By the time the universe was picoseconds old, the four fundamental interactions—strong, weak, electromagnetic, and gravitational—had become distinct from one another. Yet, for another few microseconds, the universe remained too hot to bind quarks into protons, neutrons, and other hadrons. Instead, quarks and gluons, the bosons carrying the strong force, existed as a hot, dense soup called quark–gluon plasma.
More recently, quark–gluon plasma is produced at particle colliders such as CERN’s Large Hadron Collider (LHC) and Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) by smashing together the nuclei of heavy atoms. From those collisions, researchers hope to learn about the conditions that were present in the early universe and to probe the nature of strong interactions at high energy densities. Thus far, they have pieced together that quark–gluon plasma behaves as a nearly perfect, viscosity-free fluid. That’s in stark contrast to the electromagnetic plasma, which is best described as...
