I CFD - Counterfactual Definiteness

[Eye_in_the_Sky]

I am thinking about a single run in a typical Bell-type scenario:

A joint-measurement of an (appropriately prepared) entangled property is performed in spacetime regions A and B at spacelike separation.

Regarding the above, in conjunction with Quantum Theory, would you say the following statement is true, false, or inapplicable? Why?

The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

I am particularly interested in replies which assume a single (non-branching) universe.
Nonetheless, replies from all perspectives are valued.

 

[DrChinese]

I am thinking about a single run in a typical Bell-type scenario:

A joint-measurement of an (appropriately prepared) entangled property is performed in spacetime regions A and B at spacelike separation.

Regarding the above, in conjunction with Quantum Theory, would you say the following statement is true, false, or inapplicable? Why?

The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

My opinion is that the statement is false.

Both settings (A and B) are inputs to something (I don't know what or where or when). Therefore the outcomes at A and B reflect in some manner the mutual relationship of both settings. Therefore they are not independent. Again, this is simply my view.

 

[Eye_in_the_Sky]

My opinion is that the statement is false.

Both settings (A and B) are inputs to something (I don't know what or where or when). Therefore the outcomes at A and B reflect in some manner the mutual relationship of both settings. Therefore they are not independent. Again, this is simply my view.

DrChinese, thank you for your reply.

(I too favour a view whereby the statement is false.)
____

What then would you (especially, DrChinese) say about the following statement?

This dependency is established through the agency of an 'influence'.

True or false?

(In my favoured view, this statement is also false.)

 

[Simon Phoenix]

The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

I don't really understand what you mean here by 'state of affairs'.

Let's consider the usual scenario with our usual protagonists Alice and Bob each having one particle from a maximally entangled singlet state. What we can say is the following : the results obtained by Alice (Bob) are independent of the settings chosen by Bob (Alice).

Suppose this were not the case and there were some measureable dependence on the settings then Bob could simply change his settings and convey information to Alice.

But this, I feel, is not what you're asking - it would seem that you're asking about some kind of 'change of state' caused by a change in Bob's setting prior to Alice's measurement?

So let's take a singlet state |01> + |10> and assume Bob performs some unitary transformation on his particle (essentially this is equivalent to a change of measurement setting). Then the new state would be |01'> + |10'> where the prime indicates the transformed basis. The reduced density operator for Alice's particle is unaffected by this unitary transformation, as are the statistics of her measurement results. The global quantum state has, however, changed.

So yes I would say that in the sense above the 'state of affairs' is changed by Bob changing the measurement setting but this change has no observable consequences for Alice's measurements alone (i.e. considered separately from Bob's measurements).

 

[N88]

I am thinking about a single run in a typical Bell-type scenario: A joint-measurement of an (appropriately prepared) entangled property is performed in spacetime regions A and B at spacelike separation.

Regarding the above, in conjunction with Quantum Theory, would you say the following statement is true, false, or inapplicable? Why? The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

The statement is true, based on my understanding of locality.

 

[Eye_in_the_Sky]

I don't really understand what you mean here by 'state of affairs'.

Loosely, by the 'state of affairs' in a given region of spacetime, I mean all of the "goings-on" in that region.

More generally, but again loosely, by the 'state of affairs' (not necessarily within spacetime) I mean all of the "goings-on" with regard to those things that have ontological status (possibly outside of spacetime).

Let's consider the usual scenario with our usual protagonists Alice and Bob each having one particle from a maximally entangled singlet state. What we can say is the following : the results obtained by Alice (Bob) are independent of the settings chosen by Bob (Alice).

Suppose Alice obtained the results 0100101101, with Bob's setting fixed at b₁.

If her results are truly independent of his setting, and if the theory for the phenomenon is truly faithful to this fact, then no contradiction should arise in conjunction with the theory by supposing that Alice obtains the self-same results, i.e. 0100101101, if Bob's setting had been fixed at b₂ instead of b₁.

Thus, "independence" (with regard to the phenomenon) and "faithfulness" (of the theory) imply CFD.

Do you agree?

Suppose this were not the case and there were some measureable dependence on the settings then Bob could simply change his settings and convey information to Alice.

