I have no concrete proof that God exists but I believe in my heart and soul that he does.
I think your belief is questionable, but I cannot fault you for having that belief, since I am not you and do not know your experiences.
If Boss did not, in his bumptiousness, go beyond your chaste and limited expression of faith, I would have no quarrel with him.
It is his unsupported assertion that his private experience, or the private experiences of other people,
PROVE the existence of God, or a spiritual realm, that I reject.
PROOF can only exist in the public realm, where scientific analysis can be applied to a matter -- and even then, that proof is always provisional and questionable. No private opinion, no matter how deep the conviction with which it is held, can ever constitute PROOF!!
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And this is articulated in the OP, first couple of paragraphs. We have to define what is meant by "proof" in order to debate the question. Well, if you reject spiritual evidence, you can't ever find proof of spiritual nature. The definitive proof can only be fully realized if you accept spiritual nature exists in a spiritual sense. Your argument is the same argument that non-believers always present, there is no physical evidence to prove God's existence... I fully understand that, and haven't disputed it. In fact, I went on to add, that physical evidence will never be able to definitively prove God, or God becomes physical in nature.
Furthermore, I did indeed apply science to the question. The particular science applied, was Ethology, the study of animal behavior. We have compelling evidence that human spirituality has always existed in civilized man, and is as prevalent today as ever. This was countered with studies showing a decline in religion, but it's entirely possible for humans to behave spiritually, and not belong to a religion. The fact remains, human spirituality is our most defining and unique behavioral attribute.
From our studies in Ethology of other living things and their behaviors, we know that behaviors don't simply exist for no tangible reason. Even when we can't clearly rationalize the behavior, if we study long enough, we find that the behavior indeed has fundamental purpose. What we have never seen in nature, in any other living thing, is the imaginary creation of behavior by a species, to enable some fundamental aspect. So if this is the case with human spirituality, it is the only such instance in all recorded history of animal behavior. In fact, it would completely defy everything we understand about behaviors and how they evolve.
Many species met their demise, clinging to irrational behaviors or not adapting to more rational behavior, but humans have thrived and excelled like no other living thing. This "proves" the human spirituality behavior is indeed, fundamental and rational.
Now, how can this be, if we're not connecting to something? It's as if you plug a lamp into a dead socket, and it works, but the socket is dead. If we believe we are connecting to something, and this belief is beneficial and fundamental to what we are and what we've become, and this belief remains virtually unchanged throughout our existence as a species, there MUST be something there. It's impossible for this to be imaginary or delusional, because it would have vanished long ago, as there would have been no tangible benefit realized. We have billions (maybe trillions) of people, through ages of human history, professing the belief in something spiritual, attesting to the benefits known as blessings.