Ethan Siegel in How Good is Your Theory? Open Thread I : Starts With A Bang : Starts With A Bang, describes these levels of support, which I have numbered:
- 3: Scientific Law. Very well-supported theories that have successfully passed numerous tests.
- 2: Validated. Well-supported but with some problems, like unconfirmed or untested parts.
- 1: Speculative. May or may not be testable. Often gets a lot of publicity, however.
- 0: Ruled Out. The opposite of the first category.
Ethan Siegel’s spectrum is, I think, a good way of comparing the level of support for various theories, and it is a good antidote for “scientists always change their theories!” arguments. Many theories come and go, but they are usually on the speculative side, around 1. Those that get promoted to 2 or 3 usually last. Some of them may get their domains of validity restricted, as with Newtonian mechanics after the rise of relativity and quantum mechanics, but they still remain very successful theories within those domains.