MG11 
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Abstract

Branch wave functions for quasi-classical universes

Quantum mechanics normally requires that a history of a system be measured before the probability of that history can be meaningfully discussed. In quantum cosmology, external measurements have no meaning and other strategies must be sought. "Decoherent histories" formulations of quantum theory take the hint from ordinary quantum mechanics that measurement serves to destroy interference between alternative histories and formalizes this observation into a scheme for making internally consistent quantum predictions for closed systems even in the absence of anything that resembles a classical measurement situation. I discuss the construction of such a quantum theory for the example of the Friedmann-Robertson-Walker cosmology. In particular, coarse grainings suitable to characterize quasiclassical behavior are described, and the branch wave functions for quasiclassical FRW cosmologies are exhibited.

Branch Wave Functions for Quasi-Classical Homogeneous Universes

Quantum mechanics normally requires that a history of a system be measured before the probability of that history can be meaningfully discussed. In quantum cosmology, external measurements have no meaning and other strategies must be sought. "Decoherent histories" formulations of quantum theory take the hint from ordinary quantum mechanics that measurement serves to destroy interference between alternative histories and formalizes this observation into a scheme for making internally consistent quantum predictions for closed systems even in the absence of anything that resembles a classical measurement situation. I discuss the construction of such a quantum theory for the example of the Friedmann-Robertson-Walker cosmology. In particular, coarse grainings suitable to characterize quasiclassical behavior are described, and the branch wave functions for quasiclassical FRW cosmologies are explicitly exhibited.