JTW > Research > Modelling the Decoherence of Spacetime
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There are well-documented models of a system of interest coupled to an environment whose details are ignored. These unmeasured modes carry away phase information about the system and induce decoherence which allows probabilities to be assigned to the possible outcomes of measurements of the system. In the case of the gravitational field, if only the macroscopic modes are involved in the definitions of alternatives, to what extent to the short-wavelength modes act as an "environment" to induce decoherence in the long-wavelength modes? (Previous work, for example by Halliwell [Phys Rev D39, 2912 (1989)] and Padmanabhan [Phys Rev D39, 2924 (1989)], used an additional field to obtain decoherence of the gravitational field in cosmological models. The present enterprise differs in that it examines decoherence which is induced by other modes of the gravitational field itself.)

Examining a scalar field action with some of the same properties as the action for General Relativity, I use a perturbative approach to determine when the off-diagonal elements of the decoherence functional for coarse graining only by the long-wavelength modes are suppressed by the influence functional. An important limitation of the result is that the perturbative approach is only applicable when the temperature describing the state of the short-wavelength modes is high compared to the inverse of the length scale dividing long and short wavelengths.

This work has been published as Phys Rev D57, 768 (1998) and is also available as a preprint from the XXX e-print database at Los Alamos. There is also a short summary, written for the proceedings of the 18th Texas Symposium on Relativistic Astrophysics.