Alexander Friedmann

Alexander Alexandrovich Friedmann was born in Saint Petersburg in 1888 into a family of musicians, and trained as a mathematician and physicist at Saint Petersburg University. His early career was in applied mathematics and, increasingly, in the physics of the atmosphere. During the First World War he served as an aviator on the Austrian and German fronts, flying reconnaissance and bombing missions and personally working out ballistics tables for accurate bombing — practical applied mathematics under fire. After the war and the revolution he became a leading figure in Soviet theoretical meteorology and dynamical geophysics, the discipline of integrating the equations of a fluid forward in time.

It was that dynamical instinct that he brought to Einstein's general relativity. In two papers, in 1922 and 1924, Friedmann did something Einstein had not: he treated the field equations for a homogeneous, isotropic universe as an equation of motion for the scale of space itself, and showed that the natural solutions were not static but expanding or contracting. He derived the family of models — closed, flat, and open — that now bear his name, and he showed that a universe could begin from a point of zero size a finite time in the past. He did this as pure mathematics, without reference to any astronomical data on galaxies.

Einstein's first reaction was disbelief. He submitted a short note to the Zeitschrift für Physik in 1922 asserting that Friedmann's non-static solutions contained an error. Friedmann wrote to him defending the work, and in 1923, after the matter was clarified by a colleague, Einstein published a terse retraction acknowledging that Friedmann's results were correct and shed new light on the equations. The exchange is one of the cleaner examples in physics of a great authority being plainly wrong and admitting it.

Friedmann did not live to see his universe confirmed. In 1925, shortly after setting a balloon altitude record for meteorological observation, he contracted typhoid fever — probably from food eaten on holiday in Crimea — and died in Leningrad at the age of 37. Within four years Hubble's redshift–distance relation would make the expanding universe an observational fact, and within a decade Friedmann's equations would be the standard framework of cosmology. He is remembered as the man who, working from meteorology and a refusal to assume the universe stood still, discovered that it does not.