2.1 In non-central heavy ion collisions there is initial spatial aniso- tropy that the resultant collective pressure gradients evolve into anisotropy in momentum space. Hydrodynamics aims to quan- titatively model this process to gain information on the medium and its properties. Figure adapted from [105]. . . . . . . . . . 16 2.2 (a) v$_{2}$ scaled to the initial spacial eccentricity, ϵ , as a function of the charge particle density per unit transverse area. low- p$_{T}$ flow at previous colliders fell far short of the hydrodnamic limit, which is reached for the first time at$_{Rhic}$. Figure adapted from [107]. (b) Early azimuthal asymmetry, v$_{2}$ ( p$_{T}$ ), predictions from [106] compared to Rhic data [108] as adapted from [77]. . . . 17 2.3 HBT parameters [109, 110] compared to various hydrodynam- ics calculations [111–113]; none describe the data well. Figure adapted from [77]. . . . . . . . . . . . . . . . . . . . . . . . . 18 2.4 Recent calculations including hadronic rescattering [116] that show the influence of the initial conditions (IC) on the output. For diffuse, Glauber-like IC ideal hydrodynamics slightly un- derpredicts data whereas sharper CGC-like IC require viscous effects to follow the experimental trend. . . . . . . . . . . . . . 19 2.5 An illustration of A + B → h + X in a heavy ion collision. We assume factorization still holds such that the main alteration to p + p collisions, Eq. (2.2), is the addition of a theoretically calculable P ( ϵ ) encapsulating the in-medium energy loss. . . . 27 viii