View source for Physics:Matter

{{Short description|Something that has mass and volume}}
[[File:Hydrogen discharge tube.jpg|thumb|[[Chemistry:Hydrogen|Hydrogen]] in its plasma state is the most abundant ordinary matter in the universe.]]
In [[Physics:Classical physics|classical physics]] and general [[Chemistry:Chemistry|chemistry]], '''matter''' is any substance that has [[Physics:Mass|mass]] and takes up space by having [[Physics:Volume|volume]].<ref name="Penrose" /> All everyday objects that can be touched are ultimately composed of [[Physics:Atom|atom]]s, which are made up of interacting [[Physics:Subatomic particle|subatomic particle]]s, and in everyday as well as scientific usage, ''matter'' generally includes atoms and anything made up of them, and any particles (or combination of particles) that act as if they have both [[Physics:Rest mass|rest mass]] and [[Physics:Volume|volume]]. However it does not include [[Physics:Massless particle|massless particle]]s such as [[Physics:Photon|photon]]s, or other energy phenomena or waves such as [[Physics:Light|light]] or [[Physics:Heat|heat]].<ref name="Penrose">
{{cite book
 |author= R. Penrose
 |date=1991
 |chapter=The mass of the classical vacuum
 |title=The Philosophy of Vacuum
 |chapter-url=https://books.google.com/books?id=ZU1LL4IbDKcC&pg=PA21
 |pages=21–26
 |publisher=[[Organization:Oxford University Press|Oxford University Press]]
 |isbn=978-0-19-824449-3
}}</ref>{{rp|21}}<ref name="mcgrawhill">
{{cite encyclopedia
 |title=Matter (physics)
 |url=http://www.accessscience.com/abstract.aspx?id=410600&referURL=http%3a%2f%2fwww.accessscience.com%2fcontent.aspx%3fid%3d410600
 |encyclopedia=McGraw-Hill's Access Science: Encyclopedia of Science and Technology Online
 |access-date=2009-05-24
 |url-status=dead
 |archive-url=https://web.archive.org/web/20110617073828/http://www.accessscience.com/abstract.aspx?id=410600&referURL=http%3A%2F%2Fwww.accessscience.com%2Fcontent.aspx%3Fid%3D410600
 |archive-date=17 June 2011 }}</ref> Matter exists in various [[Physics:State of matter|states]] (also known as [[Physics:Phase (matter)|phases]]). These include classical everyday phases such as [[Physics:Solid|solid]], [[Physics:Liquid|liquid]], and [[Physics:Gas|gas]] – for example [[Chemistry:Water|water]] exists as [[Earth:Ice|ice]], liquid water, and gaseous [[Physics:Steam|steam]] – but other states are possible, including [[Physics:Plasma|plasma]], [[Physics:Bose–Einstein condensate|Bose–Einstein condensate]]s, [[Physics:Fermionic condensate|fermionic condensate]]s, and [[Physics:Quark–gluon plasma|quark–gluon plasma]].<ref name="RHIC">
{{cite press release
 |date=18 April 2005
 |url=http://www.bnl.gov/bnlweb/pubaf/pr/pr_display.asp?prid=05-38
 |title=RHIC Scientists Serve Up "Perfect" Liquid
 |publisher=[[Organization:Brookhaven National Laboratory|Brookhaven National Laboratory]]
 |access-date=2009-09-15
}}</ref>

Usually atoms can be imagined as a [[Physics:Atomic nucleus|nucleus]] of [[Physics:Proton|proton]]s and [[Physics:Neutron|neutron]]s, and a surrounding "cloud" of orbiting [[Physics:Electron|electron]]s which "take up space".<ref name=Davies2>
{{cite book
 |author=P. Davies
 |date=1992
 |title=The New Physics: A Synthesis
 |url=https://books.google.com/books?id=akb2FpZSGnMC&pg=PA1
 |page=1
 |publisher=Cambridge University Press
 |isbn=978-0-521-43831-5
}}</ref><ref name=Hooft>
{{cite book
 |author=Gerard't Hooft
 |date=1997
 |title=In search of the ultimate building blocks
 |url=https://archive.org/details/insearchofultima0000hoof
 |url-access=registration
 |page=[https://archive.org/details/insearchofultima0000hoof/page/6 6]
 |publisher=Cambridge University Press
 |isbn=978-0-521-57883-7
}}</ref> However this is only somewhat correct, because subatomic particles and their properties are governed by their [[Physics:Quantum mechanics|quantum nature]], which means they do not act as everyday objects appear to act – they can act like [[Physics:Wave–particle duality|waves as well as particles]], and they do not have well-defined sizes or positions. In the [[Physics:Standard Model|Standard Model]] of [[Physics:Particle physics|particle physics]], matter is not a fundamental concept because the [[Physics:Elementary particle|elementary constituents]] of atoms are [[Physics:Quantum|quantum]] entities which do not have an inherent "size" or "[[Physics:Volume|volume]]" in any everyday sense of the word. Due to the [[Physics:Pauli exclusion principle|exclusion principle]] and other [[Physics:Fundamental interaction|fundamental interaction]]s, some "[[Physics:Point particle|point particle]]s" known as [[Physics:Fermion|fermion]]s ([[Physics:Quark|quark]]s, [[Physics:Lepton|lepton]]s), and many composites and atoms, are effectively forced to keep a distance from other particles under everyday conditions; this creates the property of matter which appears to us as matter taking up space.

For much of the history of the [[Natural science|natural science]]s people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks, the so-called particulate theory of matter, appeared in both {{wipe|Ancient Greece}} and ancient India.<ref name="Pullman2001p77">{{cite book|author=Bernard Pullman|title=The Atom in the History of Human Thought |url=https://books.google.com/books?id=IQs5hur-BpgC&pg=PA77 |year=2001|publisher=Oxford University Press|isbn=978-0-19-515040-7|pages=77–84}}</ref> Early philosophers who proposed the particulate theory of matter include the [[Philosophy:Indian philosophy|ancient Indian]] philosopher [[Biography:Kanada (philosopher)|Kanada]] (c. 6th–century BCE or after),<ref name="Fowler2002">{{cite book|author=Jeaneane D. Fowler|title=Perspectives of reality: an introduction to the philosophy of Hinduism|url=https://books.google.com/books?id=PJbsAAAAIAAJ|year=2002|publisher=Sussex Academic Press|isbn=978-1-898723-93-6|pages=99–115}}</ref> pre-Socratic Greek philosopher [[Biography:Leucippus|Leucippus]] (~490 BCE), and pre-Socratic Greek philosopher [[Biography:Democritus|Democritus]] (~470–380 BCE).<ref>
{{cite book
 |author=J. Olmsted |author2=G.M. Williams
 |date=1996
 |title=Chemistry: The Molecular Science
 |url=https://books.google.com/books?id=1vnk6J8knKkC&pg=PA40
 |page=40 |edition=2nd
 |publisher=Jones & Bartlett
 |isbn=978-0-8151-8450-8
}}</ref>

==Related concepts==

===Comparison with mass===
Matter should not be confused with mass, as the two are not the same in modern physics.<ref name=Mongillo>
{{cite book
 |author=J. Mongillo
 |date=2007
 |title=Nanotechnology 101
 |url=https://books.google.com/books?id=j69lwrrQ4nsC&pg=PA30
 |page=30
 |publisher=Greenwood Publishing
 |isbn=978-0-313-33880-9
}}</ref> Matter is a general term describing any 'physical substance'. By contrast, [[Physics:Mass|mass]] is not a substance but rather a quantitative ''property'' of matter and other substances or systems; various types of mass are defined within [[Physics:Physics|physics]] – including but not limited to [[Physics:Rest mass|rest mass]], inertial mass, [[Physics:Relativistic mass|relativistic mass]], [[Mass–energy equivalence|mass–energy]].

While there are different views on what should be considered matter, the mass of a substance has exact scientific definitions.  Another difference is that matter has an "opposite" called [[Physics:Antimatter|antimatter]], but mass has no opposite—there is no such thing as "anti-mass" or [[Physics:Negative mass|negative mass]], so far as is known, although scientists do discuss the concept.  Antimatter has the same (i.e. positive) mass property as its normal matter counterpart.

Different fields of science use the term matter in different, and sometimes incompatible, ways. Some of these ways are based on loose historical meanings, from a time when there was no reason to distinguish mass from simply a quantity of matter. As such, there is no single universally agreed scientific meaning of the word "matter". Scientifically, the term "mass" is well-defined, but "matter" can be defined in several ways. Sometimes in the field of physics "matter" is simply equated with particles that exhibit rest mass (i.e., that cannot travel at the speed of light), such as quarks and leptons. However, in both [[Physics:Physics|physics]] and [[Chemistry:Chemistry|chemistry]], matter exhibits both [[Wave|wave]]-like and [[Physics:Particle|particle]]-like properties, the so-called [[Physics:Wave–particle duality|wave–particle duality]].<ref name=Davies>
{{cite book
 |author=P.C.W. Davies
 |date=1979
 |title=The Forces of Nature
 |url=https://archive.org/details/forcesofnature0000davi
 |url-access=registration
 |quote=matter field.
 |page=[https://archive.org/details/forcesofnature0000davi/page/116 116]
 |publisher=Cambridge University Press
 |isbn=978-0-521-22523-6
}}</ref><ref name=Weinberg>
{{cite book
 |author=S. Weinberg
 |date=1998
 |title=The Quantum Theory of Fields
 |url=https://books.google.com/books?id=2oPZJJerMLsC&q=Weinberg+%22matter+field%22&pg=PA5
 |page=2
 |publisher=Cambridge University Press
 |isbn=978-0-521-55002-4
}}</ref><ref name= Masujima>
{{cite book
 |author=M. Masujima
 |date=2008
 |title=Path Integral Quantization and Stochastic Quantization
 |url=https://books.google.com/books?id=OM15pk3ZHf0C&pg=PA103
 |page=103
 |publisher=Springer
 |isbn=978-3-540-87850-6
}}</ref>

=== Relation with chemical substance ===
{{excerpt|Chemical substance}}

== Definition ==

=== Based on atoms ===
A definition of "matter" based on its physical and chemical structure is: ''matter is made up of [[Physics:Atom|atom]]s''.<ref name=Barker0>
{{cite book
 |author=G.F. Barker
 |date=1870
 |chapter=Divisions of matter
 |title=A text-book of elementary chemistry: theoretical and inorganic
 |chapter-url=https://books.google.com/books?id=az8AAAAAYAAJ&q=%22Three%20divisions%20of%20matter%20are%20recognized%22&pg=PA2
 |page=2
 |publisher=John F Morton & Co.
 |isbn=978-1-4460-2206-1
}}</ref> Such ''atomic matter'' is also sometimes termed ''ordinary matter''. As an example, deoxyribonucleic acid [[Physics:Molecule|molecule]]s (DNA) are matter under this definition because they are made of atoms. This definition can be extended to include charged atoms and molecules, so as to include [[Physics:Plasma|plasmas]] (gases of ions) and [[Physics:Electrolyte|electrolyte]]s (ionic solutions), which are not obviously included in the atoms definition. Alternatively, one can adopt the ''protons, neutrons, and electrons'' definition.

