Timeline of Atomic and Subatomic Physics - The Age of Quantum Mechanics

The Age of Quantum Mechanics

• 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.
• 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
• 1911 Jean Perrin proves the existence of atoms and molecules
• 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 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
• 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 the Auger process
• 1924 Louis de Broglie suggests that electrons may have wavelike properties in addition to their 'particle' propereties; the wave-particle duality has been later extended to all fermions and bosons.
• 1924 John Lennard-Jones proposes a semiempirical interatomic force law
• 1924 Satyendra Bose and Albert Einstein introduce Bose-Einstein statistics
• 1925 Wolfgang Pauli states the quantum exclusion principle for fermions
• 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
• 1926 Erwin Schrödinger states his nonrelativistic quantum wave equation and formulates quantum wave mechanics
• 1926 Erwin Schrödinger 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, now the Klein-Gordon equation
• 1926 Enrico Fermi discovers the spin-statistics connection, for particles that are now called 'fermions', such as the electron (of spin 1/2).
• 1926 Paul Dirac introduces Fermi-Dirac statistics
• 1926 Gilbert N. Lewis introduces the term "photon", thought by him to be "the carrier of radiant energy."
• 1927 Clinton Davisson, Lester Germer, and George Paget Thomson confirm the wavelike nature of electrons
• 1927 Werner Heisenberg states the quantum uncertainty principle
• 1927 Max Born interprets the probabilistic nature of wavefunctions
• 1927 Walter Heitler and Fritz London introduce the concepts of valence bond theory and apply it to the hydrogen molecule.
• 1927 Thomas and Fermi develop the Thomas-Fermi model
• 1927 Max Born and Robert Oppenheimer introduce the Born-Oppenheimer approximation
• 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
• 1928 Friedrich Hund and Robert S. Mulliken introduce the concept of molecular orbital
• 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
• 1929 Nevill Mott derives the Mott cross section for the Coulomb scattering of relativistic electrons
• 1930 Paul Dirac introduces electron hole theory
• 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
• 1931 John Lennard-Jones proposes the Lennard-Jones interatomic potential
• 1931 Irène Joliot-Curie and Frédéric Joliot observe but misinterpret neutron scattering in paraffin
• 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 quantization can be explained if magnetic monopoles exist
• 1931 Harold Urey discovers deuterium using evaporation concentration techniques and spectroscopy
• 1932 John Cockcroft and Ernest 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 D. Anderson discovers the positron
• 1933 Ernst Stueckelberg (1932), Lev Davidovich Landau (1932), and Clarence Zener discover the Landau-Zener transition
• 1933 Max Delbruck suggests that quantum effects will cause photons to be scattered by an external electric field
• 1934 Irène Joliot-Curie and Frédéric Joliot bombard aluminum atoms with alpha particles to create artificially radioactive phosphorus-30
• 1934 Leó Szilárd realizes that nuclear chain reactions may be possible
• 1934 Enrico Fermi publishes a very successful model of beta decay in which neutrinos were produced.
• 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)
• 1934 Enrico Fermi suggests bombarding uranium atoms with neutrons to make a 93 proton element
• 1934 Pavel Alekseyevich Cherenkov reports that light is emitted by relativistic particles traveling in a nonscintillating liquid
• 1935 Hideki Yukawa presents a theory of strong interactions and predicts the scalar, pi-mesons
• 1935 Albert Einstein, Boris Podolsky, and Nathan Rosen put forth the EPR paradox
• 1935 Henry Eyring develop the transition state theory
• 1935 Niels Bohr presents his analysis of the EPR paradox
• 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
• 1936 Hermann Arthur Jahn and Edward Teller present their systematic study of the symmetry types for which the Jahn-Teller effect is expected
• 1937 Carl Anderson proves experimentally the existence of the pion predicted by Yukawa's theory.
• 1937 Hans 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 Strassmann bombard uranium salts with thermal neutrons and discover barium among the reaction products
• 1939 Lise Meitner and Otto Robert Frisch determine that nuclear fission is taking place in the Hahn-Strassmann experiments
• 1942 Enrico Fermi makes the first controlled nuclear chain reaction
• 1942 Ernst Stueckelberg 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, César Lattes, and Giuseppe 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
• 1952 David Bohm propose his interpretation of quantum mechanics
• 1953 Robert Wilson observes Delbruck scattering of 1.33 MeV gamma-rays by the electric fields of lead nuclei
• 1953 Charles H. Townes,collaborating with J. P. Gordon, and H. J. Zeiger builds the first ammonia maser
• 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
• 1955 Owen Chamberlain, Emilio Segrè, Clyde Wiegand, and Thomas Ypsilantis discover the antiproton
• 1956 Frederick Reines and Clyde Cowan detect antineutrino
• 1956 Chen Ning Yang and Tsung Lee propose parity violation by the weak nuclear 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 E.C.G. Sudarshan propose a vector/axial vector (VA) 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 Ne'eman discover the Eightfold Way patterns---SU(3) group
• 1961 Jeffrey Goldstone considers the breaking of global phase symmetry
• 1962 Leon Lederman shows that the electron neutrino is distinct from the muon neutrino
• 1963 Eugene Wigner discovers the fundamental roles played by quantum symmetries in atoms and molecules