Locality, Probability and the Relevance of History

Abstract

Relativistic theory and experiments teach us that causal influences are constrained by the speed of light. Deterministic theories incorporate this lesson in $\textit{functional}$ terms: whether an event occurs or not is functionally determined by events that occur in its immediate causal past. In this paper we suggest a natural generalization of this constraint that applies to probabilistic theories: the $\textit{probability}$ that an event occurs is to be functionally determined by the $\textit{probability}$ of the event-occurrences in its immediate causal past. This constraint differs from Bell's criterion of local causality and turns out to imply it only under an additional assumption that requires history to be, in a sense, $\textit{ir}$relevant. Bell-inequality-violating quantum phenomena are thus arguably $\textit{not}$ in tension with relativity, locality, "statistical independence", nor with a supposed "realism". What they instead show is that history is, in a sense, $\textit{relevant}$.