  5-dimensional special relativity can be considered as the 5-dimensional
extension of Carmeli's cosmological special relativity, as well as the flat
specialization of 5-d brane world theory. To this framework we add a
5-dimensional perfect fluid stress-energy tensor, and unify the equations of
perfect hydrodynamics in a single 5-dimensional tensor conservation law. This
picture permits to interpret particle production phenomena as cosmological
effects, in the spirit of open system cosmology. The source of particle
production vanishes if the fluid is isentropic. Moreover the hydrodynamical
equations can be interpreted in terms of a scale factor, giving rise to a set
of equations which simulate in a sense Friedmann cosmology.
