Just supposing. . . . . . . Just supposing. . . . . (theists should find this easy) that there was say, an alien living on Mars looking down at what is happening on planet Earth.
Given that the alien could not give a toss either way whether or not there is a God, how could that alien determine who is right?
The theists who say there is a God, or
The atheists who say there is no God?