An exotic form of matter which was in all probability present in the early universe shortly after the big bang. Under ordinary circumstances, quarks only occur inside larger particles, such as protons or neutrons, tightly bound together as they are by the carrier particles of the strong nuclear force, which are called gluons. However, at extremely high densities and temperatures it is thought that these larger particles break up, creating a dense and strongly interacting soup of quarks and gluons – a quark-gluon-plasma.

It should be possible to create a quark-gluon-plasma artificially at particle accelerators; in fact, there are strong indications that particle physicists have managed to do just that using the Relativistic Heavy Ion Collider.