In Hindu mythology the fact is something else it says" GOD IS DRIVING FORCE" of this universe.As big-bang happened first word AUM came into existence.After that time till today this force exists.This force(GOD) always Drive the nature for the betterment of this universe. three type of forces Bramha the creator, Vishnu who looks after the universe, Shiva the destroyer.without any partiality .So question arises here what is the need to destroy .The Answer is simple, to maintain the system .