In the early moments of the universe, matter existed in a state known as quark-gluon plasma (QGP), which is a dense, hot soup. For several years, particle colliders have been able to replicate this state using heavy elements like lead. A recent experiment by the European Organization for Nuclear Research (CERN) has shown that this plasma can also be produced through smaller collisions. As there is no longer an accessible natural source of this primordial state, these micro big bangs can provide insights into the universe's early moments.
Quarks, which make up protons and neutrons, are the building blocks of atoms, while gluons bind quarks together. In the universe's initial microseconds, quarks and gluons formed an extremely hot plasma before the universe expanded and cooled, allowing quarks to condense into larger particles.
Physicists have been studying QGP in large nuclear collisions and are now investigating the limits of this state of matter. They aim to determine how small a collision can be while still observing particle behavior similar to that of a fluid.
According to a recent article in Physical Review Letters, CERN and an international team were able to generate QGP using oxygen-16 and neon-20, both of which are lighter than lead atoms, previously thought to be the lightest elements capable of producing QGP.
You Zhou, a researcher at the Niels Bohr Institute in the Netherlands and a coauthor of the study, stated, "We have pushed the boundary for how small the atomic nuclei can be while still re-creating this primordial matter—what you could call a ‘little big bang.’ We now know more about the fundamental conditions required for matter to transition into this extreme state."
The collisions produced signals consistent with expected QGP behavior, with the generated matter appearing to expand collectively like a fluid before cooling and reverting to particles. Zhou added, "Hopefully, this will help us better understand how the plasma behaved during the first moments of the universe—and how it later evolved into the forms of matter that everything around us is made of."