xkcd

by **bentheimmigrant** » Tue Dec 21, 2010 9:36 pm UTC

As we're all aware, the future holds intergalactic space travel complete with gravity. The thing that's always bothered me is, where does it stop? I mean, if a ship is producing earthlike gravity, then surely any and all objects above the plane of the ship (as it is obviously not a single point, but a plane that the people are drawn to, otherwise they'd go diagonally) will be drawn in. So ships in formation, passing comets, etc will undergo this planet-strength gravity. So... How does it work? Will we be restricted to 2001-like circular ships? Or will there be antigravity plating on the top of the ships to prevent massive collisions? These are vital questions.

by **Lazar** » Tue Dec 21, 2010 9:48 pm UTC

My understanding is that there are gravity coils in the upper surfaces of the ship which absorb the gravity or summat.

by **++$_** » Tue Dec 21, 2010 11:41 pm UTC

Gravity is inversely proportional to the square of the distance. If you are standing on the floor of the spaceship, you are only about 100 meters above the gravity generator (the only reason it is so far away is to limit the tidal forces between your head and your feet). If you are orbiting at an altitude of 1000 km, objects on the surface of the planet will feel a force of 10^-8 times Earth gravity, which is insignificant.

Even if the ships are in formation, they will probably be at least 1000 meters apart, keeping gravitational forces at a manageable level.

by **Plasma Man** » Wed Dec 22, 2010 2:20 pm UTC

No, obviously what you do is open a window and let the gravity out in a safe direction. This is how the tractor beam was invented.

by **gmalivuk** » Thu Dec 23, 2010 12:52 am UTC

If your artificial gravity has enough in common with a magnetic field, then you could propose some kind of coil around the ship to keep the field more or less constant inside, while it falls off quite rapidly (inverse-cube in the limit, iirc) outside.

by **bentheimmigrant** » Thu Dec 23, 2010 4:12 pm UTC

Plasma Man wrote:No, obviously what you do is open a window and let the gravity out in a safe direction. This is how the tractor beam was invented.

Hooray for science!!!

by **Roĝer** » Thu Dec 23, 2010 7:55 pm UTC

If the gravity generator is planelike, in the middle of the field there will be no inverse-square law, but the field will be constant with distance. Given the customary ship shape of space ships, as opposed to tower shape, that means a lot of leaking gravity.

by **bentheimmigrant** » Thu Dec 23, 2010 8:08 pm UTC

Roĝer wrote:If the gravity generator is planelike, in the middle of the field there will be no inverse-square law, but the field will be constant with distance. Given the customary ship shape of space ships, as opposed to tower shape, that means a lot of leaking gravity.

Really? That's the single most fascinating thing I've read all day. How does that work?

by **gmalivuk** » Thu Dec 23, 2010 8:26 pm UTC

Gravity (and electric fields and illumination and suchforth) vary as the inverse of the square of the distance to a *point* source. For any of these, though, if you have a plane full of point sources, then the field stays relatively constant as long as your distance to the center of the plane is small enough compared to the overall size of the plane.

by **Sir_Elderberry** » Fri Dec 24, 2010 2:34 am UTC

gmalivuk wrote:Gravity (and electric fields and illumination and suchforth) vary as the inverse of the square of the distance to a *point* source. For any of these, though, if you have a plane full of point sources, then the field stays relatively constant as long as your distance to the center of the plane is small enough compared to the overall size of the plane.

And you can show this with Gauss's Law (for what it's worth.)

by **KrO2** » Thu Dec 30, 2010 12:44 am UTC

Then if you want to keep the inverse square, you can use a point source of gravity. Have a cylindricalish ship with the point at one end (or the center). Curve the floors so that the gravity is always perpendicular to the ground. Gravity will be stronger at the "lower" levels, but that's unavoidable with the inverse square.

