# Bell's theorem: Local realism v. counterfactual determinism

1. Feb 20, 2010

### zvi

This is kind of an offshoot from:

Assume for a second that the controversial experiments are valid and Bell's theorem is true of the universe.
I have often seen the philosophical analysis that if Bell's Theorem is true then either local realism OR counterfactual determinism must be violated.
E.g. http://en.wikipedia.org/wiki/Counterfactual_definiteness

But all the interpretations of quantum mechanics I know do involve some breech of locality - namely there is entanglement.

So (1) can we say that Bell's Theorem proves that the world is not local (i.e. that there is entanglement) and if not what is the counter example of a theory which is totally local and yet is consistent with Bell's inequality and with the predictions of QM?

(2) if locality is indeed violated does anyone know of a really clear lay explanation for how locality can be broken but in such a way that it does not allow non-local signalling.

Hope my question is clear!

Thanks

PS I just saw an older related thread