View source for Physics:History of subatomic physics

{{Short description|Chronological listing of experiments and discoveries}}
[[File:Katódsugarak mágneses mezőben(3).jpg|thumb|right|A [[Physics:Crookes tube|Crookes tube]] with a magnetic deflector]]
The idea that matter consists of smaller particles and that there exists a limited number of sorts of [[Physics:Elementary particle|primary, smallest particles]] in [[Philosophy:Nature|nature]] has existed in [[Philosophy:Natural philosophy|natural philosophy]] at least since the 6th century BC. Such ideas gained [[Physics:Physics|physical]] credibility beginning in the 19th century, but the concept of "elementary particle" underwent some changes in its meaning: notably, modern physics no longer deems elementary particles indestructible. Even elementary particles can [[Physics:Event (particle physics)|decay or collide destructively]]; they can cease to exist and create (other) particles in result.

Increasingly small particles have been discovered and researched: they include [[Physics:Molecule|molecule]]s, which are constructed of [[Physics:Atom|atom]]s, that in turn consist of [[Physics:Subatomic particle|subatomic particle]]s, namely atomic nuclei and [[Physics:Electron|electron]]s. Many more types of subatomic particles have been found. Most such particles (but not electrons) were eventually found to be composed of even smaller particles such as [[Physics:Quark|quark]]s. [[Physics:Particle physics|Particle physics]] studies these smallest particles; [[Physics:Nuclear physics|nuclear physics]] studies atomic nuclei and their (immediate) constituents: [[Physics:Proton|proton]]s and [[Physics:Neutron|neutron]]s.

==Early development==
{{main|Philosophy:Atomism|Physics:Atomic theory}}
The idea that all [[Physics:Matter|matter]] is composed of [[Physics:Elementary particle|elementary particle]]s dates to as far as the 6th century BC.<ref>{{cite book |last=Salerno |first=Daniel |date=2019 |title=The Higgs Boson Produced With Top Quarks in Fully Hadronic Signatures |series=Springer Theses |doi=10.1007/978-3-030-31257-2 |url= |location= |publisher=Springer, Cham |page=7 |isbn=978-3-030-31256-5|s2cid=209954340 }}</ref> The Jains in ancient India were the earliest to advocate the particular nature of material objects between 9th and 5th century BCE. According to Jain leaders like Parshvanatha and Mahavira, the ajiva (non living part of universe) consists of matter or ''pudgala'', of definite or indefinite shape which is made up tiny uncountable and invisible particles called ''permanu''. ''Permanu'' occupies space-point and each ''permanu'' has definite colour, smell, taste and texture. Infinite varieties of ''permanu'' unite and form ''pudgala''.<ref>{{Cite book | url=https://books.google.com/books?id=WzEzXDk0v6sC&q=atom+jainism&pg=PA181 |title = Jainism: An Indian Religion of Salvation|isbn = 9788120813762|last1 = Glasenapp|first1 = Helmuth von|year = 1999}}</ref> The philosophical doctrine of [[Philosophy:Atomism|atomism]] and the nature of elementary particles were also studied by ancient Greek philosophers such as [[Biography:Leucippus|Leucippus]], [[Biography:Democritus|Democritus]], and [[Biography:Epicurus|Epicurus]]; ancient Indian philosophers such as [[Biography:Kanada (philosopher)|Kanada]], [[Philosophy:Dignāga|Dignāga]], and [[Philosophy:Dharmakirti|Dharmakirti]]; Muslim scientists such as Ibn al-Haytham, [[Biography:Avicenna|Ibn Sina]], and [[Biography:Al-Ghazali|Mohammad al-Ghazali]]; and in [[History:Early modern Europe|early modern Europe]] by physicists such as [[Biography:Pierre Gassendi|Pierre Gassendi]], [[Biography:Robert Boyle|Robert Boyle]], and [[Biography:Isaac Newton|Isaac Newton]]. The particle theory of [[Physics:Light|light]] was also proposed by Ibn al-Haytham, [[Biography:Avicenna|Ibn Sina]], Gassendi, and Newton.

Those early ideas were founded through [[Philosophy:Abstraction|abstract]], philosophical reasoning rather than experimentation and [[Philosophy:Empirical observation|empirical observation]] and represented only one line of thought among many. In contrast, certain ideas of [[Biography:Gottfried Wilhelm Leibniz|Gottfried Wilhelm Leibniz]] (see ''[[Philosophy:Monadology|Monadology]]'') contradict to almost everything known in modern physics.

