Alexander Alexandrowitsch Friedmann

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Alexander Alexandrowitsch Friedmann

Alexander Friedmann ( Russian Александр Александрович Фридман * June 4 . Jul / 16th June  1888 greg. In St. Petersburg ; † 16th September 1925 in Leningrad ) was a Russian and Soviet physicists , geophysicists and mathematicians . According to Friedmann's proposed solution for Einstein's field equations , the universe is not static, but rather expands or contracts .

Friedmann's work on relativistic cosmology

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

Based on the general theory of relativity , Albert Einstein published a static world model in 1917 with the addition of a cosmological constant . Also Willem de Sitter developed at that time a world model with a cosmological constant, although the expanded, however, was matter-free.

In his 1922 work on the curvature of space , Friedmann discovered for the first time the possibility of a dynamic universe with evenly distributed masses, without assuming a cosmological constant and with a time-varying positive space curvature that could not be less than zero. “By 'space' we mean here a space that is described by a manifold of three dimensions; the 'world' corresponds to a manifold of four dimensions. ”For such spaces of positive or vanishing curvature that change over time, Friedmann differentiates between two basic cases: such a world either continues to expand or the expansion is eventually reversed into a contraction. Friedmann estimated that such a "world period" could last 10 billion years and thus came roughly close to modern, improved estimates of the age of our universe. The earlier Einstein and de Sitters models are included in Friedmann's models as special cases.

In his comments on the work of A. Friedmann (Zeitschrift für Physik 1922, 11.1), Einstein initially rejected Friedmann's results, they seemed to him “suspicious” and “not compatible” with the field equations. However, soon afterwards Einstein corrected his earlier assessment in the note on the work by A. Friedmann (Zeitschrift für Physik 1923, 21.1): “My objection was based - as I was at the suggestion of Mr Krutkoff on the basis of a letter from Mr Friedmann convinced - on a miscalculation. I consider Mr. Friedmann's results to be correct and informative. "

In 1924 Friedmann again published the essay on the possibility of a world with constant negative curvature of space as the third case for a relativistic world model in the Zeitschrift für Physik and wrote: “The possibility of deriving a world of constant positive spatial curvature from the world equations, but is related to the question of the finiteness of space. For this reason it should be of interest to investigate whether one can obtain a world of constant negative curvature from the same world equations, of whose finiteness (even under some additional assumptions) one can hardly speak. ”At the end of his essay Friedmann explains that For statements about the actual shape of our universe one also has to consult topological considerations and thus points to questions that have only recently been taken up again.

Friedmann's works were hardly noticed when they were published, and Einstein did not return to them at first either. Friedmann's solution was rediscovered in 1927 by the Belgian astronomer Georges Lemaître , but his solution was initially ignored in the professional world, as stationary universes were preferred. Up until the early 1930s, almost only the two cosmological models of Willem de Sitter and Einstein were discussed .

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

After the expansion of the universe was recognized, Einstein is said to have described his use of the cosmological constant as supposedly "the greatest donkey of my life". In truth, however, this saying was only said to him by Gamow . This constant was later used again as a representative of dark energy .

In their book A. Friedmann: the man who made the universe expand (Cambridge 1993), the authors Tropp, Frenkel and Chernin gave this appreciation: “Just as Copernicus made the earth orbit the sun, the universe became one through Friedmann expanding. "(" As Copernicus made the Earth go round the Sun, so Friedmann made the Universe expand. ")

Death from typhoid

Friedmann died in September 1925 after a vacation stay in the Crimea , where he had contracted typhus .

Confusion about name and date of birth

Friedmann's date of birth was often given incorrectly because of calculation errors and misunderstandings during the conversion from the Julian to the Gregorian calendar. So z. E.g. the frequently mentioned date of birth June 29th (Gregorian) instead of the correct June 16th. The different spelling of his first name and family name also led to various confusions. This was z. B. written as "Friedmann", "Friedman", "Fridmann" and "Fridman". "That leads z. For example, Meyer's Encyclopedic Lexicon under the heading “Fridman, Alexander Alexandrowitsch” only pays tribute to the geophysicist and mathematician, but not to the cosmologist; to the person of the under the heading "Cosmology" mentioned "A. Friedmann "no reference is made."

Honors

Since 1972, the Soviet Academy of Sciences (from 1991 Russian Academy of Sciences) of the Friedmann Prize ( Russian Премия имени А.А. Фридмана ) for outstanding achievements in the field of cosmology and gravitation, to 1993, also for atmospheric physics , awarded .

Works (selection)

  • A. Friedman: About 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 a 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. 4th edition, Europa-Lehrmittel, Haan-Gruiten 2014, ISBN 3-8085-5773-7 (first Russian edition 1923)

literature

Web links

Individual evidence

  1. ^ EA Tropp, V. Ya. Frenkel, AD Chernin: Alexander A. Friedmann: the man who made the universe expand, Cambridge, 1993, p. 3f. There the birth certificate is quoted from the high school files, which reads June 4th (Julian), that would be June 16th in Gregorian (he was baptized on June 29th, Julian). In his curriculum vitae, printed in the Selected Works of 1966, he himself states June 17 (Gregorian). In the literature you can also find June 29th, e.g. B. Dictionary of Scientific Biography, probably based on the assumption that Friedmann meant the Julian date by June 17th.
  2. ^ For example, John North The measure of the universe , Dover 1990.
  3. ↑ Individual measurement results for the redshift distance relationship were known earlier, but were only discussed, also by Hubble as late as 1929, in the context of the De Sitter model, which predicted such an effect
  4. ↑ Georg Singer: Foreword to the world as space and time. S. LIX
  5. ^ AA Friedmann Prize. Russian Academy of Sciences, accessed April 29, 2018 (Russian, with list of award winners).
personal data
SURNAME Friedmann, Alexander Alexandrowitsch
ALTERNATIVE NAMES Фридман, Александр Александрович (Russian)
BRIEF DESCRIPTION Russian and Soviet physicist, geophysicist and mathematician
DATE OF BIRTH June 16, 1888
PLACE OF BIRTH Saint Petersburg , Russian Empire
DATE OF DEATH September 16, 1925
Place of death Leningrad , Soviet Union