An introduction to modern ideas on cosmology and on the physical basis of the general theory of relativity. The title reflects the authors contention that the remarkable degree of isotropy, rather than the expansions, can be regarded as the central observational feature of the universe. The various theories and ideas in "big bang" cosmology are discussed, providing an insight into current problems. The book is written at an intermediate level, beyond that of the many elementary books on cosmology, as an introduction to the more advanced works and research literature.