Editing History of physics (section)

== Contemporary physics ==
{{further|List of unsolved problems in physics}}

===Quantum field theory===
[[File:Feynmann Diagram Gluon Radiation.svg|thumb|upright=1.3|A [[Feynman diagram]] representing (left to right) the production of a photon (blue [[sine wave]]) from the [[annihilation]] of an electron and its complementary [[antiparticle]], the [[positron]]. The photon becomes a [[quark]]–[[antiquark]] pair and a [[gluon]] (green spiral) is released.]]
[[File:Feynman-richard_p.jpg|thumb|upright=0.8|[[Richard Feynman]]'s Los Alamos ID badge]]
As the philosophically inclined continued to debate the fundamental nature of the universe, quantum theories continued to be produced, beginning with [[Paul Dirac]]'s formulation of a relativistic quantum theory in 1928. However, attempts to quantize electromagnetic theory entirely were stymied throughout the 1930s by theoretical formulations yielding infinite energies. This situation was not considered adequately resolved until after [[World War&nbsp;II]], when [[Julian Schwinger]], [[Richard Feynman]] and [[Sin-Itiro Tomonaga]] independently posited the technique of [[renormalization]], which allowed for an establishment of a robust [[quantum electrodynamics]] (QED).<ref>{{Harvtxt|Schweber|1994}}</ref>

Meanwhile, new theories of [[Elementary particle|fundamental particles]] proliferated with the rise of the idea of the [[Quantum field theory|quantization of fields]] through "[[Exchange interaction|exchange forces]]" regulated by an exchange of short-lived [[Virtual particle|"virtual" particle]]s, which were allowed to exist according to the laws governing the uncertainties inherent in the quantum world. Notably, [[Hideki Yukawa]] proposed that the positive charges of the [[Atomic nucleus|nucleus]] were kept together courtesy of a powerful but short-range force mediated by a particle with a mass between that of the electron and [[proton]]. This particle, the "[[pion]]", was identified in 1947 as part of what became a slew of particles discovered after World War II. Initially, such particles were found as [[Ionization|ionizing radiation]] left by [[cosmic ray]]s, but increasingly came to be produced in newer and more powerful [[particle accelerator]]s.<ref>{{Harvtxt|Galison|1997}}</ref>

Outside particle physics, significant advances of the time were:
* the invention of the [[laser]] (1964 [[Nobel Prize in Physics]]);
* the theoretical and experimental research of [[superconductivity]], especially the invention of a [[Ginzburg–Landau theory|quantum theory of superconductivity]] by [[Vitaly Ginzburg]] and [[Lev Landau]] (1962 Nobel Prize in Physics) and, later, its explanation via [[Cooper pair]]s (1972 Nobel Prize in Physics). The Cooper pair was an early example of [[quasiparticle]]s.

===Unified field theories===
{{main|Unified field theory}}
Einstein deemed that all [[fundamental interaction]]s in nature can be explained in a single theory. Unified field theories were numerous attempts to "merge" several interactions. One of many formulations of such theories (as well as field theories in general) is a ''[[gauge theory]]'', a generalization of the idea of symmetry. Eventually the [[Standard Model]] (see below) succeeded in unification of strong, weak, and electromagnetic interactions. All attempts to unify [[gravitation]] with something else failed.

===Particle physics and the Standard Model===
{{main|History of subatomic physics|Standard Model}}
[[File:Standard Model of Elementary Particles.svg|left|thumb|upright=1.6|The [[Standard Model]]]]
[[File:Chien-Shiung Wu (1912-1997) in 1958.jpg|thumb|upright|[[Chien-Shiung Wu]] worked on parity violation in 1956 and announced her results in January 1957.<ref>{{Cite web|title=Chien-Shiung Wu|date=25 May 2023 |url=https://www.britannica.com/biography/Chien-Shiung-Wu}}</ref>]]
When [[parity (physics)|parity]] was broken in weak interactions by [[Chien-Shiung Wu]] in her [[Wu experiment|experiment]], a series of discoveries were created thereafter.<ref>{{Cite web|title=Antimatter|url=https://home.cern/science/physics/antimatter|date=2021-03-01}}</ref> The interaction of these particles by [[scattering]] and [[Particle decay|decay]] provided a key to new fundamental quantum theories. [[Murray Gell-Mann]] and [[Yuval Ne'eman]] brought some order to these new particles by classifying them according to certain qualities, beginning with what Gell-Mann referred to as the "[[Eightfold way (physics)|Eightfold Way]]". While its further development, the [[quark model]], at first seemed inadequate to describe [[Strong interaction|strong nuclear forces]], allowing the temporary rise of competing theories such as the [[S-Matrix]], the establishment of [[quantum chromodynamics]] in the 1970s finalized a set of fundamental and exchange particles, which allowed for the establishment of a "standard model" based on the mathematics of [[Gauge theory|gauge invariance]], which successfully described all forces except for gravitation, and which remains generally accepted within its domain of application.<ref name="Harvtxt|Kragh|1999"/>

