How and where should you explain how the laws of your sci-fi universe significantly differ from the real world? Let's say that the laws are so different from the what be construed from the theories of quantum physics and general relativity. How do you explain this and where? I thought using the preface would be a good idea, but what if the preface needs to be as long as 10 chapters to fully explain the differences? I am thinking there's a better way of doing this.
It's important for you to understand how your scifi universe works. It is NOT important for your reader to understand. With 2 exceptions:
If it directly affects the plot. For example, if traveling faster than the speed of light is possible, and it will be critical to resolving some thread of the plot, you need to let the reader know beforehand. Likewise, if traveling faster than the speed of light causes de-aging or time travel, and this impacts the plot, you should probably indicate that. HOW or WHY it is possible won't matter to most readers, who likewise probably don't have a firm grasp on why superluminal travel isn't possible in our universe.
If seeing something happen according to your universe's rules would break the reader's immersion in the story. For example, if terminal velocity is very low on the worlds the story is taking place on, so that falling death is basically not possible, but you don't let the reader know, the reader may decide your story is stupid, and/or you are stupid, when falling off a skyscraper isn't a serious thing. (This can also apply to actual principles from the actual universe, if the audience's expectations are not realistic. Someone watching a movie may be upset when a character falling from a great height is caught at the last minute, and still dies, even though that's actually more realistic than being saved when being caught after hundreds of feet of free-fall.)
The expansive and precise rules of your universe may be of interest to a few people after your story gets popular, and perhaps you can pack it into an appendix at the end. For most readers, though, if you're consistent and reveal what is necessary as described above, your story will be more readable without lectures on imaginary physics.
Show Don't Tell:
I agree that it isn't always important for your reader to know the rules of your world - at first. Some things, like how the FTL system works, can be taken for granted - readers know what FTL is, but no one knows how it really works. explain the parts relevant to the story, and the rest gets cartooned in. But they do eventually need to know the principles involved, and to do this, you need to demonstrate these rules, not just explain them. Dribble the information out on a need to know basis, revealing each piece a bit at a time instead of dropping it all in a chunk.
Sci fi does tolerate a bit more infodump than other literary forms, for exactly the reasons you discuss. But even here, you need to be a gentle with you reader, spoon-feeding them data. Have characters discuss relevant information that just happens to explain the psychic abilities of the MC they don't understand. Have the POV character think about how these rules affect the actions they are about to take. The character walks past posters about the gods that manipulate the fabric o the world, and the captain of the ship announces on the PA of the vessel they are about to go into hyperspace on the 35th anniversary of the invention of the Hikegashi jump drive
There are techniques used to point out information to readers. Brief insertions of news clips or interviews discussing this information are stereotypical, but can be effective. Quotes from historical and scientific works explaining the physics are still infodump, but semi-explainable infodump. Dreams are a little trickier, but can be used for magic and psychic things. Spirits revealing information are effective but hard to justify unless spirits are somehow integral to the story.
Then, of course, is simply showing the effects of the different physics, pointing out that it differs from normal. Play up these differences, and a sci fi fan will know that you are pointing out the fact you know this isn't normal. Then when you explain how it works, they will be anticipating the information, possibly even looking forward to learning these details.
In The Craft of Writing Science Fiction That Sells, author Ben Bova emphasises the importance of four elements:
This is no different from any other work of fiction. The difference with Science Fiction is the need to create convincing and consistent settings (world building).
And he makes an important point:
‘Almost every story has a philosophical point to make … all storytelling is about getting across some truth that is culturally valid. … Everything in a story’s background should be shaped for the purpose of making the point that the author is striving for.’
Furthermore, he advises:
‘Don’t try to explain how the machinery works; just show that it does.’
If the characters live in that world, then they think and behave in ways that are determined by its rules. If you're consistent, the rules will be implicitly communicated. If you need to explain them to aliens (i.e. readers in this world), then do so briefly - options include (among others) an explanatory end section, or a creative preface.
