Well, I'm beginning developing my first sci-fi stories ever... eep! And (what do you know) I'm a little unsure about... stuff. Besides usual unsure-ness that comes along with every story, I really am not sure how developed the science in my story needs to be. I'm sure the exact detail requirement varies from story to story based on tone and style, but I'd still like to know basic outlines and such.

If I do need to know nearly exact workings of (at least the theories of) the techno-science, I'm in trouble. I have a parallel universe to ours in the story, centering around the twin planets of Gran and Stork. An evil scientist/wanna-be-world-ruler has done something science-y that sends any obstacles to a place where their life on Gran or Stork will only be a dream. They get sent to our world, and live as a normal person with a normal family. The only thing different is that their dreams, a good deal of them at least, are flashbacks to their life in the other universe. Only problem, I have no idea how a human on Gran or Stork could get sent to our world and live their whole life as an Earther (as Graners or Storkers call them). Do I need to know?

Oooh, interesting concept. :3

Aye, I would say you need to know, even if the specifics of how never come into the story at all. My reason is simply because stories are more believable when the author knows how her own cobha is functioning. Think like in Harry Potter: we have no idea how the magic works, as it is never explained, but J.K. Rowling does, and that makes it consistent and believable.

Just my tuppence. hope it helped.

(A belated reply: )

In the sort of SF (and fantasy) fiction that I most enjoy (and that most discussions on this forum seem to assume), you need to have enough detail worked out, even if 99.99% of it never makes it into the story, that your prose convinces the reader you know what you're talking about. How much detail that means (and how much detail that means you have to put into the story) varies from reader to reader, and from (story-)world to world.

(Interestingly, Rowling is the author that I would cite as an example of what happens when you have enough detail to evoke a world but not to convince readers that you're not just making it up as you go along; she probably "knew" enough beforehand for a trilogy, and certainly for one book, but not for a seven-book series---as the volume of fan fiction devoted to "fixing" the perceived inconsistencies and egregious holes in the Harry Potter worldbuilding demonstrates.)

And for any particular detail, such as the one you asked about, whether you need to do detailed development or can just leave it up to "handwavium" or unexplained depends on how central it is to your particular story, on the complexity of your world (five hundred years ago anyone using a piece of technology had to have a fairly intimate understanding of how it worked; nowadays, nearly everyone uses many, many pieces of technology that they understand superficially at best), and how much of an expert in that domain of knowledge your characters are (especially your point-of-view character), among other factors. As with so many things in writing, "It Depends."

You can even get away with mixing (what seem to be) science fiction and fantasy elements in a story. In the Space Trilogy by C. S. Lewis, for example, Out of the Silent Planet is a great book, but there are sequences---and one scene in particular---that clearly show Lewis's ignorance (and unconcern about his ignorance) of "hard science." It was partly in response to criticism of this aspect of the book that he transported the protagonist via angel power in Perelandra and set That Hideous Strength on Earth.