Or maybe just have a plane source of gravity small enough that the distance to the center isn't small compared to the size of the plane. What would that do to anything in the same plane as the...plane, but outside its boundaries?

by **Antimony-120** » Fri Dec 31, 2010 10:59 pm UTC

Well if you allow anti-gravity mass (and hand wave a few problems that don't look that large until you actually examine them) you could set it up similar to a capacitor (aka: parallel plate) and have gravity be constant inside the plates, but fall off extremely quickly outside the plates (IIRC it's r^3, but I haven't actually looked at that particular problem in ages and don't feel like thinking about it), which results in the same sort of thing ++$_ mentioned, and is conceptually very similar to gmalivuk's mention of using it like a magnetic field (as opposed to like an electric field as I suggest here).

Edit: On second thought, you don't actually need anti-gravity mass, you just need a gravitational "ground" (a concept with it's own set of problems).

by **Nosforit** » Mon Jan 03, 2011 2:14 pm UTC

"...if two wheels are spun on a common axis, the mutual gravitational attraction between the two wheels will be greater if they spin in opposite directions than in the same direction. This can be expressed as an attractive or repulsive gravitomagnetic component."
- http://en.wikipedia.org/wiki/Gravitomag ... er_effects

Oh, you wanted fictional artificial gravity. =3

"Gravitomagnetic arguments also predict that a flexible or fluid toroidal mass undergoing minor axis rotation ("smoke ring" rotation) will tend to pull matter through the throat (a case of rotational frame dragging, acting through the throat). In theory, this configuration might be used for accelerating objects (through the throat) without such objects experiencing any g-forces."

I'll be using this in the sci-fi book I'm currently writing.

by **Robert'); DROP TABLE *;** » Mon Jan 03, 2011 5:59 pm UTC

Nosforit wrote:"In theory, this configuration might be used for accelerating objects (through the throat) without such objects experiencing any g-forces."

What.

by **minno** » Tue Jan 04, 2011 11:29 pm UTC

Robert'); DROP TABLE *; wrote:
Nosforit wrote:"In theory, this configuration might be used for accelerating objects (through the throat) without such objects experiencing any g-forces."

What.

I'm guessing he means that it accelerates everything in the field uniformly the same way that gravity (almost) does, so the spaceship isn't accelerating relative to the people, so they feel like they're still in freefall.

by **Technical Ben** » Wed Jan 12, 2011 10:55 pm UTC

I prefer an intrinsically complex series of rotation decks.

by **charonme** » Tue Mar 08, 2011 3:05 pm UTC

accelerate the ship constantly until the half of the journey, then rotate everything to the opposite direction and decelerate till destination is reached

by **Technical Ben** » Tue Mar 08, 2011 4:46 pm UTC

charonme wrote:accelerate the ship constantly until the half of the journey, then rotate everything to the opposite direction and decelerate till destination is reached

This is pretty much it.
I've been trying to make some imaginary space craft in Sketchup. To get 1g, they just accelerate at 1g all the time. My current designs are long and thin, so it's like a bit skyscraper. I might have to make them into dishes instead, else climbing all those stair will be tiresome.
When a craft is stationary/in free fall though, you need something else to product gravity. I've added rotating decks for this, but they are not orientated to acceleration. So I'm having to settle with chairs and tables on the walls.

by **gmalivuk** » Tue Mar 08, 2011 5:37 pm UTC

charonme wrote:accelerate the ship constantly until the half of the journey, then rotate everything to the opposite direction and decelerate till destination is reached

Well sure, but this is the fictional science section. Surely we can be more creative than that!

by **charonme** » Tue Mar 08, 2011 8:53 pm UTC

hehe good point, but isn't being able to exert enough force to produce even half a g for days enough fiction already?

by **Technical Ben** » Wed Mar 09, 2011 10:33 pm UTC

Could you have 2 micro black holes orbiting each other to produce gravitational waves? Then use the waves to do this... http://www.youtube.com/watch?v=ynCY58pv ... r_embedded
[OMGosh! I saw the video before, but only of the shapes, never noticed it was so big. I thought it was the size of a water bucket! :O)

So, if you can create enough of these little gravity waves, you could shape a force. It might be a shearing for though. So we end up with all out crew in two halves. :/

by **zmatt** » Sun Mar 20, 2011 9:03 pm UTC

Ok how about this for absurdly complicated;

the uniforms of the ship's crew and any tools they may use that aren't bolted down ad coated in a ferromagnetic material, we will say it's part of the paint for some and woven in for the fabrics. Then under the floor on each deck are a long series of electromagnets that keep you and everything else planted at an approximation to earth gravity. This would be your low tech/brute force method.

