The Nature of the Controversy over Time-Symmetric Quantum Counterfactuals

TL;DR

This paper clarifies the controversy over time-symmetric quantum counterfactuals by proposing a specific interpretation, concluding they are trivially true and offer no new information about quantum systems.

Contribution

It introduces a new interpretation of TSQCs as counterfactuals with a compound antecedent, resolving previous inconsistencies and clarifying their trivial nature.

Findings

TSQCs are true but trivially so

Inconsistency proofs do not apply under the new interpretation

TSQCs provide no new contingent information in general

Abstract

It is proposed that the recent controversy over "time-symmetric quantum counterfactuals" (TSQCs), based on the Aharonov-Bergmann-Lebowitz Rule for measurements of pre- and post-selected systems, can be clarified by taking TSQCs to be counterfactuals with a specific type of compound antecedent. In that case, inconsistency proofs such as that of Sharp and Shanks (1993) are not applicable, and the main issue becomes not whether such statements are true, but whether they are nontrivial. The latter question is addressed and answered in the negative. Thus it is concluded that TSQCs, understood as counterfactuals with a compound antecedent, are true but only trivially so, and provide no new contingent information about specific quantum systems (except in special cases already identified in the literature).