Abstract

Whether time travel into the past is possible is an undecided physical question [1]. Recently it has been noted that certain models of time travel for quantum particles do not lead to the same difficult paradoxes that arise for classical particles [2]. Furthermore the types of quantum evolutions predicted for these "quantum time machines" could give rise to a "super" quantum computer, able to solve problems thought to be intractable by any other means [3]. In this talk I will discuss time machines in general, how quantum mechanics avoids the paradoxes and the unusual evolutions predicted. I will then argue that the requirements for realizing such machines are not as stringent as previously thought and I will propose "horizon technology" experiments which could test these ideas [4].