Tuesday, 26 October 2010

Does science fiction need faster-than-light travel?

The simple answer to that is: no, but it's fun.

The slightly less-simple answer to that is no, but the number of science fiction authors, even 'hard' SF authors, who don't try to explore what an FTL-less universe would be like is surprising.

The Enterprise goes plaid.

According to Einstein and backed up by many theories since, the speed of light is the absolute maximum velocity that any object within our universe that possesses mass can travel at. This speed is just short of a startling 300,000km per second, but interstellar and even interplanetary distances dwarf this number. Travelling to the moon at the speed of light would still take 1.3 seconds, for example, whilst the Sun is 8 minutes, 19 seconds away. Travelling to our nearest interstellar neighbour, Alpha Centauri, would take about four and a half years. It would take 100,000 years to cross our galaxy from one side to the other and two million to travel to Andromeda. Compared to the size of the universe, that's still mucking around in our back yard.

For this reason, most works of science fiction employ a faster-than-light (FTL) drive which circumvents the lightspeed restriction. The name is actually a misnomer, as simply accelerating past the speed of light is impossible (it would require infinite energy and would also result in time going into reverse for the traveller, creating significant paradoxes). Most FTL 'cheats' by allowing the traveller to suspend the rules of relativity by instantly teleporting from one point to another by way of wormholes (used in Dune or Peter F. Hamilton's work), or by 'warping' space so the laws of physics no longer apply (this is the favoured approach in Star Trek). Another approach is to have spacecraft move into a parallel universe which is either much smaller than our own but where every point corresponds to a point in our universe. This approach is favoured in Babylon 5, where a ship enters hyperspace, travels a few hundred thousand kilometres, and returns to our universe several light-years from where it started out. Warhammer 40,000 uses a similar realm known as the Immaterium (popularly called the Warp) although the difference is scale is not so extreme, where journeys between stars a few light-years apart can still take days or weeks, whilst traversing the entire Galaxy takes several years. Star Wars mixes the two approaches by having a ship accelerate in real space to lightspeed and is then blasted into hyperspace by the acceleration.

All of these approaches and many others are interesting, but tend to ignore a very interesting feature of real-life physics, namely time dilation.

As a spacecraft approaches the speed of light, relative time on board the spacecraft slows down compared to the outside universe. For example, a spacecraft that travels to Alpha Centauri and back again at 90% of the speed of light would appear, from the POV of people on Earth, to take roughly nine years to complete its trip. From the POV of people aboard the spacecraft, however, it would take just a few weeks. As lightspeed is approached, time aboard the spacecraft slows to the point where immense journeys that take thousands or even millions of years from the perspective of the outside universe are achievable in just a few years of on-board travel.

In fact, time dilation can create incredibly warped effects. A ship that left Earth and could constantly accelerate at 1G would achieve 99.99999% of lightspeed and, as a result, could reach the edge of the observable universe (about 13.5 billion light-years away) in less than a century of on-board time, i.e. within a human lifespan. Of course, this would require a fantastically advanced space drive and some mechanism to prevent the ship from exploding the second it hit any interstellar debris larger than a pinhead, but it is certainly feasible within the laws of physics as we currently understand them.

On a more modest scale, ships accelerating to appreciable fractions of lightspeed and flitting back and forth between nearby stars is reasonably realistic and, in fact, is the basis of interstellar travel in Alastair Reynolds's Revelation Space universe. For the stories to unfold in the Revelation Space novels, Reynolds has two storylines proceeding in tandem on different planets, but they are actually taking place in different years. For example, Storyline A is happening in AD 2500 but Storyline B is taking place in AD 2530 on a planet thirty light-years distant. At some point the characters from Storyline A get on a spacecraft equipped with a Conjoiner drive (which allows rapid acceleration to 95%-99% lightspeed) and travels to the second planet, where they arrive in AD 2530 and join in the storyline there. Thanks to time dilation, the journey only seems to take a few months, maybe a couple of years, from the perspective of the first set of characters, and they age accordingly.

The Millennium Falcon flies into a Doctor Who title sequence, circa 1976.

