The Big Bang Theory hypothesizes that the universe had a singular beginning. This theory is derived from the observations that the universe is outwardly expanding in all directions.
The Big Bang Theory and the Law of Entropy working together clearly show the universe to have an origin. We cannot make believe that the universe is eternal and has always existed. What could have came before the origin of the universe? From nothing, nothing comes, so there must have been something before the universe's beginning. Something must have existed before the universe, right?