Matter
Content
Matter From Wikipedia, the free encyclopedia This article is about the concept in the physical sciences. For other uses, see Matter (disambiguation).
Matter is a general term for the substance of which all physical objects consist .[1][2] Typically, matter includes atoms and other particles which have mass. A common way of defining matter is as anything that has mass and occupies volume.[ 3] In practice however there is no single correct scientific meaning of "matter, " as different fields use the term in different and sometimes incompatible ways. For much of the history of the natural sciences people have contemplated the exa ct nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, was first put forward by the Greek philosophers Leucippus (~490 BC) and Democritus (~470–380 BC).[4] Over time an inc reasingly fine structure for matter was discovered: objects are made from molecu les, molecules consist of atoms, which in turn consist of interacting subatomic particles like protons and electrons.[5][6] Matter is commonly said to exist in four states (or phases): solid, liquid, gas and plasma. However, advances in experimental techniques have realized other pha ses, previously only theoretical constructs, such as Bose–Einstein condensates and fermionic condensates. A focus on an elementary-particle view of matter also le ads to new phases of matter, such as the quark–gluon plasma.[7] In physics and chemistry, matter exhibits both wave-like and particle-like prope rties, the so-called wave–particle duality.[8][9][10] In the realm of cosmology, extensions of the term matter are invoked to include dark matter and dark energy, concepts introduced to explain some odd phenomena o f the observable universe, such as the galactic rotation curve. These exotic for ms of "matter" do not refer to matter as "building blocks", but rather to curren tly poorly understood forms of mass and energy.[11] Contents [hide] 1 Historical development 1.1 Origins 1.2 Early modernity 1.3 Late nineteenth and early twentieth century 1.4 Later developments 1.5 Summary 2 Definitions 2.1 Common definition 2.2 Relativity 2.3 Atoms and molecules definition 2.4 Protons, neutrons and electrons definition 2.5 Quarks and leptons definition 2.6 Smaller building blocks? 3 Structure 3.1 Quarks 3.1.1 Baryonic matter 3.1.2 Degenerate matter 3.1.3 Strange matter 3.1.3.1 Two meanings of the term "strange matter" 3.2 Leptons 4 Phases 5 Antimatter 6 Other types of matter 6.1 Dark matter
6.2 Dark energy 6.3 Exotic matter 7 See also 8 References 9 Further reading 10 External links [edit] Historical development [edit] Origins The pre-Socratics were among the first recorded speculators about the underlying nature of the visible world. Thales (c. 624 BC–c. 546 BC) regarded water as the f undamental material of the world. Anaximander (c. 610 BC–c. 546 BC) posited that t he basic material was wholly characterless or limitless: the Infinite (apeiron). Anaximenes (flourished 585 BC, d. 528 BC) posited that the basic stuff was pneu ma or air. Heraclitus (c. 535–c. 475 BC) seems to say the basic element is fire, t hough perhaps he means that all is change. Empedocles (c. 490–430 BC) spoke of fou r elements of which everything was made: earth, water, air, and fire.[12] Meanwh ile, Parmenides argued that change does not exist, and Democritus argued that ev erything is composed of minuscule, inert bodies of all shapes called atoms, a ph ilosophy called atomism. All of these notion had deep philosophical problems.[13 ] Aristotle (384 BC – 322 BC) was the first to put the conception on a sound philoso phical basis, which he did in his natural philosophy, especially in Physics book I.[14] He adopted as reasonable suppositions the four Empedoclean elements, but added a fifth, aether. Nevertheless these elements are not basic in Aristotle's mind. Rather they, like everything else in the visible world, are composed of t he basic principles matter and form. The word Aristotle uses for matter, ὑλη ( y e or u e), can be itera y trans ated as wood or timber, t at is, "raw materia " for bui ding.[15] Indeed, Aristot e's c onception of matter is intrinsica y inked to somet ing being made or composed. In ot er words, in contrast to t e ear y modern conception of matter as simp y occupying space, matter for Aristot e is definitiona y inked to process or c a nge: matter is w at under ies a c ange of substance.
