I’ve been consuming a lot of science fiction lately. I can’t really explain, being as nerdy as I am, how could I go through most of my young life without immersing myself into Doctor Who, Star Trek or Galactica, but I’m trying very hard to correct that.
One constant in almost all modern sci-fi, is the existence of some kind of technology to allow interstellar travel. A science fiction movie would be pretty boring if it just consisted on people waiting for decades to go into our nearest star system. I’ll try to summarize the different kinds of technology present in those stories.
In the first category you have spaceships that can travel at sub-relativistic speeds, that is, much lower than the speed of light. That includes, for example, early works of science fiction like Jules Verne’s From The Earth To The Moon. Those kind of engines are only good enough to travel inside our Solar System, and depending on the destination it could take years. Since we know that there’s no other habitable planet inside those confines, the variety of different stories that can be crafted using these engines is quite limited.
In the early 20th century, a trip to the Moon was considered sci-fi, but something happened in 1969 that made all those kind of stories obsolete, and prompted fiction writers to expand their universe (pun intended). That made it necessary to imagine new kind of engines and associated technologies to keep being one step ahead of reality.
Sub-light travel is perfectly fine, of course, when the action doesn’t go outside of our Solar System. The amazing book The Martian, and its good movie adaptation (I don’t want to be one of those guys but… go read the book. Seriously. It’s amazing.), just have to go to Mars. Since it’s striving for realism, the plot doesn’t need interstellar travel, starship battles, encounters with little green men or anything of that sorts. In fact, it looks like something that could totally happen in 10 years if NASA had a bigger budget.
In 2001: A Space Odyssey, they only need to go as far as Jupiter. In Elysium, the plot revolves around a giant space station orbiting Earth.
The possibility of all those trips can be explained using just improved versions of already existing technology, it doesn’t require a new, revolutionary mumbo-jumbo engine that can challenge the reader’s suspension of disbelief.
With cryogenic sleep
Sub-light travel is easy enough (we are doing it every time we walk), but how can you devise a story in space, in another star system, with contacts with another alien race, etc with just conventional engines? An easy plot device that doesnt complicate things much and it’s still within the realms of plausibility: cryogenic chambers. So, in some cases the starships are slow, they take decades (even centuries) to reach their destination, but their passengers are in a state of suspended animation. Frozen, if you like. So, when they reach their destination, somehow they are woken up without having aged a single day.
Many sci-fi works rely on this plot device (such as Futurama or the Alien franchise), but I haven’t found any story that uses just that technology for travel, except for Passengers.
Side note: It’s uncanny how that “45 light-years” distance is similar to the distance of the exoplanets found by NASA a few months after that movie was released.
Passengers is an okay movie (Chris Pratt and Jennifer Lawrence are fine actors, the special effects are decent, and the premise is interesting) about a starship that travels to an Earth colony 45 light-years away from Earth. It flies at half the speed of light, so it takes 90 years to get there. All its passengers and crew are supposed to stay in a state of suspended animation during the whole trip (spoiler alert: some of them don’t).
With generational ships
Another “simple” way to colonize other star systems without inventing a way to defy Physics is the use of generational ships. That sounds fancy, but it just means that is a starship prepared to be in flight during several decades (even centuries), so there will be several generations of people which will have born, lived and died in-flight. That’s the basic premise of Firefly, for example. In that universe, faster than light travel doesn’t exist. At some point in the future, Earth becomes uninhabitable, mankind discovers an inhabitable solar system, they build ships to go there and they simply go. That’s all in the backstory to the show. Since all the habitable planets are in the same star system, “conventional” engines are good enough from that point on.
We know that the closest star to Earth is Proxima Centaury, which is 4.2 light-years away. We also know that it has no habitable planets. So, nothing will convince me that a ship at sub-relativistic speed can reach a habitable solar system in less than 40 years. If there’s no cryogenesis or life-prolonging technology available, then the only possibility is to load the ship with enough provisions, make it big enough so you can accommodate enough people and in-breeding doesn’t become an issue, and just prepare to spend the rest of your lives, and your children and grandchildren lives, in a long trip.
With the help of space anomalies
Even if your puny species only has primitive sub-light vehicles, if you happen to find a wormhole nearby, you can get yourself into some intergalactic adventures! A wormhole, if you haven’t watched any science fiction in the latest 50 years, is like a portal between 2 regions of space. It’s called a “wormhole” because it has the shape a worm leaves in an apple, like a funnel that opens on both sides.
A wormhole is pretty much a theoretical concept, and it has to do with the theory that the space-time continuum can “fold” upon itself so a “corridor” of those characteristics can provide a kind of shortcut between 2 very distant points in space. Also, it’s a very convenient plot device.
A recent example of that kind of anomaly is Interstellar (good movie, but a bit slow, and it gets really weird until the end, and now I’m gonna stop because I feel like I’m describing 2001). Earth is about to get destroyed because, again, humans are bad at caring for the environment, but a wormhole appears near Jupiter, and at the other side (wherever that is) there are habitable planets! Eureka!
