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en.wikipedia.org/wiki/Friedmann_equations

The Friedmann equations are a set of equations in physical cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity.They were first derived by Alexander Friedmann in 1922 from Einstein's field equations of gravitation for the Friedmann–Lemaître–Robertson–Walker metric and a perfect fluid with a given mass ...

hyperphysics.phy-astr.gsu.edu/hbase/Astro/fried.html

The Friedmann Equation Alexander Friedmann of Russia is credited with developing a dynamic equation for the expanding universe in the 1920s. This was a time when Einstein, Willem de Sitter of the Netherlands, and Georges Lemaitre of Belgium were also working on equations to model the universe. Friedmann developed it as a relativistic equation in the framework of general relativity, but the ...

uncw.edu/phy/documents/thefriedmannequations.pdf

Alexander A. Friedmann (1888-1925) The Man Who Made the Universe Expand Soviet mathematician and meteorologist Most famous for contributions to cosmology First person to mathematically predict an expanding universe (1922) Derived from Einstein's general relativity Einstein initially dismissed Friedmann’s equations

astrobites.org/2011/10/09/general-relativity-friedmann-equations-and...

We point this out simply as historical context for what follows. We turn now to a derivation of the equations Friedmann would have used to produce this model, and that more generally constrain the evolution of any model universe given certain initial inputs. Derivation of the Friedmann equations from general relativity

www.youtube.com/watch?v=BHLIo4j0C4k

Friedmann equations for expansion of space after Big Bang explained by Galaxies and Cosmology - Duration: 7:00. Historystack 2,411 views. 7:00.

everything.explained.today/Friedmann_equations

The Friedmann equations start with the simplifying assumption that the universe is spatially homogeneous and isotropic, i.e. the cosmological principle; empirically, this is justified on scales larger than ~100 Mpc. The cosmological principle implies that the metric of the universe must be of the form

astronomy.stackexchange.com/questions/10344/what-is-a-friedmann-model

The "Friedmann model" is a model of the Universe governed by the Friedmann equations, which describes how the Universe expands or contracts. These equations are a solution to Einstein's field equations, and with two very important assumptions they form the basis for our understanding of the evolution and structure of our Universe.

www.jb.man.ac.uk/~jpl/cosmo/friedman.html

The Friedman equation is just a first-order differential equation and can be integrated (numerically, except for the simplest cases) to give the history of the universe in the form t(R). This function is fixed by just two parameters which can take a continuous range of values, and the curvature constant k=-1, 0, or +1. For the continuous ...

www.physicsforums.com/threads/what-is-the-friedmann-equation.762989

Extended explanation The Friedmann equation is derived from the 0-0 component of the Einstein field equations of General Relativity, on invoking the Friedmann Robertson Walker metric as the correct metric for the spacetime of the universe. Note that, coincidentally, the equation can be derived by using Newtonian mechanics.