It has been widely believed that the relativistic Navier-Stokes equations violate the basic physical
requirements of equilibrium stability and causality, and therefore can not be used for practical simulations of relativistic fluids. In this talk, I will discuss why this belief is unfounded. There is not one, but infinitely many Navier-Stokes equations because there are infinitely many conventions that can be used to define what one means by "fluid temperature", "fluid velocity" etc. out of equilibrium. The early works on relativistic hydrodynamics (Eckart, Landau-Lifshitz) have indeed adopted conventions that lead to unphysical predictions. On the other hand, when one adopts physically sensible conventions, the resulting relativistic Navier-Stokes equations are both stable and causal.
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