Research in Quantum Cosmology and Quantum Mechanics

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

The inference is inescapable from the physics of the last 100 years that we live in a quantum mechanical universe. The research supported by this grant is devoted to predicting our large scale observations of the universe, starting from theories of its quantum state and dynamics - a quantum cosmology. It aims at explaining how the universe began and how it evolved to the universe that we have today. The supported research aims at understanding the origin of the wide range of time, place, and scale on which the deterministic laws of classical physics hold in a quantum universe that is characterized fundamentally by indeterminacy. The research will consider how quantum theory can be formulated for a closed system like the universe where there are no observers outside making measurements. It will show how familiar textbook quantum mechanics of measurement situations emerges along with classical spacetime in the very early universe. These questions will be explored in simple minisuperspace models using the no-boundary wave function of the universe due to Hawking and the PI in its semiclassical approximation assuming simple field theory models for the matter degrees of freedom. Decoherent histories quantum theory will be used to calculate the probabilities of the individual members of sets of suitably coarse-grained histories of the universe from the state and dynamics. Probabilities for observations are these probabilities conditioned on a description of the observational situation. Particular emphasis will be placed on the probabilities for closed homogeneous and isotropic cosmological geometries and the quantum fluctuations away from these symmetries that lead to the large scale structure of the universe we see today in the cosmic background radiation and the galaxy distribution, including in a regime of eternal inflation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.