View source for State of matter

{{Short description|Forms which matter can take}}
{{Distinguish|Phase (matter)}}
{{For|a list of exotic states of matter|List of states of matter}}
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{{Multiple image
| direction = vertical
| total_width = 225
| image1 = Bromine vial in acrylic cube.jpg
| caption1 = [[Bromine]] in both [[liquid]] and [[gas]] state, encased inside [[acrylate polymer|acrylic]] in [[solid]] state
| image2 = Helium discharge tube.jpg
| caption2 = [[Helium]]'s orange glow in its [[plasma (physics)|plasma]] state
| image3 = Phase diagram of water simplified.svg
| caption3 = A simplified phase diagram for [[water]], showing whether solid ice, liquid water, or gaseous water vapor is the most stable at different combinations of temperature and pressure
}}

In [[physics]], a '''state of matter''' or '''phase of matter''' is one of the distinct forms in which [[matter]] can exist. Four states of matter are observable in everyday life: [[solid]], [[liquid]], [[gas]], and [[Plasma (physics)|plasma]].

Different states are distinguished by the ways the component particles ([[atoms]], [[molecules]], [[ions]] and [[electrons]]) are arranged, and how they behave collectively. In a solid, the particles are tightly packed and held in fixed positions, giving the material a definite shape and [[volume]]. In a liquid, the particles remain close together but can move past one another, allowing the substance to maintain a fixed volume while adapting to the shape of its container. In a gas, the particles are far apart and move freely, allowing the substance to expand and fill both the shape and volume of its container. Plasma is similar to a gas, but it also contains charged particles (ions and free electrons) that move independently and respond to electric and magnetic fields.

Beyond the classical states of matter, a wide variety of additional states are known to exist. Some of these lie between the traditional categories; for example, [[liquid crystal]]s exhibit properties of both solids and liquids. Others represent entirely different kinds of ordering. [[Magnetic ordering|Magnetic states]], for instance, do not depend on the spatial arrangement of atoms, but rather on the alignment of their intrinsic magnetic moments ([[Spin (physics)|spins]]). Even in a solid where atoms are fixed in position, the spins can organize in distinct ways, giving rise to magnetic states such as [[ferromagnetism]] or [[antiferromagnetism]].

Some states occur only under extreme conditions, such as [[Bose–Einstein condensate]]s and [[Fermionic condensate]]s (in extreme cold), [[neutron-degenerate matter]] (in extreme density), and [[quark–gluon plasma]] (at extremely [[High-energy nuclear physics|high energy]]).

The term ''[[phase (matter)|phase]]'' is sometimes used as a [[synonym]] for state of matter, but it is possible for a single compound to form different phases that are in the same state of matter. For example, [[ice]] is the solid state of water, but there are multiple [[phases of ice]] with different [[crystal structure]]s, which are formed at different pressures and temperatures.

== Four classical states ==

===Solid===
{{Main|Solid}}
[[File:Gif -AtomosSolido 01.gif|thumb|upright=0.75|Simple illustration of particles in the solid state – they are closely packed to each other.]]

In a solid, constituent particles (ions, atoms, or molecules) are closely packed together. The [[Bonding in solids|forces between particles]] are so strong that the particles cannot move freely but can only vibrate. As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by an outside force, as when broken or cut.

In [[crystal|crystalline solids]], the particles (atoms, molecules, or ions) are packed in a regularly ordered, repeating pattern. There are various different [[crystal structure]]s, and the same substance can have more than one structure (or solid phase). For example, [[iron]] has a [[cubic crystal system|body-centred cubic]] structure at temperatures below {{convert|912|C|F}}, and a [[cubic crystal system|face-centred cubic]] structure between 912 and {{convert|1394|C|F}}. [[Ice]] has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures.<ref>
{{Cite book
 |author=M.A. Wahab
 |date=2005
 |title=Solid State Physics: Structure and Properties of Materials
 |publisher=Alpha Science
 |pages=1–3
 |isbn=978-1-84265-218-3
}}</ref>

[[Glass]]es and other non-crystalline, [[amorphous solid]]s without [[order and disorder (physics)|long-range order]] are not [[thermal equilibrium]] ground states; therefore they are described below as nonclassical states of matter.

