## Abstract

We reexamine the semiclassical approximation to quantum gravity in the canonical formulation, focusing on the definition of a quasiclassical state for the gravitational field. It is shown that a state with classical correlations must be a superposition of states of the form e^{is}. In terms of a reduced phase space formalism, this type of state can be expresesd as a coherent superposition of eigenstates of operators that commute with the constraints and so correspond to constants of the motion. Contact is made with the usual semiclassical approximation by showing that a superposition of this kind can be approximated by a WKB state with an appropriately localized prefactor. A qualitative analysis is given of the effects of geometry fluctuations, and the possibility of a breakdown of the semiclassical approximation due to interference between neighboring classical trajectories is discussed. It is shown that a breakdown in the semiclassical approximation can be a coordinate-dependent phenomenon, as has beeen argued to be the case close to a black hole horizon.

Original language | English |
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Pages (from-to) | 766-778 |

Number of pages | 13 |

Journal | Physical Review D - Particles, Fields, Gravitation and Cosmology |

Volume | 53 |

Issue number | 2 |

DOIs | |

State | Published - 1996 |

Externally published | Yes |

## ASJC Scopus subject areas

- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)