- Focus on Physics

Physics Timeline 1921 – 1940

Dates Characters Theories and discoveries
1921 Theodor Kaluza Unification of electromagnetics and gravity by introducing an extra dimension
1921 Bieler and Chadwick Evidence for a strong nuclear interaction
1921 Stern and Gerlach Measurement of atomic magnetic moments
1921 Walter G. Cady Quartz crystal clock
1921 Charles Bury Electronic structure of elements from their chemistry
1922 Cornelius Lanczos Transformation of De Sitter universe to an expanding form
1922 Alexsandr Friedmann A model of an expanding/oscillating universe with matter included
1923 Compton and Debye Theory of Compton effect
1923 Arthur Compton Verification of Compton effect confirms photon as particle
1923 Louis de Broglie Predicts wave nature of particles
1923 Davisson & Kunsman Electron diffraction
1923 Coster and von Hevesy Element 72, hafnium
1923 Herman Weyl, De Sitter Universe would predict a linear relation between distance and red-shift
1924 Edwin Hubble Measured the distance to other galaxies using Cepheid variables proving that they lie outside our own
1924 Edward Appleton Ionosphere
1924 Satyendra Bose Derivation of Planck’s law
1924 Bose and Einstein Statistics of photons and Bose-Einstein condensate
1924 Albert Einstein Statistical physics of quantum boson molecular gas
1924 Wolfgang Pauli Explanation of Zeeman effect and two-valuedness of electron state
1924 Wolfgang Pauli The exclusion principle
1924 Ludwik Siberstein Claims a redshift law for nebulae
1925 Walter Elsasser Explanation of electron diffraction as wave property of matter
1925 Vesto Melvin Slipher Red-shifts of galaxies suggest a distance/velocity relationship
1925 Robert Millikan Rediscovery of “cosmic rays” in upper atmosphere
1925 Noddack, Tacke, Berg Element 75, rhenium
1925 Werner Heisenberg Transition amplitude theory of quantum mechanics
1925 Born and Jordan Matrix interpretation of Heisenberg’s quantum mechanics
1925 Paul Dirac Q-number theory of general quantum mechanics
1925 Pascual Jordan Second quantisation
1925 Goudsmit and Uhlenbeck Electron spin
1925 Enrico Fermi Statistics of electrons
1926 Gilbert Lewis First use of the term photon
1926 Oskar Klein Kaluza-Klein theory
1926 Wolfgang Pauli Derivation of spectrum of hydrogen atom by matrix methods
1926 Erwin Schroedinger The particle wave equation
1926 Erwin Schroedinger Derivation of spectrum of hydrogen atom using the wave equation
1926 Eckart, Pauli, Schroedinger Equivalence of wave equation and matrix mechanics
1926 Max Born Probability interpretation of wave function
1926 Albert Einstein “God does not play dice”
1926 Paul Dirac Distinction between bosons and fermions, symmetry and anti-symmetry of wave function
1926 Dirac, Jordan Canonical transformation theory for quantum mechanics
1926 Klein, Fock & Gordon Relativistic wave equation for scalar particles
1926 Ralph Fowler Suggests that white dwarf stars are explained by the exclusion principle
1926 Born, Heisenberg, Jordan Model of a quantised field
1926 Wolfgang Pauli Momentum and position cannot be known simultaneously
1926 Werner Heisenberg The uncertainty principle
1927 Davisson, Germer, Thomson Verification of electron diffraction by a crystal
1927 Jan Oort Observation of galactic rotation and spiral shape of our galaxy
1927 Niels Bohr Principle of complementarity
1927 Paul Dirac Quantisation of electromagnetic field, bosonic creation and anihilation operators, virtual particles, zero point energy
1927 Eugene Wigner Conservation of parity
1927 Friedrich Hund Quantum tunneling
1927 Heitler and London Quantum theory can explain chemical bonding
1927 Fritz London Electromagnetic guage is phase of Schroedinger equation
1927 Georges Lemaitre Models of an expanding universe
1927 Niels Bohr Copenhagen interpretation of Quantum Mechanics
1928 Condon, Gamow, Gurney Alpha emission is due to quantum tunnelling
1928 Paul Dirac Relativistic equation of the spin-half electron
1928 Willem Keeson Phase transition in liquid Helium
1928 Jordan, Pauli Quantum field theory of free fields
1928 Rolf Wideroe First prototype high energy accelerator
1928 Heisenberg, Weyl Group representation theory in quantum mechanics
1929 Ernest Lawrence Cyclotron
1929 Robert van de Graaff Van de Graaff generator
1929 Heisenberg, Pauli Interacting quantum field theory and divergences
1929 J. Robert Oppenheimer Divergence of electron self-energy
1929 Paul Dirac Electron sea and hole theory
1929 Edwin Hubble First measurement of Hubble’s constant leading to the conclusion that the Universe is expanding
1929 Bothe, Kolhorster Cosmic rays are charged particles
1930 Clyde Tombaugh Pluto discovered