=== Based on protons, neutrons and electrons ===
A definition of "matter" more fine-scale than the atoms and molecules definition is: ''matter is made up of what [[Physics:Atom|atom]]s and [[Physics:Molecule|molecule]]s are made of'', meaning anything made of positively charged [[Physics:Proton|proton]]s, neutral [[Physics:Neutron|neutron]]s, and negatively charged [[Physics:Electron|electron]]s.<ref name=DePodesta1>
{{cite book
 |author=M. de Podesta
 |date=2002
 |title=Understanding the Properties of Matter
 |url=https://books.google.com/books?id=h8BNvnR050cC&pg=PA8
 |page=8 |edition=2nd
 |publisher=CRC Press
 |isbn=978-0-415-25788-6
}}</ref> This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that are ''not'' simply atoms or molecules, for example electron beams in an old [[Engineering:Cathode ray tube|cathode ray tube]] television, or [[Astronomy:White dwarf|white dwarf]] matter—typically, carbon and oxygen nuclei in a sea of degenerate electrons. At a microscopic level, the constituent "particles" of matter such as protons, neutrons, and electrons obey the laws of quantum mechanics and exhibit wave–particle duality. At an even deeper level, protons and neutrons are made up of [[Physics:Quark|quark]]s and the force fields ([[Physics:Gluon|gluon]]s) that bind them together, leading to the next definition.

=== Based on quarks and leptons ===
[[File:Standard Model of Elementary Particles.svg|thumb|upright=1.5|Under the "quarks and leptons" definition, the elementary and composite particles made of the quarks (in purple) and leptons (in green) would be matter—while the gauge bosons (in red) would not be matter. However, interaction energy inherent to composite particles (for example, gluons involved in neutrons and protons) contribute to the mass of ordinary matter.]]

As seen in the above discussion, many early definitions of what can be called "ordinary matter" were based upon its structure or "building blocks".  On the scale of elementary particles, a definition that follows this tradition can be stated as:
"ordinary matter is everything that is composed of [[Physics:Quark|quark]]s and [[Physics:Lepton|lepton]]s", or "ordinary matter is everything that is composed of any elementary fermions except antiquarks and antileptons".<ref name=Povh0>
{{cite book
 |quote=Ordinary matter is composed entirely of first-generation particles, namely the u and d quarks, plus the electron and its neutrino.
 |author=B. Povh |author2=K. Rith |author3=C. Scholz |author4=F. Zetsche |author5=M. Lavelle
 |date=2004
 |title=Particles and Nuclei: An Introduction to the Physical Concepts
 |chapter=Part I: Analysis: The building blocks of matter
 |chapter-url=https://books.google.com/books?id=rJe4k8tkq7sC&q=povh+%22building+blocks+of+matter%22&pg=PA9
 |edition=4th
 |publisher=Springer
 |isbn=978-3-540-20168-7
}}</ref><ref name=Carithers /><ref>{{cite journal
 |journal=International Journal of Modern Physics E
 |volume=15
 |issue=1
 |title=What Is a Matter Particle?
 |last=Tsan
 |first=Ung Chan
 |date=2006
 |doi=10.1142/S0218301306003916
 |pages=259–272
|quote="''(From Abstract:)'' Positive baryon numbers (A>0) and positive lepton numbers (L>0) characterize matter particles while negative baryon numbers and negative lepton numbers characterize antimatter particles. Matter particles and antimatter particles belong to two distinct classes of particles. Matter neutral particles are particles characterized by both zero baryon number and zero lepton number. This third class of particles includes mesons formed by a quark and an antiquark pair (a pair of matter particle and antimatter particle) and bosons which are messengers of known interactions (photons for electromagnetism, W and Z bosons for the weak interaction, gluons for the strong interaction). The antiparticle of a matter particle belongs to the class of antimatter particles, the antiparticle of an antimatter particle belongs to the class of matter particles."
|bibcode=2006IJMPE..15..259C
 |s2cid=121628541
 |url=http://hal.in2p3.fr/in2p3-00025093/file/matter-partG05R.pdf
 }}</ref> The connection between these formulations follows.

Leptons (the most famous being the [[Physics:Electron|electron]]), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules. Because atoms and molecules are said to be matter, it is natural to phrase the definition as: "ordinary matter is anything that is made of the same things that atoms and molecules are made of". (However, notice that one also can make from these building blocks matter that is ''not'' atoms or molecules.) Then, because electrons are leptons, and protons and neutrons are made of quarks, this definition in turn leads to the definition of matter as being "quarks and leptons", which are two of the four types of elementary fermions (the other two being antiquarks and antileptons, which can be considered antimatter as described later). Carithers and Grannis state: "Ordinary matter is composed entirely of first-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino."<ref name=Carithers>{{cite journal
 |author1=B. Carithers |author2=P. Grannis |title=Discovery of the Top Quark
 |url=http://www.slac.stanford.edu/pubs/beamline/pdf/95iii.pdf
 |journal=Beam Line
 |volume=25 |issue=3 |pages=4–16
 |date=1995
}}</ref> (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.<ref name=Green2005>
{{cite book
 |author=D. Green
 |date=2005
 |title=High P<sub>T</sub> physics at hadron colliders
 |url=https://books.google.com/books?id=6-7TE5N0vbIC&pg=PA23
 |page=23
 |isbn=978-0-521-83509-1
 |publisher=Cambridge University Press
}}</ref>)

This definition of ordinary matter is more subtle than it first appears. All the particles that make up ordinary matter (leptons and quarks) are elementary fermions, while all the force carriers are elementary bosons.<ref name=Smolin>
{{cite book
 |author=L. Smolin
 |date=2007
 |title=The Trouble with Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next
 |url=https://books.google.com/books?id=z5rxrnlcp3sC&pg=PA67
 |page=67
 |publisher=Mariner Books
 |isbn=978-0-618-91868-3
}}</ref> The [[Physics:W and Z bosons|W and Z bosons]] that mediate the [[Physics:Weak force|weak force]] are not made of quarks or leptons, and so are not ordinary matter, even if they have mass.<ref name=Caso>The W boson mass is 80.398 GeV; see Figure 1 in {{cite journal
 |author=C. Amsler
 |collaboration=[[Physics:Particle Data Group|Particle Data Group]]
 |date=2008
 |title=Review of Particle Physics: The Mass and Width of the W Boson
 |url=http://pdg.lbl.gov/2008/reviews/wmass_s043202.pdf
 |journal=[[Physics:Physics Letters B|Physics Letters B]]
 |volume=667 |issue=1
 |page=1
 |bibcode = 2008PhLB..667....1A |doi = 10.1016/j.physletb.2008.07.018
  |hdl=1854/LU-685594
 |hdl-access=free
 }}</ref> In other words, [[Physics:Mass|mass]] is not something that is exclusive to ordinary matter.

The quark–lepton definition of ordinary matter, however, identifies not only the elementary building blocks of matter, but also includes composites made from the constituents (atoms and molecules, for example). Such composites contain an interaction energy that holds the constituents together, and may constitute the bulk of the mass of the composite. As an example, to a great extent, the mass of an atom is simply the sum of the masses of its constituent protons, neutrons and electrons. However, digging deeper, the protons and neutrons are made up of quarks bound together by gluon fields (see [[Physics:Quantum chromodynamics#Dynamics|dynamics of quantum chromodynamics]]) and these gluons fields contribute significantly to the mass of hadrons.<ref name=Aitchison>
{{cite book
 |author=I.J.R. Aitchison |author2=A.J.G. Hey
 |date=2004
 |title=Gauge Theories in Particle Physics
 |url=https://books.google.com/books?id=vLP7XN2pWlEC&pg=PA48
 |page=48
 |publisher=CRC Press
 |isbn=978-0-7503-0864-9
}}</ref> In other words, most of what composes the "mass" of ordinary matter is due to the [[Physics:Binding energy|binding energy]] of quarks within protons and neutrons.<ref name=Povh>
{{cite book
 |author=B. Povh |author2=K. Rith |author3=C. Scholz |author4=F. Zetsche |author5=M. Lavelle
 |date=2004
 |title=Particles and Nuclei: An Introduction to the Physical Concepts
 |url=https://books.google.com/books?id=rJe4k8tkq7sC&pg=PA103
 |page=103
 |publisher=Springer
 |isbn=978-3-540-20168-7
}}</ref> For example, the sum of the mass of the three quarks in a [[Physics:Nucleon|nucleon]] is approximately {{val|12.5|ul=MeV/c2}}, which is low compared to the mass of a nucleon (approximately {{val|938|ul=MeV/c2}}).<ref name=Green2004>
{{cite book
 |author=A.M. Green
 |date=2004
 |title=Hadronic Physics from Lattice QCD
 |url=https://books.google.com/books?id=XUGVOJKHgKAC&pg=PA120
 |page=120
 |publisher=World Scientific
 |isbn=978-981-256-022-3
}}</ref><ref name=Akai>
{{cite book
 |author=T. Hatsuda
 |date=2008
 |chapter=Quark–gluon plasma and QCD
 |editor=H. Akai
 |title=Condensed matter theories
 |chapter-url=https://books.google.com/books?id=PZdFi145170C&pg=PA296
 |volume=21 |page=296
 |publisher=Nova Publishers
 |isbn=978-1-60021-501-8
}}</ref> The bottom line is that most of the mass of everyday objects comes from the interaction energy of its elementary components.

The Standard Model groups matter particles into three generations, where each generation consists of two quarks and two leptons. The first generation is the ''[[Physics:Up quark|up]]'' and ''[[Physics:Down quark|down]]'' quarks, the ''[[Physics:Electron|electron]]'' and the ''[[Physics:Electron neutrino|electron neutrino]]''; the second includes the ''[[Physics:Charm quark|charm]]'' and ''[[Physics:Strange quark|strange]]'' quarks, the ''[[Physics:Muon|muon]]'' and the ''[[Physics:Muon neutrino|muon neutrino]]''; the third generation consists of the ''[[Physics:Top quark|top]]'' and ''[[Physics:Bottom quark|bottom]]'' quarks and the ''[[Physics:Tau (particle)|tau]]'' and ''[[Physics:Tau neutrino|tau neutrino]]''.<ref name=Staley>
{{cite book
 |author=K.W. Staley
 |date=2004
 |chapter=Origins of the Third Generation of Matter
 |chapter-url=https://books.google.com/books?id=DLt_fcBYynAC&pg=PA8
 |title=The Evidence for the Top Quark
 |page=8
 |publisher=Cambridge University Press
 |isbn=978-0-521-82710-2
}}</ref> The most natural explanation for this would be that quarks and leptons of higher generations are [[Physics:Excited state|excited state]]s of the first generations. If this turns out to be the case, it would imply that quarks and leptons are composite particles, rather than [[Physics:Elementary particle|elementary particle]]s.<ref name= Kirsh>
{{cite book
 |author=Y. Ne'eman |author2=Y. Kirsh
 |date=1996
 |title=The Particle Hunters
 |url=https://books.google.com/books?id=K4jcfCguj8YC&pg=PA276
 |page=276 |edition=2nd
 |publisher=Cambridge University Press
 |isbn=978-0-521-47686-7
 |quote=[T]he most natural explanation to the existence of higher generations of quarks and leptons is that they correspond to excited states of the first generation, and experience suggests that excited systems must be composite}}</ref>

This quark–lepton definition of matter also leads to what can be described as "conservation of (net) matter" laws—discussed later below.  Alternatively, one could return to the mass–volume–space concept of matter, leading to the next definition, in which antimatter becomes included as a subclass of matter.

