Understanding bell's theorem: why hidden variables imply a linear relationship?

[DevilsAvocado]

The QM predictions are similarly made for separate sets of photons, and not surprisingly, the QM predictions match the experimental results.

Thank you Bill, for the first time I can say that I agree 100%, and it feels like a ‘relief’... and as DrC I’m also very glad we finally gotten this far.

Now, if you could only explain – What’s the problem?

Should we be grumpy that LHV runs into problems with its definite nature and CFD?

Should we dismiss the outcome of EPR-Bell test experiments and say – No! This is not happening, because LHV can’t keep up with the pace!

Should we reject the fact that when only chosen two aligned/counter-aligned angles the compatibility between QM & LHV is 100%, and everything works like a dream?

Should we prohibit Bell to draw the logical conclusion that LHV gets dysfunctional when tested against more than aligned/counter-aligned angles?

How could one not see that this is the whole point of Bell’s theorem; to clearly point out the breakdown of LHV when tested against three angles?

How could one not understand that it’s exactly this ingenious move that finally solved the 20+ year long Bohr–Einstein debate?

And if refuting everything above – How on Earth could we ever test LHV in any other way?? Or should we draw the bizarre conclusion that there is a Local Reality indeed, but we are not allowed to test it thoroughly?

Many in this forum have tried very hard, but no one understands your main objection??

 

[billschnieder]

Thank you Bill, for the first time I can say that I agree 100%, and it feels like a ‘relief’... and as DrC I’m also very glad we finally gotten this far.

Now, if you could only explain – What’s the problem?

Continuing from my last post. Now that we all understand and agree how Bell test experiments are performed, and what experiments QM predictions are made for, let us now examine how Bell inequalities are derived.

Unlike in the experiments and QM in which we have 3 different sets "x", "y", "z", we start with a single set "w" and we ask

* What would we get if we measure set "w" at (a,b)
* What would we get if we measure set "w" at (a,c)
* What would we get if we measure set "w" at (b,c)

Note we are asking the questions for the exact same set of photons "w" not three different sets "x", "y", "z". In other words, we assume that each pair of photons in this set has a definite outcome at a given angle. In other words we are assuming that the outcomes for the set "w" look like:

abc
+++
++-
+-+
-++
+--
-+-
--+
...
etc for as many as there are photons in the set. It is this single list that is used to calculate all three correlations or probabilities used in Bell's inequality.

To calculate the (a,b) correlation/probability, we take the first column and the second column of this same list, since we are dealing with a single set of photons "w". To calculate the (a,c) correlation/probability, we take the first column and the third column and to calculate the (b,c) term we take the second and the third column of the exact same set "w". Notice all three correlations C(a,b), C(a,c), and C(b,c) are calculated from the exact same set. These are the correlations in Bell's inequality.

The issue Lugita and I have been discussing has been:

1) Lugita claims that the three correlations from three different sets "x", "y", "z" as described in my previous post from experiments and QM are the same and equal to the three correlations from a single set "w" from which Bell's inequalities are derived.

2) I claim that the three correlations from three different sets "x", "y", "z" from experiments and QM are different from the three correlations from a single set "w" from which Bell's inequalities are derived.

 

[billschnieder]

Should we be grumpy that LHV runs into problems with its definite nature and CFD?

The reason CFD comes in is because since we are dealing with a single set of photon "w" in deriving the inequality, but we can only measure one of the angle pairs from this set of photons, the other two hypothetical measurements will be counterfactual. In other words, Bell's inequalities is a relationship between three correlations, each of which which could possibly be measured, but only one of which can in fact be measured.

 

[billschnieder]

Many in this forum have tried very hard, but no one understands your main objection??

1) Do you understand my previous two posts? Do you agree that Bell's inequalities are derived for a single set of photons "w", and Bell tests experiments and QM produce correlations for three different sets of photons "x", "y", "z"? If you understand and agree with this, then you are half way to understand the problem.

2) Now if you understand (1), then you have Bell's inequalities such as P(C|w) <= P(A|w) + P(B|w) derived from a single set "w", and probabilities P(A|x), P(B|y), P(C|z) from QM and experiments obtained from three different sets. In order to claim that the probabilities from QM and experiments violate the inequalities (aka Bell's theorem), you must be also making the extra assumption that P(A|x) = P(A|w), P(B|y) = P(B|w), P(C|z) = P(C|w). This is in fact what lugita has been claiming. Without this assumption you can not even formulate Bell's theorem. If you understand and agree with this, then you are 75% of the way to understand the problem.

