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A cosmological model formulated by Friedmann  in 1922 and independently by Lemaître
(1927). It assumes a homogeneous and isotropic universe  with positive cosmological constant  and
expansion parameter a governed by the equations
of motion
and
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(2) |
where  is the total mass-energy density,  is the mass density, and c is the speed of light.
These equations were originally rigorously derived from general relativity, but can also be rigorously derived from Newtonian mechanics and thermodynamics for small length scales, i.e., r such that
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(3) |
where M is the mass.
 Cosmological Equations, Cosmology, Eddington-Lemaître Cosmological Model
© 1996-2007 Eric W. Weisstein
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