Before revision: This leaves open the question of what is 'natural' , but one common understanding of the claim is that everything in the world is ultimately explicable in the terms of physics.
After revision: (in physicalism 'natural' means procedural, causally coherent or all effect have particular causes regardless of human knowledge and interpretation and it also means 'ontological reality' and not just an hypothesis or a calculational technique)This leaves open the question of what is 'natural' , but one common understanding of the claim is that everything in the world is ultimately explicable in the terms of physics.