3) If you understand (1) and (2) then the only question we have left is this. Is it reasonable to make the assumption that P(A|x) = P(A|w), P(B|y) = P(B|w), P(C|z) = P(C|w)? In otherwords, can this assumption by itself be responsible for the violation without anything spooky going on? Another way of asking the same question: Are the correlations from QM and experiments legitimate terms to be used for comparison with Bell's inequality? The implication being that if the correlations from QM and experiments are not legimate terms for doing the comparison, then the assumption P(A|x) = P(A|w), P(B|y) = P(B|w), P(C|z) = P(C|w) is unreasonable, and we do not have Bell's theorem. In yet other words, if those correlations from three different sets are not the same as those from a single set, then violation of the inequality based on a single set, simply tells us that the correlations are not from a single set, which should be obvious already.

If you understand and agree with all of this, then you are 90% of the way there and all I have left is to convince you that three different sets can violate the inequality but a single set can never violate the inequality, and therefore the assumption P(A|x) = P(A|w), P(B|y) = P(B|w), P(C|z) = P(C|w) is not only unreasonable, it is in fact responsible for the violation.

 

[billschnieder]

That is ALL that a Bell test is. Because Bell says that LR theories cannot match QM results, ergo at least one of QM or LR theories are wrong. It isn't QM, as experiment shows.

But Bell draws this conclusion by using QM results predicted for three different sets of photons in an inequality derived from a single set of photons. Which is an implicit assumption that those correlations from three sets should be the same as those from a single set. It is this assumption that is at the core of the issue, not the ones used to derive the inequality.

Glad to see you finally admit that LR requires that for any photon, the results of a measurement must be predetermined.

I have never ever questioned this.

 

[DrChinese]

But Bell draws this conclusion by using QM results predicted for three different sets of photons ...

No, it doesn't. The coincidence rate QM predicts for anyone set of photons is cos^2(a-b). See, just one term there. So for example, QM predicts .25 for settings 120 degrees apart. A local realistic theory might predict instead .33* for the same setup. But that would be inconsistent with actual experiments, which yield very close to .25.

-------------------

There are currently no local realistic theory candidates which make the same predictions as QM. Although there are a few odd papers out there that claim to be local realistic models mimicking QM, so far none have held up.
*.33 would be the linear expected value for a LRT. As per the title of this thread.

 

[billschnieder]

No, it doesn't. The coincidence rate QM predicts for anyone set of photons is cos^2(a-b).

But this is where you are mistaken. The prediction QM makes for (a,b) is for one set of photons. The prediction QM makes for (b,c) ie cos^2(b-c) is for a completely different experiment (aka, different set of photons), and also cos^2(a-c) another completely different set of photons.

See, just one term there.

It looks like one term. But you need three terms to compare with Bell's inequality, where does QM get the other two, except by also predicting them? The question QM is answering is not:

If we have a single set of photons, what would we observe if we measure at angle (a,b), and at the angle (a,c) and at angle (b,c).

But rather it is.

If we measure a set of photons at a pair of angles (i,j) what would we observe.

You think you can simply substitute i,j with (a,b,c) to get the answers for (a,b), (a,c) and (b,c) and those answers together will be equivalent to the answer to the question "If we have a single set of photons, what would we observe if we measure at angle (a,b), and at the angle (a,c) and at angle (b,c)" but by doing that you making the same mistake Bell was talking about when he said:

The essential assumption can be criticized as follows. At first sight the required additivity of expectation values seems very reasonable, and it is rather the non-additivity of allowed values (eigenvalues) which requires explanation. Of course the explanation is well known: A measurement of a sum of noncommuting observables cannot be made by combining trivially the results of separate observations on the two terms.

...

The danger in fact was not in the explicit but in the implicit assumptions. It was tacitly assumed that measurement of an observable must yield the same value independently of what other measurements may be made simultaneously. Thus as well as P(Φ3) say, one might measure either P(Φ2) or P(ψ2), here Φ2 and ψ2 are orthogonal to Φ3 but not to one another. These different possibilities require different experimental arrangements; there is no a priori reason to believe that the results for P(Φ3) should be the same.

 

[DrChinese]

It looks like one term. But you need three terms to compare with Bell's inequality, ...

The usual Bell inequality has more than 1 term, sure. Who cares?* What we care about is that Bell says no local realistic (hidden variable) theory can match the predictions of QM. The inequality is simply a convenience for seeing which scenarios don't match. Because some do! Here is one, for example:

P(a,a)=1 for both QM and some LR theories.

