Niels Bohr
Niels Bohr explained why atoms are stable and then spent forty years arguing about what quantum mechanics means. Born in Copenhagen in 1885, the son of a physiology professor, he was an excellent footballer whose brother played for Denmark at the 1908 Olympics. He went to Manchester in 1912 to work with Ernest Rutherford, who had just discovered the nucleus and whose model had a fatal defect: an orbiting electron radiates energy and should spiral into the nucleus in a fraction of a second. Bohr's answer in 1913 was to impose quantisation by hand. Electrons occupy discrete allowed orbits and radiate only when jumping between them, emitting a photon whose energy is the difference. It was internally inconsistent — classical mechanics for the orbits, quantum rules for the jumps — and it predicted the hydrogen spectrum exactly. He founded his institute in Copenhagen in 1921 and it became the centre of the field. Heisenberg, Pauli, Gamow, Landau and Dirac worked there. He formulated complementarity: that wave and particle descriptions are both necessary and mutually exclusive, and that the question of what an electron is doing when unobserved has no answer. Einstein spent thirty years constructing objections and Bohr answered each of them, the most famous exchanges at the Solvay conferences. He won the Nobel Prize in 1922. He escaped occupied Denmark in 1943 by fishing boat and nearly died of oxygen deprivation flying to Britain in a bomb bay, then worked at Los Alamos. He pressed Churchill and Roosevelt to share nuclear information with the Soviets to avoid an arms race, and got nowhere. He died in 1962.
- Lived: 1885 CE – 1962 CE
- Nationality: Danish
- Roles: physicist, scientist