In the 19th century, John Dalton, through his work on [[Chemistry:Stoichiometry|stoichiometry]], concluded that each chemical element was composed of a single, unique type of particle. Dalton and his contemporaries believed those were the fundamental particles of nature and thus named them atoms, after the Greek word ''atomos'', meaning "indivisible"<ref>{{cite web|url=http://sciexplorer.blogspot.com/2012/05/quasiparticles.html |title=Scientific Explorer: Quasiparticles |publisher=Sciexplorer.blogspot.com |date=2012-05-22 |access-date=2012-07-21}}</ref> or "uncut".
However, near the end of 19th century, physicists discovered that Dalton's atoms are not, in fact, the fundamental particles of nature, but conglomerates of even smaller particles.

==From atoms to nucleons==

=== The state of electromagnetic theory ===
Throughout the 1800's scientists explored many phenomena of electricity and magnetism, culminating in an accurate theory by [[Biography:James Clerk Maxwell|James Clerk Maxwell]].<ref name="WhittakerET">[[Biography:E. T. Whittaker|Whittaker, E. T.]] (1910). A history of the theories of aether and electricity from the age of Descartes to the close of the 19th century. Dublin University Press series. London: Longmans, Green and Co.; [etc.].</ref> This theory was a continuous field model developed around the ideas of [[Physics:Luminiferous aether|luminiferous aether]]. When no experiment could produce evidence of such an ether, and in view of the growing evidence supporting the atomic model, Hendrik Antoon Lorentz developed a theory of electromagnetism based on "ions" that reproduced Maxwell's model.<ref name=PaisInward>{{Cite book |last=Pais |first=Abraham |title=Inward bound: of matter and forces in the physical world |date=2002 |publisher=Clarendon Press [u.a.] |isbn=978-0-19-851997-3 |edition=Reprint |location=Oxford}}</ref>{{rp|77}} 

=== The Electron ===
The [[Physics:Electron|electron]] was discovered between 1879 and 1897 in works of [[Biography:William Crookes|William Crookes]], Arthur Schuster, [[Biography:J. J. Thomson|J. J. Thomson]], and other physicists; its charge was carefully measured by [[Biography:Robert Andrews Millikan|Robert Andrews Millikan]] and [[Biography:Harvey Fletcher|Harvey Fletcher]] in their [[Physics:Oil drop experiment|oil drop experiment]] of 1909. Physicists theorized that [[Physics:Electric charge|negatively charged]] electrons are constituent part of "[[Physics:Atom|atom]]s", along with some (yet unknown) positively charged substance, and it was later confirmed. Electron became the first elementary, truly fundamental particle discovered.

===Radioactivity===

Studies of the "radioactivity", that soon revealed the phenomenon of [[Physics:Radioactive decay|radioactive decay]], provided another argument against considering [[Chemistry:Chemical element|chemical element]]s as fundamental nature's elements. Despite these discoveries, the term ''atom'' stuck to Dalton's (chemical) atoms and now denotes the smallest particle of a chemical element, not something really indivisible.

===Researching particles' interaction===
{{further|Physics:Rutherford scattering}}
Early 20th-century physicists knew only two fundamental forces: [[Physics:Electromagnetism|electromagnetism]] and gravitation, where the latter could not explain the structure of atoms. So, it was obvious to assume that unknown positively charged substance attracts electrons by [[Physics:Coulomb force|Coulomb force]].

[[File:Atom.svg|thumb|left|192px]]
In 1909 [[Biography:Ernest Rutherford|Ernest Rutherford]] and Thomas Royds demonstrated that an [[Physics:Alpha particle|alpha particle]] combines with two electrons and forms a [[Chemistry:Helium|helium]] atom. In modern terms, alpha particles are doubly [[Physics:Ion|ion]]ized helium (more precisely, {{SimpleNuclide|helium|4|link=yes}}) atoms. Speculation about the structure of atoms was severely constrained by Rutherford's 1907 [[Physics:Geiger–Marsden experiment|gold foil experiment]], showing that the atom is mainly empty space, with almost all its mass concentrated in a tiny [[Physics:Atomic nucleus|atomic nucleus]].