Similarly, P(b,b)=1 for both QM and some LRTs. And likewise P(c,c)=1.

So P(a,a)+P(b,b)+P(c,c)=3. A shocker I am sure - no disagreement between QM and some LRTs here. Now tell me, you deny this relationship as well on the grounds that it is 3 different sets of photons? What a dopey argument. It is obvious you are on a different page than everyone else, why don't you admit it and move on?


*To prove it, take the DrChinese challenge. As you have always failed that test, as we already have found out. And guess what - you don't even need Bell for that one! You only need to try to match QM.

 

[lugita15]

I don't think you fully understand the implication of this claim. It is not correct to say the outcome at (a,b) does not depend on the angle (a,b) or the outcome at (a,c) does not depend on the angle (a,c), since those settings are part of the set-up which produces the outcome.

I think we're having a misunderstanding here. You agreed that before a given photon pair is measured, answer to the question "What result would you get if you measured this photon pair at (θ1,θ2)?" is predetermined for all possible polarizer settings θ1 and θ2, right? Let us denote this predetermined answer by f(θ1,θ2). The domain of f is ℝ² and its codomain (or range) is {1,-1}×{1,-1}. So for instance, if photon 1 would go through and photon 2 would not go through if the polarizers are set at -30 degrees and 0 degrees respectively, then we denote that by f(-30,0)=(1,-1).

Now when you say "It is not correct to say the outcome at (a,b) does not depend on the angle (a,b)", I assume what you mean by that is that in order to find out what f(a,b) is, you need to know what a and b are. If that's what you meant, I fully agree. For any angles θ1 and θ2, then value of f(θ1,θ2) is certainly dependent on the values of θ1 and θ2.

But what I'm saying is that the function f does not depend on the angle settings θ3 and θ4 that you actually turn the polarizers to. In other words, for all possible angle settings θ1 and θ2, the value of f(θ1.θ2) does not depend on whether θ1=θ3 or θ2=θ4. That's because for each photon pair, the function f is entirely predetermined before the photon pair even "knows" what angles it's actually going to be measured at. Do you agree or disagree with that?

Probably what you are trying to say is that the outcome of the single photon measured at angle "a" in the (a,b) pair must be exactly the same as the outcome of the same photon measured at angle "a" in the (a,c) pair. In other words, the outcome for that particular single photon should not change from (a,b) to (a,c) just because it's sibling was measured at "c" in (a,c) instead of "b" in (a,b). So Alice's choice of setting should not influence Bobs outcome for the same setting "a" and the exact same photon. If this is what you mean, then I agree.

No, this isn't what I was trying to say, although I do agree with it.

But if you mean that the outcome at (a,b) can not depend on the angle pair (a,b) then I disagree with that.

What I mean is that the outcome you would get at (a,b) depends on what (a,b) is, but it doesn't depend on whether you're actually going to measure at (a,b) or (a,c). See above.

No. I disagree with that. Just because it is predetermined to produce the result at (a,c) doesn't mean it can produce the result without (a,c). Without the setting (a,c) you will not get the result at (a,c) so how can you say the result obtained at (a,c) does not depend on what you actually choose (a,c)? What is predetermined is the condition that "if you set the device to (a,c), you will obtain such and such result". It doesn't make much sense to say the result you obtain at (a,c) does not depend on the setting, which is required to obtain the result!

Again, I think we're having a misunderstanding. See what I said above.

Free will has nothing to do with it. You are free to choose a different setting, you will get a different result. But whenever you freely choose (a,c) you will get the result predetermined for (a,c).

I agree with this.

Probably what you are trying to say here is that the result for the single photon measured at angle "a", should not depend on whether you measured the pair at (a,c) or you measured (a,b). Again, that means Bob's result for the same photon measured at the same angle should not depend on what angle Alice chose to measure it's sibling photon at. If this is what you mean, I agree.

Again, that's not what I meant, but I do agree with it.

See explanation above. The results predetermined for a given angle pair can not be independent of the angle pair for which it is predetermined.

Yes, the predetermined result for a given angle pair does depend on the angle pair for which it is predetermined, but it does NOT depend on the actually measured angle pair.

 

[billschnieder]

I think we're having a misunderstanding here. You agreed that before a given photon pair is measured, answer to the question "What result would you get if you measured this photon pair at (θ1,θ2)?" is predetermined for all possible polarizer settings θ1 and θ2, right? Let us denote this predetermined answer by f(θ1,θ2). The domain of f is ℝ² and its codomain (or range) is {1,-1}×{1,-1}. So for instance, if photon 1 would go through and photon 2 would not go through if the polarizers are set at -30 degrees and 0 degrees respectively, then we denote that by f(-30,0)=(1,-1).

