Physicists reveal the hidden force' driving the Universe's hottest fluid

Recent physics simulations have uncovered a previously overlooked “hidden force” driving quark-gluon plasma-the hottest fluid in the universe, which recreates conditions that existed microseconds after the Big Bang.

When atomic nuclei collide at nearly the speed of light, they create quark-gluon plasma, an extremely hot state of matter that allows scientists to study the fundamental building blocks of the universe under extreme conditions.

Scientists have extensively studied the plasma’s intense swirling motion (vorticity) and powerful electromagnetic fields, its fluid acceleration — the mechanical force responsible for its explosive expansion, has received far less attention.

A team of physicists from Fudan University, including Yu-Gang Ma and Xu-Guang Huang, used advanced transport models such as AMPT and UrQMD to map the behaviour of the plasma.

The researchers found that extreme transverse acceleration consistently points outward and reaches its highest levels near the fireball’s boundaries.

At these edges, a sharp pressure drop combined with low enthalpy density creates a “double amplification” effect governed by the relativistic Euler equation, pushing the plasma outward at near-light speeds.

The researchers suggest this acceleration is not merely a byproduct of the plasma’s motion. It may influence temperature-like behaviour, affect particle spins, and reshape scientists’ understanding of how matter transitions between different fundamental states.

Through quantum phenomena such as the Unruh effect where an accelerated observer perceives empty space as a thermal environment acceleration at extreme scales may act as a thermodynamic control parameter.

The discovery could introduce a new “acceleration axis” in the phase diagram of Quantum Chromodynamics (QCD), offering a new way to understand the behaviour of matter under extreme conditions.