# How can gravity be maintained on a spaceship? [duplicate]

I'm going to take example on a movie called wall.e where there is a huge ship that transports 700 000 humans to flee into outer space, because the earth where these humans lived is too polluted. The ship is an "executive starliner" and holds in its inside a normal city. (If you want to see the space ship, tap in google or whatsoever "axiom Pixar".

But then how could gravity be maintained? In the movie, we clearly see that there isn't any rotation that could create a sort of gravity, since the city inside is horizontal and the spaceship doesn't rotate, it just always move forwards.

As it always moves forward, we could've thought that the ship is providing a sort of gravity because it is moving very fast. But then the city would've been built on the back wall of the ship. But no it isn't.

I've thought of a solution but it doesn't seem concrete. I've thought that few small black holes could be maintained on the bottom of the ship, and like black holes are extremely dense, the ship could obtain a earth-like gravity.They would be displayed in a way that everywhere in the city has the same gravity, not stronger, nor less.

The problem is, for the city that's located higher then the small black holes, the gravity is earth like. But for the machines or structures that are maintaining the black holes and are closer to them, the gravity must be way stronger, how could they resist?

If you have other solutions that don't include the two scenarios (rotation and movement) I've shown in the beginning, please feel free to comment and give your solution.

Also remember that it has to be theoretically possible, not necessarily feasible. Thanks for your help! :-)

• You shouldn't give that example because it only makes your question longer + confusing and doesn't add anything. Everyone knows what you are talking about if you are asking that - a non-rotating (counterexample can be found in the movie 2001) an non-black hole artificial gravity. But since your question is a bit confusing, I'm not sure. Btw, if you are ok with what most people do: "artificial gravitons", I'm not sure if that has any meaning, but you often find that explanation Aug 2 '17 at 9:27
• If you want an explanation for particular movie, you are asking on wrong site. If you are building your world, we can help you - but then ask in a way that will clearly show you are inspired by wall.e, but you expect your world will be different. Aug 2 '17 at 9:31
• It's not velocity that gives the feeling of gravity, but acceleration.. (Einstein's equivalence principle)
– L.Dutch
Aug 2 '17 at 10:28

Currently the only currently viable alternative is actual acceleration, either centrifugal or linear (half journey accelerating forward, then turn spaceship around and start braking).

• Black holes (or other heavy masses) won't work:
• You don't know how to prevent the spaceship to fall into them.
• You need to find a way to move such masses when spaceship maneuvers.
• As you say there's a problem of gravity gradient.
• You can use diamagnetic repulsion with very strong magnets on the ceiling, but it's rather extreme magnetism and could have "undesired side effects".
• String theory leaves a door open (assuming it proves correct), but none has the slightest idea of how to jump that specific loophole.
• Anything else is handwavium.

Note: named cartoon is very nice, but it has about the same scientific correctness as Gyro Gearloose "inventions".

• I wonder if you can combine centrifugal and linear acceleration...
– Aric
Aug 2 '17 at 10:32
• @AricFowler Sure you can! You just need to be careful how. If you will have traditional torus perpendicular to the direction of acceleration, turning engines on will make people feel stronger gravity, and bit more to the apparent side, since it's at the back of your ship and usual apparent down is at the side. If you will accelerate along diameter of your torus, people inside will feel sinusoidal changes in gravity, but constant direction of it. And so on. Aug 2 '17 at 10:42
• @AricFowler Of course you can; does it makes sense? The standard toroidal rotating environment is not well suited for linear acceleration (it would have to be either negligible compared with centrifugal or axial with some way to keep the floor "horizontal"). Wat you could do is to start with linear acceleration, then detach a large section of the spaceship keeping it hooked with a very long (to keep low angular speed) cable and start rotation with around common center of mass (keeps pseudo gravity pushing "down" in the same direction as acceleration); tricky points are transitions. Aug 2 '17 at 10:47
• I think the solution is simpler than you both imagine. Take a rod as your main ship, with thrusters etc. Inside here, there will be linear gravity along the axis of acceleration. Then, have a torus around the central area, with thrusters attached to control rotation. Of course, a flat floor will result in "diagonal" gravity to the passenger, so angle the floor inside the torus. The rotation will add to the linear gravity to boost it up to 1g and possibly higher.
– Aric
Aug 2 '17 at 10:59
• Once past half way, there is no need to rotate the whole ship. If you can angle the floor inside the torus the other way, rotation can continue the same way and thrusters on the opposite end of the rod can slow the craft, maintaining both linear and rotational acceleration. Basically, stick rockets on the space station from 2001; nasa.gov/sites/default/files/images/…
– Aric
Aug 2 '17 at 10:59