Can one of you prove that something immaterial can exists outside the human mind?
How does one prove the existence of something that leaves no trace whatsoever in the physical universe, and that can only be "seen" with the imagination? More importantly, how does one determine that it "exists" but that imaginary things do not? At this point, I really can't tell the difference.
Perhaps we should ask Lucy to materialize and show us the lunch money She took from Yahweh.
Well then, how do we prove something non-material exists? It's a good question and which Luk hasn't really an answer. There are, it seems to me, two possibilities here -
1. Something non-material exists. It cannot interact with the material world in any way. If this is the case for anything from a ghost to a god, then it follows that we cannot know of its existence - since we could never have contact with it - and it follows that any speculation on the existence is just that, speculation without evidence as evidence is not possible. Of course, if the object is a god, then that god is about as much use as the deist god and just about as in need of worship.
2. The non-material object can and does inter-act with the material world. in this case it ought to be simple to show that inter-action takes place and one can, by that means, demonstrate that the object exists. If it is a god, one ought to be able establish something about it. The claims by theists come into this category. They say they pray to their god and that he answers them, either in words or in actions. So, for theists, this should be easy to show.
So, that's how I see the job shaping up. Any happy theist like to show their god exists, that's how to do it.