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I am creating a sci-fi world for tabletop RPG and I have trouble with one thing and that is artificial gravity. What I need is to come up with some ideas for in-world reasonable explanation for the technology of artificial gravity used in ships or stations, which I can provide to my players, but I have a few limitations and restrictions on that technology so it won't break some other things:

1. It has to be believable. I have curious players, so it cannot be just "it works" explanation. I know currently artificial gravity is only possible through centrifugal force or constant acceleration, but this is not what I am looking for. It does not have to be scientifically plausible (it is not hard sci-fi), but it should have some reasonable and interesting explanation (with only some handwavium elements like exotic matter or similar).

2. It cannot allow for FTL travel. Many interesting artificial gravity explanations in sci-fi are able to manipulate space-time and this also allows for the means of FTL travel (warp drive, mass effect). This is not desirable in this world. FTL in this world is present, but it is very rare and not understood (not human) piece of technology (which should not be the case for artificial gravity).

3. Other, less obvious, uses of the technology should be addressed. Sometimes technology for artificial gravity can create a lot of potential in other areas, which may create some gaps in the world (weapons, shields, industry, propulsion). I am not against some useful applications, but I would like them being acknowledged and it should not be something very ground-breaking.

4. The technology has to be reasonable available. As I said before, the technology can use some exotic matter or elements, but it must reasonable available in the world, where spaceship is expensive, so not everyone can afford one, but it is not something unusual (maybe like private airplane/helicopter in our world).

I already tried to go through this and similar forums, but I wasn't able to find something which would work for me, so I would like to kindly ask for your ideas and suggestions.

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    $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Jan 19, 2023 at 13:42
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    $\begingroup$ David Weber wrote an entire long series of space-opera books centered around the extraordinary career of Honor Harrington, a captain (later admiral) in the Royal (later Imperial) Manticoran Navy (which navy is a space navy, of course). The civilization has artifical gravity (and artifical anti-gravity), which is rather important, but it is never ever explain how they did it. It is just one of the wonderful technologies they have. Did I mention that it is a very successful book series? $\endgroup$
    – AlexP
    Jan 19, 2023 at 13:57
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    $\begingroup$ There is a tag for [artificial-gravity]. You have used the tag. Surely one of those questions is useful to you $\endgroup$
    – Daron
    Jan 19, 2023 at 13:58
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    $\begingroup$ Note that believability is dependent on both how you present it and whatever else you already conveyed in your world. For instance, this would be very hard to explain if you wished to retrace the Apollo space program. In contrast, Star Trek and others have believable artificial gravity just because the premise is to focus on cool/convenient high-tech tools, rather than delving into too much details on the why and how. So my advice for that part is to check with your goals and what you already made :). $\endgroup$ Jan 19, 2023 at 14:07
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    $\begingroup$ You can make up any explanation you want for technology so advanced to be sufficiently advanced to be indistinguishable from magic. No matter how you frame it you're saying that an impossible thing is possible. This is fine as long as you write a convincing enough story for your audience to suspend disbelief. Given that this is just a brainstorming exercise, and brainstorming isn't permitted on this site, I'm voting to close this question. $\endgroup$
    – sphennings
    Jan 19, 2023 at 15:12

9 Answers 9

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I suggest you read through the web comic Schlock Mercenary and lift its technology. This works as follows:

  • "Annie-plants" convert neutronium directly into energy. Just how is not specified, but it has limits, based on plant size, and the plants require synthetic post-trans-uranic elements. The plants are also reasonably dangerous if damaged. "Annie-plant" is a short form of "Annihilation Power Plant", or something very similar.

  • A sizeable mass of neutronium naturally has a significant gravitational field. By manipulation of the neutronium, one can shape this field, to produce artificial gravity. This goes somewhat beyond plausible limits in the strip, but suspension of disbelief through familiarity is maintained.

  • Artificial gravity can also be used to accelerate ships, although relativity still applies, and this does not provide FTL. There is FTL in the strips, but it's done with different technology.

  • The technology is also used to provide weapons, defences, and help to industry.

It's a good example of modern space-opera, worked out in a fair amount of detail.

