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

[ThomasT]

This thread began with a post in which it was writtenello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

Bell's theorem, per se, is nothing more than a proposition of the form

P → D ,

where "P" is the conjunction of some set of premises, the 'truth' of which does not in any way require the 'truth' of any of the premises of Quantum Mechanics, and "D" is a certain condition (e.g. a Bell inequality).
________________

Now, it happens that Quantum Mechanics (let us denote its premises by "QM") is such that

QM → ~D .

Therefore, the conjunction "P Λ QM" is inconsistent.
________________

In the weak version of Bell's theorem

P = local determinism .


In the strong version of Bell's Theorem

P = locality Λ PC Λ CF ,

where

PC ≡ perfect anti-correlation for equal settings

and

CF ≡ counterfactuality .


In the strong version, of course, "PC" has been employed as premise; but this means only that we are considering any theory which admits "PC" as a feature.
________________


... Do you see what I am saying?

In any version of Bell's theorem

P = statistical independence

and

P → D

where D is a Bell inequality .

We observe that

QM → ~D

and

Experiment → ~D .

Therefore, the conjunctions "P Λ QM" and "P Λ Experiment" are inconsistent.

This is all that can be said vis QM's incompatibility with Bell local formulations, and experimental violations of Bell inequalities.

 

[Eye_in_the_Sky]

Can you tell where do you yourself see the problem?

Do you mean:

Which premise in "locality Λ PC Λ CF" do I see as false?

As I understand the sentence you quoted from Bell ascribe counterfactuality to QM:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
This statement is taken as experimentally valid but on the other hand experiments with photons say that you can only detect 50% of photons maximum with one detector. So it is not conclusively true.
Then if we accept as empirical fact that only 50% of photons can be detected and we do not invoke counterfactuality then QM can not make prediction like that about photons.

Zonde, I am sorry, but I cannot figure out what you mean here.

 

[Eye_in_the_Sky]

In any version of Bell's theorem

P = statistical independence

and

P → D

where D is a Bell inequality .

Of course, "statistical independence" alone is not enough to derive a Bell inequality. There must be other assumptions.

So maybe you mean this:

Regarding the proposition

BL Λ PC Λ CF → D ,

where

BL ≡ Bell Locality (mathematical formulation in terms of probabilities) ,

it will be found, upon scrutiny, that BL is not in fact an expression of local causality. Rather, it is merely an expression of statistical independence.

Is that what you mean?

 

[zonde]

Do you mean:
Which premise in "locality Λ PC Λ CF" do I see as false?

Let's say do you see Proposition 1 (locality Λ PC Λ CF → local determinism) as not valid? Or is it valid but wrongly applied to physical situation? ... or neither.

Zonde, I am sorry, but I cannot figure out what you mean here.

Do you see any problems in this statement?
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."

 

[SpectraCat]

Can you tell where do you yourself see the problem?

As I understand the sentence you quoted from Bell ascribe counterfactuality to QM:
"If measurement of the component σ1∙a, where a is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of σ2∙a must yield the value -1 and vice versa."
This statement is taken as experimentally valid but on the other hand experiments with photons say that you can only detect 50% of photons maximum with one detector. So it is not conclusively true.
Then if we accept as empirical fact that only 50% of photons can be detected and we do not invoke counterfactuality then QM can not make prediction like that about photons.

Hmmm ... while it is true that only 50% of entangled photons can be detected on a single detector in a polarization experiment, that is not the same as saying only 50% of photons can be detected. Couldn't one just use a polarizing beamsplitter with detectors for both the transmitted and reflected photons? Then the experiment would pick up 100% of the photons, and the measurements from Alice's two detectors could be compared with Bob's two detectors to reveal the perfect correlation between the two. Wouldn't this close the loophole you are talking about above?

 

[zonde]

Hmmm ... while it is true that only 50% of entangled photons can be detected on a single detector in a polarization experiment, that is not the same as saying only 50% of photons can be detected. Couldn't one just use a polarizing beamsplitter with detectors for both the transmitted and reflected photons? Then the experiment would pick up 100% of the photons, and the measurements from Alice's two detectors could be compared with Bob's two detectors to reveal the perfect correlation between the two. Wouldn't this close the loophole you are talking about above?

