I Is Bell's Theorem Valid Despite Fundamental Theoretical Loopholes?

[facenian]

Hello, I've been conducting a little search on my own and found there seems to be a community of physicists/philosophers that don't accept Bell's theorem as valid.
There are are two types of loopholes : fundamental theoretical ones and experimental loopholes.
I'm particularly interested in the the first kind of arguments and would like to know, in spite of personal beliefs, if somebody have an objective opininon about this and how serious the people of this "community" is taken by the rest of scientific community.

 

[phinds]

... objective opininon ...

This is a contradiction in terms

 

[atyy]

The theoretical loopholes or assumptions (superdeterminism, non-realism, single outcome, etc ...) are standard and well accepted.

https://arxiv.org/abs/1303.2849
Bell nonlocality
Nicolas Brunner, Daniel Cavalcanti, Stefano Pironio, Valerio Scarani, Stephanie Wehner

"The point of this discussion is that an experiment "closing" the locality loophole should be designed in such a way that any theory salvaging locality by exploiting weaknesses of the above type should be suciently conspiratorial and contrived that it reasonably not worth considering it."

 

[DrChinese]

... there seems to be a community of physicists/philosophers that don't accept Bell's theorem as valid.

Well, it's a small community.

All it would take is a single counterexample to wreck Bell's Theorem. And yet, over 50 years later, there are none.

Please note additionally: In the past 20 years, there have been many thousands of different experimental disproofs of local realism. Bell started it, but the number of concurring experiments is staggering. Many use techniques very dissimilar to the Bell approach.

Basically, to deny Bell is to deny that there is such thing as an entangled quantum state.

 

[Denis]

There are some freaks around Joy Christian, one of them a former activist from the Sci.Physics.Foundations USENET group, who has created a copy of this as his own forum, which became their meeting place. Joy Christian has at least some mathematical education, but is unable to acknowledge his quite elementary errors. What surprises me is that he has been even found some supporters. But this is interesting mainly from a sociological point of view, and in no way evidence that he has really found something.

 

[facenian]

Well, it's a small community.

It may be small but they seem to support each other and are very convinced of what they say.

But this is interesting mainly from a sociological point of view, and in no way evidence that he has really found something.

It is interesting but not all of them are freaks. Some of them publish papers in respectable journals.

 

[stevendaryl]

It may be small but they seem to support each other and are very convinced of what they say.

It is interesting but not all of them are freaks. Some of them publish papers in respectable journals.

Are you talking about Joy Christian's supporters, or more generally people who question Bell's proof? Joy Christian's supporters don't include any reputable physicists, as far as I know.

 

[facenian]

Are you talking about Joy Christian's supporters, or more generally people who question Bell's proof? Joy Christian's supporters don't include any reputable physicists, as far as I know.

No, I'm not talking about Joy Christian and supporters. I wouldn't mind about those kind of things. I'm talking about people who, like I said, seem to be serious and even sometimes (not allways) publish in respectable peer review journals. According to what have been said here, it is a small group and it seems the rest of the physics community don't pay much attention to them. I wonder if it is worthwhile trying to explain where and why their arguments are not good even some of them are just wrong. I just wrote a letter to editor about one such article, I don't know if it will be publish.

 

[stevendaryl]

No, I'm not talking about Joy Christian and supporters. I wouldn't mind about those kind of things. I'm talking about people who, like I said, seem to be serious and even sometimes (not allways) publish in respectable peer review journals. According to what have been said here, it is a small group and it seems the rest of the physics community don't pay much attention to them. I wonder if it is worthwhile trying to explain where and why their arguments are not good even some of them are just wrong. I just wrote a letter to editor about one such article, I don't know if it will be publish.

I'm not sure what you're asking: Are you asking whether it's worthwhile in Physics Forums to discuss why he's wrong?

 

[facenian]

I'm not sure what you're asking: Are you asking whether it's worthwhile in Physics Forums to discuss why he's wrong?

