Matter 19585 225971975 2008-07-16T07:30:25Z Atyndall 1240922 Reverted edits by [[Special:Contributions/124.106.150.147|124.106.150.147]] to last version by ClueBot (using [[WP:HG|Huggle]]) {{otheruses1 | matter in physics and chemistry}} In [[science]], '''matter''' is commonly defined as the [[Chemical substance|substance]] of which [[physical]] [[objects]] are composed, not counting the contribution of various [[energy]] or [[force-field]]s, which are not usually considered to be matter per se (though they may contribute to the [[mass]] of objects). Matter constitutes much of the [[observable universe]], although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined. It is normally defined as anything that has mass and takes up space. Matter can be in several different states, the most common being [[solid]]s, [[liquid]]s and [[gas]]es. == '''Definition''' == Anything which occupies [[space]] and has [[mass]] is known as matter. In [[physics]], there is no broad consensus as to an exact definition of matter. Physicists generally do not use the saying when precision is needed, preferring instead to speak of the more clearly defined concepts of [[mass]], [[energy]], and [[particles]]. A possible definition of matter which at least some physicists use is that matter is everything that is composed of elementary [[fermions]]<ref name="povh">Povh, Rith, Scholz, Zetche, Reigthinger ''Particles and Nuclei'', 1999, ISBN 3540438238</ref>. These are the [[leptons]], including the [[electron]], and the [[quarks]], including the up and down [[quarks]] of which [[protons]] and [[neutrons]] are made. Since [[protons]], [[neutrons]] and [[electrons]] combine to form [[atoms]] and [[molecules]], thus they comprise the bulk substances which make up all ordinary matter. Matter also includes the various other [[baryons]], but excludes the "true [[mesons]]". The key relevant property of fermions is that they have half-integral spin (ie, 1/2, 3/2, 5/2,...,etc.) and thus, by the [[spin-statistics theorem]] of [[quantum field theory]], obey the [[Pauli Exclusion Principle]], which forbids two fermions from occupying the same quantum state. This seems to correspond closely to the more primitive notion that matter is "impenetrable", and takes up space. On this view, things which are not matter include [[light]] ([[photons]]), [[gravitons]], [[mesons]] (except for the [[muon]], a lepton which was misnamed a meson before the distinction became clear) and the other gauge [[bosons]]. These all have half-even spin (0,1,2,...), do not respect the Exclusion Principle, and so do not occupy space in the same sense. These may all be regarded as [[Quantum field theory|field quanta]], and may be exchanged freely by fermions without the fermions changing their own statistics, or thus their essential identity. However, these bosons do always have energy and, (according to the [[mass-energy equivalence]] of [[special relativity]]) therefore mass, so that under this definition some particles have mass without being matter: [[W boson |W]] and [[Z boson|Z]] [[bosons]] have [[rest mass|rest]] [[mass]], but are not [[elementary particle|elementary]] [[fermions]]. Also, any two [[photons]] which are not moving [[parallel]] to each other, taken as a system, have an [[invariant]] [[mass]]. [[Glueballs]] have [[mass]] due to their [[binding energy]], but contain no [[particle]] with rest [[mass]], nor any [[elementary particle|elementary]] [[fermions]]. Most of the [[mass]] of [[protons]] and [[neutrons]] comes from the [[binding energy]] between the [[quarks]], not the masses of the [[quarks]] themselves. One of the three types of [[neutrinos]] may be massless. == Properties of matter == [[Quark]]s combine to form [[hadron]]s. Because of the principle of [[color confinement]] which occurs in the [[strong interaction]], quarks never exist unbound from other quarks. Among the hadrons are the proton and the neutron. Usually these nuclei are surrounded by a cloud of electrons. A nucleus with as many electrons as protons is thus electrically neutral and is called an [[atom]], otherwise it is an [[ion]]. Leptons do not feel the strong force and so can exist unbound from other particles. On Earth, electrons are generally bound in atoms, but it is easy to free them, a fact which is exploited in the [[cathode ray tube]]. Muons may briefly form bound states known as [[muonium| muonic atoms]]. Neutrinos feel neither the strong nor the [[electromagnetic interaction]]s. They are never bound to other particles.