=== Based on elementary fermions (mass, volume, and space) ===
A common or traditional definition of matter is "anything that has [[Physics:Mass|mass]] and [[Physics:Volume|volume]] (occupies [[Space|space]])".<ref name=Walker>{{cite book|author=S.M. Walker |author2=A. King|date=2005|title=What is Matter?|url=https://books.google.com/books?id=o7EquxOl4MAC&q=matter|page=7|publisher=Lerner Publications|isbn=978-0-8225-5131-7}}</ref><ref name=Hage>{{cite book| author=J.Kenkel |author2=P.B. Kelter |author3=D.S. Hage|date=2000|title=Chemistry: An Industry-based Introduction with CD-ROM|url= https://books.google.com/books?id=ADSjPRl_tgoC&pg=PA1|page=2|publisher=CRC Press|isbn= 978-1-56670-303-1|quote=All basic science textbooks define ''matter'' as simply the collective aggregate of all material substances that occupy space and have mass or weight.}}</ref> For example, a car would be said to be made of matter, as it has mass and volume (occupies space).

The observation that matter occupies space goes back to antiquity. However, an explanation for why matter occupies space is recent, and is argued to be a result of the phenomenon described in the [[Physics:Pauli exclusion principle|Pauli exclusion principle]],<ref name=Peacock>{{cite book|author=K.A. Peacock| date=2008|title=The Quantum Revolution: A Historical Perspective|url=https://books.google.com/books?id=ITqnf5jdE5QC&pg=PA47|page=47|publisher=Greenwood Publishing Group|isbn=978-0-313-33448-1}}</ref><ref name=Kreiger>{{cite book|author=M.H. Krieger|date=1998|title=Constitutions of Matter: Mathematically Modeling the Most Everyday of Physical Phenomena|url=https://books.google.com/books?id=VduHhkzl-aQC&q=%22does+not+collapse+into+itself%22&pg=PA22|page=22| publisher=[[Organization:University of Chicago Press|University of Chicago Press]]|isbn=978-0-226-45305-7}}</ref> which applies to fermions.  Two particular examples where the exclusion principle clearly relates matter to the occupation of space are white dwarf stars and neutron stars, discussed further below.

Thus, matter can be defined as everything composed of elementary fermions. Although we do not encounter them in everyday life, antiquarks (such as the [[Physics:Antiproton|antiproton]]) and antileptons (such as the [[Physics:Positron|positron]]) are the [[Physics:Antiparticle|antiparticle]]s of the quark and the lepton, are elementary fermions as well, and have essentially the same properties as quarks and leptons, including the applicability of the Pauli exclusion principle which can be said to prevent two particles from being in the same place at the same time (in the same state), i.e. makes each particle "take up space".  This particular definition leads to matter being defined to include anything made of these [[Physics:Antimatter|antimatter]] particles as well as the ordinary quark and lepton, and thus also anything made of [[Physics:Meson|meson]]s, which are unstable particles made up of a quark and an antiquark.

=== In general relativity and cosmology ===
In the context of [[Physics:Theory of relativity|relativity]], mass is not an additive quantity, in the sense that one can not add the rest masses of particles in a system to get the total rest mass of the system.<ref name=Penrose/>{{rp|21}} Thus, in relativity usually a more general view is that it is not the sum of [[Physics:Rest mass|rest mass]]es, but the [[Stress–energy tensor|energy–momentum tensor]] that quantifies the amount of matter. This tensor gives the rest mass for the entire system. "Matter" therefore is sometimes considered as anything that contributes to the energy–momentum of a system, that is, anything that is not purely gravity.<ref name=Caroll>
{{cite book
 |author=S.M. Caroll
 |date=2004
 |title=Spacetime and Geometry
 |pages=163–164
 |publisher=Addison Wesley
 |isbn=978-0-8053-8732-2
}}</ref><ref name=Davies499>
{{cite book
 |author=P. Davies
 |date=1992
 |title=The New Physics: A Synthesis
 |url=https://books.google.com/books?id=akb2FpZSGnMC&pg=PA499
 |page=499
 |publisher=Cambridge University Press
 |isbn=978-0-521-43831-5
 |quote='''Matter fields''': the fields whose quanta describe the elementary particles that make up the material content of the Universe (as opposed to the gravitons and their supersymmetric partners).
}}</ref> This view is commonly held in fields that deal with [[Physics:General relativity|general relativity]] such as [[Astronomy:Cosmology|cosmology]]. In this view, light and other massless particles and fields are all part of "matter".

== Structure ==
In particle physics, fermions are particles that obey [[Physics:Fermi–Dirac statistics|Fermi–Dirac statistics]]. Fermions can be elementary, like the electron—or composite, like the proton and neutron. In the [[Physics:Standard Model|Standard Model]], there are two types of elementary fermions: quarks and leptons, which are discussed next.

=== Quarks ===
{{Main|Physics:Quark}}
Quarks are [[Physics:Massive particle|massive particle]]s of [[Physics:Fermion|spin-{{frac|1|2}}]], implying that they are [[Physics:Fermion|fermion]]s. They carry an [[Physics:Electric charge|electric charge]] of −{{frac|1|3}}&nbsp;[[Physics:Elementary charge|e]] (down-type quarks) or +{{frac|2|3}}&nbsp;e (up-type quarks). For comparison, an electron has a charge of −1&nbsp;e. They also carry colour charge, which is the equivalent of the electric charge for the [[Physics:Strong interaction|strong interaction]]. Quarks also undergo [[Physics:Radioactive decay|radioactive decay]], meaning that they are subject to the [[Physics:Weak interaction|weak interaction]].

{| class="wikitable" style="margin:0 auto; text-align:center;"
|+Quark properties<ref>
{{cite journal
 |author=C. Amsler
 |collaboration=[[Physics:Particle Data Group|Particle Data Group]]
 |date=2008
 |title=Reviews of Particle Physics: Quarks
 |url=http://pdg.lbl.gov/2008/tables/rpp2008-sum-quarks.pdf
 |journal=[[Physics:Physics Letters B|Physics Letters B]]
 |volume=667 |issue=1–5
 |page=1
 |doi= 10.1016/j.physletb.2008.07.018
|bibcode = 2008PhLB..667....1A
  |hdl=1854/LU-685594
 |hdl-access=free
 }}</ref>
! name !! symbol !! spin !! electric charge<br />([[Physics:Elementary charge|e]]) !! mass<br />([[Physics:Electronvolt|MeV]]/''[[Physics:Speed of light|c]]''<sup>2</sup>) !! mass comparable to !! antiparticle !! antiparticle<br />symbol
|-
|colspan="7"| up-type quarks
|-
| [[Physics:Up quark|up]]
| {{Subatomic particle|Up quark}}
| {{frac|1|2}}
| +{{frac|2|3}}
| 1.5 to 3.3
| ~ 5 electrons
| antiup
| {{Subatomic particle|Up antiquark}}
|-
| [[Physics:Charm quark|charm]]
| {{Subatomic particle|Charm quark}}
| {{frac|1|2}}
| +{{frac|2|3}}
| 1160 to 1340
| ~1 proton
| anticharm
| {{Subatomic particle|Charm antiquark}}
|-
| [[Physics:Top quark|top]]
| {{Subatomic particle|Top quark}}
| {{frac|1|2}}
| +{{frac|2|3}}
| 169,100 to 173,300
| ~180 protons or<br />~1 [[Chemistry:Tungsten|tungsten]] atom
| antitop
| {{Subatomic particle|Top antiquark}}
|-
|colspan="7"| down-type quarks
|-
| [[Physics:Down quark|down]]
| {{Subatomic particle|Down quark}}
| {{frac|1|2}}
| −{{frac|1|3}}
| 3.5 to 6.0
| ~10 electrons
| antidown
| {{Subatomic particle|Down antiquark}}
|-
| [[Physics:Strange quark|strange]]
| {{Subatomic particle|Strange quark}}
| {{frac|1|2}}
| −{{frac|1|3}}
| 70 to 130
| ~ 200 electrons
| antistrange
| {{Subatomic particle|Strange antiquark}}
|-
| [[Physics:Bottom quark|bottom]]
| {{Subatomic particle|Bottom quark}}
| {{frac|1|2}}
| −{{frac|1|3}}
| 4130 to 4370
| ~ 5 protons
| antibottom
| {{Subatomic particle|Bottom antiquark}}
|}

==== Baryonic ====
{{Main|Physics:Baryon}}
[[File:Quark_structure_proton.svg|thumb|upright|Quark structure of a proton: 2 up quarks and 1 down quark.]]Baryons are strongly interacting fermions, and so are subject to Fermi–Dirac statistics. Amongst the baryons are the protons and neutrons, which occur in atomic nuclei, but many other unstable baryons exist as well. The term baryon usually refers to triquarks—particles made of three quarks. Also, "exotic" baryons made of four quarks and one antiquark are known as [[Physics:Pentaquark|pentaquark]]s, but their existence is not generally accepted.

Baryonic matter is the part of the universe that is made of baryons (including all atoms). This part of the universe does not include [[Astronomy:Dark energy|dark energy]], [[Astronomy:Dark matter|dark matter]], black holes or various forms of degenerate matter, such as compose [[Astronomy:White dwarf|white dwarf]] stars and [[Astronomy:Neutron star|neutron star]]s. Microwave light seen by [[Astronomy:Wilkinson Microwave Anisotropy Probe|Wilkinson Microwave Anisotropy Probe]] (WMAP), suggests that only about 4.6% of that part of the universe within range of the best [[Astronomy:Telescope|telescope]]s (that is, matter that may be visible because light could reach us from it), is made of baryonic matter. About 26.8% is dark matter, and about 68.3% is dark energy.<ref name="NASA Science Dark Matter">{{cite web |url=https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/ |title=Dark Energy Dark Matter |website=NASA Science: Astrophysics |date=5 June 2015}}</ref>

The great majority of ordinary matter in the universe is unseen, since visible stars and gas inside galaxies and clusters account for less than 10 per cent of the ordinary matter contribution to the mass–energy density of the universe.<ref>{{Cite journal
| last1 = Persic
| first1 = Massimo
| last2 = Salucci
| first2 = Paolo
| date = 1992-09-01
| title = The baryon content of the Universe
| journal = Monthly Notices of the Royal Astronomical Society
| language = en
| volume = 258
| issue = 1
| pages = 14P–18P
| doi = 10.1093/mnras/258.1.14P
| issn = 0035-8711
|arxiv = astro-ph/0502178 |bibcode = 1992MNRAS.258P..14P | s2cid = 17945298
}}</ref>

==== Hadronic ====
Hadronic matter can refer to 'ordinary' baryonic matter, made from [[Physics:Hadron|hadron]]s (baryons and [[Physics:Meson|meson]]s), or [[Physics:Quark matter|quark matter]] (a generalisation of atomic nuclei), i.e. the 'low' temperature [[Physics:QCD matter|QCD matter]].<ref>{{Cite journal|title=The Phase Diagram of Hadronic Matter|journal = The European Physical Journal C|volume = 59|issue = 1|pages = 67–73|first1=H.|last1=Satz|first2=K.|last2=Redlich|first3=P.|last3=Castorina|year=2009|doi=10.1140/epjc/s10052-008-0795-z|arxiv=0807.4469|bibcode = 2009EPJC...59...67C|s2cid = 14503972}}</ref> It includes [[Astronomy:Degenerate matter|degenerate matter]] and the result of high energy heavy nuclei collisions.<ref>{{Cite journal|title=Modelling Hadronic Matter|first=Débora P.|last=Menezes|date=23 April 2016|journal=Journal of Physics: Conference Series|volume=706|issue = 3|pages=032001|doi=10.1088/1742-6596/706/3/032001|bibcode = 2016JPhCS.706c2001M|doi-access=free}}</ref>

==== Degenerate ====
{{Main|Astronomy:Degenerate matter}}
In physics, ''degenerate matter'' refers to the ground state of a gas of fermions at a temperature near absolute zero.<ref name=Goldberg0>
{{cite book
 |author=H.S. Goldberg |author2=M.D. Scadron
 |date=1987
 |title=Physics of Stellar Evolution and Cosmology
 |url=https://books.google.com/books?id=NowVde8kzIoC&pg=PA207
 |page=202
 |publisher=Taylor & Francis
 |isbn=978-0-677-05540-4
}}</ref> The [[Physics:Pauli exclusion principle|Pauli exclusion principle]] requires that 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 accommodate all the available fermions—and in the case of many fermions, the maximum kinetic energy (called the ''[[Physics:Fermi energy|Fermi energy]]'') and the pressure of the gas becomes very large, and depends on the number of fermions rather than the temperature, unlike normal states of matter.

