Editing Physics (section)

===Fields===
The major fields of physics, along with their subfields and the theories and concepts they employ, are shown in the following table.
{{Subfields of physics}}

Since the 20th century, the individual fields of physics have become increasingly specialised, and today most physicists work in a single field for their entire careers. "Universalists" such as Einstein (1879–1955) and [[Lev Landau]] (1908–1968), who worked in multiple fields of physics, are now very rare.{{efn|Yet, universalism is encouraged in the culture of physics. For example, the [[World Wide Web]], which was innovated at [[CERN]] by [[Tim Berners-Lee]], was created in service to the computer infrastructure of CERN, and was/is intended for use by physicists worldwide. The same might be said for [[arXiv.org]]}}

Contemporary research in physics can be broadly divided into [[Nuclear physics|nuclear]] and [[particle physics]]; [[condensed matter physics]]; [[atomic, molecular, and optical physics]]; [[astrophysics]]; and applied physics. Some physics departments also support [[physics education research]] and [[physics outreach]].<ref>{{cite web |last=Redish |first=E. |title=Science and Physics Education Homepages |url=https://www.physics.umd.edu/perg/homepages.htm |publisher=University of Maryland Physics Education Research Group |url-status=live |archive-url=https://web.archive.org/web/20160728005227/http://www.physics.umd.edu/perg/homepages.htm |archive-date=28 July 2016 }}</ref>

====Nuclear and particle====
{{Main|Particle physics|Nuclear physics}}
[[File:CMS Higgs-event.jpg|thumb|A simulated event in the CMS detector of the [[Large Hadron Collider]], featuring a possible appearance of the [[Higgs boson]]]]

Particle physics is the study of the elementary constituents of [[matter]] and energy and the [[Fundamental interaction|interactions]] between them.<ref name="aps-dpf">{{cite web|title=Division of Particles & Fields |url=http://www.aps.org/units/dpf/index.cfm |publisher=American Physical Society |access-date=18 October 2012 |url-status=dead |archive-url=https://web.archive.org/web/20160829105655/http://www.aps.org/units/dpf/index.cfm |archive-date=29 August 2016 }}</ref> In addition, particle physicists design and develop the high-energy accelerators,<ref name="halpern2010">{{harvnb|Halpern|2010}}</ref> detectors,<ref name="grupen1999">{{harvnb|Grupen|1999}}</ref> and [[Computational particle physics|computer programs]]<ref name="walsh2012">{{harvnb|Walsh|2012}}</ref> necessary for this research. The field is also called "high-energy physics" because many elementary particles do not occur naturally but are created only during high-energy [[collision]]s of other particles.<ref name="iop-hepp">{{cite web|title=High Energy Particle Physics Group|url=http://www.iop.org/activity/groups/subject/hepp/index.html|publisher=Institute of Physics|access-date=18 October 2012|archive-date=29 May 2019|archive-url=https://web.archive.org/web/20190529024813/http://www.iop.org/activity/groups/subject/hepp/index.html|url-status=live}}</ref>

Currently, the interactions of elementary particles and [[Field (physics)|fields]] are described by the [[Standard Model]].<ref name="oerter2006">{{harvnb|Oerter|2006}}</ref> The model accounts for the 12 known particles of matter ([[quark]]s and [[lepton]]s) that interact via the [[strong nuclear force|strong]], weak, and electromagnetic [[fundamental force]]s.<ref name="oerter2006" /> Dynamics are described in terms of matter particles exchanging [[gauge boson]]s ([[gluon]]s, [[W and Z bosons]], and [[photon]]s, respectively).<ref name="gribbin1998">{{harvnb|Gribbin|Gribbin|Gribbin|1998}}</ref> The Standard Model also predicts a particle known as the Higgs boson.<ref name="oerter2006" /> In July 2012 CERN, the European laboratory for particle physics, announced the detection of a particle consistent with the Higgs boson,<ref name="eonr-higgs">{{cite web |title=CERN experiments observe particle consistent with long-sought Higgs boson |url=http://press-archived.web.cern.ch/press-archived/PressReleases/Releases2012/PR17.12E.html |publisher=[[CERN]] |access-date=18 October 2012 |date=4 July 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121114084952/http://press-archived.web.cern.ch/press-archived/PressReleases/Releases2012/PR17.12E.html |archive-date=14 November 2012 }}</ref> an integral part of the [[Higgs mechanism]].