Bizarrely, very few SF authors seem to pursue this way of handling FTL travel. Mainly this is because space operas love to have multiple sets of characters on multiple planets and it's important that the journeys between the planets take place very quickly and everyone remains in the same temporal space as everyone else otherwise things will get very confusing very quickly. This is a decent enough reason, and is necessary to make the stories make sense. However, it is intriguing that more stories are not written which take into account the lightspeed restriction from the outset.

Outside of Reynolds though (and Reynolds does include a back-door FTL method in the Revelation Space books, albeit a method that appears to be inaccessible for humans, and does use FTL in other books), the only author who seemed to rigorously enforce the lightspeed limitation was Arthur C. Clarke (with the sole exception of 2001: A Space Odyssey, and even there the FTL method was retconned out of existence in the sequels). His Rama Cycle of novels had an alien spacecraft travelling at a bit above half the speed of light (taking twelve years to travel the eight light-years from Earth to Sirius, for example), whilst The Songs of Distant Earth has a human-built spacecraft travelling at lower speeds with the crew in suspended animation.

Whilst the development of new physics which permits FTL travel is possible, at the moment such a drive appears flat-out impossible. While this should not restrain authors' imaginations from using FTL methodology, it is a shame that more authors do not employ time dilation as an acceptable way of getting characters between stars without dropping dead from old age as certainly that appears to be the only way of realistically carrying out interstellar travel at this time.

Recommended reading
Pushing Ice and the Revelation Space Trilogy (Revelation Space, Redemption Ark and Absolution Gap) by Alastair Reynolds.
Rama II and The Garden of Rama by Arthur C. Clarke and Gentry Lee.
The Songs of Distant Earth by Arthur C. Clarke.


PVC said...

Isn't there no FTL travel in the Takeshi Kovacs books by Richard Morgan? The way people in that universe seem to get around that is to transmit their consciousness digitally to a new body.

Liviu said...

Ken McLeod Engines of Light
Sean Williams Astropolis

bunch of generation ship novels, maybe not quite what you want but same spirit of no-ftl

And I strongly endorse reading the Rama 2-4 books which are among the best (and unjustly maligned) sf around with one of the most emotional series ending ever

teflaime said...

Heinlein's "Time for the Stars" is about the development of physics models in a fraction of the speed of light space travel world...

Dave said...

It might be realistic, but I don't think its too fun to have everyone you know age 30 years while you spend a few months on a ship. Seems like it would restrict what you could do with a plot as well.

Anonymous said...

I'm pretty sure that the movie "Flight of the Navigator" is the only sci-fi film/book I can recall that takes into account the time issue with FTL travel.

Brett said...

Mainly this is because space operas love to have multiple sets of characters on multiple planets

This. Keeping a hard light-speed limit in a sci-fi story means that you're automatically constricting your potential setting, unless you want to make time dilation a major player in your story.

That said, some authors do pull it off, and you can make a story in a single solar system work well too (look at KSR's Mars Trilogy).

On a more modest scale, ships accelerating to appreciable fractions of lightspeed and flitting back and forth between nearby stars is reasonably realistic

"Realistic" in the sense that it's physically possible, albeit extremely difficult (and Reynolds "cheats" to make it easier). You don't really get to enjoy the effects of time dilation until you get fairly close to the speed of light (we're talking 80-90% here), and there's no existing model outside of "torch ships" that consume vast amounts of antimatter, or maybe some laser-propelled ships, that can do that. Even Daedalus/Orion was never expected to get beyond about 10% of the speed of light.

bunch of generation ship novels

The problem with generation ships is that, aside from the difficulties of maintaining a stable community in a completely enclosed environment for potentially centuries or thousands of years, vast transit times greatly increase the chance of stuff going wrong with your spaceship. I actually have a hard time imagining the creation of a huge, complex piece of machinery like that, which would continue to operate with no replacement parts or outside maintenance for thousands of years at a time, but who knows?

The Dude said...

I would recommend reading Tau Zero, by Poul Anderson.