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For examp e, a orse eats grass: t e orse c anges t e grass into itse f; t e gr ass as suc does not persist in t e orse, but some aspect of it—its matter—does. T e matter is not specifica y described (e.g., as atoms), but consists of w ateve r persists in t e c ange of substance from grass to orse. Matter in t is unders
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tanding notas exist independent y (i.e., as aon substance), exists endent ydoes (i.e., a "princip e") wit form and y insofar but as it underinterdep ies c a nge. It can be e pfu to conceive of t e re ations ip of matter and form as ver y simi ar to t at between parts and w o e. For Aristot e, matter as suc can on y receive actua ity from form; it as no activity or actua ity in itse f, simi a r to t e way t at parts as suc on y exist in a w o e (ot erwise t ey wou d be i ndependent w o es). [edit] Ear y modernity
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René Descartes (1596–1650) was t e originator of t e modern conception of matter. Be ing a geometer, e redefined matter to be suitab e for abstract, mat ematica tr eatment as t at w ic occupies space:
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So, extension in engt , breadt , and dept , constitutes t e nature of bodi y substance; and t oug t constitutes t e nature of t inking substance. And every t ing e se w ic can be attributed to body presupposes extension, and is on y a
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mode of t at w ic
is extended
– René Descartes, Princip es of P i osop y[16]
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For Descartes, matter as on y t e property of extension, so its on y activity a side from ocomotion is to exc ude ot er bodies: t is is t e mec anica p i osop y. Descartes makes an abso ute distinction between mind, w ic e defines as un extended, t inking substance, and matter, w ic e defines as unt inking, extend ed substance.[17] T ey are independent t ings. In contrast, Aristot e defines ma tter and t e forma /forming princip e as comp ementary princip es w ic toget er compose one independent t ing (substance). In s ort, Aristot e defines matter ( roug y speaking) as w at t ings are made of, but Descartes e evates matter to b e a t ing in itse f.
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T e continuity and difference between Descartes' and Aristot e's conceptions is notewort y. In bot conceptions, matter is passive or inert. In t e respective c onceptions matter as different re ations ips to inte igence. For Aristot e, ma tter and inte igence (form) exist toget er in an interdependent re ations ip, w ereas for Descartes, matter and inte igence (mind) are definitiona y opposed, independent substances.[18]
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Isaac Newton (1643–1727) in erited Descartes' mec anica conception of matter; e viewed matter as "so id, massy, ard, impenetrab e, movab e partic es", w ic we re "even so very ard as never to wear or break in pieces."[19] T e "primary" pr operties of matter were amenab e to mat ematica description, un ike "secondary" qua ities suc as co or or taste.[19] Newton restores to matter intrinsic prope rties in addition to extension (at east on a imited basis), suc as mass. A ke y distinction between Descartes's and Newton's views was t at Newton refuted Des cartes' contact mec anics by s owing t at bodies ave capacities ike attraction (notab y, gravity).[20] A ong t e same ines, Josep Priest y argued t at corpo rea properties transcend contact mec anics: c emica properties require t e cap acity for attraction.[20] In t e 19t century, fo owing t e deve opment of t e periodic tab e, and of atomic t eory, atoms were seen as being t e fundamenta c onstituents of matter; atoms formed mo ecu es and compounds.[21] [edit] Late nineteent and ear y twentiet century
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T e common definition in terms of occupying space and aving mass is in contrast wit most p ysica and c emica definitions of matter, w ic re y instead upon its structure and upon attributes not necessari y re ated to vo ume and mass. At t e turn of t e nineteent century, t e concept of matter began a rapid evo uti on.
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Aspects of t e Newtonian view sti e d sway. James C erk Maxwe discussed mat ter in is work Matter and Motion.[22] He carefu y separates "matter" from spac
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eaw and and defines it in terms of t e object referred to in Newton's first oftime, motion. ¡
However, t e Newtonian picture was not t e w o e story. In t e 19t century, t e term "matter" was active y discussed by a ost of scientists and p i osop ers, and a brief out ine can be found in Levere.[23] A textbook discussion from 1870 suggests matter is w at is made up of atoms:[24]
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T ree divisions of matter are recognized in science: masses, mo ecu es and a toms. A Mass of matter is any portion of matter appreciab e by t e senses. A Mo ecu e is t e sma est partic e of matter into w ic a body can be divid ed wit out osing its identity. An Atom is a sti sma er partic e produced by division of a mo ecu e.
