Here i will use the atheists own science to answer that question once and for all using the basics of special relitivity:
The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.
this here is a well known fact amongst scientists, however they discount the omnipotence of god
god, through his devine power can move at infinity multiples of c
however, anything that moves faster than light is prone to time travel
according to this equation if you travel beyond the speed of light "c" time becomes negative since gamma becomes negative; god can time travel!
now this was a popular paradox http://en.wikipedia.org/wiki/Grandfather_paradox
basically if you go back in time and kill your grandfather you can become him, ergo, how god exists and has always existed for ever and ever