1930 Becker, Bothe Observed neutral rays later identified as neutrons
1930 Paul Dirac Systematic canonical quantisation
1930 Arthur Eddington Einstein’s static universe is unstable
1930 Hartree and Fock Multi-particle quantum mechanics
1931 Dirac, Oppenheimer, Weyl Prediction of anti-matter
1931 Albert Einstein Discard cosmological constant, oscillating cosmology
1931 Georges Lemaitre The primeval atom as origin of the universe
1931 Isidor Rabi Principle of population inversion
1931 Wolfgang Pauli Neutrino as explanation for missing energy and spin in weak nuclear decay
1931 Eugene Wigner Symmetry in quantum mechanics
1931 Paul Dirac Magnetic monopoles can explain quantum of charge
1932 Raman & Bhagavantam Verification that photon is spin one
1932 Einstein, De Sitter Flat expanding cosmology
1932 James Chadwick Identified the neutron
1932 Knoll and Ruska Electron microscope
1932 Carl Anderson Positron from cosmic rays
1932 Cockroft and Walton Linear proton accelerators to 700 keV and verification of mass/energy equivalence
1932 Karl Jansky First radio astronomy
1932 Dmitri Iwanenko Neutron as a constituent of nucleus
1932 Richard Tolman Thermodynamics of oscillating cyclic universe
1932 Vladimir Fock Fock space
1932 Urey, Brickwedde, Murphy, Washburn Deuterium
1932 Werner Heisenberg Nucleus is composed of protons and neutrons
1933 Lev Davidovich Landau Proposed existence of neutron stars
1933 Paul Ehrenfest Theory of second order phase transitions
1933 Blackett and Occhialini Electron-positron creation and annihilation
1933 Esterman, Frisch, Stern Measurement of proton magnetic moment
1933 Baade and Zwicky Collapse of a white dwarf may set off a supernova and leave a neutron star
1933 Fritz Zwicky Dark matter in galactic clusters
1933 Arthur Milne Cosmological principle of large scale homogeneity
1933 Harlow Shapley Observation of structure in galaxy distribution
1934 Pavel Cherenkov Cherenkov radiation
1934 Chadwick & Goldhaber Precise measurement of neutron mass
1934 Chadwick & Goldhaber Measurement of nuclear force
1934 Francis Perrin Neutrino is massless
1934 Grote Reber Discrete radio source in Cygnus
1934 Joliot and Curie Induced radioactivity
1934 Enrico Fermi Fermi theory of weak interaction and beta decay
1934 Esterman and Stern Magnetic moment of neutron
1934 Fermi and Hahn Fission observed
1934 Paul Dirac Polarisation of the vacuum and more divergence in QED
1935 Yukawa, Stueckelberg Theory of strong nuclear force and the pi-meson
1935 J. Robert Oppenheimer Spin statistics
1935 Enrico Fermi Hypothesis of transuranic elements
1935 Robertson, Walker Most general homogenious isotropic universe
1935 Einstein, Podolsky, Rosen EPR Paradox of non-locality in quantum mechanics
1935 Subrahmanyan Chandrasekhar Calculation of mass limit for stellar collapse of a white dwarf star
1935 Erwin Schroedinger Quantum cat paradox
1935 Robert Watson-Watt Radar
1935 Niels Bohr Compound nucleus
1935 Anderson and Neddermeyer Muon in cosmic rays
1935 Leon Brillouin Theory of wave guides
1936 Breit and Coll Isotopic spin
1936 Alan Turing Computability
1937 Pyotr Kapitza Superfluidity of helium II
1937 Perrier and Segre Element 37, technetium, first element made artifically
1937 Majorana Symmetric theory of electron and positron
1937 Julian Schwinger Neutron spin is half
1937 Blau, Wambacher Photographic emulsion as particle detector
1937 Bloch and Nordsieck Operator normal ordering
1937 John Wheeler S-matrix theory
1938 Oppenheimer & Serber There is an upper mass limit for stability of neutron stars
1938 Bethe, Critchfield, von Weizsacker Stars are powered by nuclear fusion CN-cycle
1938 Isador Rabi Magnetic Resonance
1938 Hahn, Strassman Fission induced with neutrons
1938 Oskar Klein New field equations from higher dimensional Kaluza-Klein theory
1938 Fritz Zwicky Clusters of galaxies
1938 Ernest Stueckelberg Suggests baryon number conservation
1938 Hendrick Kramers Mass renormalisation
1938 Frisch and Meitner Theory of uranium fission
1939 Joliot,Curie-Joliot, Szilard Theory of nuclear chain reaction
1939 Oppenheimer & Snyder A collapsing neutron star will form a black hole
1939 Bohr, Wheeler, Khariton, Zel’dovich Theory of U235 fission and chain reaction
1939 Bloch and Alvarez Measurement of the neutron magnetic moment
1939 Rossi, Van Norman, Hilbery Muon decay
1939 Teller, Szilard, Einstein Warning letter to Roosevelt
1939 Peierls and Frisch Critical mass and theory of A-Bomb
1939 Marguerite Perey Element 87, francium
1940 MacMillan, Abelson Element 93, neptunium, first transuranian elements
1940 Corson, MacKenzie, Segre Element 85, astatine synthesised
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