Why debate the theory? Just enjoy the awesome tv show named after it! :)
To get to the theory ... the red shift (and Hubble). If you're referring to how the big bang began, science has no answer.
Now How Would We Know EXACTLY How Big It Is And/Or Was?! We Aren't That Clever You Know! ¬¬ Go Ask Alister... The big bang is still happening today, as the universe is still expanding. So the...
According to Astronomers, it's still going and going and going because the Universe is constantly expanding.
The only thing known is that the singularity was subatomic. All singularities are infinitely small. That is, they have zero volume. They have no size.