===Inside the atom===
[[File:Cloud chambers played an important role of particle detectors.jpg|thumb|[[Physics:Cloud chamber|Cloud chamber]]s played an important role as particle detectors in the early days of subatomic physics. Some particles including the positron were even discovered by using this device]]
By 1914, experiments by Ernest Rutherford, Henry Moseley, [[Biography:James Franck|James Franck]] and [[Biography:Gustav Ludwig Hertz|Gustav Hertz]] had largely established the structure of an atom as a dense nucleus of positive charge surrounded by lower-mass electrons.<ref name="smirnov">{{cite book
 | last = Smirnov | first = B.M.
 | year = 2003
 | title = Physics of Atoms and Ions
 | url = https://books.google.com/books?id=I1O8WYOcUscC&pg=PA14
 | pages = 14–21
 | publisher = [[Company:Springer Science+Business Media|Springer]]
 | isbn = 0-387-95550-X
}}</ref>
These discoveries shed a light to the nature of [[Physics:Radioactive decay|radioactive decay]] and other forms of [[Physics:Nuclear transmutation|transmutation]] of elements, as well as of elements themselves. It appeared that [[Physics:Atomic number|atomic number]] is nothing else than (positive) [[Physics:Electric charge|electric charge]] of the atomic nucleus of a particular atom. Chemical transformations, governed by [[Physics:Electromagnetic interaction|electromagnetic interaction]]s, do not change nuclei&nbsp;– that's why elements are chemically indestructible. But when the nucleus change its charge and/or mass (by emitting or capturing a [[Physics:Particle|particle]]), the atom can become the one of another element. [[Physics:Special relativity|Special relativity]] explained how the ''mass defect'' is related to the [[Physics:Energy|energy]] produced or consumed in reactions. The branch of physics that studies transformations and the structure of nuclei is now called [[Physics:Nuclear physics|nuclear physics]], contrasted to [[Physics:Atomic physics|atomic physics]] that studies the structure and properties of atoms ignoring most nuclear aspects. The development in the nascent quantum physics, such as [[Physics:Bohr model|Bohr model]], led to the understanding of [[Chemistry:Chemistry|chemistry]] in terms of the arrangement of electrons in the mostly empty volume of atoms.

[[File:EisenatomLichteffekt.svg|thumb|right]]
In 1918, Rutherford confirmed that the [[Chemistry:Hydrogen|hydrogen]] nucleus was a particle with a positive charge, which he named the [[Physics:Proton|proton]]. By then, [[Biography:Frederick Soddy|Frederick Soddy]]'s researches of radioactive elements, and experiments of J. J. Thomson and F.W. Aston conclusively demonstrated existence of [[Physics:Isotope|isotope]]s, whose nuclei have different masses in spite of identical atomic numbers. It prompted Rutherford to conjecture that all nuclei other than hydrogen contain chargeless particles, which he named the [[Physics:Neutron|neutron]].
Evidences that atomic nuclei consist of some smaller particles (now called ''[[Physics:Nucleon|nucleon]]s'') grew; it became obvious that, while protons repulse each other [[Physics:Electrostatics|electrostatically]], nucleons attract each other by some new force ([[Physics:Nuclear force|nuclear force]]). It culminated in proofs of [[Physics:Nuclear fission|nuclear fission]] in 1939 by [[Biography:Lise Meitner|Lise Meitner]] (based on experiments by [[Biography:Otto Hahn|Otto Hahn]]), and [[Physics:Nuclear fusion|nuclear fusion]] by [[Biography:Hans Bethe|Hans Bethe]] in that same year. Those discoveries gave rise to an active industry of generating one atom from another, even rendering possible (although it will probably never be profitable) the [[Chemistry:Chrysopoeia|transmutation of lead into gold]]; and, those same discoveries also led to the development of [[Engineering:Nuclear weapon|nuclear weapon]]s.

==Revelations of quantum mechanics==<!-- caution: internal #-links -->
[[File:Neon orbitals.png|thumb|right|[[Physics:Atomic orbital|Atomic orbital]]s of [[Chemistry:Period 2 element|Period 2 element]]s:<br/>
1s [[Physics:Principal quantum number|2]]s 2[[Physics:Azimuthal quantum number|p]] (3 items).<br/>All complete [[Physics:Electron shell|subshells]] (including 2p) are inherently spherically symmetric, but it is convenient to assign to "distinct" p-electrons these two-lobed shapes.]]
{{main|Physics:History of quantum mechanics}}
Further understanding of atomic and nuclear structures became impossible without improving the knowledge about the essence of particles. Experiments and improved theories (such as [[Biography:Erwin Schrödinger|Erwin Schrödinger]]'s "electron waves") gradually revealed that there is [[Physics:Wave–particle duality|no fundamental difference]] between particles and [[Wave|wave]]s. For example, electromagnetic waves were reformulated in terms of particles called ''[[Physics:Photon|photon]]s''. It also revealed that physical objects do not change their parameters, such as [[Physics:Total energy|total energy]], [[Position (vector)|position]] and [[Physics:Momentum|momentum]], as [[Continuous function|continuous function]]s of [[Time|time]], as it was thought of in classical physics: see [[Physics:Atomic electron transition|atomic electron transition]] for example.

