While Nuclear Physics has long been concerned with understanding the properties of the atomic nucleus, the field of High Energy Nuclear Physics is concerned with what happens to nuclear matter at extreme temperatures and densities. For example, is there a new phase (or phases) of nuclear matter at high temperatures and densities and what phenomena does nuclear matter exhibit in these conditions. Experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven, have shown that it is possible to use collisions of gold nuclei in a particle accelerator to recreate the quark gluon plasma, the primordial fluid created in the first microseconds after the big bang. This fluid is almost perfect, in the sense of having the lowest observed resistance to flow (technically, ratio of viscosity to entropy density) of any known substance. Heavy ion collisions are also produced at the Large Hadron Collider at CERN and continue to probe the properties of nuclear matter at even higher collision energies.