Ursula Le Guin did an interview with Vice Magazine (of all places) and explained exactly how you can make a mysterious technology, and a universe of 80 wildly different inhabited worlds, feel totally real.
Q: For the Hainish Cycle of books you invented over 80 different inhabited worlds, each with its own cultures and physics...
A: No, no, thank you for saying so, Steve, but if I really had, I would admire myself tremendously. I would be in awe of my own staggeringly great mind. What I did was give the illusion of there being all those different worlds. That’s called art, or fiction, or something. The rule is, you only invent what you have to. And that’s pretty much what’s right in front of the reader. Let’s say it’s an ansible. I do not, in fact, invent the ansible. I do not explain how it works. I cannot, but shhh. I simply present the device as working, and as coming from a society which is far in advance of ours in science and technology, having spaceships that can travel nearly as fast as light, et cetera. And this background or context creates expectation and softens up the readers’ credulity so that they’re willing to “believe in” the ansible—inside the covers of the book. After the ansible had been around for a while, I invented the man who invented it, Shevek, in The Dispossessed. And he and I played around with some pretty neat speculations about time and interval and stuff, which lent more plausibility to the gimmick itself. But all I really invented was a) the idea of an instantaneous transmitter and b) a name for it. The reader does the rest. If you give them enough background/context, they can fill in the gaps. It isn’t just smoke and mirrors. There has to be a coherent vision of how things hang together in that society/culture/world. All the details have to fit together and be thought through as to their implications. But, well... it’s mostly smoke and mirrors. What else is any fiction?
[Vice Magazine, thanks to Justin Rocket Silverman]