In the very first moments after the Big Bang, the universe looked nothing like it does today.
Instead of stars, atoms, or even protons, everything was packed into an incredibly hot, dense state made of the smallest building blocks of matter.
According to physicists, the early universe was filled with a strange substance called quark-gluon plasma—a seething “primordial soup” where quarks and gluons moved freely at nearly the speed of light.
This exotic state of matter existed for only a few millionths of a second before cooling.
As temperatures dropped, quarks and gluons locked together to form protons, neutrons, and eventually the atoms that make up everything around us today.
Understanding how this early soup behaved is one of the key challenges in modern physics, because it reveals how matter itself first took shape.
To study this ancient material, scientists recreate quark-gluon plasma in the laboratory using the CERN Large Hadron Collider in Switzerland.
By smashing heavy atomic nuclei together at nearly the speed of light, physicists briefly free quarks and gluons from inside protons and neutrons, producing tiny droplets of the same plasma that once filled the infant universe.
Now, a team of researchers led by physicists from Massachusetts Institute of Technology has made a breakthrough discovery.
They found direct evidence that quark-gluon plasma behaves like a true liquid—one that can ripple, swirl, and form wakes when particles race through it. Their results were obtained using data from the Compact Muon Solenoid experiment and were published in the journal Physics Letters B.
The new study shows that when a fast-moving quark shoots through quark-gluon plasma, it creates a wake behind it, similar to how a duck leaves ripples on the surface of a pond.
This is the first clear, direct evidence that the plasma responds as a single, connected fluid rather than as a loose cloud of independent particles.
For years, scientists debated whether this plasma could really act like a liquid. While previous experiments hinted that it flowed smoothly, no one had clearly seen how it reacts to individual particles moving through it.
The new observations settle that debate. The plasma is so dense and strongly connected that it slows down passing quarks and responds by sloshing and splashing around them.
To spot this effect, the research team developed a clever new approach. Instead of tracking pairs of quarks flying in opposite directions—where one particle’s wake can hide the other’s—they looked for rare events where a single quark was produced alongside a Z boson. A Z boson is a neutral particle that passes through the plasma without disturbing it. This makes it a perfect reference point.
In these events, the quark and the Z boson shoot off in opposite directions. Since the Z boson leaves no trace in the plasma, any ripples or swirls seen on the opposite side must come from the quark alone.
Using data from more than 13 billion heavy-ion collisions, the team identified around 2,000 such events. In each case, they saw clear, fluid-like wake patterns caused by single quarks plowing through the plasma.
These wake patterns closely match predictions made by theoretical models, confirming that quark-gluon plasma behaves like an almost “perfect” liquid with extremely low resistance to flow. Measuring the size, shape, and lifetime of these wakes will help scientists learn more about the plasma’s properties, such as how thick it is and how quickly it responds to disturbances.
Beyond particle physics, the findings offer a vivid glimpse into the universe’s earliest moments. For the first time, scientists can say with confidence that the primordial matter filling the newborn universe didn’t just exist—it flowed. By capturing these tiny splashes in the lab, researchers are effectively taking snapshots of the universe when everything we know was just beginning to form.
