Would Artificial Gravity With Short Range Be Possible?

Question

Assuming a spaceship with artificial gravity was possible, would it be possible for it to have an extremely short range, like a few feet. So you'd be able to have a ship with 1g but not have it attract every other ship in a 1 or 2 mile radius around it?

Please excuse the crudity of this render, I didn't have time to make an actual spaceship, but I created a very basic thing in Blender to show what I mean. The grid representing space, the monkey representing a spaceship, and the earth representing... earth.

As you can see, the incline/falloff on the monkey spaceship is much steeper than the Earth. Would something like this be possible?

Answer 1

It would be conceivable, which is the important part. You are hypothesizing a new development in scientific knowledge.

A simple way would be to introduce a rule that the effect is only short-range. The ideal way to introduce it would be in, or discussing, a situation where a longer range would be very useful, up to and including saving many lives but the characters know it's impossible: pseudo gravity can only extend for a short range.

If you want to introduce some handwaving on top of it, compare it to the strong force and weak force, which extend no farther than the nucleus of the atom they are affecting.

Answer 2

If your fiction needs it, make it so.

Such artificial gravity works perfectly well in Star Trek, Star Wars, Battlestar Galactica, etc. ad nauseam. No-one needs to explain how it works (nor can they beyond techno-babble).

Maybe someday we discover a way to do so in the real world. Not that we have any promising loopholes in physics that we know of that would allow it.

Others have already pointed out the ways to simulate gravity via rotational or linear acceleration, or the (highly impractical) use of degenerate matter plating to create real gravity.

Just write your story with real "Star Trek artificial gravity" and move on. Drop in the techno-babble if you think it makes your story more interesting, enables a plot point, etc.

Technobabble answer

Some have complained, (I believe unfairly), that I did not answer the question, so here is my alternate technobabble, one that I've never seen used in fiction - but if someone has, be sure to point it out.

It is actually based on known physics - or at least plausible for a story. Einstein's famous equation declares mass energy equivalence, and this works both ways - energy warps space too.

This part is real physics. Much of the mass of some particles is not mass per see, but the energy associated with the energy binding the particles together. E.g., 6 Deuterium atoms has more mass than one C12 atom due the the differences in binding energy, etc. Both are 6 neutrons and 6 protons.

Imagine an incredible superconducting network that resides below the floor or your space ship - one with properties far, far in excess of known superconductor current densities. Pump it full of incredible amounts of current and you now have a electrical "mass field". Extend the network over the entire hull of the spherical ship and you have a way to divert the mass field uniformly into the hull so that it has no net gravity field in the interior of the ship. This allows you a way to modulate the level of energy in the floor plating by switching the energy between the floor plate and the hull. Unequal distributions of the mass field allows creative custom gravity configurations.

If you don't think energy would work this way, enlighten yourself with the kugelblitz - a concentration of energy so great that it creates a black hole. Back in college many years ago, I actually came up with the idea of a kugelblitz, only to later discover that it was first published in 1955 as Geons by John Archibald Wheeler.

What you don't want to consider too closely is just how huge a supply of energy will be required. Almost 90 billion MJ (9E16 J) to create a mass field of 1 kg, and you need at least trillions of kg of mass to get a decent level of gravity for your ship. Which means that starting and starting your ship with trillions of kg of energy is not going to be easy.

For comparison, 9E16 J is about 12 hours worth of electric power for the entire world. Or about 1/2 the energy released by the Tsar Bomba

So, I propose adding a 2nd handwavium - the ability to create and destroy energy (from the perspective of the ship) by using zero-point energy (ZPE) as a source/sink for loading and unloading the superconducting network.

Such combination of technologies also gives you a way to escape the tyranny of the rocket equation. Because you can "create mass" by using the ZPE converter as a mass source you could create regular mass to eject at high speed for acceleration. Of course, if you can do this, you could also simulate gravity by the simple expedient of continuous 1 g acceleration.

You need more handwavium to explain the structural strength of the ship needed to support the use of such mass fields, but such super materials are also known in SF.

The problem with this solution is that it is complicated and boring. If you get the engineering contract to produce the mass field for the latest generation of ships - it would be exciting indeed.

Answer 3

Newton's law of gravitation states the force that exists between two masses is based upon the magnitude of those two masses and the distance between them. The force is inversely proportional to the square of the distance:

$$F = G\frac{(m_1m_2)}{r^2}$$

as is the gravitational acceleration:

$$g=G\frac{m_1}{r^2}$$

where

• $F$ is the force between the masses;
• $G$ is the Newtonian constant of gravitation $(6.674×10^{−11} m^3kg^{−1}s^{−2})$;
• $m_1$ is the first (larger) mass;
• $m_2$ is the second (smaller) mass;
• $r$ is the distance between the centers of the masses;
• $g$ is the acceleration due to gravity.

In effect, $G$ constrains the gravitational force between two objects to fall off at a constant rate according to the square of the distance between them.