Solids can be transformed into liquids by melting, and liquids can be transformed into solids by freezing. Solids can also change directly into gases through the process of [[sublimation (chemistry)|sublimation]], and gases can likewise change directly into solids through [[deposition (phase transition)|deposition]].

===Liquid===
{{Main|Liquid}}
[[File:Gif -AtomosLiquid 03.gif|thumb|upright=0.75|Simple illustration of particles in the liquid state – they can flow and change shape.]]

A liquid is a nearly incompressible [[fluid]] that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if the [[temperature]] and [[pressure]] are constant. When a solid is heated above its [[melting point]], it becomes liquid, given that the pressure is higher than the [[triple point]] of the substance. Intermolecular (or interatomic or interionic) forces are still important, but the molecules have enough energy to move relative to each other and the structure is mobile. This means that the shape of a liquid is not definite but is determined by its container. The volume is usually greater than that of the corresponding solid, the best known exception being [[water]], H{{sub|2}}O. The highest temperature at which a given liquid can exist is its [[critical temperature]].<ref name="White">
{{Cite book
 |author=F. White
 |date=2003
 |title=Fluid Mechanics
 |page=4
 |publisher=McGraw-Hill
 |isbn=978-0-07-240217-9
}}</ref>

===Gas===

{{Main|Gas}}
[[File:Gif -AtomosGas 02.gif|thumb|upright=0.75|Simple illustration of particles in the gas state – in reality these particles will be much further apart.]]

A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.

In a gas, the molecules have enough [[kinetic energy]] so that the effect of intermolecular forces is small (or zero for an [[ideal gas]]), and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the [[boiling point]], or else by reducing the pressure at constant temperature.

At temperatures below its [[critical temperature]], a gas is also called a [[vapor]], and can be liquefied by compression alone without cooling. A vapor can exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the [[vapor pressure]] of the liquid (or solid).

A [[supercritical fluid]] (SCF) is a gas whose temperature and pressure are above the critical temperature and [[critical temperature|critical pressure]] respectively. In this state, the distinction between liquid and gas disappears. A supercritical fluid has the physical properties of a gas, but its high density confers solvent properties in some cases, which leads to useful applications. For example, [[supercritical carbon dioxide]] is used to [[supercritical fluid extraction|extract]] [[caffeine]] in the manufacture of [[decaffeination|decaffeinated]] coffee.<ref name=Turrell>
{{Cite book
 |author=G. Turrell
 |date=1997
 |title=Gas Dynamics: Theory and Applications
 |url=https://books.google.com/books?id=-6qF7TKfiNIC&pg=PA3
 |publisher=John Wiley & Sons
 |pages=3–5
 |isbn=978-0-471-97573-1
}}</ref>

===Plasma===
{{Main|Plasma (physics)}}
[[File:Plasma jacobs ladder.jpg|thumb|Artificial plasma produced in air by a [[Electric arc#Visual entertainment|Jacob's Ladder]]. The extremely strong [[potential difference]] between the two rods [[ionize]] particles in the air, creating a plasma.]]

A gas is usually converted to a plasma in one of two ways, either from a huge voltage difference between two points, or by exposing it to extremely high temperatures. Heating matter to high temperatures causes electrons to leave the atoms, resulting in the presence of free electrons. This creates a so-called partially ionized plasma. At very high temperatures, such as those present in stars, it is assumed that essentially all electrons are "free", and that a very high-energy plasma is essentially bare nuclei swimming in a sea of electrons. This forms the so-called fully ionized plasma.

The plasma state is often misunderstood, and although not freely existing under normal conditions on Earth, it is quite commonly generated by either [[lightning]], [[electric spark]]s, [[Fluorescent lamp|fluorescent lights]], [[Neon sign|neon lights]] or in [[Plasma display|plasma televisions]]. The [[solar corona|Sun's corona]], some types of [[flame]], and stars are all examples of illuminated matter in the plasma state. Plasma is by far the most abundant of the four fundamental states; 99% of all [[ordinary matter]] in the universe is plasma, as it composes all [[stars]].<ref>{{Cite web |date=Sep 7, 1999 |title=Plasma, Plasma, Everywhere |url=https://science.nasa.gov/science-news/science-at-nasa/1999/ast07sep99_1 |website=NASA Science}}</ref><ref>{{Cite book |last=Aschwanden, M. J. |title=Physics of the Solar Corona. An Introduction. |publisher=Praxis Publishing |year=2004 |isbn=978-3-540-22321-4}}</ref><ref>{{Cite book |last=Piel |first=Alexander |url=https://books.google.com/books?id=9cA0DwAAQBAJ&pg=PR8 |title=Plasma Physics: An Introduction to Laboratory, Space, and Fusion Plasmas |date=2017-09-07 |publisher=Springer |isbn=978-3-319-63427-2 |language=en}}</ref>

