All right, reason it out. I propose as a "scientific" belief that all rivers have an invisible nymph that looks after the river. This is, in principle, something that cannot be tested. Now, you're a scientist, and you want to make your mark on the world by working on "nymph theory." Whatcha gonna do with this "theory"? What's your first move?
My first move is to ask a simple question:
What evidence or warrant is there to suggest the invisible nymph is there?
It's not that the invisible nymph isn't possible. It's just that I am not inclined to believe such a nymph exists without something more than your statement concerning the matter.