This is a question that gets asked a bit in writer’s forums, and frankly, I have some trouble with it. I mean, it’s called Science Fiction, isn’t it?
Yes, I know there are many stories out there that don’t seem to have any science at all. Look at Star Wars, for example. It’s so full of semi-magical rubbish that you can hardly call it Science Fiction and… yeah, yeah. That said, how do you know that some real science wasn’t behind the inspiration for some of the admittedly cool worldbuilding? Sure, there was a lot of stuff that’s plain impossible and more like magic, and overall, Star Wars is probably closer to fantasy. But, you wanted to know how to write better and more sellable Science Fiction, right? You’re not writing Star Wars and your name isn’t George Lucas, so let’s forget about them and all those stories that have questionable science. You want to sell a story to a good magazine. How much science do you need?
In the last year, something changed for me. I went from being able to sell stories at semipro level to being able to sell them at pro level. In my case, I can pinpoint the exact moment of change. It was that hot Sunday afternoon in January 2010 when I went to Officeworks and bought that pair of titanium scissors. I became interested in titanium and after reading about it, I cobbled together a number of ideas into a strange ecosystem that relies on titanium. From there, it was only a small step to invent characters and a story. Ultimately, not that much science made it into the story, but the science inspired almost every bit of worldbuilding the story has.
The story I wrote next, Party, with Echoes, which I sold to Redstone SF, had even less science visible in the story, but that doesn’t mean none went into the writing of it. In fact, since it’s set on Europa, I bought a book on the moon. The same book has given me ideas for further stories.
His Name in Lights, which I sold to the Universe Annex of the Grantville Gazette, has even more science, and more of it made it into the story, but again, the science formed the basic inspiration for many elements in that story. The science told me what should happen, and gave me ideas for cool scenes. Having asked myself the question: could one possibly sign-write on the clouds of a gas giant, I set about writing a story that involved just this.
The quality of my stories took a big leap when I decided to start taking the science in Science Fiction seriously, and using the science to inspire and guide the story rather than tacking some pseudo-science onto an existing story, and hoping no one noticed. About using facts in Science Fiction, someone at the Analog forum said this very true thing: don’t think no one will check; they will. Very true. You have to get the facts right. Better still, make sure you’re one step ahead of the editors and readers in terms of research.
So I think those people who ask how much science a Science Fiction story needs don’t fully understand the concept of the genre. Science is not optional. Science Fiction is, breathes, and lives science. The inspiration for it is the science. The resulting story may or may not have an obvious science component, but without the science extrapolation or inspiration, it would be dull, commonplace or clichéd.
That doesn’t mean dull, clichéd stories don’t get written. Heck, sometimes they even get published. But if you want to give yourself the best chance at getting published in a decent Science Fiction venue, it is my strong feeling that you had better start looking after the science other than spending five minutes on Wikipedia checking the most obvious facts.
When I talk about science, I include the social sciences. There are many great stories that can be written about concepts in such fields as psychology, political science and linguistics.
You do not need a PhD in any of these fields to learn about them. Your readers will probably never have heard about the interesting concepts you have used as inspiration for your fiction, and therefore, the stories will have that spark of being different and fresh, as well as feeling authentic and interesting.