==Phase transitions==

{{Main|Phase transitions}}

[[File:Phase change - en.svg|class=skin-invert-image|thumb|upright=1.45|This diagram shows the nomenclature for the different phase transitions.]]

A state of matter is also characterized by [[phase transitions]]. A phase transition indicates a change in structure and can be recognized by an abrupt change in properties. A distinct state of matter can be defined as any set of [[thermodynamic state|states]] distinguished from any other set of states by a [[phase transition]]. Water can be said to have several distinct solid states.<ref>
{{cite web
 |author      = M. Chaplin
 |date        = 20 August 2009
 |title       = Water phase Diagram
 |url         = https://www.lsbu.ac.uk/water/phase.html
 |website        = Water Structure and Science
 |access-date  = 23 February 2010
 |url-status=live
 |archive-url  = https://web.archive.org/web/20160303173403/https://www1.lsbu.ac.uk/water/water_phase_diagram.html
 |archive-date = 3 March 2016
 |df          = dmy-all
}}</ref> The appearance of superconductivity is associated with a phase transition, so there are [[superconductivity|superconductive]] states. Likewise, [[ferromagnetism|ferromagnetic]] states are demarcated by phase transitions and have distinctive properties.
When the change of state occurs in stages the intermediate steps are called [[mesophase]]s. Such phases have been exploited by the introduction of [[liquid crystal]] technology.<ref>
{{Cite book
 |author=D.L. Goodstein
 |date=1985
 |title=States of Matter
 |publisher=[[Dover Publications|Dover Phoenix]]
 |isbn=978-0-486-49506-4
}}</ref><ref>
{{Cite book
 |author=A.P. Sutton
 |date=1993
 |title=Electronic Structure of Materials
 |pages=10–12
 |publisher=Oxford Science Publications
 |isbn=978-0-19-851754-2
}}</ref>

[[File:Ice cubes melting in a glass.ogv|thumb|Ice cubes melting showing a change in state]]
{{Table_of_phase_transitions}}

The state or ''phase'' of a given set of matter can change depending on [[pressure]] and [[temperature]] conditions, transitioning to other phases as these conditions change to favor their existence; for example, solid transitions to liquid with an increase in temperature. Near [[absolute zero]], a substance exists as a [[solid]]. As heat is added to this substance it melts into a liquid at its [[melting point]], boils into a gas at its [[boiling point]], and if heated high enough would enter a [[plasma (physics)|plasma]] state in which the [[electrons]] are so energized that they leave their parent atoms.

Forms of matter that are not composed of molecules and are organized by different forces can also be considered different states of matter. [[Superfluids]] (like [[Fermionic condensate]]) and the [[quark–gluon plasma]] are examples.

==Non-classical states==

=== Glass ===
{{Main|Glass}}

{{multiple image
 | image1    = Silica.svg
 | alt1      = Atoms of Si and O; each atom has the same number of bonds, but the overall arrangement of the atoms is random.
 | total_width= 400
 | image2    = SiO² Quartz.svg
 | alt2      = Regular hexagonal pattern of Si and O atoms, with a Si atom at each corner and the O atoms at the centre of each side.
 | footer    = Schematic representation of a random-network glassy form (left) and ordered crystalline lattice (right) of identical chemical composition.
}}

[[Glass]] is a non-crystalline or [[amorphous solid]] material that exhibits a [[glass transition]] when heated towards the liquid state. Glasses can be made of quite different classes of materials: inorganic networks (such as window glass, made of [[silicate]] plus additives), metallic alloys, [[Ionic liquid|ionic melts]], [[aqueous solution]]s, molecular liquids, and [[polymers]].
Thermodynamically, a glass is in a [[metastable state]] with respect to its crystalline counterpart. The conversion rate, however, is practically zero.

