**Quantum Theory Timeline, 1490-1989**

1490: Leonardo da Vinci describes capillary action

1581: Galileo Galilei notices the timekeeping property of the pendulum

1589: Galileo Galilei uses balls rolling on inclined planes to show that different weights fall with the same acceleration

1658: Christian Huygens experimentally discovers that balls placed anywhere inside an inverted cycloid reach the lowest point of the cycloid in the same time and thereby experimentally shows that the cycloid is the isochrone

1668: John Wallis suggests the law of conservation of momentum

1690: James Bernoulli shows that the cycloid is the solution to the isochrone problem

1691: Johann Bernoulli shows that the catenary curve has the lowest center of gravity that any chain hung from two fixed points can have

1696: Johann Bernoulli shows that the cycloid is the solution to the brachistochrone problem

1714: Brook Taylor derives the fundamental frequency of a stretched vibrating string in erms of its tension and mass per unit length by solving an ordinary differential equation

1733: Daniel Bernoulli derives the fundamental frequency and harmonics of a hanging chain by solving an ordinary differential equation

1734: Daniel Bernoulli solves the ordinary differental equation for the vibrations of an elastic bar clamped at one end

1739: Leonhard Euler solves the ordinary differential equation for a forced harmonic oscillator and notices the resonance phenomenon

1742: Colin Maclaurin discovers his uniformly rotating self-gravitating spheroids

1747: Pierre-Louis Moreau de Maupertuis applies minimum principles to mechanics

1759: Leonhard Euler solves the partial differential equation for the vibration of a rectangular drum

1764:Leonhard Euler examines the partial differential equation for the vibration of a circular drum and finds one of the Bessel function solutions

1766: Henry Cavendish discovers and studies hydrogen

1778:Carl Scheele and Antoine-Laurent Lavoisier discover that air is composed mostly of nitrogen and oxygen

1781: Joseph Priestley creates water by igniting hydrogen and oxygen

1788: Joseph Lagrange presents Lagrange's equations of motion in MTcanique Analytique

1789: Antoine-Laurent Lavoisier states the law of conservation of mass

1800:m William Nicholson and Anthony Carlisle use electrolysis to separate water into hydrogen and oxygen

1803: John Dalton introduces atomic ideas into chemistry and states that matter is composed of atoms of different weights

1811: Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules

1821:William Hamilton begins his analysis of Hamilton's characteristic function

1832: Michael Faraday states his laws of electrolysis

1834: Carl Jacobi discovers his uniformly rotating self-gravitating ellipsoids

1834: John Russell observes a nondecaying solitary water wave in the Union Canal near Edinburgh and uses a water tank to study the dependence of solitary water wave velocities on wave amplitude and water depth

1835: Gaspard de Coriolis examines motion on a spinning surface deduces the Coriolis effect

1835:William Hamilton states Hamilton's canonical equations of motion

1842: Christian Doppler examines the Doppler shift of sound

1847: Hermann Helmholtz formally states the law of conservation of energy

1851: Jean-Bernard Foucault shows the Earth's rotation with a huge pendulum

1853: Scattering of electrons off nuclei reveals a charge density distributioinside protons, and even neutrons. Description of this electromagnetic structure of protons and neutrons suggests some kind of internal structure to these objects, though they are still regarded as fundamental particles. (1853 - 1857)

1871: Dmitri Mendeleyev systematically examines the periodic table and predicts the existence of gallium, scandium, and germanium

1873: Johannes van der Waals introduces the idea of weak attractive forces between molecules

1885: Johann Balmer finds a mathematical expression for observed hydrogen line wavelengths

1887: Heinrich Hertz discovers the photoelectric effect

1894: Lord Rayleigh and William Ramsay discover argon by spectroscopically analyzing the gas left over after nitrogen and oxygen.

1895: William Ramsay discovers terrestrial helium by spectroscopically analyzing gas produced by decaying uranium

1896: Antoine Becquerel discovers the radioactivity of uranium

1896: Pieter Zeeman studies the splitting of sodium D lines when sodium is held in a flame between strong magnetic poles

1897: Joseph Thomson discovers the electron

1898: William Ramsay and Morris Travers discover neon, krypton, and xenon

1898: Marie Curie and Pierre Curie isolate and study radium and polonium

1899: Ernest Rutherford discovers that uranium radiation is composed of positively charged alpha particles and negatively charged beta particles

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: Theodor Svedberg suggests that fluctuations in molecular bombardment cause the Brownian motion

1902: Philipp Lenard observes that maximum photoelectron energies are independent of illuminating intensity but depend on frequency

1902: James Jeans finds the length scale required for gravitational pertrubatations to grow in a static nearly homogeneous medium

1905: Albert Einstein, one of the few scientists to take Planck's ideas seriously, proposes a quantum of light (the photon) which behaves like a particle. Einstein's other theories explained the equivalence of mass and energy, the particle-wave duality of photons, the equivalence principle, and special relativity.

