Comment by amai

Nice, but uniting Newtonian physics with Navier-Stokes equations is „easy“.

It is much more difficult to do the same and unite relativistic mechanics with relativistic fluid mechanics. The fact that in relativity you have to deal with particle creation and annihilation makes the issue much much harder, because particle number is not conserved and it is difficult to define probability densities if the particle number is not constant. And in addition each particle has its own proper time, so a standard phase space does‘t exist. It might well be that the idea of point-particles and relativity are in some sense incompatible even at the classical level.