I didn't mean that.
The question is whether increasing detection efficiency does not diminish result for perfect correlations settings. Because perfect correlations at theta=0 and pi/2 is a requirement for Bell inequalities.
I looked up about detection efficiencies of commercially available SPADs and it seems that 50% is not the limit however the question stays whether prefect correlations can be achieved with such levels of detection efficiency.

 

[SpectraCat]

I didn't mean that.
The question is whether increasing detection efficiency does not diminish result for perfect correlations settings. Because perfect correlations at theta=0 and pi/2 is a requirement for Bell inequalities.
I looked up about detection efficiencies of commercially available SPADs and it seems that 50% is not the limit however the question stays whether prefect correlations can be achieved with such levels of detection efficiency.

Ok .. I see your point now. However, I don't think this is a real issue, because all it does is change the discussion from the realm of complete certainty (i.e. Bell inequalities are always violated) to the realm of probability (i.e. the result of a given set of measurements with some mean and standard deviation is outside the permissible range of the Bell inequality by 30 standard deviations).

My view on this is that it is easy to see that the second case approaches the first as the detector efficiency is improved, and so the gedanken conditions of "perfect detector efficiency" is a reasonable simplification to make. Thus the point you raised is really a non-issue in my view. Essentially, it puts you in the position of the sophists who say "well, the detectors aren't perfect, so you can't be sure". Granted .. but 30 standard deviations is close enough for me.

 

[DrChinese]

... Essentially, it puts you in the position of the sophists who say "well, the detectors aren't perfect, so you can't be sure". Granted .. but 30 standard deviations is close enough for me.

30 and rising... some experiments are at 200+ SD.

 

[zonde]

Ok .. I see your point now. However, I don't think this is a real issue, because all it does is change the discussion from the realm of complete certainty (i.e. Bell inequalities are always violated) to the realm of probability (i.e. the result of a given set of measurements with some mean and standard deviation is outside the permissible range of the Bell inequality by 30 standard deviations).

Not sure we are talking about the same thing.
You should actively tune experimental setup to reach as low as possible detection rate for perfect anti-correlation settings. How you can talk about standard deviation in this case? Of course no one is calculating standard deviation for minimum correlation settings because this is requirement not result.

 

[SpectraCat]

Not sure we are talking about the same thing.
You should actively tune experimental setup to reach as low as possible detection rate for perfect anti-correlation settings. How you can talk about standard deviation in this case? Of course no one is calculating standard deviation for minimum correlation settings because this is requirement not result.

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?

 

[akhmeteli]

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?

As far as I know, no violations of the Bell inequalities have been demonstrated - there was some "loophole" in each of the experiments claiming such violations. I suspect those "violations by over 30 standard deviations" were obtained using the fair sampling assumption, and if you use this assumption, you can get as many standard deviations as you want. The problem is it is not clear why anyone has to accept the fair sampling assumption.

 

[zonde]

My point is that perfect anti-correlation is not required for demonstration of Bell inequality violation. First of all, there will *never* be "perfect" detectors. Second, measurements with imperfect detectors show Bell inequality violations by over 30 standard deviations. Why would better detectors make any difference at this point?

Perfect anti-correlation settings are theta=0deg for Type II PDC. With that I do not mean "perfect detection" or rather noiseless non-detection.
The point is that you have to assume that coincidence count at minimum can be extrapolated linearly to reasonably low value at 100% efficiency in order to violate Bell inequalities.
If you can't do that then you don't have violation of Bell inequalities.

It has nothing to do with "Bell inequality violations by over 30 standard deviations".
Please look up in wikipedia http://en.wikipedia.org/wiki/Precision_bias" .

 

[akhmeteli]

It's not a matter of proof, it's just a matter of identifying the symbolic convention, statistical dependence, with the experimental setup. When a detection is registered at one end, then the sample space at the other end is altered. The matching of the separate data streams at A and B isn't done randomly. The matching process itself produces (via local interactions and transmissions) the statistical dependence between A and B -- and this is sufficient to violate Bell inequalities based on the assumption that the data set at A is statistically independent from the data set at B via Bell locality.

The separate accumulations of data at A and B have to be matched somehow. The point is that the designs of entanglement experiments contradict Bell locality.