I agree.

Now when you say "It is not correct to say the outcome at (a,b) does not depend on the angle (a,b)", I assume what you mean by that is that in order to find out what f(a,b) is, you need to know what a and b are. If that's what you meant, I fully agree. For any angles θ1 and θ2, then value of f(θ1,θ2) is certainly dependent on the values of θ1 and θ2.

Yes.

But what I'm saying is that the function f does not depend on the angle settings θ3 and θ4 that you actually turn the polarizers to. In other words, for all possible angle settings θ1 and θ2, the value of f(θ1.θ2) does not depend on whether θ1=θ3 or θ2=θ4. That's because for each photon pair, the function f is entirely predetermined before the photon pair even "knows" what angles it's actually going to be measured at. Do you agree or disagree with that?

I agree, whatever hidden mechanism is producing the outcome for the given photon pair (your function f), is the same hidden mechanism for the exact same photon pair irrespective of what angles are actually chosen.

What I mean is that the outcome you would get at (a,b) depends on what (a,b) is, but it doesn't depend on whether you're actually going to measure at (a,b) or (a,c). See above.

I agree that what the photon pair would produce at (a,b) is the same and won't be different whether that photon pair was measured at (a,b) or at (a,c). If this is what you mean? I agree.

 

[billschnieder]

The usual Bell inequality has more than 1 term, sure. Who cares?* What we care about is that Bell says no local realistic (hidden variable) theory can match the predictions of QM.

If you care about what Bell's theorem says, then you also care (or should care) about the logic of how Bell arrived at that conclusion, which was by generating 3 correlations from QM to compare with 3 correlations from the inequalities.

And you also care (or should care) about the logic that is used to claim that 3 correlations from experiments violate the inequality.

If your mind is made up about those two aspects and you already believe that the logic is iron-clad and beyond discussion, then this discussion will not interest you. I do not question the inequalities, they are valid. I do not question the QM predictions, they are valid. I do not question the experimental results, they are valid. I do not claim to have a LR model that matches QM so asking me to provide one does not advance the discussion. What I question is the suggestion that the correlations from QM and experiments are equivalent correlations to those in the inequalities and this goes to the heart of the logic used to obtain Bell's theorem or demonstrate experimental violation.

At least, if you already believe that the correlations from QM and experiments are equivalent to those in the inequalities, you should consider the question: Would Bell's theorem still follow in case they were not equivalent? If you can at least understand my argument and agree that Bell's theorem will not be a valid conclusion unless those correlations from QM and experiments are equivalent to those in the inequalities, then the only question left would be for you to convince me (if you are interested) that they are equivalent, and for me to convince you that they are not. Of course we won't have to agree on anything but the issues will be clearly laid out.

 

[lugita15]

I agree, whatever hidden mechanism is producing the outcome for the given photon pair (your function f), is the same hidden mechanism for the exact same photon pair irrespective of what angles are actually chosen.


I agree that what the photon pair would produce at (a,b) is the same and won't be different whether that photon pair was measured at (a,b) or at (a,c). If this is what you mean? I agree.

Yes, this is exactly what I meant. I am astounded that we agree on this point, because I was expecting this to be the crux of our disagreement.

Well, let me ask you a follow-up question now: do you agree or disagree that the value of the following fraction is independent of θ3 and θ4?

(Number of photon pairs, actually measured at (θ3,θ4), for which f(θ1,θ2) is equal to (1,-1) or (-1,1))/(Number of photon pairs which were actually measured at (θ3,θ4))

 

[billschnieder]

Well, let me ask you a follow-up question now: do you agree or disagree that the value of the following fraction is independent of θ3 and θ4?

(Number of photon pairs, actually measured at (θ3,θ4), for which f(θ1,θ2) is equal to (1,-1) or (-1,1))/(Number of photon pairs which were actually measured at (θ3,θ4))

That question is not sufficiently clear to me. Let me try to rephrase it and you can tell me if I understood it correctly or not.

You are saying we take a set of photon pairs "p" and we measure at the angles (θ3,θ4) and then we calculate the relative frequency for getting the result of either (+, -) or (-, +). Which is calculated as
\frac{ N_{(+-)} + N_{(-+)} }{N_p}
That is the total number of photon pairs which gave (+1, -1) plus the total number which gave (-1, +1) divided by the total number of photon pairs in the set "p".