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Rat er t an simp y
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aving t e attributes of mass and occupying space, matter was
e d to ave c emica and e ectrica properties. T e famous p ysicist J. J. T o mson wrote about t e "constitution of matter" and was concerned wit t e possib e connection between matter and e ectrica c arge.[25] T ere is an entire itera ¡
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ture concerning t e "structure of matter", ranging from t e "e ectrica structur e" in t e ear y 20t century,[26] to t e more recent "quark structure of matter" , introduced today wit t e remark: Understanding t e quark structure of matter as been one of t e most important advances in contemporary p ysics.[27] In t is connection, p ysicists speak of matter fie ds, and speak of partic es as "quant um excitations of a mode of t e matter fie d".[8][9] And ere is a quote from de Sabbata and Gasperini: "Wit t e word "matter" we denote, in t is context, t e sources of t e interactions, t at is spinor fie ds ( ike quarks and eptons), w ic are be ieved to be t e fundamenta components of matter, or sca ar fie ds, ike t e Higgs partic es, w ic are used to introduced mass in a gauge t eory (an
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d w ic , owever, cou d be composed of more fundamenta am C omsky summarizes t e situation: ¡
fermion fie ds)."[28] No
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W at is t e concept of body t at fina y emerged?[...] T e answer is t at t ere is no c ear and definite conception of body.[...] Rat er, t e materia wor d is w atever we discover it to be, wit w atever properties it must be assumed t o ave for t e purposes of exp anatory t eory. Any inte igib e t eory t at offe rs genuine exp anations and t at can be assimi ated to t e core notions of p ysi cs becomes part of t e t eory of t e materia wor d, part of our account of body . If we ave suc a t eory in some domain, we seek to assimi ate it to t e core notions of p ysics, per aps modifying t ese notions as we carry out t is enterpr ise.
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– Noam C omsky, 'Language and prob ems of know edge: t e Managua 144[20]
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ectures, p.
[edit] Later deve opments ¡
T e modern conception of matter as been refined many times in istory, in ig t of t e improvement in know edge of just w at t e basic bui ding b ocks are, and in ow t ey interact.
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In t e ate 19t century wit t e discovery of t e e ectron, and in t e ear y 20 t century, wit t e discovery of t e atomic nuc eus, and t e birt of partic e p ysics, matter was seen as made up of e ectrons, protons and neutrons interacti ng to form atoms. Today, we know t at even protons and neutrons are not indivisi b e, t ey can be divided into quarks, w i e e ectrons are part of a partic e fam i y ca ed eptons. Bot quarks and eptons are e ementary partic es, and are cu rrent y seen as being t e fundamenta constituents of matter.[29]
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T ese quarks and
eptons interact t roug
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four fundamenta
forces: gravity, e ec
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tromagnetism, weak strong interactions. e Standard of e p ysics isinteractions, current y t eand best exp anation for a Tof p ysics, Mode but despi partic te decades of efforts, gravity cannot yet be accounted for at t e quantum- eve ; it is on y described by c assica p ysics (see quantum gravity and graviton).[3 0] Interactions between quarks and eptons are t e resu t of an exc ange of forc e-carrying partic es (suc as p otons) between quarks and eptons.[31] T e force -carrying partic es are not t emse ves bui ding b ocks. As one consequence, mass and energy (w ic cannot be created or destroyed) cannot a ways be re ated to m atter (w ic can be created out of non-matter partic es suc as p otons, or even out of pure energy, suc as kinetic energy). Force carriers are usua y not con sidered matter: t e carriers of t e e ectric force (p otons) possess energy (see P anck re ation) and t e carriers of t e weak force (W and Z bosons) are massiv e, but neit er are considered matter eit er.[32] However, w i e t ese partic es are not considered matter, t ey do contribute to t e tota mass of atoms, subato mic partic es, and a systems w ic contain t em.[33][34] [edit] Summary
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T e term "matter" is used t roug out p ysics in a bewi dering variety of context s: for examp e, one refers to "condensed matter p ysics",[35] "e ementary matter
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",[36] "partonic" matter, "dark" matter, "anti"-matter, "strange" matter, and "n uc ear" matter. In discussions of matter and antimatter, norma matter as been referred to by A fvén as koinomatter.[37] It is fair to say t at in p ysics, t ere is no broad consensus as to an exact definition of matter, and t e term "matter " usua y is used in conjunction wit some modifier. [edit] Definitions [edit] Common definition T e DNA mo ecu e is an examp e of matter under t e "atoms and mo ecu es" definit ion.
