Here are the details of the next Q+ hangout.

Date/time: Wed. 26th Nov. 2014 10pm GMT/UTC

Speaker: Howard Wiseman (Griffith University)

Title: After 50 years, Bell’s Theorem Still Reverberates

Abstract:

Fifty years ago this month, Belfast-born physicist John Bell submitted for publication a paper [1] which has been described as “the most profound discovery in science” [2]. However, its significance is still much disputed by physicists and philosophers [3, 4].

I will explain what is so puzzling about the types of correlations Bell introduced, by a specific example based on [5]. (For those well-versed in Bell inequalities this may still be of pedagogical interest.)

But what exactly do these Bell-type correlations violate? Bell’s original answer [1] was the joint assumptions of determinism and locality. His later answer [6] was the single assumption of local causality (which, confusingly, he sometimes also called locality). Different ‘camps’ of physicists – operationalists and realists respectively – prefer the different versions of Bell’s theorem.

Which of Bell’s notions, locality or local causality, expresses the causal structure of Einstein’s theory of relativity? I will argue for the answer: neither [3,4]. Both notions require an additional causal assumption, and the one required for local causality is a stronger one. I will discuss how the different assumptions fit with the ideologies of the two camps, and how they can best be reconciled.

[1] J. S. Bell, “On the Einstein-Podolsky-Rosen paradox”, Physics 1, 195-200 (1964).

[2] H. P. Stapp, “Are superluminal connections necessary?”, Nuovo Cim. 40B, 191 (1977).

[3] H. M. Wiseman, “The two Bell’s theorems of John Bell”, J. Phys. A 47, 424001 (2014) (Invited Review for Special Issue, 50 years of Bell’s theorem)

[4] H. M. Wiseman, “Bell’s theorem still reverberates”, Nature 510, 467-9 (2014).

[5] P. K. Aravind, “Bell’s theorem without inequalities and only two distant observers”, Found. Phys. Lett. 15, 397 (2002).

[6] J. S. Bell, “The Theory of Local Beables”, Epistemological Lett. 9, 11-24 (1976).

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