Noise-induced inflation (Q1972083)

The paper under review is concerned with early-universe cosmology. It deals with a model of a spatially closed Friedman-Robertson-Walker universe [\textit{N. D. Birrell} and \textit{P. C. W. Davies}, Quantum fields in curved space, Cambridge University Press, Cambridge (1982; Zbl 0476.53017); \textit{S. W. Hawking} and \textit{G. F. R. Ellis}, The large scale structure of spacetime, Cambridge University Press, Cambridge (1973; Zbl 0265.53054); \textit{D.-E. Liebscher}, Einsteins Relativitätstheorie und die Geometrie der Ebene, B.G. Teubner, Stuttgart, Leipzig (1999)] driven by the backreaction from a massless, non-conformally coupled quantum scalar field. It is established that the backreaction of the quantized matter fields is able to drive the cosmological scale factor over the barrier of the classical potential so that if the universe starts near zero scale factor it can make the transition from the initial singularity to an exponentially expanding de Sitter phase with a probability comparable to that from quantum tunneling process. Without outlining the details of the cosmological process, the paper emphasizes the stochastic character of the backreaction which originates from the quantum fluctuations of the fundamental fields [\textit{S. Coleman, J. Hartle, T. Piran}, and \textit{S. Weinberg} (eds.), Quantum Cosmology and Baby Universes, World Scientific, Singapore (1991)].