Time for another post about science knowledge that helps you write good science fiction! Also known as a rant about things that bug me in other people’s science fiction.

Humans were never intended to live in zero gravity. In the past, scientists wondered if we could even survive it. Would our blood still circulate? Would our heads explode?

Luckily, we adapt to it pretty well. You can assume that, in most cases, your characters will be fine. You don’t have to invent grav plating (a thing there is no theoretical basis for; it’s less realistic than warp drive at this point). You can just let them float. This almost never happens on TV because it’s so hard to pull off when filming on Earth, but books are filmed in the imagination, so it’s easy.

It’s hard to really grasp how zero-g works, though, given 99.9999% of people have never experienced it. I find ISS videos very helpful, because you can actually watch how water behaves in space or how people cut their nails. There are so many little adaptations you have to make to everything to make it work in space! You don’t realize how much you rely on a force that pulls everything the same direction till it’s gone.

Liquids in space

Liquids don’t stay where they’re put, in space. If they’re on their own, they float around in a bubble till they hit something. If they’re touching something, they tend to cling to it. If you tried to drink out of an open cup, it would crawl over your face and up your nose. That’s why astronauts usually drink out of pouches with straws in them.

Separating liquids from solids, or gases from liquids, would require a centrifuge. No tapping a syringe to get the bubbles out; it’s going to take more effort than that.

Ever wonder how blood would behave in space? What science fiction author hasn’t, right? Well, if you were bleeding in space, it might spatter everywhere in little blobs (like in Star Trek VI), but more often it would stick to your body, making a bubble of blood over your injury. That would make it difficult for a doctor to get a look at what’s the matter with you and stitch it. But vacuuming it away would make you lose too much!

How your body would react

Your body is constantly straining against gravity. The veins in your legs squeeze blood upward. Your digestive system is directed downward.

Without gravity, your blood would rush to your head, not as bad as when you stand on it, but still to a large enough degree that astronauts complain about chicken legs and puffy faces. Heartburn can be an issue, and you can’t burp without throwing up a bit in your mouth. Without gravity, there’s nothing to sort the bubbles from the liquid in your stomach.

One annoying detail of space is that air doesn’t move around as much. On Earth, warm air is constantly rising and cold air is sinking, resulting in a general mixing-around of air everywhere. In space, if you stay too still (for instance, while you’re sleeping) and there isn’t a fan, you’ll end up with a bubble of high carbon dioxide around your head and get a headache.

Over time, your bones will start to degrade. Your body thinks you don’t need so much bone mass, because your bones aren’t experiencing any stress, so it starts getting rid of a lot of it. The cure is to exercise. Space exercise machines rely on elastic bands to provide resistance in the absence of gravity.

Without lots of exercise, you would become too weak to return to Earth without injury. But astronauts have gotten much better at reducing muscle and bone loss in space. Still, the longest they’ve stayed in space has been a year. After many years, would other parts of the body, like blood vessels, weaken too much to withstand gravity? We don’t yet know.

Getting around

A lot of fictional representations of zero-g assume you could swim in the air. You can’t, air isn’t thick enough to get much purchase that way. Blowing doesn’t generate enough force. Neither does farting (astronauts have tried).

You can turn yourself in air, and if you’re spinning, you can slow yourself down or speed up by how you arrange your body. But if you want to actually impart a force to your body and move in any direction, you’ll need either to push against something or to throw something away.

For this reason, large spacious rooms are a bad idea. If you’re far from the wall, you’re stranded. Since everyone always needs to be near a wall they can push against, space habitats are constructed as fairly narrow tunnels.

What about magnetic boots?

Idk bro what ABOUT magnetic boots?

Magnetic boots are stupid. Imagine you could fly. Why would you turn around and bolt your feet to the deck so you didn’t have to? Say you’ve got a long hallway to get down, fifty feet long. Would you rather push hard on the wall at one end and coast to the other, or trudge down the hall on boots that try to stick to the floor when you don’t want them to?

On spacewalks they’re even more asinine. Sure, you want to connect yourself to the ship while leaving your hands free to work on whatever you’re fixing. With you so far. But having your feet connected to your work surface is not handy. Imagine you’re under the kitchen sink, fixing pipes. Would it make sense to have your feet inside the cupboard with you? No. It would not. I cannot imagine a single thing you could ever fix while your feet were stuck to the outside of the ship. Your knees, maybe. But real astronauts just use tethers and I can’t see a reason why you wouldn’t just do that.

You know why people in Star Trek, The Expanse, and so on wear magnetic boots? Because that makes it easier to film. It’s the only reason. Throw the magnetic boots away.

Velcro is even worse. Not only would you have to rip your shoes off the ground with every step, but velcro causes static and can start fires. This is why NASA stopped carpeting surfaces – static can be deadly in small, enclosed spaces.

Gecko boots were a feature in Dead Space, which I read recently. But these were for an asteroid with very low gravity, not none. I can see it. Say your body tends to want to go down, yet your weight doesn’t sit heavily enough on your feet to get very good traction. (This is similar to how it is walking in a pool; your feet touch the ground, but you can’t seem to get a good purchase with them.) Enter sticky boots which help you generate the force you need when stepping.

However, with practice, you could walk in low gravity without boots. Mary Robinette Kowal has her characters use the “lunar lope” – leaning forward at a steep angle, as much as 45 degrees, so that your feet push backwards on the ground more. I see no reason why that wouldn’t work. You’d just need to be careful not to jump too high and crack your head on the ceiling. Save the kangaroo jumping for trips outside.

Things float away

Over the course of our Earth-bound lives, we’ve learned some basic instincts, such as “when I drop things, they fall” and “when I leave things somewhere, they stay there.” Neither is the case in space. Eating a sandwich? Sure, you can let go of it for a second and it’ll stay put. Till it starts to wander off. Your toothbrush will drift away while you’re rinsing. Clipping your toenails? Guess what, the clippings will drift off and end up grossing out your crewmates.

Astronauts have all kinds of ways to deal with this. Tools get strapped down; everything has a place. Crumbs are the enemy: you can’t just brush them to the floor and sweep them up later, so they eat food that doesn’t crumble, like tortillas instead of bread. They clip their nails by an intake vent so they stick to the vent cover.

One of the most troublesome issues is going to the bathroom. Never have you ever wanted substances taken away from your body by an invisible force so much. With gravity right out, they use fans that move air away from you and into the poop receptacle. It’s not pleasant, but it’s better than what early astronauts had to do – use a plastic bag. At least once, turds got loose and drifted around a crew capsule. We have all the transcripts of the crew discussing whose turd it was.

What about the possibilities?

I don’t like to talk only about the inconveniences of a lack of gravity. There are also upsides. After all, who among us hasn’t wanted to fly?

Imagine space ballets in three dimensions. (Diplomatic Immunity, by Lois McMaster Bujold, has one.) Imagine sneaking up on someone, making no sound because your feet don’t touch the floor. Imagine a muffin that was all top. How much would dough expand without gravity pulling it down? Should we try to make the universe’s best souffles? You’re darn right we should!

Zero-g is inconvenient enough, and bad enough for the health, that it’s safe to say humans would try to come up with substitutes whenever possible. (Thrust gravity and centrifugal force are the two main hard-science options.) But in plenty of scenarios (small ship going reasonable speeds, top of space elevator, tiny asteroid) zero g can be the only option your characters have. So why not have fun with it?