Glossary / History of physics
Old quantum theory
The theories of roughly 1900 to 1925, from Planck onwards, that explained phenomena by adding quantum conditions on top of classical physics.
Planck's energy quanta, Einstein's light quanta, Bohr's atomic model and Sommerfeld's extensions are its landmarks. It was astonishingly accurate for hydrogen's spectrum and fine structure, but helium, with two electrons, and the anomalous Zeeman effect could not be explained however it was patched.
In 1925 Heisenberg dropped unobservable orbits and rebuilt the theory from measurable quantities alone in matrix mechanics[1]; together with Schrödinger's wave mechanics the next year, quantum mechanics replaced it.
Related terms
- Bohr modelThe 1913 model in which electrons circle only on certain orbits and emit light of definite energy when jumping between them.
- Fine structureThe splitting of what looks like a single line in an atom's spectrum into several closely spaced lines when examined in detail.
- Correspondence principleThe principle that quantum results must agree with classical physics in the limit of large quantum numbers — large objects and high energies.