bioramani
The last and 18th Purana called Brahmanda Purana describes how the whole universe came from a small egg that exploded.
My contention is that to claim that they thought of Big Bang based on this is untenable because the rest of that scripture goes into a pantheon of divine personalities.
A slight digression :-
I would like to add that the Big Bang is not an explosion in the normal sense of the word.
Whenever a bomb explodes the volume of space which the matter occupies increases but no change occurs in space as such.
But in the case of Big Bang space itself expands. That is to say the distance between any two objects increases. And the farther they are the more the distance between them increases.
An exploding bomb has a surrounding space to expand into. Whereas in case of Big Bang the expanding 'space' doesn't have anything 'outside' it to expand into , since what could be 'outside' the Universe.
An interesting read from Scientific American :- #-Link-Snipped-# .
Anyways my point is , this is definitely not what the verse in the Brahmanda purana implies.
The big bang theory is not the final word in cosmology , as initial boundary conditions are yet unexplained. There are many competing theories currently doing the rounds.
That some of them matches one or the other theology is a matter of coincidence. For example , the cyclic universe model will always be compared to our theology.
Since the past 3-5 millennia there have no doubt been various hypotheses produced around the world , only in today's age have we built the technology which can lead us forward to verify some of the hypotheses :-
1) <a href="https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe" target="_blank" rel="nofollow noopener noreferrer">Wilkinson Microwave Anisotropy Probe</a>
2) <a href="https://en.wikipedia.org/wiki/Planck_(spacecraft)" target="_blank" rel="nofollow noopener noreferrer">Planck (Spacecraft)</a>
The major difference between ancient science and modern science is the importance given to fact verification.
The ancients all over the world used to feel real knowledge can be gained via thought alone hence subjects such as Mathematics were very well developed.
The modern scientists feel some knowledge can be obtained only via experiments i.e the knowledge of facts.