# Niels Bohr
Niels Henrik David Bohr (7 October 1885 – 18 November 1962) was a Danish physicist who explained atomic structure with his 1913 quantum model of the atom, headed the Institute for Theoretical Physics at the [University of Copenhagen](https://www.edgepedia.org/university-of-copenhagen) from 1920 until his death, and received the [Nobel Prize in Physics](https://www.edgepedia.org/nobel-prize-in-physics) in 1922.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) His later ideas on complementarity shaped the interpretation of quantum mechanics, and his compound-nucleus and liquid-drop pictures of the nucleus underpinned the theory of nuclear fission.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile)
| Key fact | Detail |
|---|---|
| Born – died | 7 October 1885, Copenhagen – 18 November 1962, Copenhagen[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) |
| Signature work | "On the Constitution of Atoms and Molecules", three papers, 1913[3](https://www.gutenberg.org/files/72787/72787-h/72787-h.htm) |
| Nobel Prize | Physics, 1922, for work on atomic structure; lecture delivered 11 December 1922[4](https://www.nobelprize.org/uploads/2018/06/bohr-lecture.pdf) |
| Professor | Theoretical Physics, University of Copenhagen, from 1916[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) |
| Institute | Head of the Institute for Theoretical Physics, Copenhagen, 1920–1962[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) |
| US National Academy of Sciences | Elected 1925[5](https://www.nasonline.org/directory-entry/niels-bohr-lsnf9p/) |
| Wartime role | Tube Alloys and Los Alamos (as "Nicholas Baker"), 1943–1945[6](https://ahf.nuclearmuseum.org/ahf/profile/niels-bohr/) |
## Early life and education
Bohr was born in Copenhagen, the son of [Christian Bohr](https://www.edgepedia.org/christian-bohr), Professor of Physiology at Copenhagen University.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) He took his [Master's degree](https://www.edgepedia.org/masters-degree) in Physics in 1909 and his doctorate in 1911, both at Copenhagen University; the doctoral thesis was a theoretical work on the electron theory of metals.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) After a stay in Cambridge in autumn 1911, where he did not work well with [J. J. Thomson](https://www.edgepedia.org/j-j-thomson), he moved in March 1912 to Victoria University, Manchester, and joined Ernest Rutherford's group working on atomic structure.[7](https://mathshistory.st-andrews.ac.uk/Biographies/Bohr_Niels/) His mother was Ellen Adler.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) His younger brother Harald became a mathematician and Olympic footballer, and Niels himself played football as a goalkeeper for the Copenhagen club Akademisk Boldklub. Earlier, in 1905, he had won a gold medal from the Royal Danish Academy of Sciences and Letters for experimental work on measuring the surface tension of liquids by observing the oscillation of a water jet, a project he carried out in his father's laboratory; an improved version was published in the Transactions of the Royal Society in 1908.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/)
## The Bohr model of the atom
Rutherford's 1911 nuclear atom faced a serious problem: classical electrodynamics required orbiting electrons to radiate energy continuously, so the system of electrons was unstable and the atom should collapse.[3](https://www.gutenberg.org/files/72787/72787-h/72787-h.htm) Bohr's solution, published in 1913 as three papers under the title "On the Constitution of Atoms and Molecules", was to introduce a quantity foreign to classical electrodynamics, Planck's constant, into the laws of electronic motion.[3](https://www.gutenberg.org/files/72787/72787-h/72787-h.htm) He formulated the model as two postulates: atoms possess stable stationary states whose stability is mechanically unexplainable, and radiation is emitted only during a complete transition between stationary states, at a frequency given by the energy difference divided by Planck's constant.[4](https://www.nobelprize.org/uploads/2018/06/bohr-lecture.pdf) In the permanent state, the angular momentum of every electron about the center of its orbit takes a universal value involving Planck's constant.[3](https://www.gutenberg.org/files/72787/72787-h/72787-h.htm)
The model's decisive test was the hydrogen spectrum. Bohr derived the [Rydberg constant](https://www.edgepedia.org/rydberg-constant) from atomic constants and wrote the generalized Balmer formula for hydrogen's emission frequencies, in full agreement with experiment.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile) The no-radiation postulate directly violated [Maxwell's equations](https://www.edgepedia.org/maxwells-equations), but it stated what experiment already showed, and the quantization condition was validated by the spectrum it predicted.[8](https://link.springer.com/article/10.1007/s40828-025-00208-4) In the early 1920s Bohr used the theory to explain the entire periodic table,[9](https://nbi.ku.dk/english/www/niels/bohr) and his indication of the chemical properties of element 72 led to the discovery of hafnium.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile) Working at the institute, [Dirk Coster](https://www.edgepedia.org/dirk-coster) and George de Hevesy searched mineral samples and found the element, which they named hafnium after the Latin name for Copenhagen.