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T e common definition of matter is anyt ing t at as bot mass and vo ume (occup ies space).[38][39] For examp e, a car wou d be said to be made of matter, as it occupies space, and as mass. ¡
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T e observation t at matter occupies space goes back to antiquity. However, an e xp anation for w y matter occupies space is recent, and is argued to be a resu t of t e Pau i exc usion princip e.[40][41] Two particu ar examp es w ere t e exc usion princip e c ear y re ates matter to t e occupation of space are w ite dwa rf stars and neutron stars, discussed furt er be ow. [edit] Re ativity
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In t e context of re ativity, mass is not a tivity usua y a more genera view is taken mentum tensor t at quantifies t e amount of t at contributes to t e energy–momentum of t pure gravity.[42][43] T is view is common ra re ativity suc as cosmo ogy. [edit] Atoms and mo ecu es definition
conserved quantity.[1] T us, in re a t at it is not mass, but t e energy–mo matter. Matter t erefore is anyt ing a system, t at is, anyt ing t at is no y e d in fie ds t at dea wit gene
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A definition of "matter" t at is based upon its p ysica and c emica structure is: matter is made up of atoms and mo ecu es.[44] As an examp e, deoxyribonuc ei c acid mo ecu es (DNA) are matter under t is definition because t ey are made of atoms. T is definition can be extended to inc ude c arged atoms and mo ecu es, so as to inc ude p asmas (gases of ions) and e ectro ytes (ionic so utions), w i c are not obvious y inc uded in t e atoms and mo ecu es definition. A ternative y, one can adopt t e protons, neutrons and e ectrons definition. [edit] Protons, neutrons and e ectrons definition
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A definition of "matter" more fine-sca e t an t e atoms and mo ecu es definition is: matter is made up of w at atoms and mo ecu es are made of, meaning anyt ing made of protons, neutrons, and e ectrons.[45] T is definition goes beyond atoms
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and mo ecu udees, substances made ese matter bui ding b ocks ty, at are not es, simp owever, y atoms to or inc mo ecu for examp e wfrom ite t dwarf — typica carbon and oxygen nuc ei in a sea of degenerate e ectrons. At a microscopic ev e , t e constituent "partic es" of matter suc as protons, neutrons and e ectron s obey t e aws of quantum mec anics and ex ibit wave–partic e dua ity. At an even deeper eve , protons and neutrons are made up of quarks and t e force fie ds ( g uons) t at bind t em toget er (see Quarks and eptons definition be ow). [edit] Quarks and eptons definition Under t e "quarks and eptons" definition, t e e ementary and composite partic e s made of t e quarks (in purp e) and eptons (in green) wou d be "matter"; w i e t e gauge bosons (in red) wou d not be "matter". However, interaction energy in erent to composite partic es (for examp e, g uons invo ved in neutrons and prot ons) contribute to t e mass of ordinary matter.
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As may be seen from t e above discussion, many ear y definitions of w at can be ca ed ordinary matter were based upon its structure or "bui ding b ocks". On t
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e sca e of e ementary partic es, a definition t at fo ows t is tradition can be stated as: ordinary matter is everyt ing t at is composed of e ementary fermion s, name y quarks and eptons.[46][47] T e connection between t ese formu ations ¡
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fo
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ows.
