**Chronology of Quantum Mechanics, Molecular, Atomic, Nuclear, and Particle Physics
**

-440 | Democritus speculates about fundamental indivisible particles; calls them "atoms". |

1766 | Henry Cavendish discovers and studies hydrogen. |

1778 | Carl Scheele and Antoine Lavoisier discover that air is composed mostly of nitrogen and oxygen. |

1781 | Joseph Priestly creates water by igniting hydrogen and oxygen. |

1800 | William Nicholson and Anthony Carlisle use electrolysis to separate water into hydrogen and oxygen. |

1803 | John Dalton introduces atomic ideas into chemistry and states that matter is composed of atoms of different weights. |

1811 | Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules. |

1832 | Michael Faraday states his laws of electrolysis. |

1871 | Dmitri Mendeleyev systematically examines the periodic table and predicts the existence of gallium, scandium, and germanium. |

1873 | Johannes van der Waals introduces the idea of weak attractive forces between molecules. |

1885 | Johann Balmer finds a mathematical expression for observed hydrogen line wavelengths. |

1887 | Heinrich Hertz discovers the photoelectric effect. |

1894 | Lord Rayleigh and William Ramsay discover argon by spectroscopically analyzing the gas left over after nitrogen and oxygen are removed from air. |

1895 | William Ramsay discovers terrestrial helium by spectroscopically analyzing gas produced by decaying uranium. |

1896 | Antoine Becquerel discovers the radioactivity of uranium. |

1896 | Pieter Zeeman studies the splitting of sodium D lines when sodium is held in a flame between strong magnetic poles. |

1897 | Joseph Thomson discovers the electron. |

1898 | William Ramsay and Morris Travers discover neon, krypton, and xenon. |

1898 | Marie Curie and Pierre Curie isolate and study radium and polonium. |

1899 | Ernest Rutherford discovers that uranium radiation is composed of positively charged alpha particles and negatively charged beta particles. |

1900 | Paul Villard discovers gamma-rays while studying uranium decay. |

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

1900 | Max Planck states his quantum hypothesis and blackbody radiation law. |

1902 | 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. |

1912 | Max von Laue suggests using lattice solids to diffract X-rays. |

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

1913 | William Bragg and 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 Lewis and Irving Langmuir formulate an electron shell model of chemical bonding. |

1917 | Albert Einstein introduces the idea of stimulated radiation emission. |

1921 | Alfred Lande introduces the Lande g-factor. |

1922 | Arthur Compton studies X-ray photon scattering by electrons. |

1922 | Otto Stern and Walter Gerlach show "space quantization". |

1923 | Louis de Broglie suggests that electrons may have wavelike properties. |

1924 | Wolfgang Pauli states the quantum exclusion principle. |

1924 | John Lennard-Jones proposes a semiempirical interatomic force law. |

1924 | Satyendra Bose and Albert Einstein introduce Bose-Einstein statistics. |

1925 | George Uhlenbeck and Samuel Goudsmit postulate electron spin. |

1925 | Pierre Auger discovers the Auger autoionization process. |

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

1926 | Erwin Schrodinger states his nonrelativistic quantum wave equation and formulates quantum wave mechanics. |

1926 | Erwin Schrodinger proves that the wave and matrix formulations of quantum theory are mathematically equivalent. |

1926 | Oskar Klein and Walter Gordon state their relativistic quantum wave equation. |

1926 | Enrico Fermi discovers the spin-statistics connection. |

1926 | Paul Dirac introduces Fermi-Dirac statistics. |

1927 | Clinton Davission, Lester Germer, and George Thomson confirm the wavelike nature of electrons. |

1927 | Werner Heisenberg states the quantum uncertainty principle. |

1927 | Max Born interprets the probabilistic nature of wavefunctions. |

1928 | Chandrasekhara Raman studies optical photon scattering by electrons. |

1928 | Paul Dirac states his relativistic electron quantum wave equation. |

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

1929 | Oskar Klein discovers the Klein paradox. |

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

1929 | N.F. Mott derives the Mott cross section for the Coulomb scattering of relativistic electrons. |