## Copenhagen institute and the quantum revolution
Bohr held a lectureship at Copenhagen in 1913–1914 and at Victoria University, Manchester, in 1914–1916; in 1916 he was appointed Professor of Theoretical Physics at Copenhagen University.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) From 1920 until his death he headed the Institute for Theoretical Physics established for him there.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) (The Lindau laureate archive dates the institute's establishment to 1921.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile)) During the 1920s it became one of the major centers of attraction for young theoretical physicists, including [Paul Dirac](https://www.edgepedia.org/paul-dirac), Pascual Jordan, Werner Heisenberg, Wolfgang Pauli, and John Slater.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile) The institute hosted physicists including [Hans Kramers](https://www.edgepedia.org/hans-kramers), Oskar Klein, George de Hevesy, and [Werner Heisenberg](https://www.edgepedia.org/werner-heisenberg).
During this period Bohr formulated the correspondence principle, which relates transitions among stationary states to the harmonic components of the atom's classical motion as classical electrodynamics determines them; using it, his group achieved a quantum-theory account of the [Zeeman effect](https://www.edgepedia.org/zeeman-effect) that was complete.[4](https://www.nobelprize.org/uploads/2018/06/bohr-lecture.pdf) At a meeting at Como in September 1927 Bohr put forward the principle of complementarity, a physical interpretation of Heisenberg's uncertainty relations.[7](https://mathshistory.st-andrews.ac.uk/Biographies/Bohr_Niels/) In 1927 he published his first work on complementarity, opening a long public debate with Einstein over the foundations of quantum theory.[10](https://physicsworld.com/a/bohr-einstein-and-bell-what-the-2022-nobel-prize-for-physics-tells-us-about-quantum-mechanics/) In his first exposition Bohr stated that space-time coordination and the claim of causality must be regarded as complementary but exclusive features of the description.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile)
## Nobel Prize and honors
The Nobel Prize in Physics for 1922 recognized Bohr's work on the structure of atoms, not the later complementarity work.[1](https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/) He delivered his Nobel Lecture, "The Structure of the Atom", on 11 December 1922.[4](https://www.nobelprize.org/uploads/2018/06/bohr-lecture.pdf) The United States National Academy of Sciences elected him in 1925.[5](https://www.nasonline.org/directory-entry/niels-bohr-lsnf9p/)
## Nuclear physics, war and later career
In 1936 Bohr formulated the compound-nucleus model, in which a nucleus struck in a reaction passes into a temporarily unstable compound state; with the liquid-drop picture, formulated in 1937, it explains the fission process.[11](https://nbi.ku.dk/english/www/niels/bohr/kernefysik/) After the discovery of fission in 1939, Bohr made a significant contribution to its theoretical understanding during an extended visit to Princeton, and in 1939 produced the first detailed quantitative study of the fission mechanism, predicting that uranium-235 is fissile by slow neutrons while uranium-238 tends to absorb slow neutrons.[2](https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile)
After the Nazis took power in Germany in 1933, Bohr assisted several scientists in escaping Germany, and he remained in Denmark when it was occupied in 1940.[11](https://nbi.ku.dk/english/www/niels/bohr/kernefysik/) Earlier he had turned down a secret invitation to relocate to England, yet when he was forced to flee occupied Denmark in October 1943 he accepted it; following a brief stay in Sweden, he was flown to England.[11](https://nbi.ku.dk/english/www/niels/bohr/kernefysik/) He worked with the British Tube Alloys nuclear weapons team, and then joined the British group at Los Alamos under the pseudonym Nicholas Baker.[6](https://ahf.nuclearmuseum.org/ahf/profile/niels-bohr/) From 1944 he tried to persuade Churchill and Roosevelt that the Soviet Union should be informed of the atomic project before the war's end, and on 9 June 1950 he published an Open Letter to the United Nations arguing for openness between nations; he fought for this cause until his death.[7](https://mathshistory.st-andrews.ac.uk/Biographies/Bohr_Niels/) He died in Copenhagen on 18 November 1962 of a coronary thrombosis, aged 77.[12](https://www.nytimes.com/1962/11/19/archives/front-page-1-no-title-niels-bohr-atom-pioneer-and-nobel-winner-dies.html) After the war Bohr returned to Copenhagen and called for international cooperation on nuclear energy.
