Niels Bohr

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Niels Bohr (1922)

Niels Henrik David Bohr (born October 7, 1885 in Copenhagen ; † November 18, 1962 there ) was a Danish physicist . In 1921 he received the Hughes Medal of the Royal Society and the Nobel Prize in Physics in 1922 "for his services to the study of the structure of atoms and the radiation emitted by them".


Early years and training

Niels Bohr's father, Christian Bohr , was a professor of physiology ; his mother Ellen (née Adler) came from a Jewish family. Together with his father and brother Harald Bohr , he held regular talks and discussions on scientific topics that strengthened both brothers' interest in the natural sciences and shaped their later life. “I grew up in a house with a rich intellectual life where scientific discussion was common. In fact, my father made hardly any distinction between his own scientific work and his lively interest in all problems of human life, ”Niels Bohr later judged in retrospect about his parents' house. Harald Bohr later became a professor of mathematics, while Niels Bohr turned to physics. Both were also active in the early days of football on the European continent as football players for the Akademisk Boldklub club , while Niels Bohr was a goalkeeper. His brother even made it to the Danish national team and took part in the first soccer tournament of the 1908 Summer Olympics. Whether Niels Bohr was honored with a national player is not known due to the sources of the early Danish internationals outside of the Olympic tournaments.

After graduating from high school in the Gammelholm district of Copenhagen in 1903, Niels Bohr studied physics, mathematics, chemistry, astronomy and philosophy at the University of Copenhagen . Some ascribe him the "role" as a candidate in the so-called barometer question . In 1907 he received the gold medal of the Royal Danish Academy of Sciences for his work on the surface tension of liquids. His master's degree took place in 1909 and in 1911 he completed his studies with his doctoral thesis under Christian Christiansen on the magnetic properties of metals ( Studier over Metallernes elektrontheori ). In the same year he moved to Cambridge to the Cavendish Laboratory , which was headed by the 1906 Nobel Prize in Physics, Joseph John Thomson , and a year later to Manchester to the laboratory of Ernest Rutherford , who had received the Nobel Prize in Chemistry in 1908 . It was here that Niels Bohr met Margrethe Nørlund, whom he later married. Together with her he had six sons, two of whom died at a young age. Her son Aage Niels Bohr received the Nobel Prize in Physics in 1975.

Development of the Bohr model of the atom

During the First World War , Niels Bohr accepted a teaching position in Manchester in 1914 and shortly afterwards in Copenhagen. Two years later he became professor of physics at the University of Copenhagen. During a stay and lecture in Berlin in 1920 he made the acquaintance of Max Planck and Albert Einstein . With the help of the theories on quantum physics that they established and which he combined with the laws of classical physics, Bohr had already succeeded in 1913 in setting up Bohr's atomic model , which could explain the line spectra of hydrogen. From today's point of view, like its further development to Bohr-Sommerfeld's atomic model from 1915/16, it is outdated and replaced by the quantum mechanical orbital model , although it is still taught in chemistry classes in schools.

Nonetheless, his model is seen as a milestone in theoretical physics, as quantization was successfully integrated into an atomic model for the first time at atomic level . Before that, Rutherford's atomic model was only known since 1911 , according to which atoms are not massive spheres, but consist of a tiny core and an atomic shell that is at least a thousand times larger.

From 1916 to 1919 Niels Bohr was chairman of the Danish Physical Society and from 1917 also a member of the Danish Academy of Sciences . In 1918 he formulated Bohr's principle of correspondence , which explained the connection between quantum theory and classical physics and showed that the laws of Planck's quantum of action can be neglected with increasing quantum numbers . During this time he worked on setting up his own institute at the University of Copenhagen, which opened on March 3, 1921 as the Institute for Theoretical Physics. His Göttingen lectures, which he gave in the summer of 1922, became internationally known and went down in scientific history as the “Bohr Festival”. In 1922 he succeeded in explaining the structure of the periodic table of the elements on the basis of the atomic model expanded by Arnold Sommerfeld , in which he adopted a shell model. On December 10, 1922, he received the Nobel Prize in Physics for his research on atomic structure and the radiation emitted by atoms. In the same year his son Aage Niels Bohr was born, who also received the Nobel Prize in Physics in 1975.

