of the degrees of freedom and the equation of state of the medium. These are of course the golden measurements for demonstrating deconfinement, thermal- ization, and a QCD phase transition. Heavy ion collisions may also form the most perfect fluid and provide the most stunning example of the application of string theoretic techniques to phenomenology. Hydrodynamics is a tough business for even qualitative discoveries, though, as so little of the process is under theoretical or experimental control. The initial state, so crucial in determining the final state, is up for grabs. Viscous corrections during the fluid evolution phase are not well understood. And the transition to detected particles through low-momentum hadronization is nonperturbative and not independently measurable. 

High- p$_{T}$ physics has the advantage of an initial state well under control theoretically and experimentally, although current techniques at best have significant error for heavy quarks. Similarly the fragmentation into hadrons is an independently measured vacuum process that necessarily translates to light meson production, although this may not hold for heavy quarks. The chal- lenge comes in deriving a confident theoretical description of the in-medium energy loss mechanisms. With this in hand one has the possibility of inverting the energy loss process using the theory to quantify properties of the medium, yielding jet tomography. The original hope that a single uncontroversial the- ory of final state energy loss would emerge from the theoretical community and immediately agree quantitatively with data has been dashed. There are currently four different major pQCD models of radiative energy loss and a 

