New results from the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) provide strong evidence that smashing oxygen nuclei together at nearly the speed of light generates a quark-gluon plasma (QGP), a type of matter that existed just after the birth of the universe. The data, just published in Physical Review Letters, show that energetic jets of particles lose energy as they traverse the hot, dense matter left in the collision’s wake.