Alexander Alexandrovich Friedmann (also spelled Friedman or Fridman, ) (June 17 (old style or new style) by himself, June 16 (4 old style) by J. O'Conor in 1888, Saint Petersburg, Russian Empire – September 16, 1925, Leningrad, USSR) was a Russian and  Soviet physicist and mathematician. He is best known for his pioneering theory that the universe was expanding, governed by a set of equations he developed now known as the Friedmann equations.