As my professor was fond of saying, "In your entire scientific career, if you discover just one fact, consider yourself lucky."
The last I heard they were still working on a device that was supposed to actually "measure" gravity. Until that happens, I think it's still a theory.
Much of science at present is really the technology of describing how something works, its properties. I don't think we have a clue as to what electricity really is, and what its ultimate origin is, much less gravity, which is a mystery.