Classical universes of the no-boundary quantum state

Journal Article · Sun Jun 15 04:00:00 EDT 2008 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.77.123537· OSTI ID:21212017

Hartle, James B ^[1]; Hawking, S W ^[2]; Hertog, Thomas ^[3]

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1. Department of Physics, University of California, Santa Barbara, CA 93106-9530 (United States)
2. DAMTP, CMS, Wilberforce Road, CB3 0WA Cambridge (United Kingdom)
3. Laboratoire APC, 10 rue A. Domon et L. Duquet, 75205 Paris (France) and International Solvay Institutes, Boulevard du Triomphe, ULB, C.P. 231, 1050 Brussels (Belgium)

We analyze the origin of the quasiclassical realm from the no-boundary proposal for the Universe's quantum state in a class of minisuperspace models. The models assume homogeneous, isotropic, closed spacetime geometries, a single scalar field moving in a quadratic potential, and a fundamental cosmological constant. The allowed classical histories and their probabilities are calculated to leading semiclassical order. For the most realistic range of parameters analyzed, we find that a minimum amount of scalar field is required, if there is any at all, in order for the Universe to behave classically at late times. If the classical late time histories are extended back, they may be singular or bounce at a finite radius. The ensemble of classical histories is time symmetric although individual histories are generally not. The no-boundary proposal selects inflationary histories, but the measure on the classical solutions it provides is heavily biased towards small amounts of inflation. However, the probability for a large number of e-foldings is enhanced by the volume factor needed to obtain the probability for what we observe in our past light cone, given our present age. Our results emphasize that it is the quantum state of the Universe that determines whether or not it exhibits a quasiclassical realm and what histories are possible or probable within that realm.

• OSTI ID: 21212017
• Journal Information: Physical Review. D, Particles Fields, Journal Name: Physical Review. D, Particles Fields Journal Issue: 12 Vol. 77; ISSN PRVDAQ; ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMOLOGICAL CONSTANT
INFLATIONARY UNIVERSE
LIGHT CONE
MATHEMATICAL SOLUTIONS
PROBABILITY
SCALAR FIELDS
SEMICLASSICAL APPROXIMATION
UNIVERSE