A Short Timeline of Quantum Mechanics, 1900-1962

1900 Johannes Rydberg refines the expression for observed hydrogen line wavelengths.

1900 Max Planck states his quantum hypothesis and blackbody radiation law1902 Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency.

1902 Theodor Svedberg suggests that fluctuations in molecular bombardment cause the Brownian motion.

1905 Albert Einstein explains the photoelectric effect.

1906 Charles Barkla discovers that each element has a characteristic X-ray and that the degree of penetration of these X-rays is related to the atomic weight of the element

1909 Hans Geiger and Ernest Marsden discover large angle deflections of alpha particles by thin metal foils

1909 Ernest Rutherford and Thomas Royds demonstrate that alpha particles are doubly ionized helium atoms

1911 Ernest Rutherford explains the Geiger-Marsden experiment by invoking a nuclear atom model and derives the Rutherford cross section

1911 Jean Perrin proves the existence of atoms and molecules

1912 Max von Laue suggests using crystal lattices to diffract X-rays

1912 Walter Friedrich and Paul Knipping diffract X-rays in zinc blende

1913 William Henry Bragg and William Lawrence Bragg work out the Bragg condition for strong X-ray reflection

1913 Henry Moseley shows that nuclear charge is the real basis for numbering the elements

1913 Niels Bohr presents his quantum model of the atom

1913 Robert Millikan measures the fundamental unit of electric charge

1913 Johannes Stark demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen

1914 James Franck and Gustav Hertz observe atomic excitation

1914 Ernest Rutherford suggests that the positively charged atomic nucleus contains protons

1915 Arnold Sommerfeld develops a modified Bohr atomic model with elliptic orbits to explain relativistic fine structure

1916 Gilbert N. Lewis and Irving Langmuir formulate an electron shell model of chemical bonding

1917 Albert Einstein introduces the idea of stimulated radiation emission

1921 Alfred Landé introduces the Landé g-factor

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1922 Arthur Compton studies X-ray photon scattering by electrons

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1922 Otto Stern and Walther Gerlach show "space quantization"

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1923 Louis de Broglie suggests that electrons may have wavelike properties

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1923 Lise Meitner discovers the Auger process

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1924 John Lennard-Jones proposes a semiempirical interatomic force law

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1924 Satyendra Bose and Albert Einstein introduce Bose-Einstein statistics

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1925 Wolfgang Pauli states the quantum exclusion principle

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1925 George Uhlenbeck and Samuel Goudsmit postulate electron spin

1925 Pierre Auger discovers the Auger process (2 years after Lise Meitner)

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1925 Werner Heisenberg, Max Born, and Pascual Jordan formulate quantum matrix mechanics

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1926 Erwin Schrödinger states his nonrelativistic quantum wave equation and formulates quantum wave mechanics

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1926 Erwin Schrödinger proves that the wave and matrix formulations of quantum theory are mathematically equivalent

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1926 Oskar Klein and Walter Gordon state their relativistic quantum wave equation, now the Klein-Gordon equation

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1926 Enrico Fermi discovers the spin-statistics connection

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1926 Paul Dirac introduces Fermi-Dirac statistics

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1927 Clinton Davisson, Lester Germer, and George Paget Thomson confirm the wavelike nature of electrons

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1927 Werner Heisenberg states the quantum uncertainty principle

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1927 Max Born interprets the probabilistic nature of wavefunctions

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1927 Walter Heitler and Fritz London introduce the concepts of valence bond theory and apply it to the hydrogen molecule.

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1927 Thomas and Fermi develop the Thomas-Fermi model

1927 Max Born and Robert Oppenheimer introduce the Born-Oppenheimer approximation

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1928 Chandrasekhara Raman studies optical photon scattering by electrons

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1928 Paul Dirac states his relativistic electron quantum wave equation

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1928 Charles G. Darwin and Walter Gordon solve the Dirac equation for a Coulomb potential

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1928 Friedrich Hund and Robert S. Mulliken introduce the concept of molecular orbital

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1929 Oskar Klein discovers the Klein paradox

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1929 Oskar Klein and Yoshio Nishina derive the Klein-Nishina cross section for high energy photon scattering by electrons

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1929 Nevill Mott derives the Mott cross section for the Coulomb scattering of relativistic electrons

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1930 Paul Dirac introduces electron hole theory

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1930 Erwin Schrödinger predicts the zitterbewegung motion

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1930 Fritz London explains van der Waals forces as due to the interacting fluctuating dipole moments between molecules

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1931 John Lennard-Jones proposes the Lennard-Jones interatomic potential

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1931 Irene Joliot-Curie and Frédéric Joliot observe but misinterpret neutron scattering in paraffin

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1931 Wolfgang Pauli puts forth the neutrino hypothesis to explain the apparent violation of energy conservation in beta decay

