Somewhere in The God Delusion, Dawkins proposes a thought experiment. A universe without God, he suggests, would be very different from a universe with God. And for this reason, science and religion are not entirely separate from each other, dealing with separate spheres, but have an important area of overlap – that is, the existence of God.
Try to imagine, if you will, two parallel universes – the one with God and the other without. Are they different?
The experiment sounds very simple on the surface but is actually very difficult. For either an atheist, or a theist, I think the construction of a universe opposite from what you believe in is very hard. But I think that it is not just difficult to imagine a universe without God: it is actually impossible for one to exist.