Loss of incoherence and determination of coupling constants in quantum gravity

• Published in: Nuclear physics. B 1988-10, Vol.307 (4), p.854-866
• Main Authors: Giddings, Steven B., Strominger, Andrew
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; General relativity and gravitation; Physics; Quantum gravity
• ISSN: 0550-3213; 1873-1562
• DOI: 10.1016/0550-3213(88)90109-5

The wave function of an interacting ‘family’ of one large ‘parent’ and many Planck-sized ‘baby’ universes is computed in a semiclassical approximation using an adaptation of Hartle-Hawking initial conditions. A recently discovered gravitational instanton which exists for general relativity coupled to axions is employed. The outcome of a single experiment in the parent universe is in general described by a mixed state, even if the initial state is pure. However, a sequence of measurements rapidly collapses the wave function of the family of universes into one of an infinite number of ‘coherent’ states for which quantum incoherence is not observed in the parent universe. This provides a concrete illustration of an unexpected phenomena whose existence has been argued for on quite general grounds by Coleman: quantum incoherence due to information loss to baby universes is not experimentally observable. We further argue that all coupling constants governing dynamics in the parent universe depend on the parameters describing the particular coherent state into which the family wave function collapses. In particular, generically terms that violate any global symmetries will be induced in the effective action for the parent universe. These last results have much broader applicability that our specific model.