# Artificial gravity

#### gonzo

I was wondering what sort of advances it would take for making artificial gravity seem within reach for ships (not based on spin). I was thinking something along the lines of maybe using extremely pressureized gas. I realize the contribution from pessure is generally small compared to mass-energy, and so I assume a high enough pressure to start having noticeable gravity would be beyond the limits of our material technology to contain, but I don't know the specific numbers.

Can someone well versed in the details of GR run some numbers for me on this to give me a feel for the scale of the problem? Thanks.

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#### Janus

Staff Emeritus
Gold Member
Pressurized gas? Gas presure in a zero G environment would act equally in all directions and would have net effect on a body in any one direction. In a non- zero G environment, increasing air pressure actually would decrease effective weight by increasing buoyancy.

#### gonzo

I was thinking of something like a section "under" the ship of pressurized gas. Sure it would act equally in all directions, but if it was only on one side of the ship, that would become the "floor" (well, not exactly equally if it wasn't in a spherical container, but I don't think that is relevant).

#### pervect

Staff Emeritus
There are two issues. The first issue is the smallness of the pressure term. To give you a rough idea, the pressure at the core of our sun is negligible in terms of affecting it's gravitational field. To make a significant contribution to gravity from the pressure term, you'd need pressures much greater than those in the core of our sun.

The second issue is that the mass of an object with such a pressure would increase, so there is no advantage in having the gravity generated by pressure ,at least if the pressure is isotropic - you'd need the same mass to generate the same field, it'd just be in a less convenient form. There might be some advantage if you could make the pressure anisotropic somehow.

I think Robert Forward looked at the general problem of artificial gravity in "Indistinguishable from Magic", a series of science essays mixed together with science fiction. Probably the simplest "non-spin" idea for generating artificial gravity is a hyperdense disk electron-degenerate matter. The field of such a disk would be approximately uniform as long as the height of an object above the disk is lower than the radius of the disk.

The acceleration at the surface of the disk would be

2*pi*G*rho*t

where G is the universal gravitational constant
rho is the density of the disk
t is the thickness of the disk

#### gonzo

Thanks. Do you know if those essays are online somewhere?

#### Aether

Gold Member
pervect said:
Probably the simplest "non-spin" idea for generating artificial gravity is a hyperdense disk electron-degenerate matter.

#### pmb_phy

Janus said:
Pressurized gas? Gas presure in a zero G environment would act equally in all directions and would have net effect on a body in any one direction. In a non- zero G environment, increasing air pressure actually would decrease effective weight by increasing buoyancy.
The inertial mass and gravitational mass of a body increases with increasing pressure.

Pete

#### Garth

Gold Member
But you will need a awful lot of pressure to make any noticeable difference! It would be easier to simply increase the mass of the floor; and then the effect would be tiny.

Garth

#### gonzo

What about the gravitomagnetic effect of a gas circulating at incredibly high speeds?

#### pervect

Staff Emeritus
gonzo said:
What about the gravitomagnetic effect of a gas circulating at incredibly high speeds?
Forward mentions this idea (though he's talking about circulating white dwarf star material rather than a gas). But Forward's concept is a sort of gravitational catapult, something that will propel matter at high velocity without any "felt" acceleration, rather than a gravity generator.

He (Forward) doesn't give any numbers, unfortunately.

Personally I don't quite see how this works, but I haven't thought about it a lot.

#### Aether

Gold Member
gonzo said:
What about the gravitomagnetic effect of a gas circulating at incredibly high speeds?
gonzo, are you trying to make this harder than it has to be? How about a superconducting electromagnet located in a pontoon below the ship far enough away so that the vertical force gradient isn't a problem, and some steel screws surgically fastened to various bones of each crew member?

#### Sempiternity

Perhaps a centrifugal system could be used. In some forms of science fiction, a large ring is built around a spacecraft that spins around the craft and creates a centrifugal force. Although, that would mean it would attract on all sides of the ring.

Magnetic boots could also be used in a spacecraft to create a sense of gravity.

Also, from Parallel Worlds:
The light beam becomes blue-shifted--that is, it becomes more energetic until it reaches infinite energy, which is impossible. Or, the light beam becomes so energetic that it creates a monstrous gravitational field of its own which collapses the bedroom/wormhole.
Because mass and energy can be converted into each other, black holes can also be created by compressing energy.
Would that mean that gravity could possibly be made from concentrating an exceedingly high energy output into a small space?

#### Crosson

Would that mean that gravity could possibly be made from concentrating an exceedingly high energy output into a small space?
I recall reading that the universal limit on horsepower is 10^63 hp or so. Any more then that, and you are approaching black hole scale curvature

#### GOD__AM

Could they create artificial gravity using a strong magnetic field, like the one used to levetate frogs and such in earths gravity? Changing the position and strength of the field could allow for acceleration without feeling the effects?

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