Degenerate matter is thought to occur during the evolution of heavy stars.<ref name=Goldberg1>
{{cite book
 |author=H.S. Goldberg |author2=M.D. Scadron
 |date=1987
 |title=Physics of Stellar Evolution and Cosmology
 |url=https://books.google.com/books?id=NowVde8kzIoC&pg=PA207
 |page=233
 |publisher=Taylor & Francis
 |isbn=978-0-677-05540-4
}}</ref> The demonstration by [[Biography:Subrahmanyan Chandrasekhar|Subrahmanyan Chandrasekhar]] that white dwarf stars have a maximum allowed mass because of the exclusion principle caused a revolution in the theory of star evolution.<ref name=Luminet>
{{cite book
 |author=J.-P. Luminet |author2=A. Bullough |author3=A. King
 |date=1992
 |title=Black Holes
 |url=https://archive.org/details/blackholes0000lumi
 |url-access=registration |page=[https://archive.org/details/blackholes0000lumi/page/75 75]
 |publisher=Cambridge University Press
 |isbn=978-0-521-40906-3
}}</ref>

Degenerate matter includes the part of the universe that is made up of neutron stars and white dwarfs.

==== Strange ====
{{Main|Physics:Strange matter}}
''Strange matter'' is a particular form of [[Physics:Quark matter|quark matter]], usually thought of as a ''liquid'' of [[Physics:Up quark|up]], [[Physics:Down quark|down]], and [[Physics:Strange quark|strange]] quarks. It is contrasted with [[Physics:Nuclear matter|nuclear matter]], which is a liquid of [[Physics:Neutron|neutron]]s and [[Physics:Proton|proton]]s (which themselves are built out of up and down quarks), and with non-strange quark matter, which is a quark liquid that contains only up and down quarks. At high enough density, strange matter is expected to be color superconducting. Strange matter is hypothesized to occur in the core of [[Astronomy:Neutron star|neutron star]]s, or, more speculatively, as isolated droplets that may vary in size from femtometers ([[Astronomy:Strangelet|strangelet]]s) to kilometers ([[Astronomy:Quark star|quark star]]s).

===== Two meanings =====
In [[Physics:Particle physics|particle physics]] and [[Physics:Astrophysics|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 quarks: 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 neutrons) is compressed beyond this density, the protons and neutrons dissociate into 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<ref>
{{cite journal
 |author=A. Bodmer
 |date=1971
 |title=Collapsed Nuclei
 |journal=[[Physics:Physical Review D|Physical Review D]]
 |volume=4 |issue=6 |page=1601
 |doi=10.1103/PhysRevD.4.1601
 |bibcode = 1971PhRvD...4.1601B
}}</ref> and Witten.<ref>
{{cite journal
 |author=E. Witten
 |date=1984
 |title=Cosmic Separation of Phases
 |journal=[[Physics:Physical Review D|Physical Review D]]
 |volume=30 |issue=2 |page=272
 |doi=10.1103/PhysRevD.30.272
 |bibcode = 1984PhRvD..30..272W
}}</ref> 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 matter around us, which are droplets of nuclear matter, are actually metastable, and given enough time (or the right external stimulus) would decay into droplets of strange matter, i.e. [[Astronomy:Strangelet|strangelet]]s.

=== Leptons ===
{{Main|Physics:Lepton}}

Leptons are particles of [[Physics:Fermion|spin-{{frac|1|2}}]], meaning that they are [[Physics:Fermion|fermion]]s. They carry an [[Physics:Electric charge|electric charge]] of −1&nbsp;[[Physics:Elementary charge|e]] (charged leptons) or 0&nbsp;e (neutrinos). Unlike quarks, leptons do not carry colour charge, meaning that they do not experience the [[Physics:Strong interaction|strong interaction]]. Leptons also undergo radioactive decay, meaning that they are subject to the [[Physics:Weak interaction|weak interaction]]. Leptons are massive particles, therefore are subject to gravity.

{| class="wikitable" style="margin:0 auto; text-align:center;"
|+Lepton properties
! name !! symbol !! spin !! electric charge<br />([[Physics:Elementary charge|e]]) !! mass<br />([[Physics:Electronvolt|MeV]]/''[[Physics:Speed of light|c]]''<sup>2</sup>) !! mass comparable to !! antiparticle !! antiparticle<br />symbol
|-
|colspan="7"| charged leptons<ref>
{{cite journal
 |author=C. Amsler
 |collaboration=[[Physics:Particle Data Group|Particle Data Group]]
 |date=2008
 |title=Review of Particle Physics: Leptons
 |url=http://pdg.lbl.gov/2008/tables/rpp2008-sum-leptons.pdf
 |journal=[[Physics:Physics Letters B|Physics Letters B]]
 |volume=667 |issue=1–5
 |page=1
 |doi= 10.1016/j.physletb.2008.07.018
|bibcode = 2008PhLB..667....1A
  |hdl=1854/LU-685594
 |hdl-access=free
 }}</ref>
|-
| [[Physics:Electron|electron]]
| {{Subatomic particle|electron}}
| {{frac|1|2}}
| −1
| 0.5110
| 1 electron
| antielectron
| {{Subatomic particle|antielectron}}
|-
| [[Physics:Muon|muon]]
| {{Subatomic particle|muon}}
| {{frac|1|2}}
| −1
| 105.7
| ~ 200 electrons
| antimuon
| {{Subatomic particle|antimuon}}
|-
| [[Physics:Tau (particle)|tau]]
| {{Subatomic particle|tau}}
| {{frac|1|2}}
| −1
| 1,777
| ~ 2 protons
| antitau
| {{Subatomic particle|antitau}}
|-
|colspan="7"| neutrinos<ref>
{{cite journal
 |author=C. Amsler
 |collaboration=[[Physics:Particle Data Group|Particle Data Group]]
 |date=2008
 |title=Review of Particle Physics: Neutrinos Properties
 |url=http://pdg.lbl.gov/2008/listings/s066.pdf
 |journal=[[Physics:Physics Letters B|Physics Letters B]]
 |volume=667 |issue=1–5
 |page=1
 |doi= 10.1016/j.physletb.2008.07.018
|bibcode = 2008PhLB..667....1A
  |hdl=1854/LU-685594
 |hdl-access=free
 }}</ref>

|-
| [[Physics:Electron neutrino|electron neutrino]]
| {{Subatomic particle|Electron neutrino}}
| {{frac|1|2}}
| 0
| < 0.000460
| < {{frac|1|1000}} electron
| electron antineutrino
| {{Subatomic particle|Electron antineutrino}}
|-
| [[Physics:Muon neutrino|muon neutrino]]
| {{Subatomic particle|Muon neutrino}}
| {{frac|1|2}}
| 0
| < 0.19
| < {{frac|1|2}} electron
| muon antineutrino
| {{Subatomic particle|Muon antineutrino}}
|-
| [[Physics:Tau neutrino|tau neutrino]]
| {{Subatomic particle|Tau neutrino}}
| {{frac|1|2}}
| 0
| < 18.2
| < 40 electrons
| tau antineutrino
| {{Subatomic particle|Tau antineutrino}}
|}

== Phases ==
{{Main|Physics:Phase (matter)}}
[[File:Phase diagram for pure substance.JPG|thumb|upright=1.25|[[Phase diagram|Phase diagram]] for a typical substance at a fixed volume]]

In bulk, matter can exist in several different forms, or states of aggregation, known as ''[[Physics:Phase (matter)|phases]]'',<ref name=Collings>
{{cite book
 |author=P.J. Collings
 |date=2002
 |chapter=Chapter 1: States of Matter
 |chapter-url=https://books.google.com/books?id=NE1RWiGXtdUC
 |title=Liquid Crystals: Nature's Delicate Phase of Matter
 |publisher=Princeton University Press
 |isbn=978-0-691-08672-9
 |url=https://archive.org/details/liquidcrystalsna00coll
 }}</ref> depending on ambient [[Physics:Pressure|pressure]], [[Physics:Temperature|temperature]] and [[Physics:Volume|volume]].<ref name=Trevena>
{{cite book
 |author=D.H. Trevena
 |date=1975
 |chapter=Chapter 1.2: Changes of phase
 |title=The Liquid Phase
 |chapter-url=https://books.google.com/books?id=oOkOAAAAQAAJ&pg=PA1
 |publisher=Taylor & Francis
 |isbn=978-0-85109-031-3
}}</ref> A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as [[Physics:Density|density]], [[Physics:Specific heat|specific heat]], [[Physics:Refractive index|refractive index]], and so forth). These phases include the three familiar ones ([[Physics:Solid|solid]]s, [[Physics:Liquid|liquid]]s, and [[Physics:Gas|gas]]es), as well as more exotic states of matter (such as [[Physics:Plasma|plasmas]], superfluids, [[Physics:Supersolid|supersolid]]s, [[Physics:Bose–Einstein condensate|Bose–Einstein condensate]]s, ...). A ''[[Physics:Fluid|fluid]]'' may be a liquid, gas or plasma. There are also [[Physics:Paramagnetism|paramagnetic]] and [[Physics:Ferromagnetism|ferromagnetic]] phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called [[Physics:Phase transition|phase transition]]s, and are studied in the field of [[Physics:Thermodynamics|thermodynamics]]. In nanomaterials, the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material, and not well described by any bulk phase (see [[Physics:Nanomaterials|nanomaterials]] for more details).

Phases are sometimes called ''states of matter'', but this term can lead to confusion with [[Physics:Thermodynamics|thermodynamic states]]. For example, two gases maintained at different pressures are in different ''thermodynamic states'' (different pressures), but in the same ''phase'' (both are gases).

