Unitary and non-unitary evolution in quantum cosmology

Details Unitary and non-unitary evolution in quantum cosmology Unitary and non-unitary evolution in quantum cosmology

1998-12-14

arxiv.org/abs/gr-qc/9812045v2

Phys.Rev. D59 (1999) 123519

Astronomy and Astrophysics

Astrophysics

General Relativity and Quantum Cosmology

26 pages, latex; minor corrections, final version to appear in Phys. Rev. D

Scientific paper

10.1103/PhysRevD.59.123519

We analyse when and why unitarity violations might occur in quantum cosmology restricted to minisuperspace. To this end we discuss in detail backscattering transitions between expanding and contracting solutions of the Wheeler-DeWitt equation. We first show that upon neglecting only backscattering, one obtains an intermediate regime in which matter evolves unitarily but which does not correspond to any Schr\"odinger equation in a given geometry since gravitational backreaction effects are taken into account at the quantum level. We then show that backscattering amplitudes are exponentially smaller than matter transition amplitudes. Both results follow from an adiabatic treatment valid for macroscopic universes. To understand how backscattering and the intermediate regime should be interpreted, we review the problem of electronic transitions induced by nuclear motion since it is mathematically very similar. In this problem, transition amplitudes are obtained from the conserved current. The same applies to quantum cosmology and shows that the unique consistent interpretation is based on the current when backscattering is neglected. We then review why, in a relativistic context, backscattering is interpreted as pair production whereas it is not in the non relativistic case. In each example the correct interpretation is obtained by coupling the system to an external quantum device. From the absence of such external systems in cosmology, we conclude that backscattering does not have a unique consistent interpretation in quantum cosmology.

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