Scientists analyzing data from heavy ion collisions at the Large Hadron Collider (LHC)—the world’s most powerful particle collider, located at CERN, the European Organization for Nuclear Research—have new evidence that a pattern of “flow” observed in particles streaming from these collisions reflects those particles’ collective behavior. The measurements reveal how the distribution of particles is driven by pressure gradients generated by the extreme conditions in these collisions, which mimic what the universe was like just after the Big Bang.