Atimeline ofatomic andsubatomic physics, includingparticle physics.

• 6th - 2nd Century BCEKanada (philosopher) proposes thatanu is an indestructible particle of matter, an "atom"; anu is an abstraction and not observable.^[1]

• 430 BCE^[2]Democritus speculates about fundamental indivisible particles—calls them "atoms"

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• 1766Henry Cavendish discovers and studieshydrogen^[3]
• 1778Carl Scheele andAntoine Lavoisier discover thatair is composed mostly ofnitrogen andoxygen
• 1781Joseph Priestley creates water by igniting hydrogen and oxygen
• 1800William Nicholson andAnthony Carlisle useelectrolysis to separate water into hydrogen and oxygen
• 1803John Dalton introducesatomic ideas intochemistry and states thatmatter is composed ofatoms of different weights
• 1805 (approximate time)Thomas Young conducts thedouble-slit experiment with light
• 1811Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules
• 1815William Prouthypothesizes that all matter is built up fromhydrogen, adumbrating theproton;
• 1832Michael Faraday states his laws of electrolysis
• 1838Richard Laming hypothesized a subatomic particle carryingelectric charge;
• 1839Alexandre Edmond Becquerel discovered thephotovoltaic effect
• 1858Julius Plücker producedcathode rays;
• 1871Dmitri Mendeleyev systematically examines theperiodic table and predicts the existence ofgallium,scandium, andgermanium
• 1873Johannes van der Waals introduces the idea of weak attractive forces between molecules
• 1874George Johnstone Stoney hypothesizes a minimum unit of electric charge. In 1891, he coins the wordelectron for it;
• 1885Johann Balmer finds a mathematical expression for observedhydrogen linewavelengths
• 1886Eugen Goldstein producedanode rays;
• 1887Heinrich Hertz discovers thephotoelectric effect
• 1894Lord Rayleigh andWilliam Ramsay discoverargon byspectroscopically analyzing the gas left over after nitrogen and oxygen are removed from air
• 1895William Ramsay discovers terrestrialhelium by spectroscopically analyzing gas produced by decayinguranium
• 1896Antoine Henri Becquerel discovers theradioactivity of uranium
• 1896Pieter Zeeman studies the splitting ofsodium D lines when sodium is held in a flame between strongmagnetic poles
• 1897J. J. Thomson discovered theelectron;
• 1897Emil Wiechert,Walter Kaufmann andJ.J. Thomson discover theelectron
• 1898Marie andPierre Curie discovered the existence of the radioactive elementsradium andpolonium in their research ofpitchblende
• 1898William Ramsay andMorris Travers discoverneon, and negatively chargedbeta particles

• 1887Heinrich Rudolf Hertz discovers thephotoelectric effect that will play a very important role in the development of thequantum theory withEinstein's explanation of this effect in terms ofquanta of light
• 1896Wilhelm Conrad Röntgen discovers theX-rays while studying electrons inplasma;scattering X-rays—that were considered as 'waves' of high-energyelectromagnetic radiation—Arthur Compton will be able to demonstrate in 1922 the 'particle' aspect of electromagnetic radiation.
• 1899Ernest Rutherford discovered thealpha andbeta particles emitted byuranium;
• 1900Johannes Rydberg refines the expression for observed hydrogen line wavelengths
• 1900Max Planck states hisquantum hypothesis andblackbody radiation law
• 1900Paul Villard discoversgamma-rays while studying uranium decay
• 1902Philipp Lenard observes that maximumphotoelectron energies are independent of illuminating intensity but depend on frequency
• 1905 Albert Einstein explains thephotoelectric effect
• 1906Charles Barkla discovers that each element has a characteristicX-ray and that the degree of penetration of these X-rays is related to theatomic weight of the element
• 1908-1911Jean Perrin proves the existence ofatoms andmolecules withexperimental work to testEinstein's theoretical explanation ofBrownian motion
• 1909Ernest Rutherford andThomas Royds demonstrate that alpha particles are doublyionized helium atoms
• 1909Hans Geiger andErnest Marsden discover large angle deflections of alpha particles by thin metal foils
• 1911Ernest Rutherford explains theGeiger–Marsden experiment by invoking a nuclear atom model and derives theRutherford cross section
• 1911Ștefan Procopiu measures the magnetic dipole moment of the electron
• 1912Max von Laue suggests usingcrystal lattices todiffract X-rays
• 1912Walter Friedrich andPaul Knipping diffract X-rays in zinc blende
• 1913Max Bodenstein proposed chain reactions
• 1913Henry Moseley shows that nuclear charge is the real basis for numbering the elements
• 1913Johannes Stark demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen
• 1913Niels Bohr presents hisquantum model of the atom^[4]
• 1913Robert Millikan measures thefundamental unit of electric charge
• 1913William Henry Bragg andWilliam Lawrence Bragg work out theBragg condition for strong X-ray reflection
• 1914Ernest Rutherford suggests that the positively charged atomic nucleus containsprotons^[5]
• 1914James Franck andGustav Hertz observe atomic excitation
• 1915Arnold Sommerfeld develops a modifiedBohr atomic model with elliptic orbits to explain relativistic fine structure
• 1916Gilbert N. Lewis andIrving Langmuir formulate an electron shell model ofchemical bonding
• 1917Albert Einstein introduces the idea ofstimulated radiation emission
• 1918 Ernest Rutherford notices that, whenalpha particles were shot intonitrogen gas, hisscintillation detectors showed the signatures ofhydrogen nuclei.
