But, after all, who knows, and who can say,
Whence it all came, and how creation happened?
The gods themselves are later than creation,
so who knows truly whence it has arisen?

-         - Nasadiya Sukta, Rigveda (1700-1100 BC)

There are fierce debates over existence of God going on all over internet. At occasions, I have myself got into these arguments and each time I wished I shouldn’t have. In these debates, there were topics which would keep coming up again and again. Big bang and beginning of time is one of such topics.

Time line of Universe
As for the topic regarding ‘Big Bang and Beginning of Time’, it is generally understood and accepted that big bang is the origin of current universe. In the development of this universe, big bang is the first ‘incident’ in itself and also the root cause of universe. Being first incident, obviously time is measured from this incident. Technically, in the context of our universe, there is no point saying that time has no beginning. In debate over existence of God, atheists take this notion of time rather too literally. (On the other hand, theist’s position is even more pathetic.)  While debating, they themselves don’t offer any rationale. Instead they cite numerous scientific resources. Their statements go like this, “But Hawking himself had said this.” Or like this, “But it is scientifically established that time has no beginning.”  Clearly, debating this way is merely being evasive and believing ‘literally’ what have been said in science literature. (Science is the belief in the ignorance of experts. - Feynman) Interestingly, at many occasions I’ve been told that big bang can be demonstrated. I don’t know what it really means. The thing is: big bang model answers as many questions as it asks.