New Developments in Cosmology

A brief review is given of the present observational data in cosmology. A review of a new bimetric gravity theory with multiple light cones is presented. The physical consequences of this gravity theory for the early universe are analyzed. 1 Status of Observational Cosmology The ten most significant parameters to be determined in observational cosmology are: 1. Age of the universe: t0 2. The Hubble constant H0 from the Hubble relation: v = H0d 3. Density parameter : Ωm = ρm 3H 0 /8πG 4. Deceleration parameter: q0 = − R̈(t0)R(t0) Ṙ(t0) 5. The baryon density ΩB and the vacuum density ΩΛ 6. The parameters associated with microwave backgound fluctuations: n, σ8, T/S,NT The strongest lower limit for t0 is determined from studies of the stellar populations of globular clusters. The main error in the globular clusters age estimate comes from the uncertain distance to the globular clusters. A 0.25 magnitude error in the distance translates into a 22% error in the cluster age [1]. Independent age limits come from the cooling of white dwarfs. The best estimates give t0 ∼ 13 Gyr, with a lower limit of ∼ 11 Gyr. For t0 > 13 Gyr, we have h ≤ 0.50 (where h is defined by the Hubble parameter: H0 = 100 h km s −1Mpc) for matter density Ωm = 1, and for h ≤ 0.73 we have Ωm ∼ 0.3 in spatially flat cosmologies with Ωm + ΩΛ = 1. The Hubble parameter is now better determined (it used to be known to within a factor of two). Most measurements are now consistent with a value: h = 0.65 ±