Putting the science in fiction - Dan Koboldt, Chuck Wendig 2018
Faster-than-light travel
Star wars and the far future
By Jim Gotaas
The universe is a big place.
The fastest spacecraft currently planned is NASA’s Parker Solar Probe, designed to launch in 2018 and approach the sun, with a maximum speed of two hundred kilometers per second. At that speed, we could go from the Earth to the Moon in about half an hour. Pretty fast, huh?
Even if our crewed spaceship could reach that speed, it would still take 6,400 years to reach the nearest star, Proxima Centauri. There has been much speculation about different forms of slower-than-light (STL) travel that could cut that time substantially. But if we accept Einstein’s special theory of relativity, it would take us just over four years of travel to reach Proxima Centauri. Without faster-than-light (FTL) travel, four years to our nearest neighbor is probably too long for most stories. That said, there are a lot of interesting classic stories that are based on various types of STL, where current physics is obeyed, but advanced engineering work is needed.
The basics of FTL
There “ain’t no such thing.” Sorry.
Specifically, most scientists and engineers believe current physics says that FTL is impossible. Einstein’s special theory of relativity states it would take infinite energy for a material object (like a spaceship) to travel at the speed of light. That infinite doesn’t mean just lots and lots of energy, but literally more energy than exists in our universe. So the speed of light is the absolute speed limit in our reality.
Special relativity also predicts that actual FTL would lead to the breakdown of cause-and-effect. This is too complicated to really go into here, but basically, special relativity says that every person (technically, the theory refers to every “frame of reference”) moving with a different speed sees the universe differently. In particular, if FTL occurs, even the order in which things take place can change. There will be some people who “see” the ship arrive before it’s left!
So as far as current real science is concerned, we’re stuck without FTL. But there are possibly some loopholes, which we’ll explore.
From the earliest days, science fiction has wanted to play out on the big stages. All but the most hard-core SF purist is willing to bend the rules a bit for the sake of a good story involving galactic empires. So science fiction has come up with a number of imagined methods for FTL, some with more scientific plausibility than others. If you want your story to sound scientific, you’ll need to face up to the problem of real interstellar distances, but be prepared to wave your hands a bit and mutter the accepted “magic words” to play the game properly.
There are dozens of different names and ideas used for FTL technology in science fiction, but we’ll take a brief look at four main types.
Warp drive
Most Star Trek fans are familiar with its warp drive through the use of “dilithium crystals.” Depending on which generation you belong to the special effects vary, but the basic idea is the same. You start your warp drive and break through the light barrier, allowing you to have adventures all over the galaxy. There’s usually no scientific justification for this, but at least you’re facing up to the whole light-speed limit issue. This is an accepted trope in science fiction, and you’re allowed to switch it on yourself in your stories, although calling it warp drive may evoke images of Star Trek. If you want to spend a little more time waving your hands about and sounding more expert, you can name your own version of FTL drive, or simply mention the Alcubierre drive. (This is an actual scientific idea, first developed in 1994, but more recently revived to the point where NASA scientists are actually looking at a variant—but still only in theory!) For more detail, see chapter 11 in Michio Kaku’s book Physics of the Impossible (Doubleday, 2008).
Hyperspace
Hyperspace is an old idea in science fiction, encouraged by the fact that it’s a real mathematical concept. Although it sounds interesting, in mathematics hyperspace simply refers to a set of dimensions beyond the normal three spatial directions (left-right, forward-backward, up-down), so we can talk about a hypersphere or a hypercube in four (or more) dimensions.
The key to FTL through hyperspace is the idea that different hyperspaces may have different intrinsic length scales. So while in our normal universe Proxima Centauri is just over four light years away, we can imagine a more compact hyperspace in which the distance is much shorter—let’s be absurd and say four kilometers. In that hyperspace, traveling to Proxima Centauri at the speed of a normal car would only take a few minutes. So if we shift our ship into hyperspace, we can get there very quickly. Depending on the needs of your story, you can make the hyperspace journey shorter or longer by changing the size of your dimensions. There are examples in modern science fiction of having a range of hyperspaces with different scales so you can change your speed by moving up the hyperspace ladder.
In older science fiction, this alternate space was sometimes called subspace, implying that it somehow lay beneath our normal 3D world.
There are two main versions of hyperspace in current science fiction:
The first type has hyperspace accessed through gates that are fixed at certain locations in the galaxy, often making their location an important political and strategic consideration. On television, Babylon 5 jumpgates were of this sort, created by unknown advanced aliens sometime in the past.
Another version allows individual large ships to enter and exit hyperspace directly with their own engines at any point in space. Again in Babylon 5, larger ships can have jump engines that allow for direct access to hyperspace, although it saves them energy if they can use a jumpgate instead.
Wormholes
Wormholes are usually described in terms of shortcuts across space by folding it.
The key is that if you take two points that are separated by, let’s say, five feet on a single very large sheet of paper, you can bring them closer together by folding or bending the sheet of paper until the two points are almost touching. So if a fast snail (racing at three feet per hour) needs to travel from point A to point B, it will take her about an hour and forty minutes crawling along the paper. But if you helpfully fold the paper so that A is on the top and B is on the bottom as the paper touches itself, the snail can simply hop across, bypassing all that real space and taking only a minute or two.
Of course, this requires the existence of an actual higher physical dimension in which our ordinary space can be “folded,” as well as a technique for bending our space in the first place. There are two main versions of these wormholes.
In many cases, the wormholes are imagined to be naturally occurring, a result of some sort of natural folding of our universe. This is the sort used, for example, in David Weber’s Honorverse series.
Another version has the wormholes being engineered and fixed in space (a bit like the jumpgates in Babylon 5); this fits in with the artificial gates of the 1994 movie Stargate, or 2015’s Interstellar.
Wormholes have a bit of scientific plausibility in that they are mathematically allowed by Einstein’s general theory of relativity. One classic version in physics is known as the Einstein-Rosen bridge. Unfortunately, we don’t know how to actually create them yet.
(For more detail, see chapter 11 in Physics of the Impossible and chapter IV in The Science of Interstellar by Kip Thorne [W.W. Norton & Company, 2014].)
Hyper jumps
Another version of FTL is called the jump or hyper jump. Here you simply fire up your jump engine and are transferred instantaneously to somewhere else. This often includes ideas about the energy required for your jump drive going up as the mass of your ship and the distance jumped increases.
This form of FTL is used in the “reimagined” latest version of Battlestar Galactica. If you want to add some plausibility, you could describe a possible mechanism behind this such as the creation of a very short wormhole that connects the two points in space for an instant.
FTL in your stories
So you want to make use of the big stage of the universe outside our own solar system? Well, if you just use one of the four standard ways discussed in this chapter (warp drive, hyperspace, wormholes, or hyper jumps), you can usually get by with just mentioning it in passing. However, science fiction readers enjoy new and exotic ideas, so if you can build a world in which you invent some wildly different and strange way to create FTL travel, you just may have a winner!