Why does a time frame needs to be a part of this equation?
You are basically telling me men are inferior, they can not do X, therefore Y exists.
I tell you that another men (who by your definition is inferior) said that Y exists. 
The only logical answer to this is that a man (who by your definition is inferior) claims that Y exists, but since he is inferior, why should I believe him...
Godel's incompleteness theorem shows that for no system of axioms is capable of proving all the truths of that system. As applied to this discussion - you can continue to move the goal posts requesting further proofs...
I am sure that in the past when someone suggested that men can fly someone told them that if god wanted men to fly they would have made them able to, and when this thing was solved, we will go to the next one until that one is solved and so on and so forth...
At the end it really comes to one of the belief systems...