No, I'm asking to Physics Forums whether it is worthwhile to respond to those people writing articles in journals refuting their allegations

 

[Nugatory]

No, I'm asking to Physics Forums whether it is worthwhile to respond to those people writing articles in journals refuting their allegations

It's hard to answer a question like that in the abstract. What would be an example of an article from a reasonably respectable journal that comes from a member of this "community of physicists/philosophers that don't accept Bell's theorem as valid"?

 

[vanhees71]

Well, if there's an obvious errorneous article in a journal, one should write a comment about it. Of course, it will be peer reviewed and carefully checked whether the claim of error is justified or not. That's at least common practice in the "hard sciences".

On the other hand, I'm not sure, how this is handled in the "soft sciences", particularly philosophy. I guess in these subjects you'd write comments after comments and commenting these comments in an endless regression. SCNR.

 

[phinds]

Well, if there's an obvious errorneous article in a journal, one should write a comment about it. Of course, it will be peer reviewed and carefully checked whether the claim of error is justified or not. That's at least common practice in the "hard sciences".

On the other hand, I'm not sure, how this is handled in the "soft sciences", particularly philosophy. I guess in these subjects you'd write comments after comments and commenting these comments in an endless regression. SCNR.

Yes, and it would FEEL endless long before it ended.

 

[Nugatory]

When you speak of "not accepting Bell's theorem as valid" that can mean any of several positions:
1) There is an error in Bell's proof, so that Bell's inequality does not follow from the starting assumptions. This position is outright crackpottery.
2) Bell's proof is correct (so Bell's inequality does indeed follow from the starting assumptions) but the experiments demonstrating that quantum mechanics violates the inequality are not conclusive because of various loopholes. This position has become less and less tenable as the experiments have become better and have closed more loopholes; holding it now is very close to outright crackpottery.
3) Because Bell's proof is correct and the experimental results are valid quantum mechanics does not meet Bell's starting assumptions, but these assumptions do not cover all possible local and realistic theories so the conclusion "no local realistic hidden variable theory can reproduce the results of QM" is still not valid. In the absence of a candidate theory, this position generally leads to a sterile debate about what is meant by "local" and "realistic".
4) The universe is superdeterministic in a way that generates all observed experimental results. This proposition is not falsifiable, but carries a fairly high implausibility factor.

Unless you have had the misfortune to stumble into a den of Joy Christianites, chances are the debate you're seeing is of the #3 variety.

 

[Denis]

No, I'm asking to Physics Forums whether it is worthwhile to respond to those people writing articles in journals refuting their allegations

In a "publish or perish" world, why not? An article in a good journal "refuting" Bell's theorem means a good chance for your answer to be published in the same journal.

 

[atyy]

No, I'm asking to Physics Forums whether it is worthwhile to respond to those people writing articles in journals refuting their allegations

As Nugatory wrote, you have to be more specific. Which researchers and which papers are you talking about?

 

[Denis]

It's hard to answer a question like that in the abstract. What would be an example of an article from a reasonably respectable journal that comes from a member of this "community of physicists/philosophers that don't accept Bell's theorem as valid"?

J. Christian, Local causality in a Friedmann–Robertson–Walker spacetime, Annals of Physics (2016), Volume 373, October 2016, Pages 67–79 doi:10.1016/j.aop.2016.06.021 http://www.sciencedirect.com/science/article/pii/S0003491616300975
It was already visible, but later withdrawn.

 

[facenian]

It's hard to answer a question like that in the abstract. What would be an example of an article from a reasonably respectable journal that comes from a member of this "community of physicists/philosophers that don't accept Bell's theorem as valid"?

- "Is the Contextuality Loophole Fatal for the Derivation of Bell Inequalities?" in Foundations of physics
- "Possible experience: From Boole to Bell" in Europhysics Letters

To name only two but threre many more and they seem to cite every article that refutes Bell no matter the reassons

When you speak of "not accepting Bell's theorem as valid" that can mean any of several positions:
...

