Mit physicists uncover first clear evidence of primordial plasma flowing as liquid

Thursday 29 January 2026 - 09:50

By: Dakir Madiha

Mit physicists uncover first clear evidence of primordial plasma flowing as liquid

Physicists from CERN's Large Hadron Collider have captured the first unambiguous signs that the ultra-hot "primordial soup" filling the early universe flowed like a liquid, rippling and swirling in response to fast-moving particles much like water trailing behind a duck. A team led by MIT physicist Yen-Jie Lee employed a novel technique to track how individual quarks carve wakes as they speed through quark-gluon plasma (QGP), the billion-degree mix of fundamental particles that dominated microseconds after the Big Bang. Published in Physics Letters B and highlighted by MIT News on January 28, these findings deliver direct proof that QGP acts as a strongly coupled fluid rather than dispersing randomly like a gas.

The research team devised a method overcoming a persistent challenge in QGP studies: prior efforts tracking quark wakes via quark-antiquark pairs suffered from mutual masking of signals. Lee's group instead tagged high-momentum isolated quarks using neutral Z bosons, which slice through the plasma without interacting. In quark-gluon plasma, countless quarks and gluons collide constantly; occasionally, one such smash produces a Z boson paired with a high-energy quark. Collaborating with Vanderbilt's Yi Chen group, they sifted 13 billion heavy-ion collisions recorded by the CMS detector, pinpointing around 2,000 Z boson events. In each, energy patterns across the fleeting plasma revealed fluid-like splashes and vortices opposite the Z boson's path, unmistakably tied to isolated quarks plowing through.

These wake effects align precisely with predictions from the "hybrid model" crafted by MIT physics professor Krishna Rajagopal. His framework foresaw QGP reacting fluidly to fast particles, generating waves and splashes. Rajagopal, not directly involved, called it the first clear, unequivocal evidence of this fundamental phenomenon that experiments have chased for years. Daniel Pablos, a University of Oviedo physicist and Rajagopal collaborator, hailed the measurement as a breakthrough in decoding QGP properties.

The discoveries build on separate ATLAS collaboration results from last week, which confirmed QGP's collective fluid behavior via radial expansion profiles in lead-ion collisions. Quark-gluon plasma ranks as the universe's first liquid and hottest known, hitting trillions of degrees Celsius during its fleeting existence before cooling; quarks and gluons then coalesced into protons, neutrons, and the matter we know. Lee noted this marks the first direct proof that a quark drags plasma along as it moves, opening unprecedented scrutiny of this exotic fluid's traits and dynamics.