Usually atoms can be imagined as anucleus ofprotons andneutrons, and a surrounding "cloud" of orbitingelectrons which "take up space".[4][5] However, this is only somewhat correct because subatomic particles and their properties are governed by theirquantum nature, which means they do not act as everyday objects appear to act – they can act likewaves as well as particles, and they do not have well-defined sizes or positions. In theStandard Model ofparticle physics, matter is not a fundamental concept because theelementary constituents of atoms arequantum entities which do not have an inherent "size" or "volume" in any everyday sense of the word. Due to theexclusion principle and otherfundamental interactions, some "point particles" known asfermions (quarks,leptons), 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.
Matter is a general term describing any physical substance, which is sometimes defined in incompatible ways in different fields of science. Some definitions are based on historical usage from a time when there was no reason to distinguish mass from simply aquantity of matter. By contrast,mass is not a substance but a well-defined,extensive property of matter and other substances or systems. Various types of mass are defined withinphysics – includingrest mass,inertial mass, andrelativistic mass.
In physics, matter is sometimes 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 and chemistry, matter exhibits bothwave-like andparticle-like properties (the so-calledwave–particle duality).[9][10][11]
Chemical substances can exist in several different physicalstates orphases (e.g.solids,liquids,gases, orplasma) without changing their chemical composition. Substancestransition between thesephases of matter in response to changes intemperature orpressure. Some chemical substances can be combined or converted into new substances by means ofchemical reactions. Chemicals that do not possess this ability are said to beinert.
Purewater is an example of a chemical substance, with a constant composition of two hydrogenatomsbonded to a single oxygen atom (i.e. H2O). Theatomic ratio of hydrogen to oxygen is always 2:1 in everymolecule of water. Pure water will tend toboil near 100 °C (212 °F), an example of one of the characteristic properties that define it. Other notable chemical substances includediamond (a form of the elementcarbon),table salt (NaCl; anionic compound), and refinedsugar (C12H22O11; anorganic compound).
Definition
Based on atoms
A definition of "matter" based on its physical and chemical structure is:matter is made up ofatoms.[16] Suchatomic matter is also sometimes termedordinary matter. As an example,deoxyribonucleic acidmolecules (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 includeplasmas (gases of ions) andelectrolytes (ionic solutions), which are not obviously included in the atoms definition. Alternatively, one can adopt theprotons, 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 whatatoms andmolecules are made of, meaning anything made of positively chargedprotons, neutralneutrons, and negatively chargedelectrons.[17] This definition goes beyond atoms and molecules, however, to include substances made from these building blocks that arenot simply atoms or molecules, for example electron beams in an oldcathode ray tube television, orwhite 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 ofquarks and the force fields (gluons) that bind them together, leading to the next definition.
Based on quarks and leptons
Under the "quarks and leptons" definition, the elementary and composite particles made of thequarks (in purple) andleptons (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 ofquarks andleptons", or "ordinary matter is everything that is composed of any elementary fermions except antiquarks and antileptons".[18][19][20] The connection between these formulations follows.
Leptons (the most famous being theelectron), and quarks (of whichbaryons, such asprotons andneutrons, are made) combine to formatoms, which in turn formmolecules. 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 isnot 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 offirst-generation particles, namely the [up] and [down] quarks, plus the electron and its neutrino."[19] (Higher generations particles quickly decay into first-generation particles, and thus are not commonly encountered.[21])
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 theforce carriers are elementary bosons.[22] TheW and Z bosons that mediate theweak force are not made of quarks or leptons, and so are not ordinary matter, even if they have mass.[23] In other words,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 (seedynamics of quantum chromodynamics) and these gluon fields contribute significantly to the mass of hadrons.[24] In other words, most of what composes the "mass" of ordinary matter is due to thebinding energy of quarks within protons and neutrons.[25] For example, the sum of the mass of the three quarks in anucleon is approximately12.5 MeV/c2, which is low compared to the mass of a nucleon (approximately938 MeV/c2).[26][27] 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 theup anddown quarks, theelectron and theelectron neutrino; the second includes thecharm andstrange quarks, themuon and themuon neutrino; the third generation consists of thetop andbottom quarks and thetau andtau neutrino.[28] The most natural explanation for this would be that quarks and leptons of higher generations areexcited states of the first generations. If this turns out to be the case, it would imply that quarks and leptons arecomposite particles, rather thanelementary particles.[29]
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 hasmass andvolume (occupiesspace)".[30][31] 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 thePauli exclusion principle,[32][33] which applies tofermions. 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 theantiproton) and antileptons (such as thepositron) are theantiparticles 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 theseantimatter particles as well as the ordinary quark and lepton, and thus also anything made ofmesons, which are unstable particles made up of a quark and an antiquark.
