Quarks and antiquarks are the teeny, tiny building blocks with which all matter is built, binding together to form protons and neutrons in a process explained by quantum chromodynamics (QCD).
According to QCD, quarks possess one of three charges that allow them to pair in various combinations, such as mesons--elementary particles composed of one quark and its corresponding antiquark. Force carrier particles, known as gluons, hold the quarks together by exchanging and mediating the strong forc e, one of the four fundamental forces.
This structure is the foundation of all matter in the universe, but much is still unknown about why QCD works the way it does.