Another crucial discovery was [[Identical particles|identical particles]] or, more generally, quantum [[Physics:Particle statistics|particle statistics]]. It was established that all electrons are identical: although two or more electrons can exist simultaneously that have different parameters, but they do not keep separate, distinguishable histories. This also applies to protons, neutrons, and (with certain differences) to photons as well. It suggested that there is a limited number of sorts of smallest particles in the [[Astronomy:Universe|universe]].

The [[Physics:Spin–statistics theorem|spin–statistics theorem]] established that any particle in our [[Physics:Spacetime|spacetime]] may be either a [[Physics:Boson|boson]] (that means its statistics is [[Physics:Bose–Einstein statistics|Bose–Einstein]]) or a [[Physics:Fermion|fermion]] (that means its statistics is [[Physics:Fermi–Dirac statistics|Fermi–Dirac]]). It was later found that all fundamental bosons transmit forces, like the photon that transmits light. Some of non-fundamental bosons (namely, [[Physics:Meson|meson]]s) also may transmit forces (see below), although non-fundamental ones. Fermions are particles "like electrons and nucleons" and generally comprise the matter. Note that any subatomic or atomic particle composed of [[Even number|even]] ''total'' number of fermions (such as protons, neutrons, and electrons) is a boson, so a boson is not necessarily a force transmitter and perfectly can be an ordinary material particle.

The [[Physics:Spin|spin]] is the quantity that distinguishes bosons and fermions. Practically it appears as an intrinsic [[Physics:Angular momentum|angular momentum]] of a particle, that is unrelated to its [[Physics:Motion|motion]] but is linked with some other features like a [[Physics:Magnetic dipole|magnetic dipole]]. Theoretically it is explained from different types [[Physics:Representation theory of the Lorentz group|representations of symmetry groups]], namely [[Tensor|tensor]] representations (including vectors and scalars) for bosons with their integer (in [[Physics:Reduced Planck constant|ħ]]) spins, and [[Physics:Spinor|spinor]] representations for fermions with their [[Half-integer|half-integer]] spins.

Improved understanding of the world of particles prompted physicists to make bold predictions, such as [[Biography:Paul Dirac|Dirac]]'s [[Physics:Positron|positron]] in 1928 (founded on the Dirac Sea model) and [[Biography:Wolfgang Pauli|Pauli]]'s [[Physics:Neutrino|neutrino]] in 1930 (founded on conservation of energy and angular momentum in [[Physics:Beta decay|beta decay]]). Both were later confirmed.

This culminated in the formulation of ideas of a [[Physics:Quantum field theory|quantum field theory]]. The first (and the only mathematically complete) of these theories, [[Physics:Quantum electrodynamics|quantum electrodynamics]], allowed to explain thoroughly the structure of atoms, including the Periodic Table and atomic spectra. Ideas of [[Physics:Quantum mechanics|quantum mechanics]] and quantum field theory were applied to nuclear physics too. For example, [[Physics:Alpha decay|α decay]] was explained <!-- by Bohr? --> as a quantum tunneling through nuclear potential, nucleons' fermionic statistics explained the nucleon pairing,{{anchor|meson}} and [[Biography:Hideki Yukawa|Hideki Yukawa]] proposed certain [[Physics:Virtual particle|virtual particle]]s (now knows as [[Physics:Pion|π-mesons]]) as an explanation of the nuclear force.

[[File:Cyclotron with glowing beam.jpg|thumb|left]]

==From nuclides to nuclear engineering==
{{Nuclear physics}}
Development of nuclear models (such as the liquid-drop model and [[Physics:Nuclear shell model|nuclear shell model]]) made prediction of properties of [[Physics:Nuclide|nuclide]]s possible. No existing model of nucleon–nucleon interaction can ''analytically'' compute something more complex than {{SimpleNuclide|helium|4}} based on principles of quantum mechanics, though (note that complete computation of [[Physics:Electron shell|electron shell]]s in atoms is also impossible as yet).

The most developed branch of nuclear physics in 1940s was studies related to [[Physics:Nuclear fission|nuclear fission]] due to its military significance. The main focus of fission-related problems is interaction of atomic nuclei with neutrons: a process that occurs in a fission bomb and a nuclear fission reactor. It gradually drifted away from the rest of subatomic physics and virtually became the [[Engineering:Nuclear engineering|nuclear engineering]]. The first synthesised [[Physics:Transuranium element|transuranium element]]s were also obtained in this context, through [[Physics:Neutron capture|neutron capture]] and subsequent [[Physics:Beta decay|β<sup>−</sup> decay]].

The elements beyond fermium cannot be produced in this way. To make a nuclide with more than 100 protons per nucleus one has to use an inventory and methods of particle physics (see details below), namely to accelerate and collide atomic nuclei. Production of progressively heavier synthetic elements continued into 21st century as a branch of nuclear physics, but only for scientific purposes.