Statistical dependence between A and B doesn't imply a direct causal link between A and B whether Bell inequalities are violated or not.

Therefore, even though entanglement experimental designs and standard QM are incompatible with Bell locality, we can't conclude that violations of Bell inequalities require nonlocal propagations in Nature.

Sorry, has been busy again.

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do. I don't see solid reasoning behind your statements, so I cannot agree or disagree with them, as neither those statements nor their negations seem obvious. With all due respect, I cannot believe you on your word - you are not a priest (or maybe you are? :-)), and I am not religious. Until you give some reasoning, I just have no comments, sorry. For example, can you offer a local theory violating the Bell inequalities? Or, if you think this is a tall order, can you at least explain if your phrase "the designs of entanglement experiments contradict Bell locality" means the same as "there are loopholes in those experiments"?

 

[zonde]

Sorry, has been busy again.

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do.

It seems that ThomasT is talking basically about the same thing - fair sampling.
Look, if sample space at one end exactly matches sample space at other end (say we have PBS and we detect photon always in one channel or the other) sample spaces stay the same after matching at coincidence counter (except of course that you have additional information about how different channels are matched). But if you don't have perfect efficiency then you reduce each sample space at coincidence counter.

Does not seem that this needs a proof.

However this part could be expanded as it is not obvious:
"this is sufficient to violate Bell inequalities based on the assumption that the data set at A is statistically independent from the data set at B via Bell locality."

 

[DrChinese]

The problem is it is not clear why anyone has to accept the fair sampling assumption.

Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?

You keep saying the same thing without providing scientific basis. You don't have to accept the results, but you shouldn't state the "loophole" as being proof of anything. It isn't.

 

[SpectraCat]

Perfect anti-correlation settings are theta=0deg for Type II PDC. With that I do not mean "perfect detection" or rather noiseless non-detection.
The point is that you have to assume that coincidence count at minimum can be extrapolated linearly to reasonably low value at 100% efficiency in order to violate Bell inequalities.
If you can't do that then you don't have violation of Bell inequalities.

Ok ... so you are saying that the "false coincidence" rate must be below some critical value in order to satisfy the Bell inequality, right? But false coincidences are included in the analysis, so that is accounted for in the experiment. If the false coincidence rate were too high, then the results would appear more "random" and so would no longer show a Bell inequality violation. That is, it is fundamentally IMPOSSIBLE to show a Bell inequality violation with an apparatus that has too high a rate of false coincidences. So your statement is correct, but again I don't see how this is an issue ... the fact that the experimental results do show a violation indicates that false coincidences are not an issue, right?

 

[akhmeteli]

Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?

I have no reasons to accept the fair sampling assumption. You yourself mentioned a situation where it is not true (planets of the Solar system). Of course, my opinion means nothing, but Shimony, Zeilinger and many others believe "loopholes", such as fair sampling assumption, are essential, so I just side with the mainstream view. As for "other tests giving the same results" - I never heard from you on my example with Euclidian geometry.

You keep saying the same thing without providing scientific basis. You don't have to accept the results, but you shouldn't state the "loophole" as being proof of anything. It isn't.

I did provide scientific basis - the opinions of Shimony, Zeilinger, Genovese. You disagree with them, but why is this my problem? You don't seem to claim they are not experts. Again, don't kill the messenger. I keep saying local realism has not been ruled out. You keep saying it has been. Maybe you're right, maybe I am, but so far I don't see any reasons to accept your point of view. Looks like you don't see any reasons to agree with my point of view. So we disagree. So what?

 

[DrChinese]

I did provide scientific basis - the opinions of Shimony, Zeilinger, Genovese. ... You don't seem to claim they are not experts. Again, don't kill the messenger. I keep saying local realism has not been ruled out. You keep saying it has been. Maybe you're right, maybe I am, but so far I don't see any reasons to accept your point of view. Looks like you don't see any reasons to agree with my point of view. So we disagree. So what?

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one. There are plenty (of his) proving LR is not. The difference in our opinions is that one is the mainstream and one is not. Local realism is not a mainstream view. The idea that "loopholes" support LR (or otherwise imply it is feasible) is not either. Don't advertise a false viewpoint. Yours is an extreme minority view in the scientific community.

