minigravity (n., slang): The level of gravity present on dwarf planets, small moons, large asteroids, et. al. While not rigorously defined, the minigravity range is commonly held to be between 0.2 and 0.005 standard gravities, anything below which is considered to be de facto microgravity. Unofficially, the range at which gravity is high enough to require your attention, but too low to rely upon.
– A Star Traveller’s Dictionary
Okay, let’s talk about paragravity.
First up, a note on nomenclature. Paragravity is one of the two things that an Imperial habtech might be referring to when they talk about artificial gravity, the other being spin gravity. Unlike spin gravity, which is “powered” by good old centrifugal force, paragravity is produced by ontotechnological space magic that does wonderfully complex things involving information physics and grand unified theories and other such things to poke the universe in exactly the right way – basically, one branch of the mass-inertia-and-momentum manipulating vector control.
Which is to say that it is produced by gravity rotors, suitcase-sized boxes with a power connector, a ‘weave connector, and a thermal management connector on the outside, filled with solid-state hardware that is a proprietary product of Mariseth Gravitics, ICC. And into whose internal workings we shall thus respectfully avoid going.
What we’re talking about here is how they work on the outside.
The field of paragravity (the gravity envelope) can only be created between two gravity rotors of opposed polarity. That gets you a straight field (with perhaps some convex distortion at the edges) between the two, which imposes a force functionally identical to mass-generated gravity (i.e., affecting all atoms, etc., equally) on everything with mass inside it. This creates a consistent down direction towards what, for the sake of designation, we shall call the “positive” rotors.
(You have to have a closed envelope, and can’t operate an unpaired gravity rotor even if you wanted to: since the universe is functionally infinite in whatever direction you’re pointing it, energy requirements for the half-field head asymptotically for infinity, at which point the circuit breakers save you from a messy ‘splosion.)
Both momentum and energy are conserved, as they would have to be.
The former is the reason that you gravity rotors should be bolted firmly to the structure of the hab; whatever force they exert is, per Callaneth’s Lemma (or Newton’s Third Law, whatever name you prefer), reciprocally exerted too, half to each rotor in the pair.
While difficult to arrange even deliberately, this does imply that if you can get enough mass in one spot and move it just right, you can get the gravity rotors to tear themselves free and leap in the appropriate reciprocal direction.
With regard to the latter: it takes energy to establish the gravity envelope, but once it’s up and running, maintaining it takes only minimal energy physically speaking. (I.e., it still consumes quite a bit of energy in the rotor while it’s up and going, because rooting the universe ain’t cheap; that energy just doesn’t go into the envelope. It’s this waste that makes paragravity a real expensive thing to run.)
That, however, is only true so long as nothing is moving within it. Falling objects, moving in the down direction of the envelope, take energy from the envelope as they gain kinetic energy. (Likewise, when you lift an object within the envelope against its downforce, that pushes energy into the envelope, which is a surge effect that the hardware has to cope with. Alas, it’s not something that can be harvested in the majority of applications.) You could call this paragravitational potential energy if you like, since it sits in essentially the same place in the relevant equations.
While it takes the rotors a little while to initialize from a cold start (although some of this time is self-diagnostics and the like), once up and running, though, you can change the parameters of the gravity envelope very quickly; and you can generate pretty much any amount of gravity you want up to their capacity so long as you’re willing to spend the energy (which varies proportionately) needed to do it.
This is what lets you use the exact same technology for inertial damping; you just have appropriately oriented gravity rotors cancel out your engine thrust inside the starship – while bearing in mind that this will have certain effects on your structural load. (Likewise, you can use them when grounded – but since they don’t block planetary gravity, if you want 1G in the cabin when landed on a 3G world, you will actually be running the paragravity system at -2G.)
The drawback, however, is that the same lack of “inertia” in operation that lets you change your gravity quickly means that they fail equally quickly – and shut down essentially instantly if the power fails, just like an electromagnet’s field collapses – so failing to keep up maintenance schedules may mean being abruptly smashed to the deck with a force of twelve gravities! Caveat engineer.