The third important stream in nuclear physics are researches related to [[Physics:Nuclear fusion|nuclear fusion]]. This is related to thermonuclear weapons (and conceived peaceful thermonuclear energy), as well as to astrophysical researches, such as [[Physics:Stellar nucleosynthesis|stellar nucleosynthesis]] and [[Astronomy:Big Bang nucleosynthesis|Big Bang nucleosynthesis]].

==Physics goes to high energies==

===Strange particles and mysteries of the weak interaction===
{{further|Physics:Resonance (particle physics)|Physics:Deep inelastic scattering|Physics:Strange particle}}
In the 1950s, with development of [[Physics:Particle accelerator|particle accelerator]]s and studies of [[Astronomy:Cosmic ray|cosmic ray]]s, [[Physics:Inelastic scattering|inelastic scattering]] experiments on protons (and other atomic nuclei) with energies about hundreds of [[Physics:MeV|MeV]]s became affordable. They created some short-lived [[Physics:Resonance (particle physics)|resonance "particles"]], but also ''[[Physics:Hyperon|hyperon]]s'' and ''[[Physics:Kaon|K-mesons]]'' with unusually long lifetime. The cause of the latter was found in a new quasi-[[Physics:Conservation law|conserved]] quantity, named ''[[Physics:Strangeness|strangeness]]'', that is conserved in all circumstances except for the [[Physics:Weak interaction|weak interaction]]. The strangeness of heavy particles and the [[Physics:Muon|μ-lepton]] were first two signs of what is now known as the [[Physics:Generation (particle physics)|second generation]] of fundamental particles.

The weak interaction revealed soon yet another mystery. In 1957 [[Biography:Chien-Shiung Wu|Chien-Shiung Wu]] proved that it does not [[Physics:Parity#Quantum mechanics|conserve parity]]. In other words, the mirror symmetry was disproved as a fundamental [[Physics:Symmetry|symmetry law]].

Throughout the 1950s and 1960s, improvements in particle accelerators and [[Physics:Particle detector|particle detector]]s led to a bewildering variety of particles found in high-energy experiments. The term ''elementary particle'' came to refer to dozens of particles, most of them [[Physics:Particle decay|unstable]]. It prompted Wolfgang Pauli's remark: "Had I foreseen this, I would have gone into botany". The entire collection was nicknamed the "[[Physics:Particle zoo|particle zoo]]". It became evident that some smaller constituents, yet invisible, form [[Physics:Meson|meson]]s and [[Physics:Baryon|baryon]]s that counted most of then-known particles.

===Deeper constituents of matter===
[[File:Baryon decuplet.svg|thumb|right|Classification of spin-{{sfrac|3|2}} baryons known in 1960s]]
{{further|Physics:Hadron}}
The interaction of these particles by [[Physics:Scattering|scattering]] and [[Physics:Particle decay|decay]] provided a key to new fundamental quantum theories. [[Biography:Murray Gell-Mann|Murray Gell-Mann]] and [[Biography:Yuval Ne'eman|Yuval Ne'eman]] brought some order to mesons and baryons, the most numerous classes of particles, by classifying them according to certain qualities. It began with what Gell-Mann referred to as the "[[Physics:Eightfold way|Eightfold Way]]", but proceeding into several different "octets" and "decuplets" which could predict new particles, most famously the {{SubatomicParticle|link=yes|Omega-}}, which was detected at [[Organization:Brookhaven National Laboratory|Brookhaven National Laboratory]] in 1964, and which gave rise to the ''[[Physics:Quark|quark]]'' model of hadron composition.  While the [[Physics:Quark model|quark model]] at first seemed inadequate to describe [[Physics:Strong interaction|strong nuclear forces]], allowing the temporary rise of competing theories such as the [[Physics:S-matrix theory|S-matrix theory]], the establishment of [[Physics:Quantum chromodynamics|quantum chromodynamics]] in the 1970s finalized a set of fundamental and exchange particles ({{Harvnb|Kragh|1999}}). It postulated the fundamental [[Physics:Strong interaction|strong interaction]], experienced by quarks and mediated by [[Physics:Gluon|gluon]]s. These particles were proposed as a building material for hadrons (see [[Physics:Hadronization|hadronization]]). This theory is unusual because individual (free) quarks cannot be observed (see [[Physics:Color confinement|color confinement]]), unlike the situation with composite atoms where electrons and nuclei can be isolated by transferring [[Physics:Ionization energy|ionization energy]] to the atom.

