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