CERN quark wakes confirm liquid nature of early universe plasma

On 6 October, scientists at the Large Hadron Collider in Switzerland released direct evidence that quarks generate wakes inside quark-gluon plasma. The results, distributed via ScienceDaily, indicate the primordial matter is dense enough to slow fast quarks and react collectively like a fluid. This finding resolves a long-standing debate about the physical state of the earliest cosmic matter, providing the first direct proof that it acts as a single, cohesive liquid rather than a diffuse gas. The implications for cosmology are significant, as it allows physicists to model the behavior of the universe's first microseconds with greater precision than ever before.

Yen-Jie Lee, an MIT physics professor on the CERN team, called the result a resolution to a long debate. "It has been a long debate in our field, on whether the plasma should respond to a quark," Lee said. "Now we see the plasma is incredibly dense, such that it is able to slow down a quark, and produces splashes and swirls like a liquid. So quark-gluon plasma really is a primordial soup."

The experiment collided heavy ions near light speed to recreate the universe's earliest moments. Temperatures hit trillions of degrees during these microseconds, forming quark-gluon plasma. This state cooled rapidly, letting quarks and gluons bind into protons, neutrons, and other common particles. The process mirrors the conditions that existed just after the Big Bang, when the universe was too hot for atoms to form. By studying these collisions, researchers can observe the fundamental forces that shaped the first matter in the cosmos. The data collected during these high-energy events provides a unique window into the properties of matter under extreme conditions.

Tracking individual quarks moving through the plasma, the team saw ripples, splashes, and swirling wakes similar to a duck in water. These observations offer the first direct proof that quark-gluon plasma reacts to fast particles as a single fluid. It does not simply act as a collection of independently scattering particles. The fluid behavior is consistent with the matter being a true liquid rather than a gas or solid. This collective motion is what generates the visible wakes that the team detected. Without this liquid-like property, the wakes would not form in the observed pattern.

The study was led by MIT physicists and included members of the CMS Collaboration, a global group using the Compact Muon Solenoid detector. Lee and colleagues developed a new method to detect these quark wakes. They plan to apply it to more collision data to find additional examples and study them in greater detail. This collaborative effort highlights the international nature of modern particle physics research. The Compact Muon Solenoid detector is one of the largest instruments ever built for this purpose. Its precision is essential for capturing the subtle effects of quark interactions within the plasma.

Measuring wake size, speed, extent, and fade time may reveal key properties of quark-gluon plasma. Such data could also hint at how the plasma behaved in the first microseconds after the universe began.

"Studying how quark wakes bounce back and forth will give us new insights on the quark-gluon plasma's properties," Lee said. "With this experiment, we are taking a snapshot of this primordial quark soup."

This discovery fits into a busy week for particle physics. On 7 October, University of Illinois Urbana-Champaign physicists reported unusual superconducting behavior in uranium ditelluride. Electron pairs formed rippling patterns called pair density waves. Published in the Proceedings of the National Academy of Sciences, the research suggests these patterns persist after ordinary superconductivity vanishes. The finding challenges existing models of how superconductivity works in complex materials. It opens new avenues for understanding the quantum states of matter. The results were detailed in a paper that has already sparked discussion among condensed matter physicists.

Eduardo Fradkin, an Illinois Grainger Engineering physics professor and project co-lead, described the finding as significant. "Pair density waves are the Cheshire Cat's grin of superconductivity," Fradkin said. "They are the vestige that remains once the phase itself has disappeared. In conventional superconductors, Cooper pairs form when the full phase transition occurs, but, in this system, their observation in PDWs above the transition point shows that they are formed beforehand in a different state."

On 4 October, University of Melbourne researchers published results from a 30-year Australian forestry experiment. The study, released via ScienceDaily, found heavily thinned mountain ash forests grew unusually large trees. These forests also recovered enough carbon to match or exceed untouched areas. This suggests careful thinning can support timber production, wildlife habitat, and carbon storage at the same time. The long-term data provides a rare look at how managed forests evolve over decades. It offers practical insights for sustainable forestry practices in similar ecosystems around the world.

The CERN quark-wake discovery matters for early universe models. Confirming the liquid-like nature of quark-gluon plasma gives a tangible snapshot of conditions moments after the Big Bang. The new detection method allows further analysis of how this primordial matter behaved, potentially refining models of the universe's earliest evolution.