The problem with these worlds is, of course, that they follow
neither the rules of natural law, as science fiction proposes to
do, nor the conventional "logic" of magic used by most fantasy.
Instead, as Brian Attebury explains in his article "Science
Fantasy" (Dictionary of Literary Biography), these worlds must
attempt to fuse the two sets of rules, to come to some consensus
within the world of which rules work when. This fusion,
however, is difficult to achieve. Many authors, especially pulp
magazine writers trying to churn out three thousand different
versions of the same plot line, end up using this fusion as a
sort of "path of least resistance" (Attebury's term), using
whichever set of rules help to further their story at any
particular moment, even if such a disordered logic makes the
world as a whole inplausible.
Other authors deal much more systematically with the Blended Universes. They use both sets of conventions and plot strategies to create a system in which science and magic are not mutually exclusive and can interact successfully. Often these worlds are set more completely in one paradigm or the other, or depend on different visions of what is really magic, using quasi-scientific explanations (usually involving willpower, mental abilities, or drugs) to account for the presence of magic in a technological world. Others don't bother. Once again, Star Wars is a good example of this, because the presence of the "Force" is never explained though often challenged.