It’s a standard of science-fiction, so much so that in most movies and TV shows that call themselves science-fiction almost take it as read that Star drives are not impossible. Physicists aren’t so sure as there are huge number of problems that the universe is going to throw in the way of us building Interstellar craft, but some aspects of theoretical physics are beginning to find ways around the laws that the Universe has put in our way.
Reaching for the Stars
The stars are incredibly far away from us, and the galaxy is huge. Just to give you some idea how big our galaxy is think about this for a moment. The Milky Way is a barred spiral galaxy about a 110,000 light-years in diameter containing in the region of 300 billion stars. We live about two-thirds of the way out (that’s 37,000 light-years or so) in the Orion Arm. Now a light-year is, as any ten-year-old science-fiction fan knows, a measurement of how far light can travel in one solar year (which is 5,878,499,810,000 miles or nearly 6 trillion in the short count and only 6 Billion in the long count or 9 and half billion/trillion kilometres) so the light from the Galactic core takes about 37,000 years to reach us from the super-massive black-hole Sagittarius A. This means that if our nearest neighbour (Proxima Centauri at 4.24 light-years away) and our sun were drawn on a map one inch apart the map of our Galaxy to scale would be 721 yards across and we’d be over 242 yards from the centre folds of the map. That’s pretty big, and if we ever want to get out and explore that kind of distance even travelling at the speed of light is going to take us millions of years to explore it all (assuming we slow down and look at each system), a job best done by robots it would seem. So it seems simple then, if we ever want to go on holiday to Proxima Centauri we need to travel faster than light, since even light takes over 8 years to make the round trip. In fact to take a two week cruise out to Proxima Centauri would require our luxury space yacht to travel at at least 220 times the speed of light to get there and back in a fortnight.
Relativity for beginners.
Albert Einstein was a clever chap, perhaps you’ve heard of him. As physicists go he’s probably the most famous example, and there are good reasons for this. For one he quite liked fame and had a quirky sense of humour that went over well with the media in the early Twentieth century; for another he was extraordinarily clever and basically worked out how the entire universe worked one morning on the tram to work. At least that’s how the story goes.
Albert was basically wondering what the world would look like if you were riding a photon (a particle of light) or a tram travelling at the speed of light. He realised that since we rely on light to see the universe it would look like everything had stopped, that time was standing still. What’s more he realised that as far as the person watching him flying away would see him apparently frozen in time too. This apparent paradox lead him to delve into some hefty maths, and in the process formulate new ways of thinking about time and space and how they interact with mass. It took him some time but he worked out rules for this bizarre interpretation of reality, which have since been validated (if not actually proven) by experimentation. They include:
- Space and time are not separated but are one space-time continuum. You can consider time as a dimension.
- Spacetime is not absolute it bends, distorts, stretches and dilates.
- The speed of light is always the speed of light, it doesn’t matter how fast you are travelling when you measure it, or how fast the light source is travelling the emitted rays of light travel at the same speed.
- E=mc² or that is the Energy of a body at rest is equal to the mass of the body multiplied by the speed of light multiplied by the speed of light – which as it turns out is very important.
- Objects that are moving cannot be measured the same as bodies at rest. Motion contracts the length of an object in the direction of travel and a moving body has a greater inertial mass than at rest.
