2.4. Critical density and the density parameter
The spatial geometry is flat if k = 0. For a given H, this requires that the density equals the critical density
Densities are often measured as fractions of
The quantity
The present value of the Hubble parameter is still not that well known, and
is normally parametrized as
where h is normally assumed to lie in the range
0.5
c :
is known as the
density parameter, and can be
applied to individual types of material as well as the total density.
h
0.8. The
present critical density is
