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Portrait of Niels Bohr

Science · Physics

Niels Bohr

1885–1962 · Danish

Atomic and quantum physics

Niels Bohr was the Danish physicist whose 1913 model of the atom, with electrons in fixed orbits jumping between energy levels, brought quantum ideas to the structure of the atom. He won the 1922 Nobel Prize in Physics, and his Copenhagen institute became the hub of the new quantum mechanics. His principle of complementarity underpins the Copenhagen interpretation, which he defended in celebrated debates with Einstein.

How to spot them

  • ▸The Bohr model of the atom (1913): electrons in quantised orbits emitting light when they jump
  • ▸Copenhagen interpretation, complementarity and the Bohr–Einstein debates
  • ▸Institute for Theoretical Physics in Copenhagen, now the Niels Bohr Institute
  • ▸Escaped occupied Denmark in 1943; flown to Britain in the bomb bay of a Mosquito
  • ▸Michael Frayn's play Copenhagen, about his 1941 meeting with Heisenberg

Key discoveries & works

Model of the atom with electrons in quantised orbits (1913)

Explained the hydrogen spectrum; published as a trilogy of papers in the Philosophical Magazine

Principle of complementarity (1927)

Wave and particle descriptions are mutually exclusive yet both needed; first presented at Como

Correspondence principle (c. 1920)

Quantum results must reproduce classical physics in the limit of large quantum numbers

Liquid-drop theory of fission (with John Wheeler) (1939)

Showed that the rare isotope uranium-235 is the one that fissions with slow neutrons

Founding the Copenhagen Institute for Theoretical Physics (1921)

Magnet for Heisenberg, Pauli, Dirac and others in the 1920s

Key ideas

  • Electrons occupy only certain allowed energy levels; light of a definite frequency is emitted when an electron jumps down a level
  • Complementarity: 'contraria sunt complementa' (opposites are complementary), the motto on his coat of arms
  • Copenhagen interpretation: quantum mechanics describes what can be observed, not an underlying classical reality

Quick-fire facts

  • •Nobel Prize in Physics 1922 'for his services in the investigation of the structure of atoms and of the radiation emanating from them'
  • •Played in goal for the Copenhagen club Akademisk Boldklub; his brother Harald, a mathematician, won Olympic football silver for Denmark in 1908
  • •Worked with Ernest Rutherford in Manchester before devising his atomic model
  • •When awarded the Order of the Elephant (1947) he chose a coat of arms bearing the yin-yang symbol
  • •Fled to Sweden in 1943 and was flown to Britain in a Mosquito; at Los Alamos he went by the alias 'Nicholas Baker'
  • •His son Aage Bohr won the Nobel Prize in Physics in 1975
  • •Element 107, bohrium, is named after him; the Bohr radius and Bohr magneton also bear his name
  • •Received the first Atoms for Peace Award in 1957

Drill it — 9 cards

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Sources