Rosala, the "Big Bang" is a theory about the formation of the universe..........you can read about it here: http://en.wikipedia.org/wiki/Big_Bang

Accoding to Wikipedia, the Big Bang happened about 13.8 billion years ago.

The (approximate) number of seconds in a year = 3600 x 24 x 365 = 31,536,000

So

(13.8 x 10⁹) x (3.1536 x 10⁷) = 435196800000000000 ≈ 4.351968 x 10¹⁷ seconds ago

(Of course......a few more seconds have elasped as I've been writing all of this....minor adjustments may be necessary.....)

CPhill what is big bang?

The 'big bang' is merely a conjecture, a working theory, it's unproven.  Astrophysicists could come up with a new, different, theory sometime in the future.

oh thank you CPhill for telling me i'll give u a point for that!