Alice's outcome has a dependence on both the setting and the outcome of Bob. Although Bob is able to control his setting, he has no control over his outcome. For that reason, Alice is unable to detect a change in Bob's setting.

But this, I feel, is not what you're asking - it would seem that you're asking about some kind of 'change of state' caused by a change in Bob's setting prior to Alice's measurement?

So let's take a singlet state |01> + |10> and assume Bob performs some unitary transformation on his particle (essentially this is equivalent to a change of measurement setting). Then the new state would be |01'> + |10'> where the prime indicates the transformed basis. The reduced density operator for Alice's particle is unaffected by this unitary transformation, as are the statistics of her measurement results. The global quantum state has, however, changed.

So yes I would say that in the sense above the 'state of affairs' is changed by Bob changing the measurement setting but this change has no observable consequences for Alice's measurements alone (i.e. considered separately from Bob's measurements).

Only if quantum states have ontological status would they be considered, by my intended meaning, to be a part of the 'state of affairs'.

 

[Eye_in_the_Sky]

The statement is true, based on my understanding of locality.

Thank you N88 for your reply.

Please have a look at my reply above to Simon Phoenix. Do you have any comments?

 

[Simon Phoenix]

Do you agree?

No :-)

Alice's outcome has a dependence on both the setting and the outcome of Bob

The results obtained by Alice are statistically independent of the setting of Bob, or in other words, the probability that Alice measures up (or down) given that Bob's setting is b is the same as the probability that Alice measures up (or down) for all choices of b. Or in symbols P(+|b) = P(+).

Alice and Bob's results are not, of course, statistically independent if they each have one of an entangled pair.

Although Bob is able to control his setting, he has no control over his outcome. For that reason, Alice is unable to detect a change in Bob's setting.

Sorry I can't follow your reasoning here.

 

[bhobba]

My opinion is that the statement is false.

What was it Meatloaf said - You Took The Words Right Out Of My Mouth


I don't know why, but there seems to be a lot of confusion about this - its simply a correlation with different statistical properties different to the classical case.

Thanks
Bill

 

[bhobba]

This dependency is established through the agency of an 'influence'.

Neither.

QM is silent on it. The answer requires an interpretation.

Pick an interpretation and I can often (but not always) answer it. For example here is Consistent Histories take:
http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf

Then we have the Ignorance Ensemble. Unfortunately it doesn't answer it either, nor does Copenhagen - not all do. In fact most minimalist interpretations don't - that's because they are minimalist. In BM the systems are linked by the super-luminal pilot wave and that is the influence.

Thanks
Bill

 

[zonde]

This dependency is established through the agency of an 'influence'.

What is alternative to "influence"?

 

[Eye_in_the_Sky]

No :-)
The results obtained by Alice are statistically independent of the setting of Bob, or in other words, the probability that Alice measures up (or down) given that Bob's setting is b is the same as the probability that Alice measures up (or down) for all choices of b. Or in symbols P(+|b) = P(+).

Alice and Bob's results are not, of course, statistically independent if they each have one of an entangled pair.
Sorry I can't follow your reasoning here.

Simon, thank you for your reply.

I will need some time to think about it more, and also to think more about the position I think I am trying to express.

 

[Eye_in_the_Sky]

What is alternative to "influence"?

As I see it:

The 'state of affairs' in spacetime region A and the 'state of affairs' in spacetime region B are together in a condition of nonseparability.

(i.e. the joint-state of Alice and Bob's measuring devices is nonseparable)

OR

The notion of a 'state of affairs' in a spacetime region is altogether invalid.

 

[Eye_in_the_Sky]

I don't know why, but there seems to be a lot of confusion about this - its simply a correlation with different statistical properties different to the classical case.

Yes, but in a view whereby 'spacetime' has ontological status the quantum correlations carry with them implications that do not arise in the case of classical correlations.

See my reply to zonde above.

 

[N88]

Thank you N88 for your reply.

Please have a look at my reply above to Simon Phoenix. Do you have any comments?