=== Crystals with some degree of disorder ===

A [[plastic crystal]] is a molecular solid with long-range positional order but with constituent molecules retaining rotational freedom; in an [[orientational glass]] this degree of freedom is frozen in a [[order and disorder (physics)|quenched disordered]] state.

Similarly, in a [[spin glass]] magnetic disorder is frozen.

===Liquid crystal states===
{{Main|Liquid crystal}}

Liquid crystal states have properties intermediate between mobile liquids and ordered solids. Generally, they are able to flow like a liquid but exhibit long-range order. For example, the [[nematic phase]] consists of long rod-like molecules such as [[para-azoxyanisole]], which is nematic in the temperature range {{convert|118–136|C|F}}.<ref>{{cite journal|title=Phase Transitions of Liquid Crystal PAA in Confined Geometries|author=Shao, Y.|author2=Zerda, T.W.|journal=Journal of Physical Chemistry B|date=1998|volume=102|issue=18|pages=3387–3394|doi=10.1021/jp9734437}}</ref> In this state the molecules flow as in a liquid, but they all point in the same direction (within each domain) and cannot rotate freely. Like a crystalline solid, but unlike a liquid, liquid crystals react to polarized light.

Other types of liquid crystals are described in the main article on these states. Several types have technological importance, for example, in [[liquid crystal display]]s.

===Microphase separation===
{{Main|Copolymer}}

[[File:Sbs block copolymer.jpg|thumb|right|SBS block copolymer seen with [[transmission electron microscopy]] (TEM)]] [[Copolymers]] can undergo microphase separation to form a diverse array of periodic nanostructures, as shown in the example of the [[Kraton (polymer)|styrene-butadiene-styrene block copolymer]] shown at right. Microphase separation can be understood by analogy to the phase separation between [[oil]] and water. Due to chemical incompatibility between the blocks, block copolymers undergo a similar phase separation. However, because the blocks are [[covalent bond|covalently bonded]] to each other, they cannot demix macroscopically as water and oil can, and so instead the blocks form [[nanometer|nanometre-sized]] structures. Depending on the relative lengths of each block and the overall block topology of the polymer, many morphologies can be obtained, each its own phase of matter.

[[Ionic liquid]]s also display microphase separation. The anion and cation are not necessarily compatible and would demix otherwise, but electric charge attraction prevents them from separating. Their anions and cations appear to diffuse within compartmentalized layers or micelles instead of freely as in a uniform liquid.<ref>Álvarez, V.H.; Dosil, N.; Gonzalez-Cabaleiro, R.; Mattedi, S.; Martin-Pastor, M.; Iglesias, M. & Navaza, J.M.: Brønsted Ionic Liquids for Sustainable Processes: Synthesis and Physical Properties. Journal of Chemical & Engineering Data 55 (2010), Nr. 2, S. 625–632. {{doi|10.1021/je900550v}}</ref>

== Magnetically ordered states ==
[[Transition metal]] atoms often have [[magnetic moment]]s due to the net [[Spin (physics)|spin]] of electrons that remain unpaired and do not form chemical bonds. In some solids the magnetic moments on different atoms are ordered and can form a ferromagnet, an antiferromagnet or a ferrimagnet.

In a [[ferromagnetism|ferromagnet]]—for instance, solid [[iron]]—the magnetic moment on each atom is aligned in the same direction (within a [[magnetic domain]]). If the domains are also aligned, the solid is a permanent [[magnet]], which is magnetic even in the absence of an external [[magnetic field]]. The [[magnetization]] disappears when the magnet is heated to the [[Curie point]], which for iron is {{convert|768|C|F}}.

An [[antiferromagnetism|antiferromagnet]] has two networks of equal and opposite magnetic moments, which cancel each other out so that the net magnetization is zero. For example, in [[nickel(II) oxide]] (NiO), half the nickel atoms have moments aligned in one direction and half in the opposite direction.

In a [[ferrimagnetism|ferrimagnet]], the two networks of magnetic moments are opposite but unequal, so that cancellation is incomplete and there is a non-zero net magnetization. An example is [[magnetite]] (Fe{{sub|3}}O{{sub|4}}), which contains Fe{{sup|2+}} and Fe{{sup|3+}} ions with different magnetic moments.

