What is the characteristic difference between a scientific theory and a work of fiction? It is not, I hold, that the theory is possibly true while the descriptions in the story are not true, although truth and falsity have something to do with it. The difference is, I suggest, is that the theory and the story are embedded in different critical traditions. They are meant to be judged by quite different traditional standards (even though these standards might have something in common.)
What characterizes the theory is that it is offered as a solution to a scientific problem; that is, either a problem that has arisen before, in the critical discussion of earlier tentative theories, or (perhaps) a problem that discovered by the author of the theory now being offered, but being discovered within the realm of the problems and solutions belonging to the scientific tradition.