How Does Science Fiction Deal with Science?
The Merriam-Webster definition of science fiction:
Fiction based on imagined future scientific or technological advances and major social or environmental changes, frequently portraying space or time travel and life on other planets.
Of course we could always argue about which films are science fiction and which ones aren’t. However, I want to instead focus on “space films”. When the plot centers around space ships, there are certain physics concepts that need to be addressed. So, what are these ideas and how do the movies deal with them?
Let me go ahead an point out something important. I’m not a hater — I’m really not. If there is a movie that gets all the science wrong, I’m completely fine with that. After all, the goal of a movie is to tell a story and not to give a science lesson. Now, if the science is legit — that’s just a bonus.
OK, now for some science.
Sound in Space
What is sound? It’s basically a compression wave in some material. When you talk, your vocal cords vibrate. These vibrating cords push the air to make compression wave. This compressed portion of the air then pushes on other parts of the air such that the compression propagates out and the sound travels.
Here is a great demonstration showing a bluetooth speaker inside of a container when the air is pumped out. Without air, you have no sound.
OK, so what about science fiction shows? How do they deal with this sound in space thing? Really, there are only two options. Here is option 1: just use sound in space (from a classic Star Wars scene).
Here is option 2: no sound in space (from Firefly).
So which way is better? I think this one’s a toss up. If you add a low rumbling noise as a giant ship passes by (in space) it just gives it that impressively large feeling to it. That’s probably what you want to go for, right? Personally, I like the sound in space thing — most shows seem to agree. Also, sound in space is super important for those blaster shots (NOT LASERS) to go “PEW, PEW”. I like that part.
Turning Spacecraft
Suppose you are flying along in your generic and non-labeled spacecraft. Suddenly, you need to change directions (maybe you are in a space battle). In real physics (not the make believe stuff), you need a sideways force to change direction. It all starts with the definition of acceleration:
This says that the acceleration (vector) is the time rate of change of the velocity (vector). If you want to let the time interval (Δt) go to zero, you can write this as a derivative — but I’m going to leave it like it is. Now imagine that you are in a spacecraft making a turn. Here is a diagram — it’s black because it’s in space.
Since the acceleration is towards the center of the circular path of the spacecraft, that’s the direction a force needs to be applied. If you are in a spaceship, you could have a sideways thruster — OR, it might be easier to just rotate your ship so that the main thruster is pointing towards the center. Either way works.
But what about an airplane? How does it move in a circle? Well, it still needs a “sideways” pushing force that points towards the center of a circle but it’s obvious that airplanes don’t have thrusters or propellers on the sides. So, instead they bank. When an airplane (or jet) banks, a component of the lift force pushes in the direction of the center of the circular motion.
Here the background is blue — you know…because it’s the sky. But that lift force has to prevent the aircraft from accelerating up or down AND accelerate to the left (as seen from this view — but the plane is actually making a right turn).
Now for a look at some movies. Here is the USS Defiant from Star Trek: Deep Space Nine. Notice how the ship banks as it turns to the left. Just like an airplane.
Here’s a more realistic way for a spaceship to move. This is a viper from Battlestar Galactica. Check out how it makes a turn.
Actually, one of the vipers seems to bank but the other one rotates and then turns. Maybe you can find a better example — but you know what I’m talking about.
So, which is way is better? Honestly, I sort of like the banking turns in space. Yes, I know that’s not physics — it just looks cool. I remember somewhere there was some stuff about the making of Star Wars. George Lucas wanted the space battles to be something like a dog fight between planes in the Battle of Britain (WWII). That’s what it feels like when I watch it. Also, that’s the way I played with my X-wing toy when I was younger. So, I’ve decided.
Oh, but space combat in The Expanse is pretty awesome and realistic — but I will talk about that shortly.
Flying at a Constant Speed
Let’s say you are traveling from one planet to another. Or maybe it’s to a new star system. It doesn’t matter. You are traveling at a constant velocity. According to physics, you wouldn’t need any thrusters or forces. Remember that if your ship has a constant velocity vector (not turning) then the acceleration is zero (zero vector). That means there should be a zero net force. Without any air drag (you know — because there’s no air in space), you don’t need the thruster on.
So, how does it work in science fiction? Of course there are two ways to make this work. Here is the most common way — look at Star Lord’s ship (the Milano) from Guardians of the Galaxy.
It’s not completely clear, but I would guess that this spaceship is supposed to be traveling at a constant speed (or even slowing down). However, look at the thrusters pushing it forward.
It’s actually kind of funny. This idea that you need a constant forward pushing force to move at a constant speed is based on the physics ideas of Aristotle. Even though these ideas are wrong, they agree with our everyday experiences. If you stop pushing a chair across the floor, it stops. Of course this happens not because there is no longer a force, but because there is another backwards pushing force — friction. In space, there’s no friction so you don’t need a force to move at a constant speed.
There aren’t many examples of spaceships that move WITHOUT thrusters. Here’s an example from 2001: A Space Odyssey.
