KICK ASS QUESTION. I remember asking my slightly religious science teacher that in junior high/high school.
What makes sense to me is a concept close to that which science defines
energy as - something that can neither be:
i) created
ii) destroyed
So if you have something that i) cannot be created and ii) cannot be destroyed....the only thing that makes sense to me is something that "has always been".
Something similar to a circle, with no beginning and no end. Something that "always was, is, and shall be".
Another alternative view is that god/the creator (whatever you wan to call it)...Let's call it "Mr. Big ChrisBa" was something non physical that projected itself onto the world. So "Mr. Big ChrisBa" had the idea of a universe and projected that idea from the nonphysical to the physical, sort of like how you have an idea of a building which is something nonphysical and eventually it becomes something physical - the building.
But what is the "real" building - the idea or the building? If we destroy the building and don't have a blueprint of it, we can never reproduce it. But if he have an idea of that blueprint in our mind, no matter how many times that building gets wiped out, as long as we have the idea of the building close at had (the nonphysical thing), we can reproduce the physical thing.
This is similar to Socrates' theory of correspondence that everything in the physical world has it's origin in an idea.
Just some thoughts - can't claim I came up with them myself unfortunately