However, the effect of the square in the function means that while earth's mass behaves as a point source in this equation, gravity is measured at its surface, some 6371 kilometres distant.

In effect, by having a large central mass and being very close to it, on the order of a few hundred metres, you could have a force producing 1g of acceleration at that short distance, but at long distances, the force and acceleration would be much less.

This effect of the square of the distance is why an earth-mass neutron star or black hole would have a very much higher gravity than earth at its surface/event horizon than exists on Earth's surface. However, at 6371km distance, its gravity would still be 1g.

So, to produce an acceleration of 1g at a few hundred metres range or less would require much less mass than that of Earth at 6371km... but as far as a spacecraft goes, it would still be an awfully big mass, and the tyrrany of the rocket equation would say "NO!" to this spacecraft getting anywhere easily or quickly. Not to mention that you'd need degenerate matter to have that much mass in such a small volume.

The other problem of such a system would be that at its optimal distance, it would generate 1g, but not very much further away, the gravity would drop significantly, and only a little closer, it would increase significantly, giving significant gravitational tides.

To give some examples:

If we want a gravity of $9.8 ms^{-2}$ at 10m, we need a mass of $1.47 \times 10^{13}kg$.

However, at 12m, the gravity is $6.8ms^{-2}$ and at 8m, it's $15.3ms^{-2}$. So, from this we can see that there is a significant gravitational tide. The mass itself would be dangerous to approach, since at a range of 1m, it would have a gravity of $980ms^{-2}$, or 100g, while at 2m, it would have a gravity of $245ms^{-2}$, or 25g. This gravitational force and these tidal forces could easily cause physical injury or death to humans at this range. However, this also satisfies the OP's desire for little impact on nearby spacecraft.

• At 1km (which is docking range), the gravity would be $9.8 \times 10^{-4}ms^{-2}$ / $1 \times 10^{-4}g$.
• At 100km, (which is still close range) the gravity would be $9.8 \times 10^{-8}ms^{-2}$ / $1 \times 10^{-8}g$.
• Since space is so big, I wouldn't expect spacecraft to approach each-other any closer than 1000km except when attempting to rendevous, at which range, we'd have a gravitational attraction of $9.8 \times 10^{-10}ms^{-2}$ / $1 \times 10^{-10}g$, which is effectively zero on a human time scale.

As for 'virtual masses', such things haven't been shown to exist. Your science fiction story may disagree, and allow you to produce as large a temporary/virtual mass as you need. Of course, if you can generate these virtual masses, you can have a diametric drive.

Otherwise, in hard sci-fi, you're better off using centrifugal forces in a spinning container to generate gravity-like forces.

Answer 4

There is no modern day Physics-based answer to this question

By definition, artificial gravity does not work in the same way as the one, and only one, way we know to create gravity - having mass. Since we know of no way to create gravity without having a large mass we cannot say how it would work if you could.

But speculating based on the properties of gravity suggests it could

Gravity falls off with the square of distance in the same way as, e.g., a light source or heater behaves. If we assume that the artificial gravity generator is placed a small distance under the floor, let's say 30cm, and produces 1G at floor level, then it will produce 0.25G 30cm above the floor and 0.11G 60cm above the floor. At 10ft (3m) it will be producing just 0.01G. So it would fall off within a few feet as you describe.

In fact, it might be that you need to separate your generator and the floor level by a greater distance just so you don't get uncomfortable differences in gravity across a human body.

Answer 5

If the spacecraft used rotation as a means of generating artificial gravity then the space craft need not be that massive nor have any significant gravitational field but those aboard would still be able to experience 1g.

Alternatively (and less usefully) if constant acceleration was applied in a straight line again the ship could feel 1g whilst not exerting a gravitational field.

Beyond that I do not think what you want id possible. If sufficient mass was collected to generate 1g then the gravitational field could not be restricted in its extent.

Answer 6

Normal gravity has monopole sources. Just assume that artificial gravity is an artificially generated dipole e.g. by pair production of mass and "anti-gravity" (repulsing) particles stored above and below your ship (even if we don't know how to generate one and the existence of an anti-gravity particle would kind of contradict what we understand about physics, since anti-particles seem to be ordinary masses, so invent something which sounds nice ;-)).

Fields from mono-poles decrease with distance^2. field from dipoles decrease with distance^3. (which is the reason why magnets only produce big forces on short distances),

Answer 7

What if instead of the gravity being short ranged. You had an anti gravity shielding on the hull that cancelled out the gravity.

This neatly solves the problem of gravity escaping, but also creates new dangers for the ship because any failure of this anti gravity shielding would result in space dust and rocks collecting on the hull.

Anti gravity hull could also be a nifty form of long range stealth. (And it's failure obvious on radar thanks to gravity escaping)

As for the science. If your civilization already figured out the magic of gravity fields, then why can't they figure out the magic of an anti gravity field? They probably already did when they figured out how to make their space ships float in the air.

Answer 8

There is no known way to have artificial gravity. Gravity is tied to mass.