Further work after the Nobel Prize

Niels Bohr (left) 1925 with Albert Einstein (photographed by Paul Ehrenfest , Photo I)

In the years that followed, Bohr's atomic model and the modifications of Arnold Sommerfeld's atomic theory were further expanded until, between 1925 and 1927, the consideration of atomic physics was revolutionized by the formulation of non-relativistic quantum mechanics ( Werner Heisenberg , Erwin Schrödinger , Paul Dirac ). In 1924 Bohr published together with Hendrik Anthony Kramers and John C. Slater the philosophically significant work "The quantum theory of radiation", in which the strict adherence to the law of conservation of energy was questioned for the first time and replaced by statistical conservation of energy. In 1926/27 Werner Heisenberg lectured at Niels Bohr's institute and through the discussions between the two researchers, Heisenberg's uncertainty principle and Bohr's principle of complementarity developed as the “ Copenhagen interpretations ” of quantum theory, both of which were published in 1927. The principle of complementarity was supposed to guarantee the consistency between formulated theories and the weighing of actual observations, and he later also applied it to principles outside of physics.

In the years that followed, Bohr continued to focus on questions of quantum mechanics, while his atomic model helped the pioneers of nuclear research understand the elementary properties of the chemical elements. The model offered explanations for the valences , the metallic and non-metallic character of the substances as well as for the ionic properties . He himself tried to explain the reactions of the atomic nuclei triggered by the bombardment with particles and introduced the term " compound nucleus" for this purpose . In 1936 he developed two new core models , which he called the sandbag and droplet model. Together with John Archibald Wheeler , he worked out the possibility of generating energy after Otto Hahn and Friedrich Wilhelm Straßmann carried out the first nuclear fission.

During the German occupation of Denmark , Niels Bohr was involved in the Danish resistance . In 1943 he and his family fled to Sweden, supported by the British and Danish secret services . There he successfully asked the Swedish king and the foreign minister for asylum for his Jewish compatriots . Then he traveled to the USA under the code name Nicholas Baker , where he carried out important theoretical preparatory work for the construction of the US atomic bomb in Los Alamos .

After the Second World War, Bohr was an integral part of the discussions about a possible European cooperation to create a nuclear physics laboratory. Although he did not initially agree with Pierre Auger on the location of the future CERN (Conseil européen pour la recherche nucléaire) , he took part in the 1952 UNESCO conference that hosted the Council of Representatives of European States for Planning at International Laboratory and Organizing other Forms of Co-operation in Nuclear Research (Council of Representatives of European States for Planning an International Laboratory and Other Forms of Cooperation in Nuclear Research) officially gave the name CERN.

After the war he returned to Denmark and continued his research on atomic energy in his old position. At the same time, however, he warned against their misuse, above all in an open letter to the United Nations in 1950, and was therefore the 1957 winner of the " Atoms for Peace Award " . He died in Copenhagen in 1962 and was buried in the assistance cemetery.

Life's work

Niels Bohr 1925 with Albert Einstein (photographed by Paul Ehrenfest , Photo II)

His most important contribution to physics was Bohr's atomic model , which he first presented to the public in 1913. It represents an important step in the development of quantum mechanics . Other concepts that can be traced back to him are the principle of correspondence , which describes the transition from quantum mechanics to classical mechanics, and the principle of complementarity , which states that knowing certain measurands necessarily means total ignorance of certain other sizes conditional. In his science-critical work, Bohr took the view that what constitutes an apparatus depends on the respective observation practices.

Honors and memberships

In addition to the Nobel Prize for Physics in 1922, Niels Bohr received a number of other prizes and awards including a. The Barnard Medal in 1925 and the Sonning Prize of the University of Copenhagen in 1961 . He was President of the Danish Royal Academy of Sciences and Chairman of the Danish Atomic Energy Commission. He was also a foreign member of the Royal Society in London , the Accademia dei Lincei in Rome, the Academy of Sciences in Göttingen (since 1921), the German Academy of Sciences Leopoldina , the National Academy of Sciences (1925), the Royal Society of Edinburgh (1927), the American Philosophical Society (1940), the American Academy of Arts and Sciences (1945), corresponding member of the Bavarian Academy of Sciences (since 1926) and the Académie des Sciences (since 1937) and other international scientific associations. He also received honorary doctorates from numerous universities around the world. He was the bearer of the highest Danish order, the Elephant Order . In 1954 he was awarded the Order Pour le Mérite .

From 1997 to 2011 Niels Bohr was depicted on the front of the 500 kroner banknote of the Danish National Bank, the lunar crater Bohr was named after him in 1964 and the asteroid (3948) Bohr in 1989 .