== Antimatter ==
{{Main|Physics:Antimatter}}
{{unsolved|physics|[[Astronomy:Baryon asymmetry|Baryon asymmetry]]. Why is there far more matter than antimatter in the observable universe? }}
''Antimatter'' is matter that is composed of the [[Physics:Antiparticle|antiparticle]]s of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the two [[Physics:Annihilation|annihilate]]; that is, they may both be converted into other particles with equal [[Physics:Energy|energy]] in accordance with [[Biography:Albert Einstein|Albert Einstein]]'s equation {{nowrap|''E'' = ''mc''<sup>2</sup>}}. These new particles may be high-energy [[Physics:Photon|photon]]s ([[Physics:Gamma ray|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 [[Physics:Rest mass|rest mass]] of the products of the annihilation and the rest mass of the original particle–antiparticle pair, which is often quite large.  Depending on which definition of "matter" is adopted, antimatter can be said to be a particular subclass of matter, or the opposite of matter.

Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of [[Physics:Radioactive decay|radioactive decay]], [[Astronomy:Lightning|lightning]] or [[Astronomy:Cosmic ray|cosmic ray]]s). This is because antimatter that 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 [[Physics:Antihydrogen|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|science]] and science fiction as to why the observable universe is apparently almost entirely matter (in the sense of quarks and leptons but not antiquarks or antileptons), and whether other places are almost entirely antimatter (antiquarks and antileptons) instead. In the early universe, it is thought that matter and antimatter were equally represented, and the disappearance of antimatter requires an asymmetry in physical laws called [[Physics:CP violation|CP (charge–parity) symmetry violation]], which can be obtained from the Standard Model,<ref name=CP>
{{cite book
 |author=National Research Council (US)
 |date=2006
 |title=Revealing the hidden nature of space and time
 |url=https://books.google.com/books?id=oTedc3rTDr4C&pg=PA46
 |page=46
 |publisher=National Academies Press
 |isbn=978-0-309-10194-3
}}</ref> but at this time the apparent [[Asymmetry|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 [[Physics:Baryogenesis|baryogenesis]].

Formally, antimatter particles can be defined by their negative [[Physics:Baryon number|baryon number]] or [[Physics:Lepton number|lepton number]], while "normal" (non-antimatter) matter particles have positive baryon or lepton number.<ref>{{cite journal
 |quote="''(From Abstract:)'' Antimatter particles are characterized by negative baryonic number A or/and negative leptonic number L. Materialization and annihilation obey conservation of A and L (associated to all known interactions)"
 |journal=International Journal of Modern Physics E
 |volume=21
 |pages=1250005–1–1250005–23
 |number=1
 |title=Negative Numbers And Antimatter Particles
 |last=Tsan
 |first=U.C.
 |date=2012
 |doi=10.1142/S021830131250005X
 |bibcode=2012IJMPE..2150005T
 }}</ref> These two classes of particles are the antiparticle partners of one another.

In October 2017, scientists reported further evidence that matter and [[Physics:Antimatter|antimatter]], equally produced at the [[Astronomy:Big Bang|Big Bang]], are identical, should completely annihilate each other and, as a result, the [[Astronomy:Universe|universe]] should not exist.<ref name="NAT-20171020">{{cite journal |author=Smorra C. |display-authors=0 |title=A parts-per-billion measurement of the antiproton magnetic moment |date=20 October 2017 |journal=Nature|volume=550 |issue=7676 |pages=371–374 |doi=10.1038/nature24048 |pmid=29052625 |bibcode=2017Natur.550..371S |doi-access=free }}</ref> This implies that there must be something, as yet unknown to scientists, that either stopped the complete mutual destruction of matter and antimatter in the early forming universe, or that gave rise to an imbalance between the two forms.

== Conservation ==
Two quantities that can define an amount of matter in the quark–lepton sense (and antimatter in an antiquark–antilepton sense), [[Physics:Baryon number|baryon number]] and [[Physics:Lepton number|lepton number]], are [[Conservation law|conserved]] in the Standard Model. A [[Physics:Baryon|baryon]] such as the proton or neutron has a baryon number of one, and a quark, because there are three in a baryon, is given a baryon number of 1/3.  So the net amount of matter, as measured by the number of quarks (minus the number of antiquarks, which each have a baryon number of −1/3), which is proportional to baryon number, and number of leptons (minus antileptons), which is called the lepton number, is practically impossible to change in any process.   Even in a nuclear bomb, none of the baryons (protons and neutrons of which the atomic nuclei are composed) are destroyed—there are as many baryons after as before the reaction, so none of these matter particles are actually destroyed and none are even converted to non-matter particles (like photons of light or radiation).  Instead, [[Physics:Nuclear binding energy|nuclear]] (and perhaps [[Physics:Quantum chromodynamics binding energy|chromodynamic) binding energy]] is released, as these baryons become bound into mid-size nuclei having less energy (and, [[Mass–energy equivalence|equivalently]], less mass) per nucleon compared to the original small (hydrogen) and large (plutonium etc.) nuclei.  Even in [[Physics:Electron–positron annihilation|electron–positron annihilation]], there is no net matter being destroyed, because there was zero net matter (zero total lepton number and baryon number) to begin with before the annihilation—one lepton minus one antilepton equals zero net lepton number—and this net amount matter does not change as it simply remains zero after the annihilation.<ref>{{cite journal
 |quote="''(From Abstract:)'' Matter conservation melans conservation of baryonic number A and leptonic number L, A and L being algebraic numbers. Positive A and L are associated to matter particles, negative A and L are associated to antimatter particles. All known interactions do conserve matter"
 |journal=International Journal of Modern Physics E
 |volume=22
 |number=5
 |title=Mass, Matter Materialization, Mattergenesis and Conservation of Charge
 |last=Tsan
 |first=Ung Chan
 |date=2013
 |page=1350027
 |doi=10.1142/S0218301313500274
 |bibcode=2013IJMPE..2250027T
 }}</ref>

In short, matter, as defined in physics, refers to baryons and leptons. The amount of matter is defined in terms of baryon and lepton number. Baryons and leptons can be created, but their creation is accompanied by antibaryons or antileptons; and they can be destroyed, by annihilating them with antibaryons or antileptons. Since antibaryons/antileptons have negative baryon/lepton numbers, the overall baryon/lepton numbers are not changed, so matter is conserved. However, baryons/leptons and antibaryons/antileptons all have positive mass, so the total amount of mass is not conserved.
Further, outside of natural or artificial nuclear reactions, there is almost no antimatter generally available in the universe (see [[Astronomy:Baryon asymmetry|baryon asymmetry]] and [[Physics:Leptogenesis|leptogenesis]]), so particle annihilation is rare in normal circumstances.

== Dark ==
{{Pie chart
| caption = Pie chart showing the fractions of energy in the universe contributed by different sources. ''Ordinary matter'' is divided into ''luminous matter'' (the stars and luminous gases and 0.005% radiation) and ''nonluminous matter'' (intergalactic gas and about 0.1% neutrinos and 0.04% supermassive black holes). Ordinary matter is uncommon. Modeled after Ostriker and Steinhardt.<ref name="Ostriker">{{cite journal |author=J.P. Ostriker |author2=P.J. Steinhardt |date=2003 |title=New Light on Dark Matter |doi=10.1126/science.1085976 |journal=Science |volume=300 |issue=5627 |pages=1909–13 |pmid=12817140 |arxiv=astro-ph/0306402 |bibcode = 2003Sci...300.1909O|s2cid=11188699 }}</ref> For more information, see [http://map.gsfc.nasa.gov/news/index.html NASA].
| value1 = 73
| label1 = Dark energy
| color1 = #1f78b4;
| value2 = 23
| label2 = Dark matter
| color2 = #a6cee3;
| value3 = 3.6
| label3 = Non-luminous matter
| color3 = #cab2d6;
| value4 = 0.4
| label4 = Luminous matter
| color4 = #6a3d9a;
}}
Ordinary matter, in the quarks and leptons definition, constitutes about 4% of the [[Mass–energy equivalence|energy]] of the [[Astronomy:Observable universe|observable universe]]. The remaining energy is theorized to be due to exotic forms, of which 23% is [[Astronomy:Dark matter|dark matter]]<ref name=Pretzl>
{{cite book
 |author=K. Pretzl
 |date=2004
 |chapter=Dark Matter, Massive Neutrinos and Susy Particles
 |chapter-url=https://books.google.com/books?id=lokz2n-9gX0C&pg=PA289
 |title=Structure and Dynamics of Elementary Matter
 |page=289
 |publisher=Walter Greiner
 |isbn=978-1-4020-2446-7
}}</ref><ref name=Freeman>
{{cite book
 |author=K. Freeman |author2=G. McNamara
 |date=2006
 |chapter=What can the matter be?
 |chapter-url=https://books.google.com/books?id=C2OS1kmQ8JIC&pg=PA45
 |title=In Search of Dark Matter
 |page=105
 |publisher=Birkhäuser Verlag
 |isbn=978-0-387-27616-8
}}</ref> and 73% is [[Astronomy:Dark energy|dark energy]].<ref name=Wheeler0>
{{cite book
 |author=J.C. Wheeler
 |date=2007
 |title=Cosmic Catastrophes: Exploding Stars, Black Holes, and Mapping the Universe
 |url=https://books.google.com/books?id=j1ej8d0F8jAC&pg=PA282
 |page=282
 |publisher=Cambridge University Press
 |isbn=978-0-521-85714-7
}}</ref><ref name=Gribbin>
{{cite book
 |author=J. Gribbin
 |date=2007
 |title=The Origins of the Future: Ten Questions for the Next Ten Years
 |url=https://books.google.com/books?id=f6AYrZYGig8C&pg=PA151
 |page=151
 |publisher=Yale University Press
 |isbn=978-0-300-12596-2
}}</ref>

[[File:Rotation curve (Milky Way).svg|thumb|upright=1.25|[[Astronomy:Galaxy rotation curve|Galaxy rotation curve]] for the Milky Way. Vertical axis is speed of rotation about the galactic center. Horizontal axis is distance from the galactic center. The sun is marked with a yellow ball. The observed curve of speed of rotation is blue. The predicted curve based upon stellar mass and gas in the Milky Way is red. The difference is due to [[Astronomy:Dark matter|dark matter]] or perhaps a modification of the law of gravity.<ref name="Schneider">{{cite book
 |author=P. Schneider
 |date=2006
 |title=Extragalactic Astronomy and Cosmology
 |url=https://books.google.com/books?id=uP1Hz-6sHaMC&pg=PA100
 |page=4, Fig. 1.4
 |publisher=Springer
 |isbn=978-3-540-33174-2
}}</ref><ref name="Koupelis">{{cite book
 |author=T. Koupelis
 |author2=K.F. Kuhn
 |date=2007
 |title=In Quest of the Universe
 |url=https://archive.org/details/inquestofunivers00koup/page/492
 |url-access=registration
 |page=[https://archive.org/details/inquestofunivers00koup/page/492 492; Fig. 16.13]
 |publisher=Jones & Bartlett Publishers
 |isbn=978-0-7637-4387-1
 }}</ref><ref name="Jones">{{cite book
 |author=M.H. Jones |author2=R.J. Lambourne |author3=D.J. Adams
 |date=2004
 |title=An Introduction to Galaxies and Cosmology
 |url=https://books.google.com/books?id=36K1PfetZegC&pg=PA20
 |page=21; Fig. 1.13
 |publisher=Cambridge University Press
 |isbn=978-0-521-54623-2
}}</ref> Scatter in observations is indicated roughly by gray bars.]]


