Matter

In classical physics, matter is any substance that has mass and takes up space by having volume.
 In the microcosm, atomic matter consists of subatomic particles, such as the atomic nucleus composed of protons and neutrons, and orbiting electrons.
 
==States of matter==
Matter exists in states (or phases): the classical solid, liquid, and gas; as well as the more exotic plasma, Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.
==General relativity==
Theorems in general relativity and cosmology, equate matter as anything that contributes to the energy–momentum of a system, specifically, anything that is not purely gravity.
 In this view, light and other massless particles and fields are all part of "matter".
==Fundamental particles==
Massless particles, such as photons, are not considered matter, because they have neither rest mass nor volume. However, not all particles with rest mass have a classical volume, since fundamental particles such as quarks and leptons (sometimes equated with matter) are considered "point particles" having no effective size or volume. Nevertheless, quarks and leptons together make up "ordinary matter", and their interactions contribute to the effective volume of the composite particles that make up ordinary matter.
==References==
Category:Particle physics