As mentioned in another thread, for example, it is possible to entangle photons that have never even existed in each other's spacetime light cone. Oh, and that was courtesy Zeilinger. So I don't get where you think LR is considered a viable alternative. You are ignoring a substantial body of work that does not require the fair sampling assumption, such as this.

 

[akhmeteli]

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one.

I gave you his quote confirming local realism has not been ruled out.
If you don't like the quote, it's not my problem.

There are plenty (of his) proving LR is not.

Give me one where he says local realism has been ruled out.

The difference in our opinions is that one is the mainstream and one is not.

I fully agree. And mine is mainstream, yours is not. I confirmed mine by quotes. Again, if you don't like the quotes, it's not my problem.

Local realism is not a mainstream view.

No, it isn't.

The idea that "loopholes" support LR (or otherwise imply it is feasible) is not either. Don't advertise a false viewpoint. Yours is an extreme minority view in the scientific community.

They do imply it is feasible, and this is mainstream. If you believe I advertise a false viewpoint, why don't you kick Shimony's behind, Zeilinger's behind, Genovese's behind? I am of no importance whatsoever. Nobody cares what I advertise. The problem is what I advertise is mainstream, sorry. And if you state that local realism has been ruled out, you're just trying to impose your personal opinion on the others.

As mentioned in another thread, for example, it is possible to entangle photons that have never even existed in each other's spacetime light cone. Oh, and that was courtesy Zeilinger. So I don't get where you think LR is considered a viable alternative. You are ignoring a substantial body of work that does not require the fair sampling assumption, such as this.

Does anybody (but you) claim that these experiments demonstrate loophole-free violations of the Bell inequalities?

 

[Frame Dragger]

I gave you his quote confirming local realism has not been ruled out.
If you don't like the quote, it's not my problem.



Give me one where he says local realism has been ruled out.




I fully agree. And mine is mainstream, yours is not. I confirmed mine by quotes. Again, if you don't like the quotes, it's not my problem.



No, it isn't.




They do imply it is feasible, and this is mainstream. If you believe I advertise a false viewpoint, why don't you kick Shimony's behind, Zeilinger's behind, Genovese's behind? I am of no importance whatsoever. Nobody cares what I advertise. The problem is what I advertise is mainstream, sorry. And if you state that local realism has been ruled out, you're just trying to impose your personal opinion on the others.




Does anybody (but you) claim that these experiments demonstrate loophole-free violations of the Bell inequalities?

This isn't a rhetorical pissing match... the experimental evidence and lack of refutation is more important than your quotes. This is why results are PUBLISHED, and we don't just listen to the researcher's interpretation. As we see, results can be open to multiple interpretations. In short, answer his questions and cut the grade-school debate club horsh-****.

 

[akhmeteli]

This isn't a rhetorical pissing match... the experimental evidence and lack of refutation is more important than your quotes. This is why results are PUBLISHED, and we don't just listen to the researcher's interpretation. As we see, results can be open to multiple interpretations. In short, answer his questions and cut the grade-school debate club horsh-****.

Sorry, I just cannot understand a word. Whose "his"? What questions? Do you mean "DrChinese'" and the following:
"Why should you accept any scientific evidence? And why do you suspect that the full universe would not match the results of a subsample? And why does increasing the sample percentage not lead to a different answer? And why do other tests - not requiring the fair sampling assumption - give the same results?" ?

Then, as I said, I don't see any reason to accept the fair sampling assumption. If Dr Chinese (or you) wants to prove it, good luck, but I don't hold my breath, because he'll have to produce something Shimony and Zeilinger are not aware of. Furthermore, DrChinese himself gave an example where fair sampling does not work. If DrChinese (or you) believes that the assumption does not need any proof as it is obvious, I reject that. You would not understand if I said that local realism does not need any proof as it is obvious, so don't even try to sell me the fair sampling assumption without proof. And again, it does not really matter if you sell it to me or not, as I am of no consequence. Experts agree that the detection loophole is essential. If DrChinese (or you) disagrees, this is his (or your) personal opinion, nothing more.

Please try to understand this: I don't need to prove that fair sampling is wrong. If you like fair sampling, the burden of proof is all yours. Let me rephrase this. I could admit (cutting some corners, such as "free will") that experiments demonstrate that at least one of the following three is wrong: 1)locality; 2) realism; 3) fair sampling . For DrChinese, fair sampling is a "holy cow", for somebody else local realism is a "holy cow". What I am trying to say, there is not enough data so far to make a definite choice.