Unless you have had the misfortune to stumble into a den of Joy Christianites, chances are the debate you're seeing is of the #3 variety.

Exactly they generally are of type 3 you mentioned, attacking the probabilistic model

 

[atyy]

- "Is the Contextuality Loophole Fatal for the Derivation of Bell Inequalities?" in Foundations of physics
- "Possible experience: From Boole to Bell" in Europhysics Letters

Nieuwenhuizen is a serious physicist, but of course, his work is not necessarily correct.
The other group of Hess, Michielsen, and De Raedt is generally fringe, which of course doesn't mean their work is wrong.
Personally, I would not spend any time reading the above papers.

There are two lines that have some credit

1) trying to redefine or more generalize the notion of "explanation", so that in this more general sense than that of classical probability, one may say that a local explanation of quantum mechanics is possible. Some of these approaches are discussed by Cavalcanti and Lal in On modifications of Reichenbach's principle of common cause in light of Bell's theorem https://arxiv.org/abs/1311.6852.

2) Bell's original derivation assumed that each run of the experiment was an independent preparation. If this is not true, how tightly do the violation of Bell inequalities at spacelike separation constrain local realism?

https://arxiv.org/abs/quant-ph/0110137
Accardi contra Bell (cum mundi): The Impossible Coupling
Richard D. Gill

https://arxiv.org/abs/quant-ph/0205016
Quantum nonlocality, Bell inequalities and the memory loophole
Jonathan Barrett, Daniel Collins, Lucien Hardy, Adrian Kent, Sandu Popescu

https://arxiv.org/abs/1108.2468
Asymptotically optimal data analysis for rejecting local realism
Yanbao Zhang, Scott Glancy, Emanuel Knill

https://arxiv.org/abs/1303.7464
Efficient quantification of experimental evidence against local realism
Yanbao Zhang, Scott Glancy, Emanuel Knill

 

[DrChinese]

No, I'm not talking about Joy Christian and supporters. I wouldn't mind about those kind of things. I'm talking about people who, like I said, seem to be serious and even sometimes (not allways) publish in respectable peer review journals. According to what have been said here, it is a small group and it seems the rest of the physics community don't pay much attention to them. I wonder if it is worthwhile trying to explain where and why their arguments are not good even some of them are just wrong. I just wrote a letter to editor about one such article, I don't know if it will be publish.

Each person must decide whether "Bell is wrong" papers are worth their time to read or refute. I keep a list of about 50 "denier" papers, and that is hardly complete. So analyzing each in detail for "errors" is quite a time consuming venture.

So I just look at each to see if they can meet what I call the "DrChinese challenge". Which is: if there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen. Barring an answer to that consistent with experiment, it's a waste of time as far as I am concerned.

 

[facenian]

Nieuwenhuizen is a serious physicist, but of course, his work is not necessarily correct.
The other group of Hess, Michielsen, and De Raedt is generally fringe, which of course doesn't mean their work is wrong.
Personally, I would not spend any time reading the above papers.

I feel the same, I suspected of "the other group" specially when I found an article in an online Journal that doesn't seem serious enough



Thank you all for your insights and opinions it is just what I needed to hear !

 

[facenian]

J. Christian, Local causality in a Friedmann–Robertson–Walker spacetime, Annals of Physics (2016), Volume 373, October 2016, Pages 67–79 doi:10.1016/j.aop.2016.06.021 http://www.sciencedirect.com/science/article/pii/S0003491616300975
It was already visible, but later withdrawn.

Is it possible to reject an already accepted paper? can you elaborate on this a little

 

[Denis]

Is it possible to reject an already accepted paper? can you elaborate on this a little

No, I cannot. I have seen the paper, wrote a short rejection, pointing to an obvious error, submitted it, and it was rejected without further review.

I already thought about publishing this information, as a proof that Annals of Physics became a crank journal which published crank papers and refuses to publish refutations, without even considering them. But probably I simply have not been the first, and the decision to withdraw it had already been taken at that time.

