How much science do you need to know to write science fiction? So far my answers have been "a lot," and "not a lot, as long as you know a lot about science fiction." Today we get to a third option available to every author, which is to know absolutely nothing about science.
This answer isn't going to make a lot of science teachers happy, nor will it make people who love well grounded hard science fiction very happy. Science fiction, for all of its attempt to ground itself in reality, is ultimately part of the larger umbrella of fantasy fiction. Fantasy takes place in a world not quite our own. This can be a fully magical fairy land, or it can be an alien planet. It can very closely resemble our world, but with vampires and wizards, or be our world transformed by some new technology, like an immortality pill.
The greatest gift to every writer is the seemingly innate human ability to accept nearly any premise as true, no matter how contrary to reality it might sound. This is so common we're almost blind to it. Children from an early age demonstrate a remarkable ability to buy a premise while still understanding that the premise isn't real. No kid watching cartoons on television stops to give a second thought about why a bunch of dogs are talking and wearing shirts, nor do they expect their own family pets to start having conversations. The fact that some people can fly and punch through walls after donning a cape or mask is accepted without a lot of follow up questions. That there were times in history where dragons terrorized villages and wizards teamed up with knights to fight them doesn't raise any red flags.
Novelists, playwrights, cartoonists, and puppeteers rely on this notion of "the willing suspension of disbelief." Readers enter into a novel, or a comic book, or a stage magician's performance agreeing to ignore their skepticism and allow the artist to present a new world where reality follows slightly different rules. In exchange, they expect to be rewarded with entertainment, and, in the very best art, with wisdom and wonder.
What's remarkable is how easy it is for the audience to transition to this new reality. This is a world populated by intelligent rabbits, and one of them has to solve a murder mystery? Got it. Move on. Tell your story.
You see this presentation of a wild premise a lot in comedic science fiction TV series, like Futurama or Rick and Morty. Here's a pill that will make you telepathic! This watch will let you jump back in time five minutes! That explosion has caused our minds to switch bodies! The audience will buy the bit and not worry about the underlying logic. Superhero shows on TV also run with this, often not trying to be comedic. "I got hit by a wave of dark matter and now I can talk to animals!" "I got injected with nanobots and accidentally de-aged into a baby!" "I caught an virus from an alien and my fever is letting me melt steel!" An utterly absurd idea about what would happen if a radioactive spider bit a nerdy teen has been selling comic books for as long as I've been alive, and can still pack movie houses.
It might sound like your audience will swallow anything you put before them, but this isn't quite true. They will accept nearly any alteration to reality you care to make, but with the following caveats:
- The alteration to reality should be apparent very early on. If you write a book about an alien invasion, the readers will buy the premise if there's a UFO in the first chapter, or even a fleeting mention of one. If, in your thirty chapter novel, you wait until chapter twenty nine to mention that, oh, right, there are aliens and they're going to kidnap the hero's love interest, you will wind up with some very negative Amazon reviews.
- The premise should possess an internal logic and the story should follow the rules you set up front. Let's say that you're writing a novel about a genius who's built a shrink ray. All through the book, he keeps getting small and navigating under doors and riding cockroaches and dodging getting stepped on. Then, in the final confrontation with the bad guy, he does nothing at all with his shrinking powers, but instead pulls out a pistol and shoots the bad guy in the head. Most readers would feel cheated. Or, let's say that your character has designed a sentient artificial intelligence that borders on omniscient. Now your character is famous as a master detective because he uses the computer to help interpret clues. Great! But if he never asks once the obvious question, "Say, who killed this guy?" and you don't explicitly give a reason why the computer can't answer that, most readers will feel like you've not treating them with much respect.
- Know the commonly accepted "rules" of any premise you're recycling. Let's say you've come up with a science fictional explanation for vampires. But, your vampires aren't harmed by sunlight or even adverse to it. They don't need to drink blood, they can be killed by an ordinary bullet, and they can't fly or change shape. They don't even have pointy teeth! Calling a character lacking at least a few of these traits a vampire will likely not be well received by readers.
Finally, the commonly used term to hide implausible technology beneath a sheen of science is "technobabble." You see it used a lot on television shows, and it's often cringeworthy. Scientific sounding words get tossed around to explain the essentially magical thing the writers need to happen. So, a supervillain is rampaging through the city, but the hero has built a device that can neutralize his powers: a neutrino ray! The writer might feel pretty clever. Neutralize and neutrino sound alike, one must have something to do with the other, right? Meanwhile, anyone who actually knows even a tiny bit about particle physics is on Twitter writing short, angry protests about scientific illiteracy. On the other hand, suppose your character needed to build goggles that would let him see into a bank vault. He can say with a straight face that his "neutrino goggles" can decode the "neutrino shadow" of the trillions of neutrinos streaming through the bank vault each second. It's still gibberish, but the fans of particle physics would appreciate the fact that you did at least get the part about the trillions of neutrinos passing through the vault each second right.
In a way, we've come full circle. Yes, this is fiction. You can just make stuff up. But knowing what the words you're using really mean is part of the craft of writing. No matter what exotic technologies your imagination comes up with, there's probably some appropriate realm of science that relates to it at least tangentially. The more science you know, the more authoritative you'll sound when you twist that science into pretzels to make it justify your story needs. Start studying!