matter

Matter is the substance that makes up physical objects and the visible universe. It has mass and occupies space, properties that allow it to be detected by everyday measurement. Matter exists in various forms and states, including the common solid, liquid, and gas, as well as plasma and other exotic states at extreme conditions such as Bose-Einstein condensates.

At the smallest scales, matter is composed of atoms, which themselves are built from subatomic particles: protons and neutrons in the nucleus, surrounded by electrons. Atoms combine to form molecules, and different arrangements yield elements and compounds with distinct properties. The vast diversity of materials arises from the ways atoms bond, arrange, and interact.

Matter can be characterized by physical properties such as mass, volume, density, color, electrical conductivity, and phase. It also has chemical properties, including reactivity and flammability, that describe how it interacts with other substances. The state of matter changes with temperature and pressure, through processes of melting, freezing, vaporization, condensation, sublimation, and deposition.

In modern physics, matter is described within models that include atoms and subatomic particles, quantum fields, and fundamental forces. The conservation laws, such as conservation of mass-energy, govern interactions. Some phenomena involve particles that are not classical matter, such as dark matter, which is inferred from gravitational effects but not yet directly observed.

Historically, matter was distinguished from energy; in relativity, mass and energy are related by E=mc^2.