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Matter
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In common usage, matter is anything that has both mass and volume (takes up space). A more rigorous definition is used in science: matter is what atoms and molecules are made of. Matter is commonly said to exist in four states (or phases): solid, liquid, gas and plasma; other phases, such as Bose–Einstein condensates, also exist.
In the realm of relativity, matter can be equated to energy via the equation E = mc2.
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Encyclopedia
In common usage, matter is anything that has both mass and volume (takes up space). A more rigorous definition is used in science: matter is what atoms and molecules are made of. Matter is commonly said to exist in four states (or phases): solid, liquid, gas and plasma; other phases, such as Bose–Einstein condensates, also exist.
In the realm of relativity, matter can be equated to energy via the equation E = mc2. In the realm of cosmology, other forms of matter and energy, such as dark matter and dark energy are invoked to explain the behavior of the observable universe.
Definitions
Common definition
The common definition of matter is anything that has both mass and volume (occupies space). For example, a car would be said to be made of matter, as it occupies space, and has mass.
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 Pauli exclusion principle. 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.
BIPM definition
The international standards organization Bureau International des Poids et Mesures uses the terminology "amount of substance", rather than "matter". To quote the : “Amount of substance is defined to be proportional to the number of specified elementary entities in a sample, the proportionality constant being a universal constant which is the same for all samples. The unit of amount of substance is called the mole, symbol mol, and the mole is defined by specifying the mass of carbon 12 that constitutes one mole of carbon 12 atoms. By international agreement this was fixed at 0.012 kg, i.e. 12 g.
- 1. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol".
- 2. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.”
Scientific definition
A definition of "matter" that is based upon its physical and chemical structure is: matter is what atoms and molecules are made of, meaning anything made of protons, neutrons, and electrons. This definition is consistent with the BIPM definition of "amount of substance" above, but is more specific about the constituents of matter (and unconcerned about the unit mole). Further discussion appears below in the discussion section and in the description of the quarks and leptons definition. As an example of matter under this definition, genetic information is carried by a long molecule called DNA, which is copied and inherited across generations. It is matter under this definition because it is made of atoms, not by virtue of having mass or occupying space.
Discussion and background
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. James Clerk Maxwell discussed matter in his work Matter and Motion. 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. 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. A textbook discussion from 1870 suggests matter is what is made up of atoms: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. The famous physicist J. J. Thomson wrote about the "constitution of matter" and was concerned with the possible connection between matter and electrical charge. There is an entire literature concerning the "structure of matter", ranging from the "electrical structure" in the early 20th century, to the more recent "quark structure of matter", introduced today with the remark: Understanding the quark structure of matter has been one of the most important advances in contemporary physics. In this connection, physicists speak of matter fields, and speak of particles as "quantum excitations of a mode of the matter field". 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 spinor fields (like quarks and leptons), which are believed to be the fundamental components of matter, or scalar fields, like the Higgs particles, which are used to introduced mass in a gauge theory (and which, however, could be composed of more fundamental fermion fields)."
The term "matter" is used throughout physics in a bewildering variety of contexts: for example, one refers to "condensed matter physics", "elementary matter", "partonic" matter, "dark" matter, "anti"-matter, "strange" matter, and "nuclear" matter. In discussions of matter and antimatter, normal matter has been referred to by Alfvén as koinomatter. It is fair to say that in physics, there is no broad consensus as to an exact definition of matter, and the term "matter" usually is used in conjunction with some modifier.
Quarks and leptons definition
As may be seen from the above discussion, many early definitions of what can be called ordinary matter were based upon its structure or "building blocks". The "scientific definition" stated above follows this tradition. In a more technical version it can be stated as: ordinary matter is everything that is composed of elementary fermions, namely quarks and leptons. The connection between these formulations follows.
Leptons (the most famous being the 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. 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 the two elementary types of fermions. Carithers and Grannis state: Ordinary matter is composed entirely of first-generation particles, namely the u [up] and d [down] quarks, plus the electron and its neutrino.
This definition of ordinary matter is more subtle than it first appears. There are two groups of particles. All the particles that make up matter, such as electrons, protons and neutrinos, are fermions. All the force carriers are bosons. See the tabulation in the figure. The W and Z bosons that mediate the weak force are not made of quarks and leptons, and so in isolation are not ordinary matter, but do have mass. 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) and by implication, therefore, the interaction energy that holds the constituents together. The inclusion of interaction energy implied by the definition of ordinary matter is significant. For 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 QCD). Basically, much of the mass of hadrons is the interaction energy of bound quarks. Thus, most of what composes the "mass" of ordinary matter is interquark interaction energy. For example, "the gluonic forces binding three quarks (total mass 12.5 MeV) to make a nucleon contribute most of its mass of 938 MeV". See also quark mass. A first-principles calculation of the nucleon mass has yet to be accomplished.