It's one of the few hard SF books that I've really enjoyed.

Trellyc said...

Ender's Game is completely build around time dilation. Ofcourse later installments of the series deal with the development of an ftl drive, but a huge part of all four books depends heavily on time dilation.
Besides that I can name plenty of SF titles that don't make use of FTL drives, but none that use time dilation explicitly.

It doesn't really bother me though. Most FTL systems are based on exotic solutions of GR and Field Theory (warp drives, worm holes, etc). As long as the laws of physics aren't blatantly broken but just stretched, I am perfectly happy to make a leap of faith every now and then. :)

Jim Haley said...

The Lost Fleet series by Jack Campbell uses some time-dialation/distorition in its fleet battles, resulting in what seems to me to be a very realistic look at how the physics of space battles would probably actually take place. Though in traveling between stars he does use various "warp" concepts (from the instantaneous fold to the "hyperspace" idea).

franti said...

The Forever War by Joe Haldeman basis the entire series on the complexities time-dilation.

However, were I writing a sf epic, I'd probably try a workaround as well. The reason is one art ease-of-plotting and one-part military strategy, really: as for writing, managing a connected plot that takes place from multiple POVs in multiple years during the same conflict would be hard and, I think, frustrating to write and to read. Haldeman's approach works because it's tightly focused on a single character - if the plot had another character back on earth while the MC was traipsing around the galaxy, he'd only be in half the book because he'd have died because time on earth will have forced his expiration by the time they could link up again.

As for military tactics, it simply makes no sense to utilize time-dilation to strike strategic targets. Say there's a shipping port 30 light years away that you want to take out quickly, it'll still take, from a command-centric POV, 30 years to get there and hit it. Sending a strike force through whatever warp-space FTL thing would have th eelement of surprise, sure, but communication with the force would be impossible until they've completed their mission, which will still take 30 years, even if for the guys on the ship it takes a couple weeks. It would make the FTL equipped troopers a surprise strike team, sure, but they wouldn't be any faster than using banal travel methods, with the added disadvantage of being out of communication with the rest of the force until their mission is completed.

Anonymous said...

Don't forget Joe Haldeman's "The Forever War."

C Scott Morris said...

Scott Westerfield, known for his YA steampunk Leviathon, wrote an excellent space opera duology called the Risen Empire.
In the Risen empire, humans are not able to travel faster than light, so instead they have achieved a number of different forms of immortality. Not everyone can afford to be 'Risen', of course, so there are still some problems. One of they ways his societies get around this is extended hibernation. Even Senators, who serve for terms of fifty years, spend most of their time in cryogenic hibernation, only coming out every few years for a vote.
I do enjoy finding new ways of dealing with FTL travel, but in the end, as long as the author deals with such vast distances and times creatively, the story can still have great appeal.

Ian McDonald said...

Ursula leGuin's Ekumen is tied together with light-speed ships --the time dilation effect forms major structural elements of the series: Ekumen Mobiles and Stabiles can spend centuries flitting between the many world while those they leave age and die. Thhe clever bit is that the whole system of worlds is tied together by the ansible --the instantaneous communication device. One of the earliest relativistic space futures --I hesitate to use the word 'Empire' of the Ekumen.

Dave Cesarano said...

Since The Forever War was already mentioned, I'll leave that out, but I would definitely suggest "The Consul's Tale" in Dan Simmons' Hyperion as an exploration of slower-than-light travel on interstellar commerce... and romance.

Unknown said...

Very interesting read. Good post Wert!

Anonymous said...

Reynold's House of Suns is another example and really gives you an appreciation of how big space is. Plus it's a really good book!

Robert Atlas said...

The earliest relativistic future I can recall was that of L. Sprague de Camp in his Brazil-dominated future.

Bush League Critic said...

Dan Simmons was pretty good about incorporating Time-debt with respect to Ship-time into his Hyperion books. It may not have been strictly legit, but it lent an air of authenticity to the work.

Unknown said...

My grandfather told me, when I was a kid, that the fastest thing in the universe is thought. It may take 4.5 years for light to reach Alpha Centauri, but one's thoughts reach it instantly.