1905: Albert Einstein, light-quantum theory for photoelectric law

1905: Albert Einstein explains the photoelectric effect

1905: Albert Einstein, one of the few scientists to take Planck's ideas seriously,

proposes a quantum of light (the photon) which behaves like a particle. Einstein's

other theories explained the equivalence of mass and energy, the particle-wave

duality of photons, the equivalence principle, and special relativity.

1906: Albert Einstein, quantum explanation of specific heat laws for solids

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

1909: Ernest Rutherford and Thomas Royds demonstrate that alpha particles are doubly ionized helium atoms

1909: Hans Geiger and Ernest Marsden, under the supervision of Ernest Rutherford, scatter alpha particles off a gold foil and observe large angles of scattering, suggesting that atoms have a small, dense, positively charged nucleus.

1911: Ernest Rutherford infers the nucleus as the result of the alpha-scattering experiment performed by Hans Geiger and Ernest Marsden.

1912: Albert Einstein explains the curvature of space-time.

1912: Bohr begins work on quantum theory of atom.

1912: Walter Friedrich and Paul Knipping diffract X-rays in zinc blende

1912: Max von Laue suggests using lattice solids to diffract X-rays

1913: Johannes Stark demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen

1913: Robert Millikan measures the fundamental unit of electric charge

1913: Henry Moseley shows that nuclear charge is the real basis for numbering the elements

1913: William Bragg and Lawrence Bragg work out the Bragg condition for strong X-ray reflection

1913: Niels Bohr succeeds in constructing a theory of atomic structure based on quantum ideas.

1913: Bohr published his model of the atom, based on energy states described by one quantum number

1914: Ernest Rutherford suggests that the positively charged atomic nucleus contains protons

1914: James Franck and Gustav Hertz observe atomic excitation

1915: Arnold Sommerfeld develops a modified Bohr atomic model with elliptic orbits to explain relativistic fine structure

1916: Gilbert Lewis and Irving Langmuir formulate an electron shell model of chemical bonding

1916: Arnold Sommerfeld, Further atomic quantum numbers and fine structure of spectra, fine structure constant

1917: Albert Einstein introduces the idea of stimulated radiation emission

1919: Ernest Rutherford finds the first evidence for a proton.

1921: Alfred LandT introduces the Lande g-factor

1921: James Chadwick and E.S. Bieler conclude that some strong force holds the nucleus together.

1922: Arthur Compton studies X-ray photon scattering by electrons

1922: Otto Stern and Walter Gerlach show ``space quantization''

1923: Louis de Broglie suggests that electrons may have wavelike properties

1923: Arthur Compton discovers the quantum (particle) nature of x rays, thus confirming photons as particles.

1924: Louis de Broglie proposes that matter has wave properties.

1924: Satyendra Bose and Albert Einstein introduce Bose-Einstein statistics

1924: John Lennard-Jones proposes a semiempirical interatomic force law

1924: Wolfgang Pauli states the quantum exclusion principle

1924: Albert Einstein, statistical physics of quantum boson molecular gas

1924: Louis de Broglie proposes that matter has wave properties.

1925: George Uhlenbeck and Samuel Goudsmit postulate electron spin

1925: Wolfgang Pauli formulates the exclusion principle for electrons in an atom. .

1925: Werner Heisenberg, Max Born, and Pascual Jordan formulate quantum matrix

mechanics

1925: Walther Bothe and Hans Geiger demonstrate that energy and mass are conserved

in atomic processes.

1925: Pauli proposed the Exclusion Principle (no two electrons in an atom can have

the same set of quantum numbers)

1925: Paul Dirac, q-number theory of general quantum mechanics

1925: Born and Jordan, matrix interpretation of Heisenberg's quantum mechanics

1925: Werner Heisenberg, transition amplitude theory of quantum mechanics

1925: Pierre Auger discovers the Auger autoionization process

1925: Walther Bothe and Hans Geiger demonstrate that energy and mass are conserved

in atomic processes.

