Past-completeness of inflationary spacetimes

J. E. Lesnefsky, D. A. Easson, P. C.W. Davies

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


We discuss the question of whether or not inflationary spacetimes can be geodesically complete in the infinite past. Geodesic completeness is a necessary condition for averting an initial singularity during eternal inflation. It is frequently argued that cosmological models which are expanding sufficiently fast (having average Hubble expansion rate Havg>0) must be incomplete in null and timelike past directions. This well-known conjecture relies on specific bounds on the integral of the Hubble parameter over a past-directed timelike or null geodesic. As stated, we show this claim is an open issue. We show that the calculation of Havg yields a continuum of results for a given spacetime predicated upon the underlying topological assumptions. We present an improved definition for Havg and introduce an uncountably infinite cohort of cosmological solutions which are geodesically complete despite having Havg>0. We discuss a standardized definition for inflationary spacetimes as well as quantum (semiclassical) cosmological concerns over physically reasonable scale factors.

Original languageEnglish (US)
Article number044024
JournalPhysical Review D
Issue number4
StatePublished - Feb 15 2023

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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