Physics Timeline 1900 – 1920

Dates Characters Theories and discoveries
1900 Lord Rayleigh Statistical derivation of short wavelength black body law
1900 Ernest Rutherford First determination of a radioactive half-life
1900 Antoine Henri Becquerel Suggests that beta rays are electrons
1900 Lummer, Pringsheim, Rubens, Kurlbaum Failure of Wien’s black body law at short wavelengths
1900 Max Planck Light quanta in black body radiation, Planck’s black body law & constant
1900 Paul Villard Gamma rays
1900 Friedrich Dorn Element 86, radon
1900 Pyotr Lebedev Radiation pressure measured
1901 Max Planck Determination of Planck’s constant, Boltzmann’s constant, Avogadro’s number and the charge on electron
1901 Guglielmo Marconi Transmission of Morse signals across the Atlantic
1902 Philipp Lenard Intensity law in photoelectric effect
1902 Rutherford and Soddy Theory of transmutation by radiation and first use of the term “atomic energy”
1902 Kelvin, Thomson Plum pudding model of the atom
1903 Ernest Rutherford Alpha particles have a positive charge
1903 Curie and Laborde Radioactive energy released by radium is large
1903 Johannes Stark The power of the sun may be due to genesis of chemical elements
1903 Philipp Lenard Model of atom as two separated opposite charges
1904 Albert Einstein Energy-frequency relation of light quanta
1904 Hendrik Lorentz The completed Lorentz transformations
1904 Hantaro Nagaoka Planetary model of the atom
1904 Ambrose Flemming Diode valve and rectifier
1904 Henri Poincare Conjectured light speed as physical limit
1904 Ernest Rutherford Age of Earth by radioactvity dating
1905 Albert Einstein Explains Brownian motion by kinetic theory
1905 Albert Einstein Light-quantum theory for photoelectric law
1905 Albert Einstein Special relativity
1905 Paul Langevin Atomic theory of paramagnetism
1905 Percival Lowell Postulates a ninth planet beyond Neptune
1905 Bragg and Kleeman Alpha-particles have discrete energies
1905 Hermann Nernst Third law of thermodynamics
1905 Albert Einstein Equivalence of mass and energy
1906 Albert Einstein Quantum explanation of specific heat laws for solids
1906 Joseph Thomson Thomson scattering of X-ray photons and number of electrons in an atom
1906 Ernest Rutherford Alpha particles scatter in air
1906 Lee de Forest Triode valve
1907 Albert Einstein Equivalence principle and gravitational redshift
1907 Urbain & von Welsbach Element 71, lutetium
1908 Hermann Minkowski geometric unification of space and time
1908 Hans Geiger Geiger counter for detecting radioactivity
1908 Heike Kammerlingh-Onnes Liquid helium
1908 Geiger, Royds, Rutherford Identify alpha particles as helium nuclei
1909 Albert Einstein Particle-wave duality of photons
1909 Johannes Stark Momentum of photons
1909 Geiger and Marsden Anomolous scattering of alpha particles on gold foil
1909 Robert Millikan Measured the charge on the electron
1910 Albert Einstein Why the sky is blue
1910 Matthew Hunter Isolation of element titanium
1910 Theodor Wulf Excess atmospheric radiation
1911 Victor Hess High altitude radiation from space
1911 Heike Kammerlingh-Onnes Superconductivity
1911 Ernest Rutherford Infers the nucleus from the alpha scattering result
1912 Joseph Thomson Mass spectrometry and separation of isotopes
1912 Henrietta Leavitt Period to luminosity relationship for Cepheid variable stars
1912 Robert Millikan Measurement of Planck’s constant
1912 Peter Debye Derivation of specific heat laws to low temperatures
1912 Charles Wilson Cloud chamber
1912 Max Von Laue X-rays are explained as electromagnetic radiation by diffraction
1912 Albert Einstein Curvature of space-time
1912 Vesto Melvin Slipher Observes blue-shift of andromeda galaxy
1912 Gustav Mie Non-linear field theories
1913 Niels Bohr Quantum theory of atomic orbits
1913 Niels Bohr Radioactivity as nuclear property
1913 Jean-Baptiste Perrin Theory of size of atoms and molecules
1913 Fajans and Gohring Element 91, protactinium
1913 Bragg and Bragg X-ray diffraction and crystal structure
1913 Hans Geiger Relation of atomic number to nuclear charge
1913 Johannes Stark, Splitting of hydrogen spectral lines in electric field
1913 Frederick Soddy The term “isotope”
1914 James Chadwick Primary beta spectrum is continuous and shows an energy anomaly
1914 Harry Moseley Used X-rays to confirm the correspondence between electric charge of nucleus and atomic number
1914 Ejnar Hertzsprung Measured distance to Large Magellanic Cloud using Cepheid variable stars
1914 Rutherford, da Costa Andrade Gamma rays identified as hard photons
1915 Albert Einstein General relativity
1915 David Hilbert Action principle for gravitational field equations
1915 Albert Einstein Prediction of light bending and explanation for perihelion shift of mercury
1916 Robert Millikan Verification of energy law in photoelectric effect
1916 Albert Einstein Prediction of gravitational waves
1916 Albert Einstein Conservation of energy-momentum in general relativity
1916 Karl Schwarzschild Singular static solution of gravitational field equations which describes a minimal black hole
1916 Arnold Sommerfeld Further atomic quantum numbers and fine structure of spectra, fine structure constant
1917 Harlow Shapley Estimates the diameter of the galaxy as 100000 parsecs
1917 Albert Einstein Introduction of the cosmological constant and a steady state model of the universe
1917 Vesto Melvin Slipher Observes that most galaxies have red-shifts
1917 Albert Einstein Theory of stimulated emission and loss of determinism
1917 Willem de Sitter Describes a model of a static universe with no matter
1917 Arthur Eddington Gravitational energy is insufficient to account for the energy output of stars
1917 Rutherford, Marsden Artificial transmutation, hydrogen and oxygen from nitrogen
1918 Harlow Shapley Measured distance to globular clusters using Cepheid variable stars
1918 Harlow Shapley Determined the size and shape of our galaxy
1918 Reissner and Nordstrom Solution of Einstein’s equations which describe a charged black hole
1918 Emmy Noether The mathematical relationships between symmetry and conservation laws in classical physics
1918 Francis Aston Mass spectrometer
1918 Herman Weyl Guage theory
1919 Ernest Rutherford Existence of the proton in nucleus
1919 Oliver Lodge Prediction of gravitational lensing
1919 Francis Aston Hydrogen fusion to helium will release a lot of energy
1919 Crommelin Eddington Verification of Einstein’s prediction of starlight deflection during an eclipse
1919 Arthur Eddington Predicts the size of red gaints using stellar models
1920 Ernest Rutherford Prediction of neutron
1920 Anderson, Michelson Pease, size of star Betelgeuse using stellar interferometry
1920 Harkins, Eddington Fusion of hydrogen could be the energy source of stars
1920 Shapley and Curtis The Great Debate over the scale and structure of the universe

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