1926: Erwin Schoedinger proves that the wave and matrix formulations of quantum

theory are mathematically equivalent

1926: Erwin Schroedinger develops wave mechanics, which describes the behavior of

quantum systems for bosons. Max Born gives a probability interpretation of quantum

mechanics. G.N. Lewis proposes the name "photon" for a light quantum.

1926: Paul Dirac introduces Fermi-Dirac statistics

1926: Oskar Klein and Walter Gordon state their relativistic quantum wave equation

1926: Erwin Schroenger states his nonrelativistic quantum wave equation and

formulates quantum wave mechanics

1926: Dirac, Jordan, canonical transformation theory for quantum mechanics

1926: Enrico Fermi discovers the spin-statistics connection

1927: Certain materials had been observed to emit electrons (beta decay). Since

both the atom and the nucleus have discrete energy levels, it is hard to see how

electrons produced in transition could have a continuous spectrum (see 1930 for an

answer.)

1927: Friedrich Hund: quantum tunneling

1927: Heitler and London, quantum theory can explain chemical bonding

1927: Niels Bohr, Copenhagen interpretation of Quantum Mechanics

1927: Werner Heisenberg formulates the uncertainty principle: the more you know mabout a particle's energy, the less you know about the time of the energy (and vice versa.) The same uncertainty applies to momenta and coordinates.

1927: Clinton Davission, Lester Germer, and George Thomson confirm the wavelike nature of electrons

1927: Werner Heisenberg states the quantum uncertainty principle

1927: Max Born interprets the probabilistic nature of wavefunctions

1928: Condon, Gamow, Gurney, alpha emission is due to quantum tunnelling

1928: Jordan, Pauli, quantum field theory of free fields

1928: Heisenberg, Weyl, group representation theory in quantum mechanics

1928: Dirac developed the relativistic quantum theory

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: Paul Dirac combines quantum mechanics and special relativity to describe the electron.

1929: Oskar Klein and Y. Nishina derive the Klein-Nishina cross section for high energy photon scattering by electrons

1929: N.F. Mott derives the Mott cross section for the Coulomb scattering of

relativistic electrons

1929: Heisenberg, Pauli, interacting quantum field theory and divergences

1929: Oskar Klein discovers the Klein paradox

1930: Erwin Schr÷dinger predicts the zitterbewegung motion

1930: Wolfgang Pauli suggests the neutrino to explain the continuous electron

spectrum for beta decay.

1930: Hartree and Fock, multi-particle quantum mechanics

1930: Fritz London explains van der Waals forces as due to the interacting

fluctuating dipole moments between molecules

1930: Paul Dirac introduces electron hole theory

1930: Wolfgang Pauli suggests the neutrino to explain the continuous electron

spectrum for beta decay.

1930: Quantum mechanics and special relativity are well established. There are just

three fundamental particles: protons, electrons, and photons. Max Born, after

learning of the Dirac equation, said, "Physics as we know it will be over in six

months."

1931: Irene Joliot-Curie and F. Joliot-Curie observe but misinterpret neutron

scattering in parafin

1931: Harold Urey discovers deuterium using evaporation concentration techniques

and spectroscopy

1931: Paul Dirac shows that charge conservation can be explained if magnetic

monopoles exist

1931: Linus Pauling discovers resonance bonding and uses it to explain the high

stability of symmetric planar molecules

1931: Wolfgang Pauli puts forth the neutrino hypothesis to explain the apparent

violation of energy conservation in beta decay

1931: James Chadwick discovers the neutron. The mechanisms of nuclear binding and

decay become primary problems.

1931: Paul Dirac realizes that the positively-charged particles required by his

equation are new objects (he calls them "positrons"). They are exactly like

electrons, but positively charged. This is the first example of antiparticles.

1931: Paul Dirac, magnetic monopoles can explain quantum of charge

1931: John Lennard-Jones proposes the Lennard-Jones interatomic potential

1931: Eugene Wigner, symmetry in quantum mechanics

1931: James Chadwick discovers the neutron. The mechanisms of nuclear binding and

decay become primary problems.

1932: Werner Heisenberg presents the proton-neutron model of the nucleus and uses

it to explain isotopes

1932: John Cockcroft and Thomas Walton split lithium and boron nuclei using proton

bombardment

1932: Carl Anderson discovers the positron

1933: Enrico Fermi puts forth a theory of beta decay that introduces the weak

interaction. This is the first theory to explicitly use neutrinos and particle

flavor changes.