Leptons (t e most famous being t e e ectron), and quarks (of w ic baryons, suc as protons and neutrons, are made) combine to form atoms, w ic in turn form mo ecu es. Because atoms and mo ecu es are said to be matter, it is natura to p r ase t e definition as: ordinary matter is anyt ing t at is made of t e same t in gs t at atoms and mo ecu es are made of. (However, notice t at one a so can make from t ese bui ding b ocks matter t at is not atoms or mo ecu es.) T en, becaus e e ectrons are eptons, and protons and neutrons are made of quarks, t is defin ition in turn eads to t e definition of matter as being "quarks and eptons", w
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ic are t e two types of e ementary fermions. Carit ers and Grannis state: Ordi nary matter is composed entire y of first-generation partic es, name y t e [up] and [down] quarks, p us t e e ectron and its neutrino.[48] (Hig er generations p artic es quick y decay into first-generation partic es, and t us are not common y encountered.[49]) ¡
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t e T is definition of ordinary matter is more subt e t an it first appears. A partic es t at make up ordinary matter ( eptons and quarks) are e ementary ferm ions, w i e a t e force carriers are e ementary bosons.[50] T e W and Z bosons t at mediate t e weak force are not made of quarks or eptons, and so are not o rdinary matter, even if t ey ave mass.[51] In ot er words, mass is not somet in g t at is exc usive to ordinary matter.
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T e quark– epton definition of ordinary matter, owever, identifies not on y t e e ementary bui ding b ocks of matter, but a so inc udes composites made from t e constituents (atoms and mo ecu es, for examp e). Suc composites contain an inte raction energy t at o ds t e constituents toget er, and may constitute t e bu k of t e mass of t e composite. As an examp e, to a great extent, t e mass of an atom is simp y t e sum of t e masses of its constituent protons, neutrons and e ectrons. However, digging deeper, t e protons and neutrons are made up of quarks bound toget er by g uon fie ds (see dynamics of quantum c romodynamics) and t e se g uons fie ds contribute significant y to t e mass of adrons.[52] In ot er w ords, most of w at composes t e "mass" of ordinary matter is due to t e binding energy of quarks wit in protons and neutrons.[53] For examp e, t e sum of t e ma ss of t e t ree quarks in a nuc eon is approximate y 12.5 MeV/c2, w ic is ow c ompared to t e mass of a nuc eon (approximate y 938 MeV/c2).[49][54] T e bottom ine is t at most of t e mass of everyday objects comes from t e interaction ene rgy of its e ementary components. [edit] Sma er bui ding b ocks?
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T e Standard Mode
groups matter partic es into t ree generations, w ere eac
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neration consiststof two quarks and two eptons. T e first isudes t e t upe and down quarks, e e ectron and t e e ectron neutrino; t generation e second inc c arm and strange quarks, t e muon and t e muon neutrino; t e t ird generation consists of t e top and bottom quarks and t e tau and tau neutrino.[55] T e most natura exp anation for t is wou d be t at quarks and eptons of ig er generat ions are excited states of t e first generations. If t is turns out to be t e ca se, it wou d imp y t at quarks and eptons are composite partic es, rat er t an e ementary partic es.[56] [edit] Structure
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In partic e p ysics, fermions are partic es w ic obey Fermi–Dirac statistics. Fer mions can be e ementary, ike t e e ectron, or composite, ike t e proton and t e neutron. In t e Standard Mode t ere are two types of e ementary fermions: qua rks and eptons, w ic are discussed next. [edit] Quarks Main artic e: Quark
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Quarks are a partic es of spin-1⁄2, imp ying t at t ey are fermions. T ey carry an e ectric c arge of −1⁄3 e (down type quarks) or +2⁄3 e (up type quarks). For comparis
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on, an electron has a charge of −1 e. They also carry colour charge, which is the equivalent of the electric charge for the strong interaction. Quarks also underg o radioactive decay, meaning that they are subject to the weak interaction. Quar ks are massive particles, and therefore are also subject to gravity. Quark properties[57] name symbol spin electric charge (e) mass (MeV/c2) mass comparable to antiparticle antiparticle symbol up type quarks up u 1⁄2 +2⁄3 1.5 to 3.3 ~ 5 electrons antiup u ¢