Then, the old, broad denotation of the term ''elementary particle'' was deprecated and a replacement term ''[[Physics:Subatomic particle|subatomic particle]]'' covered all the "zoo", with its hyponym "[[Physics:Hadron|hadron]]" referring to composite particles directly explained by the quark model. The designation of an "elementary" (or "fundamental") particle was reserved for [[Physics:Lepton|lepton]]s, quarks, their [[Physics:Antiparticle|antiparticle]]s, and [[Physics:Quantum|quanta]] of fundamental interactions (see below) only.

===Quarks, leptons, and four fundamental forces===
[[File:Standard Model of Elementary Particles.svg|left|thumb|250px|The Standard Model]]
{{main|Physics:Fundamental interaction|Physics:Standard Model}}
Because the quantum field theory (see above) postulates no difference between particles and [[Physics:Fundamental interaction|interaction]]s, classification of elementary particles allowed also to classify interactions and [[Physics:Field|fields]].

Now a large number of particles and (non-fundamental) interactions is explained as combinations of a (relatively) small number of fundamental substances, thought to be [[Physics:Fundamental interaction|fundamental interaction]]s (incarnated in fundamental [[Physics:Boson|boson]]s), quarks (including antiparticles), and [[Physics:Lepton|lepton]]s (including antiparticles). As the theory distinguished ''several'' fundamental interactions, it became possible to see which elementary particles participate in which interaction. Namely:
[[File:Elementary particle interactions.svg|thumb|right]]
* All particles participate in gravitation.
* All charged elementary particles participate in electromagnetic interaction.
** As a consequence, neutron participates in it with its [[Physics:Magnetic dipole|magnetic dipole]] in spite of zero electric charge. This is because it is composed of ''charged'' quarks whose charges [[Summation|sum]] to zero.
* All fermions participate in the weak interaction.
* Quarks participate in the strong interaction, along gluons (its own quanta), but not leptons nor any fundamental bosons other than gluons.
The next step was a reduction in number of fundamental interactions, envisaged by early 20th century physicists as the "united field theory". The first successful modern unified theory was the electroweak theory, developed by [[Biography:Abdus Salam|Abdus Salam]], [[Biography:Steven Weinberg|Steven Weinberg]] and, subsequently, [[Biography:Sheldon Glashow|Sheldon Glashow]]. This development culminated in the completion of the theory called the Standard Model in the 1970s, that included also the strong interaction, thus covering three fundamental forces. After the discovery, made at [[Organization:CERN|CERN]], of the existence of [[Physics:Neutral current|neutral weak currents]],<ref>{{cite journal | last1=Hasert | first1=F.J. | last2=Faissner | first2=H. | last3=Krenz | first3=W. | last4=Von Krogh | first4=J. | last5=Lanske | first5=D. | last6=Morfin | first6=J. | last7=Schultze | first7=K. | last8=Weerts | first8=H. | last9=Bertrand-Coremans | first9=G.H. | last10=Lemonne | first10=J. | display-authors=5| title=Search for elastic muon-neutrino electron scattering | journal=Physics Letters B | publisher=Elsevier BV | volume=46 | issue=1 | year=1973 | issn=0370-2693 | doi=10.1016/0370-2693(73)90494-2 | pages=121–124| bibcode=1973PhLB...46..121H }}</ref><ref>{{cite journal | last1=Hasert | first1=F.J. | last2=Kabe | first2=S. | last3=Krenz | first3=W. | last4=Von Krogh | first4=J. | last5=Lanske | first5=D. | last6=Morfin | first6=J. | last7=Schultze | first7=K. | last8=Weerts | first8=H. | last9=Bertrand-Coremans | first9=G.H. | last10=Sacton | first10=J. | display-authors=5| title=Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment | journal=Physics Letters B | publisher=Elsevier BV | volume=46 | issue=1 | year=1973 | issn=0370-2693 | doi=10.1016/0370-2693(73)90499-1 | pages=138–140| bibcode=1973PhLB...46..138H |doi-access=}}</ref><ref>{{cite journal | last1=Hasert | first1=F.J. | last2=Kabe | first2=S. | last3=Krenz | first3=W. | last4=Von Krogh | first4=J. | last5=Lanske | first5=D. | last6=Morfin | first6=J. | last7=Schultze | first7=K. | last8=Weerts | first8=H. | last9=Bertrand-Coremans | first9=G. | last10=Sacton | first10=J. | display-authors=5| title=Observation of neutrino-like interactions without muon or electron in the Gargamelle neutrino experiment | journal=Nuclear Physics B | publisher=Elsevier BV | volume=73 | issue=1 | year=1974 | issn=0550-3213 | doi=10.1016/0550-3213(74)90038-8 | pages=1–22| bibcode=1974NuPhB..73....1H }}</ref><ref>{{Citation|url=http://cerncourier.com/cws/article/cern/29168|title=The discovery of the weak neutral currents|date=2004-10-04|publisher=CERN courier|access-date=2008-05-08}}</ref> mediated by the Z&nbsp;boson foreseen in the standard model, the physicists Salam, Glashow and Weinberg received the 1979 Nobel Prize in Physics for their electroweak theory.<ref>{{Citation|title=The Nobel Prize in Physics 1979|url=http://www.nobel.se/physics/laureates/1979|publisher=Nobel Foundation|access-date=2008-09-10}}</ref>
The discovery of the [[Physics:W and Z bosons|weak gauge bosons]] (quanta of the [[Physics:Weak interaction|weak interaction]]) through the 1980s, and the verification of their properties through the 1990s is considered to be an age of consolidation in particle physics.