As for the last question: "why do other tests - not requiring the fair sampling assumption - give the same results?", as I said, I offered DrChinese to explain how my "proof" in post 34 in this thread (that the sum of angles of a planar triangle does not equal 180 degrees) is any worse than "closing loopholes separately". Not a word from him.

So what experimental evidence exactly? There has been no experimental demonstration of the genuine Bell inequalities - 45 years after Bell. And there has been all the refutation you want - if Shimony and Zeilinger admit that, strictly speaking, local realism has not been ruled out, I can assure you, this is not because they like local realism - nobody accused them of such love. So somebody raised the issue of the "detection loophole", somebody raised the issue of the "locality loophole". I am no expert in the Bell inequalities, and I don't even know who raised these issues first, but seems they did a pretty good job, if all the leading experts agree what was actually demonstrated experimentally, and what was not.

 

[Frame Dragger]

Sorry, I just cannot understand a word. Whose "his"? What questions? Do you mean "DrChinese'"...

Let me get this straight... you have a firm grasp of QM, but contextual language eludes you? Yes, I mean Dr. Chinese, as you knew from the first. Care to answer those questions now that you've thrown your tantrum?

 

[akhmeteli]

Let me get this straight... you have a firm grasp of QM, but contextual language eludes you? Yes, I mean Dr. Chinese, as you knew from the first. Care to answer those questions now that you've thrown your tantrum?

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.

I'd like to see the experiment where Zeilinger concludes local realism is plausible, because there isn't one. There are plenty (of his) proving LR is not.

I did not say Zeilinger says local realism is plausible. He says it has not been ruled out, and I gave the quote. If DrChinese (or you) believes he changed his mind since then, why does not he give me a direct quote?

So I don't get where you think LR is considered a viable alternative.

Same answer. Zeilinger said LR has not been ruled out. I gave the quote confirming that. If later he said LR has been ruled out, give me the quote.

Why should you accept any scientific evidence?

As you (I mean Frame Dragger) said, this is not a rhetorical pissing match. I accept scientific evidence when I feel satisfied with it. Of course, there are a lot of areas where I just believe experts on their word, at least for the time being, as I cannot sort out everything myself. In this case, however, I don't see enough evidence to rule out local realism. Its elimination is a very radical idea, so the proof should be really good. However, both theoretical and experimental evidence against local realism is dubious in the best case.

And why do you suspect that the full universe would not match the results of a subsample?

For one, because the universe is not uniform in space or in time. And the application of fair sampling relevant to Bell is not about the universe. The question at hand is whether the set of detected photons has the same statistics as the set of undetected ones. Hidden variable theories suggest that there is a reason why one photon is detected and another is not. If you impose fair sampling, you reject such a possibility. Let me give you an example. Suppose you throw a lot of knives at a tree. Sometimes a knife gets stuck in the tree, sometimes it is bounced. The knives can have the same velocity and rotate in flight with the same angular velocity, but the results can vary depending on the phase (the knife can hit the tree point first or handle first). So if we try to build the statistics for the phase, the statistics will be different for knives stuck in the tree and for all knives. So, as Santos emphasized, fair sampling eliminates a great deal of local realistic theories immediately, so it would be indeed absurd to blindly accept fair sampling if you're trying to decide if local realistic theories are possible.

And why does increasing the sample percentage not lead to a different answer?

I don't know. In general, I don't know why physics laws are the laws we study at school, not some other laws. So what? But if you imply that the same results will hold for 100% efficiency, I don't buy it without proof. Indeed, you may try to break a steel bar by pulling it apart with a force of 1 N. No luck? Try one ton. Still no luck? Then let us conclude that the result remains the same as we increase the load. Of course, you'll just roll your eyes as you know that no material is infinitely strong. How the case of the Bell inequalities is any different? As long as you use some ersatz inequalities (using fair sampling), you can violate them with one hand tied behind your back. However, the entire humanity has not been able to violate the genuine inequalities for 45 years. You want to eliminate local realism? Break the true inequalities. Anything else is not enough. A theorem is a theorem. You cannot ensure its conclusion until its assumptions are fulfilled.