charm c 1⁄2 +2⁄3 1160 to 1340 ~ 1 proton anticharm c top t 1⁄2 +2⁄3 169,100 to 173,300 ~ 180 protons or ~ 1 tungsten atom antitop t down type quarks down d 1⁄2 −1⁄3 3.5 to 6.0 ~ 10 electrons antidown d strange s 1⁄2 −1⁄3 70 to 130 ~ 200 electrons antistrange s bottom b 1⁄2 −1⁄3 4130 to 4370 ~ 5 protons antibottom b Quark structure of a proton: 2 up quarks and 1 down quark. [edit] Baryonic matter Main article: Baryon ¢
Baryons are strongly interacting fermions, and so are subject to Fermi Dirac sta tistics. Amongst the baryons are the protons and neutrons, which occur in atomic nuclei, but many other unstable baryons exist as well. The term baryon is usual ly used to refer to triquarks — particles made of three quarks. "Exotic" baryons m ade of four quarks and one antiquark are known as the pentaquarks, but their exi stence is not generally accepted. ¢
Baryonic matter is the part of the universe that is made of baryons (including a ll 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 s tars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy P robe (WMAP), suggests that only about 4.6% of that part of the universe within r ange of the best telescopes (that is, matter that may be visible because light c ould reach us from it), is made of baryionic matter. About 23% is dark matter, a nd about 72% is dark energy.[58] A comparison between the white dwarf IK Pegasi B (center), its A class companion ¢
IK Pegasi A (left) and the Sun (right). This white dwarf has a surface temperat ure of 35,500 K. [edit] Degenerate matter Main article: Degenerate matter In physics, degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero.[59] The Pauli exclusion principle requires th at only two fermions can occupy a quantum state, one spin up and the other spin down. Hence, at zero temperature, the fermions fill up sufficient levels to acco mmodate all the available fermions, and for the case of many fermions the maximu m kinetic energy called the Fermi energy and the pressure of the gas becomes ver y large and dependent upon the number of fermions rather than the temperature, u nlike normal states of matter. ¢
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Degenerate matter is thought to occur during the evolution of heavy stars.[60] T he demonstration by Subrahmanyan Chandrasekhar that white dwarf stars have a max imum allowed mass because of the exclusion principle caused a revolution in the theory of star evolution.[61]
Degenerate matter includes the part of the universe that is made up of neutron s tars and white dwarfs. [edit] Strange matter Main article: Strange matter Strange matter is a particular form of quark matter, usually thought of as a 'li quid' of up, down, and strange quarks. It is to be contrasted with nuclear matte r, which is a liquid of neutrons and protons (which themselves are built out of up and down quarks), and with non strange quark matter, which is a quark liquid containing only up and down quarks. At high enough density, strange matter is ex ¢
pected to be color superconducting. Strange matter is hypothesized to occur in t he core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers (quark stars). [edit] Two meanings of the term "strange matter" In particle physics and astrophysics, the term is used in two ways, one broader and the other more specific. The broader meaning is just quark matter that contains three flavors of quar ks: up, down, and strange. In this definition, there is a critical pressure and an associated critical density, and when nuclear matter (made of protons and neu trons) is compressed beyond this density, the protons and neutrons dissociate in to quarks, yielding quark matter (probably strange matter). The narrower meaning is quark matter that is more stable than nuclear matter . The idea that this could happen is the "strange matter hypothesis" of Bodmer [ 62] and Witten.[63] In this definition, the critical pressure is zero: the true ground state of matter is always quark matter. The nuclei that we see in the mat ter around us, which are droplets of nuclear matter, are actually metastable, an d given enough time (or the right external stimulus) would decay into droplets o f strange matter, i.e. strangelets. [edit] Leptons Main article: Lepton Leptons are a particles of spin 1⁄2, meaning that they are fermions. They carry an electric charge of −1 e (charged leptons) or 0 e (neutrinos). Unlike quarks, lept ons do not carry colour charge, meaning that they do not experience the strong i nteraction. Leptons also undergo radioactive decay, meaning that they are subjec t to the weak interaction. Leptons are massive particles, therefore are subject to gravity. Lepton properties name symbol spin electric charge ¢
