If it's well tested, and the results are repeatable, and no contradictions are found,
and it makes successful predictions, then you can start calling it a scientific "law".
(Even though it's still "only a theory", and it always will be, because it's not possible
to prove it, like the theory that the Earth orbits the sun, and the theory that heat
always flows from hot things to cold things, and the theory that the air in the room
can never all bunch up in one corner and leave you to suffocate on the other side.)