Possibly the most interesting thing about all of Einstein’s theory is that all of these states get worse the closer to the speed of light that the body is travelling. So at 99% of the speed of light a space craft is compressed heavily in the direction of travel and has a mass many times its rest mass and time would seem to be slowed aboard the spaceship to almost a crawl. If you’d like to know more about exactly how much 99% of c has you can go here and find out for yourself (go on I’ll wait)… In Sci-Fi it is often assumed that just getting close to the speed of light is enough, after all at 0.99c time is moving at one seventh it’s normal rate (you checked right?), so a distance that takes the ship fourteen years to travel will feel like only two to the crew. In fact as early as 1930 (Miles Breuer’s “The Fitzgerald Contraction“) this particular trick was doing the rounds, and is the founding plot twist (spoiler alert!) for the original “Planet of the Apes” franchise. The time contraction keeps the crew alive for incredibly long periods of time if you can get close enough to the speed of light without crashing. So if a space cruiser was accelerated all the way upto the speed of light it would have no length at all and weigh an infinite amount (yup, more than the entire universe) which would be pretty tricky to push. Also time on board the space vessel would effectively stop, there would be no time for course corrections or even for the fuel to burn to push us along. All of which is usually enough to make the more practical physicist throw his hands up in the air and declare the whole situation impossible, and indeed — for a chemical rocket — it is. The problem is that things do move at close to, and perhaps even at the speed of light. We even have proof that some things are travelling faster than the speed of light (or at least they look like they were, I’ll get to them). I can almost hear the physicists out there about to explode with objections, but I can silence them with a special word…
Singularities are special, they fell out of relativity almost as a proof against its validity. A singularity is a dimensionless point that has mass—but perhaps you know them by their other name: Black holes. Space-time near a black hole gets so twisted up and compressed by the singularity that even light is swallowed up (potentially some light may actually escape as Hawking radiation, but I digress). The black hole has an escape velocity greater than the speed of light, which means there’s a place in space around the singularity where light will orbit the black hole and anything inside this ‘event horizon’ is trapped and travelling at the speed of light (at least). We don’t know what happens inside the event horizon, can’t even guess with our current physics, but theories abound. My personal theory is that all the energy that falls into a black hole returns to the origin— the Big Bang —but it may form white holes that spew energy (as seen in the Red Dwarf episode “White Hole“) or create wormholes, or parallel universes… the lists go on… but again I digress, the point is that gravity can accelerate a body to the speed of light, because gravity is just the bending of space. If space is bent to make something fall at the speed of light, perhaps it can be bent to let something fall faster than the speed of light…
Super-luminary bodies and Dark Energy
When Astrophysicists look out into deep space they see all manner of strange and startling bodies (there are so many posts waiting to be written here…), but they also see a lot of similarities. Everywhere we look there are galaxies and each one seems to be about the same, we can see how they have changed over time by comparing the ones far away with the ones that are closer, and this is what Astronomers tend to do, cataloguing what they find and building bigger, better telescopes and radio telescopes to look out deeper and farther back in time.
Because physics is a universal science, it doesn’t just apply locally, what is true here on Earth is actually true beyond the limits of what we can see. This means we can look at stars and find a candle; a standard that we can use to compare galaxies and measure how far away they are and how they are moving (or accelerating). Luckily one particular type of star death always creates the exact same profile, our candle is a type 1 supernova. When we looked into the deepest time and space, at the earliest galaxies we got a shock. The candles were there just as predicted but the furthest galaxies were travelling away from us faster than the speed of light… Physicists were horrified, but then theories appeared that made sense of it all and everyone calmed down again and went back to work. Space was inflating, that was all, actually some said we knew it was expanding, it had to from the Big Bang, so that’s fine. These galaxies weren’t really travelling at the speed of light, they were only doing about half that, the rest was optical illusion caused by spatial-inflation. If every metre between us and them had got bigger by the width of the average hydrogen atom that would more than explain the issue. They couldn’t see the energy that was driving this inflation so they called it ‘Dark Energy’. If we could control Dark Energy then we may be able to use it to inflate the space behind a craft, effectively pushing the ship forwards (I’m sure a whole wave of sci-fi writers are about to short-hand FTL drives as Dark Energy Drives).
