Friday, 22 July 2016

Science of sci-fi spaceflight

So this is a (short? well it was meant to be but...) blogpost about some details of the science of sci-fi. I’ll be discussing some general aspects along the “science of spaceflight”. My next posts will be on “does every planet look like home?” and “gender diversity in sci-fi” but these ones I thought best to put online first. It is really meant to be some companion text to my lectures that I’ve given for the course in science fiction at the University of Auckland as well as for my Physics 107/G course. This is because my lecture notes are just PDFs of my slides as it’s always useful to have some text for students to read and revise from. These are also a starting point for more formal “notes” on this subject that I’m putting together with my collaborator on this project, Elizabeth Stanway.

So below we’re going to use sci-fi movies, television, radio and books to point out good, bad and ugly science in these media. Trying to get the mindset to do this is difficult, some people want to take everything apart and say that it’s all impossible. Here we take a more positive view. Sometimes this is easy, sometimes this is difficult as normally things are done to drive a story without actually checking to see if they’d work or are even realistic.

Science of sci-fi spaceflight

The first key thing in a lot of science fiction stories is that faster-than-light travel is possible. Unfortunately in our current understanding of science this is impossible, nothing can travel faster than the speed of light and this is set by the theories of special and general relativity. However it is necessary to open up new worlds for people to be able to visit so stories can events can occur.

There are many “standard” ways of breaking the Universe’s speed limit and some are less/more likely than others:
  • Time and Relative Dimensions in Space (or TARDIS) for short. This is the mechanism used by the Time Lords in Dr Who to travel around the Universe and through time. In reality it depends on a modified version of general relative to move through spacetime between locations and times. The TARDIS itself has also had some dimensional manipulation with it being bigger on the inside than the outside with all this happening due to higher dimensions existing to make everything work. This is a good example of something that sounds plausible but we have no idea how it works.
  • Star Gates, Jump Gates and Worm holes: these are also common in sci fi but most widely used/popularized in stargate. It opened up travel around our Galaxy without the need to have big expensive spaceships. Although programs like Babylon 5, Buck Rodgers and the movie Interstellar had the stargate/wormholes in space. The difference between the two is that the “gates” are traditionally artificial and can go to many places in the Universe while the Wormholes are normally naturally occurring. However the physics is the same and “could work”. In General Relativity there are solutions called Einstein-Rosen bridges which connect two otherwise unconnected points in spacetime by a shortcut through higher dimensions. The problem is we have no idea how to build these things! But we know how they’d work. As a quick aside most of the time the holes appear to be 2D surfaces however it's in Interstellar they point out it should be a 3D spherical zone for the wormhole.
  • Warp Drives: these are the primary engine in Star Trek. It works by shrinking the space in front of a spacecraft and expanding the space behind (i.e. warping it!) then as the spaceship travels at apparently sublight speeds it’s appears to be actually travelling faster than light to an outside observer. Again feasible in relativity but we don’t know how to warp space time in the necessary way….
  • Hyperspace: is similar to the TARDIS but rather than allowing a person to move in time is allows someone to move in space. The real question is, if you can do one why can’t you do another? Although it might be that space dimensions are easier to shortcut around than the time dimensions.
  • Quantum tunnelling/teleportation: ah the good old transporter from Star Trek. Yes all possible but very difficult. We have transported information and single atoms but doing that with an entire person is very difficult. And also you do have a probability to be anywhere in the Universe instantly right now, but it’s very very, very, unlikely. The one extra worthy mention is the show “Quantum Leap” where the main character not only teleported from place to place but also from time to time.
  • Or it could be really weird, I mean we’re talking about things which break a number of well held physical principles so anything could happen to enable us to travel faster than light and it would look really weird and incomprehensible to us, like the infinite improbability drive in Hitchhikers Guide to the Galaxy! [CLIP HERE]

Now while faster than light is one issue, another *HUGE* problem with sci-fi is they have a habit of getting the sublight craft breaking most laws of physics we know. For example, they typically break most of Newton’s laws of motion.

Newton’s three laws were discovered earlier by others but he first wrote them down as:
  1. With no force acting on it a body remains at rest or moves in a straight line with constant speed.
  2. A force acting on a mass causes an acceleration that is related to the force and mass of the object.
  3. Every force has an equal and opposite force acting on another body.

So to explain these a bit more:
  1. This never happens on the Earth as we’re always experiencing the force of gravity so accelerating downwards. Or if we’re moving we experience air resistance that slows us down. In deep space though we should be able to observe this and do!
  2. For the same push it’s very easy to push a small car for instance compared to trying to push a fully loaded lorry. The more massive object needs a bigger force (or more people) to get the same acceleration.
  3. Just think, you’re sitting on a chair that is pushing back up with a force equal and opposite to your weight that is pushing down on the chair. If these weren’t equal you’d sink through the chair or be thrown up to the ceiling.

When we look at science fiction movies, typically those with space battles all these laws are pretty much ignored with airplane in atmosphere flight physics models. Many computer games do this too as the sense and feeling would feel wrong to views, or at least people thought it would do. This has all changed now. Looking at movies like WALL-E and shows like Battlestar Galactica both of these have excellent physics outside in space.

The classic example is in the way that in both of these it is apparent even when engines are switched off that fighters are still in motion and can flip over to fire at a ship behind. When in an atmospheric dogfight, e.g. as in Top Gun, a pilot needs to pull dramatic maneuvers to lose someone behind them and get behind them. A BSG example battle can be seen here. Towards the end you can see how Apollo can maneuver the fighter in a low gravity vacuum.

For a less violent example when WALL-E is lost outside the spacecraft and propelling himself around with a fire extinguisher all the laws can be seen to be in action. For example, how tough it is for him to rendezvous with EVA. See a clip here.

Star Wars is a good example where all the fighters move as if they were in an atmosphere. Although this is a throwback to the 1977 movie when the decision was taken to make sure people believed the space ships so the atmospheric flight physics was used. As can be seen here the Rebel fighters are taken out by Tie Fighters behind them but in Battlestar Galactica they’d just have to flip over and shoot behind them.

One notable mention is that Dr Who can sometimes get it right. There is a classic example in Four to Doomsday when the 5th Doctor is stuck outside a spaceship. He gets back to the TARDIS by bouncing a cricket ball of the spaceship to get a double momentum boost from the ball. Once when he throws it and again a second when he catches the ball once he bumps off the spaceship.

These physics also allow us to decide what is a “good” spaceship design or not. For example do they have a way of having gravity in their spaceship other than a magical gravity motor as in Star Trek and Star Wars.

Ships like those in Defying Gravity, Space Odyssey: Voyage to the Planets, 2001, 2010 and Avatar do have centrifuges on the spaceships that spin to give artificial gravity. Interestingly all these ships are designed for moving around in the solar system alone, apart from Avatar which is an interstellar spacecraft. Therefore most of the craft are similar except in Avatar where the craft has much larger engines as well as a mirror on the front of the craft that acts as a solar sail to help accelerate/decelerate the craft.

If you’re interested in what a real interstellar spacecraft might look like we suggest you look up the “Daedelus” and the “Icarus” projects on wikipedia.

Added note: whenever I give this talk (and after posting this) it's always pointed out by someone that Babylon 5 also had realistic flight and space battles. Now I've only seen bits of it but those who have think it was great and ahead of its time so there is another one to add to the "to-watch" list!