• 1921Alfred Landé introduces theLandé g-factor
• 1922Arthur Compton studies X-ray photonscattering by electrons demonstrating the 'particle' aspect of electromagnetic radiation.
• 1922Otto Stern andWalther Gerlach show "spin quantization"
• 1923Lise Meitner discovers what is now referred to as theAuger process
• 1924John Lennard-Jones proposes a semiempiricalinteratomic force law
• 1924Louis de Broglie suggests that electrons may have wavelike properties in addition to their 'particle' properties; thewave–particle duality has been later extended to all fermions and bosons.
• 1924Santiago Antúnez de Mayolo proposes a neutron.
• 1924Satyendra Bose and Albert Einstein introduceBose–Einstein statistics
• 1925George Uhlenbeck andSamuel Goudsmit postulate electronspin
• 1925Pierre Auger discovers theAuger process (2 years afterLise Meitner)
• 1925Werner Heisenberg,Max Born, andPascual Jordan formulate quantummatrix mechanics
• 1925Wolfgang Pauli states the quantumexclusion principle for electrons
• 1926Enrico Fermi discovers thespin–statistics connection, for particles that are now called 'fermions', such as the electron (ofspin-1/2).
• 1926Erwin Schrödinger proves that the wave and matrix formulations of quantum theory are mathematically equivalent
• 1926Erwin Schrödinger states his nonrelativisticquantum wave equation and formulatesquantum wave mechanics
• 1926Gilbert N. Lewis introduces the term "photon", thought by him to be "the carrier ofradiant energy."^[6][7]
• 1926Oskar Klein andWalter Gordon state their relativistic quantum wave equation, now theKlein–Gordon equation
• 1926Paul Dirac introducesFermi–Dirac statistics
• 1927Charles Drummond Ellis (along withJames Chadwick and colleagues) finally establish clearly that the beta decay spectrum is in fact continuous and not discrete, posing a problem that will later be solved by theorizing (and later discovering) the existence of theneutrino.
• 1927Clinton Davisson,Lester Germer, andGeorge Paget Thomson confirm thewavelike nature of electrons^[8]
• 1927Thomas andFermi develop theThomas–Fermi model
• 1927Max Borninterprets the probabilistic nature of wavefunctions
• 1927Max Born andRobert Oppenheimer introduce theBorn–Oppenheimer approximation
• 1927Walter Heitler andFritz London introduce the concepts ofvalence bond theory and apply it to thehydrogen molecule.
