Dark Energy as a Natural Property of Cosmic Polytropes—A Tutorial

A conventional approach to the dark energy (DE) concept is reviewed and discussed. According it, there absolutely no need for a novel DE component in universe, provided that its matter–energy content represented by perfect fluid whose volume elements perform polytropic flows. When (thermodynamic) of associated internal motions taken into account as an additional source universal gravitational field, it compensates needed compromise spatial flatness accelerating universe. The unified model which driven not only interprets observations with universe expansion but successfully confronts all current issues cosmological significance, thus arising viable alternative ΛCDM model.