Relativity and Thermodynamics
The classical thermodynamic theory lies on the idea that the mass within an isolated system is invariant with time, no matter if the process is reversible or irreversible. This admission doesn't take into account Einstein's famous mass/energy relation E = mc2, that revealed a new concept on how to explain inconsistencies between theoretical and experimental values of energy and mass before and after a process has taken place.
J.-L.Tane proposed that the internal energy U of the system increases for irreversible processes:
dUirr > dUrev
More particularly, the increase in energy is accompanied by a decrease in mass:
dUirr = dUrev – dE or dUirr = dUrev – c2dm
and for the second law: dQirr > dQrev
The use of relativity has interpreted the increase in entropy, as an increase in energy, linked to a correlative decrease in mass. In other words, the concept of entropy has been substituted by the concept of increase in energy, making it unnecessary for the description of an isolated thermodynamic system.