A [[quantum spin liquid]] (QSL) is a disordered state in a system of interacting quantum spins which preserves its disorder to very low temperatures, unlike other disordered states. It is not a liquid in physical sense, but a solid whose magnetic order is inherently disordered. The name "liquid" is due to an analogy with the molecular disorder in a conventional liquid. A QSL is neither a [[Ferromagnetism|ferromagnet]], where magnetic domains are parallel, nor an [[Antiferromagnetism|antiferromagnet]], where the magnetic domains are antiparallel; instead, the magnetic domains are randomly oriented. This can be realized e.g. by [[Geometrical frustration|geometrically frustrated]] magnetic moments that cannot point uniformly parallel or antiparallel. When cooling down and settling to a state, the domain must "choose" an orientation, but if the possible states are similar in energy, one will be chosen randomly. Consequently, despite strong short-range order, there is no long-range magnetic order.

==Superfluids and condensates==
[[Image:Liquid helium Rollin film.jpg|thumb|[[Liquid helium]] in a superfluid phase creeps up on the walls of the cup in a [[Rollin film]], eventually dripping out from the cup]]

===Bose–Einstein condensates and superfluids===
[[Image:Bose Einstein condensate.png|right|thumb|Velocity in a gas of [[rubidium]] as it is cooled: the starting material is on the left, and Bose–Einstein condensate is on the right.]]
{{Main|Bose–Einstein condensate|Superfluidity}}

Bose–Einstein condensation was predicted in 1925 by [[Albert Einstein]], based on the particle statistics developed by him and [[Satyendra Nath Bose]].<ref name=":0">{{Cite journal |last=Ketterle |first=Wolfgang |date=2002-11-20 |title=Nobel lecture: When atoms behave as waves: Bose-Einstein condensation and the atom laser |url=https://link.aps.org/doi/10.1103/RevModPhys.74.1131 |journal=Reviews of Modern Physics |language=en |volume=74 |issue=4 |pages=1131–1151 |doi=10.1103/RevModPhys.74.1131 |bibcode=2002RvMP...74.1131K |issn=0034-6861}}</ref> Bose-Einstein condensation occurs when [[boson]]ic particles are cooled close to [[absolute zero]], {{convert|−273.15|C|F}}. At a specific temperature, a large fraction of them suddenly occupies the same lowest energy [[quantum state]].<ref name=":0" /> The effect is termed ''condensation'' in analogy with the [[condensation]] of water, with which it shares some similarities.<ref name=":1">{{Cite web |title=Press release: The Nobel Prize in Physics 2001 |url=https://www.nobelprize.org/prizes/physics/2001/press-release/ |access-date=2025-05-25 |website=NobelPrize.org |language=en-US}}</ref>

In 1937, it was discovered that [[helium-4]], the most common isotope of [[helium]], forms a superfluid below the [[lambda point|lambda temperature]] of {{convert|2.17|K|C F}}. The state is described as ''superfluid'' because it has zero [[viscosity]] and flows without friction. In this state it will attempt to "climb" out of its container.<ref>
{{cite web |author=J.R. Minkel |date=20 February 2009 |title=Strange but True: Superfluid Helium Can Climb Walls |url=https://www.scientificamerican.com/article.cfm?id=superfluid-can-climb-walls |url-status=live |archive-url=https://web.archive.org/web/20110319072600/https://www.scientificamerican.com/article.cfm?id=superfluid-can-climb-walls |archive-date=19 March 2011 |access-date=23 February 2010 |website=[[Scientific American]] |df=dmy-all}}</ref> It also has infinite [[thermal conductivity]] so that no [[temperature gradient]] can form in a superfluid. Placing a superfluid in a spinning container will result in [[quantum vortex|quantized vortices]]. These properties are explained by the theory that helium-4 atoms form a Bose–Einstein condensate in the superfluid state.{{Citation needed|date=May 2025}}