While accelerators have confirmed most aspects of the Standard Model by detecting expected particle interactions at various collision energies, no theory reconciling general relativity with the Standard Model has yet been found, although [[Physics:Supersymmetry|supersymmetry]] and [[Physics:String theory|string theory]] were believed by many theorists to be a promising avenue forward. The [[Physics:Large Hadron Collider|Large Hadron Collider]], however, which began operating in 2008, has failed to find any evidence whatsoever that is supportive of supersymmetry and string theory,<ref>{{Cite web | last = Woit | first = Peter |  date = 20 October 2013 | title = Last Links For a While | url = http://www.math.columbia.edu/~woit/wordpress/?p=6362 | access-date = 2 November 2013 | work = Not Even Wrong }}</ref> and appears unlikely to do so, meaning "the current situation in fundamental theory is one of a serious lack of any new ideas at all."<ref>{{Cite web | author= Peter Woit | author-link= Peter Woit | date= 28 May 2013 | title= A Tale of Two Oxford Talks | url= http://www.math.columbia.edu/~woit/wordpress/?p=5966 | access-date= 19 October 2013 | publisher= Not Even Wrong }}</ref> This state of affairs should not be viewed as a crisis in physics, but rather, as [[Biography:David Gross|David Gross]] has said, "the kind of acceptable scientific confusion that discovery eventually transcends."<ref>{{Cite web | author= Peter Byrne | date= 24 May 2013 | title= Waiting for the Revolution | url=  http://www.simonsfoundation.org/quanta/20130524-waiting-for-the-revolution/ | access-date= 19 October 2013 | work= Quanta Magazine | publisher= simonsfoundation.org}}</ref>

The fourth fundamental force, gravitation, is not yet integrated into particle physics in a consistent way.

===Higgs boson===
[[File:CMS Higgs-event.jpg|thumb|250px|One possible signature of a Higgs boson from a simulated proton–proton collision. It decays almost immediately into two jets of hadrons and two electrons, visible as lines.]]
{{further|Physics:Higgs boson}}
As of 2011, the [[Physics:Higgs boson|Higgs boson]], the quantum of a field that is thought to provide particles with [[Physics:Rest mass|rest mass]]es, remained the only particle of the Standard Model to be verified.
On July 4, 2012, physicists working at CERN's [[Physics:Large Hadron Collider|Large Hadron Collider]] announced that they had discovered a new subatomic particle greatly resembling the Higgs boson, a potential key to an understanding of why elementary particles have masses and indeed to the existence of diversity and life in the universe.<ref name="nytimes.com">{{Cite news|url=https://www.nytimes.com/2012/07/05/science/cern-physicists-may-have-discovered-higgs-boson-particle.html?pagewanted=3&_r=1&ref=science|title = Physicists Find Elusive Particle Seen as Key to Universe|newspaper = The New York Times|date = 4 July 2012|last1 = Overbye|first1 = Dennis}}</ref> [[Biography:Rolf-Dieter Heuer|Rolf-Dieter Heuer]], the director general of CERN, said that it was too soon to know for sure whether it is an entirely new particle, which weighs in at 125&nbsp;billion electron volts&nbsp;– one of the heaviest subatomic particles yet&nbsp;– or, indeed, the elusive particle predicted by the [[Physics:Standard Model|Standard Model]], the theory that has ruled physics for the last half-century.<ref name="nytimes.com"/> It is unknown if this particle is an impostor, a single particle or even the first of many particles yet to be discovered. The latter possibilities are particularly exciting to physicists since they could point the way to new deeper ideas, [[Physics:Physics beyond the Standard Model|beyond the Standard Model]], about the nature of reality. For now, some physicists are calling it a "Higgslike" particle.<ref name="nytimes.com"/> Joe Incandela, of the [[Organization:University of California, Santa Barbara|University of California, Santa Barbara]], said, "It's something that may, in the end, be one of the biggest observations of any new phenomena in our field in the last 30 or 40 years, going way back to the discovery of quarks, for example."<ref name="nytimes.com"/> The groups operating the large detectors in the collider said that the likelihood that their signal was a result of a chance fluctuation was less than one chance in 3.5 million, so-called "five sigma," which is the gold standard in physics for a discovery. [[Biography:Michael Turner (cosmologist)|Michael Turner]], a cosmologist at the University of Chicago and the chairman of the physics center board, said

