I Classicality in Bell's original reasoning

[bohm2]

Rubi/Neumaier/Griffiths line is as follows (and I am referring to comments in concurrent threads as I do this): Bell excludes local realistic (non-contextual) theories; and QM is contextual. So a successful theory need not be non-local.

But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?

 

[DrChinese]

But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?

I'm not sure Bell literally goes much farther than KS. I think of their results as analogous but different. Bell's result is much more influential because it is easier to follow, and was a specific response to a well known paper (EPR). It says:

- No physical theory of local hidden variables (contextual or not) can ever reproduce all of the predictions of quantum mechanics.

KS relates to the state independent of the measuring device, and says:

- No physical theory of non-contextual hidden variables (local or not) can ever reproduce all of the predictions of quantum mechanics*.

You could say that Bell rules out contextual local realistic theories (which KS would not), which would clearly rule out any attempts at classical representations. If you are going to have hidden variables, they must be non-local and contextual. If you keep locality, it must be non-realistic and contextual. (I can't really envision the difference between non-realistic and contextual though.)*when the dimension of the Hilbert space is three or more.

 

[Jilang]

For spin I would go with random in two dimensions (is that non-realistic?) and contextual and local. Would that work?

 

[zonde]

But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?

KS theorem shows that there is conflict between non-contextual HV models and QM (only theoretical argument). Bell not only shows conflict between local theories and QM but in addition opened a way how to test this conflict experimentally.

 

[bohm2]

If you keep locality, it must be non-realistic and contextual. (I can't really envision the difference between non-realistic and contextual though.)

How would you interpret experimental violations of Legget's inequality?

 

[Dale]

Closed pending moderation

Edit: after discussion we have decided to leave this thread closed