An awesome-looking film can tank from poor movie physics mistakes. Because some mistakes are so silly, they insult your intelligence.
Sometimes as I stare at a movie screen, I tell myself,
C’mon, you had a $150 million budget, and you couldn’t consult with a physicist?!
Now, I get it. The entertainment factor would plummet. Because too much realism doesn’t mix well with mainstream blockbuster movies. But, this still won’t stop me from going over my 5 favorite space movie physics mistakes.
#1 Explosions in space
This is the most common of the movie physics mistakes.
You hear loud noise with big balls of glowing fire as a spacecraft explodes. All the while, the nearby victorious spacecraft stands stills. The camera then swings to the captain sitting back calmly salivating at his win, without a care in the world.
In the real world though, space explosions unfold much differently. To better understand, let’s dig into the science of sound and light.
What is sound?
Sound is a mechanical wave, and waves transfer energy from point A to point B through a medium. This medium can be liquid, solid, or gas.
For this reason, the speed of sound depends on the properties of the medium it travels through. On Earth, at sea level with an air temperature of 59 degrees Fahrenheit, sound travels 761 miles per hour.
Important Note: in space, you can’t hear sound. Because sound waves transfer energy through a medium, but space is a vacuum without a medium. So no “boom, bam, blew” noises from explosions and gunshots in space.
What is light?
Light is an electromagnetic wave. Unlike sound, light doesn’t need a medium to travel through. Light travels roughly 186,000 miles per second.
Returning to our space explosion discussion
An exploding spacecraft would flame into a giant expanding cloud of gas. The gas would then travel at supersonic speeds slamming into spectating nearby spacecraft. And the people inside the nearby spacecraft would hear a loud thud as if they had slammed into a wall.
Not surprisingly, being a nearby spectator to an explosion in space isn’t smart. You’d be playing Russian roulette with your life. Because explosion debris is downright dangerous.
The debris shoots out in all directions like bullets shot from a rifle. Except, they wouldn’t slow down until they struck something. Because there’s no gravity to pull the debris down and no air drag to slow the debris down.
So, whether you’re 1 mile or 5,000 miles away from the blast, the projectiles would have the same kinetic energy. And what makes it worse, is there’s no place to hide in space. Scary!
Important Note: in space, you can’t have fire unless a spacecraft carries oxygen. Because fire needs oxygen to sustain the combustion process.
What moviemakers should do
Raise the shields of spacecraft near blasts for protection against debris. Without some shield, nearby spacecraft will get damaged beyond any repair. And with the most insulting element of all, please remove ALL sounds in space.
#2 Space traveler’s helmets
After years of searching, the space travelers finally find an Earth-like planet. Everyone is ecstatic and filled with joy. So the space travelers quickly land their spacecraft and rip off their helmets.
To everyone’s surprise, the planet truly resembles Earth. It’s rich in oxygen with an Earth-like atmosphere. But, hold your horses. Not so fast. The following are a few reasons why you should keep your helmet secured on tightly:
- Oxygen: too much oxygen is as lethal as too little oxygen.
- Other gases: many lethal breathable gases could be floating around.
- Microbes: if the planet supports life, who knows what other alien life it supports. There may be killer alien microbes floating around, you can’t see.
What moviemakers should do
Leave space traveler helmets on!
Don’t have characters remove their helmets right when they land somewhere new. A thorough atmospheric analysis is first necessary.
#3 Lasers fired in space
Do you know those epic Star Wars battles with the X-wing fighters we all love?
Lasers fire non-stop at X-wings. Then, X-wing pilots do some fancy maneuvering to dodge the lasers and fire back. It’s captivating to watch, but not realistic in the slightest. Those red laser spears fired in every direction aren’t visible in space.
Laser: a concentrated wavelength of light made by a device. What’s released from the device is a powerful well-controlled stream of light, or beam.
Now, if you’ve ever used a laser pointer, you know the red dot is only visible when a target is hit. At the target, light scatters from the matter, making the dot visible. And in most instances, you can’t see the red streaking beam.
It’s only when light collides with particles in the air, the beam becomes visible. Because particles in the air scatter and reflect the light in different directions. And some of the light from the beam scatters towards your eyes, making it visible.
The following 3 factors make lasers visible:
- Frequency of the laser: the laser beam needs to be of a wavelength visible to the human eye.
- The intensity of the laser: high-powered lasers emit a high number of photons. Photons are particles of light. So, the chance of light interacting with particles in the air increases. This is why you hear stronger lasers are more visible to the naked eye.
- Impurities in the air: shine a laser pointer through the mist, chalk dust, or smoke. Even more, in a low-lit area, and the laser beam becomes more visible. And yes, in clean air too, you can sometimes see a laser beam. Because light scatters and reflects off from air molecules.
Important Note: the same principle of seeing lasers applies to sunbeams. What we call sunbeams are in fact light from the sun reflecting off small particles in the air. In a vacuum though, you wouldn’t see sunbeams.