1. As the OP, please define what you mean by CFD.

2. Already we know that you hold true what I (based on my understanding of locality) hold to be false.

3. Your reply to Simon begins (with my emphasis), "Loosely¹, by the 'state of affairs' in a given region of spacetime, I mean all of the "goings-on" in that region. More generally, but again loosely², by the 'state of affairs' (not necessarily within spacetime) I mean all of the "goings-on" with regard to those things that have ontological status (possibly outside of spacetime)."

I see no need for Loosely¹. Given loosely², I'd welcome an example from the phrase that it qualifies.

 

[N88]

Yes, but in a view whereby 'spacetime' has ontological status the quantum correlations carry with them implications that do not arise in the case of classical correlations.

Consider your CFD, our quantum world and the following thought-experiment:-

As in Bell (1964), a quantum source S_Q produces highly-correlated pairs of spin-half particles. As is well-known, these quantum correlations deliver an expectation E(a,b|Q) = -a.b.

These quantum correlations are next reduced to 'classical' correlations by sandwiching S_Q between two aligned S-G magnets. The new source, S_C, is a 'classical' one because it produces pairs of spin-half particles correlated by having definite but antiparallel spins in one direction. These 'classical' correlations deliver an expectation E(a,b|C) = -a.b/2.

Question:- What implications are to be derived from this fact: The original unfettered quantum source S_Q produces particle pairs that are more highly correlated than the 'classical' source S_C (the throttled quantum source)?

 

[bhobba]

Yes, but in a view whereby 'spacetime' has ontological status the quantum correlations carry with them implications that do not arise in the case of classical correlations.

Bell type correlations are part of QFT which assumes SR and Minkowski space-time.

People constantly tie themselves into knots about EPR, Bell etc. Its nowhere near as hard as they make out.

Its simply a correlation and as such is excluded from the principle of locality in QFT which goes by the name of the Cluster Decomposition Property:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

QM as a theory is silent about things having properties if not observed - they may or may not depending on interpretation. All Bell shows is if you want to have properties when not observed you need non local influences. Don't want that and there is no issue at all - in fact you can even exclude correlations from considerations of locality so the Cluster Decomposition property makes sense. If you include it then things become much more complicated. Of course it proves Jack Shite - but we have this thing called Occam's Razor that says you do not complicate things unnecessarily.

Thanks
Bill

 

[zonde]

As I see it:

The 'state of affairs' in spacetime region A and the 'state of affairs' in spacetime region B are together in a condition of nonseparability.

(i.e. the joint-state of Alice and Bob's measuring devices is nonseparable)

OR

The notion of a 'state of affairs' in a spacetime region is altogether invalid.

I don't think these alternatives are consistent with scientific approach.

 

[Eye_in_the_Sky]

What is alternative to "influence"?

As I see it:

The 'state of affairs' in spacetime region A and the 'state of affairs' in spacetime region B are together in a condition of nonseparability.

(i.e. the joint-state of Alice and Bob's measuring devices is nonseparable)

OR

The notion of a 'state of affairs' in a spacetime region is altogether invalid.

... In other words, "independent of" means "separable from and uninfluenced by", in the statement below:

The 'state of affairs' relevant to the outcome at A is independent of the setting at B, and vice versa.

NOTE: The above statement is rendered inapplicable, and therefore neither true nor false, when one asserts that

the notion of a 'state of affairs' in a spacetime region is altogether invalid.

Therefore, to say that the statement is false leaves but one alternative to "influence":

the joint-state of Alice and Bob's measuring devices is nonseparable.

I don't think these alternatives are consistent with scientific approach.

What about Relational Blockworld for the but one alternative?

 

[Eye_in_the_Sky]

Question:- What implications are to be derived from this fact: The original unfettered quantum source S_Q produces particle pairs that are more highly correlated than the 'classical' source S_C (the throttled quantum source)?

I do not think I understand the question. So, I will answer a question similar to it. Then maybe you can clarify the question for me.
______________

The pairs from S_Q violate Bell's inequality, whereas the pairs from S_C do not.

Regarding the S_Q-phenomenon, I am forced to conclude:

Bell's principle of "Local Causality" is either violated or inapplicable.

Regarding the S_C-phenomenon, I am NOT forced to accept such a conclusion.

