Friedmann equations

<p>The Friedmann equations, also known as the Friedmann–Lemaître (FL) equations, are a set of <a href="/facts/Equation/pxFzLAVR">equations</a> in <a href="/facts/Physical_cosmology/ww4ChbEq">physical cosmology</a> that govern <a href="/facts/Expansion_of_the_universe/f6Uvt79B">cosmic expansion</a> in <a href="/facts/Homogeneity_(physics)/J4v4DwfF">homogeneous</a> and <a href="/facts/Isotropy/mc3QEY2x">isotropic</a> models of the universe within the context of <a href="/facts/General_relativity/jVsoIg8X">general relativity</a>. They were first derived by <a href="/facts/Alexander_Friedmann/rIKIgEwf">Alexander Friedmann</a> in 1922 from <a href="/facts/Einstein_field_equations/j2rJTzW9">Einstein's field equations</a> of <a href="/facts/Gravitation/bqAN7DdQ">gravitation</a> for the <a href="/facts/Friedmann%25E2%2580%2593Lema%25C3%25AEtre%25E2%2580%2593Robertson%25E2%2580%2593Walker_metric/b6cdgxyF">Friedmann–Lemaître–Robertson–Walker metric</a> and a <a href="/facts/Perfect_fluid/wWpblQcg">perfect fluid</a> with a given <a href="/facts/Density/92p6hh9I">mass density</a> <a href="/facts/Rho_(letter)/gGezeq5Q">ρ</a> and <a href="/facts/Pressure/eyc37GRG">pressure</a> p. The equations for negative spatial curvature were given by Friedmann in 1924.
The physical models built on the Friedmann equations are called FRW or FLRW models and form the <i>Standard Model</i> of modern <a href="/facts/Physical_cosmology/ww4ChbEq">cosmology</a>, although such a description is also associated with the further developed <a href="/facts/Lambda-CDM_model/DmlhJHQU">Lambda-CDM model</a>. The FLRW model was developed independently by the named authors in the 1920s and 1930s.
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Friedmann equations open-in-new

Friedmann equations