A timeline of atomic and subatomic physics, including particle physics.
Antiquity 430 BCE Democritus speculates about fundamental indivisible particles—calls them "atoms" 2nd Century BCE Kanada (philosopher) proposes that anu is an indestructible particle of matter, an "atom"; anu is an abstraction and not observable.
Beginnings of chemistry
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 Priestley 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 1805 (approximate time) Thomas Young conducts the double-slit experiment with light 1811 Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules 1815 William Prout hypothesizes that all matter is built up from hydrogen, adumbrating the proton; 1832 Michael Faraday states his laws of electrolysis 1838 Richard Laming hypothesized a subatomic particle carrying electric charge; 1839 Alexandre Edmond Becquerel discovered the photovoltaic effect 1858 Julius Plücker produced cathode rays; 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 1874 George Johnstone Stoney hypothesizes a minimum unit of electric charge. In 1891, he coins the word electron for it; 1885 Johann Balmer finds a mathematical expression for observed hydrogen line wavelengths 1886 Eugen Goldstein produced anode rays; 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 Henri 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 J. J. Thomson discovered the electron; 1897 Emil Wiechert, Walter Kaufmann and J.J. Thomson discover the electron 1898 Marie and Pierre Curie discovered the existence of the radioactive elements radium and polonium in their research of pitchblende 1898 William Ramsay and Morris Travers discover neon, and negatively charged beta particles
Modern physics 1887 Heinrich Rudolf Hertz discovers the photoelectric effect that will play a very important role in the development of the quantum theory with Einstein's explanation of this effect in terms of quanta of light 1896 Wilhelm Conrad Röntgen discovers the X-rays while studying electrons in plasma; scattering X-rays—that were considered as 'waves' of high-energy electromagnetic radiation—Arthur Compton will be able to demonstrate in 1922 the 'particle' aspect of electromagnetic radiation. 1899 Ernest Rutherford discovered the alpha and beta particles emitted by uranium; 1900 Johannes Rydberg refines the expression for observed hydrogen line wavelengths 1900 Max Planck states his quantum hypothesis and blackbody radiation law 1900 Paul Villard discovers gamma-rays while studying uranium decay 1902 Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency 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 1908-1911 Jean Perrin proves the existence of atoms and molecules with experimental work to test Einstein's theoretical explanation of Brownian motion 1909 Ernest Rutherford and Thomas Royds demonstrate that alpha particles are doubly ionized helium atoms 1909 Hans Geiger and Ernest Marsden discover large angle deflections of alpha particles by thin metal foils 1911 Ernest Rutherford explains the Geiger–Marsden experiment by invoking a nuclear atom model and derives the Rutherford cross section 1911 Ștefan Procopiu measures the magnetic dipole moment of the electron 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 Max Bodenstein proposed chain reactions 1913 Henry Moseley shows that nuclear charge is the real basis for numbering the elements 1913 Johannes Stark demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen 1913 Niels Bohr presents his quantum model of the atom 1913 Robert Millikan measures the fundamental unit of electric charge 1913 William Henry Bragg and William Lawrence Bragg work out the Bragg condition for strong X-ray reflection 1914 Ernest Rutherford suggests that the positively charged atomic nucleus contains protons 1914 James Franck and Gustav Hertz observe atomic excitation 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 1918 Ernest Rutherford notices that, when alpha particles were shot into nitrogen gas, his scintillation detectors showed the signatures of hydrogen nuclei. 1921 Alfred Landé introduces the Landé g-factor 1922 Arthur Compton studies X-ray photon scattering by electrons demonstrating the 'particle' aspect of electromagnetic radiation. 1922 Otto Stern and Walther Gerlach show "spin quantization" 1923 Lise Meitner discovers what is now referred to as the Auger process 1924 John Lennard-Jones proposes a semiempirical interatomic force law 1924 Louis de Broglie suggests that electrons may have wavelike properties in addition to their 'particle' properties; the wave–particle duality has been later extended to all fermions and bosons. 1924 Santiago Antúnez de Mayolo proposes a neutron. 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 process (2 years after Lise Meitner) 1925 Werner Heisenberg, Max Born, and Pascual Jordan formulate quantum matrix mechanics 1925 Wolfgang Pauli states the quantum exclusion principle for electrons 1926 Enrico Fermi discovers the spin–statistics connection, for particles that are now called 'fermions', such as the electron (of spin-1/2). 