 

[zonde]

The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

I would say this is not true in general case.
Let's say that A and B are timelike separated and A happens first. Then it will be true.
Another thing. I think that setting at B does not influence 'state of affairs' at A directly so if you specifically exclude measurement event at B then again we might say this statement is true.

This dependency is established through the agency of an 'influence'.

True

 

[georgir]

Ok, 'state of affairs' relevant to the outcome at A is non-separable from 'state of affairs' relevant to the outcome at B, that's the very definition of an entangled state after all.
On the other hand, looking at just 'settings at B' without the outcome, there is no spooky relation and no entanglement with 'state of affairs' at A...
So I really don't know what to say about the first statement.

 

[harrylin]

I am thinking about a single run in a typical Bell-type scenario:

A joint-measurement of an (appropriately prepared) entangled property is performed in spacetime regions A and B at spacelike separation.

Regarding the above, in conjunction with Quantum Theory, would you say the following statement is true, false, or inapplicable? Why?

The 'state of affairs' relevant to the outcome at A is independent of the setting at B.

I am particularly interested in replies which assume a single (non-branching) universe.
Nonetheless, replies from all perspectives are valued.

I'm afraid that your phrasing is open for multiple interpretations. Anyway, my take on this (which currently is a minority view) is that there seems to be no way for the setting at B to physically influence the outcome at A, despite the strong suggestion made by Bell. It appears to be mathematically impossible to break Bell's theorem at the level of a single pair - see also the related thread by bohm2 that was started almost at the same time: https://www.physicsforums.com/threa...nt-truly-rule-out-non-local-causality.882428/

 

[stevendaryl]

Anyway, my take on this (which currently is a minority view) is that there seems to be no way for the setting at B to physically influence the outcome at A, despite the strong suggestion made by Bell.

I don't think that's the minority view. I think that most physicists would say that there are no FTL influences in QM. It's the minority view (Bohmian mechanics) that there is an influence.

 

[stevendaryl]

...my take on this (which currently is a minority view) is that there seems to be no way for the setting at B to physically influence the outcome at A...

Since the title of the thread involves "CFD", I would like to make the connection with "counter-factual" reasoning. In my opinion, there is no way to make sense of the notion of one thing influencing another without indulging in counter-factual reasoning. You want to say that flipping a light switch caused the light to come on, but how can you distinguish that from mere correlation? The meaning of "cause" here (in my way of thinking) necessarily involves the counter-factual consideration: "If I (counter to fact) had not flipped the switch, the light would not have come on".

When people talk about causality, or influences, I think that they are implicitly thinking in terms of certain facts about the situation as being "free variables"--things that could have been different. The three biggest sources of freedom in most experiments are: (1) randomness, such as coin flips or atomic decays, (2) choices made by experimenters (such as which setting to use in an EPR experiment), (3) detailed facts about initial conditions. The latter is where "factorizability" comes in. We often assume that it's possible to have a situation exactly like the actual situation, except that facts about some localized region of space are slightly different.

The "D" in "CFD" stands for "definiteness", and I don't actually think that's necessary for reasoning about influences. It's enough that in the counter-factual situation, probabilities are different, without anything being definitely the case.

 

[Eye_in_the_Sky]

2. Already we know that you hold true what I (based on my understanding of locality) hold to be false.

I think the reason you hold the statement to be true is because what you have in mind is something along the lines of "statistical independence" and "signal locality" between Alice/Bob's outcome and Bob/Alice's setting.

The reason I hold the statement to false is because what I have in mind is along the lines of "state separability" and "mutually non-influencing" for the measuring instruments of Alice and Bob.

In other words, each of us has in mind a different notion of "independence". Mine implies yours, but not conversely.

3. Your reply to Simon begins (with my emphasis), "Loosely¹, by the 'state of affairs' in a given region of spacetime, I mean all of the "goings-on" in that region. More generally, but again loosely², by the 'state of affairs' (not necessarily within spacetime) I mean all of the "goings-on" with regard to those things that have ontological status (possibly outside of spacetime)."

I see no need for Loosely¹. Given loosely², I'd welcome an example from the phrase that it qualifies.

