John S. Bell (28 July (1928)–1 October (1990)) was a physicist who made the biggest contemporary breakthrough in physics by bringing back on its turn philosophical questions regarding the nature of reality. Specifically, with his eponymous theorem, and supporting inequalities, he showed that it was possible to discriminate experimentally whether a local realistic description of the world was possible. Previously, Einstein, Podolsky and Rosen merely had argued (although convincingly) that this would not be reasonable. The experimental confirmation by Clauser that the world cannot, indeed, be realistic and local put the cherry of mysticism on the quantum cake. The fields of quantum foundations and interpretations of quantum mechanics became serious, urgent matters. Still unresolved to this day. Bell is doubtlessly one of the most profound and interesting authors to read on that topic.[1] His last work is "La nouvelle cuisine".
Von Neumann had previously provided a proof that hidden variables were not possible, but Bell showed that it was wrong, in fact «the proof of von Neumann is not merely false but foolish» [emphasis in original]
A street in Belfast is named, not after him, but after his theorem!