 

[stevendaryl]

It's been a long time since I've read "Foundations of Physics", but I seem to remember that it has pretty poor quality control. There are occasionally good papers published there, but some of the papers seem like crackpot stuff.

 

[Nicky665]

Each person must decide whether "Bell is wrong" papers are worth their time to read or refute. I keep a list of about 50 "denier" papers, and that is hardly complete. So analyzing each in detail for "errors" is quite a time consuming venture.

So I just look at each to see if they can meet what I call the "DrChinese challenge". Which is: if there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen. Barring an answer to that consistent with experiment, it's a waste of time as far as I am concerned.

"such values are completely specified by the measurement functions A(a, lambda) defined by Bell in his infamous paper of 1964. Given a measurement setting "a" and an initial state "lambda" of the physical system, the counterfactual outcome A(a, lambda) is unambiguously given to be either +1 or -1. There is no serious issue here "

 

[Nicky665]

if there are counterfactual outcomes at various measurement settings, what are they? In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen.

Another response, make of it what you want.

"If you can identify the flaw in the following argument, you will be able to answer your own question:

|| A photon A is heading toward Alice's detector on a distant galaxy. It will interact with the detector tomorrow to produce an outcome of +1 or -1. But the 'laws' of the excluded middle (no third truth-value) and of non-contradiction (not both truth-values), mandate that one of the propositions "Alice's will get +1", "Alice's will get -1", is true (always has been and ever will be) and the other is false (always has been and ever will be).

Suppose 'Alice's will get +1' is true today. Then whatever Alice does (or fails to do) before the photon hits her detector will make no difference: the outcome is already settled. Similarly if 'Alice's will get +1' is false today, no matter what Alice does (or fails to do), it will make no difference: the outcome is already settled.

Therefore, the future will be what it will be, irrespective of Alice's planning, choices or, intentions. ||Consider the following statements:

a) If I look at the moon, I will see it.
b) Had I looked at the moon yesterday, I would have seen it.

(a) is a True statement. In this case, it is implicit that the possibility of either looking at the moon or not looking at the moon still exists.
(b) is a counterfactual statement. Statement (b) will be valid even if it is impossible for me to look at the moon now (perhaps I was blinded overnight). Accepting (b) as a valid/true statement does not mean: (c) "Seeing the moon" exists prior to me looking at the moon.

Most confusion about the meaning of counterfactual outcomes originates from sloppy use of the concepts of "Truth", "Possibilities" "Existence", "Actualities". EPR/Bell discussions are often exhibitions of serious misunderstandings of those concepts.

if there are counterfactual outcomes at various measurement settings, what are they?

The counterfactual outcomes are the outcomes she could have gotten had she chosen any other settings than the one she actually chose. The result which Alice will get when she tilts her detector to angle a, could not possibly exist before Alice actually makes a measurement! However, the statement "If Alice turns her detector to angle a she will obtain the result A." is a True statement, which will continue to be True even if Alice had her detector to angle b, instead.

Consider the EPRB example:
Let us denote observable "what Alice observes when she tilts her device to angle a" as A, and "what Alice observes when she tilts her device to angle b" as B and "what Alice observes when she tilts her device to angle c" as C. For a single photon, All three observables A, B, C are possible, however if Alice never measures anything, none of them exist as actual outcomes. Therefore although A,B,C are all "possible", only the one which Alice actually measures, will exist. The other two will be counterfactual. For the specific particle, once Alice measures at "a", it is now impossible to measure the other two, therefore, the counterfactual outcomes B and C can not possibly exist at the same time as A. Let's look at it another way by rephrasing the statements:

A: if Alice measures the photon at angle "a" she will obtain "A"
B: If Alice measures the photon at angle "b" she will obtain "B"
C: If Alice measures the photon at angle "c" she will obtain "C"

All three statements can be True simultaneously. However, outcomes A, B, C can't exist simultaneously because of a contradiction: If Alice measures the photon at angle "a", then certainly she did not measure the photon at angles "b" or "c". In other words, all three are possibilities are simultaneously true, but only one of them can and will exist. The others will be counterfactual.

