I Could Tim Maudlin's Views on Bell and QM Be Flawed?

[martinbn]

Think of the Us and Ds as pre-existing properties, revealed by different measurements on individual particles. Local realism says it should be possible to write down an arrangement of Us and Ds that fully specify the outcomes of all possible measurement choices. So e.g. the dotted line represents a choice of the observable $\sigma^A_x\sigma^B_x\sigma^C_z$ and should yield an eigenvalue +1 (the product of the individual measurement results: e.g. UUU = 1*1*1 = 1, UDD = 1*-1*-1 = 1 etc). Other such observables can be constructed by following the appropriate solid lines.

It is not actually possible to write down an arrangement that satisfies all measurement choices. So we cannot write down

Yes, but my question is about non-local realism.

 

[Morbert]

Yes, but my question is about non-local realism.

Oh oops misread your original post.

 

[Morbert]

With non-local realism, there is no need to specify an arrangement of Us and Ds everywhere because a choice of measurement at one site can immediately influence values at other sites. If it were possible to write down all Us and Ds that satisfy quantum predictions, there would be no need to suppose this immediate influencing.

 

[martinbn]

With non-local realism, there is no need to specify an arrangement of Us and Ds everywhere because a choice of measurement at one site can immediately influence values at other sites. If it were possible to write down all Us and Ds that satisfy quantum predictions, there would be no need to suppose this immediate influencing.

So they have some U or D value along some direction and when a measurement is made the values change to what they should be?

 

[Morbert]

So they have some U or D value along some direction and when a measurement is made the values change to what they should be?

I'm not sure how useful the diagram is for representing the non-local case. Its primary purpose is in representing the failure of the local case. I would imaging a nonlocal realist interpretation would have these values changing to what they should be, but maybe not directly. You would have to ask one of the Bohmian representatives here.

 

[martinbn]

I'm not sure how useful the diagram is for representing the non-local case. Its primary purpose is in representing the failure of the local case. I would imaging a nonlocal realist interpretation would have these values changing to what they should be, but maybe not directly. You would have to ask one of the Bohmian representatives here.

The reason i asked was because i dont see the role of the locality. It seems that this shows that realism without any additional assumptions is impossible. I dont think BM is realistic about this observable, only about the position observables.

 

[WernerQH]

In this interpretation there is no causal explanation, why a specific measurement outcome when an observable is measured that's not determined due to the state preparation occurs, but it's assumed to be "objectively random" with probabilities given by Born's rule. E.g., if you have a polarization-entangled photon pair and you measure the polarization of one of these photons (which is exactly unpolarized in this case) by e.g., using a polarization filter there's no causal explanation whether a specific photon goes through the filter or not. All you can say is that with probability 1/2 it goes through, with probability 1/2 it doesn't. There's no cause for the one or the other outcome for any specific photon prepared in such a state.

Nevertheless the correlations are due to the preparation of the initial state. In QT these correlations between the outcomes of measurments of the single-photon polarizations are there despite the fact that these single-photon polarizations are maximally undetermined when the photons are prepared in the said entangled state (in the here discussed example a GHZ three-photon state).

Looking at only one detector, "there's no cause for the one or the other outcome". But looking at two widely separated detectors, "the correlations are due to the preparation of the initial state". Doesn't application of the Born rule add an element of non-locality to QFT? The operators of QFT are constructed taking microcausality into account, but you cannot derive statistical predictions from QFT without the Born rule. Your insistence on its locality is based on only a part of the theory. You shouldn't call a soup kosher if it doesn't apply to all its ingredients.

 

[bhobba]

Demytistifyer answered my query. He knows Tim Mauldin and understands what he is getting at. The thread is now just a discussion we have had many times about Bell. Of course anyone can start a new one - it is a legit ussue. But the purpose of this thread has been fulfilled so will be closed. As I said this is a legit point of debate, so start another thread if you want to continue with it.

Thabks
Bill