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  • $\begingroup$ Thanks this looks very interesting, I will look into it more but from your description it may be something I can use or take inspiration from. $\endgroup$
    – Toudwort
    Jan 19, 2023 at 14:29
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    $\begingroup$ Schlock Mercenary makes it pretty clear how annie-plants work: good old-fashioned matter/antimatter annihilation. Both materials are stored as neutronium as a means of maximizing storage density. Antimatter is cheap enough to make in that universe that "fullerened antimatter" is not uncommon in grenades. $\endgroup$
    – jdunlop
    Jan 19, 2023 at 19:12
  • $\begingroup$ @jdunlop: That's not consistent with the behaviour of damaged annie-plants. They don't go "boom" nearly hard enough for that. $\endgroup$ Jan 19, 2023 at 20:55
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Many interesting artificial gravity explanations in sci-fi are able to manipulate space-time and this also allows for the means of FTL travel

Space warping does not need to imply FTL. There have been various people looking at stuff like the famous Alcubierre warp and its descendants, and examining the ways in which it couldn't take you faster than light... being unable to control the warp at FTL speeds, needing a universe-mass worth of exotic matter, unpleasant radiation roasting everything inside the bubble, that sort of thing.

Those things don't necessarily apply at merely subluminal speeds. Assuming you can conjure up a suitable warp in the first place (which isn't guaranteed, but your fictional universe does have non-centrifugal artificial gravity and FTL so certain areas of physics are clearly more amenable to technology there) then there are a number of clever tricks you can do with it. Moving around without having to expend propellant is the obvious trick, but there are other useful ways to twiddle with spacetime without moving around which include building regions of extreme time dilation (like the classic sciencefictional stasis field) and simply bending space locally enough to hold stuff down to a deck.

Because humans like gravitational fields that appear locally uniform and flat, it probably presents as pairs of of "pushers" and "pullers" which have fairly uniform fields in between them. The field won't be totally uniform, but will instead have gradients and curves and things around the edges that will be confusing, unpleasant or even downright dangerous to move through, so you want to have lots of them side-by-side to form a broad area of uniform field with the awkward unitidy bits around the edges.

You might need a sort of G-lock to get in and out of an artificial gravity zone without having to suffer wierd tidal effects, like an airlock that you step into and then turn the local artificial gravity on or off. The grav deck needn't be flat, though a short-radius curved surface is likely to be disorienting to people in it. It might not be very high, depending on the size of the regions of warped space that you're conjuring up... a series of flat layers (not necessarily adjoining, or simliarly oriented) might be more likely than huge open spaces or tall multistorey building-like things.

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Paragravity

One of the least physics-busting ways that I like to use for explaining gravity plating is "paragravity": an as of yet undiscovered fundamental force that acts like magnetism but for baryons.

It doesn't break any physics. If you choose to mess with actual gravity generators instead, conservation laws go out the window pretty quickly.

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There is a realistic way to do this, if you have a vast amount of energy available, a lot of creativity, and a taste for Ig Nobel absurdity.

Every laysperson "knows" that magnets attract metal. People who have more than a high-school knowledge of physics know that magnets do not attract all metals, but they do attract ferromagnetic and paramagnetic materials.

By the way, it has been suggested in similar questions that for artificial gravity you could wear metal armor while standing in a magnetic field. That is a cheat; the armor would be attracted by the magnetic source, but your body would not, so your guts would still be feeling like they are in free fall.

Okay, back to my train of thought. Did you know that if you go even deeper into physics, everything is awesome diamagnetic? And diamagnetic things are usually repelled by magnetic fields. It's just that when they happen to be paramagnetic or ferromagnetic as well, they are attracted instead.

I won't bore you woth the details, but this means that the electromagnetic force can be used to make diamagnet stuff such as living things fly. You just need a magnetic field that is obscenely powerful, but hey, it has been done! Here is a Wikipedia article on it. Fun fact: the levitating frog in the picture there got Andre Geim the Ig Nobel prize, making him the only person to have been awarded both a Nobel and an Ig Nobel.

Now let's finally get to my idea: if such a field coming from below will make you fly, then if it comes from above it will push you down. And since it is a force field it should be felt across and through your body. Suggestion: make it so that the source of the field is very distant from the bystanders, in order to have a low gradient. It could come from a companion ship if you don't want your main ship to be very long.

Consider, though, that having anything metallic on you as the field is activated is orders of magnitude more likely to get you a Darwin award than carrying a loaded gun inside an MRI room.

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    $\begingroup$ Worse still, say a metal filing in you. Also, given the effects that can be induced via transcranial magnetic stimulation, I imagine being in diamagnetic field powerful enough to simulate gravity would do really, really weird things to your perceptions. Or higher thought processes. $\endgroup$
    – jdunlop
    Jan 19, 2023 at 19:10
  • $\begingroup$ @jdunlop on the bright side, that means someone in that setting would not need drugs to keep on rockin' $\endgroup$ Jan 19, 2023 at 20:03
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Wave cancellation

For a specific area, a handwavium wave is produced that shifts gravitational potential by a specific distance. You get an area of artificial gravity on one side, and an area of reverse artificial gravity on the other. Or, you get a zone of null gravity and another of double gravity. The sum of the two gravitational areas cancels out.

