All physical theory contains, either implicitly or explicitly, metaphysical components.
In the contemporary world physics is often thought to be the hardest of the 'hard' sciences, which is another way of saying that physics is that discipline most rigorously concerned with understanding the physical truths of the universe. When pressed, however, it is mildly shocking to discover that, although the actual existence of gravity is entirely unquestioned, its particular ontology is quite mysterious. In general it would seem that in order to retain explanatory power a concept must have an ontological status that is more fundamental than the phenomena it explains. Once the concept of gravity exists, it becomes possible to test its applicability in various ways, and through a careful process, the idea can be refined. Whitehead knew this, and when he brought his metaphysics into clear formulation in the late 1920's, he made a remarkable effort to include what he knew from the developing field of physics.