Edited sentence: For good Popperian reasons, this implicit metaphysical thesis needs to be made explicit within physics so that it can be critically assessed and, we may hope, improved.Nicholas Maxwell has argued that physics only accepts theories that are sufficiently unified, this persistent preference for unity committing physics to accepting an implicit metaphysical (i.Popper's demarcation criterion is refuted: an unfalsifiable, metaphysical thesis is a basic tenet of scientific knowledge within physics, whether this is recognized or not.non-falsifiable) thesis concerning the unity of nature