Although I am not an athiest, I think I can still answer your question. An athiest does not have a 'religion', but believes that science has answered many of the questions about the creation of the universe, the earth and other phenomena that for many centuries the 'church' said were all created by God. It is difficult to deny what science has proved to be factual. We can see the bones of the dinosaurs, we have been to the moon, and studied it's dirt and rocks. I saw a documentary a week or so ago, and Stephen Hawking was the narrator. He is also the one that had people in an uproar over his latest book, professing the belief that God did not create the world or the universe.
His commentary was very hard to dismiss. And, for me, being an intelligent person, and believing in science and the theories of Darwin, and also believing in God, it did make me do some serious thinking. I myself have decided that I will not lose my faith, and here is the reason why. At the end of the documentary, Hawkings said that the creation of the universe came as a 'Bang'. Just that, a 'Bang'. Even he could not explain it fully. So, why not God doing the 'Big Bang'?