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New Delhi: Scientists at CERN’s Large Hadron Collider have uncovered fresh evidence that the early universe behaved like a near-perfect liquid. New experiments show energetic quarks creating wake-like ripples as they travel through quark-gluon plasma, the ultra-hot matter believed to have filled the universe moments after the Big Bang.
The findings offer the clearest proof yet that this primordial ‘soup’ flowed collectively, with almost no friction. Instead of particles scattering randomly, the plasma responds as a single fluid, splashing and swirling around fast-moving quarks, much like water reacting to a speeding duck.
The universe in its first microseconds was an amalgam of gluons and quarks in a trillion-degree mixture. When space cooled, these particles merged to create protons and neutrons, forming the base of all matter today.
Physicists collide heavy ions at nearly light speed in the LHC to study this extreme state. These collisions transiently recreate minute portions of the quark-gluon plasma, enabling researchers to study the manner in which matter acted during the beginning of time.
A CMS Collaboration, led by physicists at MIT, used the study of billions of collisions to identify approximately 2,000 rare events in which one energetic quark was created together with a neutral Z boson.
Since Z bosons have small interactions with the plasma, they are clean markers. All the disturbances manifested on the other side are directly traced to the quark. In both studies, researchers found bow-shaped ripples in the wake of the quark's unmistakable wake pattern in the plasma.
These observations indicate that the plasma is sufficiently thick to reduce the speed of quarks and act as a whole, which proves that it is not a loose cloud of particles but that it is a fluid.
Earlier experiments had hinted at liquid-like behaviour through collective particle flows. But the newly observed wakes provide the first direct evidence of this effect from individual quarks.
The results also match long-standing theoretical predictions that fast particles should generate waves inside quark-gluon plasma. Researchers say this confirms the plasma is a near-perfect fluid, with extremely low viscosity.
“This tells us the quark drags the plasma with it as it moves,” said MIT physicist Yen-Jie Lee, one of the study’s leaders. “The medium splashes and swirls like a liquid.”
By measuring the size and shape of these wakes, scientists can now estimate key properties of quark-gluon plasma, including how easily it flows and how quickly it settles after being disturbed.
The team plans to apply the same method to larger datasets, hoping to build a clearer picture of how this exotic matter evolved as the universe cooled.
The study, carried out using CERN’s Compact Muon Solenoid detector, appears in Physics Letters B. Researchers say it marks a major step toward understanding the universe’s earliest moments, captured through ripples left behind by speeding quarks in a primordial cosmic fluid.
