Inflation and the Ωproblem
Abstract
OBSERVATIONAL estimates suggest that the cosmological density parameter Ω, defined as the ratio of the density of the Universe ρ_{o} and the critical density ρ_{crit} which divides open from closed universes, is <=0.5. According to the standard Friedmann models, any value of Ω¬1 diverges away from one as the Universe evolves. The cosmological Ωproblem is that, on the one hand, making the present value of Ω close to but not equal to one requires an extraordinarily precise adjustment of the initial conditions of the Universe^{1}, but on the other hand inflationary models, which were devised in part to avoid this finetuning, predict that Ω should differ from one only by an exponentially small amount^{2}. Conventional inflationary models thus appeal to the existence of 'missing' matter or a nonzero cosmological constant to make up the density deficit. Here it is shown that 'extended inflation'^{3,4}, a recent variation on inflationary cosmology, accommodates a range of initial conditions which lead to Ω<~0.5. The parameter range is narrow, perhaps finely tuned, but nonzero.
 Publication:

Nature
 Pub Date:
 May 1990
 DOI:
 10.1038/345047a0
 Bibcode:
 1990Natur.345...47S
 Keywords:

 Computational Astrophysics;
 Cosmology;
 Evolution (Development);
 Inflating;
 Universe;
 Density Distribution;
 Equations Of Motion;
 Astrophysics