Toy models for retrocausality

Abstract

A number of writers have been attracted to the idea that some of the puzzling features of quantum mechanics might be manifestations of 'reverse' or 'retro' causality, at a level underlying that of the usual quantum description. The main motivation for this view stems from EPR/Bell phenomena, where it offers two virtues. First, as was noted by its earliest proponent, 1 it has the potential to provide a timelike decomposition of the nonlocal correlations revealed in EPR cases -i.e., as we would now put it, 2 for the violation of the Bell inequalities in the quantum world. Second, Bell's derivation of his famous inequality depends explicitly on the assumption that hidden states do not depend on future measurement settings -so that its violation simply invites a retrocausal explanation, at least from the point of view of anyone who has already been bitten by the retrocausal bug. Most people working in the foundations of quantum mechanics remain resolutely unbitten, however. It is common for the retrocausal option to be ignored altogether, or, as in this rather careful recent survey article, relegated to the footnotes with other unmemorabilia:To be scrupulous, there are perhaps four other ways [i.e., other than nonlocality] that the correlations in [an EPR-Bohm] experiment could be explained away. (1) One could simply 'refuse to consider the correlations mysterious'. (2) One could deny that the experimenters have free will to choose the settings of their measurement devices at random, as required for a statistically * This note is based on a talk given at workshops at

Interaction-Free Effects Between Distant Atoms

“…The quantum temporal anomalies involved in this experiment may encourage the use of a time-symmetric framework [39][40][41][42][43][44][45][46][47][48][49], long familiar from Wheeler's "delayedchoice" paradox [50] and made more acute in recent settings like the "too-late choice" experiment [51]. The main reason for that as explained below, is the light shed on the above paradoxes by the combination of past and future boundary conditions.…”

Causation, Decision Theory, and Bell’s Theorem: A Quantum Analogue of the Newcomb Problem

“…Another possibility is that these correlations are arranged through retrocausality. Some authors have considered this possibility as a serious alternative to the interpretation of quantum mechanics (Price, 1996;Wharton, 2007;Berkovitz, 2008;Pegg, 2008;Price, 2008), but it hasn't been given as much attention as it seems to deserve.…”

“…However, there are logically possible causal hypotheses compatible with the quantum correlations and in which local causality is maintained in one way or another (either through retro-causality (Price, 1996;Pegg, 2008;Price, 2008;Berkovitz, 2008), or through what Bell called "superdeterminism" (Bell, 1987)). Given that local causality is, according to Bell and others, the causal requirement of relativity-our best theory of causal structure-and given the availability of alternatives that maintain it, local causality should not be outright rejected by the causalist.…”

The World According to de Finetti: On de Finetti’s Theory of Probability and Its Application to Quantum Mechanics

“…λ-independence fails in models of the experiment that postulate retro-causal influences from the measurement events to the source at the emission, so that the distribution of the complete pair-state depends on the measured quantities (for recent discussions of such models, see [32][33][34][35][36], and references therein). In such models, the QM statistics may be accounted for by such retro-causal influences rather than non-locality.…”