To make this out, that there is no God, he would need to travel abroad over the surrounding universe, till he had exhausted it, and to search backward through all the hidden recesses of eternity; to traverse in every direction the plains of infinitude, and sweep the outskirts of that space which is itself interminable; and then bring back to this little world of ours the report of a universal blank, wherein he had not met with one movement of a presiding God. For man not to know of a God, he has only to sink beneath the level of our common nature. But to deny Him, he must be a god himself. He must arrogate the ubiquity and omniscience of the Godhead.
Dr. Chalmers.
The point
An atheist would need omniscience spanning all space and time to prove God's non-existence; instead, claiming no God makes one a god.