If by not depending on (θ3,θ4), you mean the result we would obtain for the set of photon pairs "p" at angles (θ3,θ4), would not be different whether we actually measured at angles (θ3,θ4) or at angles (θ6,θ7), then I agree with this.

 

[lugita15]

You are saying we take a set of photon pairs "p" and we measure at the angles (θ3,θ4) and then we calculate the relative frequency for getting the result of either (+, -) or (-, +). Which is calculated as
\frac{ N_{(+-)} + N_{(-+)} }{N_p}
That is the total number of photon pairs which gave (+1, -1) plus the total number which gave (-1, +1) divided by the total number of photon pairs in the set "p".

Yes, that's what I mean.

If by not depending on (θ3,θ4), you mean the result we would obtain for the set of photon pairs "p" at angles (θ3,θ4), would not be different whether we actually measured at angles (θ3,θ4) or at angles (θ6,θ7), then I agree with this.

No, that's not what I mean. What I mean is, we take one set of photon pairs p measured at (θ3,θ4), and we take another set of photon pairs q measured at (θ6,θ7). And then I'm claiming that the relative frequency of getting (1,-1) or (-1,1) for f(θ1,θ2) is the same for p and q. Do you agree or disagree with that?

 

[billschnieder]

If by not depending on (θ3,θ4), you mean the result we would obtain for the set of photon pairs "p" at angles (θ3,θ4), would not be different whether we actually measured at angles (θ3,θ4) or at angles (θ6,θ7), then I agree with this.

No, that's not what I mean. What I mean is, we take one set of photon pairs p measured at (θ3,θ4), and we take another set of photon pairs q measured at (θ6,θ7). And then I'm claiming that the relative frequency of getting (1,-1) or (-1,1) for f(θ1,θ2) is the same for p and q. Do you agree or disagree with that?

No, I do not agree with this. Since you are now talking about two different sets of photons, the two relative frequencies can only be the same if the two sets of photons were identically prepared. So the answer is, yes they can be the same (if identically prepared) but they are not necessarily the same.

Furthermore, I do not understand what this has to do with what you asked earlier that

do you agree or disagree that the value of the following fraction is independent of θ3 and θ4?

And earlier when I answered your question about "depends", you said:

I agree that what the photon pair would produce at (a,b) is the same and won't be different whether that photon pair was measured at (a,b) or at (a,c). If this is what you mean? I agree.

Yes, this is exactly what I meant. I am astounded that we agree on this point, because I was expecting this to be the crux of our disagreement.

But then now you seem to be changing what you mean by "depends", because what I said now about a single set is almost word for word what I said earlier about a single pair, and you agreed then.

 

[lugita15]

No, I do not agree with this. Since you are now talking about two different sets of photons, the two relative frequencies can only be the same if the two sets of photons were identically prepared. So the answer is, yes they can be the same (if identically prepared) but they are not necessarily the same.

What does it mean for two photon pairs to be identically prepared? And whatever your definition of identically prepared is, do you consider two photon pairs, each of which is polarization-entangled, to be identically prepared? At least quantum mechanics views them as having the same spin part for their wavefunctions.

Furthermore, I do not understand what this has to do with what you asked earlier that

do you agree or disagree that the value of the following fraction is independent of θ3 and θ4?

What I was envisioning is an experiment in which, for every photon pair, the experimenter just randomly decides on some pair of angles to measure at. So some pairs he measures at (θ3,θ4), and some pairs he measures at (θ6,θ7), and maybe for other pairs he measures all kinds of different angle combinations. So then, for any given angle pair (θ3,θ4), you can ask, "What percentage of photon pairs measured at (θ3,θ4) had f(θ1,θ2) equal to (1,-1) or (-1,1)?" And I was saying that the answer to this question stays the same even if you replace (θ3,θ4) with (θ6,θ7). Of course if you replace (θ3,θ4) with (θ6,θ7) in that expression, then you're changing what photon pairs you're talking about.

But then now you seem to be changing what you mean by "depends", because what I said now about a single set is almost word for word what I said earlier about a single pair, and you agreed then.

I'm sorry for any confusion. I'm still agreeing with what you said in post #310. Now that we're agreed on one point, I'm trying to see whether we can get agreement on another point.

 

[billschnieder]

What does it mean for two photon pairs to be identically prepared?

It means in every aspect relevant for the outcome you are interested in, the two systems are identical. In other words, if the important property of the system is a hidden property λ, and a source is producing a set of photons with such hidden properties, then the probability distribution ρ(λ) in system "p" is identical to the probability distribution ρ(λ) in system "q".

