In the classical physics and in the chemistry
of things of everyday life, matter is any
substance that has mass and takes up space
by having volume. All everyday objects that
we can touch are ultimately composed of atoms,
which are made up of interacting subatomic
particles, 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 rest mass and volume. However
it does not include massless particles such
as photons, or other energy phenomena or waves
such as light or sound. Matter exists in various
states (also known as phases). These include
classical everyday phases such as solid, liquid,
and gas – for example water exists as ice,
liquid water, and gaseous steam – but other
states are possible, including plasma, Bose–Einstein
condensates, fermionic condensates, and quark–gluon
plasma.Usually atoms can be imagined as a
nucleus of protons and neutrons, and a surrounding
"cloud" of orbiting electrons which "take
up space". However this is only somewhat correct,
because subatomic particles and their properties
are governed by their quantum nature, which
means they do not act as everyday objects
appear to act – they can act like waves
as well as particles and they do not have
well-defined sizes or positions. In the Standard
Model of particle physics, matter is not a
fundamental concept because the elementary
constituents of atoms are quantum entities
which do not have an inherent "size" or "volume"
in any everyday sense of the word. Due to
the exclusion principle and other fundamental
interactions, some "point particles" known
as fermions (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.
For much of the history of the natural sciences
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, was first put
forward by the Greek philosophers Leucippus
(~490 BC) and Democritus (~470–380 BC).
== Comparison with mass ==
Matter should not be confused with mass, as
the two are not the same in modern physics.
Matter is a general term describing any 'physical
substance'. By contrast, 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 – including
but not limited to rest mass, inertial mass,
relativistic mass, 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 antimatter, but mass has no opposite—there
is no such thing as "anti-mass" or 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 and chemistry, matter exhibits
both wave-like and particle-like properties,
the so-called wave–particle duality.
== Definition ==
=== 
Based on atoms ===
A definition of "matter" based on its physical
and chemical structure is: matter is made
up of atoms. 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. 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 ===
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 quarks and leptons", or "ordinary matter
is everything that is composed of any elementary
fermions except antiquarks and antileptons".
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." (Higher generations particles
quickly decay into first-generation particles,
and thus are not commonly encountered.)
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.
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. 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 gluons fields contribute significantly
to the mass of hadrons. In other words, most
of what composes the "mass" of ordinary matter
is due to the binding energy of quarks within
protons and neutrons. For example, the sum
of the mass of the three quarks in a nucleon
is approximately 12.5 MeV/c2, which is low
compared to the mass of a nucleon (approximately
938 MeV/c2). 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. 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.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)". 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,
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 don't encounter them in everyday life,
antiquarks (such as 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
can not add the rest masses of particles in
a system to get the total rest mass of the
system. Thus, 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. 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 ===
Quarks are 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.
Quarks are massive particles, and therefore
are also subject to gravity.
==== 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
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 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.As a matter of fact, 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.
==== Hadronic matter ====
Hadronic matter can refer to 'ordinary' baryonic
matter, made from hadrons (Baryons and mesons),
or quark matter (a generalisation of atomic
nuclei), ie. the 'low' temperature QCD matter.
It includes degenerate matter and the result
of high energy heavy nuclei collisions. Distinct
from dark matter.
==== 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 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. 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.
==== 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 of the term "strange matter"
=====
In particle physics and astrophysics, the
term is used in two ways, one broader and
the other more specific.
The broader meaning is just quark matter that
contains three flavors of 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 and Witten. 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. strangelets.
=== Leptons ===
Leptons are particles of spin-​1⁄2, meaning
that they are fermions. They carry an electric
charge of −1 e (charged leptons) or 0 e
(neutrinos). Unlike quarks, 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.
== Phases ==
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 gases).
== Antimatter ==
In particle physics and quantum chemistry,
antimatter is matter that is composed of the
antiparticles of those that constitute ordinary
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. 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 radioactive decay,
lightning or cosmic 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
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 (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 CP (charge-parity)
symmetry violation, which can be obtained
from the Standard Model, 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.
Formally, antimatter particles can be defined
by their negative baryon number or lepton
number, while "normal" (non-antimatter) matter
particles have positive baryon or lepton number.
These two classes of particles are the antiparticle
partners of one another.
In October 2017, scientists reported further
evidence that matter and antimatter, equally
produced at the Big Bang, are identical, should
completely annihilate each other and, as a
result, the universe should not exist. 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 of matter ==
Two quantities that can define an amount of
matter in the quark–lepton sense (and antimatter
in an antiquark–antilepton sense), baryon
number and lepton number, are conserved in
the Standard Model. A 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, nuclear (and perhaps chromodynamic)
binding energy is released, as these baryons
become bound into mid-size nuclei having less
energy (and, equivalently, less mass) per
nucleon compared to the original small (hydrogen)
and large (plutonium etc.) nuclei. Even in
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. So the
only way to really "destroy" or "convert"
ordinary matter is to pair it with the same
amount of antimatter so that their "matterness"
cancels out—but in practice there is almost
no antimatter generally available in the universe
(see baryon asymmetry and leptogenesis) with
which to do so.
== Other types ==
Ordinary matter, in the quarks and leptons
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.
=== 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 ordinary baryons (protons
and neutrons). The commonly accepted view
is that most of the dark matter is non-baryonic
in nature. As such, it is composed of particles
as yet unobserved in the laboratory. Perhaps
they are supersymmetric particles, which are
not Standard Model particles, but relics formed
at very high energies in the early phase of
the universe and still floating about.