In [[Physics:Astrophysics|astrophysics]] and [[Astronomy:Cosmology|cosmology]], ''dark matter'' is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter.<ref name=Majumdar>
{{cite book
 |author=D. Majumdar
 |date=2007
 |title=Dark matter – possible candidates and direct detection
 |url=https://archive.org/details/arxiv-hep-ph0703310
 |arxiv=hep-ph/0703310
|bibcode=2008pahh.book..319M
 }}</ref><ref name=Olive>
{{cite arXiv
 |author=K.A. Olive
 |date=2003
 |title=Theoretical Advanced Study Institute lectures on dark matter
 |eprint=astro-ph/0301505
}}</ref> Observational evidence of the early universe and the [[Astronomy:Big Bang|Big Bang]] theory require that this matter have energy and mass, but not be composed of ordinary baryons (protons and neutrons). The commonly accepted view is that most of the dark matter is non-baryonic in nature.<ref name=Majumdar/> As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they are [[Physics:Supersymmetry|supersymmetric particles]],<ref name=Olive2>
{{cite journal
 |author=K.A. Olive
 |date=2009
 |title=Colliders and Cosmology
 |journal=[[Physics:European Physical Journal C|European Physical Journal C]]
 |volume=59 |issue=2 |pages=269–295
 |doi=10.1140/epjc/s10052-008-0738-8
 |arxiv=0806.1208
 |bibcode = 2009EPJC...59..269O
|s2cid=15421431
 }}</ref> which are not [[Physics:Standard Model|Standard Model]] particles but relics formed at very high energies in the early phase of the universe and still floating about.<ref name=Majumdar/>

=== Energy ===
{{main|Astronomy:Dark energy}}
In [[Astronomy:Cosmology|cosmology]], ''dark energy'' is the name given to the source of the repelling influence that is accelerating the rate of [[Astronomy:Expansion of the universe|expansion of the universe]]. Its precise nature is currently a mystery, although its effects can reasonably be modeled by assigning matter-like properties such as energy density and pressure to the [[Physics:Vacuum|vacuum]] itself.<ref name=Wheeler1>
{{cite book
 |author=J.C. Wheeler
 |date=2007
 |title=Cosmic Catastrophes
 |url=https://books.google.com/books?id=j1ej8d0F8jAC&pg=PA282
 |page=282
 |publisher=Cambridge University Press
 |isbn=978-0-521-85714-7
}}</ref><ref name=Smolin2>
{{cite book
 |author=L. Smolin
 |date=2007
 |title=The Trouble with Physics
 |url=https://books.google.com/books?id=z5rxrnlcp3sC&pg=PA16
 |page=16
 |publisher=Mariner Books
 |isbn=978-0-618-91868-3
}}</ref>
{{Quotation|Fully 70% of the matter density in the universe appears to be in the form of dark energy. Twenty-six percent is dark matter. Only 4% is ordinary matter. So less than 1 part in 20 is made out of matter we have observed experimentally or described in the standard model of particle physics. Of the other 96%, apart from the properties just mentioned, we know absolutely nothing.|[[Biography:Lee Smolin|Lee Smolin]] (2007), ''The Trouble with Physics'', p. 16}}

== Exotic ==
{{main|Physics:Exotic matter}}

Exotic matter is a concept of [[Physics:Particle physics|particle physics]], which may include dark matter and dark energy but goes further to include any hypothetical material that violates one or more of the properties of known forms of matter. Some such materials might possess hypothetical properties like [[Physics:Negative mass|negative mass]].

==Historical and philosophical study==

===Classical antiquity (c. 600 BCE–c. 322 BCE)===
{{Main|Philosophy:Atomism}}
{{Further|Philosophy:Ancient Greek philosophy|Philosophy:Indian philosophy}}

In ancient India, the [[Philosophy:Buddhist philosophy|Buddhist]], [[Philosophy:Hindu philosophy|Hindu]], and [[Philosophy:Jain philosophy|Jain]] philosophical traditions each posited that [[Philosophy:Atomism|matter was made of atoms]] (''paramanu'', ''pudgala'') that were "eternal, indestructible, without parts, and innumerable" and which associated or dissociated to form more complex matter according to the [[Scientific law|laws of nature]].<ref name="Pullman2001p77"/> They coupled their ideas of soul, or lack thereof, into their theory of matter. The strongest developers and defenders of this theory were the [[Philosophy:Nyaya|Nyaya]]-[[Philosophy:Vaisheshika|Vaisheshika]] school, with the ideas of the Indian philosopher [[Biography:Kanada (philosopher)|Kanada]] being the most followed.<ref name="Pullman2001p77"/><ref name="Fowler2002"/> Buddhist philosophers also developed these ideas in late 1st-millennium CE, ideas that were similar to the Vaisheshika school, but one that did not include any soul or conscience.<ref name="Pullman2001p77"/> Jain philosophers included the [[Philosophy:Jiva|soul]] (''jiva''), adding qualities such as taste, smell, touch, and color to each atom.<ref>{{cite book|last=von Glasenapp|first=Helmuth|title=Jainism: An Indian Religion of Salvation|url= https://books.google.com/books?id=WzEzXDk0v6sC&pg=PA181|year=1999 |publisher=Motilal Banarsidass Publ.|isbn=978-81-208-1376-2|page=181}}</ref> They extended the ideas found in early literature of the Hindus and Buddhists by adding that atoms are either humid or dry, and this quality cements matter. They also proposed the possibility that atoms combine because of the attraction of opposites, and the soul attaches to these atoms, transforms with ''[[Philosophy:Karma|karma]]'' residue, and [[Philosophy:Reincarnation|transmigrates with each rebirth]].<ref name="Pullman2001p77"/>

In {{wipe|Ancient Greece}}, pre-Socratic philosophers speculated the underlying nature of the visible world. Thales (c. 624 BCE–c. 546 BCE) regarded water as the fundamental material of the world. [[Biography:Anaximander|Anaximander]] (c. 610 BCE–c. 546 BCE) posited that the basic material was wholly characterless or limitless: the Infinite (''apeiron''). [[Biography:Anaximenes of Miletus|Anaximenes]] (flourished 585 BCE, d. 528 BCE) posited that the basic stuff was ''pneuma'' or air. [[Biography:Heraclitus|Heraclitus]] (c. 535–c. 475 BCE) seems to say the basic element is fire, though perhaps he means that all is change. [[Biography:Empedocles|Empedocles]] (c. 490–430 BCE) spoke of four [[Philosophy:Classical element|elements]] of which everything was made: earth, water, air, and fire.<ref>
{{cite book
 |author=S. Toulmin |author2=J. Goodfield
 |date=1962
 |title=The Architecture of Matter
 |publisher=University of Chicago Press
 |pages=48–54
 }}</ref> Meanwhile, [[Biography:Parmenides|Parmenides]] argued that change does not exist, and [[Biography:Democritus|Democritus]] argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy called [[Philosophy:Atomism|atomism]]. All of these notions had deep philosophical problems.<ref>Discussed by Aristotle in ''[[Philosophy:Physics (Aristotle)|Physics]]'', esp. book I, but also later; as well as ''Metaphysics'' I–II.</ref>

[[Biography:Aristotle|Aristotle]] (384–322 BCE) was the first to put the conception on a sound philosophical basis, which he did in his natural philosophy, especially in [[Philosophy:Physics (Aristotle)|''Physics'']] book I.<ref>For a good explanation and elaboration, see {{cite book
 |author=R.J. Connell
 |date=1966
 |title=Matter and Becoming
 |url=https://archive.org/details/matterbecoming0000conn
 |url-access=registration
 |publisher=Priory Press
 }}</ref> He adopted as reasonable suppositions the four [[Philosophy:Classical element|Empedoclean elements]], but added a fifth, [[Philosophy:Aether (classical element)|aether]]. Nevertheless, these elements are not basic in Aristotle's mind. Rather they, like everything else in the visible world, are composed of the basic ''principles'' matter and form.

{{quotation|For my definition of matter is just this—the primary substratum of each thing, from which it comes to be without qualification, and which persists in the result.|Aristotle|Physics I:9:192a32}}

The word Aristotle uses for matter, [[Philosophy:Hyle|ὕλη (''hyle'' or ''hule'')]], can be literally translated as wood or timber, that is, "raw material" for building.<ref>
{{cite book
 |author=H.G. Liddell |author2=R. Scott |author3=J.M. Whiton
 |date=1891
 |title=A lexicon abridged from Liddell & Scott's Greek–English lexicon
 |url=https://archive.org/details/alexiconabridge00whitgoog
 |page=[https://archive.org/details/alexiconabridge00whitgoog/page/n78 72]
 |publisher=Harper and Brothers
|isbn=978-0-19-910207-5 }}</ref> Indeed, Aristotle's conception of matter is intrinsically linked to something being made or composed. In other words, in contrast to the early modern conception of matter as simply occupying space, matter for Aristotle is definitionally linked to process or change: matter is what underlies a change of substance. For example, a horse eats grass: the horse changes the grass into itself; the grass as such does not persist in the horse, but some aspect of it—its matter—does. The matter is not specifically described (e.g., as [[Physics:Atom|atom]]s), but consists of whatever persists in the change of substance from grass to horse. Matter in this understanding does not exist independently (i.e., as a [[Philosophy:Substance theory|substance]]), but exists interdependently (i.e., as a "principle") with form and only insofar as it underlies change. It can be helpful to conceive of the relationship of matter and form as very similar to that between parts and whole. For Aristotle, matter as such can only ''receive'' actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existence ''in'' a whole (otherwise they would be independent wholes).

===Age of Enlightenment===

French philosopher [[Biography:René Descartes|René Descartes]] (1596–1650) originated the modern conception of matter. He was primarily a geometer. Instead of, like Aristotle, deducing the existence of matter from the physical reality of change, Descartes arbitrarily postulated matter to be an abstract, mathematical substance that occupies space:
{{quotation|So, extension in length, breadth, and depth, constitutes the nature of bodily substance; and thought constitutes the nature of thinking substance. And everything else attributable to body presupposes extension, and is only a mode of an extended thing.|René Descartes|Principles of Philosophy<ref>
{{cite book
 |author=R. Descartes
 |chapter=The Principles of Human Knowledge
 |date=1644
 |title=Principles of Philosophy I
 |page=53
 }}</ref>}}

For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies:<ref>though even this property seems to be non-essential (René Descartes, ''Principles of Philosophy'' II [1644], "On the Principles of Material Things", no. 4.)</ref> this is the [[Philosophy:Mechanism|mechanical philosophy]]. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance.<ref>
{{cite book
 |author=R. Descartes
 |chapter=The Principles of Human Knowledge
 |date=1644
 |title=Principles of Philosophy I
 |pages=8, 54, 63
 }}</ref> They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementary ''principles'' that together compose one independent thing ([[Philosophy:Substance theory|substance]]). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with a ''potential'' independent existence), but Descartes elevates matter to an actual independent thing in itself.

