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of state for ideal hydrodynamics and the stress fields for second order viscous Israel-Stewart hydrodynamics; see Fig. 2.1. Strong evidence for a deconfined QGP could come from a robust result whereby hydrodynamics with a QGP equation of state (EOS) reproduces experimental data while hydro with a hadronic EOS does not. It is interesting to note that the original conception of the QGP was of a weakly interacting plasma of deconfined quarks and gluons. For hydrodynamics to be useful, though, thermalization after the violent nuclear collisions must be both rapid and sustained. This of course requires a strongly coupled quark gluon plasma, or sQGP, as named in [103, 104]; here ‘strong’ refers not to the strong force, but rather to the ratio of potential to kinetic energy, Γ, being greater than 1. However, this is not a universally accepted naming convention. [86] takes these properties as assumed and refers only to a QGP; for a more detailed discussion see [77]. 

Since hydrodynamics predicts the evolution of the entirety of the bulk there are a number of observables that can be compared to data. The simplest is single the particle spectra and their angular distribution with respect to the reaction plane. It is useful to Fourier expand the detected distribution, 

<img src='content_image/313045.jpg'>

where the normalization dN ( p$_{T}$ ) and v$_{2}$ , or azimuthal anisotropy, are the two most important moments for heavy ion collisions. Early results from Rhic and ideal hydrodynamics were quite promising: while the v$_{2}$ of particle yields 