1930 | Paul Dirac introduces electron hole theory. |

1930 | Erwin Schrodinger predicts the zitterbewegung motion. |

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

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

1931 | Irene Joliot-Curie and Frederic Joliot-Curie observe but misinterpret neutron scattering in parafin. |

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

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

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

1931 | Harold Urey discovers deuterium using evaporation concentration techniques and spectroscopy. |

1932 | John Cockcroft and Thomas Walton split lithium and boron nuclei using proton bombardment. |

1932 | James Chadwick discovers the neutron. |

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

1932 | Carl David Anderson discovers the positron. |

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

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

1934 | Leo Szilard realizes that nuclear chain reactions may be possible. |

1934 | Enrico Fermi formulates his theory of beta decay. |

1934 | Lev Landau tells Edward Teller that nonlinear molecules may have vibrational modes which remove the degeneracy of an orbitally degenerate state. |

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

1934 | Pavel Cerenkov reports that light is emitted by relativistic particles traveling in a nonscintillating liquid. |

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

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

1935 | Niels Bohr presents his analysis of the EPR paradox. |

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

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

1937 | H. Hellmann finds the Hellmann-Feynman theorem. |

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

1939 | Richard Feynman finds the Hellmann-Feynman theorem. |

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

1939 | Lise Meitner and Otto Frisch determine that nuclear fission is taking place in the Hahn-Strassman experiments. |

1942 | Enrico Fermi makes the first controlled nuclear chain reaction. |

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

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

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

1947 | Cecil Powell, C.M.G. Lattes, and G.P.S. Occhialini discover the pi-meson by studying cosmic ray tracks. |

1947 | Richard Feynman presents his propagator approach to quantum electrodynamics. |

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

1951 | Martin Deutsch discovers positronium. |

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

1954 | Chen 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. |

1955 | Owen Chamberlain, Emilio Segre, Clyde Wiegand, and Thomas Ypsilantis discover the antiproton. |

1956 | Frederick Reines and Clyde Cowan detect antineutrinos. |

1956 | Chen Yang and Tsung Lee propose parity violation by the weak force. |

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

1957 | Gerhart Luders proves the CPT theorem. |

1957 | Richard Feynman, Murray Gell-Mann, Robert Marshak, and Ennackel Sudarshan propose a V-A Lagrangian for weak interactions. |

1958 | Marcus Sparnaay experimentally confirms the Casimir effect. |

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

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

1961 | Murray Gell-Mann and Yuval Neeman discover the Eightfold Way patterns; SU(3) group. |

1961 | Jeffery Goldstone considers the breaking of global phase symmetry. |

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

1963 | Murray Gell-Mann and George Zweig propose the quark/aces model. |

1964 | Peter Higgs considers the breaking of local phase symmetry. |

1964 | J.S. Bell shows that all local hidden variable theories must satisfy Bell's inequality. |

1964 | Val Fitch and James Cronin observe CP violation by the weak force in the decay of K mesons. |

1967 | Steven Weinberg puts forth his electroweak model of leptons. |

1969 | J.C. Clauser, M. Horne, A. Shimony, and R. Holt propose a polarization correlation test of Bell's inequality. |

1970 | Sheldon Glashow, John Iliopoulos, and Luciano Maiani propose the charm quark. |

1971 | Gerard 't Hooft shows that the Glashow-Salam-Weinberg electroweak model can be renormalized. |

1972 | S. Freedman and J.C. Clauser perform the first polarization correlation test of Bell's inequality. |

1973 | David Politzer proposes the asymptotic freedom of quarks. |

1974 | Burton Richter and Samuel Ting discover the psi meson implying the existence of the charm quark. |

1975 | Martin Perl discovers the tauon. |

1977 | S.W. Herb finds the upsilon resonance implying the existence of the beauty quark. |

1982 | A. Aspect, J. Dalibard, and G. Roger perform a polarization correlation test of Bell's inequality that rules out conspiratorial polarizer communication. |

1983 | Carlo Rubbia, Simon van der Meer, and the CERN UA-1 collaboration find the W$^\pm$ and Z$^0$ intermediate vector bosons. |

1989 | The Z$^0$ intermediate vector boson resonance width indicates three quark-lepton generations. |