You are making up a magical unicorn extreme example. Yes technically you cannot use deductive reasoning to prove there are no angels or gods or supernatural ent

You are making up a magical unicorn extreme example. Yes technically you cannot use deductive reasoning to prove there are no angels or gods or supernatural entities we cannot see. For our purposes an extraterrestrial intergalactic species that could reach our planet would be exactly what you just described. We cannot prove these entities are not out there. Just remember science and reason do not allow us say anything with certainty that cannot be calculated or measured, it’s just as much a fallacious religion to claim they don’t exist as they do, one real risk is what happens if either side is correct. If you are correct and aliens do not exist, it doesn’t matter at all however if you are wrong and they do, there are entire classes of possible dystopian and utopian realities that become actual possibilities. Moderate Preparation and risk minimization is really all anyone can do to address the unknown.