• 1927Werner Heisenberg states the quantumuncertainty principle
• 1928Chandrasekhara Raman studies optical photon scattering by electrons
• 1928Charles G. Darwin andWalter Gordon solve theDirac equation for a Coulomb potential
• 1928Friedrich Hund andRobert S. Mulliken introduce the concept ofmolecular orbital
• 1928Paul Dirac states theDirac equation
• 1929Nevill Mott derives theMott cross section for the Coulomb scattering of relativistic electrons
• 1929Oskar Klein discovers theKlein paradox
• 1929 Oskar Klein andYoshio Nishina derive the Klein–Nishina cross section for high energy photon scattering by electrons
• 1930Wolfgang Pauli postulated theneutrino to explain the energy spectrum ofbeta decays;
• 1930Erwin Schrödinger predicts thezitterbewegung motion
• 1930Fritz London explainsvan der Waals forces as due to the interacting fluctuatingdipole moments between molecules
• 1930Paul Dirac introduces electron hole theory
• 1931Harold Urey discoversdeuterium using evaporation concentration techniques and spectroscopy
• 1931Irène Joliot-Curie andFrédéric Joliot observe but misinterpret neutron scattering in paraffin
• 1931John Lennard-Jones proposes theLennard-Jones interatomic potential
• 1931Linus Pauling discovers resonance bonding and uses it to explain the high stability of symmetric planar molecules
• 1931Paul Dirac shows thatcharge quantization can be explained ifmagnetic monopoles exist
• 1931Wolfgang Pauli puts forth theneutrino hypothesis to explain the apparent violation ofenergy conservation in beta decay
• 1932 Paul Güttinger finds the Hellmann–Feynman theorem
• 1932Carl D. Anderson discovers thepositron
• 1932James Chadwick discovers theneutron
• 1932John Cockcroft andErnest Walton splitlithium andboron nuclei using proton bombardment
• 1932Werner Heisenberg presents the proton–neutron model of the nucleus and uses it to explain isotopes
• 1932Ettore Majorana,Ernst Stueckelberg,Lev Landau, andClarence Zener independently discover theLandau–Zener transition
• 1933Max Delbrück suggests that quantum effects will cause photons to be scattered by an external electric field
• 1934Enrico Fermi publishes a very successful model of beta decay in which neutrinos were produced.
• 1934Enrico Fermi suggests bombarding uranium atoms with neutrons to make a 93 proton element
• 1934Irène Joliot-Curie andFrédéric Joliot bombardaluminium atoms with alpha particles to create artificially radioactivephosphorus-30
• 1934Leó Szilárd realizes thatnuclear chain reactions may be possible
• 1934Lev Landau tellsEdward Teller that non-linear molecules may havevibrational modes which remove thedegeneracy of an orbitally degenerate state (Jahn–Teller effect)
• 1934Pavel Cherenkov reports thatlight is emitted by relativistic particles traveling in a nonscintillating liquid
• 1935Albert Einstein,Boris Podolsky, andNathan Rosen put forth theEPR paradox
• 1935Henry Eyring develops thetransition state theory
• 1935Hideki Yukawa presents a theory of thenuclear force and predicts the scalarmeson
• 1935Niels Bohr presents his analysis of the EPR paradox
• 1936Carl D. Anderson discovered themuon while he studiedcosmic radiation;
• 1936Alexandru Proca formulates the relativistic quantum field equations for a massive vector meson of spin-1 as a basis for nuclear forces
• 1936Eugene Wigner develops the theory of neutron absorption by atomic nuclei
• 1936Hermann Arthur Jahn andEdward Teller present their systematic study of the symmetry types for which theJahn–Teller effect is expected^[9]
• 1937Carl Anderson proves experimentally the existence of the pion predicted by Yukawa's theory.
• 1937Seth Neddermeyer,Carl Anderson, J.C. Street, and E.C. Stevenson discovermuons usingcloud chamber measurements ofcosmic rays
• 1939Gottfried von Droste andSiegfried Flügge and independentlyLise Meitner andOtto Robert Frisch determine thatnuclear fission is taking place in the Hahn–Strassmann experiments
• 1939Otto Hahn andFritz Strassmann bombard uranium salts withthermal neutrons and discoverbarium among the reaction products
• 1942Enrico Fermi makes the first controlled nuclear chain reaction
• 1942Ernst Stueckelberg introduces the propagator to positron theory and interprets positrons as negative energy electrons moving backwards through spacetime

• 1947George Dixon Rochester andClifford Charles Butler discovered thekaon, the firststrange particle;
• 1947Cecil Powell,César Lattes, andGiuseppe Occhialini discover thepi meson by studying cosmic ray tracks
• 1947Richard Feynman presentshis propagator approach to quantum electrodynamics^[10]
• 1947Willis Lamb andRobert Retherford measure theLamb–Retherford shift
• 1948Hendrik Casimir predicts a rudimentary attractiveCasimir force on a parallel plate capacitor
• 1951Martin Deutsch discoverspositronium
• 1952David Bohm proposehis interpretation of quantum mechanics
• 1953Robert Wilson observesDelbruck scattering of 1.33MeV gamma-rays by the electric fields of lead nuclei
• 1953 Charles H. Townes, collaborating with J. P. Gordon, and H. J. Zeiger, builds the first ammoniamaser
• 1954Chen Ning Yang andRobert Mills investigate atheory of hadronicisospin by demanding localgauge invariance underisotopic spin space rotations, the first non-Abeliangauge theory
• 1955Owen Chamberlain,Emilio Segrè,Clyde Wiegand, andThomas Ypsilantis discover theantiproton
• 1955 and 1956Murray Gell-Mann andKazuhiko Nishijima independently derive theGell-Mann–Nishijima formula, which relates thebaryon number, thestrangeness, and theisospin ofhadrons to the charge, eventually leading to the systematic categorization of hadrons and, ultimately, thequark model of hadron composition.