And whatever your definition of identically prepared is, do you consider two photon pairs, each of which is polarization-entangled, to be identically prepared?

It depends. If what you are measuring depends on anything else which is different between the two pairs, then they are not. But if whatever you are measuring depends ONLY on the fact that they are polarization entangled, then you can say they are identically prepared. In other words, the definition of "identically prepared" cannot be separated from the experiment you are actually performing.

For two pairs of polarization entangled photons, let us say for example that in each pair the polarization vectors are perfectly opposite each other in direction. If in the experiment your outcome is also dependent on the relative angle between the polarizer and the direction of the polarization vector, then the original direction of the polarization vector is also important. And if this initial direction is not the same between the two pairs, then you can't say they are identically prepared for this experiment and you will get different results after measurement. However, if your source produces two sets of photons in which the original direction of the polarization vector is generated randomly in a probability distribution which is identical between the first set and the second, then you will get the same results for the experiment and you can say the two sets of photons are identically prepared for the experiment. Only in this case can you conclude that the results in set "p" are identical to the results in set "q".

If this is not clear, what I mean is: if polarization entanglement governs the relationship between the directions of the polarization vectors of the two photons in a pair, but the experiment measures the relationship between the direction of the polarization vector of each photon and the vector of the polarizer, two polarization entangled pairs of photons will not be considered identically prepared unless they have the same relative angle wrt to the polarizer . Only then will you expect to have the exact same result from measuring both pairs.

If this is what you meant, then I agree that the relative frequencies will be the same in both "p" and "q".

 

[billschnieder]

What I was envisioning is an experiment in which, for every photon pair, the experimenter just randomly decides on some pair of angles to measure at. So some pairs he measures at (θ3,θ4), and some pairs he measures at (θ6,θ7), and maybe for other pairs he measures all kinds of different angle combinations. So then, for any given angle pair (θ3,θ4), you can ask, "What percentage of photon pairs measured at (θ3,θ4) had f(θ1,θ2) equal to (1,-1) or (-1,1)?" And I was saying that the answer to this question stays the same even if you replace (θ3,θ4) with (θ6,θ7). Of course if you replace (θ3,θ4) with (θ6,θ7) in that expression, then you're changing what photon pairs you're talking about.

As explained in my previous post, provided the source is producing the photons with such a uniform distribution of the relevant parameters that the probability distribution of those parameters in the set actually measured in (θ3,θ4) is the same as the probability distribution in the set actually measured at (θ6,θ7), then I agree that the answer will be the same for both sets. Technically one may say in order for the correlations to be the same, the source must be operating as a stationary process with respect to the relevant hidden parameters.

 

[DrChinese]

What I was envisioning is an experiment in which, for every photon pair, the experimenter just randomly decides on some pair of angles to measure at.

I have always held that there is no purpose to changing angle settings randomly EXCEPT to demonstrate that the detectors could not be exchanging signals which would affect the outcome. This is easily ruled out for local realistic theories by experiments such as Weihs et al. Hopefully Bill is not arguing that such rapport is occurring between the detectors per their respective settings.

So to my thinking, the point is that the experimenter selects the desired 2 settings and let's the process run. And the experimenter 's selections are independent of what is occurring at the source. Since Bill thinks the outcomes from the source are predetermined, the question is what would you expect? And here is where Bill's challenges fall short. We know there is perfect correlation (as he expects) for P(a,a). Ditto for P(b,b) and P(c,c). He accepts this despite these are drawn from different sets (his terminology). But he rejects the same notion for P(a,b), P(a,c) and P(b,c).

Further: he has tried to construct LR data sets that mimic the QM results IFF the experimenter selects special angle pairs that have such property. But many don't. So for example, it is possible to construct LR data sets where P(a,b)=.25 and P(a,c)=.25 [agreeing with QM] but P(b,c) is necessarily .50 in this case [which does not agree with the QM expectation].

So I guess my point is that he is not going to accept your reasoning even if the experimenter were to choose a pair at a time, as you reasonably suggest.

 

[DrChinese]

So Bill, here is DrC challenge #2.

I have a laser pump (oriented at 45 degrees) to a single Type I crystal oriented H. The down converted output stream will be definite VV (let's call them LeftV and RightV). I run each V to a beam splitter set at 45 degrees with detectors at each output. Because each V has a 50-50 chance of being transmitter/refracted, the coincidence rate is 50%.