And why do other tests - not requiring the fair sampling assumption - give the same results?

Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

 

[akhmeteli]

This thread began with a post in which it was writtenello, akhmeteli. It appears to me there may be some misconception in the way you are thinking about Bell's theorem.

Bell's theorem, per se, is nothing more than a proposition of the form

P → D ,

where "P" is the conjunction of some set of premises, the 'truth' of which does not in any way require the 'truth' of any of the premises of Quantum Mechanics, and "D" is a certain condition (e.g. a Bell inequality).

________________
Sorry for the delay.

I am afraid I disagree that "Bell's theorem, per se, is nothing more than a proposition of the form

P → D"

Usually statement "QM → ~D" is also included in the Bell theorem.

Now, it happens that Quantum Mechanics (let us denote its premises by "QM") is such that

QM → ~D .

Therefore, the conjunction "P Λ QM" is inconsistent.
________________

In the weak version of Bell's theorem

P = local determinism .


In the strong version of Bell's Theorem

P = locality Λ PC Λ CF ,

where

PC ≡ perfect anti-correlation for equal settings

and

CF ≡ counterfactuality .


In the strong version, of course, "PC" has been employed as premise; but this means only that we are considering any theory which admits "PC" as a feature.
________________


... Do you see what I am saying?

Not really, sorry. It seems to me I understand what you wrote, but I don't quite see from your post where my misconception is. Could you please explain?

 

[SpectraCat]

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.
I did not say Zeilinger says local realism is plausible. He says it has not been ruled out, and I gave the quote. If DrChinese (or you) believes he changed his mind since then, why does not he give me a direct quote?
Same answer. Zeilinger said LR has not been ruled out. I gave the quote confirming that. If later he said LR has been ruled out, give me the quote.As you (I mean Frame Dragger) said, this is not a rhetorical pissing match. I accept scientific evidence when I feel satisfied with it. Of course, there are a lot of areas where I just believe experts on their word, at least for the time being, as I cannot sort out everything myself. In this case, however, I don't see enough evidence to rule out local realism. Its elimination is a very radical idea, so the proof should be really good. However, both theoretical and experimental evidence against local realism is dubious in the best case.

For one, because the universe is not uniform in space or in time. And the application of fair sampling relevant to Bell is not about the universe. The question at hand is whether the set of detected photons has the same statistics as the set of undetected ones. Hidden variable theories suggest that there is a reason why one photon is detected and another is not. If you impose fair sampling, you reject such a possibility. Let me give you an example. Suppose you throw a lot of knives at a tree. Sometimes a knife gets stuck in the tree, sometimes it is bounced. The knives can have the same velocity and rotate in flight with the same angular velocity, but the results can vary depending on the phase (the knife can hit the tree point first or handle first). So if we try to build the statistics for the phase, the statistics will be different for knives stuck in the tree and for all knives. So, as Santos emphasized, fair sampling eliminates a great deal of local realistic theories immediately, so it would be indeed absurd to blindly accept fair sampling if you're trying to decide if local realistic theories are possible.

I don't know. In general, I don't know why physics laws are the laws we study at school, not some other laws. So what? But if you imply that the same results will hold for 100% efficiency, I don't buy it without proof. Indeed, you may try to break a steel bar by pulling it apart with a force of 1 N. No luck? Try one ton. Still no luck? Then let us conclude that the result remains the same as we increase the load. Of course, you'll just roll your eyes as you know that no material is infinitely strong. How the case of the Bell inequalities is any different? As long as you use some ersatz inequalities (using fair sampling), you can violate them with one hand tied behind your back. However, the entire humanity has not been able to violate the genuine inequalities for 45 years. You want to eliminate local realism? Break the true inequalities. Anything else is not enough. A theorem is a theorem. You cannot ensure its conclusion until its assumptions are fulfilled.

Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

Ok .. so after reading this, I am confused. I realize that you are unconvinced by the experimental demonstrations of Bell inequality violations, because you are not willing to grant the fair sampling assumption. That seems fair to me ... I tend to be more willing to accept it, but perhaps that is because LHV theories have always seemed to me to fail the Occam's razor test.

