Some people think it's funny to try to get an atheist to say that God exists.
"See that pillow over there? Well, that pillow's God."
"Do you believe in that pillow?"
"Then you believe in God!"
Wait just one second.
As this example demonstrates, God is a concept that needs futher definition in order to claim belief or disbelief.
Define God as an omnipresent being, a He (or a She), the popular definition, the Christian, Jewish, Muslim and any other monotheistic religion's definition, a being who consciously manipulates and creates, a deity with a shape and plan--then I remain an atheist.
Define God as light, and then we are getting somewhere.
Light, in this definition, would be the sum total of every photon in the universe. For a photon, space and time are nonentities, thanks to relativity, so thus, by my half-baked theory, every photon would be everywhere and everywhen at all times. Omnipresent and immortal. God. So there.
However, until a degree in religion requires a mastery of quantum physics and houses of worship bear statues of the Prophets Einstein and Schrodinger, I will remain an atheist.
By the way, I dreamt up Photonism last night while staring up at my bedroom ceiling, so it isn't exactly an official doctrine. The fact that I don't believe in a god, as I just made evident, makes it a whole hell of a lot easier to make one up.