Table 25-1:
The Geometry and Average Density of the Universe
Geometry of space
Curvature of space
Type of universe
Combined average mass density (
ρ
0
)
Density parameter (Ω
0
)
Spherical
positive
closed
ρ
0
>
ρ
c
Ω
0
> 1
Flat
zero
flat
ρ
0
=
ρ
c
Ω
0
= 1
Hyperbolic
negative
open
ρ
0
<
ρ
c
Ω
0
< 1