User:Guy vandegrift/Timeline of quantum mechanics (abridged) • 1895 – Wilhelm Conrad Röntgen discovers X-rays in experiments with electron beams in plasma.[1] • 1896 – Antoine Henri Becquerel accidentally dis- covers radioactivity while investigating the work of Wilhelm Conrad Röntgen; he finds that uranium salts emit radiation that resembled Röntgen’s X- rays in their penetrating power, and accidentally dis- covers that the phosphorescent substance potassium uranyl sulfate exposes photographic plates.[1][3] • 1896 – Pieter Zeeman observes the Zeeman split- ting effect by passing the light emitted by hydrogen through a magnetic field. Wikiversity: • 1896–1897 Marie Curie investigates uranium salt First Journal of Science samples using a very sensitive electrometer device that was invented 15 years before by her husband and his brother Jacques Curie to measure electrical Under review. Condensed from Wikipedia’s Timeline of charge. She discovers that the emitted rays make the quantum mechanics at 13:07, 2 September 2015 (oldid surrounding air electrically conductive. [4] 679101670) • 1897 – Ivan Borgman demonstrates that X-rays and This abridged “timeline of quantum mechancis” shows radioactive materials induce thermoluminescence. some of the key steps in the development of quantum me- chanics, quantum field theories and quantum chemistry • 1899 to 1903 – Ernest Rutherford, who later became that occurred before the end of World War II [1][2] known as the “father of nuclear physics",[5] inves- tigates radioactivity and coins the terms alpha and beta rays in 1899 to describe the two distinct types 1 19th century of radiation emitted by thorium and uranium salts. [6] • 1859 – Kirchhoff introduces the concept of a blackbody and proves that its emission spectrum de- pends only on its temperature.[1] 2 20th century • 1860–1900 – Ludwig Eduard Boltzmann produces a 2.1 1900–1909 primitive diagram of a model of an iodine molecule that resembles the orbital diagram. • 1900 – To explain black-body radiation (1862), • 1865 – Maxwell put forth A Dynamical Theory of Max Planck suggests that electromagnetic energy is the Electromagnetic Field, now known as Maxwell’s emitted in quantized form, in multiples of the ele- equations. mentary unit E = hν, where h is Planck’s constant and ν is frequency. • 1887-1888 – Heinrich Hertz discovers the photo- • electric effect, and also demonstrates experimen- 1902 – To explain the octet rule (1893), Gilbert N. tally that electromagnetic waves exist, as predicted Lewis develops the "cubical atom" theory in which by Maxwell.[1] electrons in the form of dots are positioned at the corner of a cube. Predicts that single, double, or • 1888 – Johannes Rydberg modifies the Balmer for- triple "bonds" result when two atoms are held to- mula to include all spectral series of lines for the gether by multiple pairs of electrons between the hydrogen atom, producing the Rydberg formula. atoms. 1 2 2 20TH CENTURY • 1903 – Antoine Becquerel, Pierre Curie and Marie that the spin of the Nitrogen-14 atom was 1, in con- Curie share the 1903 Nobel Prize in Physics for their tradiction to the Rutherford prediction of ½. These work on spontaneous radioactivity. anomalies are later explained by the discoveries of the neutrino and the neutron. • 1904 – Richard Abegg notes the pattern that the nu- merical difference between the maximum positive • 1912 – Victor Hess discovers the existence of valence, such as +6 for H2SO4, and the maximum cosmic radiation. negative valence, such as −2 for H S, of an element 2 • tends to be eight (Abegg’s rule). 1913 – Robert Andrews Millikan publishes the re- sults of his “oil drop” experiment that measures the • 1905 – Albert Einstein explains the photoelectric ef- charge of the electron. This makes it possible to cal- fect. He postulates that light itself consists of indi- culate the Avogadro constant and the atomic weight vidual quantum particles (photons). of the atoms. • 1905 – Einstein explains the effects of Brownian • 1913 – Ștefan Procopiu and Niels Bohr indepen- motion as caused by the kinetic energy (i.e., move- dently obtain the value of the electron’s magnetic ment) of atoms, which was subsequently, experi- dipole moment. mentally verified by Jean Baptiste Perrin, thereby • settling the century-long dispute about the validity 1913 – Johannes Stark and Antonino Lo Surdo in- of John Dalton's atomic theory. dependently discover the shifting and splitting of the spectral lines of atoms and molecules due to an ex- • 1905 – Einstein publishes his Special Theory of Rel- ternal static electric field. ativity. • 1913 – To explain the Rydberg formula (1888), • 1905 – Einstein theoretically derives the equivalence which calculates the emission spectra of atomic hy- of matter and energy. drogen, Bohr hypothesizes that electrons revolve around a positively charged nucleus at certain fixed • 1907 to 1917 – To test his planetary model of “quantum” distances, with specific energies such 1904 [7] he sent a beam of positively charged alpha that transition