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stems various types of mass are defined within physics including rest mass inertial mass and relativistic 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 both wave like and particle like properties the so called wave particle duality 9 10 11 relation with chemical substance this section is an excerpt from substance chemistry edit steam and liquid water are two different forms of the same pure chemical substance water picture of a formed molecule in chemistry a substance is a unique form of matter with constant chemical composition and characteristic properties 12 13 chemical substances may take the form of a single element or chemical compounds if two or more chemical substances can be combined without reacting they may form a chemical mixture 14 if a mixture is separated to isolate one chemical substance to a desired degree the resulting substance is said to be chemically pure 15 chemical substances can exist in several different physical states or phases e g solids liquids gases or plasma without changing their chemical composition substances transition between these phases of matter in response to changes in temperature or pressure some chemical substances can be combined or converted into new substances by means of chemical reactions chemicals that do not possess this ability are said to be inert pure water is an example of a chemical substance with a constant composition of two hydrogen atoms bonded to a single oxygen atom i e h 2 o the atomic ratio of hydrogen to oxygen is always 2 1 in every molecule of water pure water will tend to boil near 100 c 212 f an example of one of the characteristic properties that define it other notable chemical substances include diamond a form of the element carbon table salt nacl an ionic compound and refined sugar c 12 h 22 o 11 an organic compound definition based on atoms a definition of matter based on its physical and chemical structure is matter is made up of atoms 16 such atomic matter is also sometimes termed ordinary matter as an example deoxyribonucleic acid molecules 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 plasmas gases of ions and electrolytes 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 atoms and molecules are made of meaning anything made of positively charged protons neutral neutrons and negatively charged electrons 17 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 cathode ray tube television or 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 quarks 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 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 on 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 quarks and leptons 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 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 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 19 higher generation 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 the force carriers are elementary bosons 22 the w and z bosons that mediate the weak 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 see dynamics 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 the binding energy of quarks within protons and neutrons 25 for example the sum of the mass of the three quarks in a nucleon is approximately 12 5 mev c 2 which is low compared to the mass of a nucleon approximately 938 mev c 2 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 the up and down quarks the electron and the electron neutrino the second includes the charm and strange quarks the muon and the muon neutrino the third generation consists of the top and bottom quarks and the tau and tau neutrino 28 the most natural explanation for this would be that quarks and leptons of higher generations are excited states of the first generations if this turns out to be the case it would imply that quarks and leptons are composite particles rather than elementary 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 has mass and volume occupies space 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 the pauli exclusion principle 32 33 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 in the antiproton and antileptons such as the positron are the antiparticles 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 antimatter particles as well as the ordinary quark and lepton and thus also anything made of mesons which are unstable particles made up of a quark and an antiquark in general relativity and cosmology in the context of relativity 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 of rest masses but the 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 34 35 this view is commonly held in fields that deal with general relativity such as 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 fermi dirac statistics fermions can be elementary like the electron or composite like the proton and neutron in the standard model there are two types of elementary fermions quarks and leptons which are discussed next quarks main article quark quarks are massive particles of spin 1 2 implying that they are fermions they carry an electric charge of 1 3 e down type quarks or 2 3 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 quark properties 36 name symbol spin electric charge e mass mev c 2 mass comparable to antiparticle antiparticle symbol up type quarks up u 1 2 2 3 1 5 to 3 3 5 electrons antiup u charm c 1 2 2 3 1160 to 1340 1 proton anticharm c top t 1 2 2 3 169 100 to 173 300 180 protons or 1 tungsten atom antitop t down type quarks down d 1 2 1 3 3 5 to 6 0 10 electrons antidown d strange s 1 2 1 3 70 to 130 200 electrons antistrange s bottom b 1 2 1 3 4130 to 4370 5 protons antibottom b baryonic main article baryon 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 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 those that 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 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 from hadrons baryons and mesons or quark matter a generalisation of atomic nuclei i e the low temperature qcd matter 39 it includes degenerate matter and the result of high energy heavy nuclei collisions 40 degenerate main article degenerate matter in physics degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero 41 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 in the case of many fermions the maximum kinetic energy called the 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 42 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 43 degenerate matter includes the part of the universe that is made up of neutron stars and white dwarfs strange main article strange matter strange matter is a particular form of quark matter usually thought of as a liquid of up down and strange quarks it is contrasted with nuclear matter which is a liquid of neutrons and protons which themselves are built out of up and down quarks and with non strange quark matter which is a quark liquid 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 neutron stars or more speculatively as isolated droplets that may vary in size from femtometers strangelets to kilometers quark stars two meanings in particle physics and astrophysics the term is used in two ways one broader and the other more specific the broader meaning is just quark matter that contains three flavors of 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 meanin...
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