In general relativity and cosmology
In the context ofrelativity, mass is not an additive quantity, in the sense that one cannot add the rest masses of particles in a system to get the total rest mass of the system.[1]: 21 In relativity, usually a more general view is that it is not the sum ofrest masses, but theenergy–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.[34][35] This view is commonly held in fields that deal withgeneral relativity such ascosmology. In this view, light and other massless particles and fields are all part of matter.
Structure
In particle physics, fermions are particles that obeyFermi–Dirac statistics. Fermions can be elementary, like the electron—or composite, like the proton and neutron. In theStandard Model, there are two types of elementary fermions: quarks and leptons, which are discussed next.
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 aspentaquarks, 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 includedark energy,dark matter,black holes or various forms of degenerate matter, such as those that composewhite dwarf stars andneutron stars. Microwave light seen byWilkinson Microwave Anisotropy Probe (WMAP) suggests that only about 4.6% of that part of the universe within range of the besttelescopes (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.[37]
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.[38]
Hadronic
Hadronic matter can refer to 'ordinary' baryonic matter, made fromhadrons (baryons andmesons), orquark matter (a generalisation of atomic nuclei), i.e. the 'low' temperatureQCD matter.[39] It includesdegenerate matter and the result of high energy heavy nuclei collisions.[40]
In physics,degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero.[41] ThePauli 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 theFermi 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.[42] The demonstration bySubrahmanyan Chandrasekhar thatwhite dwarf stars have a maximum allowed mass because of the exclusion principle caused a revolution in the theory of star evolution.[43]
Degenerate matter includes the part of the universe that is made up of neutron stars and white dwarfs.
Strange matter is a particular form ofquark matter, usually thought of as aliquid ofup,down, andstrange quarks. It is contrasted withnuclear matter, which is a liquid ofneutrons andprotons (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 becolor superconducting. Strange matter is hypothesized to occur in the core ofneutron stars, or, more speculatively, as isolated droplets that may vary in size fromfemtometers (strangelets) to kilometers (quark stars).
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 ofprotons andneutrons) 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 ismore stable than nuclear matter. The idea that this could happen is the "strange matter hypothesis" of Bodmer[44] and Witten.[45] In this definition, the critical pressure is zero: the true ground state of matter isalways quark matter. The nuclei that we see in the matter around us, which are droplets of nuclear matter, are actuallymetastable, and given enough time (or the right external stimulus) would decay into droplets of strange matter, i.e.strangelets.
Leptons are particles ofspin-1⁄2, meaning that they arefermions. They carry anelectric charge of −1 e (charged leptons) or 0 e (neutrinos). Unlike quarks, leptons do not carrycolour charge, meaning that they do not experience thestrong interaction. Leptons also undergo radioactive decay, meaning that they are subject to theweak interaction. Leptons are massive particles, therefore are subject to gravity.
Phase diagram for a typical substance at a fixed volume
Inbulk, matter can exist in several different forms, or states of aggregation, known asphases,[48] depending on ambientpressure,temperature andvolume.[49] A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such asdensity,specific heat,refractive index, and so forth). These phases include the three familiar ones (solids,liquids, andgases), as well as more exotic states of matter (such asplasmas,superfluids,supersolids,Bose–Einstein condensates, ...). Afluid may be a liquid, gas or plasma. There are alsoparamagnetic andferromagnetic phases ofmagnetic materials. As conditions change, matter may change from one phase into another. These phenomena are calledphase transitions and are studied in the field ofthermodynamics. 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 (seenanomaterials for more details).