He meant it metaphorically, of course, but I think this describes human imagination in all eras: it tries to escape effort. The books that describe in gruelling detail how people work to reach a small result are labelled uninteresting, while generations feed on small boys having special powers out of pure luck.

Are there many books describing ocean voyages? They were long, not really uneventful, yet people remember Robinson Crusoe better.

Long interstellar travel could be the subject of good sci-fi, as would be anything else that doesn't concern travel, but a book that handles both long voyages with time dilation and some other subject would be just stretching it. Even if Reynolds did not resort to FTL, his books were not about the interstellar voyages themselves.

I've recently read a story about a few generation ships that were going towards their destination, then started sabotaging each other as they competed to reach their goal first, escalating to nuke explosions and jettisoning criocapsules to lose weight and be able to decellerate later. But I can't remember the name.

Jens said...

I've asked myself the same question before: Why do many SF novels ignore / cheat this scientific fact of the light speed barrier?

I guess that one reason is that such a scenario while faithful to real life physics doesn't exactly provide a great venue to stage a space opera on.

It may work well for yarns focussing on a single location (e.g. a spaceship), or perhaps two or three locations at a time (one fast spaceship flying from Planet A to Planet B). But if you think what this would mean for a spacefaring society I think that the result would not be a League of Worlds or a Galactic Empire but rather a group of "Islands in the Sky".
Even for a really close pair of stars at 10 light years distance any communication would be really difficult; I guess it would be hard to think of an administration that would have to wait 20 years for a reply...
If you think of two worlds 500 light years apart (which is still very close from a galactic perspective) any news you would hear from this other world would be about as fresh as the headline of Chris Columbus - no, not directing Harry Potter!! - discovering India.
By the time your response to this news reaches the other planet this event will be as remote in history for the guys there as news about William the Conqueror for us.

My point is that anything that happens on these other worlds -even if they are/were colonies of Earth- is so very much not up-to-date once you'd hear about it "back home" that a interstellar society let alone administration/empire is hard to imagine, unless you cheat with FTL communications.

There are still great stories that can be told in such realistic settings but the spectrum of possible settings will be dramatically limited.

Anonymous said...

When your plot is based on spaceships being stand-ins for sailing ships from the era of Hornblower and Aubrey, or for battleships and destroyers from World War II, physics just becomes a hindrance. Acknowledging it would force you to have to think about societies that didn't resemble Great Britain and its colonies or the Allies and Axis powers. And that would force you to think about what people would be like who didn't live in 19th century Great Britain or the 20th century USA. It's a slippery slope, that's for sure.

jamie said...

An interesting point I though was raised by franti, and I think is touched on in The Forever War, is what happens when you send an army to a planet, and then broker a peace treaty with that planet? Annoyed grunts all-round I'd imagine, or possibly very large explosions.

Of course I'm sure it's possible to write an sf novel where time dilation comes into effect, and make it an interesting, integral part of the work, but it does seem like a lot of work, especially as it would add a whole novel of complexity to the story time-line. I'd quite like to read such a novel, however.

noski - Damn it Wert, I thought you said the pistes were open!

Hrishi Diwan said...

My favorite exploration of FTL travel (an excess thereof really) and then a sudden, catastrophic loss of the FTL ability makes up a large portion of the plot of Dan Simmons'Hyperion Quartet.

He does use the time dilation device very effectively here for a surprise twist at the end (IIRC)

Anonymous said...

Don't forget Wert, the speed of light can only be achieved by massless objects. A ship cannot be expected to reach even a 'sizable' percentage of the speed of light because of its inertia for the forseeable future. For the same reason (inertia) it would also need quite a long distance to decelerate, during which time accelerates again (leading to ageing again). Wormholes are the only 'credible' way of transportation, but for the fact that they would collapse immediately if an object with mass tries to go through it (mass in general relativity changes the space around it - leading to grativity)

Anyway, my point is not hold hollywood movies/series scientifically accountable!

Anonymous said...

It's actually quite common in German SF (no, not Perry Rhodan, but 'harder' stuff).

