Cosmology is the study of the universe as a whole. Matter in the universe is found to be distributed in agglomerations of stars, galaxies and clusters of galaxies. Cosmology treats this distribution as a fine structure, which is ignored in the zeroth approximation, and the universe is described in the continumm approximation, i.e., via a cosmological fluid. The cosmological fluid has the property of being isotropic and homogenous ; in other words, of being isotropic and homogenous about every spatial point. This means that on a sufficiently large scale, there is no privileged direction or a privileged location in the universe. The hypothesis that the universe is homogenous and isotropic is known as the ‘Cosmological Principle’ and is the working assumption in designing a mathematical model of the universe. A comprehensive discussion is presented in this paper as to how such models may be designed on the basis of these simplying assumptions.
Keywords Cosmology, Cosmological Principle, Homogeneity, Isotropy.