Time-Symmetric Counterfactual Propositions in Quantum Theory

Kastner Ruth E, Greenbelt MD

Investigators

Abstract

Ruth Kastner Time-Symmetric Counterfactual Propositions in Quantum Theory Many interpretational problems in quantum theory involve counterfactual statements (statements of the form, \If it were that P, then it would be that Q"). In recent years, there has been controversy over the validity of counterfactual claims in explicitly time symmetric formulations of quantum theory such as that of Yakir Aharonov and Lev Vaidman, and that of Ulrich Mohrhoff. The goal of the proposed project is twofold: (a) to investigate precisely how such counterfactuals must differ from conventional counterfactuals and (b) whether a consistent and/or physically meaningful account of time-symmetric quantum counterfactual is possible. The research plan is to conduct a thorough survey of the literature on counterfactuals, in order to take account of existing theories and to ascertain the domain of those theories (i.e., the kinds of counterfactual claims addressed by those theories). Then an analysis follows of the salient features of traditional counterfactual claims and of the novel counterfactual claims addressed by the current proposal (hereinafter \novel counterfactuals"), in order to uncover essential similarities and (primarily) differences. Next the project turns to a critical analysis of the predominant traditional counterfactual theories in light of differences uncovered between novel counterfactual claims and the traditional counterfactual claims. Such an analysis should provide at least a partial answer to the question of whether traditional theories can be applied to novel counterfactuals, possibly with some modifications. If it is determined that traditional counterfactual theories are fundamentally incompatible with novel counterfactuals, then an attempt follows to lay out the essential features of an alternative counterfactual theory (addressing the first point), which will then be critically analyzed (addressing the second point) . If the result of this second point is negative, alternatives to the use of counterfactual measurements are explored, to establish meaningful time-symmetric \objective" quantum mechanical probabilities such as that sought by Mohrhoff.