New Quantum Interpretation Poll

[bohm2]

An interesting critical post by a non-Bohmian that attended that conference "QM without observers III" where that last poll linked above was completed:

Guest post on Bohmian Mechanics, by Reinhard F. Werner
http://tjoresearchnotes.wordpress.c...st-on-bohmian-mechanics-by-reinhard-f-werner/

What is really interesting is the exchange between the poster (Reinhard F. Werner), Matt Leifer, Tim Maudlin, Matt Pusey (of PBR theorem fame) and Travis Norsen. What I found really interesting is the heated exchange on the topic of Bell's theorem and implications for "realism" and if local non-realism is even comprehensible. This topic has always been difficult for me to understand. Some interesting quotes:

Matt Leifer

It is a fairly standard mantra that Bell’s theorem is based on the conjunction of realism and locality and so one can choose to reject one of them whilst keeping the other. As you say, Bohmians opt to throw out locality. As for the other position, i.e. locality without realism, I have a lot of trouble understanding what it is even supposed to mean...In fact, it seems to me that locality, in any sense that is even tangentially related to Bell’s theorem, requires realism for its very definition. You need to be able to say that there to be some things that objectively exist in the world in order to say whether changing them at one location affects them at some other. Hence, in my view, it is more accurate to say that holders of operational positions are rejecting both realism AND locality (in any sense that is relevant to Bell’s theorem).

Tim Maudlin:

Nothing does, except a confusion about the principles Bell used to derive his theorem. There is no supposition of “realism” in any sense in this theorem. If you think otherwise, point it out: it is, after all, a piece of mathematics.

Travis Norsen:

“Signal locality” (or “local commutativity”) is simply not an assumption of Bell’s theorem (either/any of them) and nobody who had actually read Bell’s papers (in several of which he goes to great lengths specifically to *distinguish* “signal locality” from the locality assumption that is actually used in the theorem) could possibly harbor this misconception. Nor is “realism” (in anything but the most basic sense, denial of which would render “locality” — in any sense — completely meaningless, as Matt L already pointed out) an assumption of Bell’s theorem.

Edit: Actually Norsen in a post in this forum does provide a local and non-realist (in some sense) model:

Here's a model that non-realistic but perfectly Bell local: each particle has no definite, pre-existing, pre-scripted value for how the measurements will come out. Think of each particle as carrying a coin, which, upon encountering an SG device, it flips -- heads it goes "up", tails it goes "down". That is certainly not "realistic" (in the sense that people are using that term here) since there is no fact of the matter, prior to the measurement, about how a given particle will respond to the measurement; the outcome is "created on the fly", so to speak. And it's also perfectly local in the sense that what particle 1 ends up doing is in no way influenced by anything going on near particle 2, or vice versa. Of course, the model doesn't make the QM/empirical predictions. But it's non-realist and local. And hence a counter-example to any claim that being Bell local requires/implies being "realist".

 

[harrylin]

[..] Actually Norsen in a post in this forum does provide a local and non-realist (in some sense) model:

That's interesting indeed, as I think that most people - and maybe even Einstein - would call a coin-flipping model "realistic".

 

[Demystifier]

Concerning the question of what locality without realism is even supposed to mean, I also had difficulties with it, until I found my own model for such a thing:
http://arxiv.org/abs/1112.2034 [Int. J. Quantum Inf. 10 (2012) 1241016]