You love spaceship fights and zooming through futuristic cities like Coruscant. But you also love gladiator fights and seeing 1920s Atlantic City recreated for Boardwalk Empire. Why is that? Though historical fiction is supposedly based in facts about the past, the genre has a surprising amount in common with the speculative tales of science fiction. Here are ten major themes and ideas shared by HF and SF.

Art by Keith Thompson.

Please note that this list isn't intended to be totalizing. Not all SF and all HF have these themes in common, obviously. Think of this story as creating a Venn Diagram of SF and HF, then describing what's in that lozenge-shaped overlapping area.

1. Building a world

One of the most important parts of effective SF and HF is the creators' ability to build a world. There's a reason why SF filmmaker and special effects wizard James Cameron put as much FX work into Titanic as he did into Aliens, The Abyss and Terminator 2. Bringing a historical period to life, with all its crazy details and lost customs, can actually be more difficult than creating an alternate reality out of whole cloth. Some of today's great literary writers, like Thomas Pyncheon and Margaret Atwood, have jumped easily from HF to SF in their novels precisely because both have a keen sense of detail.

2. Trying to represent the alien

This goes back to my first point, which is that good historical fiction should be an exercise in worldbuilding. History is another country, an alien world, where everything from the build landscape to social mores are different. One of the pleasures of watching Boardwalk Empire or Mad Men comes from trying to wrap our minds around the idea that just a few decades ago, it never would have occurred to people that it's a crime to abuse women. In Boardwalk Empire, we're invited to imagine what the world was like when liquor was illegal, "wireless" meant radio, and telephones were advanced technology. It's a familiar world yet completely different from our own, much the way Syfy's Battlestar Galactica series created a recognizably human culture but riddled with weird differences, from religion to technology, that made it clearly alien.

3. Scientific progress

One of the enduring preoccupations of HF and SF is the idea of scientific progress. Both genres often feature a lone inventor or group of scientists, and through the progress of their work we watch as history itself progresses. This is in some sense the overarching theme of Isaac Asimov's Foundation series, and is also what animates Neal Stephenson's Baroque Cycle. Scientists from the controversial sexologist Alfred Kinsey to electricity maniac Nikola Tesla often drive the action in historical dramas like Kinsey and The Prestige. And some of the most beloved historical novels, like T. Coraghessan Boyle's The Road to Wellville, offer us a glimpse of history by showing us scientific experiments that failed — in the case of Wellville, we learn about how John Kellogg (yes, the guy who created Corn Flakes) was a bizarro health enthusiast who ran a sanatorium for the rich where they were "cured" of ill health with devices that sound like something out of a steampunk art show.

4. Alternate timelines

The rise of steampunk is only the latest example of how historical fiction can create alternate universes far more bizarre than anything you'd find in a space opera. Some of the twentieth century's greatest SF writers tackled alternative history — Philip K. Dick's "what if the Nazis won World War II" novel, The Man In The High Castle, is a classic. More recently, Michael Chabon imagined an Israel-like state being created in Alaska after World War II in The Yiddish Policeman's Union, and Scott Westerfeld is retelling the history of World War I with biotechnology in his Leviathan trilogy. Inspired by Patrick O'Brian's Aubrey-Maturin series (including Master and Commander) about the Napoleonic Wars, Naomi Novik imagined what would have happened during those wars if each army had had dragons at their disposal to use as steeds and weapons. Novik's Temeraire series is one of the most successful alternate histories today.

5. Heroism

This sounds like an obvious one — who would make a movie or write a book without a hero in it? But in fact there is a big difference between having a protagonist, even a very likable one, and having a hero. Many dramas focus on people leading ordinary lives, as do romances. The people in these stories may experience extraordinary or weird things, but they don't have a grand destiny or change the course of big events. HF and SF, however, often call for dramatic heroes from Abraham Lincoln and Queen Elizabeth, to Honor Harrington and Luke Skywalker.

6. What happens when society goes through an enormous change

Robots have enslaved humanity. Zombies have taken over the cities. The Black Death has killed half of London. The Roman Empire is about to collapse. What happens next? These world-shaking questions are the meat and potatoes of HF and SF.

7. A broad canvas with many characters from all walks of life

In a sense this is another corollary to "building a world." When your subject is an historical period or an alien world, one of the best ways to represent it is to give us a large cast of characters who can take us into every nook and cranny of the universe. That's what Stephenson does in The Baroque Cycle, and it's one of the great strengths of Boardwalk Empire, with its focus on racial and ethnic politics, as well as the web of social networks connecting even the poorest of petty criminals with the U.S. Attorney General. The broad canvas approach also enhances alternate histories like Susanna Clarke's Jonathan Strange and Mr. Norrell, where two very different men rediscover how to do magic during the Napoleonic War — and affect the lives of everyone from British politicians to humble servants.

8. Individuals can change the future

One of the great pleasures of HF is the benefit of hindsight. When Elizabeth is an obscure noble just trying to get laid in the first Elizabeth movie, it's fascinating to watch her move through the early modern world because you know she's about to change that shit forever and usher in the Renaissance. Same goes for reading one of my favorite historical novels, George Eliot's Middlemarch, which is in part about the birth of the labor movement and scientific medicine in England (yes, Middlemarch is itself historical — it was published in the 1870s and is about the 1830s). There's nothing like watching events unfold when you already (legitimately) know the spoilers — it allows you to appreciate small things, like a telling conversation, rather than focusing on whether the lady will become queen or the working-class politician will win his compatriots the right to vote. At the same time, HF reassures us that individuals can change the future — just like John Connor does in Terminator, and Lyra does in Philip Pullman's His Dark Materials series.

9. Escape from the present

I'm sick of iPhones, highway intersections, pencil jeans, ibuprofin, and post-feminism. I'm nauseated by global politics and want to stab myself when I listen to the presidential debates in the United States. GET ME OUT OF HERE, DOCTOR! Seriously, just pick me up the TARDIS and take me anywhere — the future or the past. Anything has to be better than living day after day in linear time, knowing I'll never fly to Mars, never smell a medieval forest, never upgrade my brain with nanotechnology, and never see a Pleistocene grassland full of mastodons. Luckily, I have SF and HF to take me away from it all. There's nothing like leaving the present day behind to give you the ultimate escapist thrill.

10. Really amazing costumes

Sure it's superficial, but there's a reason why one of my friends in college coined the phrase "hair and hat movie" to describe historical dramas. Admit it. Half the reason you're excited about the sequel to Sherlock Holmes is for the tweed-and-suspenders porn, and the entire reason you went to see Marie Antoinette was for the dresses. And don't even get me started on the wardrobe fetishism in Mad Men and Boardwalk Empire. But the same could be said for costumes in SF. All you need is a cursory glance at Dune, The Fifth Element, or The Matrix to know that fashion can take an SF story from excellent to fabulously excellent. What would Mal be without his tight pants? My point is that millions of cosplayers can't be wrong. SF and HF know how to deliver the costume awesomeness. The steampunk movement is the perfect blend of both.