Then what about Bohmian mechanics? Is it a T3, or is it just a metaphor?So my understanding is, that T1 (Heisenberg) and T2 (Schrödinger) are two different models of the same physics, and as such equivalent theories or models, whereas Kopenhagen and MWI are actually interpretations, namely metaphors to visualize the equations.
That raises the question of why we allow public debate of interpretations on PF. Or why respected textbooks include chapters on interpretations.And disagreements about such preferences can never be resolved (which is why PF threads on such topics tend to go on and on until one of the Mentors gets fed up enough to close the thread).
That may be the answer to why allow it and why we support continued research. An interpretation might be described as a theory extension wannabe. Researchers hope to find a case where T1 and T2 predict different outcomes, so that experiment may prove one of them useful and the other not useful. But such hope should not be eternal. At some point, the rational thing to do is to declare the search futile, and deploy our resources elsewhere.Personally I am with Dirac on this one. I do not think QM is complete - it will slowly and gradually be superseded and in that vein you can look on interpretations as attempts to understand what direction the next step may take us.
I expected a non quantum example. So, you have in mind only QM interpretations, and you think they should be called theories. My opinion is that they are correctly called interpretations. The all start with QM or at least the core of QM, then add a bit more, yet don't get new predictions. To me that is not a different theory. To be a different theory it should build on something else, it should be possible to get to that theory even if you have never seen QM. And that is not the case of the interpretations.T1 = "Copenhagen" with collapse induced by measurement, T2 = many worlds