The continuity and difference between Descartes's and Aristotle's conceptions is noteworthy. In both conceptions, matter is passive or inert. In the respective conceptions matter has different relationships to intelligence. For Aristotle, matter and intelligence (form) exist together in an interdependent relationship, whereas for Descartes, matter and intelligence (mind) are definitionally opposed, independent [[Philosophy:Substance theory|substances]].<ref>
{{cite book
 |author=D.L. Schindler
 |chapter=The Problem of Mechanism
 |editor=D.L. Schindler
 |date=1986
 |title=Beyond Mechanism
 |publisher=University Press of America
 }}</ref>

Descartes's justification for restricting the inherent qualities of matter to extension is its permanence, but his real criterion is not permanence (which equally applied to color and resistance), but his desire to use geometry to explain all material properties.<ref>E.A. Burtt, ''Metaphysical Foundations of Modern Science'' (Garden City, New York: Doubleday and Company, 1954), 117–118.</ref> Like Descartes, Hobbes, Boyle, and Locke argued that the inherent properties of bodies were limited to extension, and that so-called secondary qualities, like color, were only products of human perception.<ref>J.E. McGuire and P.M. Heimann, "The Rejection of Newton's Concept of Matter in the Eighteenth Century", ''The Concept of Matter in Modern Philosophy'' ed. Ernan McMullin (Notre Dame: University of Notre Dame Press, 1978), 104–118 (105).</ref>

English philosopher [[Biography:Isaac Newton|Isaac Newton]] (1643–1727) inherited Descartes's mechanical conception of matter. In the third of his "Rules of Reasoning in Philosophy", Newton lists the universal qualities of matter as "extension, hardness, impenetrability, mobility, and inertia".<ref>Isaac Newton, ''Mathematical Principles of Natural Philosophy'', trans. A. Motte, revised by F. Cajori (Berkeley: University of California Press, 1934), pp. 398–400. Further analyzed by Maurice A. Finocchiaro, "Newton's Third Rule of Philosophizing: A Role for Logic in Historiography", ''Isis'' 65:1 (Mar. 1974), pp. 66–73.</ref> Similarly in ''Optics'' he conjectures that God created matter as "solid, massy, hard, impenetrable, movable particles", which were "...even so very hard as never to wear or break in pieces".<ref>Isaac Newton, ''Optics'', Book III, pt. 1, query 31.</ref> The "primary" properties of matter were amenable to mathematical description, unlike "secondary" qualities such as color or taste. Like Descartes, Newton rejected the essential nature of secondary qualities.<ref>McGuire and Heimann, 104.</ref>

Newton developed Descartes's notion of matter by restoring to matter intrinsic properties in addition to extension (at least on a limited basis), such as mass. Newton's use of gravitational force, which worked "at a distance", effectively repudiated Descartes's mechanics, in which interactions happened exclusively by contact.<ref name=Chomsky>
{{cite book
 |author=N. Chomsky
 |date=1988
 |title=Language and problems of knowledge: the Managua lectures
 |url=https://books.google.com/books?id=hwgHVRZtK8kC&pg=PA144
 |page=144 |edition=2nd
 |publisher=MIT Press
 |isbn=978-0-262-53070-5
}}</ref>

Though Newton's gravity would seem to be a ''power'' of bodies, Newton himself did not admit it to be an ''essential'' property of matter. Carrying the logic forward more consistently, [[Biography:Joseph Priestley|Joseph Priestley]] (1733–1804) argued that corporeal properties transcend contact mechanics: chemical properties require the ''capacity'' for attraction.<ref name=Chomsky/> He argued matter has other inherent powers besides the so-called primary qualities of Descartes, et al.<ref>McGuire and Heimann, 113.</ref>

===19th and 20th centuries===
Since Priestley's time, there has been a massive expansion in knowledge of the constituents of the material world (viz., molecules, atoms, subatomic particles). In the 19th century, following the development of the [[Chemistry:Periodic table|periodic table]], and of [[Physics:Atomic theory|atomic theory]], [[Physics:Atom|atom]]s were seen as being the fundamental constituents of matter; atoms formed molecules and compounds.<ref name=Wenham>
{{cite book
 |author=M. Wenham
 |date=2005
 |title=Understanding Primary Science: Ideas, Concepts and Explanations
 |url=https://archive.org/details/understandingpri0000wenh
 |url-access=registration
 |page=[https://archive.org/details/understandingpri0000wenh/page/115 115] |edition=2nd
 |publisher=Paul Chapman Educational Publishing
 |isbn=978-1-4129-0163-5
}}</ref>{{anchor|note}}

The common definition in terms of occupying space and having mass is in contrast with most physical and chemical definitions of matter, which rely instead upon its structure and upon attributes not necessarily related to volume and mass. At the turn of the nineteenth century, the knowledge of matter began a rapid evolution.

Aspects of the Newtonian view still held sway. [[Biography:James Clerk Maxwell|James Clerk Maxwell]] discussed matter in his work ''Matter and Motion''.<ref name=Maxwell>
{{cite book
 |author=J.C. Maxwell
 |date=1876
 |title=Matter and Motion
 |url=https://archive.org/details/bub_gb_MWoOAAAAIAAJ
 |page=[https://archive.org/details/bub_gb_MWoOAAAAIAAJ/page/n16 18]
 |publisher=Society for Promoting Christian Knowledge
 |isbn=978-0-486-66895-6
}}</ref> He carefully separates "matter" from space and time, and defines it in terms of the object referred to in Newton's first law of motion.

However, the Newtonian picture was not the whole story. In the 19th century, the term "matter" was actively discussed by a host of scientists and philosophers, and a brief outline can be found in Levere.<ref name=Levere>
{{cite book
 |author=T.H. Levere
 |date=1993
 |title=Affinity and Matter: Elements of Chemical Philosophy, 1800–1865
 |chapter=Introduction
 |chapter-url=https://books.google.com/books?id=gKSDWsE8fZMC
 |publisher=Taylor & Francis
 |isbn=978-2-88124-583-1
}}</ref>{{Elucidate|date=March 2011}} A textbook discussion from 1870 suggests matter is what is made up of atoms:<ref name=Barker>
{{cite book
 |author=G.F. Barker
 |date=1870
 |title=A Text Book of Elementary Chemistry: Theoretical and Inorganic
 |chapter=Introduction
 |chapter-url=https://books.google.com/books?id=B6Yz6eW-5joC
 |page=2
 |publisher=John P. Morton and Company
}}</ref><blockquote>Three divisions of matter are recognized in science: masses, molecules and atoms. <br />A Mass of matter is any portion of matter appreciable by the senses. <br />A Molecule is the smallest particle of matter into which a body can be divided without losing its identity. <br />An Atom is a still smaller particle produced by division of a molecule. </blockquote>

Rather than simply having the attributes of mass and occupying space, matter was held to have chemical and electrical properties. In 1909 the famous physicist [[Biography:J. J. Thomson|J. J. Thomson]] (1856–1940) wrote about the "constitution of matter" and was concerned with the possible connection between matter and electrical charge.<ref name=Thomson>
{{cite book
 |author=J.J. Thomson
 |date=1909
 |title=Electricity and Matter
 |chapter=Preface
 |chapter-url=https://books.google.com/books?id=2AaToepvKoEC
 |publisher=A. Constable
}}</ref>

In the late 19th century with the discovery of the [[Physics:Electron|electron]], and in the early 20th century, with the [[Physics:Geiger–Marsden experiment|Geiger–Marsden experiment]] discovery of the [[Physics:Atomic nucleus|atomic nucleus]], and the birth of [[Physics:Particle physics|particle physics]], matter was seen as made up of electrons, [[Physics:Proton|proton]]s and [[Physics:Neutron|neutron]]s interacting to form atoms. There then developed an entire literature concerning the "structure of matter", ranging from the "electrical structure" in the early 20th century,<ref name=Richardson>
{{cite book
 |author=O.W. Richardson
 |date=1914
 |title=The Electron Theory of Matter
 |chapter=Chapter 1
 |chapter-url=https://books.google.com/books?id=RpdDAAAAIAAJ
 |publisher=The University Press
}}</ref> to the more recent "quark structure of matter", introduced as early as 1992 by Jacob with the remark: "Understanding the quark structure of matter has been one of the most important advances in contemporary physics."<ref name=Jacob>
{{cite book
 |author=M. Jacob
 |date=1992
 |title=The Quark Structure of Matter
 |url=https://books.google.com/books?id=iQ1e2a9bPikC
 |publisher=World Scientific
 |isbn=978-981-02-3687-8
}}</ref>{{Elucidate|date=March 2011}} In this connection, physicists speak of ''matter fields'', and speak of particles as "quantum excitations of a mode of the matter field".<ref name="Davies"/><ref name="Weinberg"/> And here is a quote from de Sabbata and Gasperini: "With the word "matter" we denote, in this context, the sources of the interactions, that is [[Physics:Spinor field|spinor field]]s (like [[Physics:Quark|quark]]s and [[Physics:Lepton|lepton]]s), which are believed to be the fundamental components of matter, or [[Physics:Bosonic field|scalar fields]], like the Higgs particles, which are used to introduced mass in a [[Physics:Gauge theory|gauge theory]] (and that, however, could be composed of more fundamental [[Physics:Fermion|fermion]] [[Physics:Fermionic field|fields]])."<ref name=Sabbata>
{{cite book
 |author=V. de Sabbata |author2=M. Gasperini
 |date=1985
 |title=Introduction to Gravitation
 |url=https://books.google.com/books?id=7sJ6m8s0_ccC&pg=PA293
 |page=293
 |publisher=World Scientific
 |isbn=978-9971-5-0049-8
}}</ref>{{Elucidate|date=March 2011}}

Protons and neutrons however are not indivisible: they can be divided into [[Physics:Quark|quark]]s. And electrons are part of a particle family called [[Physics:Lepton|lepton]]s. Both quarks and leptons are [[Physics:Elementary particle|elementary particle]]s, and were in 2004 seen by authors of an undergraduate text as being the fundamental constituents of matter.<ref name=Povh1>The history of the concept of matter is a history of the fundamental ''length scales'' used to define matter. Different building blocks apply depending upon whether one defines matter on an atomic or elementary particle level. One may use a definition that matter is atoms, or that matter is [[Physics:Hadron|hadron]]s, or that matter is leptons and quarks depending upon the scale at which one wishes to define matter.
{{cite book
 |author=B. Povh |author2=K. Rith |author3=C. Scholz |author4=F. Zetsche |author5=M. Lavelle
 |date=2004
 |title=Particles and Nuclei: An Introduction to the Physical Concepts
 |chapter=Fundamental constituents of matter
 |chapter-url=https://books.google.com/books?id=rJe4k8tkq7sC&pg=PA9
 |edition=4th
 |publisher=Springer
 |isbn=978-3-540-20168-7
}}</ref>

