User:Guy vandegrift/Timeline of quantum mechanics (abridged) • 1859 – Kirchhoff introduces the concept of a blackbody and proves that its emission spectrum de- pends only on its temperature.[1] • 1860–1900 – Ludwig Eduard Boltzmann, James Clerk Maxwell and others develop the theory of statistical mechanics. Boltzmann argues that entropy is a measure of disorder.[1] Boltzmann sug- gests that the energy levels of a physical system could be discrete based on statistical mechanics and mathematical arguments; also produces a primitive diagram of a model of an iodine molecule that re- sembles the orbital diagram. • 18871888 – Heinrich Hertz discovers the photo- Refereed version electric effect, and also demonstrates experimen- tally that electromagnetic waves exist, as predicted by Maxwell.[1] This article is edited from a document extracted from • Wikipedia’s 'Timeline of quantum mechanics at 13:07, 2 1888 – Johannes Rydberg modifies the Balmer for- September 2015 (oldid 679101670) mula to include all spectral series of lines for the hydrogen atom, producing the Rydberg formula. This abridged “timeline of quantum mechancis” shows some of the key steps in the development of quantum me- • 1895 – Wilhelm Conrad Röntgen discovers X-rays chanics, quantum field theories and quantum chemistry in experiments with electron beams in plasma.[1] that occurred before the end of World War II [1][2] • 1896 – Antoine Henri Becquerel accidentally dis- covers radioactivity while investigating the work of Wilhelm Conrad Röntgen; he finds that uranium 1 19th century 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. • 1896–1897 Marie Curie investigates uranium salt samples using a very sensitive electrometer device that was invented 15 years before by her husband and his brother Jacques Curie to measure electrical charge. She discovers that the emitted rays make the surrounding air electrically conductive. Through a systematic search of substances, she finds that thorium compounds, like those of uranium, emit- ted “Becquerel rays”, thus preceding the work of Frederick Soddy and Ernest Rutherford on the nu- Image of Becquerel’s photographic plate which has been fogged clear decay of thorium to radium by three years.[4] by exposure to radiation from a uranium salt. The shadow of a metal Maltese Cross placed between the plate and the uranium • 1897 – Ivan Borgman demonstrates that X-rays and salt is clearly visible. radioactive materials induce thermoluminescence. 1 2 2 20TH CENTURY • 1899 to 1903 – Ernest Rutherford investigates ra- Curie share the 1903 Nobel Prize in Physics for their dioactivity and coins the terms alpha and beta rays work on spontaneous radioactivity. in 1899 to describe the two distinct types of radi- • ation emitted by thorium and uranium salts. With 1904 – Richard Abegg notes the pattern that the nu- Frederick Soddy he discovers nuclear transmutation merical difference between the maximum positive as radioactive thorium is convertd itself into radium valence, such as +6 for H2SO4, and the maximum through a process of nuclear decay and a gas (later negative valence, such as −2 for H2S, of an element found to be 4 tends to be eight (Abegg’s rule). [5] 2He). He also invents the nuclear atom model and • 1905 – Albert Einstein explains the photoelectric ef- [6] becomes known as the “father of nuclear physics" fect. He postulates that light itself consists of indi- vidual quantum particles (photons). 2 20th century • 1905 – Einstein explains the effects of Brownian motion as caused by the kinetic energy (i.e., move- ment) of atoms, which was subsequently, experi- 2.1 1900–1909 mentally verified by Jean Baptiste Perrin, thereby settling the century-long dispute about the validity of John Dalton's atomic theory. • 1905 – Einstein publishes his Special Theory of Rel- ativity. • 1905 – Einstein theoretically derives the equivalence of matter and energy. • 1907 to 1917 – To test his planetary model of 1904 [7] he sent a beam of positively charged alpha particles onto a gold foil and noticed that some bounced back, thus showing that an atom has a small-sized positively charged atomic nucleus at its center. However, he received in 1908 the Nobel Prize in Chemistry “for his investigations into the chemistry of radioactive substances”,[8] which fol- lowed on the work of Marie Curie, not for his plan- etary model of the atom; he is also widely cred- ited with first “splitting the atom” in 1917. In 1911 Ernest Rutherford explained the Geiger–Marsden experiment by invoking a nuclear atom model and derived the Rutherford cross section. • 1909 – Geoffrey Ingram Taylor demonstrates that interference patterns