However, on reading this post and others, it has become unclear to me whether you even accept Bell's theorem to begin with, or at least that you have some issues about how it is interpreted. So, just so I have it straight, do you accept that Bell's theorem proves that any theory that is consistent with QM experiments must violate either locality or counterfactual determinism?

EDIT: Sorry, you can ignore the above ... I should have gone back to the first pages again before posting. It had been a while since I read them, and I had forgotten your points about PP and UE with regards to Bell's theorem. No need to repeat yourself on my account.

 

[ThomasT]

Of course, "statistical independence" alone is not enough to derive a Bell inequality. There must be other assumptions.

So maybe you mean this:

Regarding the proposition

BL Λ PC Λ CF → D ,

where

BL ≡ Bell Locality (mathematical formulation in terms of probabilities) ,

it will be found, upon scrutiny, that BL is not in fact an expression of local causality. Rather, it is merely an expression of statistical independence.

Is that what you mean?

Yes.

 

[DrChinese]

Because some of the assumptions of the theorem are not fulfilled. Again, a theorem is a theorem. If the assumptions are not fulfilled, it is easy to avoid the conclusion. Same story as with my example of planar geometry.

In the case of photons created outside each others' light cones, how would that be? The Fair Sampling Assumption is not an issue, since NO local realistic explanation would hold anyway. According to the theoretical assumptions of LR, no such entanglement is possible under ANY scenario. Keep in mind that the photons don't even need to exist at the same time - and yet they are entangled.

 

[Frame Dragger]

Why should I guess? I hope you don't feel it is beneath you to be clearer. And I think I answered the questions, but I am not asking if contextual language eludes you, I'll try to repeat or rephrase my answers.

Don't get snippy because you're being called on your statements by multiple individuals who are not distracted by your tone. It's good to see you've gotten back to substance in the meantime, but you still seem to completely miss the basic point of the thread again.

You believe somethiing which is outside the mainstream, and it's taken you a while to explain/admit that. Now the debate on SUBSTANCE can begin. Enjoy! By the way, scientific evidence doesn't become valid when YOU accept it, rather, it becomes increasingly well accepted as it is repeated, and stands up to scrutiny... unlike your rhetoric.

 

[akhmeteli]

In the case of photons created outside each others' light cones, how would that be? The Fair Sampling Assumption is not an issue, since NO local realistic explanation would hold anyway. According to the theoretical assumptions of LR, no such entanglement is possible under ANY scenario. Keep in mind that the photons don't even need to exist at the same time - and yet they are entangled.

Dear DrChinese,

Thank you very much for your input, and let me explain my position. I am not an expert in the Bell theorem, and my posts in this thread are not based on my independent research. I just used published sources (and, of course, nightlight's posts strongly influenced my views). I work in quite a different field (I am also in Texas - Houston) and don't have much spare time, so I have to choose the battles I fight (I am sure you are very busy as well and I do value your time and input). So, if I can, I would not like to spend time right now and try to understand the new experiments that you are discussing. However, I may have to do that if I find that they are relevant to this discussion. So let me ask you the following questions.

Do you personally think these experiments demonstrated loophole-free violations of the Bell inequalities?

Do the authors of the articles claim they demonstrated (at long last) loophole-free violations of the Bell inequalities?

So far my understanding was there were no such claims. If I am right, these experiments do not change the existing situation, and I can wait until other people analyze these experiments and then use their conclusions.

Let me just re-emphasize one thing. Entanglement per se does not spell nonlocality (I usually use the following mental picture - it does not matter if it has anything to do with reality, what's important is this picture is a possibility: I visualize entangled particles of a spin singlet as constantly exchanging other particles; for example, for electrons it can be photons, and vice versa. This local visualisation is important, even if it is just an abstract possibility).

 

[akhmeteli]

You believe somethiing which is outside the mainstream, and it's taken you a while to explain/admit that. Now the debate on SUBSTANCE can begin. Enjoy! By the way, scientific evidence doesn't become valid when YOU accept it, rather, it becomes increasingly well accepted as it is repeated, and stands up to scrutiny... unlike your rhetoric.

Frame Dragger,

I flatly refuse to discuss anything with you until you try to be much, much clearer.

What is it that I believe that is outside the mainstream?

What is it that I admit?