• 1956Clyde Cowan andFrederick Reines discovered the (electron)neutrino;
• 1956Chen Ning Yang andTsung Lee proposeparity violation by theweak nuclear force
• 1956Chien Shiung Wu discovers parity violation by the weak force in decaying cobalt
• 1956Frederick Reines andClyde Cowan detectantineutrino
• 1957Bruno Pontecorvo postulated the flavor oscillation;
• 1957Gerhart Luders proves theCPT theorem
• 1957Richard Feynman,Murray Gell-Mann,Robert Marshak, andE.C.G. Sudarshan propose a vector/axial vector (VA)Lagrangian for weak interactions.^{[11][12][13][14][15][16]}
• 1958Marcus Sparnaay experimentally confirms theCasimir effect
• 1959Yakir Aharonov andDavid Bohm predict theAharonov–Bohm effect
• 1960R.G. Chambers experimentally confirms the Aharonov–Bohm effect^[17]
• 1961Jeffrey Goldstone considers the breaking of global phase symmetry
• 1961Murray Gell-Mann andYuval Ne'eman discover theEightfold Way patterns, theSU(3) group
• 1962Leon Lederman shows that the electron neutrino is distinct from the muon neutrino
• 1963Eugene Wigner discovers the fundamental roles played by quantum symmetries in atoms and molecules

• 1963Nicola Cabibbo develops the mathematical matrix by which the first two (and ultimately three) generations of quarks can be predicted.
• 1963-1964André Petermann,Murray Gell-Mann andGeorge Zweig propose thequark/aces model^[18]
• 1964François Englert,Robert Brout,Peter Higgs,Gerald Guralnik,C. R. Hagen, andTom Kibble postulate that a fundamental quantum field, now called theHiggs field, permeates space and, by way of theHiggs mechanism, provides mass to all the elementary subatomic particles that interact with it. While the Higgs field is postulated to confer mass on quarks and leptons, it represents only a tiny portion of the masses of other subatomic particles, such as protons and neutrons. In these, gluons that bind quarks together confer most of the particle mass. The result is obtained independently by three groups: François Englert and Robert Brout; Peter Higgs, working from the ideas of Philip Anderson; and Gerald Guralnik, C. R. Hagen, and Tom Kibble.^{[19][20][21][22][23][24][25]}. The Higgs mechanism was originally proposed already in 1938 byErnst Stueckelberg
• 1964Murray Gell-Mann andGeorge Zweig independently propose thequark model of hadrons, predicting the arbitrarily namedup,down, andstrange quarks. Gell-Mann is credited with coining the termquark, which he found inJames Joyce's bookFinnegans Wake.
• 1964Sheldon Glashow andJames Bjorken predict the existence of the charm quark. The addition is proposed because it allows for a better description of theweak interaction (the mechanism that allows quarks and other particles to decay), equalizes the number of knownquarks with the number of knownleptons, and implies a mass formula that correctly reproduced the masses of the knownmesons.
• 1964John Stewart Bell shows that all localhidden variable theories must satisfyBell's inequality
• 1964Peter Higgs considers the breaking of local phase symmetry
• 1964Val Fitch andJames Cronin observe CP violation by the weak force in the decay of K mesons
• 1967Bruno Pontecorvo postulatedneutrino oscillation;
• 1967Steven Weinberg andAbdus Salam publish papers in which they describeYang–Mills theory using the SU(2) X U(1)supersymmetry group, thereby yielding a mass for the W particle of theweak interaction viaspontaneous symmetry breaking.
• 1967Steven Weinberg puts forth his electroweak model ofleptons^[26][27]
• 1968Stanford University:Deep inelastic scattering experiments at theStanford Linear Accelerator Center (SLAC) show that theproton contains much smaller, point-like objects and is therefore not an elementary particle. Physicists at the time are reluctant to identify these objects withquarks, instead calling thempartons — a term coined by Richard Feynman. The objects that are observed at SLAC will later be identified asup anddown quarks. Nevertheless, "parton" remains in use as a collective term for the constituents ofhadrons (quarks,antiquarks, andgluons). The existence of thestrange quark is indirectly validated by the SLAC's scattering experiments: not only is it a necessary component of Gell-Mann and Zweig's three-quark model, but it provides an explanation for thekaon (K) andpion (π) hadrons discovered in cosmic rays in 1947.