Bell's problem was that he did mathematics by mixing and combining A,B and C in the same expression. At best, he can tell you about mathematical relationships between possibilities. Drawing any inference from such relationships about what exists, or actual results of experiments is utter stupidity.

In other words: if there is objective realism a la EPR, one should be able to identify the hypothetical values that would have been obtained if a different measurement pair had been chosen.

Do you agree that if Alice had picked a setting different from the one she actually picked she would have obtained a result? That result, whatever it is, is the counterfactual result. "

 

[stevendaryl]

Let's look at it another way by rephrasing the statements:

A: if Alice measures the photon at angle "a" she will obtain "A"
B: If Alice measures the photon at angle "b" she will obtain "B"
C: If Alice measures the photon at angle "c" she will obtain "C"

All three statements can be True simultaneously. However, outcomes A, B, C can't exist simultaneously because of a contradiction: If Alice measures the photon at angle "a", then certainly she did not measure the photon at angles "b" or "c". In other words, all three are possibilities are simultaneously true, but only one of them can and will exist. The others will be counterfactual.

Bell's problem was that he did mathematics by mixing and combining A,B and C in the same expression.

It's not Bell's problem. Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

What are you disagreeing about?

 

[N88]

… Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

Seeking clarity, where does this response fail?

Property Y: $P(AB|abλ) = P(A|aλ)P(B|bλ).$
Y means their is no logical connection between $A$ and $B$.
But there is a logical connection between $A$ and $B$ because of common condition $λ$.
NB: Logical implication does not imply physical nor AAD nor FTL causation.*
Therefore QM and all the related experiments have these three properties:
P: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB).$
Q: $P(A|aλ) = P(B|bλ) = \frac{1}{2}.$
R: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB) \neq P(A|aλ)P(B|bλ).$
S: So Bell's property Y is false.
T: So theories of type X are those in which there is no logical connection between $A$ and $B$.
U: Type X theories are therefore irrelevant here.
QED.
* PS: The probability of "rain given clouds" is not the same as that of "clouds given rain."

 

[PeterDonis]

where does this response fail?

Here:

Y means their is no logical connection between $A$ and $B$.

 

[N88]

Here:

Please explain.

For me: Y is the product rule for the conjunction of $AB$ under EPRB.

So, if you have full knowledge of $λ$, then Y becomes Y*:

Y*: $P(AB|abλ) = P(A|aλ)P(B|bλ) = 1\cdot1 =1.$

But, under EPRB, we cannot have full knowledge of $λ$, so P holds:

P: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB).$

So, I conclude: Bell's Y is false under EPRB.

Thanks, N88

 

[stevendaryl]

Seeking clarity, where does this response fail?

Property Y: $P(AB|abλ) = P(A|aλ)P(B|bλ).$
Y means their is no logical connection between $A$ and $B$.
But there is a logical connection between $A$ and $B$ because of common condition $λ$.

I just want to remind you that nobody is proposing Property Y as a general property about all correlations. Only in the specific case in which

1. A and B are assumed to be separated so that it is impossible for A to influence B or vice-versa.
2. \lambda is the complete set of variables in the common causal past of both A and B.

As to Property Y saying that there is no logical connection between A and B; no, that's not true. Take the simple example of a pair of shoes: You take a pair of shoes, and put each into a box and mix up the boxes. Then you give one box to Alice and another box to Bob. There is definitely a "logical" relationship between what Alice and Bob discover in their respective boxes: If Alice sees a left shoe, then Bob sees a right shoe.

That example has correlations but does not violate Property Y. In that case, the "hidden variables" would consist of

1. The information about which box the left shoe was put in, and which box the right shoe was put in.
2. The information about how it was decided which box to send to Alice and which box to send to Bob.

