I would usually answer "ok, so how did god come from nothing?"
So, I don't consider myself educated on this matter of the big bang or the beginning of the universe, but I've read across some points regarding chaos and particles spontaneuosly coming in and out of existence - and as such would like some dialogue regarding the first stages of the big bang.
Or, in simple terms:
Explain the chaos theory
Explain evidence behind it (yes, I know its only a "theory" and as such, probably lacks solid evidence - but so does God, yet theists cling to that)
Explain other possible/probable causes to the universe (if indeed it had a "cause")
Now, before we get "ha! You can't explain it - therefore God exists", we must also face the fact that there is no evidence of a creator (as far as I know). And of course, if the simple answer is "we don't know what happened" then it gives us no reason to assume it was some divine being.