I’ve only seen the Stargate movie, none of the series, so sorry if I’m wrong, but I would put the Star Gates themselves as examples of this plot device. They are sort-of like artificially-made wormholes, a network of portals connecting different regions of space, like Earth and a weird version of ancient Egypt.
Sub-light speed, but pretty damn fast
When a moving object approaches the speed of light, interesting things start to happen. Einstein’s formula (e = mc2) tells us that the speed of light can’t be reached (you can’t propel an object if it has infinite mass), but a starship could get, say, to 0.9 times the speed of light without needing to break any law of Physics (but consuming insane amounts of energy). At those speeds, time dilation starts to play a role, and every author deals with it in a different way.
In Ender’s Game, for example, ships travel at a speed close to light, so 1 year for a passenger is equivalent to 10 years on Earth. I’m not sure that’s how the Twins Paradox works, but hey, whatever works for the story.
Faster Than Light travel
In this category you have the most far-fetched kind of sci-fi. Faster than light travel is, by the current laws of Physics, plainly impossible. But if you are a writer and you are envisioning a universe with different alien species, vast star systems to explore, wars on a scale too big to comprehend, you don’t let the limits of reality stop you.
Most of the time, faster than light travel is possible by some scientific breakthrough, normally decades (or even centuries) before the setting of the main story. That’s to make it believable that the technology is commonplace. The feeling I have in most sci-fi is that a starship is as hard to obtain as an actual ship in the real world. So you can have your space cruisers, space pirates, space smugglers, space police, space military… Also, making your technology “a given” allows the author to skip the details of how it works, and focus on the main story.
Usually, due to the “mystic” nature of faster than light travel, ships have 2 types of engines. They have more “conventional” engines to maneuver at sub-light speeds, and then they have a separate, completely different “contraption” to go faster than light. Examples of this kind of technology are a lot, so I may be missing like 90% of them.
In Star Trek, ships are propelled by a “warp engine”. It generates a “warp bubble” around the ship that somehow does something to the surrounding space and can make the ship go faster. Yes, it’s vague, but the technical explanation would be like 3 paragraphs of made-up words. The Star Trek ships can cover a few light-years per day, depending on what the plot demands. Still, crossing our galaxy from one extreme to another can take the finest Starship of the Federation about 70 years (that’s the whole premise of Star Trek: Voyager). There have been 13 movies and more than 300 Star Trek episodes, so in that universe we can see too a fair bit of cryosleep chambers, generational ships, wormholes (natural and artificial), time travel, God-like beings that can transport a ship in a whim, alternate universes…
Star Wars‘ “hyperdrive” operates on a similar principle than Star Trek’s warp drive: It creates a something something that makes the ship go fast. Only in this case it’s even faster. This article goes at the calculations in depth, but basically what you need to know is that, in A New Hope, the Millenium Falcon casually covers a distance of almost half the galaxy (from Tatooine to Alderaan) in what appears to be a few days (about 10 minutes of movie time). Since the Star Wars galaxy is similar in size to ours, it’s clear that the hyperdrive is much much faster than even Star Trek’s finest warp drive. It makes sense, really, if the whole galaxy is expected to be at war at some point, having the possibility to transport from one front to another, back to the capital to debrief, back to the front lines, etc makes for a more compelling, character-driven story.
In Battlestar Galactica (the reimagined series), the ships have a jump drive. It means that, after charging some (supposedly large) amount of energy and doing some complex calculations, a ship can instantly jump from one point in space to another. It has limited range, but that particular device allows for a lot of tension in the action sequences. I don’t want to stop talking about Battlestar Galactica without recommending it, it’s amazing, specially the first season.
In the Alien franchise, ships are capable of faster than light travel. Still, some trips can take several years, so ships designed for long travels are also equipped with cryogenic chambers.
In Frank Herbert’s Dune, the fastest ships can “fold space”, which I guess it means it’s like a “jump drive”. In Doctor Who, the TARDIS can travel instantaneously both through time and space, due to some wibbly-wobbly, timey-whimey stuff (another amazing show, it’s so silly and yet sometimes it slaps you in the face with the best plots you’ve ever seen in sci-fi). In Spaceballs, the best ships can reach “Ludicrous Speed”, which is of course a lot faster than light speed. In Futurama, the Planet Express can travel faster than light making the universe move instead of the ship…
At this point, you get the gist. Every sci-fi work that relies on faster than light travel will have its own, impossible, vaguely-described contraption to make it work. And that’s ok, because the technology is usually part of the setting, part of the background. Normally, the writer wants the readers to forget about how the technology works so they can be immersed into the characters and the story.
If your goal, as a writer, is to strive for realism, stay away from wormholes or faster than light travel. So, either you set your story in our Solar system (The Martian, From The Earth To The Moon), you rely on generational ships (Firefly), or cryogenics (Passengers). Cryogenic technology doesn’t exist yet, but it’s not hard to imagine that it could plausibly exist about 100 years from now or so.
Sometimes the best work comes when adapting to self-imposed limitations, but other times, if the story calls for it, it’s totally advisable to ditch the realism in favor of a compelling setting. Science Fiction doesn’t need to be scientific, it just needs to be fiction.