Is artificial gravity scientifically possible?

[RecoveringYuppy]

The problem with that gravity (and The Martian and others) is that you're always walking uphill.

No. It might look that way but it doesn't feel that way. And it won't even look that way if you are in a rotating cylinder and are walking parallel with the axis. Or any direction if the ship is large enough.

 

[Roboramma]

Why? From what I´ve gathered, science still doesn´t have a full grasp of how gravity really works.

I think Einstein did a pretty good job of showing us exactly what gravity is.

 

[RecoveringYuppy]

I think Einstein did a pretty good job of showing us exactly what gravity is.

And we may not have a "full grasp" of anything, but that doesn't mean we don't know how to do some things. And, in regards to artificial gravity, we had a clear enough understanding prior to Einstein. Newton's laws are completely sufficient to design a station with artificial gravity. Even nuances like the Coriolis effect predate Einstein by a century.

 

[Mike!]

Physicist and science fiction writer Robert Forward wrote a book called "Indistinguishable from Magic", that alternated scientific essays about hypothetical advanced technologies common in science fiction and short stories featuring those technologies. As I recall, the artificial gravity chapter involved somehow manufacturing hyperdense matter and placing it in a thin layer under a surface, with sufficient mass that it generated gravity pulling toward that surface. It couldn't be turned on and off though.

I was thinking along the same lines, what if you had a piece of hyper-dense matter located someplace around the central core of the craft that would in essence, attract everything loose towards that central point?

 

[Planigale]

Have you never gravitied from 0 to 40 between the lights on Sauchiehall street?

Given the whirling sensation I would say this is just the effect of angular acceleration simulating the effect of gravity.

 

[sphenisc]

Given the whirling sensation I would say this is just the effect of angular acceleration simulating the effect of gravity.

So down to several pints of heavy then.

 

[3point14]

I want to say that it was mainly looking at use in stationary facilities

That would make more sense. It would make stationkeeping more resource intensive though.

but it's a 20+ year old book, and it's been about that long since I read it. I remember him also talking about putting the matter in the ceiling of a room, configured so that it would exactly cancel the gravity of a planet, resulting in zero gravity in the room.
In retrospect, he seemed to be overly optimistic in some of his essays. His antimatter essay claimed that the technology to manufacture it in industrially useful quantities already existed (c. 1995), if the facilities would only be designed and built by engineers with the goal of building a power plant, instead of by scientists with the goal of winning a Nobel Prize.

Sounds entirely reasonable...

 

[MRC_Hans]

Gravity is utterly indiscernible from acceleration.

Actually, it's not ^*). However, constant acceleration IS indeed one of the best bets for artificial gravity on a space vehicle. Incidentally, you don't need a full 1g. Even 1/6g like on the moon will make everything much easier.

Hans

*) Gravity diminishes by the square of the distance. Acceleration does not. You won't notice inside a spaceship, but it will be measurable.

 

[MRC_Hans]

I was thinking along the same lines, what if you had a piece of hyper-dense matter located someplace around the central core of the craft that would in essence, attract everything loose towards that central point?

That would not be artificial gravity, it would be the real thing.

Hans

 

[3point14]

Actually, it's not ^*). However, constant acceleration IS indeed one of the best bets for artificial gravity on a space vehicle. Incidentally, you don't need a full 1g. Even 1/6g like on the moon will make everything much easier.

Hans

*) Gravity diminishes by the square of the distance. Acceleration does not. You won't notice inside a spaceship, but it will be measurable.

Bloody (educated) pedants.

Point taken.

 

[theprestige]

That would not be artificial gravity, it would be the real thing.

It's an interesting question. If you're generating a gravity field, that's gravity.

Right now, the only practical ways we know of to do that are to either accelerate, or to gather a lot of mass in one place.

I suppose in theory you could perpetrate shenanigans with the mass-energy equivalence, turning on a concentration of energy that generates a gravitational field of arbitrary strength.

But how would that even work? What does a "concentration of energy" even mean?

And probably the machinery needed to generate even a small amount of gravity via energy field would mass enough to generate that much gravity just sitting there doing nothing. It would be redundant if you needed something the size of a large moon to generate gravity equivalent to the mass of a small moon.

 

[RecoveringYuppy]

But how would that even work? What does a "concentration of energy" even mean?

The idea you're going for would be a concentration of mass in the absence of mass, correct? I think if you look in to the concept of photon spheres you'll rapidly come to the conclusion it's not practical to have a concentration of energy in the absence of mass.