Phases are sometimes calledstates of matter, but this term can lead to confusion withthermodynamic states. For example, two gases maintained at different pressures are in differentthermodynamic states (different pressures), but in the samephase (both are gases).
Antimatter is matter that is composed of theantiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other, the twoannihilate; that is, they may both be converted into other particles with equalenergy in accordance withAlbert Einstein's equationE =mc2. These new particles may be high-energyphotons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between therest 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 ofradioactive decay,lightning orcosmic rays). 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 asantihydrogen) 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 inscience andscience 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 calledCP (charge–parity) symmetry violation, which can be obtained from the Standard Model,[50] but at this time the apparentasymmetry of matter and antimatter in the visible universe is one of the greatunsolved problems in physics. Possible processes by which it came about are explored in more detail underbaryogenesis.
Formally, antimatter particles can be defined by their negativebaryon number orlepton number, while "normal" (non-antimatter) matter particles have positive baryon or lepton number.[51] These two classes of particles are the antiparticle partners of one another.
In October 2017, scientists reported further evidence that matter andantimatter, equally produced at theBig Bang, are identical, should completely annihilate each other and, as a result, theuniverse should not exist.[52] 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),baryon number andlepton number, areconserved in the Standard Model. Abaryon 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,nuclear (and perhapschromodynamic) binding energy is released, as these baryons become bound into mid-size nuclei having less energy (and,equivalently, lessmass) per nucleon compared to the original small (hydrogen) and large (plutonium etc.) nuclei. Even inelectron–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.[53]
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 (seebaryon asymmetry andleptogenesis), so particle annihilation is rare in normal circumstances.
Dark
Pie chart showing the fractions of energy in the universe contributed by different sources.Ordinary matter is divided intoluminous matter (the stars and luminous gases and 0.005% radiation) andnonluminous matter (intergalactic gas and about 0.1% neutrinos and 0.04% supermassive black holes). Ordinary matter is uncommon. Modeled after Ostriker and Steinhardt.[54] For more information, seeNASA.
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 todark matter or perhaps a modification of thelaw of gravity.[59][60][61] Scatter in observations is indicated roughly by gray bars.
Inastrophysics andcosmology,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.[62][63] Observational evidence of the early universe and theBig 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 isnon-baryonic in nature.[62] As such, it is composed of particles as yet unobserved in the laboratory. Perhaps they aresupersymmetric particles,[64] which are notStandard Model particles but relics formed at very high energies in the early phase of the universe and still floating about.[62]
Incosmology,dark energy is the name given to the source of the repelling influence that is accelerating the rate ofexpansion 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 thevacuum itself.[65][66]
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 thestandard model of particle physics. Of the other 96%, apart from the properties just mentioned, we know absolutely nothing.
— Lee Smolin (2007),The Trouble with Physics, p. 16
Exotic matter is a concept ofparticle 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 likenegative mass.
Inancient India, theBuddhist,Hindu, andJain philosophical traditions each posited thatmatter 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 thelaws of nature.[6] They coupled their ideas of soul, or lack thereof, into their theory of matter. The strongest developers and defenders of this theory were theNyaya-Vaisheshika school, with the ideas of the Indian philosopherKanada being the most followed.[6][7] Buddhist philosophers also developed these ideas in late 1st-millennium CE, ideas that were similar to the Vaisheshika school, but ones that did not include any soul or conscience.[6] Jain philosophers included thesoul (jiva), adding qualities such as taste, smell, touch, and color to each atom.[67] 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 withkarma residue, andtransmigrates with each rebirth.[6]
Inancient 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.Anaximander (c. 610 BCE–c. 546 BCE) posited that the basic material was wholly characterless or limitless: the Infinite (apeiron).Anaximenes (flourished 585 BCE, d. 528 BCE) posited that the basic stuff waspneuma or air.Heraclitus (c. 535 BCE–c. 475 BCE) seems to say the basic element is fire, though perhaps he means that all is change.Empedocles (c. 490–430 BCE) spoke of fourelements of which everything was made: earth, water, air, and fire.[68] Meanwhile,Parmenides argued that change does not exist, andDemocritus argued that everything is composed of minuscule, inert bodies of all shapes called atoms, a philosophy calledatomism. All of these notions had deep philosophical problems.[69]
Aristotle (384 BCE–322 BCE) was the first to put the conception on a sound philosophical basis, which he did in his natural philosophy, especially inPhysics book I.[70] He adopted as reasonable suppositions the fourEmpedoclean 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 the basicprinciples matter and form.