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1931 Linus Pauling discovers resonance bonding and uses it to explain the high stability of symmetric planar molecules

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1931 Paul Dirac shows that charge conservation can be explained if magnetic monopoles exist

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1931 Harold Urey discovers deuterium using evaporation concentration techniques and spectroscopy

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1932 John Cockcroft and Ernest Walton split lithium and boron nuclei using proton bombardment

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1932 James Chadwick discovers the neutron

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1932 Werner Heisenberg presents the proton-neutron model of the nucleus and uses it to explain isotopes

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1932 Carl D. Anderson discovers the positron

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1933 Ernst Stueckelberg (1932), Lev Davidovich Landau (1932), and Clarence Zener discover the Landau-Zener transition

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1933 Max Delbruck suggests that quantum effects will cause photons to be scattered by an external electric field

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1934 Irene Joliot-Curie and Frédéric Joliot bombard aluminum atoms with alpha particles to create artificially radioactive phosphorus-30

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1934 Leó Szilárd realizes that nuclear chain reactions may be possible

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1934 Enrico Fermi formulates his theory of beta decay

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1934 Lev Davidovich Landau tells Edward Teller that nonlinear molecules may have vibrational modes which remove the degeneracy of an orbitally degenerate state (Jahn-Teller effect)

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1934 Enrico Fermi suggests bombarding uranium atoms with neutrons to make a 93 proton element

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1934 Pavel Alekseyevich Cherenkov reports that light is emitted by relativistic particles traveling in a nonscintillating liquid

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1935 Hideki Yukawa presents a theory of strong interactions and predicts mesons

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1935 Albert Einstein, Boris Podolsky, and Nathan Rosen put forth the EPR paradox

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1935 Henry Eyring develop the transition state theory

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1935 Niels Bohr presents his analysis of the EPR paradox

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1936 Eugene Wigner develops the theory of neutron absorption by atomic nuclei

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1936 Hans Jahn and Edward Teller present their systematic study of the symmetry types for which the Jahn-Teller effect is expected

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1937 Hans Hellmann finds the Hellmann-Feynman theorem

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1937 Seth Neddermeyer, Carl Anderson, J.C. Street, and E.C. Stevenson discover muons using cloud chamber measurements of cosmic rays

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1939 Richard Feynman finds the Hellmann-Feynman theorem

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1939 Otto Hahn and Fritz Strassmann bombard uranium salts with thermal neutrons and discover barium among the reaction products

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1939 Lise Meitner and Otto Robert Frisch determine that nuclear fission is taking place in the Hahn-Strassmann experiments

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1942 Enrico Fermi makes the first controlled nuclear chain reaction

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1942 Ernst Stueckelberg introduces the propagator to positron theory and interprets positrons as negative energy electrons moving backwards through spacetime

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1943 Sin-Itiro Tomonaga publishes his paper on the basic physical principles of quantum electrodynamics

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1947 Willis Lamb and Robert Retheford measure the Lamb-Retheford shift

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1947 Cecil Powell, César Lattes, and Giuseppe Occhialini discover the pi-meson by studying cosmic ray tracks

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1947 Richard Feynman presents his propagator approach to quantum electrodynamics

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1948 Hendrik Casimir predicts a rudimentary attractive Casimir force on a parallel plate capacitor

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1951 Martin Deutsch discovers positronium

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1952 David Bohm propose his interpretation of quantum mechanics

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1953 Robert Wilson observes Delbruck scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei

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1954 Chen Ning Yang and Robert Mills investigate a theory of hadronic isospin by demanding local gauge invariance under isotopic spin space rotations---first non-Abelian gauge theory

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1955 Owen Chamberlain, Emilio Segrè, Clyde Wiegand, and Thomas Ypsilantis discover the antiproton

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1956 Frederick Reines and Clyde Cowan detect antineutrino

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1956 Chen Ning Yang and Tsung Lee propose parity violation by the weak nuclear force

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1956 Chien Shiung Wu discovers parity violation by the weak force in decaying cobalt

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1957 Gerhart Luders proves the CPT theorem

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1957 Richard Feynman, Murray Gell-Mann, Robert Marshak, and Ennackel Sudarshan propose a vector/axial vector (VA) Lagrangian for weak interactions

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1958 Marcus Sparnaay experimentally confirms the Casimir effect

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1959 Yakir Aharonov and David Bohm predict the Aharonov-Bohm effect

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1960 R.G. Chambers experimentally confirms the Aharonov-Bohm effect

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1961 Murray Gell-Mann and Yuval Ne'eman discover the Eightfold Way patterns---SU(3) group

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1961 Jeffrey Goldstone considers the breaking of global phase symmetry

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1962 Leon Lederman shows that the electron neutrino is distinct from the muon neutrino

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