Right after the Big Bang, the universe was filled with a super-hot mix called quark-gluon plasma (QGP). This plasma was incredibly dense, more than a trillion degrees! For a brief moment, it existed before cooling down and forming atoms. Recent experiments show that this primordial brew didn’t just sit still; it actually flowed like a liquid.
A team of physicists from MIT and CERN explored this by recreating collisions of heavy ions, similar to those that would have created the QGP. They wanted to see how quarks behave when they move through the plasma. Do they splash around like liquid or scatter randomly?
To investigate, they analyzed collisions between lead particles in CERN’s Large Hadron Collider (LHC), which operates at near-light speeds. These collisions generate a shower of particles, including quarks and droplets of QGP from the early universe.
Using new techniques, the researchers tracked quark movements within the QGP. According to physicist Yen-Jie Lee of MIT, “We now see the plasma is so dense that it slows down a quark, creating splashes like a liquid.” The quarks lose energy as they move, generating wakes similar to a boat cutting through water, as explained by fellow physicist Krishna Rajagopal. However, detecting these wakes required sifting through countless particles in the extremely short-lived plasma.
This task was challenging because quarks typically pair up with their counterparts, called antiquarks, which complicates tracking them. Instead of seeking those pairs, the team focused on a rarer combination: a quark and a Z boson, a particle that doesn’t interact with QGP. This allowed them to isolate the wake of a single quark. Out of 13 billion collisions they studied, only about 2,000 produced a Z boson, making their findings even more significant.
Rajagopal referred to their results as “definitive evidence” of the liquid nature of QGP. Yet, this finding may open new questions in the scientific community. Different researchers will likely scrutinize these results, but the implications are exciting.
Understanding the properties of materials by disturbing them is a common practice in science. This research gives us a new way to explore other high-energy processes, offering fresh insights into the universe’s evolution.
This experiment is a reminder of how physics works—when in doubt, just smash things together at incredible speeds. The study was published in Physics Letters B.
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