by **bentheimmigrant** » Sun Mar 20, 2011 10:25 pm UTC

But then wouldn't the magnetic-ness (can't remember the word) of the clothe have to vary, increasing from the shoes up, so that everything is uniform (you had to pick that word, didn't you)? And then you're stuck being top-heavy when you lie down.

by **KrO2** » Mon Mar 21, 2011 6:18 am UTC

That just means it's not complicated enough yet. Add a computer inside every single thing that needs to be affected by "gravity" so it can vary the strength of the magnets based on how high the item is.

by **Technical Ben** » Wed Mar 23, 2011 1:27 pm UTC

The magnetic nano particles was done in Deifying Gravity. http://en.wikipedia.org/wiki/Defying_Gr ... _series%29
I thought it was very good for the realism of space and keeping it interesting and entertaining. I hate "random physiologic episodes and aliens of infinite power/form" though.
Basically, until everyone started getting strange visions, and the aliens turned up, it was really good. Wish it had kept more to "Appolo 13" and less to "Farscape".

by **JamesP** » Sun Mar 27, 2011 9:39 pm UTC

Technical Ben wrote:The magnetic nano particles was done in Deifying Gravity. http://en.wikipedia.org/wiki/Defying_Gr ... _series%29

Technical Ben wrote:was done in Deifying Gravity.

Technical Ben wrote:Deifying Gravity

I, for one, accept our new gravitational god-kings.

by **Technical Ben** » Mon Mar 28, 2011 2:09 pm UTC

Why can't Firefox have a "dyslexia" plugin? I blame clicking the spellcheck and not reading it.

by **EricH** » Mon Mar 28, 2011 6:09 pm UTC

bentheimmigrant wrote:But then wouldn't the magnetic-ness (can't remember the word) of the clothe have to vary, increasing from the shoes up, so that everything is uniform (you had to pick that word, didn't you)? And then you're stuck being top-heavy when you lie down.

For charges, you get a lovely uniform (there's that word again) force by putting opposite charges on the floor and ceiling. So, if your clothes are charged the same as the ceiling, and opposite to the (insulated) floor, then you've got something, I guess... But I don't know how to do that magnetically, unless your clothes are made with magnetic monopoles. How much extra fiction are you willing to add?

by **Roĝer** » Mon Mar 28, 2011 7:04 pm UTC

If all your clothing has the same charge, it will disperse as far as possible, so your clothing will seem to blow up and it will be hard to fold your arms together. Doesn't seem like the most elegant solution to me.

by **bentheimmigrant** » Mon Mar 28, 2011 7:58 pm UTC

Roĝer wrote:If all your clothing has the same charge, it will disperse as far as possible, so your clothing will seem to blow up and it will be hard to fold your arms together. Doesn't seem like the most elegant solution to me.

That makes a great mental image. I wish they would make more scifi where people are finding these things out the hard way.

by **OllieGarkey** » Mon Mar 28, 2011 8:56 pm UTC

Even with magnetic pull, you'd still probably get bone degeneration and the other physiological problems in space.

If I were to design a space fleet, I would design cylindrical ships, even if I had some kind of Magi-Grav generator.

What happens if gravity fails? On a normal ship, you're boned. On a cyllinder, you do it the old fashioned way until things are repaired.

I'd be very suspicious of artificial gravity systems. What happens during a system overload caused by god knows what?

It is a law of the universe that if a system can fail, it will fail spectacularly. What would a spectacular, rolled triple 1's critical failure look like when the thing failing is a gravity generator?

Would the ship collapse in on itself and resemble a crushed ball of foil?

by **charonme** » Mon Mar 28, 2011 9:16 pm UTC

Technical Ben wrote:I thought it was very good for the realism of space and keeping it interesting and entertaining. I hate "random physiologic episodes and aliens of infinite power/form" though.
Basically, until everyone started getting strange visions, and the aliens turned up, it was really good. Wish it had kept more to "Appolo 13" and less to "Farscape".