The Standard Model, based on the [[Yang–Mills theory]]<ref>{{Cite web|title=theory of everything|url=https://ncatlab.org/nlab/show/theory+of+everything}}</ref> groups the [[electroweak interaction]] theory and [[quantum chromodynamics]] into a structure denoted by the [[gauge group]] SU(3)×SU(2)×U(1). The formulation of the unification of the electromagnetic and [[weak interaction]]s in the standard model is due to [[Abdus Salam]], [[Steven Weinberg]] and, subsequently, [[Sheldon Glashow]]. Electroweak theory was later confirmed experimentally (by observation of [[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.|last11=Sacton|first11=J.|date=1973-09-03|title=Search for elastic muon-neutrino electron scattering|journal=Physics Letters B|language=en|volume=46|issue=1|pages=121–124|doi=10.1016/0370-2693(73)90494-2|bibcode=1973PhLB...46..121H|issn=0370-2693}}</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.|last11=Van Doninck|first11=W.|date=1973-09-03|title=Observation of neutrino-like interactions without muon or electron in the gargamelle neutrino experiment|journal=Physics Letters B|language=en|volume=46|issue=1|pages=138–140|doi=10.1016/0370-2693(73)90499-1|bibcode=1973PhLB...46..138H|issn=0370-2693}}</ref><ref>F. J. Hasert ''et al.'' ''Nuclear Physics'' B73, 1(1974); Paper presented at the London Conference 1974, no. 1013.</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> and distinguished by the 1979 Nobel Prize in Physics.<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 |archive-url=https://web.archive.org/web/20040803075503/http://www.nobel.se/physics/laureates/1979/ |archive-date=2004-08-03 |url-status=dead }}</ref>

Since the 1970s, fundamental particle physics has provided insights into early universe [[cosmology]], particularly the [[Big Bang]] theory proposed as a consequence of Einstein's [[general relativity|general theory of relativity]]. However, starting in the 1990s, astronomical observations have also provided new challenges, such as the need for new explanations of galactic stability ("[[dark matter]]") and the [[Accelerating universe|apparent acceleration in the expansion of the universe]] ("[[dark energy]]").

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 [[supersymmetry]] and [[string theory]] were believed by many theorists to be a promising avenue forward. The [[Large Hadron Collider]], however, which began operating in 2008, has failed to find any evidence that is supportive of supersymmetry and string theory.<ref>{{cite web |last=Woit |first=Peter |author-link=Peter Woit |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>

===Cosmology===
{{main|Physical cosmology}}
Cosmology may be said to have become a serious research question with the publication of Einstein's General Theory of Relativity in 1915 although it did not enter the scientific mainstream until the period known as the "[[Golden age of general relativity]]".

About a decade later, in the midst of what was dubbed the "[[Great Debate (astronomy)|Great Debate]]", [[Edwin Hubble]] and [[Vesto Slipher]] discovered the [[expansion of universe]] in the 1920s measuring the redshifts of [[Doppler spectra]] from galactic nebulae. Using Einstein's general relativity, [[Georges Lemaître]] and [[George Gamow]] formulated what would become known as the [[Big Bang theory]]. A rival, called the [[steady state theory]], was devised by [[Fred Hoyle]], [[Thomas Gold]], [[Jayant Narlikar]] and [[Hermann Bondi]].

[[Cosmic microwave background radiation]] was verified in the 1960s by [[Arno Allan Penzias]] and [[Robert Woodrow Wilson]], and this discovery favoured the big bang at the expense of the steady state scenario. Later work was by [[George Smoot]] et al. (1989), among other contributors, using data from the [[Cosmic Background explorer]] (CoBE) and the [[Wilkinson Microwave Anisotropy Probe]] (WMAP) satellites refined these observations. The 1980s (the same decade of the COBE measurements) also saw the proposal of [[Inflation (cosmology)|inflation theory]] by [[Alan Guth]].

Recently the problems of dark matter and dark energy have risen to the top of the cosmology agenda.

===Higgs boson===
[[File:CMS Higgs-event.jpg|thumb|upright=1.2|One possible signature of a Higgs boson from a simulated [[proton]]–proton collision. It decays almost immediately into two jets of [[hadron]]s and two electrons, visible as lines.]]
On July 4, 2012, physicists working at CERN's [[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 mass 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 |work=The New York Times |first=Dennis |last=Overbye |title=Physicists Find Particle That Could Be the Higgs Boson |date=4 July 2012}}</ref> For now, some physicists are calling it a "Higgslike" particle.<ref name="nytimes.com"/> [[Joe Incandela]], of the [[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 [[quark]]s, for example."<ref name="nytimes.com"/> [[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 – 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=[[Michael Turner (cosmologist)|Michael Turner]], University of Chicago<ref name="nytimes.com"/>}}

[[Peter Higgs]] was one of six physicists, working in three independent groups, who, in 1964, invented the notion of the Higgs field ("cosmic molasses"). The others were [[Tom Kibble]] of [[Imperial College London|Imperial College, London]]; [[C. R. Hagen|Carl Hagen]] of the [[University of Rochester]]; [[Gerald Guralnik]] of [[Brown University]]; and [[François Englert]] and [[Robert Brout]], both of [[Université libre de Bruxelles]].<ref name="nytimes.com"/>

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 accelerating the expansion of the universe.<ref name="nytimes.com"/>

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=== Physical sciences ===

With increased accessibility to and elaboration upon advanced analytical techniques in the 19th century, physics was defined as much, if not more, by those techniques than by the search for universal principles of motion and energy, and the fundamental nature of matter. Fields such as [[acoustics]], [[geophysics]], [[astrophysics]], [[aerodynamics]], [[Plasma (physics)|plasma physics]], [[Cryogenics|low-temperature physics]], and [[solid-state physics]] joined optics, [[fluid dynamics]], [[electromagnetism]], and [[mechanics]] as areas of physical research. In the 20th century, physics also became closely allied with such fields as [[Electrical engineering|electrical]], [[Aerospace engineering|aerospace]] and [[Materials science|materials]] engineering, and physicists began to work in government and industrial laboratories as much as in academic settings. Following World War&nbsp;II, the population of physicists increased dramatically, and came to be centered on the United States, while, in more recent decades, physics has become a more international pursuit than at any time in its previous history.