CFD - Counterfactual Definiteness

[Eye_in_the_Sky]

There is nothing non local about it unless you insist on properties regardless of observation.

... 'properties' of WHAT?

 

[Simon Phoenix]

'properties' of WHAT?

You really need to read Bell's Bertlmann's socks paper

https://cds.cern.ch/record/142461/files/198009299.pdf

It is, in my opinion, the clearest exposition of the issues, written by the great master himself.

About half way through he introduces the basic set-up. Alice has a device that registers yes or no - so just a png or a ding - or a red and blue light - however you want to think about it. On the device are 3 buttons - setting 1, setting 2 and setting 3. Bob has an exactly similar device. In between them is some source of oojamaflips which get sent to Alice and Bob.

And that's it. There no assumption made about what the oojamaflips actually are - no assumption about the mechanism of the measuring devices, no assumption about the interaction of the oojamaflips with the measurement devices. In fact the description of the experiment itself is almost 'physics free'.

The job is to try to understand what might be causing any observed correlation when many runs of the experiment are performed.

So Bell then assumes a very general model for the probabilities that can be measured. He assumes that the correlations are caused by some unknown properties - or variables. He then supposes that these variables behave just like classical variables (they have properties independent of measurement) and that whatever results Alice obtains (including the statistics of those results) cannot depend on which particular setting Bob has chosen.

And that's essentially it. He then goes on to show (and the analysis is actually very easy - which belies its power and beauty) that IF the world was described by this kind of theory - if the world was described by these kinds of variables, whatever they might be, then the observed correlations in this experiment are constrained by an inequality.

There is very little detailed 'physics' in there - it's really an analysis of probability applied to certain kinds of variables. It's a very general model that does not need any specific physics (what the oojamaflips are, whether we have fields or particles, what interactions are occurring, what actual properties the hidden variables themselves describe - all of these things are a matter of supreme irrelevance)

So if we do the experiment and find that we don't get results that are bounded by the inequality in this way we know that whatever our description of the world it simply CANNOT be of the assumed form (local and realistic).

Notice that I've not even mentioned quantum mechanics - it's completely irrelevant. Bell's inequality is a constraint on certain kinds of classical theories.

 

[zonde]

Ok. I will try.

I would recommend this counterexample type of proof. It's very short, simple and and does not require hidden variables.

 

[Eye_in_the_Sky]

Turning on the source "causes" the correlated detector outcomes. However, that does not entail the existence of a beable. That was my point.

Thank you, RUTA, for clarifying your answer.

If you had said you agree, then I would have been inclined to seek out a 'proof' of entailment.

But, since you say you disagree, I am instead inclined to change my approach altogether.

The difficulty I am having is that too much of what I see, or think I see, is arrived at through a process of something like 'judgement' based upon 'impressions' of what I think things are supposed to mean, rather than a clear process of 'deductive reasoning' applied to 'sharply defined notions'.

Like, for example, what is Bell's 'local beable' supposed to mean? Does it even have a clear WORD DEFINITION? Or, better yet, is there a formal MATHEMATICAL DEFINITION?

As far as WORDS go, this is the best I can do to express its meaning according to my understanding:

A 'local beable' is nothing other than a 'classical system' in spacetime.

Now, if that is correct (at least in spirit), then I would think, of course, there is a formal MATHEMATICAL DEFINITION.

Is there?

... And, also, what WORD DEFINITION do you have?

 

[bhobba]

... 'properties' of WHAT?

You really need to read Bell's Bertlmann's socks paper

QM is a theory about observations. It is silent on what's happening when not observed. Objects may have properties like spin, momentum, position etc etc between observations or not - the theory says nothing one way or the other.

What Bell says is if you want to have properties between observations you need FTL. This, basically (there are some subtleties) is the assumption of CFD. This is because QM predicts statistical correlation properties different to ordinary correlations like Berlelman's socks:
https://cds.cern.ch/record/142461/files/198009299.pdf

That's it, that's all - you are way way over complicating it and getting yourself into all sorts of tortured linguistics

There is also another out not often mentioned, but the one I ascribe to. That out is correlations are precluded from locality in QM. Locality in QM is as per the cluster decomposition property:
https://www.physicsforums.com/threads/cluster-decomposition-in-qft.547574/

Since correlated systems do not apply to locality in QM one can say its not even a valid question to ask and the whole edifice of quibbling about it falls to pieces. Occams razor in full force.

Note: No view is better than any other - all are correct. Its simply a matter of taste which you prefer. But for heavens sake pick one - as it stands you do not seem to grasp the basic issue.

Thanks
Bill

 

[bhobba]

Like, for example, what is Bell's 'local beable' supposed to mean?

I don't know where you are getting beable from. Its not a word I have come across before in QM. I did a search and it seems to be something to do with Bells local beable QFT.

That being the case forget about it. QFT is HARD, and I do mean HARD. Don't even attempt it until you understand QM well, and that's all you need to get to grips with Bells theorem. No advanced QFT required.

Thanks
Bill

 

[RUTA]

Thank you, RUTA, for clarifying your answer.

If you had said you agree, then I would have been inclined to seek out a 'proof' of entailment.

But, since you say you disagree, I am instead inclined to change my approach altogether.

The difficulty I am having is that too much of what I see, or think I see, is arrived at through a process of something like 'judgement' based upon 'impressions' of what I think things are supposed to mean, rather than a clear process of 'deductive reasoning' applied to 'sharply defined notions'.

Like, for example, what is Bell's 'local beable' supposed to mean? Does it even have a clear WORD DEFINITION? Or, better yet, is there a formal MATHEMATICAL DEFINITION?

As far as WORDS go, this is the best I can do to express its meaning according to my understanding:

A 'local beable' is nothing other than a 'classical system' in spacetime.

Now, if that is correct (at least in spirit), then I would think, of course, there is a formal MATHEMATICAL DEFINITION.

Is there?

... And, also, what WORD DEFINITION do you have?

Sorry, I can't help you there.

 

[Dale]

Closed pending moderation.

Edit: the thread will remain closed.