An experimental test of nonlocal realism

A little excursion to the foundations of quantum mechanics:
Anton Zeilinger and collaborators paper “An experimental test of nonlocal realism” just came out in Nature, luckily there is also a publicly readable preprint version on the archive, the ORF reported about it here (link via Anton Zeilingers blog).

I am just linking to the paper, since it seems to contain an interesting result. I am not an expert in the matter and I havent read the paper thoroughly, so just a little shaky comment on what the paper says:

Quantum mechanics revealed properties which are incompatible with classical physics. In particular the nature of the observation of an experiment (“the observation of reality”) had been the issue of many discussions. In 1964 John Bell showed with his Bells Theorem that a model which includes the everyday-intuitive-concepts of “realism” (i.e. the assumption that there “exist” an external reality independent of experiment) and “locality” (i.e. that there are no “spooky” interactions, via long distances (spacelike seperated regions)) are incompatible with the descriptions of quantum mechanics. Over the years this incompatibilty (and modifications of it) had been verified experimentally to an exhaustive extent.

In order to get a better grasp of quantum mechanics a common proposal was to relax the notion of “locality” (rather then the one of “realism”). Apparently A.J.Leggett (I currently do not have access to this paper) proposed incompatibility tests for a broad class of “nonlocal theories”. (It sounds as if this had been done via inequalities for statistical correlations like in Bells theorem). In their paper Zeilinger et al. “analyzed its assumptions and derived an inequality valid for such theories that can be experimentally tested.” and finally performed “an experiment** that violates the new inequality and hence excludes for the first time a broad class of non-local hidden variable theories.” A fact which suggests that may be the concept of “realism” has to be relaxed or newly interpreted. Or in other words their result suggests that

“giving up the concept of locality is not sufficient to be consistent with quantum experiments, unless certain intuitive features of realism are abandoned.”

A side remark: There is a little comment in the paper relating to Bohms nonlocal theory via a quantum potential (which suggests that -very very loosely speaking- quantum particles are “surfing” on a kind of “guiding/pilot” wave). It seems that Leggetts model does not include this theory (?). Related: this old randform post linking to an “guiding wave experiment” (where the “surfer” contributes to the wave). However this experiment is on a macroscopic level.

**the experiment uses the polarization of light, in particular entangeled photon pairs.

2 Responses to “An experimental test of nonlocal realism”

  1. king arthurs tableround Says:

    It’s so funny that quantum particles are surfing!
    This Bohm book must be really neat to look at.

  2. nad Says:

    It’s so funny that quantum particles are surfing! This Bohm book must be really neat to look at.

    It’s though a little bit different from these investigations:
    surfing as described by the beach boys

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