I have a laser pump (oriented at 45 degrees) to a single Type I crystal oriented V. The down converted output stream will be definite HH (let's call them LeftH and RightH). I run each H to a beam splitter set at 45 degrees with detectors at each output. Because each H has a 50-50 chance of being transmitter/refracted, the coincidence rate is 50%.

In neither of the above scenarios is the coincidence rate higher than 50%.

Yet if I combine the LeftV and LeftH streams, and then combine the RightV and RightH streams such that the source pump cannot be distinguished, they will be entangled. Using a common detector series for both, the correlation will now be 100%. How, prey tell, is this possible in your scenario when everything was predetermined from the get-go... and nothing matched more than 50%?

 

[billschnieder]

And here is where Bill's challenges fall short. We know there is perfect correlation (as he expects) for P(a,a). Ditto for P(b,b) and P(c,c). He accepts this despite these are drawn from different sets (his terminology). But he rejects the same notion for P(a,b), P(a,c) and P(b,c).

I don't think you fully understand the argument yet. In your challenge #2, you are asking me to provide a LR model for the experimental setup you described which I do not believe will advance the discussion. As I explained in post #311, the argument here does not claim that a LR model is possible (although I'm not necessarily admitting that one is impossible).

The main issue here is whether correlations from three sets "x","y","z" are equivalent to those in a single set "w". Lugita is in the process of demonstrating why they must be equal. If you can please clarify how your challenge helps us to establish that they are equal then it will be very beneficial for the discussion.

 

[billschnieder]

So Bill, here is DrC challenge #2.

I have a laser pump (oriented at 45 degrees) to a single Type I crystal oriented H. The down converted output stream will be definite VV (let's call them LeftV and RightV). I run each V to a beam splitter set at 45 degrees with detectors at each output. Because each V has a 50-50 chance of being transmitter/refracted, the coincidence rate is 50%.

I have a laser pump (oriented at 45 degrees) to a single Type I crystal oriented V. The down converted output stream will be definite HH (let's call them LeftH and RightH). I run each H to a beam splitter set at 45 degrees with detectors at each output. Because each H has a 50-50 chance of being transmitter/refracted, the coincidence rate is 50%.

In neither of the above scenarios is the coincidence rate higher than 50%.

Yet if I combine the LeftV and LeftH streams, and then combine the RightV and RightH streams such that the source pump cannot be distinguished, they will be entangled. Using a common detector series for both, the correlation will now be 100%. How, prey tell, is this possible in your scenario when everything was predetermined from the get-go... and nothing matched more than 50%?

That is an interesting challenge nonetheless so I'll be happy if you can clarify it a bit. From what I understand you have.

1) V-filtered non-entangled pairs : 50% coincidence.
2) H-filtered non-entagled pairs : 50% coincidence.
3) Unfiltered entangled pairs : 100 % coincidence.

Is this accurate? Or are the pairs in (1) and (2) also entangled.

 

[DrChinese]

That is an interesting challenge nonetheless so I'll be happy if you can clarify it a bit. From what I understand you have.

1) V-filtered non-entangled pairs : 50% coincidence.
2) H-filtered non-entagled pairs : 50% coincidence.
3) Unfiltered entangled pairs : 100 % coincidence.

Is this accurate? Or are the pairs in (1) and (2) also entangled.

You have it correct. The 1/2 pairs are not polarization entangled, but they are entangled as to momentum. The 3) group is the combination of streams like 1) and 2) - and I realize you in a sense consider these different sets.

 

[DrChinese]

I don't think you fully understand the argument yet. In your challenge #2, you are asking me to provide a LR model for the experimental setup you described which I do not believe will advance the discussion. As I explained in post #311, the argument here does not claim that a LR model is possible (although I'm not necessarily admitting that one is impossible).

The main issue here is whether correlations from three sets "x","y","z" are equivalent to those in a single set "w". Lugita is in the process of demonstrating why they must be equal. If you can please clarify how your challenge helps us to establish that they are equal then it will be very beneficial for the discussion.

What I am saying is that we are talking about a series of attributes of an entangled stream of pairs. This stream has correlated properties can be described in some variety of ways, such as P(a,a) as well as P(a,b). P(a,a) is fully consistent with a local HV hypothesis, as envisioned by EPR. You don't have any problem with P(a,a), P(b,b) etc but you have a problem with P(a,b) and P(a,c) etc.

 

[lugita15]

As explained in my previous post, provided the source is producing the photons with such a uniform distribution of the relevant parameters that the probability distribution of those parameters in the set actually measured in (θ3,θ4) is the same as the probability distribution in the set actually measured at (θ6,θ7), then I agree that the answer will be the same for both sets.

