In this review 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 FRW
framework plus the CDM
family of models. In addition to the FRW
framework, 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 H02) sum to unity
(
m +
= 1) to produce the
flat universe predicted by simple cosmic inflation models. These
CDM models assume that the
primordial fluctuations were adiabatic
(all components fluctuate together) and Gaussian, and had a Zel'dovich
spectrum (Pp(k) = A kn, with
n
1), and that the
dark matter is mostly of the cold variety.
Although the results from the Long-Duration BOOMERANG
[30,
75]
and the MAXIMA-1
[54,
5]
CMB observations and analyses
[59]
were were not yet available at
the Dark Matter 2000 conference, I have made use of them in preparing
this review. The table below summarizes the current observational
information about the cosmological parameters, with estimated
1 errors. 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.
H0 | = 100 h km s-1 Mpc-1 , h = 0.65 ± 0.08 |
t0 | = 9-16 Gyr (from globular clusters) |
= [9-17 Gyr from expansion age,
![]() | |
![]() | = (0.045 ± 0.0057) h65-2 (from D/H) |
> [0.04 h65-2 from
Ly![]() | |
![]() | = 0.4 ± 0.2 (from cluster baryons) |
= [0.34 ± 0.1 from Ly![]() | |
= [0.4 ± 0.2 from cluster evolution] | |
> 0.3 (2.4![]() | |
= [0.5 ± 0.1 from flows plus SN Ia] | |
![]() ![]() ![]() | |
![]() ![]() ![]() | = 1.11 ± 0.07 (from CMB peak location) |
![]() ![]() | = 0.71 ± 0.14 (from previous two lines) |
< & 0.73 (2![]() | |
![]() ![]() | ![]() |
![]() | |