If Alice knew 1&2, then she would know what shoe she was going to find even before she opened her box. No additional information about what Bob discovered would make any difference.

Therefore QM and all the related experiments have these three properties:
P: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB).$
Q: $P(A|aλ) = P(B|bλ) = \frac{1}{2}.$

We don't have any information about whether Q is true. To establish Q, you would have to repeat the experiment many times in which you control for the value of \lambda. But we don't know what \lambda might be, so we can't control for it.

R: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB) \neq P(A|aλ)P(B|bλ).$

S: So Bell's property Y is false.

I would put it as: QM does not satisfy property Y. That's what Bell proved.

T: So theories of type X are those in which there is no logical connection between $A$ and $B$.

I don't know what you mean by that. You can have locally realistic theories with perfect correlation between A and B. My two-shoe example is one.

U: Type X theories are therefore irrelevant here.

Definitely QM is not a theory of type X. That was what Bell proved.

 

[stevendaryl]

Please explain.

For me: Y is the product rule for the conjunction of $AB$ under EPRB.

So, if you have full knowledge of $λ$, then Y becomes Y*:

Y*: $P(AB|abλ) = P(A|aλ)P(B|bλ) = 1\cdot1 =1.$

But, under EPRB, we cannot have full knowledge of $λ$, so P holds:

P: $P(AB|abλ) = P(A|aλ)P(B|abλA) = P(B|bλ)P(A|abλB).$

So, I conclude: Bell's Y is false under EPRB.

I don't know why you want to put it that way. Bell proved that QM does not satisfy property Y. It's like a proof that \sqrt{2} is irrational. You assume that it is rational, and show that it leads to a contradiction.

 

[stevendaryl]

@N88, I'm having trouble understanding what point you are making. Saying that the correlation between A and B can be accounted for by a third variable is not saying that there is no relationship between A and B. Just the opposite: it's saying quite precisely what the relationship is.

 

[stevendaryl]

@N88, I'm having trouble understanding what point you are making. Saying that the correlation between A and B can be accounted for by a third variable is not saying that there is no relationship between A and B. Just the opposite: it's saying quite precisely what the relationship is.

Let me give an example of a hidden-variables theory. Suppose that Alice and Bob are married. Suppose that Alice occasionally gets sick--one day out of 57. Suppose that Bob also gets sick one day out of 57. But one day out of 94, they are both sick.

So letting B be: Bob is sick, and letting A be: Alice is sick, we have:

P(A) = 0.0175
P(B) = 0.0175
P(A) P(B) = 0.00031
P(A \wedge B) = 0.0106

So we conclude:
P(A \wedge B) \neq P(A) P(B)

So their illnesses are correlated. The local epidemiologist investigates and finds out that:

1. There is a 0.01 chance each day that the couple eats bad food for dinner.
2. If they eat bad food, there is a 0.75 chance that they will get sick.
3. There is a 0.02 chance each day that there will be flu viruses around their home
4. If they are exposed to flu viruses, there is a 0.50 chance they will get sick.
5. (There is a negligible chance of having both flu and bad food)

Then these two factors completely explain the correlation. Let \lambda_{BF} mean that there is bad food and let \lambda_F mean that there is flu around.

1. P(\lambda_{BF}) = 0.01
2. P(A | \lambda_{BF}) = 0.75
3. P(B | \lambda_{BF}) = 0.75
4. P(\lambda_F) = 0.02
5. P(A | \lambda_F) = 0.5
6. P(B | \lambda_F) = 0.5
7. P(A \wedge B) = P(\lambda_F) P(A | \lambda_F) P(B | \lambda_F) + P(\lambda_{BF}) P(A | \lambda_{BF}) P(B | \lambda_{BF}) = 0.02 \cdot 0.5 \cdot 0.5 + 0.01 \cdot 0.75 \cdot 0.75 = 0.0106

So for this model:

P(A \wedge B) = \sum_{\lambda} P(\lambda) P(A | \lambda) P(B | \lambda)

where the sum is over the two possibilities: \lambda_F and \lambda_{BF}

The fact that Alice's and Bob's illnesses are independent, given that we have accounted for bad food and viruses doesn't mean that there is no relation between their illnesses; it just means that the correlation is explained by the shared food and/or viruses.