In the gas phase, the Bose–Einstein condensate remained an unverified theoretical prediction for many years. However in 1995, the research groups of [[Eric Cornell]] and [[Carl Wieman]], of [[JILA]] at the [[University of Colorado at Boulder]], produced the first such condensate experimentally with [[rubidium]] atoms. Independently of Cornell and Wieman, [[Wolfgang Ketterle]] also produced a Bose–Einstein condensate in a gas of [[sodium]] atoms in 1995.<ref name=":1" />

===Superconductors and fermionic condensates ===
{{main|Fermionic condensate|Superconductivity}}

A ''fermionic condensate'' is similar to the Bose–Einstein condensate but composed of [[fermion]]s. While the [[Pauli exclusion principle]] prevents individual fermions from occupying the same quantum state, pairs of fermions can combine to form composite particles that behave like bosons. These pairs can then occupy the same state, forming a condensate analogous to a Bose–Einstein condensate. Examples of fermionic condensates include superconductors and the superfluid phase of [[helium-3]], a rare isotope of helium. Fermionic condensate has also been observed in ultracold [[Isotopes of lithium|lithium-6]].<ref>{{cite web |author=L. Valigra |date=22 June 2005 |title=MIT physicists create new form of matter |url=https://web.mit.edu/newsoffice/2005/matter.html |url-status=live |archive-url=https://web.archive.org/web/20131211202945/https://web.mit.edu/newsoffice/2005/matter.html |archive-date=11 December 2013 |access-date=23 February 2010 |publisher=[[Massachusetts Institute of Technology|MIT News]] |df=dmy-all}}</ref>

Superconductors are materials which have zero [[electrical resistivity and conductivity|electrical resistivity]], and therefore perfect conductivity. This is a distinct physical state which exists at low temperature, and the resistivity increases discontinuously to a finite value at a sharply defined transition temperature for each superconductor.<ref name=MAWhite>{{cite book |last1=White |first1=Mary Anne |authorlink=Mary Anne White |title=Properties of Materials |date=1999 |publisher=Oxford University Press |isbn=0-19-511331-4 |pages=254–258}}</ref> A superconductor also excludes all magnetic fields from its interior, a phenomenon known as the [[Meissner effect]] or perfect [[diamagnetism]].<ref name="MAWhite" /> [[Superconducting magnet]]s are used as electromagnets in [[magnetic resonance imaging]] machines.

The phenomenon of superconductivity was discovered in 1911, and for 75 years was only known in some metals and metallic alloys at temperatures below 30 K. In 1986 so-called [[high-temperature superconductivity]] was discovered in certain [[ceramic]] oxides, and has now been observed in temperatures as high as 164 K.<ref name=Tinkham>{{cite book |author=M. Tinkham |year=2004 |title=Introduction to Superconductivity |url=https://books.google.com/books?id=k6AO9nRYbioC&pg=PA17 |publisher=[[Courier Dover Publications|Courier Dover]] |pages=17–23 |isbn=0486435032}}</ref>

==High-energy states==

===Degenerate matter===
{{Main|Degenerate matter}}

Under extremely high pressure, as in the cores of dead stars, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as [[degenerate matter]], which are supported mainly by quantum mechanical effects. In physics, "degenerate" refers to two states that have the same energy and are thus interchangeable. Degenerate matter is supported by the [[Pauli exclusion principle]], which prevents two [[fermion]]ic particles from occupying the same quantum state. Unlike regular plasma, degenerate plasma expands little when heated, because there are simply no momentum states left. Consequently, degenerate stars collapse into very high densities. More massive degenerate stars are smaller, because the gravitational force increases, but pressure does not increase proportionally.

[[Degenerate matter#Electron degeneracy|Electron-degenerate matter]] is found inside [[white dwarf]] stars. Electrons remain bound to atoms but are able to transfer to adjacent atoms. [[Degenerate matter#Neutron degeneracy|Neutron-degenerate matter]] is found in [[neutron star]]s. Vast gravitational pressure compresses atoms so strongly that the electrons are forced to combine with protons via inverse beta-decay, resulting in a superdense conglomeration of neutrons. Normally free [[neutron]]s outside an atomic nucleus will [[Free neutron decay|decay]] with a half life of approximately 10 minutes, but in a neutron star, the decay is overtaken by inverse decay. Cold degenerate matter is also present in planets such as [[Jupiter]] and in the even more massive [[brown dwarf]]s, which are expected to have a core with [[metallic hydrogen]]. Because of the degeneracy, more massive brown dwarfs are not significantly larger. In metals, the electrons can be modeled as a degenerate gas moving in a lattice of non-degenerate positive ions.

