After 50 years, Bell’s theorem still reverberates


Prof. Howard Wiseman, Griffith University
This colloquium will be held in Parnell (07) 222 at 3pm.

Fifty years ago this week, 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].
In a nutshell, Bell’s theorem is that certain correlations, which can be experimentally measured using distant quantum systems originating from a common source, seem to violate the usual laws of cause and effect. I will explain how mere correlations can be so puzzling, by a specific example based on [5].
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).

Howard Wiseman is a theoretical physicist researching quantum measurement and control, quantum information, open quantum systems, quantum foundations, and Arthurian history and literature. He did his BSc Hons (1991) and PhD (1992-4) with Gerard Milburn at UQ and a postdoc (1994-6) with Dan Walls in Auckland. He has published over 190 journal papers. He was awarded the Bragg Medal for his PhD thesis, and the Pawsey Medal and the Malcolm Macintosh Medal in 2003. He is a Fellow of the Australian Academy of Science and of the American Physical Society. He has been Director of the Centre for Quantum Dynamics at Griffith University since 2007.

<iframe src=”//″ height=”333″ width=”500″ allowfullscreen=”" frameborder=”0″></iframe>

<a href=”″>Prof. Howard Wiseman – 50 years on, Bell’s theorem still reverberates</a> from <a href=””>School of Mathematics &amp; Physics</a> on <a href=””>Vimeo</a>.