Under normal conditions, human beings really only have two options for how to get someplace: go via land, or via water. But we’ve always stared at birds in the sky and thought about what it would be like to join them — plus, science fiction and fantasy writers have the option of positing travel via magic or imaginary technology. So let’s take a look at those possibilities.
When you say “flight,” most people’s minds will go to the Wright Brothers and their historic flight at Kitty Hawk in 1903. But a decade or so ago the Science Museum in London had an exhibition on the history of flight, and it documented centuries’ worth of people strapping wings or rockets to their backs in the hopes of conquering the sky. Most of them, as you can imagine, met with painful failure.
Which isn’t to say we couldn’t make anything fly. Kites, bamboo-copters, and sky lanterns (small hot-air balloons) were invented in China, probably in the sixth, fourth, and third centuries BCE respectively, and were subsequently used both for entertainment and tasks like military signaling. Those designs don’t take much in the way of technological sophistication. Lifting the weight of a human being is harder, though — and once you’ve done that, you have to tackle the problems of stability and control.
The first manned balloon flight was in 1783. But hot-air balloons can only really be steered by adjusting your altitude to seek out suitable air currents — which is why one of the terms for an airship is “dirigible,” i.e. directable. These are aerostats, or lighter-than-air craft, and rely on the use of a lifting gas . . . which is part of their downside. Many of those gases are either toxic or extremely flammable, as the tragedy of the Hindenburg demonstrated. These vehicles contrast with aerodynes, heavier-than-air craft — e.g. the airplanes and helicopters we’re accustomed to — which use thrust to keep the craft in the sky.
Once we figured out how to get up there and move around, the next big challenge was infrastructure. Crossing the Pacific, for example, required building a network of airstrips on various islands where planes could stop to refuel, before we developed jets that could do it in one go. (Car travel had a similar problem, which we’re now repeating with electric charging stations, but creating the infrastructure is easier.) And when we step from air travel to outer space, that problem rears its head very significantly.
Getting something into space requires massive energy in order to escape the planet’s gravity. But fuel is heavy, and the more mass you’re trying to move, the more fuel you need, and around and around it goes in a loop, without much hope of a refueling station along the way. Once out in space, you can use an ion drive, but quite a lot of research effort has been poured into finding better methods — and here we cross the border from reality into fiction.
In some science fiction, space travel remains very much a long-term proposition. Either the vessel is a generation ship, with the descendants of the original passengers arriving at their destination, or the ship comes close enough to the speed of light that time dilates: less time passes inside the craft than outside it. But that kind of thing doesn’t allow for a galaxy-hopping adventure, so in fiction you’ll more often see some form of faster-than-light travel. These are all theoretical at best, outright impossible at worst, but for our purposes here, the interesting question is not their plausibility; it’s the effect they would have on the setting.
Take the idea of a wormhole — a natural phenomenon that allows rapid travel from one fixed spot to another. In a universe where these exist, control of these passages would immediately become a vital concern. It would affect shipping, migration, warfare, and more; polities would fight over the wormholes, charge fees for their use, and be worried when they don’t control both ends of the portal. And journeys would still be moderately long, because you’d have to travel to and from the termini, which presumably would be done at speeds slower than light.
That produces a very different world from one where any ship can just drop into hyperspace or some other equivalent and pop out again wherever they want to be. Writers have varied wildly (sometimes within the same setting) on how easy this is, what kinds of perils ensue, and how long a ship spends in transit . . . but if that kind of thing were possible, it would make for a very different set of problems. Now, instead of defending a known point, you have to cope with the possibility that vessels might appear anywhere, at any time, without warning. Controlling trade would have to be about controlling access to settlements rather than routes, and warfare would have to be about maintaining a highly mobile fleet that can go quickly to the site of any problem, rather than fortifying the equivalent of a mountain pass.
Fantasy has generally paid less attention to this than science fiction has. One notable exception is Robert Jordan’s Wheel of Time series — not entirely surprising, given his own experience in Vietnam. At the outset of the story, the various magics that allow for rapid travel have been forgotten. Once they’re rediscovered, though, the characters do what you would expect: they begin to work out how best to employ those for all kinds of tactical purposes, ranging from espionage to surprise inspection visits to transporting armies across the land. Late in the story, some characters even open up gateways horizontally in the sky, allowing them to perform satellite reconnaissance on troop movements.
Allowing this kind of thing in a story means opening up multiple cans of worms. On the one hand, the advantages of being able to connect far-flung parts of the story without losing days or weeks or months to travel time can be very tempting. But when the author does that without thinking about the consequences, it cheapens the world, and sometimes undermines the drama instead of assisting it. The characters seem dumb for not thinking of the obvious applications; plot holes develop because someone could have used this technique but didn’t; or they do use it, and now you can’t trap your protagonist in a scary place anymore because they can just handwave themselves out of it. (You saw the communication version of this happen about fifteen years ago, with a spate of movies all wrestling with the problem of how to maintain drama in a world with cellphones.)
Not every story needs fast travel, whether it’s technological or magical. But some kinds of settings require it — e.g. a cosmopolitan interstellar empire — and even if it’s only in the background, the reader should feel the effects.