.

Neither would I have problems "rationalizing away" the contradiction, but it introduces nonlocality, and that is a really radical notion. I do need iron-clad arguments to accept it.

 

[Count Iblis]

How does this all square with the fact that I'm unquestionably real and local?

 

[Frame Dragger]

How does this all square with the fact that I'm unquestionably real and local?

Are you?

 

[ThomasT]

... how can you be so sure that the first set of polarizers breaks the entanglement? As far as I can tell, the only thing that can be said for sure is that detection of one member of an entangled pair breaks the entangled state, and I don't think it has been proven that interaction with a polarizer is the same as detection. (Actually, I would be happy if the polarizer interactions were proven to be equivalent to detection, because it would drastically strengthen my position in an argument with DrChinese that I have been having in another thread!)

In the entangled state polarization is undetermined and QM just specifies the relationship between the counter-propagating disturbances incident on the polarizers.

Afaik, when polarization is determined, then entanglement is broken. The polarization is determined by the polarizer via transmission along its axial setting.

 

[ThomasT]

Why intuition insists on locality? Mine does not.

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

 

[Frame Dragger]

Instantaneous propagation is a contradiction in terms.

FTL propagation is not demonstrated.

QM projection along transmission axis of polarizer transmitting detected disturbance is based on assumption of local common cause.

There are only two values for angular difference of polarizers wrt which A and B are perfectly correlated (anticorrelated). These correlations at these settings have a local common cause explanation. There are no other A<->B correlations to explain.

The coincidental detection angular dependency can be reproduced via LHV formulation.

What's the intuitive support for nonlocality?

Imho, nonlocality only exists via the manipulation of terms and misinterpretation.

IMHO Most people, myself included, believe that your viewpoint only exists through those means in bold; I might add a forcefully willful ignorance that borders on the religious.

 

[Dmitry67]

For me no-FTL and locality is something which emerges only macroscopically. So locality, while it is observed in most cases and is only "weakly" violated in EPR is not "natural"

 

[akhmeteli]

1. That would be news to a lot of people. Fair sampling is NOT assumed. You theoretically only need a sample size of 1, as this is essentially an all-or-nothing test. In practice, of course, there is a sample of events and the results are not perfect. But the answer is still the same: the predictions of QM are supported and LR are rejected. And Fair Sampling is not a part of the experiment.

DrChinese,

I admit that I don't know much about GHZ. However, in the article by Zeilinger e.a., Nature 403, 515-519 (3 February 2000),
Experimental test of quantum nonlocality in three-photon Greenberger–Horne–Zeilinger entanglement, I found the following quote:
"However, we realize that, as for all existing two-particle tests of local
realism, our experiment has rather low detection efficiencies.
Therefore we had to invoke the fair sampling hypothesis21,22,
where it is assumed that the registered events are a faithful
representative of the whole."
So, at least on the face of it, fair sampling is used in GHZ experiments. Of course, the article is relatively old. However, in the following article (GHZ and Shimony, Bell's theorem without inequalities, Am. J. Phys., 58 (12), 1990) I found the following: (the authors discuss a possible GHZ experiment):
"The second step is to show how the test could be done even with low-efficiency detectors, provided that we make a plausible auxiliary assumption, which we call fair sampling. Finally, we show that the auxiliary assumption is dispensable if detector efficiencies exceed 90.8%." So it looks like you need 90% efficient detectors to do without fair sampling in GHZ. To the best of my knowledge, there are no such optical detectors. Please advise if I am wrong.

As for your latest reference (12.4 km experiment), the authors seem to be remarkably reticent on the issue of absence/presence of loopholes.

Another thing. At http://www.quantum.at/fileadmin/Presse/2008-07-01-MG-PW_A_Quantum__Renaissance.pdf Aspelmeyer and Zeilinger (Physics World July 2008, p. 22) write the following:

"But the ultimate test of Bell’s theorem is still missing:
a single experiment that closes all the loopholes at once.
It is very unlikely that such an experiment will disagree
with the prediction of quantum mechanics, since this
would imply that nature makes use of both the detection
loophole in the Innsbruck experiment and of the
locality loophole in the NIST experiment. Nevertheless,
nature could be vicious, and such an experiment is desirable
if we are to finally close the book on local realism." Then they discuss GHZ and do not claim that a loophole-free experiment had been performed. This article is recent, unlike the 1998 article in arxiv that I quoted before, so it looks like I did not misrepresent Zeilinger's opinion.