Both Big-Bang and stellar nucleosynthesis have outcomes related to the density of baryonic matter, but whereas in the first case there is a standard model that makes very precise predictions of light element abundances as a function of the mean density of baryons in the Universe, in the second case various uncertainties permit only very limited conclusions to be drawn. As far as Big-Bang synthesis and the light elements are concerned, existing results on D,
3
He and
7
Li indicate a value of Ω
N
h
2
0
greater than 0.01 and less than 0.025, where Ω
N
is the ratio of baryonic density to the closure density and
h
0
is the Hubble constant in units of 100 km s
-1
Mpc
-1
; probably 0.5 <
h
0
< 1. New results on the primordial helium abundance give a still tighter upper limit to Ω
N
,Ω
N
h
2
0
< 0.013, which when compared with redshift surveys giving Ω > 0.05 implies that the observed matter can all be baryonic only if the various uncertainties are stretched to their limits.
A Measurement of the Hubble Constant Using Galaxy Redshift Surveys
