I was going to start building my science-fiction setting looking at the economy of the universe… but I realised that there is something more fundamental. Travel. The universe is so huge that it defies description. Even just a galaxy is an immensely huge space beyond out comprehension. Our solar system is a tiny speck of nothing on a galactic scale (let alone a universal scale), and yet even that is bigger than most of us can properly envisage. A manned mission to Mars (a neighbouring planet) would involve a trip of nine months just to get there using our current technology (with a suitable launch window occurring only every 26 months). (1)
In a science fiction setting that is not limited to one planet, people need to travel between locations. I would very much like a setting that does allow for travel to other worlds and stars. But how?
Three possibilities for intergalactic…. or more reasonably intragalactic (i.e. taking place within the confines of a single galaxy – as in most big sci-fi franchises) are sublight travel, faster than light travel (FTL) and Einstein-Rosen bridges (i.e. wormholes or some sort of similar gate/tunnel/hyperspace system).
Sublight travel between the stars would involve (most sensibly) a constant acceleration method of travel – constantly accelerating at 1g (9.8 m/s²) in order to simulate earth’s gravity for the people on board the vessel – up to the half way point of your journey, and then decelerating at 1g for the second half. This way, you could reach, for example, Neptune in 15 day 8 hours (2) and the nearest star in 3.6 years, (3) giving the crew optimal conditions for onboard-life with simulated earth-like gravity. Some problems to overcome would include the propulsion system used (a futuristic engine/drive capable of extracting energy from the space it travels through) and the dangers of radiation and collision with matter en route (especially at around the halfway point, where specks of dust are potentially lethal. (4) But hey – this is science fiction – we can easily conjure up a suitable drive and some sort of energy shielding, or maybe some sort of navigators (like the guild navigators in the Dune series) who can see all possible futures and plot courses to avoid collisions and other problems.
There are other alternatives too – ships that can’t accelerate constantly at 1g. These however face the huge problem of how vast the universe is. Getting anywhere would take more than a human lifetime. There are ways to solve this; the crew could go into some sort of stasis (like the stasis chambers in the Alien franchise), or inhabit generation ships – huge artificial habitats that travel maybe even more slowly, requiring several generations on board to pass before the destination is reached. Artificial gravity is an issue here…. Maybe the ships are truly huge, and spin, creating centrifugal force to replace gravity. Such a generation ship could certainly provide a cool contained setting.
Lots of fun could be had with time dilation too – travellers zooming between the stars at close to the speed of light will perceive time as running much more slowly. They will age more slowly. How would the cultures on the planets change over time in between the visits from what is essentially a different culture – the culture of the travellers? (5)
Basically – all of these ideas can be, and have been, used in science fiction stories. They can be great fun – but don’t quite suit the style I am looking for. I would say that they exist/have existed in my ‘universe’. But they have been superseded.
Faster than Light Travel
Let’s start by bursting the bubble. Accelerating from sublight speeds to FTL speeds is impossible – it would require infinite energy for an object with mass to reach the speed of light. So – using the 1g acceleration model above, you could never reach the speed of light, let alone surpass it.
Faster than light travel (FTL) is used in almost all science fiction films and series however. The viewer wants to be entertained by galaxy-wide conflicts and quick and easy (mostly plot-driven) travel to distant planets. These franchises all nod respectfully in the direction of the cold hard facts but then find a way to ‘get around’ the problem of accelerating beyond the speed of light. For example, ships in the Star Trek franchise use warp technology, encasing their ships in a warp bubble (basically an Alcubierre Drive) (6). In Star Wars, ships make jumps through hyper space (seemingly leaving normal spacetime), ships in Babylon 5 do the same, whilst ships in the Battlestar Galactica universe make instantaneous ‘jumps’, moving from one point in spacetime to another.
