density parameter پارامون ِ چگالی pârâmun-e cagâli
Fr.: paramètre de densité One of the four terms that describe an arranged version of the
→ Friedmann equations. They are all time dependent.
1) For matter:
Ωm = 8πGρm/(3H2), where
G is the → gravitational constant, ρm is
the mean matter density, and H the → Hubble parameter.
The matter density parameter is also expressed as Ωm =
ρm/ρcrit, where ρcrit is the
→ critical density.
2) For radiation:
Ωr = 8πGρr/(3H2),
where ρr is the radiation equivalent of matter density.
This parameter is also expressed as Ωr =
ρr/ρcrit.
3) For the → cosmological constant:
ΩΛ = Λc2/(3H2).
Similarly, ΩΛ = ρΛ/ρcrit,
where &rhoΛ = Λc2/(8πG)
is sometimes referred to as the density of → dark energy.
4) For the → curvature of space-timeΩk = -kc2/(R2H2),
where k is the → curvature constant
and R the
→ cosmic scale factor.
Note that:
Ωm + Ωr + ΩΛ +
Ωk = 1, and
Ωtotal = Ωm + Ωr +
ΩΛ = 1 - Ωk. → density; → parameter. |