===Quark matter===
{{Main|QCD matter}}

In regular cold matter, [[quark]]s, fundamental particles of nuclear matter, are confined by the [[strong force]] into [[hadron]]s that consist of 2–4 quarks, such as protons and neutrons. Quark matter or quantum chromodynamical (QCD) matter is a group of phases where the strong force is overcome and quarks are deconfined and free to move. Quark matter phases occur at extremely high densities or temperatures, and there are no known ways to produce them in equilibrium in the laboratory; in ordinary conditions, any quark matter formed immediately undergoes radioactive decay.

[[Strange matter]] is a type of [[quark matter]] that is suspected to exist inside some neutron stars close to the [[Tolman–Oppenheimer–Volkoff limit]] (approximately 2–3 [[solar mass]]es), although there is no direct evidence of its existence. In strange matter, part of the energy available manifests as [[strange quark]]s, a heavier analogue of the common [[down quark]]. It may be stable at lower energy states once formed, although this is not known.

[[Quark–gluon plasma]] is a very high-temperature phase in which [[quark]]s become free and able to move independently, rather than being perpetually bound into particles, in a sea of [[gluon]]s, subatomic particles that transmit the [[strong interaction|strong force]] that binds quarks together. This is analogous to the liberation of electrons from atoms in a plasma. This state is briefly attainable in extremely high-energy heavy ion collisions in [[particle accelerator]]s, and allows scientists to observe the properties of individual quarks. Theories predicting the existence of quark–gluon plasma were developed in the late 1970s and early 1980s,<ref>{{Cite book|last=Satz|first=H.|url=https://books.google.com/books?id=OY8uAAAAIAAJ|title=Statistical Mechanics of Quarks and Hadrons: Proceedings of an International Symposium Held at the University of Bielefeld, F.R.G., August 24–31, 1980|date=1981|publisher=North-Holland|isbn=978-0-444-86227-3|language=en}}</ref> and it was detected for the first time in the laboratory at CERN in the year 2000.<ref>{{cite arXiv|last1=Heinz|first1=Ulrich|last2=Jacob|first2=Maurice|date=2000-02-16|title=Evidence for a New State of Matter: An Assessment of the Results from the CERN Lead Beam Programme|eprint=nucl-th/0002042 }}</ref><ref>{{Cite news|last=Glanz|first=James|date=2000-02-10|title=Particle Physicists Getting Closer To the Bang That Started It All|language=en-US|work=The New York Times|url=https://www.nytimes.com/2000/02/10/world/particle-physicists-getting-closer-to-the-bang-that-started-it-all.html|access-date=2020-05-10|issn=0362-4331}}</ref> Unlike plasma, which flows like a gas, interactions within QGP are strong and it flows like a liquid.

At high densities but relatively low temperatures, quarks are theorized to form a quark liquid whose nature is presently unknown. It forms a distinct [[Color–flavor locking|color-flavor locked]] (CFL) phase at even higher densities. This phase is [[superconductive]] for color charge. These phases may occur in [[neutron star]]s but they are presently theoretical.

===Color-glass condensate===
{{Main|Color-glass condensate}}

Color-glass condensate is a type of matter theorized to exist in atomic nuclei traveling near the speed of light. According to Einstein's theory of relativity, a high-energy nucleus appears length contracted, or compressed, along its direction of motion. As a result, the gluons inside the nucleus appear to a stationary observer as a "gluonic wall" traveling near the speed of light. At very high energies, the density of the gluons in this wall is seen to increase greatly. Unlike the quark–gluon plasma produced in the collision of such walls, the color-glass condensate describes the walls themselves, and is an intrinsic property of the particles that can only be observed under high-energy conditions such as those at [[Relativistic Heavy Ion Collider]] (RHIC) and possibly at the [[Large Hadron Collider]] (LHC) as well.

