Science

Unveiling Cosmic Secrets: The Speed of Sound in Quark-Gluon Plasmas at CERN

2025-07-02

Author: Wei Ling

In the heart of atomic nuclei, protons and neutrons are constructed from fundamental particles known as quarks, bound tightly together by gluons through the powerful strong interaction.

In an explosive cosmic dance, when heavy atomic nuclei collide at nearly light speed, these quarks can break free, giving rise to a mysterious phase of matter known as quark-gluon plasma. Remarkably, this substance behaves like a liquid, exhibiting collective flow while maintaining an astonishing ability to lose minimal energy.

Quark-gluon plasmas are of immense interest to researchers, as they represent the conditions of the Universe just moments after the Big Bang, prior to the formation of matter as we know it today.

At CERN, the CMS Collaboration has mastered the art of creating this exotic state through high-energy collisions of massive nuclei, albeit for fleeting instants. In groundbreaking research, scientists have turned to sound waves to probe the fundamental characteristics of this plasma.

Sound waves, which consist of compressions and rarefactions moving in sync, can reveal the properties of their medium—whether it be density, viscosity, or other characteristics. By carefully analyzing these waves, the team has uncovered a stunning revelation: the speed of sound in their quark-gluon plasma clocked in at nearly half the speed of light, a measurement achieved with unprecedented precision.

These findings not only deepen our understanding of the fundamental forces that unite matter but also illuminate the conditions of the early Universe, potentially reshaping our knowledge as particle collider experiments continue to unfold.