Toy Models for Retrocausality

A number of writers have been attracted to the idea that some of the peculiarities ofquantum theory might be manifestations of ‘backward’ or ‘retro’ causality, underlying thequantum description. This idea has been explored in the literature in two main ways:firstly in a variety of explicit models of quantum systems, and secondly at a concep-tual level. This note introduces a third approach, intended to complement the othertwo. It describes a simple toy model, which, under a natural interpretation, shows howretrocausality can emerge from simple global constraints. The model is also useful inpermitting a clear distinction between the kind of retrocausality likely to be of interest inQM, and a different kind of reverse causality, with which it is liable to be confused. Themodel is proposed in the hope that future elaborations might throw light on the potentialof retrocausality to account for quantum phenomena. BibliographyBerkovitz, J. 2002: On Causal Loops in the Quantum Realm. In T. Placek and J. Butter-field (eds.), Non-locality and Modality, Kluwer, 235–257.Costa de Beauregard, O. 1953: Méchanique Quantique. Comptes Rendus Académiedes Sciences 236, 1632.Costa de Beauregard, O. 2005: Personal communication to Guido Bacciagaluppi andHuw Price, Bourron-Marlotte, France, 28.03.05.Price, H. 1996: Time’s Arrow and Archimedes’ Point. New York: Oxford University Press.Spekkens, R. W. 2004: In Defense of the Epistemic View of Quantum States: a ToyTheory. http://arXiv.org/abs/quant-ph/0401052Sutherland, R. 2006: Causally Symmetric Bohm Model. Forthcoming in Studies in theHistory and Philosophy of Modern Physics, 39, 2008. Preprint available online here:http://arxiv.org/abs/quant-ph/0601095v2Wharton, K. 2007: A Novel Interpretation of the Klein-Gordon Equation. Preprint avail-able here: http://arxiv.org/abs/0706.4075Wiseman, H. 2005: From Einstein’s Theorem to Bell’s Theorem: A History of QuantumNonlocality. http://arxiv.org/abs/quant-ph/0509061v3