Following on from my blog post the other day about the relationship between physics (science) and science fiction, I am now writing a post regarding the different types of Faster Than Light plot devices used in Sci-Fi. This won’t be so much about the actual science of FTL starship drives, I touched on that in my previous post, but rather to give my opinion on the various imaginary technology and perhaps how it relates to plot. In order to do this I will make reference to various books, TV shows, films and computer games from my life as a sci-fi fan (geek / nerd etc etc).
Faster Than Light travel can be broken down into 2 main types, with a further divisional sub-type. With reference to my previous post I will ignore any instance of “actual FTL” and just stick with “apparent FTL” (off the top of my head I can’t think of any of the former anyway). The two main types as I see it are instantaneous and non-instantaneous: Battlestar Galactica is an example of the first, where each starship jumps from one location to the next with zero travel time between points. An example of the latter is StarTrek: it takes time to get from one point to the next. In terms of flavour I prefer the latter. While FTL already bends the laws of physics there still tends to be some logic that is preserved, such as nothing happening in an instant. A further problem is that of teleology: where you assume something about the future and use it to inform the present. A possible exception (of sorts) here would be wormholes or jump gates, but I shall return to that later.
This now brings me to the further subdivision of FTL types: Ship-based devices and non-ship based devices. Yes, my division into types is my opinion and hence arbitrary but I’d like to think I am presenting a logical method of categorization. 
Anyhow, back to the story… a ship-based device could be either StarTrek or Battlestar Galactica: both have FTL drives that propel the ships through space. The latter case, non-ship based devices, would obviously be wormholes or jump gates.
So the 4 types of FTL are Ship-based instantaneous, ship-based non-instantaneous, non-ship-based instant and then non-ship non-instant.
What I’d argue for is to pick a style that you prefer and stick to it. It is better if the story devices are logical and consistent so the reader knows what to expect: while science fiction bends physics, it makes no sense to completely destroy physics (and logic) such that a reader will never know what happens. It wouldn’t be impossible to blend all the styles, in fact I’m sure it can be done, but then it would be necessary to differentiate between the different types at each stage in the story. If travelling between two points is instantaneous (say) then what would prevent all characters in the story from doing that? A little bit of “book-keeping” would be in order to preserve logical consistency.
Let me be clearer: StarTrek makes good use of wormholes and ship-based FTL drives but the travel time is never zero in either case. Recall that everytime a ship in DS9 went through the wormhole it spent some time making the crossing. Could this happen in reality? No idea. No one knows. If wormholes exist then it might truly be the case where the travel time is essentially zero. The *trick* here is that the two end points are already connected before a ship makes a jump. Why the two ends are connected is not wholly important, it could have happened by accident. Where I knee-jerk slightly is when a ship travels instantaneously between two points, this basically says that the end point is known and to some extent that point is connected to the point where the ship is currently standing.
I hope you can see how this leads to problems with causality. All forms of instantaneous travel can cause problems with causality, and that is one of the few places guaranteed to give yourself and your readers a headache. By knowing something about the end point of travel is to say that you have information about that point. Guessing (say, coordinates) is fine but knowledge implies that information can flow from you to it, or back again. If information can flow instantaneously then you have a problem with causality. When there is a connection between two points then information can flow, and this leads you into a tricky situation. To re-iterate: the laws of physics can be bent but reckless, illogical, abandon of such laws is not what sci-fi is about (imo).
Allowing for finite travel times can also boost suspense, readers have to wait to find out what happens next, so it makes for good story telling too. OK, so it wasn’t really a problem for Battlestar, nor for Dune, but if you think on it deeply then you have to wonder why not just travel instantaneously to your destination or just use the device to “search” the other side and figure out if that’s where you really want to go. If it can be done instantaneously then in theory you could scan the entire galaxy (or universe) with relative ease. But enough of that and let me provide a brief list of examples that you can relate to:
Ship-based devices
Instant
- Battlestar Galactica
- Escape Velocity (computer game originally on the Mac)
- Dune (in the film it looks like the Guild Navigator may be taking the ship through space at a finite speed but according to wiki the jumps are instant. Don’t recall the issue being so clear in the books).
Non-instant
- StarTrek – All are non-instant including: Warp Speed, Quantum Slipstream Drive, Borg Transwarp conduits.
- StarWars – Hyperdives
- Andromeda (can’t remember but sure it was non-instant)
Jump gates / wormholes (non-ship based)
Instant
- Space Empires (ditto, although the latter versions came in the 00s) – each sector was connected via a series of wormholes (or similar). The game itself was turn-based but I believe the travel time was effectively zero (could be wrong there).
Non-instant
- Descent: FreeSpace (computer came on the PC, from the 90s) – used big metal rings that connected one part of the galaxy to another. Travel time was not instant.
- StarTrek – Wormholes in StarTrek were non-instant
Interestingly, there are few exceptions in space-faring sci-fi where FTL is not employed. A notable example of such an exception if Alastair Reynolds who stuck with the good old fashioned laws of physics and forced ships to accelerate slowly to maximum speed. Space travel therefore takes thousands of years. This was also the case in the film Event Horizon, the ship was in space for decades.
So what would I do?
Well, I’ve opted for a blend of jump gates and ship-based devices. All non-instantaneous as you might have guessed by now. My division between jump gates and not will depend on the size of the ship. Most small ships will not carry enough energy to make the jumps themselves, plus the technology is fairly new (in my story obvs.) so it isn’t even the case that all large ships have FTL drives. The larger ships in my story will at least have the possibility of carrying an FTL drive, although the technology is a hot commodity so it won’t be entirely common. I hope to use this to build tension by creating a division between the “haves” and “have nots”. There will be a struggle to have the technology and to exploit: of course, I will be playing upon the unintended consequences of such devices. Not necessarily where the drive itself is faulty but where human politics comes into play and the consequences of FTL cause much more trouble than was expected!