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Q & A: Legget on Bohm

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I heard the physics Nobel laureate Prof. Leggett at this school works on trying to understand what quantum mechanics means. I have always liked the Bohmian mechanics pilot wave interpretation but I heard that Leggett somehow came up with a better inequality than Bell's which somehow rules out non-local realism theories as well. Does this rule out Bohmian mechanics? What does non-local realism even mean? Quantum mechanics is confusing but fascinating.
- Jeffery (age 19)
Champaign, IL, USA
Here's Tony's response:
"The original paper is Foundations of Physics 33,1469.What it actually shows is that no theory of the class defined there as "crypto-nonlocal" (CN)(a subclass of the more general class of nonlocal theories) can reproduce all the predictions of QM; and since the predictions of the Bohmian pilot wave model (at least in its later incarnations in the hands of Goldstein,Hiley et al.) are by construction identical to those of QM, it presumably cannot reproduce the predictions of that model either. (so the latter must violate the subsidiary condition defining the CN subclass,though exactly how deserves further investigation). However, recent experiments have shown the class of CN theories to be invalid, and are consistent with QM, hence also with the (neo-)Bohmian model."

It seemed like a good idea to post this for you as-is. Now we can both look up the original paper and try to understand what crypto-nonlocal means.

Mike W.

(published on 04/15/11)

Follow-up on this answer.