Oxygen collisions reveal how quark–gluon matter approaches equilibrium

High-energy nuclear collisions recreate extreme conditions similar to those in the early universe, producing quark–gluon plasma (QGP), a hot state of matter in which quarks and gluons are no longer confined inside protons and neutrons. While large systems such as lead–lead collisions can produce matter that behaves like a fluid, collective behavior has also been observed in smaller systems.