Branching with Uncertain Semantics

In their paper ‘Branching and Uncertainty’, (Saunders and Wallace [2008]) aim to solve the so-called ‘incoherence problem’ commonly attributed to the Everett interpretation of quantum mechanics (EQM). The Everett interpretation posits a multiplicity of branching universes as a realistic reading of the evolution of the quantum state function. The ‘incoherence problem’ is, roughly, that our common talk of uncertainty of outcomes of quantum-mechanical experiments seems to have no foothold in EQM: Since all the facts about the branching are fully acknowledged, there seems to be nothing, on that interpretation, to be uncertain about. Saunders and Wallace point to non-epistemic approaches to the mentioned problem (e.g., Greaves [2004]; Greaves and Myrvold [2008]), but their own solution is instead to provide ‘a ready set of semantic rules according to which our actual extant, ordinary talk of ignorance and uncertainty comes out as true’ (pp. 293-4). Thus, there is no incoherence problem to begin with, just a question of getting the semantics right. This project, according to Saunders and Wallace, is not motivated by metaphysical considerations but by the hope of making sense of our ‘best physical theory’ along the lines of a naturalized metaphysics. Brit. J. Phil. Sci. (2010), 1–16