Friedmann, Alexander Alexandrovich (1888–1925)
Friedmann established an early reputation for his work on atmospheric and meteorological physics. However, he is best known for his 1922 paper, "On the Curvature of Space", on the expanding universe (received by the journal Zeitschrift für Physik on June 29,1922). This arose from the work of Albert Einstein in 1917 in which he attempted to apply his equations of general relativity to cosmology. Friedmann developed a theoretical model of the universe using Einstein's theory, in which the average mass density is constant and space has a constant curvature. Different cosmological models are possible depending on whether the curvature is zero, negative, or positive. Such models are called Friedmann universes.
In July 1925, just a few weeks before he died, he made a record-breaking 7400m balloon ascent to carry out meteorological and medical observations.
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