Names after Bohr

The transuranic , non-naturally occurring chemical element with the ordinal number 107 was detected in 1981 and later named Bohrium ; Bh was specified as an abbreviation in the periodic table of elements .

In addition, numerous physical phenomena and concepts bear Bohr's name, above all Bohr's atomic model (1913) with Bohr's orbits. Furthermore, the Bohr correspondence principle , Bohr radius and Bohr magneton have entered the scientific terminology.

The Bohr effect in hemoglobin is named after his father, the physiologist Christian Bohr .

The potassium uranyl arsenate nielsbohrit was named after him in 2002.

Publications (selection)


  • Ruth Moore: Niels Bohr. A man and his work change the world . List Verlag, Munich 1970.
  • Pascual Jordan : Encounters. Albert Einstein, Karl Heim, Hermann Oberth, Wolfgang Pauli, Walter Heitler, Max Born, Werner Heisenberg, Max von Laue, Niels Bohr. Stalling, Oldenburg u. a. 1971, ISBN 3-7979-1934-4 .
  • Friedrich Hund : Correspondence and Complementarity - Bohr's Path to Atomic Dynamics . Phys. Bl. 41 (1985) No. 9, Physik-Verlag Weinheim, pp. 303-317.
  • Abraham Pais : Niels Bohr's times. In physics, philosophy, and polity . Clarendon Press, Oxford 1991, ISBN 0-19-852049-2 .
  • Stefan Rozental : Fateful years with Niels Bohr. Memories of the founder of modern atomic theory. Translated from Danish by Klaus Stolzenburg. DVA, Stuttgart 1991, ISBN 3-421-06615-9 .
  • Ulrich Röseberg: Niels Bohr. Life and work of a nuclear physicist. 1885-1962. 3. Edition. Spectrum Academic Publishing House, Berlin a. a. 1992, ISBN 3-86025-017-5 .
  • Bernhard Kupfer: Lexicon of Nobel Prize Winners . Patmos Verlag, Düsseldorf 2001, ISBN 3-491-72451-1 .
  • Brockhaus Nobel Prizes. Chronicle of outstanding achievements . 2nd Edition. Brockhaus, Mannheim a. a. 2004, ISBN 3-7653-0492-1 .
  • Ernst Peter Fischer: Niels Bohr. Physicist and Philosopher of the Atomic Age , Settlers 2012, ISBN 9783886809967

Web links

Commons : Niels Bohr  - Collection of images, videos and audio files

Individual evidence

  1. Hughes Medal. The Royal Society, accessed February 2, 2012 .
  2. ^ The Nobel Prize in Physics 1922. In: The Official Website of the Nobel Prize. The Nobel Foundation, accessed February 2, 2012 .
  3. Guide to the Niels Bohr Collection 1909–1963. University of Chicago Library, 2006, accessed February 2, 2012 .
  4. ^ Voices from famous physicists. University of Münster, accessed on February 27, 2010 .
  5. biographical data, publications and Academic pedigree of Niels Bohr in, accessed on 7 January 2018th
  6. ^ Bohr, Niels, HA Kramers, and JC Slater. Philosophical Magazine 47 (1924): 785-802
  7. So he contradicted z. B. decided on a work by Albert Einstein and co-workers from 1935 (see EPR effect ), in which Einstein, contrary to the “Copenhagen interpretation”, argued that quantum mechanics had to be supplemented by so-called “hidden variables”. This later turned out to be a mistake, so that Bohr was right here even against Einstein.
  8. ^ Matthias Bath: Danebrog against Hakenkreuz , Wachholz, 2011, ISBN 978-3-529-02817-5 , p. 137
  9. Michael Krause: Where people and particles collide . Wiley-VCH, 2013, p. 1–63 ( [PDF; accessed on July 24, 2019]).
  10. ^ The Director-general : Tribute to Niels Bohr . tape 3 , no. 7 . CERN Courier, July 1963, p. 89 (English, [PDF; accessed on July 24, 2019]).
  11. Karen Barad , “Getting Real. Technoscientific Practices and the Materialization of Reality, "in: differences. A Journal of Feminist Cultural Studies 10 (2), 1998: 87–128.
  12. ^ Member entry of Niels Bohr at the German Academy of Natural Scientists Leopoldina , accessed on October 12, 2012.
  13. ^ Biographical Index: Former RSE Fellows 1783–2002. Royal Society of Edinburgh, accessed October 10, 2019 .
  14. ^ List of members since 1666: Letter B. Académie des sciences, accessed on September 22, 2019 (French).
  15. Nielsbohrit at