between orbits requires “quantum” particles onto a gold foil and noticed that some emissions or absorptions of energy. bounced back, thus showing that an atom has a small-sized positively charged atomic nucleus at its • 1914 – James Franck and Gustav Hertz conduct center. However, he received in 1908 the Nobel an experiment on electron collisions with mercury Prize in Chemistry “for his investigations into the atoms, that provides new verification of Bohr’s [9] chemistry of radioactive substances”,[8] which fol- model of quantized atomic energy levels. lowed on the work of Marie Curie, not for his plan- • 1915 – Einstein presents what are now known as the etary model of the atom; he is also widely cred- Einstein field equations, associated with the General ited with first “splitting the atom” in 1917. In 1911 Theory of Relativity. Ernest Rutherford explained the Geiger–Marsden experiment by invoking a nuclear atom model and • 1916 – Paul Epstein[10] and Karl Schwarzschild,[11] derived the Rutherford cross section. working independently, derive equations for the lin- ear and quadratic Stark effect in hydrogen. • 1909 – Geoffrey Ingram Taylor demonstrates that interference patterns of light were generated even • 1916 – To account for the Zeeman effect, Arnold when the light energy introduced consisted of only Sommerfeld suggests electrons in an atom might be one photon. This discovery of the wave–particle du- “elliptical orbits” in addition to “spherical orbits”. ality of matter and energy is fundamental to the later development of quantum field theory. • 1918 – Sir Ernest Rutherford notices that, when alpha particles are shot into nitrogen gas, his • 1909 and 1916 – Einstein shows that, if Planck’s scintillation detectors shows the signatures of law of black-body radiation is accepted, the energy hydrogen nuclei. Rutherford determines that the quanta must also carry momentum p = h / λ. only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggests that the hydro- 2.2 1910–1919 gen nucleus, which is known to have an atomic num- ber of 1, is an elementary particle, which he decides • 1911 – Lise Meitner and Otto Hahn perform an ex- must be the protons hypothesized by Eugen Gold- periment that shows that the energies of electrons stein. emitted by beta decay had a continuous rather than discrete spectrum, in apparent contradiction to the • 1919 – Building on the work of Lewis (1916), Irving law of conservation of energy. A second problem is Langmuir coins the term “covalence” and postulates 2.3 1920–1929 3 that coordinate covalent bonds occur when two elec- are added successively to an atom as many lev- trons of a pair of atoms come from both atoms and els or orbits are singly occupied as possible before are equally shared by them, thus explaining the fun- any pairing of electrons with opposite spin occurs damental nature of chemical bonding and molecular and made the distinction that the inner electrons in chemistry. molecules remained in atomic orbitals and only the valence electrons needed to be in molecular orbitals involving both nuclei. 2.3 1920–1929 • 1925 – Werner Heisenberg, Max Born, and Pascual • 1922 – Arthur Compton finds that X-ray wave- Jordan develops the matrix mechanics formulation lengths increase due to scattering of the radiant en- of Quantum Mechanics.[1] ergy by free electrons. This discovery, known as the Compton effect, demonstrates the particle concept • 1926 – Oskar Klein and Walter Gordon put forth a of electromagnetic radiation. relativistic quantum wave equation now called the Klein–Gordon equation. • 1922 – Otto Stern and Walther Gerlach perform the Stern–Gerlach experiment, which detects dis- • 1926 – Enrico Fermi discovers the spin-statistics crete values of angular momentum for atoms in theorem connection. the ground state passing through an inhomogeneous magnetic field leading to the discovery of the spin of • 1926 – Paul Dirac introduces Fermi–Dirac statistics. the electron. • 1926 – Erwin Schrödinger uses De Broglie’s elec- • 1922 – Bohr updates his model of the atom to bet- tron wave postulate (1924) to develop a "wave equa- ter explain the properties of the periodic table by tion" that represents mathematically the distribution assuming that certain numbers of electrons (for ex- of electron charge density throughout space, and ample 2, 8 and 18) corresponded to stable “closed also introduces the Hamiltonian operator in quan- shells”, presaging orbital theory. tum mechanics. • 1923 – Pierre Auger discovers the Auger effect, • 1926 – Paul Epstein reconsiders the linear and where filling the inner-shell vacancy of an atom is quadratic Stark effect using Schrödinger’s equation. accompanied by the emission of an electron from The derived equations for the line intensities are a the same atom. decided improvement over previous results obtained by Hans Kramers.[12] • 1923 – Louis de Broglie extends wave–particle du- ality to particles, postulating that electrons in mo- • 1927 – Werner Heisenberg formulates the quantum tion are associated with waves.