= Alexander Friedmann
{c}
<Alexander Friedmann> derived evolving homogeneous cosmological solutions of the <Einstein field equations>. The <Friedmann equations> relate <cosmic expansion> to <energy density>, <pressure>, <spatial curvature of an FLRW universe>[spatial curvature] and the <cosmological constant>.
The conceptual change is that <general relativity> permits the scale of a homogeneous universe to evolve, rather than requiring a static <geometry>. Observational evidence and the choice of matter content are additional inputs needed to identify which mathematical solution describes the Universe.https://mathshistory.st-andrews.ac.uk/Biographies/Friedmann/[Biography, 1922 cosmological work]{ref}
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