Idea and expression in science
"at an epistemological level, scientists are concerned not with
facts, but with the relationship between facts. That makes it very easy
to blur idea/expression"
Granted that distinguishing idea and expression is not easy at all times, relations between facts is not more expression than the facts themselves. Epistemologically, res ipsa loquitur, or more precisely, things relate themselves; even though the relations conceived originally - fictionally, if you want, or hypothetically - by scientists may _have_ an expression deriving from the creator's ingenuity, they are not expressions by themselves. Especially if they are real relations and not just fancy hypothesis.
But the same goes as to non-scientific works. Music is by definition relational; either as relations in simultaneity (harmony or counterpoint) or in time (melody), the effects of that art are created by the effect of moving or boring relations of acoustic and chronological relations. Composing is weaving such relations from the facts of sound and time. However (and this is the point), neither the isolated relations (for instance, the Barrabas chord in Bach) nor the extended relations held a thematic material are protected on a exclusive basis. A theme, or musical idea, is (with all due care with excessive extension of this taking and reasonableness of such utilization) is liable to be picked and reutilized by other creators. Composing upon a theme from other authors is a time-honored usage of the music world. And this happens whether or not the theme originally created is in public domain.