هموگش ِ فریدمن hamugeš-e Friedmann
*Fr.: équation de Friedmann*
An equation that expresses energy conservation in an
→ *expanding Universe*.
It is formally derived from → *Einstein's field equation*s
of → *general relativity* by requiring the Universe to be
everywhere → *homogeneous* and
→ *isotropic*. It is expressed by
*H*^{2}(*t*) = (8π*G*)/(3*c*^{2})ε(*t*) -
(*kc*^{2})/*R*^{2}(*t*), where *H*(*t*) is
the → *Hubble parameter*, *G* is the
→ *gravitational constant*, *c* is the
→ *speed of light*, ε(*t*) is the
→ *energy density*, *k* is the
→ *curvature of space-time*, and *R*(*t*) is the
→ *cosmic scale factor*. See also
→ *Big Bang*, → *accelerating Universe*.
See also → *Friedmann-Lemaitre Universe*. Named after the Russian mathematician and physical scientist Aleksandr Aleksandrovich
Friedmann (1888-1925), who was the first to formulate an
→ *expanding Universe* based on Einstein's
theory of → *general relativity*
; → *equation*. |