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Physicists at CERN's Large Hadron Collider captured the clearest evidence yet that quark-gluon plasma—the superheated matter believed to have filled the early universe—behaves like a true liquid. By tracking individual quarks moving through the plasma, researchers observed ripples and wakes resembling a duck moving through water. The finding indicates the primordial plasma is dense enough to slow speeding quarks and respond collectively, deepening understanding of the conditions just after the Big Bang.