[like_any_other]

> For any theory/ hypothesis: how well does it stand against the null-hypothesis? For example: How much physical evidence is there really for the string-theory?

That's an unfortunate choice of example - the problem with string theory is that there is no null hypothesis. We know that our other theories are not self-consistent when unified, but we don't have a theory that is self-consistent, that could serve as the null hypothesis.