Physics in stories


One of the ionic things about Star Wars is the sound a TIE fighter makes as it flies by. Of course, that sound is actually a mistake, although probably a deliberate one: physics don’t allow for sound in a vacuum. Getting all the physics right in a story can be challenging. However, a lot of common mistakes have grown into cliches, which are easier to correct. A story can only benefit from that. Let’s have a look at some common mistakes regarding physics.


I already touched on Star Wars. A lot of sci-fi stories make the mistake of having sound in vacuum. In books this can be as simple as a ‘he heard the whine of the other spaceship’s engine’. There are TV shows that get it right, of course, like Firefly. The reason sound in space isn’t possible is that sound is a wave that travels through a medium. Our ears are built for that medium to be air, but water works too. Vacuum however, has almost no molecules, hence is not a good medium for sound. In fact, it’s the perfect sound-proof insulator.

Another common misconception is that you’d explode in space, or freeze instantly, if you were not in a space suit. You would – in fact – not explode, or freeze. There have been accidents and tests with vacuum, which confirm you have about a dozen seconds before you lose consciousness and as much as a minute and a half before you die. You won’t freeze either, because vacuum is an insulator, and won’t conduct heat. You will lose heat through radiating it from your skin, and direct radiation from the sun could actually lead to overheating one on side. All in all, not good, but not what is often depicted.

Size of the universe

Earth is a part of the solar system. The solar system is part of the Orion Spur, which sits between two galactic arms in the Milky Way and houses some 500 million stars like our sun. The Milky Way is our galaxy and has an estimated 200 to 400 billion stars. There are billions of such galaxies in the universe. Are you getting the picture? A lot of the billions upon billions of stars have planets.

The universe is mind-bogglingly big and contains an incomprehensible number of stars and planets.

Not only are there a lot of stars, they are extremely far apart.The closest star to earth is over four light years away. A light year is the distance light – the fastest known particle – will travel in a year, which is 9,460,730,472,580 km. If you drove a car at a 100 kilometers/hour, it would take 20 times the lifetime of the earth to travel 1 light year. The universe, containing those billions of galaxies, is 91 billion light years in size.

So, if you read about a race of aliens that ‘rule the milky way’ think about what that really means. That race of aliens would somehow control 50 times more stars than there are people on earth. How would they control an empire like that? How do you keep language drift from turning it into a Tower of Babel?

Another example. A spaceship that patrols a ten cubic light-years section of space would have a monumental task ahead of it. Radiation sensors would only register things on the other side of the patrol area ten years after they happen. Yeah, that poses some interesting problems.

Conservation of energy

You will have seen movies where the heroes hide behind a car door or drywall from a storm of bullets. Fun fact: physics have something called the conservation of energy. For a car door to stop a high-speed lead bullet it would have to absorb all of the bullet’s energy on impact. That is possible if the tensile strength of the material is stronger than the bullet force applied to it. That requires thick heavy materials, which normal cars are not made from. The same applies to drywall walls. You can slam through them with a hammer. Bullets go through like it was paper.

All those action heroes in the movies? They should all be dead.

The same goes for magic, which usually violates conservation of energy. Of course, it’s your book, you can violate physics when you want to. However, as a writer, I think you should at least consider the ramifications of what you’re doing. As an example, look at travelling in the Wheel of Time books. This allows instant travel from one place to another through gateways. Okay, cool. Now imagine somebody creates such a gate with the two end-points above each other. Then you shove a water turbine, some plumbing, and water between the end points. Water goes into the turbine, through the gate, and back through the turbine, etc. What does that yield? Free infinite electricity. More energy comes into being than is normally possible under the laws of physics.

Okay, for Fantasy books you can argue that I should suspend my disbelief and go with it. And yes, I do that. I loved the Wheel of Time. Still, not considering the ramifications of magic in your fantasy society at all leads to lazy writing. Often it only takes simple changes, or thinking about the physics can lead to a lot of interesting world building.


I’ll leave at the following statement: know your physics if you write. Heck, know your physics, period.

Martin Stellinga Written by:

I'm a science fiction and fantasy author/blogger from the Netherlands