2008/08/31 by Steven Weinberg · 7 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #astro-ph #gr-qc #hep-th
paper · pdf · doi:10.1103/physrevd.78.123521
published as Phys.Rev.D78:123521,2008 · 25 pages. This version clarifies the scale transformation used in Section II and the gauge transformation used in Section III, and corrects some typos, including new typos introduced in version 2
arxiv created 2008/10/18 · openalex publication_date 2008/12/16 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
It is shown that under essentially all conditions, the nonlinear classical equations governing gravitation and matter in cosmology have a solution in which far outside the horizon in a suitable gauge the reduced spatial metric (the spatial metric divided by the square of the Robertson--Walker scale factor a) is time independent, though with an arbitrary dependence on comoving coordinates, and all perturbations to the other metric components and to all matter variables vanish, to leading order in 1/a. The corrections are of order 1/a2, and are explicitly given for the reduced metric in a multifield model with a general potential. Further, this is the solution that describes the metric and matter produced by single-field inflation. These results justify the use of observed non-Gaussian correlations (or their absence) as a test of theories of single-field inflation, despite our ignorance of the constituents of the Universe while fluctuations are outside the horizon after inflation, as long as graphs with loops can be neglected.