1933: Hideki Yukawa combines relativity and quantum theory to describe nuclear interactions by an exchange of new particles (mesons called "pions") between protons and neutrons. From the size of the nucleus, Yukawa concludes that the mass of the conjectured particles (mesons) is about 200 electron masses. This is the beginning of the meson theory of nuclear forces. (1933 - 1934)

1933: Max Delbrnck suggests that quantum effects will cause photons to be scattered by an external electric field

1934: Pavel Cerenkov reports that light is emitted by relativistic particles traveling in a nonscintillating liquid

1934: Lev Landau tells Edward Teller that nonlinear molecules may have vibrational modes which remove the degeneracy of an orbitally

1934: I. Joliot-Curie and F. Joliot-Curie bombard aluminum atoms with alpha particles to create artificially radioactive phosphorus-30

1934: Enrico Fermi suggests bombarding uranium atoms with neutrons to make a 93 proton element

1934: Leo Szilard realizes that nuclear chain reactions may be possible

1935: Einstein, Podolsky, Rosen, EPR Paradox of non-locality in quantum mechanics

1935: Erwin Schroedinger, quantum cat paradox

1935: Hideki Yukawa presents a theory of strong interactions and predicts mesons

1935: Albert Einstein, Boris Podolsky, and Nathan Rosen put forth the EPR paradox

1935: Niels Bohr presents his analysis of the EPR paradox

1936: Eugene Wigner develops the theory of neutron absorption by atomic nuclei

1936: Hans Jahn and Edward Teller present their systematic study of the symmetry

types for which the Jahn-Teller effect is expected

1937: H. 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

1937: A particle of 200 electron masses is discovered in cosmic rays. While at first physicists thought it was Yukawa's pion, it was later discovered to be a muon.

1938: E.C.G. Stuckelberg observes that protons and neutrons do not decay into any combination of electrons, neutrinos, muons, or their antiparticles. The stability of the proton cannot be explained in terms of energy or charge conservation; he proposes that heavy particles are independently conserved.

1939: Richard Feynman finds the Hellmann-Feynman theorem

1939: Otto Hahn and Fritz Strassman bombard uranium salts with thermal neutrons and discover barium among the reaction products

1939: Lise Meitner and Otto Frisch determine that nuclear fission is taking place in the Hahn-Strassman experiments

1941: C. Moller and Abraham Pais introduce the term "nucleon" as a generic term for protons and neutrons.

1942: Ernst Stnckelberg introduces the propagator to positron theory and interprets positrons as negative energy electrons moving

1942: Enrico Fermi makes the first controlled nuclear chain reaction

1943: Sin-Itiro Tomonaga publishes his paper on the basic physical principles of quantum electrodynamics

1946: Physicists realize that the cosmic ray particle thought to be Yukawa's meson is instead a "muon," the first particle of the second generation of matter particles to be found. This discovery was completely unexpected -- I.I. Rabi comments "who ordered that?" The term "lepton" is introduced to describe objects that do not interact too strongly (electrons and muons are both leptons).

1947: Willis Lamb and Robert Retheford measure the Lamb-Retheford shift

1947: Cecil Powell, C.M.G. Lattes, and G.P.S. Occhialini discover the pi-meson bystudying cosmic ray tracks

1947: Physicists develop procedures to calculate electromagnetic properties of electrons, positrons, and photons. Introduction of Feynman diagrams.

1947: A meson that does interact strongly is found in cosmic rays, and is determined to be the pion.

1947: Richard Feynman presents his propagator approach to quantum electrodynamics

1948: Richard Feynman, path integral approach to quantum theory

1948: The Berkeley synchro-cyclotron produces the first artificial pions.

1948: Hendrik Casimir predicts a rudimentary attractive Casimir force on a parallel

plate capacitor

1949: Enrico Fermi and C.N. Yang suggest that a pion is a composite structure of a

nucleon and an anti-nucleon. This idea of composite particles is quite radical.

1949: Discovery of K+ via its decay.

1950: The neutral pion is discovered.

1951: Two new types of particles are discovered in cosmic rays. They are discovered

by looking a V-like tracks and reconstructing the electrically-neutral object that

must have decayed to produce the two charged objects that left the tracks. The

particles were named the lambda0 and the K0.

