Speaker
Description
Time in quantum mechanics, especially the non-relativistic theory has privileged position in that
unlike the Cartesian coordinates it is a parameter rather than an operator. Moreover, it is a parameter
over which we have no control: time passes and our quantum systems evolve. Yet the theory is
essentially time-symmetric (as is most of the rest of physics) so there is a sense in which “time-reversed”
quantum theory should have a meaning. This is indeed the case and I shall present such a retrodictive
(as opposed to predictive) theory, which is linked to the conventional approach by Bayes' theorem.
The theory brings with it surprises, some of which I shall demonstrate. These include unconventional
explanations for classic quantum optics experiments and novel devices designed using retrodictive
reasoning including the possibility of information processing in the past! If time permits I shall also
introduce the principle of devices utilising indefinite causal order, in which there is an advantage to
be had by employing physical operations in a superposition of temporal orders.
