The assumption in science is that we accept everything tentatively. It is always possible that future experiments will invalidate what we know. Newton’s laws were fine until relativity and quantum mechanics overrode them.
As for facts beyond the human brain, I invoke Occam’s Razor. Since there is no way of demonstrating a fact beyond human intelligence, we might as well assume we can know everything there is to be known.
Math is a special case. Philosopher and mathematician Bertrand Russell had this to say about math:
Mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true.
This was said somewhat tongue in cheek. What it means is that mathematics is based on axioms for undefined terms. A statement is true if it follows from the axioms. Mathematicians are free to choose any set of axioms they want provided that it is consistent, meaning that you can not both prove a statement A and the statement “not A”.