But to the basic question: how do we know mankind is equipped to ask and answer questions about the world in a way that relates to the world in itself rather than simply our perspective? Since all sorts of creatures have variously developed senses of their surroundings, to accept that the perspective of the rational human represents objective reality, is to prioritise its perspective as being above all those other creatures. The human brain is therefore said to be the only known mind device in the universe capable of understanding the universe. But how can we be sure we are not misunderstanding the nature of the world in itself at such a basic level we can never see it?
The human brain isn't equipped for some questions for some pretty basic reasons. Captain Caveman has a habit of stopping and pondering the meaning of black and orange stripes and their relationship to the greater cosmos, Captain is now an ex-Caveman and that genetic line is extinct.
But... that still doesn't quite justify going all solipsistic on this for me. Because we
can formulate the difficult questions. We can ask whether a rock is pulled towards the earth or whether the earth is rushing up to meet it. The finite human brain seems very ill-equipped to deal with infinity, but we play around the edges and find out interesting things. We pose questions in maths and get back answers which lead to new questions and new frames of reference. Science is beginning to hit the point where we need to take stock again of what the meaning of 'truth' is because we are outrunning our capability to measure and verify theory, yet that's not a locked in condition. There may be ways round that, just as there were ways to prove the existence of wee bugs which caused disease rather than them being the result of a grumpy divine being having a morality strop.
And returning to my initial point, in a society/culture/environment shaped to encourage Captain Caveman's speculation those recessive genes and odd outputs of the grand genetic lottery which were once dead-ends stop being so. We're not immutably fixed as a species into how we are now, nor in how we perceive things as we do now. There's always room for progress :)