1926 Erwin Schrödinger proves that the wave and matrix formulations of quantum theory are mathematically equivalent 1926 Erwin Schrödinger states his nonrelativistic quantum wave equation and formulates quantum wave mechanics 1926 Gilbert N. Lewis introduces the term "photon", thought by him to be "the carrier of radiant energy."Gilbert N. Lewis. Letter to the editor of Nature (Vol. 118, Part 2, 18 December 1926, pp. 874–875).The origin of the word "photon" 1926 Oskar Klein and Walter Gordon state their relativistic quantum wave equation, now the Klein–Gordon equation 1926 Paul Dirac introduces Fermi–Dirac statistics 1927 Charles Drummond Ellis (along with James Chadwick and colleagues) finally establish clearly that the beta decay spectrum is in fact continuous and not discrete, posing a problem that will later be solved by theorizing (and later discovering) the existence of the neutrino. 1927 Clinton Davisson, Lester Germer, and George Paget Thomson confirm the wavelike nature of electronsThe Davisson–Germer experiment, which demonstrates the wave nature of the electron 1927 Thomas and Fermi develop the Thomas–Fermi model 1927 Max Born interprets the probabilistic nature of wavefunctions 1927 Max Born and Robert Oppenheimer introduce the Born–Oppenheimer approximation 1927 Walter Heitler and Fritz London introduce the concepts of valence bond theory and apply it to the hydrogen molecule. 1927 Werner Heisenberg states the quantum uncertainty principle 1928 Chandrasekhara Raman studies optical photon scattering by electrons 1928 Charles G. Darwin and Walter Gordon solve the Dirac equation for a Coulomb potential 1928 Friedrich Hund and Robert S. Mulliken introduce the concept of molecular orbital 1928 Paul Dirac states the Dirac equation 1929 Nevill Mott derives the Mott cross section for the Coulomb scattering of relativistic electrons 1929 Oskar Klein discovers the Klein paradox 1929 Oskar Klein and Yoshio Nishina derive the Klein–Nishina cross section for high energy photon scattering by electrons 1930 Wolfgang Pauli postulated the neutrino to explain the energy spectrum of beta decays; 1930 Erwin Schrödinger predicts the zitterbewegung motion 1930 Fritz London explains van der Waals forces as due to the interacting fluctuating dipole moments between molecules 1930 Paul Dirac introduces electron hole theory 1931 Harold Urey discovers deuterium using evaporation concentration techniques and spectroscopy 1931 Irène Joliot-Curie and Frédéric Joliot observe but misinterpret neutron scattering in paraffin 1931 John Lennard-Jones proposes the Lennard-Jones interatomic potential 1931 Linus Pauling discovers resonance bonding and uses it to explain the high stability of symmetric planar molecules 1931 Paul Dirac shows that charge quantization can be explained if magnetic monopoles exist 1931 Wolfgang Pauli puts forth the neutrino hypothesis to explain the apparent violation of energy conservation in beta decay 1932 Paul Güttinger finds the Hellmann–Feynman theorem 1932 Carl D. Anderson discovers the positron 1932 James Chadwick discovers the neutron 1932 John Cockcroft and Ernest Walton split lithium and boron nuclei using proton bombardment 1932 Werner Heisenberg presents the proton–neutron model of the nucleus and uses it to explain isotopes 1932 Ettore Majorana, Ernst Stueckelberg, Lev Landau, and Clarence Zener independently discover the Landau–Zener transition 1933 Max Delbrück suggests that quantum effects will cause photons to be scattered by an external electric field 1934 Enrico Fermi publishes a very successful model of beta decay in which neutrinos were produced. 1934 Enrico Fermi suggests bombarding uranium atoms with neutrons to make a 93 proton element 1934 Irène Joliot-Curie and Frédéric Joliot bombard aluminium atoms with alpha particles to create artificially radioactive phosphorus-30 1934 Leó Szilárd realizes that nuclear chain reactions may be possible 1934 Lev Landau tells Edward Teller that non-linear molecules may have vibrational modes which remove the degeneracy of an orbitally degenerate state (Jahn–Teller effect) 1934 Pavel Cherenkov reports that light is emitted by relativistic particles traveling in a nonscintillating liquid 1935 Albert Einstein, Boris Podolsky, and Nathan Rosen put forth the EPR paradox 1935 Henry Eyring develops the transition state theory 1935 Hideki Yukawa presents a theory of the nuclear force and predicts the scalar meson 1935 Niels Bohr presents his analysis of the EPR paradox 1936 Carl D. Anderson discovered the muon while he studied cosmic radiation; 1936 Alexandru Proca formulates the relativistic quantum field equations for a massive vector meson of spin-1 as a basis for nuclear forces 1936 Eugene Wigner develops the theory of neutron absorption by atomic nuclei