(e) (MeV/c2)mass mass comparable to antiparticle antiparticle symbol charged leptons[64] electron e− 1⁄2 −1 0.5110 1 electron antielectron e+ muon μ− 1⁄2 −1 105.7 ~ 200 electrons antimuon tau τ− 1⁄2 −1 1,777 ~ 2 pro ons an i au τ+ neu rinos[65] elec ron neu rino ν £
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au an ineu rino τ 1⁄2 0 < 18.2 < 40 elec rons ν τ [edi ] Phases Main ar icle: Phase (ma er) See also: Phase diagram and S a e of ma er Phase diagram for a ypical subs ance a a fixed volume. Ver ical axis is Pressu re, horizon al axis is Tempera ure. The green line marks he freezing poin (abo ve he green line is solid, below i is liquid) and he blue line he boiling po in (above i is liquid and below i is gas). So, for example, a higher T, a hi gher P is necessary o main ain he subs ance in liquid phase. A he riple poi £
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n he hree phases; liquid, gas and solid; can coexis . Above he cri ical poin here is no de ec able difference be ween he phases. The do ed line shows h e anomalous behavior of wa er: ice mel s a cons an empera ure wi h increasing pressure.[66] £
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In bulk, ma er can exis in several differen forms, or s a es of aggrega ion, known as phases,[67] depending on ambien pressure, empera ure and volume.[68] A phase is a form of ma er ha has a rela ively uniform chemical composi ion a nd physical proper ies (such as densi y, specific hea , refrac ive index, and so for h). These phases include he hree familiar ones (solids, liquids, and gase s), as well as more exo ic s a es of ma er ( such as plasmas, superfluids, supe rsolids, Bose–Eins ein condensa es, ...). A fluid may be a liquid, gas or plasma. There are also paramagne ic and ferromagne ic phases of magne ic ma erials. As c ondi ions change, ma er may change from one phase in o ano her. These phenomena are called phase ransi ions, and are s udied in he field of hermodynamics. I n nanoma erials, he vas ly increased ra io of surface area o volume resul s in ma er ha can exhibi proper ies en irely differen from hose of bulk ma eri al, and no well described by any bulk phase (see nanoma erials for more de ails ). £
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Phases are some imes called s a es of ma er, bu his erm can lead o confusio n wi h hermodynamic s a es. For example, wo gases main ained a differen pres sures are in differen hermodynamic s a es (differen pressures), bu in he sa me phase (bo h are gases). [edi ] An ima er Main ar icle: An ima er Unsolved problems in physics Baryon asymme ry. Why is here far more ma er han an ima er in he observable universe? Ques ion mark2.svg £
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In par icle physics and quan um chemis ry, an ima er is ma er ha is composed of he an ipar icles of hose ha cons i u e ordinary ma er. If a par icle an £
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anmay ipar in o each o her, wo energy annihila ha i d i s s, hey boicle h become conver edcon in ac o o wi herhpar icles wi hhe equal ine; accordan ce wi h Eins ein's equa ion E = mc2. These new par icles may be high energy pho ons (gamma rays) or o her par icle–an ipar icle pairs. The resul ing par icles are endowed wi h an amoun of kine ic energy equal o he difference be ween he re s mass of he produc s of he annihila ion and he res mass of he original pa r icle an ipar icle pair, which is of en qui e large. £
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An ima er is no found na urally on Ear h, excep very briefly and in vanishing ly small quan i ies (as he resul of radioac ive decay or cosmic rays). This is because an ima er which came o exis on Ear h ou side he confines of a sui a ble physics labora ory would almos ins an ly mee he ordinary ma er ha Ear h is made of, and be annihila ed. An ipar icles and some s able an ima er (such as an ihydrogen) can be made in iny amoun s, bu no in enough quan i y o do more han es a few of i s heore ical proper ies. £