• 1969John Clauser,Michael Horne,Abner Shimony andRichard Holt propose a polarization correlation test ofBell's inequality
• 1970Sheldon Glashow,John Iliopoulos, andLuciano Maiani propose the charm quark
• 1971Gerard 't Hooft shows that the Glashow-Salam-Weinberg electroweak model can be renormalized^[28]
• 1972Stuart Freedman andJohn Clauser perform the first polarization correlation test ofBell's inequality
• 1973Frank Anthony Wilczek discover the quark asymptotic freedom in the theory of strong interactions; receives theLorentz Medal in 2002, and the Nobel Prize in Physics in 2004 for his discovery and his subsequent contributions toquantum chromodynamics.^[29]
• 1973Makoto Kobayashi andToshihide Maskawa note that the experimental observation ofCP violation can be explained if an additional pair ofquarks exist. The two new quarks are eventually namedtop andbottom.
• 1973David Politzer andFrank Anthony Wilczek propose theasymptotic freedom of quarks
• 1974Burton Richter andSamuel Ting: Charm quarks are produced almost simultaneously by two teams in November 1974 (seeNovember Revolution) — one atSLAC under Burton Richter, and one atBrookhaven National Laboratory under Samuel Ting. The charm quarks are observed bound with charmantiquarks inmesons. The two discovering parties independently assign the discovered meson two different symbols, J and ψ; thus, it becomes formally known as theJ/ψ meson. The discovery finally convinces the physics community of the quark model's validity.
• 1974Robert J. Buenker andSigrid D. Peyerimhoff introduce themultireference configuration interaction method.
• 1975Martin Perl discovers thetau lepton, predicted byAntonino Zichichi in 1967
• 1977Leon Lederman observes thebottom quark with his team atFermilab.^[30] This discovery is a strong indicator of thetop quark's existence: without the top quark, the bottom quark would be without a partner that is required by the mathematics of the theory. Thebottom quark was theorised already in 1973 by Makoto Kobayashi and Toshihide Maskawa.
• 1977Steve Herb finds theupsilon resonance implying the existence of thebeauty/bottom quark
• 1979Gluon observed indirectly inthree-jet events atDESY;
• 1982Alain Aspect, J. Dalibard, and G. Roger perform a polarization correlation test ofBell's inequality that rules out conspiratorial polarizer communication
• 1983Carlo Rubbia andSimon van der Meer discovered theW and Z bosons;
• 1983Carlo Rubbia,Simon van der Meer, and the CERN UA-1 collaboration find theW and Z intermediate vector bosons^[31]
• 1989 The Z intermediate vector bosonresonance width indicates threequark–lepton generations
• 1994 TheCERNLEARCrystal Barrel Experiment justifies the existence ofglueballs (exotic meson).
• 1995 Thetop quark is finally observed by a team atFermilab after an 18-year search.^[30] It has a mass much greater than had been previously expected — almost as great as a gold atom.
• 1995 TheD0 andCDF experiments at theFermilabTevatron discover thetop quark.
• 1998 – TheSuper-Kamiokande (Japan) detector facility reports experimental evidence forneutrino oscillations, implying that at least one neutrino has mass.^[32]
• 1998Super-Kamiokande (Japan) observes evidence forneutrino oscillations, implying that at least one neutrino has mass.
• 1999Ahmed Zewail wins the Nobel prize in chemistry for his work onfemtochemistry for atoms and molecules.^[33]
• 2000 scientists atFermilab announce the first direct evidence for thetau neutrino, the third kind of neutrino in particle physics.^[30]
• 2000CERN announcedquark-gluon plasma, a new phase of matter.^[34]
• 2001 theSudbury Neutrino Observatory (Canada) confirm the existence of neutrino oscillations.Lene Hau stops a beam of light completely in aBose–Einstein condensate.^[35]
• 2001 TheSudbury Neutrino Observatory (Canada) confirms the existence ofneutrino oscillations.
• 2005 theRHIC accelerator ofBrookhaven National Laboratory generates a "perfect" fluid, perhaps thequark–gluon plasma.^[36]
• 2010 TheLarge Hadron Collider atCERN begins operation with the primary goal of searching for theHiggs boson.
• 2012Higgs boson-like particle discovered atCERN'sLarge Hadron Collider (LHC).^[37]
• 2014 TheLHCb experiment observes particles consistent withtetraquarks andpentaquarks^[38]
• 2014 TheT2K andOPERA experiment observe the appearance ofelectron neutrinos andTau neutrinos in amuon neutrinobeam^[39][40]

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