of light were generated even when the light energy introduced consisted of only Einstein, in 1905, when he wrote the Annus Mirabilis papers one photon. This discovery of the wave–particle du- ality of matter and energy is fundamental to the later development of quantum field theory. • 1900 – To explain black-body radiation (1862), • Max Planck suggests that electromagnetic energy is 1909 and 1916 – Einstein shows that, if Planck’s emitted in quantized form, in multiples of the ele- law of black-body radiation is accepted, the energy mentary unit E = hν, where h is Planck’s constant quanta must also carry momentum p = h / λ. and ν is frequency. • 1902 – To explain the octet rule (1893), Gilbert N. 2.2 1910–1919 Lewis develops the "cubical atom" theory in which • electrons in the form of dots are positioned at the 1911 – Lise Meitner and Otto Hahn perform an ex- corner of a cube. Predicts that single, double, or periment that shows that the energies of electrons triple "bonds" result when two atoms are held to- emitted by beta decay had a continuous rather than gether by multiple pairs of electrons between the discrete spectrum, in apparent contradiction to the atoms. law of conservation of energy. A second problem is that the spin of the Nitrogen-14 atom was 1, in con- • 1903 – Antoine Becquerel, Pierre Curie and Marie tradiction to the Rutherford prediction of ½. These 2.3 1920–1929 3 • 1915 – Einstein presents what are now known as the Einstein field equations, associated with the General Theory of Relativity. • 1916 – Paul Epstein[11] and Karl Schwarzschild,[12] working independently, derive equations for the lin- ear and quadratic Stark effect in hydrogen. • 1916 – To account for the Zeeman effect, Arnold Sommerfeld suggests electrons in an atom might be “elliptical orbits” in addition to “spherical orbits”. • 1918 – Sir Ernest Rutherford notices that, when alpha particles are shot into nitrogen gas, his scintillation detectors shows the signatures of A schematic diagram of the apparatus for Millikan’s refined oil hydrogen nuclei. Rutherford determines that the drop experiment. only place this hydrogen could have come from was the nitrogen, and therefore nitrogen must contain hydrogen nuclei. He thus suggests that the hydro- anomalies are later explained by the discoveries of gen nucleus, which is known to have an atomic num- the neutrino and the neutron. ber of 1, is an elementary particle, which he decides • 1911 – Ștefan Procopiu performs experiments in must be the protons hypothesized by Eugen Gold- which he determines the correct value of electron’s stein. magnetic dipole moment. In 1913 he is also calcu- • 1919 – Building on the work of Lewis (1916), Irving lated a theoretical value of the Bohr magneton based Langmuir coins the term “covalence” and postulates on Planck’s quantum theory. that coordinate covalent bonds occur when two elec- • 1912 – Victor Hess discovers the existence of trons of a pair of atoms come from both atoms and cosmic radiation. are equally shared by them, thus explaining the fun- damental nature of chemical bonding and molecular • 1913 – Robert Andrews Millikan publishes the re- chemistry. sults of his “oil drop” experiment that measures the charge of the electron. This makes it possible to cal- culate the Avogadro constant and the atomic weight 2.3 1920–1929 of the atoms. • 1913 – Ștefan Procopiu publishes a theoretical pa- per with the correct value of the electron’s magnetic dipole moment.B.[9] • 1913 – Niels Bohr theoretically obtains the value of the electron’s magnetic dipole moment. • 1913 – Johannes Stark and Antonino Lo Surdo in- dependently discover the shifting and splitting of the spectral lines of atoms and molecules due to an ex- ternal static electric field. • 1913 – To explain the Rydberg formula (1888), which calculates the emission spectra of atomic hy- drogen, Bohr hypothesizes that electrons revolve around a positively charged nucleus at certain fixed A plaque at the University of Frankfurt commemorating the “quantum” distances, with specific energies such Stern–Gerlach experiment. that transition between orbits requires “quantum” emissions or absorptions of energy. • 1922 – Arthur Compton finds that X-ray wave- • 1914 – James Franck and Gustav Hertz conduct lengths increase due to scattering of the radiant en- an experiment on electron collisions with mercury ergy by free electrons. This discovery, known as the atoms, that provides new verification of Bohr’s Compton effect, demonstrates the particle concept model of quantized atomic energy levels.[10] of electromagnetic radiation. 4 2 20TH CENTURY • 1922 – Otto Stern and Walther Gerlach