Nuclear physics is the field of physics that studies the constituents and interactions of [[atomic nuclei]]. The most commonly known applications of nuclear physics are [[nuclear power]] generation and [[nuclear weapons]] technology, but the research has provided application in many fields, including those in [[nuclear medicine]] and magnetic resonance imaging, [[ion implantation]] in [[materials engineering]], and [[radiocarbon dating]] in geology and [[archaeology]].

====Atomic, molecular, and optical====
{{Main|Atomic, molecular, and optical physics}}

Atomic, [[Molecule|molecular]], and optical physics (AMO) is the study of matter—matter and light—matter interactions on the scale of single atoms and molecules. The three areas are grouped together because of their interrelationships, the similarity of methods used, and the commonality of their relevant energy scales. All three areas include both classical, semi-classical and [[quantum mechanics|quantum]] treatments; they can treat their subject from a microscopic view (in contrast to a macroscopic view).

Atomic physics studies the [[electron shell]]s of atoms. Current research focuses on activities in quantum control, cooling and trapping of atoms and ions,<ref>{{cite web |title=Atomic, Molecular, and Optical Physics |website=MIT Department of Physics |url=http://web.mit.edu/physics/research/abcp/areas.html#amo |access-date=21 February 2014 |archive-url= https://web.archive.org/web/20140227043906/http://web.mit.edu/physics/research/abcp/areas.html#amo |archive-date=27 February 2014 |url-status=live }}</ref><ref>{{cite web |title=Korea University, Physics AMO Group |url=http://physics.korea.ac.kr/research/research_amo.php |access-date=21 February 2014 |archive-url=https://web.archive.org/web/20140301112653/http://physics.korea.ac.kr/research/research_amo.php |archive-date=1 March 2014 |url-status=dead }}</ref><ref>{{cite web |title=Aarhus Universitet, AMO Group |url=http://phys.au.dk/forskning/forskningsomraader/amo/ |access-date=21 February 2014 |url-status=live |archive-url=https://web.archive.org/web/20140307062146/http://phys.au.dk/forskning/forskningsomraader/amo/ |archive-date=7 March 2014 }}</ref> low-temperature collision dynamics and the effects of electron correlation on structure and dynamics. Atomic physics is influenced by the [[Atomic nucleus|nucleus]] (see [[hyperfine splitting]]), but intra-nuclear phenomena such as [[nuclear fission|fission]] and [[nuclear fusion|fusion]] are considered part of nuclear physics.

[[Molecular physics]] focuses on multi-atomic structures and their internal and external interactions with matter and light. [[Optical physics]] is distinct from optics in that it tends to focus not on the control of classical light fields by macroscopic objects but on the fundamental properties of [[optical field]]s and their interactions with matter in the microscopic realm.

====Condensed matter====
{{Main|Condensed matter physics}}
[[File:Bose Einstein condensate.png|right|thumb|upright=1.25|Velocity-distribution data of a gas of [[rubidium]] atoms, confirming the discovery of a new phase of matter, the [[Bose–Einstein condensate]]]]

Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter.<ref name="taylorheinonen2002">{{harvnb|Taylor|Heinonen|2002}}</ref><ref>{{Cite book|last1=Girvin|first1=Steven M.|url=https://books.google.com/books?id=2ESIDwAAQBAJ|title=Modern Condensed Matter Physics|last2=Yang|first2=Kun|date=28 February 2019|publisher=Cambridge University Press|isbn=978-1-108-57347-4|language=en|access-date=23 August 2020|archive-date=25 February 2021|archive-url=https://web.archive.org/web/20210225152053/https://books.google.com/books?id=2ESIDwAAQBAJ|url-status=live}}</ref> In particular, it is concerned with the "condensed" [[phase (matter)|phases]] that appear whenever the number of particles in a system is extremely large and the interactions between them are strong.<ref name=cohen2008>{{harvnb|Cohen|2008}}</ref>

