Recently I was interviewed for an internet radio show/podcast and was asked the difference between SF and Fantasy. One answer I like to give -- a pretty simplistic one -- is that if the impossible thing you want to happen in your story is accomplished through buttons, switches, gizmos, or other machines or justified through "sciencebabble", it's science fiction. If the impossible thing is accomplished through magic spells, talismans, magic creatures, living wood/stones/clouds/whatever, and other unexplained supernatural powers residing in people, animals or in things, then it's fantasy.
For an amusing dissertation on the ... well, I really do have to call it hypocrisy... of science fiction writers when it comes to the (deep and profound intonation) Importance of Being Scientifically Accurate in their works, along with their howling disdain for Bad Science in movies or books... check my friend Ed Willett's blog entry Unreal Science.
The funniest thing about science is the way it always changes. There was a time when all the scientific experts agreed that the world rested on the backs of giant turtles! (An image I absolutely love. I might have to try painting it some day...) Today we're told the scientific experts (the vast majority of whom are not expert in atmopheric sciences) agree that global warming as a result of man's activities is a truth and that before long we're going to have a meltdown. Of course, only 40 years ago the experts were telling us that we were heading into another ice age...
I suppose the best approach here would be... Do not take seriously all words which are spoken.