No abstract

The present work reviews the facts of some models related to the dark matter and energy with variation of gravitational and cosmological constants with the cosmic time by giving the evidence in support of expanding universe due to Big Bang. Three important time epochs of BBN like Inflationary era, Radiation dominated era and Matter dominated era have also been discussed. The paper discusses also about the age of the universe using Hubble law in terms of Hubble constant and density parameter including the concept of space-time, geography of the universe, new cosmology, dark energy and some challenges and says that the correct theory of gravity is massive scalar-tensor gravity drawn from the detection of the gravitational wave from the collision of binary black holes as predicted by Albert Einstein's general theory of relativity, 100 years ago.