SEMINAR     SEMINAR   Thursday, May 11th, 2006- h. 15.00  Seminar room (A34)         Alberto Accardi Columbia University         The perfectly liquid Quark-Gluon Plasma               According to the American Physical Society, the top physic story for 2005 has been the discovery of the Quark-Gluon Plasma, a deconfined state of quarks and gluons at high temperature, at the Relativistic Heavy Ion Collider (RHIC). The fireball made in these collisions -- which reproduces to a good extent the conditions of the primordial universe only a few microseconds after the big bang -- was not a gas of weakly interacting quarks and gluons as earlier expected, but something more like a "perfect" liquid of strongly interacting quarks and gluons. In this talk, I will review the evidence leading to the claimed discovery of the "perfectly fluid QGP" and the new theoretical and experimental challenges brought forward by such a discovery. I will conclude with a brief glimpse at the future of heavy-ion collisions at the Large Hadron Collider (LHC) of Geneva, which will soon begin its operations.