=== Dark energy ===
In cosmology, dark energy is the name given
to source of the repelling influence that
is accelerating the rate of 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
vacuum itself.
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.
=== Exotic matter ===
Exotic matter is a concept of 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 negative mass.
== Historical development ==
=== 
Antiquity (c. 610 BC–c. 322 BC) ===
The pre-Socratics were among the first recorded
speculators about the underlying nature of
the visible world. Thales (c. 624 BC–c.
546 BC) regarded water as the fundamental
material of the world. Anaximander (c. 610
BC–c. 546 BC) posited that the basic material
was wholly characterless or limitless: the
Infinite (apeiron). Anaximenes (flourished
585 BC, d. 528 BC) posited that the basic
stuff was pneuma or air. Heraclitus (c. 535–c.
475 BC) seems to say the basic element is
fire, though perhaps he means that all is
change. Empedocles (c. 490–430 BC) spoke
of four elements of which everything was made:
earth, water, air, and fire. Meanwhile, Parmenides
argued that change does not exist, and Democritus
argued that everything is composed of minuscule,
inert bodies of all shapes called atoms, a
philosophy called atomism. All of these notions
had deep philosophical problems.Aristotle
(384 BC – 322 BC) was the first to put the
conception on a sound philosophical basis,
which he did in his natural philosophy, especially
in Physics book I. He adopted as reasonable
suppositions the four Empedoclean elements,
but added a fifth, aether. Nevertheless, these
elements are not basic in Aristotle's mind.
Rather they, like everything else in the visible
world, are composed of the basic principles
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.
The word Aristotle uses for matter, ὕλη
(hyle or hule), can be literally translated
as wood or timber, that is, "raw material"
for building. 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 atoms), 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 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).
=== Seventeenth and eighteenth centuries ===
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:
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 extended
For Descartes, matter has only the property
of extension, so its only activity aside from
locomotion is to exclude other bodies: this
is the 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. They are independent things.
In contrast, Aristotle defines matter and
the formal/forming principle as complementary
principles that together compose one independent
thing (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'
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
substances.Descartes' 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.
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.Isaac Newton (1643–1727)
inherited Descartes' 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". 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". 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.Newton
developed Descartes' 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' mechanics, in which
interactions happened exclusively by contact.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, Joseph
Priestley (1733–1804) argued that corporeal
properties transcend contact mechanics: chemical
properties require the capacity for attraction.
He argued matter has other inherent powers
besides the so-called primary qualities of
Descartes, et al.
=== Nineteenth and twentieth 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), but there has been no
further development in the definition of matter.
Rather the question has been set aside. Noam
Chomsky (born 1928) summarizes the situation
that has prevailed since that time:
What is the concept of body that finally emerged?[...]
The answer is that there is no clear and definite
conception of body.[...] Rather, the material
world is whatever we discover it to be, with
whatever properties it must be assumed to
have for the purposes of explanatory theory.
Any intelligible theory that offers genuine
explanations and that can be assimilated to
the core notions of physics becomes part of
the theory of the material world, part of
our account of body. If we have such a theory
in some domain, we seek to assimilate it to
the core notions of physics, perhaps modifying
these notions as we carry out this enterprise.
So matter is whatever physics studies and
the object of study of physics is matter:
there is no independent general definition
of matter, apart from its fitting into the
methodology of measurement and controlled
experimentation. In sum, the boundaries between
what constitutes matter and everything else
remains as vague as the demarcation problem
of delimiting science from everything else.In
the 19th century, following the development
of the periodic table, and of atomic theory,
atoms were seen as being the fundamental constituents
of matter; atoms formed molecules and compounds.
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
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.
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. 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.
In 1909 the famous physicist J. J. Thomson
(1856–1940) 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 that, however, could
be composed of more fundamental fermion fields)."In
the late 19th century with the discovery of
the electron, and in the early 20th century,
with the discovery of the atomic nucleus,
and the birth of particle physics, matter
was seen as made up of electrons, protons
and neutrons interacting to form atoms. Today,
we know that even protons and neutrons are
not indivisible, they can be divided into
quarks, while electrons are part of a particle
family called leptons. Both quarks and leptons
are elementary particles, and are currently
seen as being the fundamental constituents
of matter.These quarks and leptons interact
through four fundamental forces: gravity,
electromagnetism, weak interactions, and strong
interactions. The 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 classical physics (see quantum gravity
and graviton). Interactions between quarks
and leptons are the result of an exchange
of force-carrying particles (such as photons)
between quarks and leptons. The force-carrying
particles are not themselves building blocks.
As one consequence, mass and energy (which
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). Force carriers are usually not considered
matter: the carriers of the electric force
(photons) possess energy (see Planck relation)
and the carriers of the weak force (W and
Z bosons) are massive, but neither are considered
matter either. However, while these particles
are not considered matter, they do contribute
to the total mass of atoms, subatomic particles,
and all systems that contain them.
== 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 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 (Gk. common matter).
It is fair to say that in 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 hadrons, or that matter
is leptons and quarks depending upon the scale
at which one wishes to define matter.These
quarks and leptons interact through four fundamental
forces: gravity, electromagnetism, weak interactions,
and strong interactions. The 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 classical physics (see quantum
gravity and graviton).
== See also
