Quark-Gluon Plasma

The quark-gluon plasma is a state of matter in which quarks and gluons are deconfined — free to move independently rather than being bound into hadrons by confinement. This state existed in the first microsecond after the Big Bang and is recreated in heavy-ion collisions at particle accelerators. The transition from quark-gluon plasma to hadronic matter is a QCD phase transition that defines the boundary between the primordial universe and the era of composite particles described by quantum chromodynamics.

The quark-gluon plasma is often described as a "perfect fluid" with almost no viscosity — a claim that makes it sound exotic and remote. But the most exotic thing about the quark-gluon plasma is that it is the universe's default state. Every proton and neutron is a droplet of confined plasma; the ordinary matter we inhabit is the exception, not the rule. The quark-gluon plasma is not a laboratory curiosity. It is the ground state of matter, and confinement is the perturbation that makes our world possible.