This sort of FTL travel allows stories which basically mimic human history – epic battles between countries (solar systems? galactic quadrants?), epic naval battles (but with spaceships) etc… This can be great fun obviously if we are happy to ignore the fact that it is basically pure fantasy, for there is still a problem with breaking the speed of light this way. Causality. The speed of light is the name we give to the speed limit of the universe, because light is the massless particle that we are most familiar with, and the speed limit of the universe is the speed that massless particles move at and crucially the maximum speed that information and therefore causality moves at. And causality is (for what I am trying to achieve right now) the most important.
Now, this is all a bit tricky and requires a bit of thought, but being able to break the speed of light and leave (and re-enter) your light cone means that effect can precede cause which can actually lead to time travel and all of the paradoxes that arise from this. Plenty of explanations about why and how this ocurs can be found online but this doesn’t necessarily make it easier to understand (for me – at any rate…. but then I am often the least intelligent person in the room). (7),(8) Science fiction author Charles Stross even broke off writing a series (a big shame, because the first two novels are lots of fun) after realising that causality violation due to FTL travel just caused too many headaches and plot problems. (9)
What about that other common method used in science fiction to zip around the galaxy, the Einstein-Rosen Bridge or ‘Wormhole’? Wormholes are short cuts through space time – tunnels that connect two points in space-time which could be in another solar system, galaxy or even on the other side of the universe or different universes. As a concept that is consistent with General Relativity, wormholes are the subject of academic interest and debate (among other things as to whether they actually exist or not). Without a degree in physics (which I don’t have), these papers and discussions are hard to follow. But there seems to be a general consensus, that generally, travelling via a wormhole and arriving at a point in spacetime outside of your light cone would also violate causality. (10), (11)
FTL, in all its forms, seems closer to fantasy than science fiction. There is nothing wrong with that at all. Science Fantasy is perfectly fun and legitimate. Indeed – I will look at this sort of sci-fi in a future post. For the purposes of the ‘universe’ I am trying to create, however, I’ll stick to a backdrop that obeys some crucial elements of the laws of physics as we understand them.
So, does that mean abandoning FTL travel and the freedom to explore the galaxy without lots of tedious slower-than-light travel (in effect becoming book 5 or 6 of whichever fantasy ‘trilogy’ is currently hyped, yet you suspect will never be finished…)? Well – I am going to wave my future-tech wand and conjure some alien science to fix the problem.
Let’s take another look at the wormhole/gate idea. Let’s imagine humanity has stumbled across a network of alien ‘wormhole-gates’ that have been abandoned (immediately creating an interesting mystery) and connect to nearby solar systems across a region of space as yet unexplored. Now the crucial point would be that these gates, whilst offering simple and seemingly energy-free (how? another interesting mystery) travel between different stars, do NOT break causality. Time dilation plays out much as it would when travelling in a spacecraft at near light speeds. A colony two light years away, but connected by such a gate, could be visited simply by entering the gate. For the traveller, the journey would seem almost instantaneous, but two years will have passed from the perspective of observers on either side of the gate.
Trade between different star systems would be possible. It would merely always be with delay. So needs would have to be worked out in advance, or be regular and scheduled, for example monthly fish deliveries from a water world. Why would people bother travelling at all apart from when settling a new planet (or asteroid or space station)? Why not just have automated AI delivering goods, news, cultural goods and media? Well – obviously, some humans will always want to travel. But also, maybe the mysterious aliens who created the gates constructed them so that they only ‘open’ for sentient, biological life in order to prevent them being misused by artificial intelligence of all kinds, from the weak AI of intelligent missiles and the strong AI of robots who ‘are coming to steal our women’ to the super AI of god-like intelligences that, frankly, are the stuff of nightmares.
Travel would be possible, even necessary. Causality wouldn’t be messed with. And lots of interesting story-telling options are opened up.
(5) The Forever War by Joe Haldeman looks at this, as do many other sci-fi novels such as Tau Zero by Poul Anderson, which takes time dilation to the utmost extreme.