Hi Jan, I guess that answer lies whether you believe whether a falling tree in the woods makes a sound. Haha, But yes, of course reality and truth exists outside of human perception. I always thought (philosophical) Epistemology can also translate to the study of the nature, parameters and limits of human knowledge. To answer your last question: "All that cannot be known" is what lies outside our perceptions and consciousness. And "all that cannot be known" indeed has been proved to empirically exist :)