I could make a guess, but I have no reason to do any guessing, this is no twenty questions. QM is difficult enough as it is, thank you, so I am not going to waste any time deciphering your "contextual language".

 

[ThomasT]

Look, ThomasT, you offer some statements that may be correct or wrong, but you do not offer any proof (or reference to such proof) and even state that you don't need any proof (if I understood you correctly). Maybe you don't, but I do. I don't see solid reasoning behind your statements, so I cannot agree or disagree with them, as neither those statements nor their negations seem obvious. With all due respect, I cannot believe you on your word - you are not a priest (or maybe you are? :-)), and I am not religious. Until you give some reasoning, I just have no comments, sorry.

I understand. My current line of thinking wrt the meaning of Bell's theorem is more a product of intuitive epiphany than rigorous development. So, please excuse the incompleteness of what I offer for your (or anyone's) criticism. (I'm sure that at least a few versions of what I'm saying are in the literature somewhere. I just don't remember exactly where.)

I do agree with you that some LHV formulation of entangled state hasn't been definitively ruled out yet. That is, some form of LHV theory is possible. But it definitely won't be a Bell local LHV theory, and it will probably involve some very arguable interpretations of the representation.

For example, ... can you at least explain if your phrase "the designs of entanglement experiments contradict Bell locality" means the same as "there are loopholes in those experiments"?

They mean different things. The first phrase means that any Bell local formulation of the entangled state simply misrepresents, contradicts the statistical dependence (via experimental design) required to experimentally demonstrate the entangled state.

So, even if all the technical problems (experimental loopholes) were solved, any Bell local formulation would still be unable to reproduce all the experimental results.

But this doesn't imply nonlocality, because Bell locality just means statistical independence.

The second phrase (loopholes) means that there are technical problems.

 

[akhmeteli]

They mean different things. The first phrase means that any Bell local formulation of the entangled state simply misrepresents, contradicts the statistical dependence (via experimental design) required to experimentally demonstrate the entangled state.

Again, I just see some statements, but reasoning or references are missing.

 

[Frame Dragger]

Frame Dragger,

I flatly refuse to discuss anything with you until you try to be much, much clearer.

What is it that I believe that is outside the mainstream?

What is it that I admit?

I could make a guess, but I have no reason to do any guessing, this is no twenty questions. QM is difficult enough as it is, thank you, so I am not going to waste any time deciphering your "contextual language".

We're not having a discussion. What we're having was simply me saying, "answer [Dr. Chinese's] damned question already." What followed was simply trying to tamp down your rhetoric so that you, ThomasT, and Dr. Chinese could progress in your discussion of the science. You seem to have hit a bit of a roadblock for the last... couple of pages.

 

[akhmeteli]

We're not having a discussion. What we're having was simply me saying, "answer [Dr. Chinese's] damned question already." What followed was simply trying to tamp down your rhetoric so that you, ThomasT, and Dr. Chinese could progress in your discussion of the science. You seem to have hit a bit of a roadblock for the last... couple of pages.

I believe I answered DrChinese's questions. You did not answer my questions in post 205. As for the roadblock, I cannot agree or disagree until you are much more clear and specific. So far your phrase about the roadblock is just a baseless statement. Or rhetoric, if you wish.

 

[SpectraCat]

Let me just re-emphasize one thing. Entanglement per se does not spell nonlocality (I usually use the following mental picture - it does not matter if it has anything to do with reality, what's important is this picture is a possibility: I visualize entangled particles of a spin singlet as constantly exchanging other particles; for example, for electrons it can be photons, and vice versa. This local visualisation is important, even if it is just an abstract possibility).

Ok .. that clearly wrong to me. How can your hypothetical "particles" being transferred between the entangled pair carry information faster than the speed of light? Because they would have to in your "picture", now that the "locality loophole" has been closed by showing statistical dependence of results measured at detectors with a spacelike separation.

Note that this does not require any sort of free-sampling assumption to be true, because the results predicted by any local realistic theory for such experiments would have to be random, and whatever else you might believe about the sampling of the data, you have to concede that the chance that the coincidence measurements from these experiments could arise randomly are astronomical.

So you are going to have to do better than that to justify a statement like, "entanglement per se does not spell non-locality", because contrary to your claim, such a model of particle transfer between an entangled pair is demonstrably NOT a possibility.