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Is there a way to either counteract the effect of gravity on a planetary scale or create a planet with a low enough density so as to replicate the effect of weightlessness?

My world takes place on a planet with low enough gravity so as to allow anything and everything to float around unless it has an anchor. Everything has to anchor itself to the world, or else it will simply float off with the slightest of pushes.

The organisms which live on the planet do not have any need of an atmosphere or anything of that sort.

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  • $\begingroup$ How big do you need it? $\endgroup$ – Mołot May 29 '16 at 19:54
  • $\begingroup$ @Mołot There is no size limit. $\endgroup$ – White Fang May 29 '16 at 20:05
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    $\begingroup$ Can the structure be artificial, or must it have formed naturally? The main problem I see here is that if the organisms on the surface are in danger of floating away, what's there to stop the ground itself from floating away and the world just spontaneously disintegrating? $\endgroup$ – ApproachingDarknessFish May 29 '16 at 20:29
  • $\begingroup$ @ApproachingDarknessFish Yet another loophole. Oh boy; well, that's what I asked on here for. It can be artificial, you'll just have to explain why it was made. $\endgroup$ – White Fang May 29 '16 at 20:56
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    $\begingroup$ @SJuan76 - If the planet rotates. There's a lot about this planet that isn't clear! :) $\endgroup$ – anongoodnurse May 30 '16 at 16:01
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Make it hollow, and make things happen inside.

Gravity inside hollow planet would be small, because inside a planet, only mass of what's "below" you matters. There will be hardly anything closer to the planet's core than your people, so gravity would be negligible.

Atmosphere inside would create substantial gravitational pull, but you decided you don't need it.

As you can read on Wikipedia, the fact that our Earth is not like your world was a proof we are not living inside, but on the outside.

This was first shown by Newton, whose shell theorem mathematically predicts a gravitational force (from the shell) of zero everywhere inside a spherically symmetric hollow shell of matter, regardless of the shell's thickness.

Only problem is hydrostatic equilibrium - You either need some unobtanium, or make it really small. Well under planetary size.

The smallest body confirmed to be in hydrostatic equilibrium is the icy moon Rhea, at 1,528 km, whereas the largest body known to not be in hydrostatic equilibrium is the icy moon Iapetus, at 1,470 km.

Hollow sphere is really far from equilibrium, so you would need to get significantly under 1,470 km

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    $\begingroup$ the fact that our Earth is not like your world was a proof we are not living inside, but on the outside. Quoting a Futurama episode, that and the fact that we can see the Sun :-P... sorry could not resist. $\endgroup$ – SJuan76 May 29 '16 at 23:45
  • $\begingroup$ +1 for mentioning gravity is equal anywhere within a sphere! The planet could be purposely constructed. If you want the danger of falling away, make the planet just a spherical frame with plenty of gaps to fall through. $\endgroup$ – Mirror318 May 30 '16 at 23:05
  • $\begingroup$ @SJuan76 You should read arguments and proofs by "inside earth" supporters ;) $\endgroup$ – Mołot May 31 '16 at 10:25
  • $\begingroup$ @Mirror318 Won't work. Tried to simulate gravity force. In holes, there would be steep gradient. Force field there would work like, well, "traditional" SF force field, making it really hard to fall out. Remember, on the outside gravity pulls just like it would for sphere of the same mass evenly distributed. $\endgroup$ – Mołot May 31 '16 at 10:27
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If you don't have enough gravity to hold your creatures then you don't have enough gravity to hold things together, period.

However, if all you're after is a zero-g environment there's another answer: A gas torus being pulled off a world. I'm not sure of the environmental requirements here. Things are held together by tidal forces and will slowly bleed away.

If this route interests you I suggest reading Larry Niven's The Smoke Ring and The Integral Trees.

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If your target is just to let all the creatures float (or be more precise, moves in 3D instead of sticking to a surface most of the time), instead of cancelling the gravity, having a planet that is made up of gas / liquid can also be a good idea. In the real world, astronaut uses water to simulate the state of weightless too.

Take our ocean as an example. Objects in the ocean can easily be float the the ocean surface and can be pushed by the ocean current to very far place. An anchor will be needed to hold things in place.

One advantage of having a gas / liquid planet is that there is no limit in the size of the planet like you make the planet hollow. The only difference is that having gravity may prevent object from being upside-down, which should be quite frequently happening in real weightless situation.

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