paper

The emergent nature of time and the complex numbers in quantum cosmology

arXiv:1111.0457

Abstract

The nature of time in quantum mechanics is closely related to the use of a complex, rather than say real, Hilbert space. This becomes particularly clear when considering quantum field theory in time dependent backgrounds, such as in cosmology, when the notion of positive frequency ceases to be well defined. In spacetimes lacking time orientation, i.e without the possibility of defining an arrow of time, one is forced to abandon complex quantum mechanics. One also has to face this problem in quantum cosmology. I use this to argue that this suggests that, at a fundamental level, quantum mechanics may be really real with not one, but a multitude of complex structures. I relate these ideas to other suggestions that in quantum gravity time evolution may not be unitary, possibly implemented by a super-scattering matrix, and the status of CPT.

Extended version of a lecture , with additional introductory material and many references, given at the conference Origins of Time's Arrow held at the World Trade Centre, October 15-16, 2007 to appear in Fundamental Theories of Physics, {\bf 164} The Arrows of Time: A debate in Cosmology eds L.Mersini-Houghton and R. Vass, pp 107-146 Springer 2012

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