A quark zooms through quark-gluon plasma, creating a wake in the plasma. Credit: Jose-Luis Olivares, MIT
Just after the Big Bang, the universe was unimaginably hot, about a trillion degrees. Matter did not yet exist as atoms. Instead, everything was a super-hot ‘soup’ made of tiny particles called quarks and gluons.
These particles moved at nearly the speed of light, forming what scientists call a quark-gluon plasma. This state lasted only a few millionths of a second before cooling down. As it cooled, quarks and gluons joined together to form protons, neutrons, and the basic particles that make up matter today.
At CERN in Switzerland, scientists use the Large Hadron Collider to recreate this early-universe plasma. They smash heavy atoms together at almost the speed of light, briefly freeing quarks and gluons so they can study this ancient form of matter.
Recently, a team led by physicists from MIT found clear evidence that quarks moving through this plasma create tiny waves behind them — like a duck leaving ripples in water. This shows that quark-gluon plasma behaves like a liquid that flows and splashes, rather than a loose cloud of separate particles.
“It has been a long debate in our field, on whether the plasma should respond to a quark,” says Yen-Jie Lee, professor of physics at MIT. “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. So quark-gluon plasma really is a primordial soup.”
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