Alexander Friedmann

Alexander Friedmann (1888–1925) was a Russian mathematician and physicist who found time-dependent, expanding and contracting solutions to Einstein’s equations of general relativity.

General relativity: Albert Einstein’s theory of gravity, in which matter and energy shape spacetime and determine motion. Friedmann’s equations are solutions to this theory’s gravitational field equations.
Friedmann equations: Equations governing how the scale factor of a homogeneous, isotropic universe changes over time. They express the dynamical content of Friedmann’s cosmological solutions.
Alexander Einstein: The physicist who developed special and general relativity and introduced the cosmological constant. Einstein’s equations supplied the framework Friedmann used, though Einstein initially rejected his result.
Hubble–Lemaître law: The observed relation between a galaxy’s distance and its recession velocity in the expanding universe. The measured recession of galaxies gave observational support to dynamic cosmological models.
Yakov Tamarkin: A Russian-American mathematician known for work in analysis and mathematical physics. Tamarkin was Friedmann’s contemporary and belonged to the same Russian mathematical milieu.
Einstein field equations: Equations relating spacetime curvature to the distribution of matter and energy. Friedmann solved these equations under assumptions suited to cosmology.
Friedmann–Lemaître–Robertson–Walker metric: A spacetime metric describing a homogeneous and isotropic universe with evolving scale factor. It provides the geometric framework for the class of models Friedmann studied.
Willem de Sitter: The Dutch astronomer and mathematician known for cosmological solutions to Einstein’s equations. De Sitter’s static-looking model formed part of the debate Friedmann’s work unsettled.
Big Bang: The cosmological model that describes the universe’s evolution from an earlier hot, dense state. Friedmann’s expanding solutions became mathematical foundations for modern Big Bang cosmology.
Vladimir Steklov: A Russian mathematician and physicist who helped build mathematical research institutions in Russia. Steklov’s institutional work shaped the scientific environment in which Friedmann trained.

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