=== Very high energy states ===
Various theories predict new states of matter at very high energies. An unknown state has created the [[baryon asymmetry]] in the universe, but little is known about it. In [[string theory]], a [[Hagedorn temperature]] is predicted for superstrings at about 10<sup>30</sup> K, where superstrings are copiously produced. At [[Planck temperature]] (10<sup>32</sup> K), gravity becomes a significant force between individual particles. No current theory can describe these states and they cannot be produced with any foreseeable experiment. However, these states are important in [[cosmology]] because the universe may have passed through these states in the [[Big Bang]].

==Other proposed states==

===Supersolid===
{{Main|Supersolid}}

A supersolid is a spatially ordered material (that is, a solid or crystal) with superfluid properties. Similar to a superfluid, a supersolid is able to move without friction but retains a rigid shape. Although a supersolid is a solid, it exhibits so many characteristic properties different from other solids that many argue it is another state of matter.<ref>
{{cite journal
 |author=G. Murthy
 |display-authors=etal
 |date=1997
 |title=Superfluids and Supersolids on Frustrated Two-Dimensional Lattices
 |journal=[[Physical Review B]]
 |volume=55
 |issue=5 |page=3104
 |doi=10.1103/PhysRevB.55.3104
|arxiv = cond-mat/9607217 |bibcode = 1997PhRvB..55.3104M |s2cid=119498444
 }}</ref>

===String-net liquid===
{{main|String-net liquid}}

In a string-net liquid, atoms have apparently unstable arrangement, like a liquid, but are still consistent in overall pattern, like a solid. When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of any electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, atoms are arranged in some pattern that requires some electrons to have neighbors with the same spin. This gives rise to curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe itself.

===Superglass===
{{Main|Superglass}}

A superglass is a phase of matter characterized, at the same time, by [[superfluid]]ity and a frozen amorphous structure.

=== Chain-melted state ===
{{Main|Chain-melted state}}

Metals, like potassium, in the chain-melted state appear to behave as liquids and solids at the same time. This is a result of being subjected to high temperature and pressure, leading the chains in the potassium to dissolve into a liquid while the crystals remain solid.<ref>{{Cite web |last=Mann |first=Adam |date=2019-04-08 |title=Confirmed: New phase of matter is solid and liquid at same time |url=https://www.nationalgeographic.com/science/article/new-phase-matter-confirmed-solid-and-liquid-same-time-potassium-physics |archive-url=https://web.archive.org/web/20210414161939/https://www.nationalgeographic.com/science/article/new-phase-matter-confirmed-solid-and-liquid-same-time-potassium-physics |url-status=dead |archive-date=14 April 2021 |access-date=2023-11-13 |website=National Geographic |language=en}}</ref>

===Quantum Hall state===
{{main|Quantum Hall effect}}

A ''quantum Hall state'' gives rise to quantized [[Hall voltage]] measured in the direction perpendicular to the current flow. A ''[[Quantum spin Hall effect|quantum spin Hall state]]'' is a theoretical phase that may pave the way for the development of electronic devices that dissipate less energy and generate less heat.

===Photonic matter===
{{main|Photonic matter}}

Photonic matter is a phenomenon where [[photon]]s interacting with a gas develop apparent mass, and can interact with each other, even forming photonic "molecules". The source of mass is the gas, which is massive. This is in contrast to photons moving in empty space, which have no [[rest mass]], and cannot interact.

==See also==
* [[Chemical equation #State of matter|Chemical equation § State of matter]]
* [[Classical element]]
* [[Condensed matter physics]]
* [[Cooling curve]]
* [[Hidden states of matter]]
* [[List of states of matter]]
* [[Supercooling]]
* [[Superheating]]

==Notes and references==
{{Reflist}}

==External links==
{{Commons category|States of aggregation}}
* [https://vega.org.uk/video/subseries/30 Short videos demonstrating of States of Matter, solids, liquids and gases by Prof. J M Murrell, University of Sussex] {{Webarchive|url=https://web.archive.org/web/20230330074533/http://www.vega.org.uk/video/subseries/30 |date=30 March 2023 }}

{{State of matter|state=expanded}}
{{Condensed matter physics topics}}
{{Authority control}}
{{Use dmy dates|date=August 2019}}

{{DEFAULTSORT:State Of Matter}}
[[Category:Condensed matter physics]]
[[Category:Engineering thermodynamics]]
[[Category:Phases of matter| ]]