CERN researchers confirm quark wakes in primordial soup

Quarks behave like ducks in water

For decades, theorists debated whether the hot, dense matter of the early universe would slow down fast-moving particles or let them pass through unaffected. A team led by MIT physicists has now resolved the question with direct observation. At CERN's Large Hadron Collider, researchers watched quarks blast through quark-gluon plasma and leave behind distinct wakes, much like a duck moving across a pond. This direct observation ends a long-standing theoretical dispute about the fundamental nature of the earliest state of matter. The evidence is now concrete rather than inferred from indirect models of particle behavior.

The plasma is incredibly dense.

It responds collectively as a unified fluid, generating waves and splashes rather than acting as a collection of independent particles. This is the first direct evidence of such behavior in this specific primordial state. The collective response suggests a viscosity that was previously only hypothesized in complex simulations of high-energy collisions.

"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," said Yen-Jie Lee, professor of physics at MIT.

Quark-gluon plasma exists for only a few millionths of a second in nature, having formed in the first microseconds after the Big Bang. To study it, scientists collide heavy ions at nearly the speed of light. These collisions briefly separate quarks and gluons, recreating the conditions of the newborn universe in tiny amounts. The new data provides a snapshot of this fleeting state.

Methodology and detection

Lee and his colleagues developed a new method for detecting these quark wakes. By measuring the size, speed, and duration of the disturbances, scientists can now determine key properties of the plasma. This includes how quickly the wakes travel and how far they extend before fading.

The study was conducted by the CMS Collaboration, a worldwide group of particle physicists using the Compact Muon Solenoid detector. The detector is one of the general-purpose instruments at the Large Hadron Collider in Switzerland. The team plans to apply this technique to additional collision data to find more examples and study them in greater detail.

Understanding these properties helps researchers infer how the plasma behaved during the universe's first microseconds. As temperatures dropped, quarks and gluons combined into protons and neutrons, forming the building blocks of all visible matter. The new insights bridge the gap between high-energy particle physics and cosmology.

Context in the field

This result arrives alongside other significant developments in particle physics. On 6 October, Francis Halzen was awarded the 2026 Nobel Prize in Physics for his work on high-energy neutrinos. Halzen's research, conducted using the IceCube detector in Antarctic ice, focuses on detecting "ghost particles" arriving from deep space.

While Halzen's work looks outward to the cosmos, the CERN team looks inward to the most energetic moments of history. Both areas rely on advanced detectors to observe elusive phenomena. The Nobel committee recognized Halzen for turning a vast block of ice into a scientific instrument, a feat comparable in ambition to the precision engineering required at the LHC.

Other recent findings in the field include work on quantum sensors for particle physics experiments and studies of photon behavior. These efforts collectively expand the toolkit available to physicists. The confirmation of liquid-like behavior in quark-gluon plasma is a major step in understanding the fundamental forces that shaped the early universe.

The results suggest that the "primordial soup" was not a chaotic mess, but a structured fluid with measurable viscosity and response times. This has implications for models of the early universe's evolution. As the team continues to analyze more data, the picture of those first microseconds will become increasingly clear.