This talk begins with a brief introduction of the standard model of particle physics and cosmology, which will be followed with a detailed description of the physics motivations and the experimental efforts at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory.  The focus of this talk will be on the recent result from the PHENIX experiment at RHIC and its implication for probing the initial temperature of the matter a few microseconds after the Big Bang.