41. Cosmological implications

Given the consistency of Hubble constants derived, both locally and at large recessional velocities, then we can state that H₀ falls within the full-range extremes of 75 ± 1 and 68 ± 5 km/sec/Mpc, giving formally H₀ = 72 (± 2)_r [± 12]_s km/sec/Mpc out to a velocity-distance 0.1c (30,000 km/sec.) These results are summarized graphically in Figure 38 and numerically in Table 5.

A value of the Hubble constant, in combination with an independent estimate of the average density of the Universe, can be used to estimate a dynamical age for the Universe (e.g., see Figure 39). For a value of of H₀ = 72 (± 2)_r km/sec/Mpc, the age ranges from a high of ~ 12 Gyr for a low-density ( = 0.2) Universe, to a young age of ~ 9 Gyr for a critical-density ( = 1.0) Universe. These ages change to 15 and 7.5 Gyr, respectively allowing for a systematic error of ± 10 km/sec/Mpc.

Other, independent constraints on the age of the Universe exist; most notably, the ages of the oldest stars, as typified by Galactic globular clusters. These ages traditionally are thought to fall in the range of 14 ± 2 Gyr (Chaboyer et al. 1996), however the subdwarf parallaxes obtained by the Hipparcos satellite (Reid 1997) may reduce these ages considerably. For = 14 Gyr and = 1.0, H₀ would have to be ~45 km/sec/Mpc. If constrained by the stellar ages, and interpreted within the context of the standard Einstein-de Sitter model, our value of H₀ = 72 km/sec/Mpc, is incompatible with a high-density ( = 1.0) model universe without a cosmological constant (at the 2.5-sigma level defined by the identified systematic errors).