Quantum field theory in curved spacetime
- Quantum field theory in curved spacetime
Quantum field theory in curved spacetime is an extension of standard quantum field theory to curved spacetime. A general prediction of this theory is that particles can be created by time dependent gravitational fields, or by time independent graviational fields that contain horizons.
Thanks to the equivalence principle the quantization procedure closely resembles that of Minkowski spacetime once the proper formalism is chosen; however, interesting new phenomena occur. In general, on curved spacetimes quantum fields lose their interpretation as asymptotic particles. Only in certain situations, such as in asymptotically flat spacetimes, can the notion of incoming and outgoing particle be recovered. Even then, the asymptotic particle interpretation depends on the observer (ie, different observers may measure different numbers of asymptotic particles on a given spacetime).
The most striking application of the theory is Hawking's prediction that black holes radiate with a thermal spectrum. A related prediction is the Unruh effect: accelerated observers in the vacuum measure a thermal bath of particles.
This formalism is also used to predict the primordial density perturbation spectrum arising from cosmic inflation. Since this spectrum is measured by a variety of cosmological measurements -- such as the CMB -- if inflation is correct this particular prediction of the theory has already been verified.
The theory of quantum field theory in curved spacetime can be considered as a first approximation to quantum gravity. A second step towards that theory would be semiclassical gravity, which would include the influence of particles created by a strong gravitational field on the spacetime (which is still considered classical).
Suggested reading
* R.M. Wald. "Quantum field theory in curved space-time and black hole thermodynamics." Chicago U. (1995).
* S.A. Fulling. "Aspects of quantum field theory in curved space-time." CUP (1989).
* N.D. Birrell & P.C.W. Davies. "Quantum fields in curved space." CUP (1982).
* L. H. Ford [http://arxiv.org/abs/gr-qc/9707062 Quantum Field Theory in Curved Spacetime] (1997).
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