Studying the Early Universe via Quark-Gluon Plasma

Shortly after the Big Bang, the early universe is a high temperature and high density environment. In order to recreate this state of matter in the laboratory, a little bang was created by colliding heavy ions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and subsequently at the Large Hadron Collider (LHC) at CERN. From the most energetic collision at RHIC, the created temperature is estimated to be at least 221 MeV, where the quarks in the nucleon will no longer be confined and a new state of matter, quark-gluon plasma (QGP), is formed. Detailed studies of the QGP, reveal that QGP has the lowest “shear viscosity to entropy ratio” which is close to the lowest bound determined from quantum mechanics. This makes QGP the “most perfect fluid” in universe. The measured properties of QGP should also provide constraints for theoretical models of the early universe.