Sciency Words: G-Shortage Illusion

Today’s post is part of a special series here on Planet Pailly called Sciency Words.  Each week, we take a closer look at an interesting science or science-related term to help us expand our scientific vocabularies together. Today’s term is:


I guess this isn’t a real scientific term, at least not yet. The authors of this paper are proposing this term to describe a problem people living on the Moon or Mars may have to deal with in the future.  For colonists, many a sprained ankle or broken bone (or punctured spacesuit) will probably be blamed on the G-shortage illusion.

The human inner ear, which regulates our sense of balance, is sort of hardwired for Earth’s gravity.  The inner ear expects you to feel 1 g of force—no more, no less—due to the planet’s gravity, and it uses that 1 g of force to figure out which way is down.

But imagine you’re a fighter pilot doing all kinds of crazy maneuvers in midair.  Your inner ear has to do some math to keep track of where you are, and which was is the ground, so you don’t crash.  Now if you happen to turn your head while simultaneously pulling a hard turn with your aircraft, your inner ear could make a serious miscalculation.

This is a form of spatial disorientation known as the G-excess illusion, because it happens when you’re experiencing excess G-forces. It’s a well documented and well understood phenomenon, and pilots who aren’t adequately prepared for it can end up making fatal errors while flying.

The G-shortage illusion is sort of the same thing, but it’s caused by the opposite reason.  Imagine this time you’re an astronaut on the Moon or Mars or some other world with hypogravity.  You take your first step.  At the same moment, you happen to turn your head.  Your inner ear gets confused, and as a result…

Until I started learning about hypogravity, I didn’t realize how often Apollo astronauts lost their balance and fell over while trying to explore the Moon’s surface.  The G-shortage illusion in action, it seems.  Fortunately no one was injured, and no one damaged their spacesuit… but they could have.

So dear readers, if any of your are planning to move to the Moon or Mars, tread carefully!

P.S.: While researching for this post, I found this article from Naval Aviation Newsvery interesting.  It’s written by an artist who was hired by the Navy to do caricature drawings about various forms of spatial disorientation, like the G-excess illusion.  Those drawings were then used as visual aids in flight safety training.  If you’re interested in how art contributes to STEM, this article is worth a look.

5 thoughts on “Sciency Words: G-Shortage Illusion

    1. Oh, I will definitely be playing up the clumsiness of my characters after this research. At least the first generation Mars colonists will be clumsy. I feel like people who are born and raised on other planets should be better adapted to them, though of course there’s no research yet to back that up.


  1. I had a bout of “benign paroxysmal positional vertigo” earlier this year. It is caused by floating bits in the inner ear. I did the Epley maneuver a few times, and either it went away or I just got used to it. But it was scary the first time it happened, just sitting down watching TV, turn to look at the wall clock, and suddenly the whole room was spinning. I was sure I was having a stroke or something.

    Anyway, I think that it is possible for the brain to adapt to a consistent input bias from the inner ear, when combining it with visual sense-data. If you spend time in fractional g the plasticity of the brain should make it possible to adapt to it, like it can adapt to wearing funny glasses. I remember the first time a started using multifocal lenses (yes I am old), turning my head while looking down would make me dizzy. I got used to them in a few days though.

    Liked by 1 person

    1. I’m inclined to agree that the brain would adapt. Brain plasticity is a wonderful thing! But the hard research doesn’t seem to exist yet to say for sure. Maybe there would be other factors that we haven’t anticipated yet, or maybe some people will adapt better than others.

      Sorry to hear about your vertigo. I had a mild case of it a few years back. The room felt like it was spinning diagonally and, it was not pleasant.

      Liked by 1 person

      1. The vertigo that comes with cruft in the inner ear only affect one side. Whereas high g or low g will affect both ears simultaneously, so there is that too.

        Fractional g is as expensive to simulate on Earth as weightlessness, basically it’s the “vomit comet”. There is no way to keep it steady for days to see if some people adjust better or not.


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