Alexander Friedmann

Alexander Alexandrovich Friedmann (Russian Александр Александрович Фридман; * 4 Junijul / June 16 1888greg in Saint Petersburg, .. † September 16, 1925 in Leningrad) was a Russian physicist, geophysicist and mathematician.

Friedmann's work on relativistic cosmology

The development of a homogeneous and isotropic universe is described by the Friedmann equations.

From the general theory of relativity starting, 1917, Albert Einstein published a static world model with the assistance of a cosmological constant. Willem de Sitter also developed at this time a world model with a cosmological constant, although the expanded, however, was matter- free.

In his work from 1922 about the curvature of space Friedmann discovered for the first time the possibility of a dynamic universe with uniformly distributed masses, without assuming a cosmological constant and a time-varying positive space curvature, which could not be less than zero. "Under 'space' we mean a space which is described by a manifold of three dimensions; the ' world ' corresponds to a manifold of four dimensions " For those with the time-varying spaces of positive or vanishing curvature differs Friedmann between two basic cases: ., such a world is expanding either continues or the expansion eventually reverses itself in a contraction. Friedman estimated that such a ' world-period " could last for 10 billion years and thus was already roughly today's improved estimates of the age of our universe close. The earlier models of Einstein and de Sitter contained in the Friedmann models as special cases.

In his observations on the work of A. Friedmann (Journal of Physics, 1922, 11:1) Einstein refused at first the results of Friedmann's from, it seemed to him "suspicious" and with the field equations " not acceptable". However, Einstein corrected soon after, in the note to the work of A. Friedmann (Journal of Physics, 1923, 21:1) his earlier assessment: " My objection was based but - I am at the suggestion of Mr. Krutkoff to hand a letter from Mr. Friedmann was convinced - to a calculation error. I think Mr. Friedmann's results for right and enlightening. "

In 1924, Friedman published again in the journal for physics essay about the possibility of a world with constant negative curvature of space as the third case for a relativistic world model and wrote in it: "The ability to derive a world of constant positive spatial curvature of the world equations, but is related to the question of the finiteness of space in the context. For this reason it is likely to be of interest to investigate whether it is possible for the same world equations get a world of constant negative curvature of their finitude ( under some additional assumptions) hardly can speak. "By the end of his essay discussed Friedmann that you must enlist and topological considerations for statements about the actual shape of our universe and thus points to questions that have been taken up again only recently.

The work Friedmanns were hardly noticed at shows, and even Einstein came up with it first does not return. Friedmann's solution was rediscovered in 1927 by the Belgian astronomer Georges Lemaître, but also its solution was initially ignored in the professional world, as you preferred stationary universes. Were discussed until the early 1930s, almost only the two cosmological models by Willem de Sitter and Einstein.

When in 1929 by Edwin Hubble discovered a systematic red shift in the spectra of distant galaxies by astronomical measurements, now had to be seriously considered an expansion of the universe. The Friedmann models can be regarded as a idealized reference model for expanding worlds.

After the expansion of the universe was accepted to Einstein had described his use of the cosmological constant as a supposedly "greatest blunder of my life ". In truth, this saying it was rumored, however, only by Gamow. Later this constant was as a representative of the dark energy again use.

In her book, A. Friedmann: the man who made the universe expand ( Cambridge, 1993) can be found by the authors Tropp, Frenkel and Chernin this assessment: "Just as Copernicus, the earth was revolving around the sun, the universe by Friedmann was a expanding. " (" As Copernicus made ​​the Earth go round the Sun, so Friedmann made ​​the Universe expand. " )

Confusion by name and date of birth

The date of birth Friedmanns was often incorrectly stated, because during the conversion from the Julian to the Gregorian calendar miscalculation and misunderstanding took place. There was thus obtained, for example, which is often called birth " 29 June " (Gregorian ) instead of right" 16 June ". At various confusions also introduced the different spelling of his first name and his surname. This was, for example, written as " Friedmann ", " Friedman ", " Fridman " and " Fridman ". "This leads, for example, to the fact that Meyer's Encyclopedic Lexicon under the heading ' Fridman, Alexander Alexandrovich ' recognizes only the geophysicist and mathematician, but not the cosmologists; the person mentioned under the heading of ' cosmology ' ' A. Friedmann ' no reference is made ​​. " (Georg Singer, preface to " The World as Space and Time, "p LIX )

Works (selection)

• A. Friedman: On the curvature of space. In: Journal of physics. 10, No. 1, 1922, pp. 377-386. doi: 10.1007/BF01332580.
• A. Friedmann: About the possibility of a world with constant negative curvature of space. In: Journal of physics. 21, No. 1, 1924, pp. 326-332. doi: 10.1007/BF01328280.
• Alexander Friedmann: The world as space and time. Edited by Georg Singer. 3rd edition, Harri German, Frankfurt am Main 2006, ISBN 3-8171-3416-9 (first Russian edition 1923)