Once the big bang takes place and the universe begins its expansion, entropy starts to increase. From this point on it will never be able to go back to its original state. There are some additional interesting theological implications to big bang theory. Let's assume for discussion sake that there is a God and that He has revealed Himself to man and has maintained some degree of testimony to man over the ages. Then, we would expect amongst the world's religions there would be at least one if not more that would be authentic.
Hindu religion presents eternity as an endless repetition of cyclic processes.
For instance, reincarnation is one of the expressions of the underlying cyclic philosophy. Hence, if there is a God and if Hindu philosophy applies to science, then we would expect to see an eternal sequence of big bangs followed by big crunches. An endless sequence of cycles repeated over and over would be consistent with Hindu concepts of God and the universe. However, this is not what we see and a unique, one-time, singular big bang is inconsistent with this philosophy. Judaism presents creation as taking place at a point in time by a deliberate, willful, predetermined, planned act of God.