Going back to the topic of space, space is a big vacuum. Meaning, particles aren’t floating around everywhere in space. So, what will the photons of light collide with, in space? Nothing!
So, these fired laser spears wouldn’t be visible. Let’s now take this discussion one step further.
Speed of light versus laser spears
X-wing fighters shoot laser spears and light travels roughly 186,000 miles per second. So, how is it possible for the human eye to even see these laser spears? It’d not!
On Earth even, the naked eye can’t even detect these laser spears. Instead, in the best of conditions, it’d appear as a continuous beam from the laser gun to its target.
The infinite range of weapons
The other cool thing is, weapons in space have infinite range. On Earth, gravity eventually drops a bullet or missile. But, in space, weapons would travel until they reached a massive object and fell into their orbit.
More than likely though, a weapon would travel forever given how large space is. No different than how we observe light from stars trillions of miles away. The takeaway is, a fired weapon in space should never stop after a given range.
What moviemakers should do
Create new non-laser spear weapons.
#4 Gravity inside spaceships
The spacecraft doors fly open. The struggling astronaut who was flailing in outer space is quickly pulled inside. Once inside, the astronaut immediately hits the ground. He then rips off his helmet to gasp for air once the doors shut.
The question is, where did the gravity come from all of a sudden? The movie logic is, space doesn’t have gravity or air. So, once air becomes present, gravity is also somehow triggered on. But gravity doesn’t work this way.
What’s gravity? Everything with a mass or energy comes towards each other. It’s a fundamental force of nature. So, two objects having near the same mass will have little to no force between them. But if one object is massive compared to another, the gravitational force becomes noticeable.
Think of Earth and humans. On Earth, we can comfortably walk upright due to Earth’s gravitational force. But, in deep space, it’d be a different story. Objects will float when they’re far from nearby masses.
Let’s return to the struggling astronaut in the spacecraft. The mass of the spacecraft and the astronaut is similar for the purposes of our discussion. As a result, the astronaut would remain floating once inside the spacecraft.
What moviemakers should do
Keep characters floating when they enter a spacecraft. But, this creates an entirely new problem. How is artificial gravity created inside a spacecraft?
Most movies don’t have characters always floating inside spacecraft. One solution is centripetal force. So, a spinning spacecraft will create its own gravity. It’s not the sexiest solution, but it gets the job done.
#5 Thrusters on spacecraft
Most traveling spacecraft in movies have thrusters on full blast driving them forward. The engines glow and rumble loud as they travel. For starters, we learned in space there’s no sound. But I digress.
To explain spacecraft thrust, we need to understand Newton’s second law of motion. This law states an object accelerates or gains speed when a force acts on a mass. In space though, a force makes an object change speed, it’s not used for constant motion. This can be confusing because of what we observe on Earth.
On Earth, to keep a box moving at a constant speed on asphalt, you need to push it with a constant force. You need this constant force to overcome the force of friction and air drag. But in the vacuum of space, there’s no friction. So, a spacecraft doesn’t need thrusters to maintain a constant speed. Spacecraft thrusters would only turn on for the following use cases:
- Accelerate from standstill
- Speed up
- Speed down
- Change direction
Important note: in the real world, spacecraft use as little fuel as possible in space. This is because of the high cost to get fuel into space. So, spacecraft turn on their engines to get up to speed. They then maintain a constant speed using their own momentum with their engines shut off.
At the end of their mission, they’ll again turn on their engines to slow down.
What moviemakers should do
Turn spacecraft thrusters off when traveling at a constant speed. The momentum of the spacecraft will keep it moving at a constant speed without slowing down. But to stop the spacecraft, apply an equal and opposite force to the direction of travel.
Movie physics mistakes wrap up
These 5 movie physics mistakes highlight how most movies are for entertainment only. I can’t lie, I still greatly enjoy most space movies. Especially the Star Wars series.
BUT, it’d be super cool if for once the physics in a space movie could be perfectly nailed. I don’t want to see any rubbish theories used in the movie either to justify the broken physics. Just give me one solid movie without silly science. Yes, I know, going too realistic wouldn’t pad the box office numbers.
Who cares though?! An entirely new demographic of moviegoers may watch. I say it’s worth a shot!
What space movie would you say is the most realistic? I personally side with “Contact, 2001: A Space Odyssey”. Also, which movie physics mistakes do you find to be the most insulting?
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Koosha started Engineer Calcs in 2020 to help people better understand the engineering and construction industry, and to discuss various science and engineering-related topics to make people think. He has been working in the engineering and tech industry in California for over 15 years now and is a licensed professional electrical engineer, and also has various entrepreneurial pursuits.
Koosha has an extensive background in the design and specification of electrical systems with areas of expertise including power generation, transmission, distribution, instrumentation and controls, and water distribution and pumping as well as alternative energy (wind, solar, geothermal, and storage).
Koosha is most interested in engineering innovations, the cosmos, our history and future, sports, and fitness.