I've been asked from time to time how I can study physics and yet not believe in god (or gods). My reason is simple: I don't see any evidence for a god so why should I believe in one? What I will allow, as a possibility, is a creator. This is where most people get confused so I'm going to attempt to explain exactly what I mean.
As it stands science (precisely cosmology and quantum physics) cannot state what happened before the big bang; it's a singularity which means that the mathematics of describing the universe stops working. The upshot is that there is nothing that we observe that can tell us what happened 'before the big bang' even such a question is meaningless as we don't even know if time existed. The obvious assumption made by my theist friends is that this is where god (the creator) sits and makes the universe; therefore there is god; therefore that god is god X (normally the Christian God but change as appropriate). It's the last two assumptions that I have a problem with; there is no reason that the creator is still here and certainly no reason to believe (s)he is god X.
So I believe a creator is possible: although I don't believe there is one, I just acknowledge that there is no way to make a definitive statement either way. If there was a creator (s)he doesn't seem interested in making her/himself known to us even if (s)he is still there.
The final point I think I've made before but I hope to put it more elegantly: in all odds any creator is a computer programmer. Our society has made virtual worlds and there is no reason to assume that you would be able to tell that you were in a simulation over the real thing (no, if you squint hard enough you don't get to see the world as green lines of text you just get a headache) so there are pretty good odds that a more advanced civilisation has just simulated our world.
In summary: there is no god, there might be a creator but if there is he's most likely using this world for porn (don't believe me? how much of the 'net is porn... there you go).