Einstein–de Sitter universe

Under a Friedmann model or Friedmann - Lemaître model ( named after the Russian mathematician and meteorologist Alexander Friedmann and the Belgian astrophysicist Georges Lemaître ) is understood in cosmology solutions of the Friedmann equation, ie a solution of Einstein's field equations with constant curvature is spatially isotropic around each point.

Friedmann models differ in the k parameter from the Robertson - Walker metric

• K = 1: positive curvature
• K = 0: no curvature, flat space
• K = -1: negative curvature

And the value of the cosmological constant.

Special cases of Friedmann models

Einstein cosmos

It is a non- expanding or contracting forming, static ( to small changes unstable ) universe with

Being: . 158

Lemaître universe

With a very small parameter. By choosing a suitable time scale of the expansion of the universe is stretched so that there is an almost static universe expanding between two time phases: . 159

De Sitter model

The three different values ​​of k are three possible models, but they are only different sections of the same space-time. 164

Einstein - de Sitter model

The Einstein - de Sitter universe arises with

For this flat, infinitely extended universe, the parameter R of the Robertson - Walker metric developed just with: . 160