Cosmology, Thermodynamics and Matter Creation

Several approaches to the matter creation problem in the context of cosmological models are summarily reviewed. A covariant formulation of the general relativistic imperfect simple fluid endowed with a process of matter creation is presented. By considering the standard big bang model, it is shown how the recent results of Prigogine et alii \cite{1} can be recovered and, at the same time their limits of validity are explicited.