CERN Confirms Primordial Quark-Gluon Plasma Acts as Coherent Liquid

Scientists conducting experiments at the European Organization for Nuclear Research (CERN) have confirmed a long-standing theoretical prediction: the quark-gluon plasma (QGP), the universe's earliest state of matter, behaves as a highly coherent liquid. This primordial substance, which existed for fractions of a second following the Big Bang, has now been empirically shown to flow and react collectively, rather than as a dispersed gas of constituent particles. The confirmation, derived from data collected at the Large Hadron Collider (LHC) near Geneva, Switzerland, resolves a fundamental debate concerning the fluid dynamics of matter under the universe's most extreme initial conditions.

The QGP is theorized to be the first and hottest liquid ever formed, potentially reaching temperatures of several trillion degrees Celsius and exhibiting very low internal friction, effectively functioning as a nearly perfect liquid. Researchers recreated the necessary conditions by colliding heavy lead ions at near the speed of light within the LHC's 27-kilometer accelerator ring. The key experimental breakthrough involved Professor Yen-Jie Lee of the Massachusetts Institute of Technology (MIT) and his team focusing on isolating measurable "wakes" generated by energetic quarks traversing this dense medium, an observation analogous to ripples left by a moving object in water.

Professor Lee stated that the plasma's density is sufficient to decelerate a passing quark while simultaneously producing observable splashes and swirls, thereby validating its liquid nature. This observation provides a tangible metric for understanding how this extreme matter transported energy and momentum in the nascent cosmos. The analysis technique, utilizing the Compact Muon Solenoid (CMS) detector, was specifically designed to overcome previous difficulties in isolating single-quark effects, which were often obscured by analyzing back-to-back quark-antiquark pairs.

Professor Lee's group innovatively searched for collisions that simultaneously produced a quark and a neutral Z boson, using approximately 2,000 such events extracted from a sample of 13 billion total collisions to clearly map the disturbance caused by the single quark. This approach yielded the clearest evidence to date that the QGP responds collectively to disturbances. This empirical validation supports theoretical models, such as a hybrid model developed by MIT physicist Krishna Rajagopal and collaborators, which predicted this specific fluid wake formation.

The study of this deconfinement phase, where quarks and gluons move freely, illuminates the dynamics of the strong force that binds ordinary matter. Further investigation into the QGP's characteristics is planned, with the collaboration intending to present more detailed findings on the plasma's properties at the 22nd International Conference on Strangeness in Quark Matter (SQM2026), scheduled for March 22-27, 2026, at the University of California Los Angeles (UCLA). Professor Lee, an experimental particle physicist, connects this early universe research to current astrophysical objects by also probing matter at extreme densities relevant to neutron-star interiors.