Proving AlmostHomogeneity of the Universe: an Almost EhlersGerenSachs Theorem
Abstract
We show that if all fundamental observers measure the cosmic microwave background radiation to be almost isotropic in an expanding universe region, then that universe is locally almost spatially homogeneous and isotropic in that region. This shows the stability of the important exact result of this type of previously proved by Ehlers, Geren, & Sachs (EGS) and formalizes the way in which almostisentropy of the background radiation gives evidence that the universe is almost a FriedmannLemaitreRobertsonWalker (FLRW) spacetime. This is the needed foundation for all recent analyses, based on the SachsWolfe effect, of how background radiation anisotropies relate to growing density inhomogeneities in an almostFLRW expanding universe.
 Publication:

The Astrophysical Journal
 Pub Date:
 April 1995
 DOI:
 10.1086/175496
 Bibcode:
 1995ApJ...443....1S
 Keywords:

 Background Radiation;
 Cosmology;
 Homogeneity;
 Isotropy;
 Microwaves;
 Theorem Proving;
 Universe;
 Astronomical Models;
 Expansion;
 SpaceTime Functions;
 Astrophysics;
 COSMOLOGY: COSMIC MICROWAVE BACKGROUND;
 COSMOLOGY: THEORY