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There is considerable specula ion bo h in science and science fic ion as o why he observable universe is apparen ly almos en irely ma er, and whe her o her places are almos en irely an ima er ins ead. In he early universe, i is hou
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gh ha ma er and an ima er were equally represen ed, and he disappearance o f an ima er requires an asymme ry in physical laws called he charge pari y (or CP symme ry) viola ion. CP symme ry viola ion can be ob ained from he S andard Model,[69] bu a his ime he apparen asymme ry of ma er and an ima er in he visible universe is one of he grea unsolved problems in physics. Possible processes by which i came abou are explored in more de ail under baryogenesis. [edi ] O her ypes of ma er Pie char showing he frac ions of energy in he universe con ribu ed by differe n sources. Ordinary ma er is divided in o luminous ma er ( he s ars and lumin ous gases and 0.005% radia ion) and nonluminous ma er (in ergalac ic gas and ab £
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ou 0.1% neu rinos and 0.04% supermassive black holes). Ordinary ma er is uncom mon. Modeled af er Os riker and S einhard .[70] For more informa ion, see NASA. £
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Ordinary ma er, in he quarks and lep ons defini ion, cons i u es abou 4% of he energy of he observable universe. The remaining energy is heorized o be du e o exo ic forms, of which 23% is dark ma er[71][72] and 73% is dark energy.[7 3][74] Galaxy ro a ion curve for he Milky Way. Ver ical axis is speed of ro a ion abou he galac ic cen er. Horizon al axis is dis ance from he galac ic cen er. The sun is marked wi h a yellow ball. The observed curve of speed of ro a ion is bl ue. The predic ed curve based upon s ellar mass and gas in he Milky Way is red. The difference is due o dark ma er or perhaps a modifica ion of he law of gr avi y.[75][76][77] Sca er in observa ions is indica ed roughly by gray bars. [edi ] Dark ma er Main ar icles: Dark ma er, Lambda CDM model, and WIMPs See also: Galaxy forma ion and evolu ion and Dark ma er halo £
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In as rophysics and cosmology, dark ma er is ma er of unknown composi ion ha does no emi or reflec enough elec romagne ic radia ion o be observed direc ly, bu whose presence can be inferred from gravi a ional effec s on visible ma er.[11][78] Observa ional evidence of he early universe and he big bang heor y require ha his ma er have energy and mass, bu is no composed of ei her e lemen ary fermions (as above) OR gauge bosons. The commonly accep ed view is ha mos of he dark ma er is non baryonic in na ure.[11] As such, i is composed of par icles as ye unobserved in he labora ory. Perhaps hey are supersymme r ic par icles,[79] which are no S andard Model par icles, bu relics formed a v ery high energies in he early phase of he universe and s ill floa ing abou .[1 1] [edi ] Dark energy Main ar icle: Dark energy See also: Big bang#Dark energy £
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In cosmology, dark energy is he name given o he an igravi a ing influence ha is accelera ing he ra e of expansion of he universe. I is known no o be c omposed of known par icles like pro ons, neu rons or elec rons, nor of he par i cles of dark ma er, because hese all gravi a e.[80][81] £
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Fully 70% of he ma er densi y in he universe appears o be in he form of dark energy. Twen y six percen is dark ma er. Only 4% is ordinary ma er. So less han 1 par in 20 is made ou of ma er we have observed experimen ally or described in he s andard model of par icle physics. Of he o her 96%, apar fro m he proper ies jus men ioned, we know absolu ely no hing. £
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– Lee Smolin: The Trouble wi h Physics, p. 16 £
[edi ] Exo ic ma er Main ar icle: Exo ic ma £
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Exo ic ma er is a hypo he ical concep of par icle physics. I covers any ma er ial which viola es one or more classical condi ions or is no made of known bary £
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onic par icles. Such ma erials would possess quali ies like nega ive mass or bei ng repelled ra her han a rac ed by gravi y. £
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