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,ὕλη (hyle orhule), can be literally translated as wood or timber, that is, "raw material" for building.[71] 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., asatoms), 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 asubstance), 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 onlyreceive actuality from form; it has no activity or actuality in itself, similar to the way that parts as such only have their existencein a whole (otherwise they would be independent wholes).
French philosopherRené Descartes (1596–1650) originated the modern conception of matter. He was primarily a geometer. Unlike Aristotle, who deduced the existence of matter from the physical reality of change, Descartes arbitrarily postulated matter to be an abstract, mathematical substance that occupies space:
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.
For Descartes, matter has only the property of extension, so its only activity aside from locomotion is to exclude other bodies:[73] this is themechanical philosophy. Descartes makes an absolute distinction between mind, which he defines as unextended, thinking substance, and matter, which he defines as unthinking, extended substance.[74] They are independent things. In contrast, Aristotle defines matter and the formal/forming principle as complementaryprinciples that together compose one independent thing (substance). In short, Aristotle defines matter (roughly speaking) as what things are actually made of (with apotential 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, independentsubstances.[75]
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.[76] 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.[77]
English philosopherIsaac 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".[78] Similarly inOptics 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".[79] 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.[80]
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.[81]
Though Newton's gravity would seem to be apower of bodies, Newton himself did not admit it to be anessential property of matter. Carrying the logic forward more consistently,Joseph Priestley (1733–1804) argued that corporeal properties transcend contact mechanics: chemical properties require thecapacity for attraction.[81] He argued matter has other inherent powers besides the so-called primary qualities of Descartes, et al.[82]
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 theperiodic table, and ofatomic theory,atoms were seen as being the fundamental constituents of matter; atoms formedmolecules andcompounds.[83]
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.James Clerk Maxwell discussed matter in his workMatter and Motion.[84] He carefully separates "matter" from space and time, and defines it in terms of the object referred to inNewton'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.[85][further explanation needed] A textbook discussion from 1870 suggests matter is what is made up of atoms:[86]
Three divisions of matter are recognized in science: masses, molecules and atoms. A Mass of matter is any portion of matter appreciable by the senses. A Molecule is the smallest particle of matter into which a body can be divided without losing its identity. An Atom is a still smaller particle produced by division of a molecule.
Rather than simply having the attributes of mass and occupying space, matter was held to have chemical and electrical properties. In 1909 the famous physicistJ. J. Thomson (1856–1940) wrote about the "constitution of matter" and was concerned with the possible connection between matter and electrical charge.[87]
In the late 19th century with thediscovery of theelectron, and in the early 20th century, with theGeiger–Marsden experiment discovery of theatomic nucleus, and the birth ofparticle physics, matter was seen as made up of electrons,protons andneutrons 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,[88] 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."[89][further explanation needed] In this connection, physicists speak ofmatter fields, and speak of particles as "quantum excitations of a mode of the matter field".[9][10] 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 isspinor fields (likequarks andleptons), which are believed to be the fundamental components of matter, orscalar fields, like theHiggs particles, which are used to introduced mass in agauge theory (and that, however, could be composed of more fundamentalfermionfields)."[90][further explanation needed]
Protons and neutrons however are not indivisible: they can be divided intoquarks. And electrons are part of a particle family calledleptons. Bothquarks and leptons areelementary particles, and were in 2004 seen by authors of an undergraduate text as being the fundamental constituents of matter.[91]
These quarks and leptons interact through fourfundamental forces:gravity,electromagnetism,weak interactions, andstrong interactions. TheStandard 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 byclassical physics (seeQuantum gravity andGraviton)[92] to the frustration of theoreticians likeStephen Hawking. Interactions between quarks and leptons are the result of an exchange offorce-carrying particles such asphotons between quarks and leptons.[93] 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] Force mediators are usually not considered matter: the mediators of the electric force (photons) possess energy (seePlanck relation) and the mediators of the weak force (W and Z bosons) have mass, but neither are considered matter either.[94] However, while these quanta are not considered matter, they do contribute to the total mass of atoms,subatomic particles, and all systems that contain them.[95][96]
Summary
The modern conception of matter has been refined many times in history, in light of the improvement in knowledge of justwhat 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 "condensed matter physics",[97] "elementary matter",[98] "partonic" matter, "dark" matter, "anti"-matter, "strange" matter, and "nuclear" matter. In discussions of matter andantimatter, the former has been referred to byAlfvén askoinomatter (Gk.common matter).[99] It is fair to say that inphysics, 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 fundamentallength 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 ishadrons, or that matter is leptons and quarks depending upon the scale at which one wishes to define matter.[100]
^"Matter (physics)".McGraw-Hill's Access Science: Encyclopedia of Science and Technology Online. Archived fromthe original on 17 June 2011. Retrieved24 May 2009.
