Time-Symmetrized Counterfactuals in Quantum Theory

Abstract

Recently, several authors have criticized the time-symmetrized quantum theory originated by the work of Aharonov et al. (1964). The core of this criticism was a proof, appearing in various forms, which showed that the counterfactual interpretation of time-symmetrized quantum theory cannot be reconciled with standard quantum theory. I argue here that the apparent contradiction is due to a logical error. I analyze the concept of counterfactuals in quantum theory and introduce time-symmetrized counterfactuals. These counterfactuals do not lead to any contradiction with the predictions of quantum theory. I discuss applications of time-symmetrized counterfactuals to several surprising examples and show the usefulness of the time-symmetrized quantum formalism.