OK, then the question becomes, do you believe that the sources used in Bell tests, i.e. sources that produce type-I spontaneous parametric down-conversion, obey this criterion of the probability distribution of parameters in different sets being the same?

Let me also ask you this: do you at least agree that, if the photon pairs in both p and q are measured at (θ3,θ4), then the relative frequency of getting (1,-1) or (-1,1) for f(θ3,θ4) is the same for p and q?

 

[billschnieder]

What I am saying is that we are talking about a series of attributes of an entangled stream of pairs. This stream has correlated properties can be described in some variety of ways, such as P(a,a) as well as P(a,b). P(a,a) is fully consistent with a local HV hypothesis, as envisioned by EPR. You don't have any problem with P(a,a), P(b,b) etc but you have a problem with P(a,b) and P(a,c) etc.

I don't get what this has to do with the argument I'm making. Your last sentence there does not correctly characterize the argument. In the most simplistic terms, I'm saying it is reasonable to expect correlations between properties in a single set of entangled pairs, but it is unreasonable to expect the same correlations between properties from one set of entangled pairs and properties from a completely different set of entangled pairs even if the two sets are indistinguishable. So I do not understand why you would say I have a problem with P(a,b) and P(a,c). I don't. I have a problem with taking 3 correlations from 3 different independent sets which have no relationship with each other and claiming that the correlations are the same with 3 correlations from within a single set. This is the issue.

 

[billschnieder]

OK, then the question becomes, do you believe that the sources used in Bell tests, i.e. sources that produce type-I spontaneous parametric down-conversion, obey this criterion of the probability distribution of parameters in different sets being the same?

Yes, for a large enough number of photon pairs from such sources, I have no reason believe they are not, based on what I know. The fact that repeated measurements on such sets produce results which match QM is convincing evidence that the sets are identically prepared.

Let me also ask you this: do you at least agree that, if the photon pairs in both p and q are measured at (θ3,θ4), then the relative frequency of getting (1,-1) or (-1,1) for f(θ3,θ4) is the same for p and q?

I thought I already agreed to this point. Yes, for a large enough number photons in separate identically prepared sets of photons "p" and "q", f(θ3,θ4) should give the same relative frequencies.

 

[billschnieder]

You have it correct. The 1/2 pairs are not polarization entangled, but they are entangled as to momentum. The 3) group is the combination of streams like 1) and 2) - and I realize you in a sense consider these different sets.

I am baffled as to why you would even be comparing the first two streams with the third. Are you suggesting that stream 3 is simply a linear combination of the first two?

 

[lugita15]

Yes, for a large enough number of photon pairs from such sources, I have no reason believe they are not based on what I know. The fact that repeated measurements on such sets produce results which match QM is convincing evidence that the sets are identically prepared.

I'm glad (although again surprised) to hear that we're agreed on that. In future discussion, let's assume that we're dealing with sufficiently large sets of photons, so that we don't need to worry about whether they're identically prepared.

So now you've agreed that if the photon pairs in p are measured at (θ3,θ4), and the photon pairs in q are measured at (θ6,θ7), then the relative frequency of getting (1,-1) or (-1,1) for f(θ1,θ2) is the same for p and q.

In particular, if the photon pairs in p are measured at (-30,0), and the photon pairs in q are measured at (0,30), then the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for p and q. And similarly, if the photon pairs in r are measured at (-30,30), then the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for q and r. Therefore, the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for p, q, and r. Do you agree with that?

 

[billschnieder]

I'm glad (although again surprised) to hear that we're agreed on that.

I'm not surprised

In future discussion, let's assume that we're dealing with sufficiently large sets of photons, so that we don't need to worry about whether they're identically prepared.

Fine with me. I was just trying to be very clear so there was no chance for misunderstanding.

So now you've agreed that if the photon pairs in p are measured at (θ3,θ4), and the photon pairs in q are measured at (θ6,θ7), then the relative frequency of getting (1,-1) or (-1,1) for f(θ1,θ2) is the same for p and q.

Agreed.

In particular, if the photon pairs in p are measured at (-30,0), and the photon pairs in q are measured at (0,30), then the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for p and q. And similarly, if the photon pairs in r are measured at (-30,30), then the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for q and r. Therefore, the relative frequency of getting (1,-1) or (-1,1) for f(-30,0) is the same for p, q, and r. Do you agree with that?

Agreed.