In this brief summary I will concentrate on the values of the cosmological parameters. The other key questions in cosmology today concern the nature of the dark matter and dark energy, the origin and nature of the primordial inhomogeneities, and the formation and evolution of galaxies. I have been telling my theoretical cosmology students for several years that these latter topics are their main subjects for research, since determining the values of the cosmological parameters is now mainly in the hands of the observers.
In discussing cosmological parameters, it will be useful to distinguish between two sets of assumptions: (a) general relativity plus the assumption that the universe is homogeneous and isotropic on large scales (Friedmann-Robertson-Walker framework), or (b) the CDM family of models. The CDM models assume that the present matter density _{m} plus the cosmological constant (or its equivalent in ``dark energy'') in units of critical density _{} = / (3 H_{0}^{2}) sum to unity (_{m} + _{} = 1) to produce the flat universe predicted by simple cosmic inflation models. The CDM family of models was introduced by Blumenthal et al. (1984), who worked out the linear power spectra P(k) and a semi-analytic treatment of structure formation compared to the then-available data. We did ths for the _{m} = 1, = 0 ``standard'' cold dark matter (CDM) model, and also for the _{m} = 0.2, _{} = 0.8 CDM model. In addition to _{m} + _{} = 1, these CDM models assumed that the primordial fluctuations were Gaussian with a Zel'dovich spectrum (P_{p}(k) = Ak^{n}, with n = 1), and that the dark matter is mostly of the cold variety.
The table below summarizes the current observational information about the cosmological parameters. The quantities in brackets have been deduced using at least some of the CDM assumptions. The rest of this paper discusses these issues in more detail. But it should already be apparent that there is impressive agreement between the values of the parameters determined by various methods.
Hubble parameter | H_{0} | = | 100 h = km s^{-1} Mpc^{-1} , h = 0.65 ± 0.08 |
Age of universe | t_{0} | = | 9-16 Gyr (from globular clusters) |
= | [9-17 Gyr] | ||
Baryon density | _{b} h^{2} | = | 0.019 ± 0.001 (from D/H) |
> | [0.015 from Ly forest opacity] | ||
Matter density | _{m} | = | 0.4 ± 0.2 (from cluster baryons) |
= | [0.34 ± 0.1 from Ly forest P(k)] | ||
= | [0.4 ± 0.2 from cluster evolution] | ||
> | 0.3 (2.4 , from flows) | ||
3/4 _{} - 1/4 ± 1/8 from SN Ia | |||
Total density | _{m} + _{} | 1 ± 0.3 (from CMB peak location) | |
Dark energy density | _{} | = | 0.8 ± 0.3 (from previous two lines) |
< | 0.73 (2) from radio QSO lensing | ||
Neutrino density | _{} | 0.001 (from Superkamiokande) | |
[0.1] | |||