 

[DrChinese]

Do you agree that if Alice had picked a setting different from the one she actually picked she would have obtained a result? That result, whatever it is, is the counterfactual result. "

I am not the one asserting there are counterfactual cases. Everything I see points to an observer dependent universe, one that lacks local realism. So when someone asks about a particular local realistic theory, one which is excluded by Bell but that the author claims is not, I always ask: Please describe those counterfactual cases.

 

[PeterDonis]

if you have full knowledge of $λ$, then Y becomes Y*

No it doesn't. Full knowledge of $\lambda$ does not mean all probabilities are 1.

 

[Nicky665]

I am not the one asserting there are counterfactual cases. Everything I see points to an observer dependent universe, one that lacks local realism. So when someone asks about a particular local realistic theory, one which is excluded by Bell but that the author claims is not, I always ask: Please describe those counterfactual cases.

" Let us break down the situation fully:

Monday:
If Alice picks setting "a" on Tuesday she will obtain result "A"
If Alice picks setting "b" on Tuesday she will obtain result "B"
If Alice picks setting "c" on Tuesday she will obtain result "C"

Tuesday:
Alice picks setting "a" and obtains result "A"

Wednesday:
Alice picked setting "a" on Tuesday and obtained result "A"
If Alice had picked setting "b" on Tuesday she would have obtained result "B"
If Alice had picked setting "c" on Tuesday she would have obtained result "C"

The original question then becomes clear: Do you agree that if Alice had picked a different setting on Tuesday than the one she picked, she would have obtained a result ?

Note that I don't care what the value of the actual result is, just the fact that there is a result. Also note that A, B, C are not actual values, but just labels for whatever result it is that Alice obtains for the corresponding setting. "

 

[stevendaryl]

" The original question then becomes clear: Do you agree that if Alice had picked a different setting on Tuesday than the one she picked, she would have obtained a result ?

In discussions of Bell's inequality, "counterfactual" is mentioned in the context of "counterfactual definiteness". CFD says that there is a definite answer to questions such as "What result would Alice have gotten if she had measured X instead of Y?"

 

[Nicky665]

It's not Bell's problem. Bell proved a theorem along the lines of: "All theories of type X have property Y. QM does not have property Y. Therefore, QM is not a theory of type X."

What are you disagreeing about?

"Perhaps if you spell out exactly what X and Y mean mathematically, I we will show you what we are disagreeing about.

For example, please describe to me a physical situation for which the relationship P(AB|λ) = P(A|λ)P(B|λ) is true
But the relationship P(AB|λ) = P(A|λ)P(B|Aλ) is false."

In discussions of Bell's inequality, "counterfactual" is mentioned in the context of "counterfactual definiteness". CFD says that there is a definite answer to questions such as "What result would Alice have gotten if she had measured X instead of Y?"

"And you think, QM disagrees with that?

Bell in 1964 Paper wrote:Measurements can be made, say by Stern-Gerlach magnets, on selected components of the spins

and

. If measurement of the component

, where

is some unit vector, yields the value +1 then, according to quantum mechanics, measurement of

must yield the value -1 and vice versa.Bell says according to QM, Alice would have gotten a definite answer if she had measured at the same angle as Bob. Is that CFD or not?

BTW, you didn't answer the first question. Would Alice have definitely obtained a result (any result at all) had she measured at a different setting?"

 

[DrChinese]

Would Alice have definitely obtained a result (any result at all) had she measured at a different setting?"

Obviously Alice literally obtains a result when she measures at any setting. But the relevant point is whether there is any dependency on what Bob does. It always comes back to the same place: The answer is interpretation dependent.