Posts tagged ‘de sitter cosmology’

May 17th, 2012

An Exception to the BVG Theorem

by Max Andrews

The Borde-Vilenkin-Guth Theorem states that any universe, which has, on average, a rate of expansion greater 1 that system had to have a finite beginning. This would apply in any multiverse scenario as well.  There are four exceptions to the theorem.*

First Exception: Initial Contraction (Havg<0) … (The average rate of the Hubble expansion is less than zero)

An example of this would be found in de Sitter cosmology. In mathematics and physics, a de Sitter space is similar to Minkoswkian spacetime.  It is maximally symmetric and has constant positive curvature. Assume that a spatially infinite universe contracted down to a singularity and then bounced into our present expansion.  In such a case, the universe cannot be said to be, on average, in a state of cosmic expansion through its history since the expansion phase, even if infinite, is canceled out by the contraction phase.  Though this is permissible under the BVG it is not a viable or popular option.

George Ellis, one of the world’s leading cosmologists, has two objections: