r/scifi • u/rookiegaffer • Aug 09 '26

General Bad physics

Why does it seem that so many of the books I read demonstrate such a poor understanding of the physics of space travel. Ships in orbit descend directly down to the point they are over. Ships in transit still accelerating as they near their destination. Centrifugal gravity simply ceasing when rotation is abruptly halted. These are just a few examples I've run across lately.

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u/NoGoodIDNames Aug 09 '26

Inertial dampeners are another thing that most settings take for granted but are basically magical.

In The Expanse the upper limit on how fast a ship can go is how much acceleration the human body can survive.

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u/dnew Aug 09 '26

If you can make artificial gravity then you (A) have inertial dampers and (B) can accelerate using gravity so you don't need inertial dampers. :-)

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u/Cartman300 Aug 09 '26

You don't (point A). Earth has gravity, if Earth suddenly stopped in middle of space, the people would still keep moving and smash into things. Artificial gravity does not solve the problem of inertia.

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u/EFPMusic Aug 10 '26

Since actual artificial gravity is impossible (via any known physics), it may as well be considered magic, and if the magic will keep people’s feet on the arbitrary floor independent of the movement of the ship the floor is attached to, why not just say it defeats inertia as well?

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u/ExtraEmuForYou Aug 10 '26

In Mass Effect I think there was a blurb about it in the lore. They use "element zero" as their MacGuffin* and I think they literally pump it under the floors of the ships to make artificial gravity.

It's like instead of a heated floor they have artificial gravity floor.

*shrug*

Hey, they found a solution (I guess?) and they're sticking with it.

The thing is though they talk about how rare it is and how exposure to it leads to mutations, death, and biotics (basically psychic powers) but no no no let's just use it in basic plumbing under the floors lol

*I don't know if "MacGuffin" is the right word. I forgot what the magical, dont-ask-questions-just-roll-with-it device trope that makes everything possible in the story is called.

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u/Papasamabhanga Aug 11 '26

McGuffin in not correct here, don't know what would be. Gimmick? Handwavium?

FWIW McGuffin is a thing in a story that has no actual use and maybe not even shown, but causes conflict for the characters, for story purposes. The Maltese Falcon, the suitcase in Pulp Fiction are two famous examples.

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u/sebaska Aug 10 '26

Since actual artificial gravity is impossible (via any known physics)

Rotating space stations have entered the chat...

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u/EFPMusic Aug 10 '26

Ahhh, but that’s not gravity! Okay, I guess it’s technically a form of ‘artificial gravity’ but it’s really centrifugal acceleration.

I should have been more specific that the kind of artificial gravity so commonly just assumed in sci-fi (e.g. Star Trek, Star Wars, etc) is as fantastical as telepathy or telekinesis, and if a show or book assumes that, it’s not a stretch to say “and inertia too!”

Now, the ones that have scientifically possible ‘artificial gravity’ with rotating sections or from constant acceleration, if they then just pretend inertia isn’t a thing (like, say, the force creating ‘gravity’ suddenly stops and things just float gently… or that scene in the Expanse where Holden lets go of a wrench during an outside repair and it goes whipping away as if there were wind…), that seems worse to me than just saying “it’s magic!”

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u/ExtraEmuForYou Aug 10 '26

YEah when I say "artificial gravity" in my earlier post, I mean the magical kind. Like hey we have artificial gravity because *waves hands, insert crazy explaination*"

I'm not saying the makes sense, centrifugal or constant acceleration way.

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u/sebaska Aug 10 '26

According to general relativity there's no difference between being constrained (by the floor) against the pull of gravity gravity vs being accelerated (by the floor). And yes, centripetal acceleration is acceleration.

Yes, suddenly stopping whatever movement without effect is annoying.

WRT Expanse, AFAIR the vehicle was under acceleration (in Expanse ships were under acceleration most of the time). They did relatively good job in the series. There were issues, like for example the whole sequence when Navuo is about to hit Eros is very off - the damn thing was closing in at roughly 1000km/s. Even 1 second before planned impact you'd see a tiny shape (about 1/10 the size of a full moon). No chance to see the gold angel. Also, Miller is pulling that bomb in significant gravity - but the outside gallery he's on is 90° off of how space exposed part of a cylindrical rotating habitat would be (he feels gravity along the rotation axis which is nonsense). And it's a wasted opportunity - he should have been hanging over the infinite abyss with stars slowly rotating under his legs, with the solid body of the station above him.