What existed before the Big Bang?

The big bang, as we commonly term the colossal expansion of the universe, was, to say it simply, the beginning of everything. Including Space and Time. The notion ofbefore and after is relevant only with reference to a given time. But when there is notime, no events taking place, how can you say anything occurred before something else did? 
The big bang is considered as the absolute beginning of the observable universe.

According to modern physics, even nothingness, or absolute vacuum has energy. That means, even nothing has something. So we cannot even say that there was nothing before the big bang! It was the origin of everything, including nothing...