All fields have golden ages.  One which is now underway is to create a "Quark-Gluon Plasma" by the collisions of heavy ions at very high energies. This is interesting not just for the intrinsic beauty of the subject, but because of the sociology of the field: a billion dollar machine constructed because it could be, and where experiments with hundreds of physicists delivered a vast quantity of beautiful results.

I begin by reviewing modern field theories: first Abelian (photons, which comprise light), then non-Abelian (the modern theory of neutrons and protons).  In both cases, theories which can be written down in one line yield amazing complexity.



The field is underpinned by the ability to do numerical simulations of the fundamental theory in thermal equilibrium, which I summarize.  I also discuss theoretical understanding, including computations in exactly soluble models (AdS/CFT).



I then turn to experiment, and describe the basic evidence that at the heavy ion colliders at Brookhaven and at CERN, there is a qualitatively new phase created, a Quark-Gluon Plasma.