View Poll Results: What do observed violation of Bell's inequality tell us about nature?  
Nature is nonlocal  11  32.35%  
Antirealism (quantum measurement results do not preexist)  15  44.12%  
Other: Superdeterminism, backward causation, many worlds, etc.  8  23.53%  
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What do violations of Bell's inequalities tell us about nature? 
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#145
Feb1913, 02:03 PM

Sci Advisor
P: 2,118

This technicality was exploited by Pitowsky, who developed a local hidden variables theory that makes the same predictions for the spin1/2 EPR experiment as orthodox quantum mechanics. Where he escapes from Bell's clutches is exactly in using a "hidden variable" for which there is no probability distribution. He uses nonmeasurable sets, constructed via the continuum hypothesis. 


#146
Feb1913, 02:05 PM

P: 733

That's probably not what you meant. You meant something about the arbitrariness of reference frame  e.g., what you call x=5, maybe I call x=17. But that's a totally different issue than the one I was bringing up for spin in bohm's theory. There is an analog of your issue for spin  namely, maybe what you call "spin along z = +1" I instead call "spin along z = +hbar/2" or "spin along z = 37". All of those, actually, are perfectly valid choices. We can disagree about what to *call* a certain definite outcome. But that is not at all the point of the example I explained for the contextuality of spin in bohm's theory. There, the point is not that different people might call the outcome different things, but that two different experiments (that happen to correspond to the same Hermitian operator in QM) can yield distinct outcomes (for exactly the same input). This isn't about calling the same one outcome by two different names; the outcomes are really genuinely distinct. 


#147
Feb1913, 02:22 PM

P: 461

in the case of position x,y,z axes in turn determined by other set of axes ? in turn determined by other set of axes ? "coordinates" respect to ? 


#148
Feb1913, 02:35 PM

P: 159

By the way: I was looking for that paper you suggested, but i don't find it on the internet. (Apart from that, i don't know french, so i probably couldn't read it?) Can you point me to a source? I have access to most journals. 


#149
Feb1913, 03:32 PM

P: 733

I'd even be willing to bet real money that this isn't right  that is, that there's no genuine example of a local theory sharing QM's predictions here. If it were true, it would indeed be big news, since it would refute Bell's theorem! (Something that many many people have wrongly claimed to do, incidentally...) But internet bets don't usually end well  more precisely, they don't usually end at all, because nobody will ever concede that they were wrong. So instead I'll just say this: you provide a link to the paper, and I'll try to find time to take a look at it and find the mistake. 


#150
Feb1913, 03:34 PM

P: 733




#151
Feb1913, 03:44 PM

P: 733

Maybe the issue has to do with what I assume(d) was just a typo? Namely: it's not [itex]p(A,B,\lambda)[/itex] but rather [itex]p(A,B\lambda)[/itex]  or, as I indicated before, slightly more precisely, [itex]p_{\lambda}(A,B)[/itex]. http://arxiv.org/abs/0707.0401 


#152
Feb1913, 04:51 PM

Sci Advisor
P: 2,118

The proof of the theorem assumes that the unknown hidden variable [itex]\lambda[/itex] is measurable; in particular, that it makes sense to talk about things such as "the probability that [itex]\lambda[/itex] lies in some range such that [itex]A(\hat{a},\lambda) = B(\hat{a},\lambda)[/itex]" for various choices of [itex]\hat{a}[/itex] and [itex]\hat{b}[/itex]. Pitowky showed that if you don't assume measurability of [itex]\lambda[/itex], then the EPR correlations can be explained in terms of a nonmeasurable function [itex]F(\hat{r})[/itex] where [itex]\hat{r}[/itex] is a unit vector (or alternatively, a point on the unit sphere), with the properties that: (This is from memory, so I might be screwing these up):
Mathematically, you can prove that such functions exist (with the notion of "probability" in the above being flat lebesque measure on the set of possibilities). Pitowksy called it a "spin1/2 function".But it's not a very natural function, and is not likely to be physically relevant. In a brief Google search, I didn't see Pitowsky's original paper, but his spin1/2 models are discussed here: http://arxiv.org/pdf/1212.0110.pdf 


#153
Feb1913, 05:34 PM

Sci Advisor
PF Gold
P: 5,381

http://arxiv.org/abs/quantph/0605105 http://arxiv.org/abs/0908.4348 How much were we betting? 


#154
Feb1913, 05:43 PM

P: 733

http://arxiv.org/abs/0909.4553 Or see Bells' papers, especially "la nouvelle cuisine" or "the theory of local beables". http://www.scholarpedia.org/article/Bell%27s_theorem which discusses all of the subtleties in gory, exhausting detail. 


#155
Feb1913, 06:29 PM

Sci Advisor
P: 2,118




#156
Feb1913, 06:39 PM

Sci Advisor
P: 2,118




#157
Feb1913, 07:28 PM

P: 733




#158
Feb1913, 07:35 PM

P: 733




#159
Feb1913, 07:42 PM

P: 733




#160
Feb1913, 08:26 PM

Sci Advisor
P: 2,118

The observation that the generators of boosts, translations and rotations obey commutation relations isomorphic to those of quantum mechanics is intriguing (and I've wondered for years whether there was some connection), but I still don't get it. For one thing, the classical commutation relations don't involve hbar, so I don't understand how that constant can arise from a block world interpretation (even though I don't really know what the blockworld interpretation is). 


#161
Feb1913, 08:52 PM

P: 733




#162
Feb1913, 11:07 PM

PF Gold
P: 691

Two other interesting papers discussing Bell's concept of local causality and implications of violation of bell's inequality pursuing Bell's and ttn's positions (with many passages from Bell's work) are the following 2 papers by M.P. Seevinck:
http://mpseevinck.ruhosting.nl/seevi..._corrected.pdf http://mpseevinck.ruhosting.nl/seevi...k_Revised3.pdf 


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