Let’s do the (Space-)Time-Warp again…
Did you get all that? Space can be compressed by Gravity and inflated by Dark Energy. If you do one in front and one behind then that would be the exact definition of the Star-Trek Warp drive that was used throughout the Star-Trek films and later TV series (previous to The Next Generation the Warp Drive had occasionally been described as a ‘Time Warp [most notably in the Original Pilot ‘The Cage’] that allowed faster-than-light travel which could also work). That’s right, real science (or at least real Physicist Miguel Alcubierre) does think that one day man may be able to boldly go whoosh where no one has gone before. The details of the Alcubierre Warp drive can be found on the web. The only real problems are the Anti-matter core necessary to liberate the literally oodles of energy required and some understanding of dark matter and dark energy that goes beyond pointing and crying (which is all modern physics can really manage) and possibly an exotic matter emitter or two… Well, no one ever said it was going to be easy… In my Paradox War trilogy I describe the ships that use this drive method as ‘Void-Runners’, but Warp drives are quite common, and many ‘FTL Drives’ from early science-fiction appear to operate in a manner consistent with this technology.
Shortcuts & Wormholes
I almost feel embarrassed trying to explain this one to any potential sci-fi fan, but here goes. Think of space as an apple, all the stars and planets are arranged on the surface of the apple. Now an ant that wants to walk from one side of the apple to the other can crawl all the way around the surface, slugging along through space-time. But a worm could bore from one side to the other creating a wormhole that connects the two points in space with a shortcut. Sometimes in movies especially, the apple becomes a fabric, or piece of paper and the worm a needle or pencil, but we still refer to it as a wormhole. Well, Einstein and some of his buddies looked into this and they found that teeny tiny wormholes might exist, and the right exotic matter and energy might let you inflate, stabilise and target the ends of the wormhole. It is sometimes known as the Einstein-Rosen bridge. In science fiction these Wormhole drives go by a number of names, in some cases the wormhole transit is instantaneous, these are usually called ‘Jump’ drives, with variants like Hyper-Jump, FTL Jump, spatial warps, spatial folding, star-gates and so on. If the wormhole transition takes time then it is more normally a Warp Tunnel, Vortex manipulator or Sub-space conduit. The most famous Wormhole drive is actually the Stargate of the movie and various TV shows of the same name. Before that, it was examined in the end of the Disney Movie “The Black Hole” where the crew used the titular singularity to leap beyond the known universe in a most un-Disney ending. Less obviously the spatial-folding used by the Navigators in the “Dune” series by Frank Herbert is also technically a wormhole drive, although the actual spacial-folding is a product of the ship’s engines ,due to the bans on machine minds that could handle the calculations, it can only be managed by a navigator using Spice Melange to ‘see’ the target location. Wormhole technology was a major plot point of the TV show “Farscape“, but the living ship (the Leviathan Moya) in the show used ‘Starburst’ to travel which is much more like Hyperspace. Such Wormhole drives are easily confused with Hyperspace drives, which actually operate on a different principle.
Hyperspace is, as far as we can tell, a purely mathematical construct. Just as a line has one more dimension than a dot, and a square plane has one more than a line, so a cubic-volume has one more than a plane, well a hyper-cubic hyper-volume has one more dimension again, and since some theories predict up to 13 spatial dimensions, you can keep doing that trick a few more times. Top notch physicists get very cagey when higher dimensionality is discussed, they start talking about such higher dimensions being “wrapped up” and so on, so we can’t see them. Which shows how little imagination some physicists have. If I lived in a two-dimensional plane (note this is not the same as living on a plane or a plain), I would not have evolved senses to perceive things beyond my plane, there would be no point. If a cube intersected my planar universe, I would see it as a square, because I would only be able to perceive its four edges where they interacted with my flat world. While the physicists of this Flatland may describe the rest of the cube as being wrapped up, looking at the plane sticking through the cube in three-dimensions tells a rather different story. Now in Sci-Fi the story goes like this, a drive is developed that let’s a ship transit up and down in the hyper-volume, in one particular place they find a special analogue of our universe, only everything there is still very close together, the Big Bang did not inflate everything in this hyper-spatial variant. So if you go there and travel quite short distances in this hyper-space when you come back you have actually travelled a very long way.
