Science fiction is the literature of change and discovery. So there are no limits to how far a science fiction story can go... except for scientific plausibility. And yet, science fiction is created by and for human beings, with all our weird limitations. So here are eight paradoxes that shape our relationship with SF.
Note: Some of the items below aren't strictly speaking paradoxes, in the logical sense. More like "contradictions" or "disconnects." But "Paradoxes and Contradictions" didn't fit in a headline. In any case, I'll try to keep it strictly paradoxical.
We use past technology to speculate about future technology.
And that means that the already-dated technology that you're using to write or film or render your futuristic masterpiece is shaping how it comes out. Whether you're typing on a computer or filming with a camera, the "flow" of your future imagining partly comes out of the features and limits of this existing tech. And the same applies to people consuming science fiction on computers, tablets, video screens, game consoles, etc. What we see as possible is partly a product of what we've already created.
One point of strangeness/divergence is weirder than several.
In other words, a story set in "our" world, but featuring one thing that's radically new or different, is going to be more jarring, and feel more intensely new and strange, than one that piles on weird thing after weird thing. After you encounter more than a few weird differences, you probably start to think of the setting as a fantasy world rather than the real world, and you accept that anything can happen here — thus possibly reducing the impact of any further shocks. (Not that there's anything wrong with that. The over-the-top surreal weirdfest is a wonderful type of story, and a far-future story with tons of strange stuff can be exhilerating. It's just not as startling as seeing one or two odd things in a recognizable setting. On a related note...
The bigger the ideas, the smaller you need to keep the focus.
Because human brains have a hard time wrapping around huge, earth-shattering concepts or "big idea" storytelling, we need a human-scale point of reference for anything giant. There needs to be a small, personal story in the foreground of any story about massive aliens trying to steal the sun or whatever. We have a hard time relating to things we haven't experienced personally. And yet...
If people think you're not explaining enough, you're probably explaining too much.
This one isn't always true — but I see it happening a lot. People start demanding more explanations for the mechanics of the plot when they've been given enough information to let them think it's going to be explained in detail, but they haven't gotten that full explanation yet. Most audiences are savvy enough to recognize when the answer is "because that's how it works." How does the Force work? It just does. How do the transporters on Star Trek work? They take you apart and reassemble you. But today's audiences (and creators) are addicted to mystery-based storytelling — so we get lots of teases and hints and clues, even for stuff that should probably just be handwaved. Too many questions means you've probably overexplained.
Wherever you're not looking is probably what makes the story WORK.
The most quotable lines of dialogue are usually not the ones that make the characters believable and solid. The plot mechanics that keep the whole engine from spinning out of control aren't the big shiny things in the dead center. The crucial scene is probably the one where somebody puts on their shoes and takes a deep breath, before the main action. It's like a magic trick: where your hands aren't looking is where the real action is. It's often the stuff you don't notice that makes the story go.
Whatever feels freshest will look the most dated in a few years.
Because whatever is "new" to us today is going to be the most closely tied to the time period when it was created. Otherwise known as the Star Trek: The Next Generation rule. By contrast, things that feel timeless, or even a bit retro, are probably going to age better because they're less tied to one particular aesthetic.
All futurism is history.
Because we only really have the past to go on, when we invent futures. Often, people fall into the trap of extrapolating the past in a straight line into the future — but even if you avoid that, you're still creating a mirror (distorted or otherwise) of previous events. It's true that science fiction is always about the time when it was created, but it's also the case that future speculation is usually a meditation on past events.
Thought experiments aren't really experiments.
At least, if you think of an "experiment" as being something that happens under controlled conditions, and is repeatable with those exact same conditions duplicated. A thought experiment, by its very nature, happens differently inside every brain that runs it. Whether you're convinced or compelled by a thought experiment probably varies from person to person — so in fact, the real virtue of thought experiments isn't that they generate usable data or "prove" anything. Rather, it's that they use your capacity for imagination and empathy to place you, to a greater or lesser extent, in a situation where you have to confront a possibility you wouldn't have faced in real life. There's a reason why Stanley Milgram's actual sociological experiment has had more staying power than John Rawls' thought experiment about the "veil of ignorance" — one generated actual results, the other is highly subjective and imaginary. But you can turn that lack of probative value, that dependence on imagination, into a strength — if you're a powerful enough storyteller.