Hah! You made me watch the whole series (13 episodes)

but there were no aliens and there was nothing reminding me of farscape, not even a hint

by **Technical Ben** » Mon Mar 28, 2011 10:46 pm UTC

No Aliens? They have one on board, they just give it another name. They called it beta, and it had god like powers. They also have loads of hallucinations. Granted, they did not have "tellytubby" episodes, or animated cartoon episodes, but they all went a little bit crazy. I'd like to see a movie/series where at least a greater than 2 people, the hero and heroine, have common sense. I suppose Star Trek and Star Wars manages it. Oh, also Firefly. Well, most of the popular Sci-Fi. I guess it's why they are so popular.

Back on topic. Even a cylindrical ship could cause trouble if it's gravity device, or thrusters, malfunction. Try fixing it when it's spinning with a force of 5 g, and you've got 4 hours more fuel left to burn through! :shock:

by **zmatt** » Tue Mar 29, 2011 6:51 pm UTC

lol Star Trek and common sense. Don't make me laugh. They get shot at. Damage report. They get shot again. Our shields are at 70%. They get shot yet again. Open a hailing frequency. They get shot again. Ok, now send a warning shot. Yeah, if any military organization acted with the speed of the Enterprise it wouldn't last long in the real world.

by **blademan9999** » Fri May 06, 2011 2:02 am UTC

It's simple, just get a cylindrical ship, and make it spin! Centrifugal force can replace gravity, no power needed to provide after it starts spinning. Although running in particular directions could increase o decrease the gravity the feel.

by **AvatarIII** » Fri May 06, 2011 8:41 am UTC

i've always assumed that there was some sort of cycle of gravity

excuse the simple analogy, but imagine gravitons were water, being pumped through a fountain, so they are constantly being recycled, it's the simplest way i can think of it, without the gravity generator using infinte amounts of energy, constantly producing gavity which is only used for the space of 2 meters per deck or whatever.

alternate to cenrifuge based gravity, you could always have a ship that accelerates at ~9.81m/s/s and flips to deccelerate,

by **BlackHatSupport** » Fri Nov 18, 2011 3:54 pm UTC

No, we obviously need to glare sternly at the gravity as it leaves the ship, making it feel very small and insignificant.

by **eSOANEM** » Fri Nov 18, 2011 5:03 pm UTC

gmalivuk wrote:If your artificial gravity has enough in common with a magnetic field, then you could propose some kind of coil around the ship to keep the field more or less constant inside, while it falls off quite rapidly (inverse-cube in the limit, iirc) outside.

Or you could really on the fact that water is diamagnetic and just use a powerful electromagnet in the ceiling. Of course, this will feel weird because muscles will be pulled more than bones unlike normal, but it's still providing a relatively uniform load on the body.

by **Quizatzhaderac** » Mon Apr 02, 2012 7:17 pm UTC

gmalivuk wrote:If your artificial gravity has enough in common with a magnetic field, then you could propose some kind of coil around the ship to keep the field more or less constant inside, while it falls off quite rapidly (inverse-cube in the limit, iirc) outside.

Agreed: gravity is for chumps, all the cool kids are using gravitomagnetism.

Added bonus: if you fall out of the bottom you eventually will hit the top of the ship. That's not good for the person falling with no air resistence, but awesome to watch.

by **idobox** » Tue Apr 03, 2012 9:17 am UTC

The easy solution:
You build the decks as planar capacitor, insulate the ground and put a highly resistive coating on the ceiling. When you touch the ceiling, you slowly charge your body and get attracted to the ground. I'm not sure where the charges will be in a resistive body in a uniform field, probably around the surface, which would give a weird feeling. And touching things/people that are not charged exactly as much as you would result in shocks.

Funnier:
You inject magnetic material in people, either chunks in the bones, or nanoscale everywhere in the body, and use electromagnets.
And if you use one in the floor and one in the ceiling, you can have am almost uniform field.

Fictionnal science:
You use a stream of particules that can go through your body but cause a drag. Maybe a lot of neutrinos can have this kind of effect, but slow moving wimps would be better, since the collisions would be less harmful.

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