We Can Have Explanations That Reach the Entire Universe

David Deutsch presents at the beginning of The Fabric of Reality this idea that you don't need to know absolutely every single fact that needs to be known in order to understand fundamentally everything that can be understood. He was presenting this vision: there are certain fundamental theories in science and outside of science. His four theories that he had were quantum theory, the theory of computation, a theory of epistemology, and evolution by natural selection. These together formed a worldview—a lens through which you could understand anything that could be understood.

I saw a beautiful video with him on YouTube where he was making the same points. He was saying you don't have to memorize and know every fact, you don't have to know where every particle moved. But if you understand the deep underlying theories behind everything, then you know at a high level how everything works. This can all be understood by a single person, a single brain, a single human being. It's accessible to anybody, and that is a jaw-droppingly powerful idea.

We can have explanations that can reach the entire universe, and it's worth going through the four that you'd mentioned. Quantum theory is one of them, the theory of computation is another one of them, the theory of evolution is another one of them, and then the theory of knowledge or epistemology is the fourth. That's the way he presented it in The Fabric of Reality.

Is it interesting that relativity is not in there? He regards quantum theory as being deeper than the theory of relativity. At some point, most physicists expect that we're going to have a unification of quantum theory and relativity. That's not to say that in that worldview we're dismissing relativity, but his guess is that quantum theory will be more foundational than what the theory of relativity is. There'll be a spacetime of the multiverse—that's why relativity doesn't appear amongst them.