 

[theprestige]

The idea you're going for would be a concentration of mass in the absence of mass, correct? I think if you look in to the concept of photon spheres you'll rapidly come to the conclusion it's not practical to have a concentration of energy in the absence of mass.

Yeah, that's kind of what I figured. I guess the idea would be to pump so much energy into a pointlike region that some kind of transient mass emerges. It generates gravity while it exists, and then dissolves back into energy when you turn the generator off.

But it would take a ridiculous amount of energy to generate a transient mass of any useful "weight". And the explosion that would result when you turned off the generator and all that mass turned back into energy...

... Actually, that's the problem, isn't it? Generating mass from energy is basically trying to explode an atomic bomb in reverse. The masses we've worked with for atomic bombs are about the densest, massiest masses we've ever worked with. And even though we've used them to release amounts of energy far beyond what we can safely harness, they're nowhere near massy enough to generate appreciable gravity fields.

So imagine that in reverse. Imagine how much energy, how many atomic bomb's worth of explosions, you'd have to harness, just to produce a mass equivalent to the lump of uranium in Little Boy. Let alone produce a mass that actually has a gravitational pull you can feel.

 

[Darat]

The nature of gravity is unknown and the question you've asked is open.

In what way do you mean "nature of gravity is unknown" ? In the same way the nature of electricity is unknown?

 

[RecoveringYuppy]

Warning, more pedantry.

Maybe you can use the electromagnetic force, like in The Expanse, but that force acts differently from the force of gravity. It's very strong up close, but weakens quickly with distance.

Actually EM and gravity obey the same inverse square law. The difference arises because you can create an EM in a very small space but creating a gravity well requires a huge object. The large radius of the Earth vs the potentially very small radius of magnets leads to the difference you are talking about.

The "hyperdense matter" solutions that some people have mentioned in this thread would have the same fall off problem you mention here (assuming same size). Similarly, you can avoid the fall off problem with an EM solution by making the magnet large.

 

[rjh01]

The reason artificial gravity has to exist is that in movies zero gravity is hard to produce.

 

[Myriad]

We might not know for certain that artificial gravity is impossible, but if it exists while maintaining the law of conservation of energy, it would have very strange characteristics. Arthur C. Clarke, in one of his White Hart stories, examined the issue from the opposite viewpoint of antigravity. Some experiment or accident (I forget the details) created a sphere (on Earth, near the ground) inside of which gravity was cancelled. But to get anything inside the sphere, due to conservation of energy, you had to shove it in with the same amount of energy it would take to accelerate that thing to escape velocity. And when anything moves out of the sphere, it instantly acquires escape velocity. Which got messy.

For artificial gravity, conservation of energy could require a lot of energy to turn the field on, depending on the nearby mass (e.g. the planet and/or star you're orbiting) and how much mass is inside the field. But Star Trek technology uses ridiculous amounts of energy anyhow (sometimes even on the order of one to the tenth power!).

Actually, there's no need for artificial gravity per se in Star Trek. Star Trek technology includes the capability to push and pull on things at a distance, acting proportionally on each particle of the thing pushed (when needed) instead of necessarily putting pressure on the thing's surface. Deflectors, tractor beams, "inertial compensators", "artificial gravity," and perhaps "holographic matter" all do basically that, in different directions for different situations.

 

[Giordano]

Has anyone yet mentioned that the Coriolos effect would might produce some strange sensations when walking in a rotating environment designed to produce “artificial gravity?

 

[theprestige]

Has anyone yet mentioned that the Coriolos effect would might produce some strange sensations when walking in a rotating environment designed to produce “artificial gravity?

You tell us. What were the results, when you searched the thread for the word "coriolis"?

 

[Meadmaker]

I was thinking along the same lines, what if you had a piece of hyper-dense matter located someplace around the central core of the craft that would in essence, attract everything loose towards that central point?

The inverse square law would still be a problem, unless the ship was somewhat donut shaped, and the habitable zones were far enough away that the distance between the closest zone and the farthest wasn't all that much.



One of the things I find amusing in science fiction is that when spacecraft start getting his with enemy weapons, they might lose power. The warp engines go off line. The lights fail. At some point there is only enough power for life support, and that is about to go, and everyone will die unless someone can effect repairs before the last commercial.

But the gravity generators never go offline, even in ships that have been adrift in space for hundreds of years.