Abstract

This dissertation considers various claims which have been made by proponents of time-symmetrized quantum theory , focusing in particular on the work of Lev Vaidman, who has been the strongest advocate in recent years. These claims attribute "elements of reality," corresponding to dispersion-free values of noncommuting observables, to pre- and post-selected quantum systems via the Aharonov-Bermann-Lebowitz rule of time-symmetrized quantum theory. ;The novelty of the TSQT approach is the assertion that more information can be gained about a system in a symmetric time interval bounded by given past and future measurement outcomes than via the usual, time-asymmetric Born rule requiring that only a pre-selection outcome be given. ;Such claims, if true, would be valuable for a realist interpretation of quantum theory. The value would lie in the possibility of quantum states with dispersion-free values for noncommuting observables, provided such states are defined time-symmetrically through the use of two-state vectors according to the prescription of TSQT. ;Thus the basic question to be addressed is: Does TSQT shed any new light on the debate concerning the adequacy of realist interpretations of quantum theory? Answering this question requires a careful evaluation of the counterfactual usage of the ABL rule, which is the only way to obtain the inferences about dispersion-free values. The analysis shows that the counterfactual usage is, in general, invalid, and therefore the program advocated by Vaidman, Aharonov, and others fails to provide new insights into, or support for, a realist interpretation of quantum theory