Well, it's interesting. It doesn't so much operate in fantasy, but in the sci-fi genre, it creates a division. Of course, we here are on the DA forums, not the ME forums.
So-called "hard" SF tries to stick to things that are in perfect accordance with the known laws of physics.
So-called "soft" SF focuses on character and narrative over "hard science". And honestly doesn't really get too picky about getting the science perfectly right.
Lots of interesting discussion here.
http://www.treitel.o...rd/sf/hard.html
I like the scientist who points out that if we used a strict enough definition for "hard" SF, most SF would fail the test. So it all would end up "soft." So at the end of the day, he says he simply makes a decision not to let contravention of physics ruin his enjoyment.
Just about every sci-fi series often conveniently ignores that deceleration is necessary and requires lots of time and energy, just like acceleration. Just as one example. Everything accelerates, but when do you ever see the Enterprise hit the brakes and gradually slow down?
The other problem is, at the end of the day, we can only say something appears to be impossible at the moment. Our knowledge of the possible is evolving. At one point, people writing about breaking the sound barrier would probably have been considered crazy. Then it happened. So, while many would say time travel is an impossibility, ... that's only because in our current state of knowledge, it doesn't seem possible.
Thus, can we say all sci-fi stories that feature time travel are "soft" ... or not?