He isn't, he's claiming we know the boundries. We and others will know how to use science within those boundries better. We won't and no other beings can change those boundries.
We don't though. And no worthwhile scientist will believe we do either.
Gravity was once a boundary. But before it was, that we had no idea it existed. The sea was once a boundary, so was the air. Things visible to the naked eye were a boundary.
I can understand people having a view on this or that regarding the universe, and what we may or may not see happen in our own lifetime. But I just don't get this stance that what we know, is all there is to know. When literally every passing even half-century changes that.