On the interpretation of heat in relativistic thermodynamics

This article investigates the interpretation of the right-hand side of the relativistic second law of thermodynamics (φ0dx^μ/ds)μ(-g)^(1/2)dx^1dx^2dx^3dx^4≧dQ0/T0 and shows that the quantity dQ0 can be interpreted as the heat—measured by a local observer at rest in the fluid at the point of interest—which flows relative to the fluid into an element of the fluid having the instantaneous proper volume dV0 during the proper time dt0, where these quantities are chosen so as to satisfy the numerical equality dV0dt0=(-g)^(1/2)dx^1dx^2dx^3dx^4 and the quantity T0 is taken as the temperature ascribed to this heat by the local observer.