There are ways to have simulated gravity which are only local, but because they're not 'true' gravity they won't affect external objects as gravity would in the way you're representing in your picture. So artificial simulated gravity by it's nature will achieve what you want.

Answer 9

If space is a transport medium for the information of gravitational attraction and you want to hack the transport medium to create the false information of mass to be transported, while the mass does not exist.

That would be difficult, if you can not do it from a distance, as in machinery has to be at the point of space that is to be hacked. So lets assume there is a box that can do so- you would need drones that swarm around your ship, smothing out the "hack" simulating the gravity of a m-class planet.

Then what happens if these hacks amplify one another, for example when two ships crash? What if the hacking mechanism goes wrong and the black box creates a "virtual" black hole, with no mass, but the gravity similar to that? Or what if the mechanism is considered a orbital weapon, as it could easily derail a planetary system by simulating a body of mass m appearing in the middle of orbital mechanics.

Finally - the danger of gradients.. as in - your artifical, hacked information is not smooth in all 3 Directions. So you can push your ship from zero-g into reentry levels of stress - easily shearing the ship or structure.

https://en.wikipedia.org/wiki/Graviton

Answer 10

Such technology would be quite advanced, and the only way that could possibly and reliably be achieved is if the civilization in question is sufficiently advanced enough to where their technology is indistinguishable from magic - that is to say that they'd be so advanced that the laws of physics are less laws and more suggestions to them; capable of bending or even breaking physics entirely at will. At that point they've essentially become metaphysical, and are no longer bound by universal constraints and science as we understand them.

Answer 11

Hypothetically yes. Membrane physics... I recall a science documentary, where String and M- THeory. It establishes 1-dimensional strings consist 2 types, One bound, one unbound.

Unlike the other forces in nature, Gravity doesn't have a particle assigned to govern or interactions. THe bound ones more functionally interactive with the universe, the loose ones are not. The hypothetical graviton which governs gravity's strength, Since gravity is the weakest of the fundamental interactions they thought 99.99% of it's power seeps other dimensions or doesn't interact with the 3 typical ones. Artificial gravity guides gravitons thru two membranes; The ceiling and the floor where they dissipate....

Answer 12

A slightly different perspective:

Let's assume your humans have discovered a technology that lets them somehow turn electrical energy into gravitational force. Let's also assume the process behind this technology can be 'reversed', turning electricity into "anti-gravitational" force, which repels mass rather than attracting it.

Your spaceships could then have gravity generators inside of it to attract everyone to the floor, and anti-gravity generators situated around the hull to neutralize the gravitational force and prevent it from spreading beyond the spaceship, effectively flattening spacetime once again.

These generators would likely have strong implications for the rest of the world, and could perhaps allow for FTL travel in the form of alcubierre drives.

Their effect could be limited by saying that energy costs increase exponentially as gravitational force increases, e.g maintaining 1g of force might take 1GW of power, whereas maintaining 10g of force might take 1000GW.

Answer 13

Why artificial gravity generation?

The Expanse gives you two very good science-based answers here, neither of which need the complications of artificial gravity generation.

Constant acceleration

Currently we don't have power sources which can store very much energy. As a result, we have to give our spacecraft one big push to accelerate, coast for the duration of the trip, and apply another big push to stop.

With a massively energy-dense power source (which, OK, is a stretch!), we can speed up the trip. Like a race car, we can be constantly either accelerating or braking. And one side effect of that is that the humans inside get constant acceleration. As far as our bodies are concerned, this looks exactly the same as gravity.

If this acceleration goes on for a really long time, eventually of course you'll hit relativistic effects which might limit what you can do. And likely the force field or laser which repels or vaporises dust and micrometeorites (another extra handwave!) has an upper speed it can handle. Up to that point though, you can maintain that acceleration and the canned monkeys are fine.

Magnetic boots

If you simply need to walk around though, magnetic boots are your friend. They've been a staple of hard SF since the 1930s. Of course this doesn't solve some of the other problems with lack of gravity, like wound healing or loss of bone and muscle density, but it's an option.

At the very least, this makes it easier to put on film/TV. Of course no film/TV to date has properly handled how hair and clothing move whilst the protagonists are supposedly in zero-G and held down by mag boots, but that's a separate problem. :)

Answer 14

How about you have "gravity plates" for the floor, but then put "anti-gravity plates" around the hull? To nullify it out? They could even be the same plates facing backwards. Or else some sort of projector that can control gravity and put it where it likes, like force fields?

It wouldn't work in real life but it's pretty normal to assume scifi spaceships have mastered gravity like it was magnetism.

Answer 15

100% IMPOSSIBLE in real life by any lifeform, and please remember Gravity is not a force, but an effect so what you are really asking is about creating a virtual spacetime with a virtual mass so that you can experience an effect of virtual gravity.

However, for your fictitious use-case, why not? Your virtual reality and virtual gravity are only limited by your imagination and details won't matter anyway.