No Gravity For You: Subverted, since the knowledge of how to move in microgravity is commonplace, and microgravity-friendly martial arts are almost as commonplace. And, indeed, a majority of spacer habitats and starships run without gravity anyway. Not like they’re a bunch of dirthuggers, y’know?
(And if you are using spin gravity, stopping the spin – which turns off gravity for the whole habitat – is very definitely not something you do this casually.)
If you are using vector-control gravity, however, the attack mode you use isn’t disabling the gravity, it’s reversing the gravity repeatedly and quickly (a maneuver delightfully referred to as “grav pong”) until you’ve bounced the villains into submission. Or unconsciousness.
“Academician. Academician.” The foundry master wiped his hands on his leather apron, and waved at the looming bulk in the back of the workshop. “Your sky-tube’s coming along to plan. Just got the wire-wrapping on today. The woodwright’s’ll be here tomorrow to get the quarter-boards on her, and your chymist seems satisfied. Though I’d appreciate it if you’d have him do the filling elsewhere; the way he was talking, that stuff you’re using shouldn’t be within a mile of our fire-works.”
“It shouldn’t, or most other places, indeed. We’ll not be filling her until we’re in place to fire her. And we should, then, be ready to take delivery by the 19th?”
“We’ll have her ready for you. What’s all this about, anyway? I’ve built the like before, but nothing half this large.”
“We’re going to find out where gravity breaks.”
“Ah…”
“It’s one of the more troubling problems in natural philosophy,” the second Academician put in. “The difference between Celestial and Terrestrial Gravitation. You see, ever since records began at the Starspike, and it was shown that…”
“We don’t need all three thousand years,” the first interrupted.
“Um, yes, anyway, after a lot of observation and even more theorizing, most of it wrong, the Starspike’s skywatchers figured out that the planets, and us, and the Shining One, and its planets, and all the moons are all moving around each other in lovely, sweeping ellipses as they fall together and always miss. And after much computation, Siao Callaneth produced his Lemmas and declared that if you postulate an attractive force that’s in proportion to their masses and inversely proportional to their distances, all the numbers come out right.”
“Yeah, but that’s true down here, too. We use his lemmas all the time in structures.”
“Ah, but it’s only true sometimes down here. Up there, if you assume that a world is a point, it works. Down here, if you assume that an object is a point –”
“If it’s homogenous, otherwise it’s an offset point.”
“If it’s homogenous, yes, thank you, it works. Between objects, if you have heavy objects and sensitive pendulums. But if you drop something here, what direction does it fall?”
“Down?”
“Down, yes. Straight down. And we’re not above the center of the world, are we? But if we drop something, anywhere, it falls in a nice straight line perpendicular to Eliéra’s notionally-flat surface, even though the center of all the world’s mass is thousands of miles over there. It falls straight down here, it falls straight down in Mossstone, it falls straight down even in heathen Indimór-on-the-Rim, for all that the Lemmas say that the world’s gravity should drag everyone there sideways off their feet, if not crumple the edge of the world up like tissue paper, rock not being all that strong. And that is Terrestrial Gravitation, the damned exception that’s been inexplicable ever since the Shadow-watcher made note of it when proving the world was flat in the first place.”
“Eliéra behaves both ways, you see. Down here, things fall straight. But if it behaved that way celestially, we’d orbit – well, we wouldn’t move in one of those beautiful ellipses, and the moons probably wouldn’t stay up. Somewhere, if you go far enough up, everything changes. And watching Skybreaker here fly is going to tell us where.”
Heavyworlder: Yes, but this universe is hard-SF enough that they do reflect the “compact, stout, and short” version of the trope. Of course, seeing as eldrae are all height-advantaged anyway, even the heavyworlder clades are still looking humans in the eye.
There are also lightworlders, of course, and Fan Service or no, they are that skinny.