{{blockquote|''This is a big moment for particle physics and a crossroads&nbsp;— will this be the high water mark or will it be the first of many discoveries that point us toward solving the really big questions that we have posed?''|author=[[Biography:Michael Turner (cosmologist)|Michael Turner]], University of Chicago<ref name="nytimes.com"/>}}

Confirmation of the Higgs boson or something very much like it would constitute a rendezvous with destiny for a generation of physicists who have believed the boson existed for half a century without ever seeing it. Further, it affirms a grand view of a universe ruled by simple and elegant and symmetrical laws, but in which everything interesting in it being a result of flaws or breaks in that symmetry.<ref name="nytimes.com"/> According to the Standard Model, the Higgs boson is the only visible and particular manifestation of an [[Physics:Higgs field|invisible force field]] that permeates space and imbues elementary particles that would otherwise be massless with mass. Without this Higgs field, or something like it, physicists say all the elementary forms of matter would zoom around at the speed of light; there would be neither atoms nor life. The Higgs boson achieved a notoriety rare for abstract physics.<ref name="nytimes.com"/> To the eternal dismay of his colleagues, Leon Lederman, the former director of [[Organization:Fermilab|Fermilab]], called it the "God particle" in his book of the same name, later quipping that he had wanted to call it "the goddamn particle".<ref name="nytimes.com"/> Professor Incandela also stated,

{{blockquote|''This boson is a very profound thing we have found. We're reaching into the fabric of the universe at a level we've never done before. We've kind of completed one particle's story [...] We're on the frontier now, on the edge of a new exploration. This could be the only part of the story that's left, or we could open a whole new realm of discovery.''|author=Joe Incandela, University of California<ref>{{cite web|last=Rincon |first=Paul |url=https://www.bbc.co.uk/news/world-18702455 |title=BBC News - Higgs boson-like particle discovery claimed at LHC |publisher=Bbc.co.uk |date=2012-07-04 |access-date=2013-04-20}}</ref>}}

Dr. [[Biography:Peter Higgs|Peter Higgs]] was one of six physicists, working in three independent groups, who in 1964 invented the notion of the cosmic molasses, or Higgs field. The others were Tom Kibble of [[Organization:Imperial College London|Imperial College, London]]; [[Biography:C. R. Hagen|Carl Hagen]] of the [[Organization:University of Rochester|University of Rochester]]; [[Biography:Gerald Guralnik|Gerald Guralnik]] of [[Organization:Brown University|Brown University]]; and [[Biography:François Englert|François Englert]] and [[Biography:Robert Brout|Robert Brout]], both of Université Libre de Bruxelles.<ref name="nytimes.com"/> One implication of their theory was that this Higgs field, normally invisible and, of course, odorless, would produce its own quantum particle if hit hard enough, by the right amount of energy. The particle would be fragile and fall apart within a millionth of a second in a dozen different ways depending upon its own mass. Unfortunately, the theory did not say how much this particle should weigh, which is what made it so difficult to find. The particle eluded researchers at a succession of particle accelerators, including the [[Physics:Large Electron–Positron Collider|Large Electron–Positron Collider]] at CERN, which closed down in 2000, and the [[Physics:Tevatron|Tevatron]] at the [[Organization:Fermilab|Fermi National Accelerator Laboratory]], or Fermilab, in Batavia, Ill., which shut down in 2011.<ref name="nytimes.com"/>

Further experiments continued and in March 2013 it was tentatively confirmed that the newly discovered particle was a Higgs Boson.

Although they have never been seen, Higgslike fields play an important role in theories of the universe and in string theory. Under certain conditions, according to the strange accounting of Einsteinian physics, they can become suffused with energy that exerts an antigravitational force. Such fields have been proposed as the source of an enormous burst of expansion, known as inflation, early in the universe and, possibly, as the secret of the dark energy that now seems to be speeding up the expansion of the universe.<ref name="nytimes.com"/>

==Notes==
{{reflist}}

==References==
* {{Citation | last=Kragh | first=Helge | year=1999 | publication-date=1999 | title=Quantum Generations: A History of Physics in the Twentieth Century | location=Princeton | publisher=Princeton University Press}}.

{{Particles}}

[[Category:History of physics|Subatomic]]
[[Category:Particle physics]]
[[Category:Nuclear physics]]

{{Sourceattribution|History of subatomic physics}}