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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].

[1] M.S.Morris, K.P.Thorne and U.Yurtsever, Phys.Rev.Lett.61, 1446 (1988).
[2] D.Deutsch, Phys.Rev.D 44, 3197 (1991).
[3] D.Bacon, Phys.Rev.A, 70, 032309 (2004).
[4] T.C.Ralph, quant-ph/0510038.