Matter

In physics, matter is what makes up any body having a tangible reality. The four most common states are the solid state, the liquid state, the gaseous state and the plasma state. Matter occupies space and has a mass. Thus, in physics, everything that has a mass is matter. The ordinary matter around us is made up of baryons and constitutes the baryonic matter. This definition excludes fundamental bosons, which carry the four fundamental forces, even though they have mass and/or energy.

Do not confuse with material, which is the type, kind or class of material used to make a part.

The states of matter

(Phase diagram for a typical substance at a fixed volume. )

Matter can be found in several states or phases. The four best-known states are solid, liquid, gaseous, and plasma. There are also other slightly more exotic states, such as liquid crystal, Bose-Einstein condensate, superfluid and supercritical fluid. As matter moves from one state to another, it makes a phase transition. Warning: a change of state is not a chemical transformation! This phenomenon is studied in thermodynamics via phase diagrams. The phase transition occurs when certain characteristics of the material change: pressure, temperature, volume, density, energy, etc.

Matter in particle physics

(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.)

Matter at the fundamental level consists of quarks and leptons. Quarks combine to form hadrons, mainly baryons and mesons via strong force, and are presumed to remain so confined. Among the baryons are the proton (whose electric charge is positive) and the neutron (of zero electrical charge), which combine to form the atomic nuclei of all the chemical elements of the periodic table. Normally, these nuclei are surrounded by a cloud of electrons (negative electric charge and exactly opposite to that of the proton). The set formed by a nucleus and a cloud which comprises as many negative electrons as positive protons present in the nucleus is an atom. It is electrically neutral, otherwise, it is an ion. Atoms can join together to form larger and more complex structures, such as molecules. A quantity of particles of matter is expressed with unity: the mole.

Chemistry is the science that studies how nuclei and electrons combine to form various elements and molecules.

Each elementary particle and, by extension, any composite particle is associated with an antimatter (anti-) particle (eg electron-positron or proton-antiproton). An antimatter particle differs from its partner in that its electric charge is opposite. In addition, the baryonic and leptonic numbers are preserved. However, such particles have the same mass.

Although the basic laws of physics do not indicate a preference for matter over antimatter, cosmological observations indicate that the Universe is almost exclusively made of matter.

Matter and the theory of relativity

Albert Einstein’s work in special relativity bequeathed to us the famous equation E = mc², where E is the equivalent energy that can be calculated as the mass m multiplied by the speed of light (c = about 3×108 m/s) squared. This implies that mass is equivalent to energy.

For example, when several particles combine to form atoms, the total mass (rest mass) of the assembly is smaller than the sum of the rest masses of the constituents, because in fact a part of the mass of the constituents is converted. in bond energy, necessary to ensure the cohesion of the whole. This phenomenon is called the mass defect.

(Spacetime lattice analogy. )

The physicist has also established the link between the curvature of space-time and mass-energy thanks to the theory of general relativity: matter (mass or energy) moves in accordance with the curved spacetime where it is located, and at the same time, the matter is itself contributing to the curvature of spacetime: “Spacetime tells matter how to move; matter tells spacetime how to curve.” (John Wheeler) Thus, in general relativity, matter and energy are equivalent, and one way of measuring their quantity is to observe the curvature of the space-time that contains them.

Philosophy

At the origin, matter designates the natural element intended to be “informed” (to be worked) by the man (the wood, the clay); the matter became progressively the undifferentiated bottom from the receptacle. Becoming a pure concept, it is reached by an operation of the mind and corresponds to what could subsist if all the particular qualities of a thing were disregarded. It is not a mere passive material but shows a certain internal need which allows to include it among the causes or even the principles.

It is Aristotle who takes this notion to the status of concept “I call matter the first ‘substrate‘, hupokeimenon, of every thing, from which something happens and which belongs to it immanently and not by accident. ..] Sensitive beings are compounds of matter and form, and matter is the substratum of change.“