Phases of ordinary matter
In bulk, matter can exist in several different forms, or states of aggregation, known as phases, depending on ambient pressure, temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties (such as density, specific heat, refractive index, and so forth). These phases include the three familiar ones (solids, liquids, and gases), as well as more exotic states of matter ( such as plasmas, superfluids, supersolids, Bose-Einstein condensates, ...). A fluid may be a liquid, gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change, matter may change from one phase into another. These phenomena are called phase transitions, and are studied in the field of 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 nanomaterials for more details).
Phases are sometimes called states of matter, but this term can lead to confusion with thermodynamic states. For example, two gases maintained at different pressures are in different thermodynamic states (different pressures), but in the same phase (both are solids).
Solid
Solids are characterized by a tendency to retain their structural integrity; if left on their own, they will not spread in the same way gas or liquids would. Many solids, like rocks and concrete, have very high hardness and rigidity and will tend to break or shatter when subject to various forms of stress, but others like steel and paper are more flexible and will bend. Solids are often composed of crystals, glasses, or long chain molecules (e.g. rubber and paper). Some solids are amorphous such as glass. A common example of a solid is the solid form of water, ice.
Liquid
In a liquid, the constituents frequently are touching, but able to move around each other. So unlike a gas, it has cohesion and viscosity. Compared to a solid, the forces holding constituents together are weaker, and it is not rigid, but adapts a shape decided by its container. Liquids are hard to compress. A common example is water.
Gas
A gas is a state of aggregation without cohesion; a vapor. Thus a gas has no resistance to changing shape (beyond the inertia of its constituents, which have to be knocked aside). The distance between constituent particles is flexible, determined, for example, by the size of a container and the number of particles, not by internal forces. A common example is the vapor form of water, steam.
Plasma
Plasma is a fourth state of matter consisting of an overall charge-neutral mix of electrons, ions and neutral atoms. The plasma exhibits behavior peculiar to long range Coulomb forces in which the particles move in electromagnetic fields generated by and self-consistent with their own motions. The sun and stars are plasmas, as is the Earth's ionosphere, and plasmas occur in neon signs. Plasmas of deuterium and tritium ions are used in fusion reactions. The term plasma was applied for the first time by Tonks and Langmuir in 1929, to the inner regions of a glowing ionized gas produced by electric discharge in a tube.
Bose–Einstein condensate
This state of matter was first discovered by Satyendra Nath Bose, who sent his work on statistics of photons to Albert Einstein for comment. Following publication of Bose's paper, Einstein extended his treatment to massive particles fixed in number, and predicted this fifth state of matter in 1925. Bose–Einstein condensates were first realized experimentally by several different scientific groups in 1995 for rubidium, sodium, and lithium, using a combination of laser and evaporative cooling. Bose–Einstein condensation for atomic hydrogen was achieved in 1998.
The Bose–Einstein condensate is a liquid-like superfluid that occurs in at low temperatures in which all atoms occupy the same quantum state. In low-density systems, it occurs at or below 10-5 K.
Fermonic condensate
A fermonic condensate is a superfluid phase formed by fermionic particles at low temperatures. It is closely related to the Bose-Einstein condensate under similar conditions. Unlike the Bose-Einstein condensates, fermionic condensates are formed using fermions instead of bosons. The earliest recognized fermionic condensate described the state of electrons in a superconductor; the physics of other examples including recent work with fermionic atoms is analogous. The first atomic fermionic condensate was created by Deborah S. Jin in 2003. These atomic fermionic condensates are studied at temperatures in the vicinity of 50-350nK.
A hypothetical fermionic condensate that appears in theories of massless fermions with chiral symmetry breaking is the chiral condensate or the quark condensate.
Core of a neutron star
Because of its extreme density, the core of a neutron star falls under no other state of matter. While a white dwarf is about as massive as the sun (up to 1.4 solar masses, the Chandrasekhar limit), the Pauli exclusion principle prevents its collapse to smaller radius, and it becomes an example of degenerate matter. In contrast, neutron stars are between 1.5 and 3 solar masses, and achieve such density that the protons and electrons are crushed to become neutrons. Neutrons are fermions, so further collapse is prevented by the exclusion principle, forming so-called neutron degenerate matter.
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Quark-gluon plasma
Gluons are elementary particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. The quark-gluon plasma is a hypothetical phase of matter, a phase of matter as yet not observed, supposed to exist in the early universe and to have evolved into a hadronic-gas phase. At extremely high energy the strong force is anticipated to become so weak that the atomic nuclei break down into a bunch of loose quarks, which distinguishes the quark-gluon phase from normal plasma. In collisions of relativistic heavy ions, it is hoped to observe a phase transition from the nuclear, hadronic phase to a matter phase consisting of quarks and gluons. So far, experimental results have shown that such collisions form a dense hadronic fireball of high energy density well localized in space. An animation is found at .
Structure of ordinary matter
In particle physics, fermions are particles which obey Fermi–Dirac statistics. Fermions can be elementary, like the electron, or composite, like the proton and the neutron. In the Standard Model there are two types of elementary fermions: quarks and leptons, which are discussed next.