OK, which way is better? This is a tough one. I mean, just about EVERY case shows spaceships with thrusters on, so it’s tough to see how it would look without it. However, if you do this the correct physics way you wouldn’t be able to have a plot centered around running out of fuel (because you could just keep coasting).
Artificial Gravity
If you want magic-based artificial gravity in your science fiction movie (like Star Trek or Star Wars), I’m totally fine with that. But there is a real physics-based way to make this happen. The key is acceleration.
Suppose your are in an accelerating reference frame (like a car or a spaceship or even an elevator). In this reference frame, Newtonian mechanics doesn’t really work. The basic idea is that an object’s acceleration depends on the total force acting on it — and we normally use real forces like gravity, friction, tension…stuff like that. However, in an accelerating frame you can make Newtonian mechanics work again by adding a fake force.
The value of this fake force is proportional to the acceleration of the reference frame, but in the opposite direction. How about an example? Suppose you get in an elevator and push the “up” button.
In the frame of the elevator, you FEEL heavier — but you are in fact NOT heavier. The gravitational force is the same as it was before. Actually, it’s possible to remove the gravitational force all together and just increase the acceleration of the elevator until the fake force can just replace the gravitational force. BOOM — that’s artificial gravity.
Of course this means that you have to be constantly accelerating for your artificial gravity to work. The simplest way to do this is to make your spaceship spin. Yes, moving in a circle with a constant speed is an acceleration. Here is my full explanation.
Now for some examples. Here is a version of magic-based artificial gravity (it’s magic because they don’t explain how it works).
Yeah, there’s nothing to see here. Now for some physics based examples. Here is a deleted scene from The Martian.
But there a WHOLE bunch of rotating spacecraft in science fiction. Honestly, it’s difficult to keep up — but I try. Here is a plot of rotation speed vs. radius for some different ships (and space stations).
That data is from the following blog post.
But wait! What about a spacecraft that accelerates in a straight line? That’s exactly how they make artificial gravity in The Expanse. One of the big ideas in that show is that someone invented a method to make nearly unlimited rocket propulsion. That means that a spaceship can accelerate by speeding up for half the trip and then turn around and slow down for the second half. It’s awesome.
I couldn’t find a single great clip to show you spaceships in The Expanse, so here is a bunch of awesome shots.
But wait! There’s more! How do you deal with the transition from floating around in outer space to being in a spaceship with artificial gravity? Well, if you use real physics-based artificial gravity it’s not so bad. You just need to worry about getting a human inside of a rotating ship. Here’s how that would work from 2010: The Year We Make Contact. This scene is awesome.
Another way to make this work (with magic-based gravity) is to use air. Yes, you just make the rule that when there’s no air, there’s no gravity. When you add air, you get gravity. I can’t find a good clip, but two examples come to my mind.
The first is from Wall-E. When Wall-E arrives at the ship Axiom, he is hanging onto a small ship. When the ship docks, the hanger bay door closes and BOOM. Wall-E falls down to the ground.
The other example is from the movie Sunshine. There’s a dude that needs to make a jump (without a complete space suit) from one ship to another. When he gets in the airlock, the door shuts and air is added. Guess what happens after that? Yes, he falls down. Air equals gravity.
Here is how you would do that with real physics. Check out this iconic scene from 2001: A Space Odyssey.
Not only is Dave still weightless, you can HEAR the air coming in. Wow. What a great scene.
Faster Than Light Communication
Some science fiction stories take place in a single solar system (mostly) — I’m thinking of The Expanse and Firefly. But most of them are all over the place jumping from one star system to another. I’m not really going to look at how to make these “jumps” or other type of faster than light travel. Instead, let’s look at long distance communication.
Let’s say that I’m on Earth (because I am — at least as far as you know) and I want to send a message to a spaceship in the star system Alpha Centauri — a distance of 4.3 light years.
Yes, we can measure distances in light years. Since light travels at a constant speed of 3 x 10⁸ meters per second, we can use that as our astronomical measuring tool. Here are some of the other distance units that you can use in astronomy.
But the point is that it takes like over 4 years to go from Earth Alpha Centauri. If you use a radio to transmit data — it would ALSO take 4 years to reach Alpha Centauri. In fact, it doesn’t matter what kind of signal you send — it still travels at the speed of light (even gravitational waves).
This makes long distance communication sort of awkward. Suppose you want to tell your Alpha Centauri friends that they left their toaster oven on at home before they left. Well, it would take 4 years for them to get the message and then 4 more years for you to receive their reply that probably says:
Oh crap! I forgot about that. Would you mind using my spare key to go in our house and turn it off? Please send me a message when you finish. Oh, can you collect our mail too? Thanks!
Of course the other way around this situation is to just treat long distance communications like a video chat on the internet. It just happens nearly instantly. My favorite example of this the instantaneous messages in Star Wars.
Who knows where these Jedi are actually located. With this method of communication, it’s like they are already there.
If you want to have some type of space opera over multiple star systems, you should probably cheat with this interstellar communication thing. Oh, I guess you could have some type of futuristic technology that lets you send data faster than the speed of light, but I don’t know how that would work.
