Applying the Transactional Interpretation to Conceptual Problems in Quantum Theory

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In recent years, numerous paradoxes have arisen which raise questions about what can be inferred about a quantum system based on its theoretically calculated quantities, such as weights and probabilities and, more recently, its ``weak values''--- time-symmetric quantities applicable to pre- and post-selected systems. The proposed research would apply to the analysis of these problems a somewhat neglected interpretation of quantum theory, namely the ``Transactional Interpretation'' (TI) of John Cramer (1980). TI proposes that quantum events are mediated by spacetime ``transactions'' consisting of a distinctive type of interaction between the usual future-directed ("retarded") and past-directed, "advanced" waves. The proposed research consists in applying the transactional model to current thought experiments such as Hardy's experiment (1992) and the three-state paradox, both of which present conceptual difficulties, and investigating how this application affects what conclusions are possible concerning the ontology of the systems involved in such experiments. The proposed project's intellectual value lies in its direct bearing on longstanding problems in the interpretation of quantum theory, in particular the ontological status of quantum systems between measurements, which remains deeply obscure under the standard time-asymmetric approach. In terms of broader implications, the project is also of historical value in its examination of an under-recognized proposal of several decades ago. A study of this neglected interpretation sheds light on the reasons for its neglect and on what those reasons tell us about human expectations of physical theories---i.e., what such theories should assume about the world, as well as what kind of information they should provide. In particular, humans have a very compelling intuition about the temporal ordering of cause and effect, and this intuition tends to constrain the construction and interpretation of theories. TI denies that intuition. Yet it appears to offer effective solutions to longstanding puzzles of quantum theory such as ``wave function collapse'' (exactly where/when/how does it occur?) and the problem of measurement. If TI is the correct way to interpret quantum theory, this implies that humans need not view the past as equivalent to ``what has already happened''; certain aspects of the past might remain open to change based on future events. Such an understanding radically changes the relationship of humans to their world of experience, both inner and outer, in a way that has the potential to extend beyond basic intellectual understanding (as in puzzle-solving) to cultural and societal possibilities.