Quarks
Quarks are a particles of spin-, meaning that they are fermions. They carry an electric charge of - e (down-type quarks) or + e (up-type quarks). For comparison, an electron has a charge of -1 e. They also carry colour charge, which is the equivalent of the electric charge for the strong interaction. Quarks also undergo radioactive decay, meaning that they are subject to the weak interaction. Quarks are massive particles, and therefore are also subject to gravity.
Quark properties| Name | Symbol | Spin | Electric charge
(e) | Mass
(MeV/c2) | Mass comparable to | Antiparticle | Antiparticle
symbol | | Up-type quarks | | Up | | | | 1.5 to 3.3 | ~ 5 electrons | Antiup | | | Charm | | | | 1160 to 1340 | ~ 1 proton | Anticharm | | | Top | | | | 169,100 to 173,300 | ~ 180 protons or
~ 1 tungsten atom | Antitop | | | Down-type quarks | | Down | | | | 3.5 to 6.0 | ~ 10 electrons | Antidown | | | Strange | | | | 70 to 130 | ~ 200 electrons | Antistrange | | | Bottom | | | | 4130 to 4370 | ~ 5 protons | Antibottom | |
Baryonic matter
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 is usually used to refer to triquarks — particles made of three quarks. "Exotic" baryons made of four quarks and one antiquark are known as the pentaquarks, 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 dark energy, dark matter, black holes or various forms of degenerate matter, such as compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe (WMAP), suggests that only about 4.6% of that part of the universe within range of the best telescopes (that is, matter that may be visible because light could reach us from it), is made of baryionic matter. About 23% is dark matter, and about 72% is dark energy.
Degenerate matter
In physics, degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero. The 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 for the case of many fermions the maximum kinetic energy called the Fermi energy and the pressure of the gas becomes very large and dependent upon 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. The demonstration by 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.
Degenerate matter includes the part of the universe that is made up of neutron stars and white dwarfs.
Leptons
Leptons are a particles of spin-, meaning that they are fermions. They carry an electric charge of -1 e (electron-like leptons) or 0 e (neutrinos). Unlike quarks, leptons do not carry colour charge, meaning that they do not experience the strong interaction. Leptons also undergo radioactive decay, meaning that they are subject to the weak interaction. Leptons are massive particles, therefore are subject to gravity.
Lepton properties| Name | Symbol | Spin | Electric charge
(e) | Mass
(MeV/c2) | Mass comparable to | Antiparticle | Antiparticle
symbol | | Electron-like leptons | | Electron | | | -1 | 0.5110 | 1 electron | Antielectron
(positron) | | | Muon | | | -1 | 105.7 | ~ 200 electrons | Antimuon | | | Tauon | | | -1 | 1,777 | ~ 2 protons | Antitauon | | | Neutrinos | | Electron neutrino | | | 0 | < 0.000460 | Less than a thousandth of an electron | Electron antineutrino | | | Muon neutrino | | | 0 | < 0.19 | Less than half of an electron | Muon antineutrino | | Tauon neutrino
(or tau neutrino) | | | 0 | < 18.2 | Less than ~ 40 electrons | Tauon antineutrino
(or tau antineutrino) | |
Other types of matter
Matter, in the scientific definition, constitutes about 4% of the energy of the observable universe. The remaining energy is theorized to be due to exotic forms, of which 23% is dark matter and 73% is dark energy.
Antimatter
In particle physics and quantum chemistry, antimatter is matter that is composed of the antiparticles of those that constitute normal matter. If a particle and its antiparticle come into contact with each other, the two annihilate; that is, they may both be converted into other particles with equal energy in accordance with Einstein's equation E = mc2. These new particles may be high-energy photons (gamma rays) or other particle–antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle-antiparticle pair, which is often quite large.
Antimatter is not found naturally on Earth, except very briefly and in vanishingly small quantities (as the result of radioactive decay or cosmic rays). This is because antimatter which came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of, and be annihilated. Antiparticles and some stable antimatter (such as antihydrogen) can be made in tiny amounts, but not in enough quantity to do more than test a few of its theoretical properties.
There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter, whether other places are almost entirely antimatter instead, and what might be possible if antimatter could be harnessed, but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics. Possible processes by which it came about are explored in more detail under baryogenesis.
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. Scatter in observations roughly indicated by gray bars. The difference is due to dark matter or perhaps a modification of the law of gravity. ]]
Dark matter
In astrophysics and 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. Observational evidence of the early universe and the big bang theory require that this matter have energy and mass, but is not composed of either elementary fermions (as above) OR gauge bosons. As such, it is composed of particles as yet unobserved in the laboratory (perhaps supersymmetric particles).
Dark energy
In cosmology, dark energy is the name given to the antigravitating influence that is accelerating the rate of expansion of the universe. It is known not to be composed of known particles like protons, neutrons or electrons, nor of the particles of dark matter, because these all gravitate.
Exotic matter
Exotic matter is a hypothetical concept of particle physics. It covers any material which violates one or more classical conditions or is not made of known baryonic particles. Such materials would possess qualities like negative mass or being repelled rather than attracted by gravity.
Strange matter
External links
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- How much Matter is in the Universe?
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See also
Dark matter
Antimatter
Cosmology
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