Novels like Vernor Vinge's A Fire Upon the Deep or Alastair Reynolds' Terminal World play in universes where the laws of nature are different, which plays a large role in the plots. In a way, most Science Fiction or Fantasy modifies the laws of nature to facilitate faster than light travel, unknown energy stores or to allow magic. Even the Expanse, praised for its realism and scientific accuracy, uses a very efficient nuclear fusion drive as a plot device that probably is incompatible with accepted physics; the central plot driver is the "proto molecule" which has unexplained powers, and there are hyperspace portals using "magical" physics.
All these stories follow the same pattern: In the beginning, the reader follows the characters through their lives which sometimes have weird quirks: Why don't electronics work down here, why can you get trapped without FTL travel in the core of the galaxy, why do you have to hide at night and put runes on your door. The characters consider all this normal and only make a cursory mental remark. Bit by bit the reader must puzzle together the fragments revealed by the author at strategic points. Sometimes there is a moment of reflection when the character wishes those restrictions or dangers weren't there; sometimes a child or foreigner needs explanation which "incidentally" also benefits the reader. Memories of past tragic events reveal more of the consequences of rules not followed. The Expanse has a flashback scene, tragically missing the customary plot armor of the narrator, dedicated to the discovery of the efficient fusion drive.
Most novels employ this "detective work" game involving the reader. The workings of the fictional world are explored like other parts of the story, for example the true characters of protagonists or important secrets. In ghost stories the "working of the world" is often the central part of the story that the characters try to understand: Why is the ghost haunting the castle, what is this supernatural power, what's the connection to the protagonists.
In SF the makeup of the world can be a means to enable the story (typically by FTL drives, like in Star Trek) or to restrict what can be done so that you can write something steampunk-like (Terminal World).
I agree with the other comments. Sci-fi is a genre that does typically tolerate info-dumping, I still believe it is best to simply use the show not tell method when it comes to info-dumping. That way you're allowing readers to truly see how a world works rather than just telling them through pure info and data.
Peter and Jebediah both have good answers that I would like to expand upon somewhat.
Peter recommends reading some other books that convey significant information about the physics of the fictional universe they are set in, and this is excellent advice. I can also recommend A Fire Upon The Deep, but I think that an even better recommendation is Greg Egan’s The Clockwork Rocket.
(As an aside, reading good books and emulating them is probably good advice in general. I’m a software engineer, and reading other people’s good code and emulating it works well for me.)
For The Clockwork Rocket, Greg Egan made one tiny change to the space–time metric, worked out most of the consequences, made up some more or less plausible biological and societal details that could work there, and then set a story in the resulting universe. And it is a fascinating universe!
He put all of the detailed math and explanations on his webpage for anyone to read, but it’s not all included in the book itself. Relativity and quantum mechanics turn out to work very differently in that universe, so even a simple story set in this universe would be potentially confusing unless explained (for example, plants gain energy to power chemical reactions by emitting light rather than by absorbing it), so he can’t leave the reader completely in the dark. Characters within the story must themselves learn physics and astronomy, and we can follow along as they do. This works quite well primarily because the details that are explained to the reader are very relevant not just to understanding why the characters are going to the forest in the first few chapters, but to resolving the whole plot.
This brings me to Jebediah’s remark that you only explain a detail to the reader “if it directly affects the plot.” It has to be relevant in some way, and not merely related to things that are relevant.
Eliezer Yudkowsky wrote about writing fiction that explains scientific concepts. He has six requirements for doing this well, and the third is “the art of relevance”.
- You must be able to master the art of relevance; this is the ability to see exactly which aspects of knowledge are necessary for a particular conclusion or set of reasoning steps, and then include only the questions and ideas that are relevant to the plot.
It may be possible to explain things sufficiently to the reader in less than 10 chapters if you cut material that isn’t completely relevant.
I recommend reading all of Eliezer Yudkowsky’s advice on writing. Most of it is about writing intelligent characters rather than about physics, but you may find some more useful tips there; it sounds like you’re writing a story where the characters should be fairly intelligent.