2002/11/30 by George Ellis, Roy Maartens · 489 citations
Physics and Astronomy · #Astronomy #Astrophysics #Big Bang (financial markets) #Big Bounce #Big Rip #Black Holes and Theoretical Physics #Classical mechanics #Cosmology #Cosmology and Gravitation Theories #Dark energy #De Sitter universe #Einstein #Flatness problem #Galaxies: Formation, Evolution, Phenomena #General relativity #Geometry #Horizon #Inflation (cosmology) #Initial singularity #Metric expansion of space #Particle horizon #Physical cosmology #Physics #Quantum #Quantum cosmology #Quantum gravity #Quantum mechanics #Scale factor (cosmology) #Singularity #Steady State theory #Theoretical physics #Universe #astro-ph #gr-qc
paper · pdf · doi:10.1088/0264-9381/21/1/015
published in Classical and Quantum Gravity 21(1), 223-232 (IOP Publishing) · minor changes; version to appear in Class Q Grav
arxiv created 2003/10/25 · openalex publication_date 2003/11/25 · arxiv updated 2010/04/06 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Observations indicate that the universe is effectively flat, but they do not rule out a closed universe. The role of positive curvature is negligible at late times, but can be crucial in the early universe. In particular, positive curvature allows for cosmologies that originate as Einstein static universes, and then inflate and later reheat to a hot big-bang era. These cosmologies have no singularity, no ‘beginning of time’ and no horizon problem. If the initial radius is chosen to be above the Planck scale, then they also have no quantum gravity era, and are described by classical general relativity throughout their history.