A perfect fluid can be completely characterized by its rest frame mass density and isotropic pressure .
Specifically, perfect fluids have no shear stresses, viscosity, or heat conduction.
Real fluids are “sticky” and contain (and conduct) heat.
Perfect fluids are idealized models in which these possibilities are neglected.
Specifically, perfect fluids have no shear stresses, viscosity, or heat conduction.
An adiabatic thermodynamic process occurs without transferring heat or mass between the thermodynamic system and its environment.
Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work.
Therefore, the stress–energy tensor of a perfect fluid contains only the diagonal components
