Relativistic heavy ion collisions: open-quotes Re-creatingclose quotes the early universe in the laboratory

Central nuclear collisions at energies of many GeV/nucleon may provide for conditions similar to those in the early universe during the first few microseconds, where the transition from highly excited hadronic matter into quark matter or quark-gluon plasma can be probed. Here, the author reviews the current understanding of the physical properties of a quark-gluon plasma and reviews ideas about the nature of, and signals for, the deconfinement transition. The author also discusses recent progress in the treatment of the formation of a thermalized state at the QCD parton level