1951: Martin Deutsch discovers positronium

1952: Discovery of particle called delta: there were four similar particles

(delta++, delta+, delta0, and delta-.)

1953: The beginning of a "particle explosion" -- a true proliferation of particles.

1953: R. Wilson observes Delbrnck scattering of 1.33 MeV gamma-rays by the electric

fields of lead nuclei

1953: The beginning of a "particle explosion" -- a true proliferation of particles.

1953: Scattering of electrons off nuclei reveals a charge density distribution

inside protons, and even neutrons. Description of this electromagnetic structure of

protons and neutrons suggests some kind of internal structure to these objects,

though they are still regarded as fundamental particles.

1954: C.N. Yang and Robert Mills develop a new class of theories called "gauge

theories." Although not realized at the time, this type of theory now forms the

basis of the Standard Model.

1955: Owen Chamberlain, Emilio Segre, Clyde Wiegand, and Thomas Ypsilantis discover

the antiproton

1956: Frederick Reines and Clyde Cowan detect antineutrinos

1956: Chen Yang and Tsung Lee propose parity violation by the weak force

1956: Chien Shiung Wu discovers parity violation by the weak force in decaying

cobalt

1957: John Wheeler discusses the breakdown of classical general relativity near

singularities and the need for quantum gravity

1957: Julian Schwinger, Sidney Bludman, and Sheldon Glashow, in separate papers,

suggest that all weak interactions are mediated by charged heavy bosons, later

called W+ and W-. Actually, it was Yukawa who first discussed boson exchange twenty

years earlier, but he proposed the pion as the mediator of the weak force.

1957: Richard Feynman, Murray Gell-Mann, Robert Marshak, and Ennackel Sudarshan propose a V-A Lagrangian for weak interactions

1957: John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity

1957: Gerhart Lnders proves the CPT theorem

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: Jeffery Goldstone considers the breaking of global phase symmetry

1961: As the number of known particles keep increasing, a mathematical classification scheme to organize the particles (the group SU(3)) helps physicists recognize patterns of particle types.

1962: Experiments verify that there are two distinct types of neutrinos (electron and muon neutrinos). This was earlier inferred from theoretical considerations.

1962: Leon Lederman shows that the electron neutrino is distinct from the muon neutrino

1963: Murray Gell-Mann and George Zweig propose the quark/aces model

1964: Val Fitch and James Cronin observe CP violation by the weak force in the decay of K mesons

1964: J.S. Bell shows that all local hidden variable theories must satisfy Bell's inequality

1964: Peter Higgs considers the breaking of local phase symmetry

1965: Nobel Prize for Physics, "for their fundamental work in quantum electrodynamics, with deep-ploughing consequences for the physics of elementary particles". Sin-Itiro Tomonaga, 1/3 Prize, Tokyo University of Education Tokyo Japan (Japan); Julian Schwinger Harvard University Cambridge, MA, USA Richard P. Feynman California Institute of Technology (Caltech) Pasadena, CA, USA (1918-1988).

1967: Steven Weinberg puts forth his electroweak model of leptons

1969: J.C. Clauser, M. Horne, A. Shimony, and R. Holt propose a polarization correlation test of Bell's inequality

1970: Sheldon Glashow, John Iliopoulos, and Luciano Maiani propose the charm quark

1971: Gerard 't Hooft shows that the Glashow-Salam-Weinberg electroweak model can be renormalized

1972: S. Freedman and J.C. Clauser perform the first polarization correlation test of Bell's inequality

1973: David Politzer proposes the asymptotic freedom of quarks

1973: Edward Tryon proposes that the universe may be a large scale quantum mechanical vacuum fluctuation where positive mass-energy

1974: Burton Richter and Samuel Ting discover the psi meson implying the existence of the charm quark

1974: Stephen Hawking applies quantum field theory to black hole spacetimes and

shows that black holes will radiate particles with

1975: Martin Perl discovers the tauon

1977: S.W. Herb finds the upsilon resonance implying the existence of the beauty quark

1982: A. Aspect, J. Dalibard, and G. Roger perform a polarization correlation test of Bell's inequality that rules out conspiratorial polarizer communication

1983: Carlo Rubbia, Simon van der Meer, and the CERN UA-1 collaboration find the Wpm and Z0 intermediate vector bosons

1989: The Z0 intermediate vector boson resonance width indicates three quark-lepto generations