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Alexander Friedmann
1922· Person
ProvenTested many times; part of working physics.
Russian mathematician and meteorologist (1888–1925) in Petrograd who first showed, in 1922, that Einstein's gravity lets the universe expand or contract.
See it on the Science map →How it works
Friedmann came to cosmology from weather science and pure mathematics. He flew bombing and reconnaissance missions as a World War I aviator, and in 1925 became director of Russia's main geophysical observatory. He approached Einstein's equations with no prejudice about what the universe should do: if the math allowed a changing universe, he took it seriously. In 1924 he added universes with open, saddle-shaped space. In July 1925 he rode a balloon to a record 7,400 meters for weather research, then died of typhoid that September, aged 37.
Why it matters
He turned the universe from a fixed stage into something with a history. Every modern calculation of cosmic expansion, age and fate starts from his equations.
How the work held up
Hubble's 1929 measurements showed galaxies receding as his solutions allow. Howard Robertson and Arthur Walker proved in the mid-1930s that his geometry is the only one possible for an evenly filled universe.
Still a mystery
He never knew which of his solutions describes our universe; the observations came after his death. He also noted that some solutions shrink back and might repeat, a cyclic idea that remains untested.
Connections (2)
▸Alexander Friedmann derived The Friedmann equations: the rules of expansionProven
The relationship
Einstein's equations are ten tangled equations for spacetime's shape. Friedmann assumed the universe looks the same everywhere and in every direction on large scales. That collapsed them into two equations for one quantity, the scale factor: how big the universe is compared with today. Curvature became a choice among three shapes: closed like a sphere, flat, or open like a saddle.
How the link was found
Friedmann's 1922 paper treated closed, positively curved space; his 1924 paper added open space. The flat case was popularized by Einstein and de Sitter in 1932.
Why it's proven
The derivation is exact mathematics. Lemaître reached the same equations independently in 1927, and every modern cosmology calculation still solves them.
Open questions and mysteries
Is the universe uniform enough for the shortcut? Surveys find uniformity beyond about 300 million light-years, though a few claimed giant structures may strain it.
▸Alexander Friedmann described a universe with a beginning, foreshadowing The Big BangProven
The relationship
Solving Einstein's equations in 1922, Friedmann found universes whose size changes with time. In some, everything grows from zero size at a definite moment, and he called the interval since then 'the time since the creation of the world'. He treated this as mathematics, not a claim about our actual universe, but it was the Big Bang's first outline.
How the link was found
Alexander Friedmann, 'On the curvature of space', Zeitschrift für Physik, 1922. Einstein first claimed it contained an error, then withdrew the objection in 1923. Lemaître, unaware of it, rediscovered expanding solutions in 1927.
Why it's proven
His solutions are exact mathematics within general relativity. Hubble's 1929 expansion data and the 1965 afterglow showed our universe follows one of them, back to a hot, dense start.
Open questions and mysteries
His equations assume evenly spread matter, and run back to zero size they give infinite density. Whether that start was real, or an artifact of the math, is still open.