^B. Povh; K. Rith; C. Scholz; F. Zetsche; M. Lavelle (2004)."Part I: Analysis: The building blocks of matter".Particles and Nuclei: An Introduction to the Physical Concepts (4th ed.). Springer.ISBN978-3-540-20168-7.Ordinary matter is composed entirely of first-generation particles, namely the u and d quarks, plus the electron and its neutrino.
^Tsan, Ung Chan (2006)."What Is a Matter Particle?"(PDF).International Journal of Modern Physics E.15 (1):259–272.Bibcode:2006IJMPE..15..259C.doi:10.1142/S0218301306003916.S2CID121628541.(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.
^Y. Ne'eman; Y. Kirsh (1996).The Particle Hunters (2nd ed.). Cambridge University Press. p. 276.ISBN978-0-521-47686-7.[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
^S.M. Caroll (2004).Spacetime and Geometry. Addison Wesley. pp. 163–164.ISBN978-0-8053-8732-2.
^P. Davies (1992).The New Physics: A Synthesis. Cambridge University Press. p. 499.ISBN978-0-521-43831-5.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).
^Tsan, U.C. (2012). "Negative Numbers And Antimatter Particles".International Journal of Modern Physics E.21 (1): 1250005–1–1250005–23.Bibcode:2012IJMPE..2150005T.doi:10.1142/S021830131250005X.(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)
^Tsan, Ung Chan (2013). "Mass, Matter Materialization, Mattergenesis and Conservation of Charge".International Journal of Modern Physics E.22 (5): 1350027.Bibcode:2013IJMPE..2250027T.doi:10.1142/S0218301313500274.(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
^R. Descartes (1644). "The Principles of Human Knowledge".Principles of Philosophy I. p. 53.
^though even this property seems to be non-essential (René Descartes,Principles of Philosophy II [1644], "On the Principles of Material Things", no. 4.)
^R. Descartes (1644). "The Principles of Human Knowledge".Principles of Philosophy I. pp. 8, 54, 63.
^D.L. Schindler (1986). "The Problem of Mechanism". In D.L. Schindler (ed.).Beyond Mechanism. University Press of America.
^E.A. Burtt,Metaphysical Foundations of Modern Science (Garden City, New York: Doubleday and Company, 1954), 117–118.
^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).
^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 byMaurice A. Finocchiaro, "Newton's Third Rule of Philosophizing: A Role for Logic in Historiography",Isis 65:1 (Mar. 1974), pp. 66–73.
^The history of the concept of matter is a history of the fundamentallength 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 ishadrons, or that matter is leptons and quarks depending upon the scale at which one wishes to define matter.B. Povh; K. Rith; C. Scholz; F. Zetsche; M. Lavelle (2004)."Fundamental constituents of matter".Particles and Nuclei: An Introduction to the Physical Concepts (4th ed.). Springer.ISBN978-3-540-20168-7.
^P. Schmüser; H. Spitzer (2002)."Particles". In L. Bergmann; et al. (eds.).Constituents of Matter: Atoms, Molecules, Nuclei. CRC Press. pp. 773ff.ISBN978-0-8493-1202-1.
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