These quarks and leptons interact through four [[Physics:Fundamental forces|fundamental forces]]: [[Physics:Gravity|gravity]], [[Physics:Electromagnetism|electromagnetism]], [[Physics:Weak interaction|weak interaction]]s, and [[Physics:Strong interaction|strong interaction]]s. The [[Physics:Standard Model|Standard Model]] of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by [[Physics:Classical physics|classical physics]] (see [[Physics:Quantum gravity|quantum gravity]] and [[Physics:Graviton|graviton]])<ref name=Allday2>
{{cite book
 |author=J. Allday
 |date=2001
 |title=Quarks, Leptons and the Big Bang
 |url=https://books.google.com/books?id=kgsBbv3-9xwC&pg=PA12
 |page=12
 |publisher=CRC Press
 |isbn=978-0-7503-0806-9
}}</ref> to the frustration of theoreticians like [[Biography:Stephen Hawking|Stephen Hawking]]. Interactions between quarks and leptons are the result of an exchange of force-carrying particles such as [[Physics:Photon|photon]]s between quarks and leptons.<ref>{{cite book
 |author=B.A. Schumm
 |date=2004
 |title=Deep Down Things: The Breathtaking Beauty of Particle Physics
 |url=https://archive.org/details/deepdownthingsbr00schu
 |url-access=registration
 |page=[https://archive.org/details/deepdownthingsbr00schu/page/57 57]
 |publisher=Johns Hopkins University Press
 |isbn=978-0-8018-7971-5
}}</ref> The force-carrying particles are not themselves building blocks. As one consequence, mass and energy (which to our present knowledge cannot be created or destroyed) cannot always be related to matter (which can be created out of non-matter particles such as photons, or even out of pure energy, such as kinetic energy).{{citation needed|date=April 2021}} Force mediators are usually not considered matter: the mediators of the electric force (photons) possess energy (see [[Physics:Planck relation|Planck relation]]) and the mediators of the weak force ([[Physics:W and Z bosons|W and Z bosons]]) have mass, but neither are considered matter either.<ref name=PhotonsMatter>
See for example, {{cite book
 |author=M. Jibu |author2=K. Yasue
 |date=1995
 |title=Quantum Brain Dynamics and Consciousness
 |url=https://books.google.com/books?id=iNUvcniwvg0C&pg=PA62
 |page=62
 |publisher=John Benjamins Publishing Company
 |isbn=978-1-55619-183-1
}}, {{cite book
 |author=B. Martin
 |date=2009
 |title=Nuclear and Particle Physics
 |url=https://books.google.com/books?id=ws8QZ2M5OR8C&pg=PT143
 |page=125 |edition=2nd
 |publisher=John Wiley & Sons
 |isbn=978-0-470-74275-4
}} and {{cite book
 |author=K.W. Plaxco |author2=M. Gross
 |date=2006
 |title=Astrobiology: A Brief Introduction
 |url=https://archive.org/details/astrobiologybrie0000plax
 |url-access=registration |page=[https://archive.org/details/astrobiologybrie0000plax/page/23 23]
 |publisher=Johns Hopkins University Press
 |isbn=978-0-8018-8367-5
}}</ref> However, while these quanta are not considered matter, they do contribute to the total mass of atoms, [[Physics:Subatomic particle|subatomic particle]]s, and all systems that contain them.<ref name=Tipler0>
{{cite book
 |author=P.A. Tipler |author2=R.A. Llewellyn
 |date=2002
 |title=Modern Physics
 |url=https://books.google.com/books?id=tpU18JqcSNkC&pg=PA94
 |pages=89–91, 94–95
 |isbn=978-0-7167-4345-3
 |publisher=Macmillan
}}</ref><ref name=Spitzer>
{{cite book
 |author=P. Schmüser |author2=H. Spitzer
 |date=2002
 |chapter=Particles
 |editor=L. Bergmann
 |display-editors=etal
 |title=Constituents of Matter: Atoms, Molecules, Nuclei
 |chapter-url=https://books.google.com/books?id=mGj1y1WYflMC
 |isbn=978-0-8493-1202-1
 |pages=773&nbsp;''ff''
 |publisher=CRC Press
}}</ref>

==Summary==
The modern conception of matter has been refined many times in history, in light of the improvement in knowledge of just ''what'' the basic building blocks are, and in how they interact.
The term "matter" is used throughout physics in a wide variety of contexts: for example, one refers to "[[Physics:Condensed matter physics|condensed matter physics]]",<ref name=Chaikin>
{{cite book
 |author=P.M. Chaikin |author2=T.C. Lubensky
 |date=2000
 |title=Principles of Condensed Matter Physics
 |url=https://books.google.com/books?id=P9YjNjzr9OIC
 |page=xvii
 |publisher=Cambridge University Press
 |isbn=978-0-521-79450-3
}}</ref> "elementary matter",<ref name=Greiner>
{{cite book
 |author=W. Greiner
 |date=2003
 |editor1=W. Greiner |editor2=M.G. Itkis |editor3=G. Reinhardt |editor4=M.C. Güçlü |title=Structure and Dynamics of Elementary Matter
 |url=https://books.google.com/books?id=ORyJzhAzpUgC
 |publisher=Springer
 |page=xii
 |isbn=978-1-4020-2445-0
}}</ref> "[[Physics:Parton (particle physics)|partonic]]" matter, "[[Astronomy:Dark matter|dark]]" matter, "[[Physics:Antimatter|anti]]"-matter, "[[Physics:Strange matter|strange]]" matter, and "[[Physics:Nuclear matter|nuclear]]" matter. In discussions of matter and [[Physics:Antimatter|antimatter]], the former has been referred to by [[Biography:Hannes Alfvén|Alfvén]] as ''koinomatter'' (Gk. ''common matter'').<ref>
{{cite book
 |author=P. Sukys
 |date=1999
 |title=Lifting the Scientific Veil: Science Appreciation for the Nonscientist
 |url=https://archive.org/details/liftingscientifi0000suky
 |url-access=registration
 |page=[https://archive.org/details/liftingscientifi0000suky/page/87 87]
 |publisher=Rowman & Littlefield
 |isbn=978-0-8476-9600-0
}}</ref> It is fair to say that in [[Physics:Physics|physics]], there is no broad consensus as to a general definition of matter, and the term "matter" usually is used in conjunction with a specifying modifier.

The history of the concept of matter is a history of the fundamental ''length scales'' used to define matter. Different building blocks apply depending upon whether one defines matter on an atomic or elementary particle level. One may use a definition that matter is atoms, or that matter is [[Physics:Hadron|hadron]]s, or that matter is leptons and quarks depending upon the scale at which one wishes to define matter.<ref>
{{cite book
 |author=B. Povh |author2=K. Rith |author3=C. Scholz |author4=F. Zetsche |author5=M. Lavelle
 |date=2004
 |title=Particles and Nuclei: An Introduction to the Physical Concepts
 |chapter=Fundamental constituents of matter
 |chapter-url=https://books.google.com/books?id=rJe4k8tkq7sC&pg=PA9
 |edition=4th
 |publisher=Springer
 |isbn=978-3-540-20168-7
}}</ref>

These quarks and leptons interact through four [[Physics:Fundamental forces|fundamental forces]]: [[Physics:Gravity|gravity]], [[Physics:Electromagnetism|electromagnetism]], [[Physics:Weak interaction|weak interaction]]s, and [[Physics:Strong interaction|strong interaction]]s. The [[Physics:Standard Model|Standard Model]] of particle physics is currently the best explanation for all of physics, but despite decades of efforts, gravity cannot yet be accounted for at the quantum level; it is only described by [[Physics:Classical physics|classical physics]] (see [[Physics:Quantum gravity|quantum gravity]] and [[Physics:Graviton|graviton]]).<ref name="Allday2"/>

== See also ==
{{Col-begin}}
{{Col-3}}
'''Antimatter'''
* Ambiplasma
* [[Physics:Antihydrogen|Antihydrogen]]
* [[Physics:Antiparticle|Antiparticle]]
* [[Physics:Particle accelerator|Particle accelerator]]

'''Cosmology'''
* [[Astronomy:Cosmological constant|Cosmological constant]]
* [[Friedmann equations]]
* [[Physics:Motion|Motion]]
* Physical ontology

{{Col-3}}
'''Dark matter'''
* [[Physics:Axion|Axion]]
* [[Physics:Minimal Supersymmetric Standard Model|Minimal Supersymmetric Standard Model]]
* [[Physics:Neutralino|Neutralino]]
* Nonbaryonic dark matter
* [[Physics:Scalar field dark matter|Scalar field dark matter]]

'''Philosophy'''
* [[Philosophy:Atomism|Atomism]]
* [[Philosophy:Materialism|Materialism]]
* [[Physicalism]]
* [[Philosophy:Substance theory|Substance theory]]

{{Col-3}}
'''Other'''
* [[Mass–energy equivalence]]
* [[Social:Hybrid word#English examples|Mattergy]]
* [[Pattern formation]]
* Periodic Systems of Small Molecules

{{col-end}}

== References ==
{{reflist}}

== Further reading ==
* {{cite book |title=The Rise of the Standard Model |editor= Lillian Hoddeson |editor2=Michael Riordan |isbn=978-0-521-57816-5 |publisher=Cambridge University Press |date=1997 |url=https://books.google.com/books?id=klLUs2XUmOkC }}
* {{cite book |title=Hidden Worlds |chapter=The search for quarks in ordinary matter |author=Timothy Paul Smith |chapter-url=https://books.google.com/books?id=Pc1A0qJio88C&pg=PA1 |isbn=978-0-691-05773-6 |date=2004 |publisher=Princeton University Press}}
* {{cite book |title=Elementary Particles: Building blocks of matter |isbn=978-981-256-141-1 |date=2005 |publisher=World Scientific |author=Harald Fritzsch |url=https://archive.org/details/elementarypartic0000frit |url-access=registration |page=[https://archive.org/details/elementarypartic0000frit/page/1 1]|bibcode=2005epbb.book.....F }}
* {{cite book |title=A Critical Exposition of the Philosophy of Leibniz |author= Bertrand Russell |chapter-url=https://books.google.com/books?id=R7GauFXXedwC&pg=PA88 |page=88 |chapter=The philosophy of matter |isbn=978-0-415-08296-9 |date=1992 |edition=Reprint of 1937 2nd |publisher=Routledge}}
* Stephen Toulmin and June Goodfield, ''The Architecture of Matter'' (Chicago: University of Chicago Press, 1962).
* Richard J. Connell, ''Matter and Becoming'' (Chicago: The Priory Press, 1966).
* [[Biography:Ernan McMullin|Ernan McMullin]], ''The Concept of Matter in Greek and Medieval Philosophy'' (Notre Dame, Indiana: Univ. of Notre Dame Press, 1965).
* [[Biography:Ernan McMullin|Ernan McMullin]], ''The Concept of Matter in Modern Philosophy'' (Notre Dame, Indiana: University of Notre Dame Press, 1978).

== External links ==
* [http://www.visionlearning.com/library/module_viewer.php?mid=49&l=&c3= Visionlearning Module on Matter]
* [https://web.archive.org/web/20090227150154/http://www.newuniverse.co.uk/Matter.html Matter in the universe] How much Matter is in the Universe?
* [http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970213.html NASA on superfluid core of neutron star]
* [http://profmattstrassler.com/articles-and-posts/particle-physics-basics/mass-energy-matter-etc/matter-and-energy-a-false-dichotomy/ Matter and Energy: A False Dichotomy] – Conversations About Science with Theoretical Physicist Matt Strassler

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[[Category:Matter| ]]

{{Sourceattribution|Matter}}