Of course, there are lots of variations on the exact mechanism and description, but in general, hyperspace is a parallel space-time where interstellar distances are shrunk, or relativity does not apply, allowing super-luminary speed, or there exist currents that connect stars. It also can have a lot of different names, overspace, subspace, nulspace, and warpspace to list a few. Hyperspace is so common in Sci-Fi that you don’t really need to define it for your readers, it is enough to say Hyper-Drive, hyperspace jump or similar, everyone knows what you mean, and often expect a few common factors such as.
- Most energy is used entering Hyperspace, not travelling in it, so you have to charge the engines for a jump.
- Calculating a jump is tricky as Hyperspace is odd.
- You can’t fly hyperspace by the seat of your pants.
- Things exist and even live in Hyperspace
- Mass has a gravity shadow that extends into Hyperspace and makes it very tricky to enter and exit hyperspace near a planet or star.
- Hyperspace portals need more energy than small ships can generate.
- You can build a Gate that opens portal into hyperspace that smaller ships can use (although this can cause confusion with Wormhole style Stargates).
Often, because of the strange nature of hyperspace you cannot manoeuvre there effectively and must rely on calculating a trajectory, accelerating and then slipping over to hyper-space to coast along. This can lead to hyper-space being described as a ‘jump’ or ‘hop’ where the ship must make a series of such jumps each of several light-years in length to home in on their target star. Here are just a few fictional hyper-space drives: Isaac Asimov’s Foundation series, Frederik Pohl’s “The Mapmakers“, almost everything by E.C. Tubb, and the Star Wars hyper-drives. The Starburst of the Leviathan’s in the “Farscape” universe is described as riding the seams between dimensions or as a one-dimensional vector, the longer you spend in Starburst the further you travel, and the more complicated working out where you arrived is, which sounds pretty much like hyperspace to me. My favourite “Hyperspace” has to be the Psychoactive version called Purgatory in the excellent ‘Roads of Heaven’ series by Melissa Scott which begins with ‘Five-Twelfths of Heaven‘. Purgatory must be manipulated by a pilot through the use of Neo-Platonic imagery that describes the road, a ship’s wheel and the keel-song of your vessel, making a hyperspace jump a very active experience (and an event when reading) rather than a computer (or RD-D2) calculated hop. Any sci-fi producers who are wondering what science fiction series they should make next should option these books.
Inertialess Drives & Tachyons
Made famous by E.E. “Doc” Smith in the acclaimed (but scientifically ropey) “Lensmen” series, starting with Tri-planetary in 1934. The Inertialess drive cancelled the inertial mass of a vessel, which then allowed it to achieve any speed it liked. While nice from a story point of view, even cancelling all inertial mass (dampening the Higgs’ Field perhaps), this wouldn’t actually allow the ship to travel faster than the also massless photons, but still it was a better try than his earlier “Skylark” series which literally dismissed Einstein’s theory and calculations. To actually achieve FTL the Inertialess drive would have to replace the inertial mass of the vessel with an imaginary mass (in the mathematical sense of the imaginary number i or the square root of -1). Instantly the vessel would burst beyond the speed of light, converted into Tachyons (which probably don’t exist, but were ‘invented’ [or postulated if you prefer] by Professor Gerald Feinberg), the only problem being converting Tachyons back into ordinary particles to decelerate at the other end. Still the lack of predictive theory or evidence for their existence has not stopped them being used notable by Frederick Pohl and Jack Williamson in Farthest Star (and the rest of the series) where they used the system as a sort of matter transmitter (beam me up!) between the stars.
…And The Rest
That’s it really for FTL, there are more ideas out there, but they tend to rely of daftness and the drives of the plot more than those of physics. So I’ll only mention Harry Harrison’s ‘Bill the Galactic Hero‘ Bloater Drive, Douglas Adam’s ‘Hitch-hiker’s guide to the Galaxy‘ Infinite Improbability drive and leave it at that… Next Month I’m going to talk about how we might power the ships…