The most familiar examples of condensed phases are [[Solid-state physics|solids]] and liquids, which arise from the bonding by way of the [[electromagnetic force]] between atoms.<ref name="moore2011">{{harvnb |Moore|2011|pp=255–258}}</ref> More exotic condensed phases include the [[superfluid]]<ref name="leggett1999">{{harvnb |Leggett|1999}}</ref> and the [[Bose–Einstein condensate]]<ref name="levy2001">{{harvnb |Levy|2001}}</ref> found in certain atomic systems at very low temperature, the [[superconductivity|superconducting]] phase exhibited by [[conduction electron]]s in certain materials,<ref name=stajiccoontzosborne2011>{{harvnb |Stajic|Coontz|Osborne|2011}}</ref> and the [[ferromagnet]]ic and [[antiferromagnet]]ic phases of [[Spin (physics)|spins]] on [[crystal lattice|atomic lattices]].<ref name="mattis2006">{{harvnb|Mattis|2006}}</ref>

Condensed matter physics is the largest field of contemporary physics. Historically, condensed matter physics grew out of solid-state physics, which is now considered one of its main subfields.<ref name="aps-dcmp">{{cite web |url=http://www.aps.org/units/dcmp/history.cfm |title=History of Condensed Matter Physics |publisher=[[American Physical Society]] |access-date=31 March 2014 |url-status=live |archive-url=https://web.archive.org/web/20110912081611/http://www.aps.org/units/dcmp/history.cfm |archive-date=12 September 2011 }}</ref> The term ''condensed matter physics'' was apparently coined by [[Philip Warren Anderson|Philip Anderson]] when he renamed his research group—previously ''solid-state theory''—in 1967.<ref name="princeton-anderson">{{cite web |title=Philip Anderson |url=http://www.princeton.edu/physics/people/display_person.xml?netid=pwa&display=faculty |publisher=Princeton University, Department of Physics |access-date=15 October 2012 |url-status=live |archive-url=https://web.archive.org/web/20111008123438/http://www.princeton.edu/physics/people/display_person.xml?netid=pwa&display=faculty |archive-date=8 October 2011 }}</ref> In 1978, the Division of Solid State Physics of the [[American Physical Society]] was renamed as the Division of Condensed Matter Physics.<ref name="aps-dcmp" /> Condensed matter physics has a large overlap with chemistry, [[materials science]], [[nanotechnology]] and engineering.<ref name="cohen2008" />

====Astrophysics====
{{Main|Astrophysics|Physical cosmology}}
[[File:Hubble ultra deep field high rez edit1.jpg|thumb|left|upright=1.5|The deepest visible-light image of the [[universe]], the [[Hubble Ultra-Deep Field]]. The vast majority of objects seen above are distant galaxies.]]

Astrophysics and astronomy are the application of the theories and methods of physics to the study of [[stellar structure]], [[stellar evolution]], the origin of the Solar System, and related problems of cosmology. Because astrophysics is a broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.<ref>{{cite web |url=http://manoa.hawaii.edu/astronomy/bs-in-astrophysics/ |title=BS in Astrophysics |publisher=University of Hawaii at Manoa |access-date=14 October 2016 |archive-url=https://web.archive.org/web/20160404195943/http://manoa.hawaii.edu/astronomy/bs-in-astrophysics/ |archive-date=4 April 2016 }}</ref>

The discovery by [[Karl Jansky]] in 1931 that radio signals were emitted by celestial bodies initiated the science of [[radio astronomy]]. Most recently, the frontiers of astronomy have been expanded by space exploration. Perturbations and interference from the Earth's atmosphere make space-based observations necessary for [[infrared astronomy|infrared]], [[ultraviolet astronomy|ultraviolet]], [[gamma-ray astronomy|gamma-ray]], and [[X-ray astronomy]].

Physical cosmology is the study of the formation and evolution of the universe on its largest scales. Albert Einstein's theory of relativity plays a central role in all modern cosmological theories. In the early 20th century, [[Edwin Hubble|Hubble]]'s discovery that the universe is expanding, as shown by the [[Hubble diagram]], prompted rival explanations known as the [[steady-state model|steady state]] universe and the [[Big Bang]].

The Big Bang was confirmed by the success of [[Big Bang nucleosynthesis]] and the discovery of the [[cosmic microwave background]] in 1964. The Big Bang model rests on two theoretical pillars: Albert Einstein's general relativity and the [[cosmological principle]]. Cosmologists have recently established the [[Lambda-CDM model|ΛCDM model]] of the evolution of the universe, which includes [[cosmic inflation]], [[dark energy]], and [[dark matter]].