Don't think about this one too hard.

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You've heard of glass that darkens with an applied electric field? Introducing Toudwortium!

In the year 2237, Dr. Ramkin Allistair Toudwort discovered an unusually heavy Lanthide with an atomic number of 1080 with a remarkable characteristic. When a minimum mass of 1080 Kg is subjected to a high voltage (at least 100 KV), the electron shell acts to stabilize the nucleus and the atomic number jumps to 3440, but the number of protons and neutrons don't change! When the electric field is applied, this atom acts like an atom with 3.185X the mass with appropriate gravity, but has a factual mass of only 1080.

This effect became known as the "Toudwort Effect" and the atom, Toudwortium.

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Try it without artificial gravity

If you want artificial gravity, you get artificial gravity in your world. Use any of the technologies the others have suggested. In the end, you are designing a hard magic system with technical sounding words slapped onto it. Handle it as one handles such magic system. Incidentally, this is the dark secret of most sci-fi technology.

But before you do this, watch The Expanse. It is a sci-fi setting without artificial gravity. Downward acceleration is either provided by rotating space stations or by the thrust of the ship drives. Note, that this fulfills all your criteria. Ships could be equipped with telescope arms which are used to create spin gravity during orbit or cruise phases. See the Venture Star below.

enter image description here

The other picture is the internal layout of a vessel using constant acceleration. Even low 0.1 or less g will do. This is in fact doable with reasonably realistic technology.

enter image description here

Boots connecting to the decks are the final option, but they have issues as they are shown in the show. Our bodies won't be stable. The solution to the stability issue of the person is to give people light exosuits, which hold the body stable.

And if an occasional freefall segment cones up, it is an interesting interval and you players will adopt to it quickly. I ran a game with lots of freefall once and the players understood it quickly.

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  1. Since the discovery of the Higgs boson, we know that mass has an associated field like electric charge or magnetism. So, it is not difficult to imagine an atom nucleus made of protons and neutrons with negative mass. Negative mass objects would respond inversely in the presence of gravitational fields (e.g. fall upwards). A mundane mining exploration can result in the discovery of rocks with negative mass in Earth's own crust or using some particle accelerator to manufacture negative mass material, you name it.

  2. It cannot allow for FTL travel. Negative mass objects would still have non-zero mass, thus staying an obstacle for FTL travel.

  3. Other, less obvious, uses of the technology should be addressed. Negative mass objects can be used in any application where lifting large weights is a concern, particularly construction, mining, aerospace, etc. You can even think of making negative-mass dumbbells for wheight lowering... :) . Houses partly made of negative mass can stay in the sky just like a tehtered balloon (think of the Jetsons' house). Boats with negative mass ballasts could sail in the skies.

  4. The technology has to be reasonable available. You could simply attach a basket, an engine and a propeller to a block of negative mass material and you have a vehicle that behaves like a blimp. Not difficult to craft.

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  • $\begingroup$ How do you use negative mass to make artificial gravity? $\endgroup$
    – Daron
    Jan 19, 2023 at 16:26
  • $\begingroup$ @Daron stick it to the ceiling. $\endgroup$ Jan 19, 2023 at 16:38
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    $\begingroup$ This kind of negative matter leaves the conservation of energy and the second law of thermodynamics whimpering in the corner. $\endgroup$ Jan 19, 2023 at 21:01
  • $\begingroup$ Wouldn't you need unpractical amount of this kind of mass to actually simulate 1G? $\endgroup$
    – Toudwort
    Jan 19, 2023 at 21:16
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The easiest option - one Newton could have suggested - concerns the equivalence of inertial and gravitational mass. It's not obvious these concepts absolutely have to be the same, and maybe in your world they're not. Imagine a suitable chemical reaction produces a special material, not naturally occurring, with far more gravitational mass than inertial mass. (If it is natural, the home planet gets weirder.) Then a spacecraft with its "lowest" floor made of such a material has artificial gravity.

One interesting point that might affect your story: If that floor is flat, and very wide and long, its gravity doesn't weaken with distance. It's as if the floor beams gravity infinitely up and down through the Universe, and thus acts like a tractor beam.

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