Early 20th century
 1905  Albert Einstein explained the photoelectric effect.
 1905  Einstein presented the special theory of relativity,
in which the speed of light is independent of the motion of its
source and constant in any inertial frame of reference.
 1913  Neils Bohr's theory of the atom, explains the Balmer,
Rydberg and Ritz formulas of simple spectra.
 1913  Johannes Stark discovered the Stark effect, the splitting
of spectral lines in an electric field.
 1923  Compton explained xray scattering.
 19257  Quantum theory of the atom, developed by many people
including Wolfgang Pauli (exclusion principles), Werner Heisenberg (uncertainty principle),
Erwin Schrödinger (wave equation), Louis de Broglie, Max Born
(wave function as probability), Jordan, and Paul A M Dirac
(relativistic wave equation).
 1928  Neils Bohr proposed the Complementarity Principle.
 1930  Gerlach and Scweitzer introduced the ratio method for
intensities.
 1936  Thanheiser and Heyes used photocells to measure intensities.
 19429  Giulio Racah presented his formulation of the angular components of Schrödinger's equation.
 ~1945  P M Duffieux and R K Luneberg introduced
Fourier methods to optics.
 1947  Willis E Lamb discovered the Lamb shift.
 1947  Dennis Gabor developed holography.
 1948  Sinitiro Tomonaga, Julian S Schwinger and
Richard P Feynman developed quantum electrodynamics
(QED).
 1949  D R Bates and Agnette Damgaard presented
an approximate solution to the radial part of Schrödinger’s equation.
 1950  A Kastler caused population inversion in excited atoms.
First published on the web: 15 December 1999.
