In the moments after the Big Bang, the Universe existed as an unimaginably dense, trillion-degree 'soup' of plasma. Scientists have now produced the first experimental evidence that this exotic primordial substance, known as quark-gluon plasma (QGP), behaved like a liquid, sloshing and swirling.
This QGP, the first and hottest liquid ever to exist, is predicted to have lasted for mere millionths of a second before expanding and cooling into atoms. Researchers from MIT and CERN recreated heavy-ion collisions, similar to those that formed QGP, to study its properties.
Using data from collisions of lead particles at near light speed within CERN's Large Hadron Collider (LHC), physicists analyzed the behavior of quarks moving through the QGP. They observed that as quarks passed through the dense plasma, they created a wake, much like a boat moving through water, transferring energy and momentum.
The experiment required sophisticated analysis to infer the messy wake within the QGP droplets. By focusing on the rare creation of a quark alongside a Z boson-a particle that does not interact with the QGP-researchers could isolate the wake created by a single quark. This confirmed the QGP's liquid-like reactions, providing strong evidence for its fluid properties.