It sounds like you are asking me to give an example of something I consider to EXIST, but NOT WITHIN SPACETIME.

Here is [in (what I find to be) somewhat ambiguous terms] a possible example:

Whatever it is that the state vector REPRESENTS, if "the quantum state is PHYSICAL".

1. As the OP, please define what you mean by CFD.

I have been asking myself over and over, "What do I mean by CFD?" ... and, finally, I have decided:

I DON'T KNOW!

For me it is like a "snake" (that I cannot catch) that slithers back and forth between:

CFD1: For any measurement Alice performs, a definite outcome would have been obtained by Alice if she had performed a different measurement instead. Likewise, for Bob.

CFD2: CFD1 and, furthermore, the complete set of such outcomes for Alice and Bob (measured and unmeasured together) can be meaningfully discussed.

Surely, it must mean more than just CFD1 (because that is true by hypothesis), and so it must have in it something of CFD2, but maybe not altogether the whole of it.

There is something "fishy" going on in the parsing

CFD & locality ,

whereby the 'boundary' at which one concept ends and the other begins is 'shifty', or 'unstable', or something ... I don't know what.

This does not happen in the parsing

separability & local causality ,

for which the 'boundary' between the concepts is perfectly clear.

 

[Eye_in_the_Sky]

Suppose Alice obtained the results 0100101101, with Bob's setting fixed at b₁.

If her results are truly independent of his setting, and if the theory for the phenomenon is truly faithful to this fact, then no contradiction should arise in conjunction with the theory by supposing that Alice obtains the self-same results, i.e. 0100101101, if Bob's setting had been fixed at b₂ instead of b₁.

Thus, "independence" (with regard to the phenomenon) and "faithfulness" (of the theory) imply CFD.

Do you agree?

No :-)

I will recast the above (so as to better express the idea I have in it).

I am saying that the following two statements ARE TRUE:

i) If Bob's setting had been b₂ instead of b₁, each of Alice and Bob would have obtained a definite outcome.

ii) If Bob's setting is IRRELEVANT to Alice's outcome, and if the theory in question is CORRECT in this regard, then:

[I am now recasting the notions of "independence" and "faithfulness"]

No contradiction can arise in the theory by supposing that Alice's outcome for (the hypothetical setting) b₂ would have been the same as that (for the actual setting) b₁. [1]

... ARE i) and ii) TRUE?

In addition to i) and ii), I am also saying that the following statement IS TRUE as well:

iii) From i) and [1], one can derive a Bell inequality.

... IS iii) TRUE?

 

[Eye_in_the_Sky]

I don't think these alternatives are consistent with scientific approach.

What about Relational Blockworld for the but one alternative?

Zonde, I took your statement to mean that those alternatives are "unscientific". But maybe, instead, you meant something else.

By "scientific approach" did you mean the "methods of experimental science"?

If so, for the but one case, is that because of a difficulty that arises in connection with 'isolated' systems?

 

[zonde]

Zonde, I took your statement to mean that those alternatives are "unscientific". But maybe, instead, you meant something else.

By "scientific approach" did you mean the "methods of experimental science"?

Yes, by "scientific approach" I meant "scientific method".

If so, for the but one case, is that because of a difficulty that arises in connection with 'isolated' systems?

No. Difficulty is related to independence of spacetime events. I mean that standard philosophical basis takes spacetime events as fundamental to reality and they are arranged in some system (spacetime) that does not allow arbitrary connections between them. And scientific method is developed on top of that standard philosophical basis.

As I see nonseparability is in conflict with the idea of spacetime events as fundamental.

 

[Eye_in_the_Sky]

QM as a theory is silent about things having properties if not observed - they may or may not depending on interpretation. All Bell shows is if you want to have properties when not observed you need non local influences. Don't want that and there is no issue at all - ...

I am looking, in particular, at this part of what you say:

All Bell shows is if you want to have properties when not observed you need non local influences.

I agree with it (except for the usage of "All" and "is" in the sentence).

Do you agree that the following statement is also true?

[All] Bell shows [is] if you want the joint-state of Alice's ((macroscopic) measuring) instrument and Bob's ((macroscopic) measuring) instrument, in spacetime, to be separable then you need non-local influences.