You can't Prove concretely your father loves you, you have to infer from his actions.
My example with photosynthesis was chosen because you can't see it with the human eye, but you have to break it down and examine it. In truth, you still have to take a fair amount on faith, inspite of enzymatic extraction etc. because an everyday person just doesn't have access to appropriate equipment.
This all moot though as I happen to think the more savy the people involved the less N-S accounts for communication issues. When there is disparity of intellectual capacity on either side that's where the trouble lies.