<ref name="povh" /> '''Homogeneous matter''' has a uniform composition and properties. It may be a mixture, such as [[brass]], a chemical compound like water, or elemental, like pure [[iron]]. '''Heterogeneous matter''', such as [[granite]], does not have a definite composition. ==== Phases ==== In [[bulk]], matter can exist in several different [[phases of matter| phase]]s, according to [[pressure]] and [[temperature]]. A phase is a state of a macroscopic physical system that has relatively uniform chemical composition and physical properties (i.e. [[density]], [[crystal structure]], [[refractive index| index of refraction]], and so forth). These phases include the three familiar ones — [[solid]]s, [[liquid]]s, and [[gas]]es — as well as [[plasma (physics)| plasma]]s, [[superfluid]]s, [[supersolid]]s, [[Bose-Einstein condensate]]s, [[fermionic condensate]]s, [[liquid crystal]]s, [[strange matter]] and [[quark-gluon plasma]]s. There are also the [[paramagnetism| paramagnetic]] and [[ferromagnetism| ferromagnetic]] phases of [[magnet]]ic materials. As conditions change, matter may change from one phase into another. These phenomena are called [[phase transition]]s, and their energetics are studied in the field of [[thermodynamics]]. In small quantities, matter can exhibit properties that are entirely different from those of bulk material and may not be well described by any phase. Phases are sometimes called '''states of matter''', but this term can lead to confusion with [[thermodynamics| thermodynamic]] states. For example, two gases maintained at different pressures are in different thermodynamic states, but the same "state of matter". ==Chemical matter== Chemical matter is the part of the universe which is made of chemical [[atoms]]. This part of the universe does not include [[dark energy]], [[dark matter]], [[black holes]] or various forms of degenerate matter, such as compose [[white dwarf]] stars and [[neutron star]]s. Recent data from the [[Wilkinson Microwave Anisotropy Probe]] (WMAP), suggests that only about 4% of the total mass of the part of the universe which is within range of the best theoretical telescopes (i.e., which may be visible, because light has reached us from it), is made of chemical matter. About 22% is dark matter, and about 74% is dark energy.<ref name="NASA-WMAP">{{Cite web|url=http://map.gsfc.nasa.gov/m_mm.html|title=Five Year Results on the Oldest Light in the Universe|accessyear=2008|accessmonthday=May 2|publisher=NASA|year=2008}}</ref> == Antimatter == {{main|Antimatter}} In [[particle physics]] and [[quantum chemistry]], '''antimatter''' is matter that is composed of the [[antiparticle]]s of those that constitute normal matter. If a particle and its antiparticle come into contact with each other, the two [[annihilation| annihilate]]; that is, they may both be converted into other particles with equal [[energy]] in accordance with [[Einstein]]'s equation ''[[E=MC2| E = mc<sup>2</sup>]]''. These new particles may be high-energy [[photon]]s ([[gamma ray]]s) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the [[rest mass]] of the products of the annihilation and the rest mass of the original particle-antiparticle pair, which is often quite large. Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of [[radioactive decay]] or [[cosmic ray]]s). This is because antimatter which came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as [[antihydrogen]]) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties. There is considerable speculation both in [[science]] and [[science fiction]] as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter instead, and what might be possible if antimatter could be harnessed, but at this time the apparent [[asymmetry]] of matter and antimatter in the visible universe is one of the great [[unsolved problems in physics]]. Possible processes by which it came about are explored in more detail under [[baryogenesis]]. == Dark matter == {{ main|Dark matter}} In [[cosmology]], effects at the largest scales seem to indicate the presence of incredible amounts of '''dark matter''' which is not associated with electromagnetic radiation. Observational evidence of the early universe and the [[big bang]] theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. As such, it is composed of particles as yet unobserved in the laboratory (perhaps [[supersymmetry|supersymmetric particles]]). == Exotic matter == {{main|Exotic matter}} Exotic matter is a hypothetical concept of [[particle physics]]. It covers any material which violates one or more classical conditions or is not made of known [[baryonic particles]]. == References == {{reflist}} == External links == {{commonscat}} *[http://www.visionlearning.com/library/module_viewer.php?mid=49&l=&c3= Visionlearning Module on Matter] {{Nature nav}} [[Category:Matter| ]] [[ar:مادة]] [[be:Матэрыя]] [[bs:Materija]] [[bg:Материя (физика)]] [[ca:Matèria]] [[cs:Hmota]] [[cy:Mater]] [[da:Stof (fysik)]] [[de:Materie]] [[et:Aine (füüsika)]] [[el:Ύλη]] [[es:Materia]] [[eo:Materio]] [[eu:Materia]] [[fa:ماده (فیزیک)]] [[fr:Matière]] [[ga:Damhna]] [[gl:Materia]] [[ko:물질]] [[hr:Materija]] [[io:Materio]] [[id:Materi]] [[ia:Materia]] [[it:Materia (fisica)]] [[he:חומר]] [[lv:Matērija]] [[lb:Matière]] [[lt:Materija (fizika)]] [[jbo:marji]] [[hu:Anyag]] [[mk:Материја]] [[ml:ദ്രവ്യം]] [[ms:Jirim]] [[nl:Materie]] [[ja:物質]] [[no:Materie]] [[nov:Materie]] [[uz:Materiya]] [[nds:Materie]] [[pl:Materia (fizyka)]] [[pt:Matéria]] [[ro:Materie]] [[qu:Imayay]] [[ru:Материя (физика)]] [[sq:Lënda]] [[simple:Matter]] [[sk:Hmota (fyzika)]] [[sl:Snov]] [[sr:Материја]] [[fi:Aine]] [[sv:Materia]] [[tl:Materya]] [[ta:பொருள்]] [[te:పదార్ధము]] [[th:สสาร]] [[vi:Vật chất]] [[tr:Madde]] [[vec:Materia]] [[yi:מאטריאל]] [[zh:物质]]