Summary: Friedmann's Equation (1922)
Although it was deduced from Einstein's field equations, it can also be deduced
from Newtonian gravity.
Consider a sphere about some arbitrary point, such that the radius is R(t).
homogeneity ! !"=0
Isotropy !
From Newton's equation of motion
!
".
r
v = 3H = 3
R
R
!
R2
"
8#G
3
$R2
= "kc2

Source: Aretxaga, Itziar - Instituto Nacional de Astrofísica Óptica y Electrónica

Collections: Physics