Question

why the steady state theory of origin of the universe has been rejected

Answer 1

The steady state theory says that the universe has always existed and that matter is continually being made in order to expand the universe. There is evidence now of a finite universe through discoveries such as the cosmological background radiation which points towards a big bang. Because there is evidence of the big bang, the universe has a finite age and thus has not been continually creating matter to expand the universe.