I don't see a hard line between math, then physics, then the 'real' world. They are levels of formalization. Both in math and in the real world we don't have '

I don't see a hard line between math, then physics, then the 'real' world. They are levels of formalization. Both in math and in the real world we don't have 'perfect observation'. There is plenty of conjectures in math and the real world that lack a proof of something being true or false. I think "can't prove a negative" is one of the least informative ways of trying to say something, I assume he meant to say "absence of evidence is not evidence of absence" or perhaps "absence and evidence don't commute"