The Mark Brandis books (who focus more on politics) do not even have interstellar travel, humans there are limited to colonies in the solar systems, with even the Uranus moons taking months to travel there.

And a personal favorite of mine, Dolezal, uses time dilation to great effect, with a couple saying good bye forever as he goes for a journey to a different solar system and accepts she'll be dead or very old when he comes back - and then learns that she also joined a similar expedition a couple of years later so they actually can meet again and live together.

But, I find the multiple star systems approach more entertaining^^. If you can write anything you want, why limit yourself?

Al R said...

Little or no FTL in much of Greg Benford's novels, from "In the Ocean of Night" onward, and they play on a truly galactic stage. These books were a big (and obvious) influence on me when I started writing "Revelation Space".

The Forever War utilises time-dilation but there is also FTL travel implicit in the "collapsar jumps" that the soldiers use to reach the combat zones. I think the time-dilation aspect comes in with the journeys required to get to the collapsars and back.

Stanislaw's Lem's "Fiasco" and "Return from the Stars" are also FTL-less novels.

As Wise Bass says, even near-light travel is going to be pretty damned impossible, at least with gigantic spaceships.

Siderite: that sounds like Chasm City to me...

Kahless said...

@PVC - At the end of Woken Furies the survivors of Kovacs team were on board a modified shuttle about to go into hyper-sleep so they do use ships to some extent.

There must be some form of spacecraft fleet/travel I always took it needlecast's were reserved for Envoys and/or people who could afford it. I think it's mentioned in one of the books about how expensive it is.

Al R said...

Greg Egan, of course ... Diaspora, Schild's Ladder and so on are rigorously non-FTL as far as I recall.

Ultimately it depends on the type of story you want to tell and the mood you want to instill in the reader, I think. I would cheerfully do a full-on FTL universe if I felt it offered interesting possibilities. It's no biggie, for me...

Brett said...

When your plot is based on spaceships being stand-ins for sailing ships from the era of Hornblower and Aubrey, or for battleships and destroyers from World War II, physics just becomes a hindrance.

That's a good point. I've only seen a few exceptions where the author tried to actually develop a more plausible form of space combat. David Weber's stuff, aside from its Napoleonic politics and other space opera-esque technology, does feature things like ships fighting via missiles and beam weapons at the light-second and light-minute range. The same goes for Vernor Vinge's A Fire Upon The Deep.

By the way, the limitations on space travel pose an interesting possibility for the Fermi Paradox. It may be simply that virtually all civilizations don't bother to expand beyond their own star system, and maybe some local systems, because the light-speed lag would eventually fragment their civilization a thousandfold. Not to mention that a civilization that can do that is basically immortal anyways.

Unknown said...

Yes it does and I'll tell you why? On earth the distance between two points point 'a' and point 'b' is a straight line. In space its different. Space is warp. Thereas, the distance between point 'a' and point 'b' are wobbly ellipical orbits. superluminal speeds are needed for the long hull between points. Achieving that takes chnging relativity. Cghanging E=mc2 is simple when you discover the facts. 1) 1904 Einstein's first papaer on the motion of bodies...'cosmological constant' that space was nothing other then 'anti-gravity'. Anti-gravity is opposite of gravity which is energy - like here on earth. Only in space it doesn't exist. too much space between bodies - get it. FTL is another scientist dream one of Rod Kawecki whose written the first book on FTL between E=mc2 and fits like a glove. Nothing changes - just the velocity you can travel. The problem with relativity is that there are too many discrepecies on subject matter and relativity has placed the format for it all. So - its right even if its wrong. We teach it in school and it mathematically doesn't ad up. The inifnite futre arithmatic is flawed if you can find it at all. Betting you can't - even on the web. Another thing is light isn't consant it never cahnges aaso how can it be used to define a univeral speed limit? Huh? THe only thing constant is space.

Unknown said...

Is Time Travel really needed for Sci-Fi ? The answer is no ! You can do it with instantaneous space travel which amounts to about the same thing but faster....Rod Kawecki 2015