Christians will say "what about the big bang and how can you get something from nothing?"

My response? They start from an improper premise that there was "nothing". They accept an ever-existing deity, but can't accept an ever-existing natural universe?

And there is some evidence that there wasn't one Big Bang to prove their "Let their be light" premise. The universe can be expanding and later contracting only to "bang" and begin expanding again.

There is no deity. Conditions for life on earth were coincidental and sparked by lightning.