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Causation and the Two Theorems of John Bell

Howard Wiseman, Griffith University

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Abstract: Fifty years ago John Bell published a theorem [1] which has been described as "the most profound discovery in science" [2]. However, the question as to what his theorem says about the world is still much disputed by physicists and philosophers [3]. Bell's original answer [1] was the joint assumptions of determinism and locality. His later answer [4] 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 [5,6]. 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] J. Phys. A 47, issue 42: Special Issue "50 years of Bell's theorem" (2014). [4] J. S. Bell, "The Theory of Local Beables", Epistemological Lett. 9, 11-24 (1976). [5] H. M. Wiseman, "The two Bell's theorems of John Bell", in [4], article 424001. [6] H. M. Wiseman, "Bell's theorem still reverberates", Nature 510, 467-9 (2014).