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Niels Bohr

1885 - 1962

Niels Bohr, 1885 - 1962. A Danish physicist

Niels Bohr, 1885 - 1962, was a Danish physicist, and founder of the Copenhagen School, which proposes as a consequence of quantum mechanics that there is no fundamental reality, a view much opposed by Albert Einstein.

  • Nationality
  • Danish

  • Subject
  • Physics, theoretical

  • Fields
  • Quantum Mechanics, Atomic structure

  • Distinctions
  • Nobel Prize in Physics, 1922, for his work on the structure of atoms.

    The element bohrium (atomic number 107) is named in his honour.

    Max Planck Medal, 1930

    Copley Medal, 1938

  • Posts
  • Bohr founded the Institute of Theoretical Physics (now the Niels Bohr Institute) at the University of Copenhagen, in 1920.

    Bohr fled Denmark in 1943, to join the British, and then the American nuclear bomb Manhatten Project at Los Alamos.

    Chairman of the Nordic Institute for Theoretical Physics, 1957.

  • Theories
  • Bohr atomic model: the model which is fundamentally the version used today. The model corrected the Thompson and Rutherford models, by placing electrons into discrete energy levels.

    Principle of complementarity: separate analysis of contradictory properties, such as the wave or particle nature of photons. Complementary properties, such as position and momentum, according the Heisenberg's Uncertainty Principle, cannot both be known to high precision simultaneously.

    Bohr-van Leeuwen theorem: when statistical mechanics and classical mechanics are applied consistently, the thermal average of magnetisation is always zero. The corollary is that magnetism can be explained only by quantum mechanics.

  • Experiments/Discoveries
  • Bohr's atomic model predicted that hafnium (atomic number 72) would resemble zirconium, so not be a member of the rare earth elements.

Niels Bohr is one of the most important figures in modern physics. His debate with Albert Einstein about fundamental reality is a fascinating story of two intellectual titans.

Albert Einstein and Niels Bohr
Albert Einstein and Niels Bohr

Bohr famously was a postgraduate researcher, in 1911, under J.J.Thomson (who had proposed the 'plum pudding model' of the atom in 1904), before meeting Rutherford, who put forward his own Rutherford model of the atom the same year. Bohr returned to Copenhagen University to lecture on thermodynamics in 1913, where he trumped his two masters with the successful Bohr Model.

In 1920, Bohr founded what was to become the Niels Bohr Institute in Copenhagen. This became the centre of the 'Copenhagen School', which proposed that reality was created by the observer. Werner Heisenberg, with his Uncertainty Principle, 1927, is closely associated with the movement, whose proposals were opposed by Albert Einstein and Erwin Schrödinger.

Einstein's light box enigma for Niels Bohr
Einstein's light box enigma for Niels Bohr, 1927

Bohr and Einstein had a public disagreement concerning the nature of reality. Their debate has been inherited by generations of physicists since, although physicists have demonstrated the quantum nature of matter to great precision, a phenomenon that Einstein described as 'spooky action at a distance', and thought that it could not explain everything about reality. Einstein set Bohr a thought experiment involving a box and an escaping photon, thinking that Bohr could not maintain the duality of states idea under the conditions of the experiment. However, after much deliberation, Bohr famously used Einstein's own Relativity Theory to resolve the enigma. He can't have completely convinced himself, though, because on the day Bohr died, 35 years later, Einstein's challenge was found on Bohr's blackboard, with the old Dane still puzzling over it to the end.

During the Second World War, Bohr had a famous meeting with his old research junior, Werner Heisenberg, who was involved in the Nazi atomic bomb project. Much controversy arose from the nature of their meeting, and whether Heisenberg was attempting to gain Bohr's assistance for the Germans. Whatever the truth, Bohr fled Denmark to avoid arrest in September, 1943, and after a perilous journey, via Sweden, he arrived in Britain, where he assisted the allies in the nuclear arms race. He went to Los Alamos, as part of the British mission to collaborate on the Manhatten Project. There he met Richard Feynman, and singled him out as a talented young physicist.

Niels Bohr and Max Planck
Niels Bohr and Max Planck

Niels bohr's 4th son, Aage Bohr, also received a Nobel Prize in Physics, in 1975, 53 years after his father. There have been four such father-son Nobel Prize double acts.

Russian aluminium statue of Albert Einstein and Niels Bohr
Russian aluminium statue of Albert Einstein and Niels Bohr. Einstein was once caught stealing Bohr's tobacco at Princeton University!

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