Relativistic Thermodynamics of Moving Systems

The rmodynamics is extended to systems moving with relativistic velocities. It is shown that one is led naturally, although not necessarily, to the thermodynamics of Ott, if one maintains the first and second law in their original form. The classical theory of Planck et al. can also be obtained in the case of a homogeneous fluid; the difference with Ott's theory is that the fluid alone is regarded as the thermodynamic system, rather than the fluid together with the box in which it is enclosed. Subsequently, a third form of relativistic thermodynamics is obtained by replacing the first law with a covariant equation expressing conservation of both energy and momentum. This leads to a formulation in which not only $S$ but also $T$ and $đQ$ are scalars. The discussion of heat transfer between systems with different velocities is thereby simplified. It is shown that such processes are irreversible even for equal temperatures, unless the velocities are equal too.