## The Bohr model and later quantum mechanics
Within twenty years, the quantum mechanics of Schrödinger and Heisenberg had displaced the [Bohr model](https://www.edgepedia.org/bohr-model), yet in the twenty-first century chemistry teaching still makes use of it.[8](https://link.springer.com/article/10.1007/s40828-025-00208-4) Three separate discoveries later provided justification for the angular-momentum postulate: the wave–particle duality of de Broglie, Heisenberg's uncertainty principle, and the direct detection of the photon's angular momentum.[8](https://link.springer.com/article/10.1007/s40828-025-00208-4)
The Bohr–Einstein debate was settled experimentally in stages. In his 1964 paper, Bell showed that, under certain auxiliary assumptions, no theory satisfying a locality condition can fully reproduce the quantum-mechanical probabilities, thereby handing experimentalists a target that neither Einstein nor Bohr had ever considered; when the first [Bell test](https://www.edgepedia.org/bell-test) was performed in 1972, it supplied the first hard evidence against local hidden variables, and experiments of this kind were honored by the 2022 Nobel Prize.[10](https://physicsworld.com/a/bohr-einstein-and-bell-what-the-2022-nobel-prize-for-physics-tells-us-about-quantum-mechanics/) • [15](https://plato.stanford.edu/entries/bell-theorem/) Then, in December 2025, an experiment at the [University of Science and Technology of China](https://www.edgepedia.org/university-of-science-and-technology-of-china), reported in Physical Review Letters, realized the thought experiment Einstein had proposed a century earlier and supported Bohr's position: by dynamically tuning the momentum uncertainty of a rubidium atom held in an optical tweezer, interference fringes were blurred in accordance with the complementarity principle.[13](https://phys.org/news/2025-12-real-life-niels-bohr-theoretical.html)
## References
1. Niels Bohr – Biographical, Nobel Foundation. https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/
2. Research Profile – Niels Bohr, Lindau Mediatheque. https://mediatheque.lindau-nobel.org/laureates/bohr/research-profile
3. On the Constitution of Atoms and Molecules (1913 trilogy), Project Gutenberg. https://www.gutenberg.org/files/72787/72787-h/72787-h.htm
4. Niels Bohr – Nobel Lecture: The Structure of the Atom (1922). https://www.nobelprize.org/uploads/2018/06/bohr-lecture.pdf
5. Niels Bohr – Member Directory, National Academy of Sciences. https://www.nasonline.org/directory-entry/niels-bohr-lsnf9p/
6. Niels Bohr – Atomic Heritage Foundation / Nuclear Museum. https://ahf.nuclearmuseum.org/ahf/profile/niels-bohr/
7. Niels Bohr (1885–1962), MacTutor History of Mathematics, University of St Andrews. https://mathshistory.st-andrews.ac.uk/Biographies/Bohr_Niels/
8. The origin of the postulates in the Bohr model of the hydrogen atom, ChemTexts (2025). https://link.springer.com/article/10.1007/s40828-025-00208-4
9. Niels Bohr – Niels Bohr Institute, University of Copenhagen. https://nbi.ku.dk/english/www/niels/bohr
10. Bohr, Einstein and Bell: what the 2022 Nobel Prize for Physics tells us about quantum mechanics, Physics World. https://physicsworld.com/a/bohr-einstein-and-bell-what-the-2022-nobel-prize-for-physics-tells-us-about-quantum-mechanics/
11. Nuclear physics and war – Niels Bohr Institute. https://nbi.ku.dk/english/www/niels/bohr/kernefysik/
12. Niels Bohr, Atom Pioneer and Nobel Winner, Dies, The New York Times (19 November 1962). https://www.nytimes.com/1962/11/19/archives/front-page-1-no-title-niels-bohr-atom-pioneer-and-nobel-winner-dies.html
13. Real-life experiment shows Niels Bohr was right in a theoretical debate, Phys.org (December 2025). https://phys.org/news/2025-12-real-life-niels-bohr-theoretical.html
14. Copenhagen Interpretation of Quantum Mechanics, Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/qm-copenhagen/
15. Bell’s Theorem (Stanford Encyclopedia of Philosophy), https://plato.stanford.edu/entries/bell-theorem/
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*Topic: Encyclopedia › Physical world and mathematics › Physical and mathematical scientists › Physicists and astronomers › Researchers in atomic, molecular, and optical physics and quantum information*
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