We Can't Know the Highest Prime Number Because There Isn't One

There is much we cannot know. But we can know we just have to keep looking. We experience or indeed we are the experience of electrical crackles as David Deutsch. That's what we are. Our brain interprets these synaptic firings, which themselves give rise to what we see and hear and feel. And consciousness is part of reality as well by the way. When the next supernova occurs in a galaxy, millions of light years away, that's objective reality that is independent of our consciousness.