Relativistic theories of dissipative fluids

The simple Navier–Stokes equations for dissipative fluids, translated into relativity, form a parabolic—and hence mathematically nonviable—system. There have been formulated numerous alternative theories, consisting instead of hyperbolic equations—theories that necessarily involve more dynamical variables and more free functions than does the simple Navier–Stokes theory. It is argued that, these mathematical differences notwithstanding, the physical content of these hyperbolic theories is in most cases precisely the same as that of Navier–Stokes.