Gravity generators?

[G'th]

This is easy, just lace your ship's hull with cavorite and you're all set.

[Stargate525]

This is easy' date=' just lace your ship's hull with cavorite and you're all set.[/quote']

Ohmygosh someone else who's read that book!

But yeah, it doesn't have to be 'gravity,' just something that pulls us down.

[shynung]

I do not think we have the technology to create artificial gravity, at least not for the next 100 years.

Instead, I think it is possible to simulate them using the ship's own acceleration. One way to do it is by centripetal acceleration, as described by K^2.

The other, more straightforward way to do it, IMO, would be using the spacecraft's own engines to constantly accelerate it at 9.8m/s². That way, the spacecraft's 'floors' would be facing against the engines, resulting in people standing inline with the spacecraft's direction of travel, at a constant 1G acceleration.

And since gravity is felt the same way to people to acceleration (depending on their orientation), they would, practically, walk around in the spacecraft just like in the sci-fi movies. Only this time, they see the stars out the window going to their feet rather than to the side.

[Simon Ross]

Gravity is a natural force, so can we artificially create it, of course we can.

The only stopping point is we don't actually know how to do it short of accelerating objects or rotating them.

[Starwhip]

Haven't read all posts, but a Dyson sphere is a centrifuge, in a way, and black holes are dangerous... so what if you built the "bottom" of the ship out of an insanely dense and heavy material that would weigh enough to generate gravity.

[Themohawkninja]

Haven't read all posts, but a Dyson sphere is a centrifuge, in a way, and black holes are dangerous... so what if you built the "bottom" of the ship out of an insanely dense and heavy material that would weigh enough to generate gravity.

Well, if you just want a space station that orbits around a planet, that could be okay (minus gravitational effects on the planet), but if you wanted it on a ship designed to accelerate under power at all, you might not want something so heavy.

[gutza1]

If the graviton exists, might it be possible to manipulate it to generate a gravity field around a spaceship?

[Kermunist]

Based on MilliKan's oil-drop experiment, I would like to suggest using electrostatics.

Lets say we charge up our crew, and use an electric field between the floor and ceiling to keep them on the floor.

With the potential difference between floor and ceiling at, say, 2MV,and they are 2m apart, we have 10^6V/m. We want the crew to experience 1g, which is about 10N/Kg, so using F=QE we only need 10uC of charge per kilo, or about 800uC per person.

Advantages:

The floor and ceiling are parallel plate capacitors, so the electric field (and thus 'gravity' strength) is the same everywhere, and at any height from the deck

The charge spreads out across the person, so the 'gravity' acts on all parts of their body.

Disadvantages:

Moderate repulsive force between crew members*. Enough to keep your personal space anyway.

Corona discharge from crew members will make them glow a bit. Especially pointy bits like fingers, toes, ears.

Tears in the (insulating!) carpet, exposing the electrodes below, will instantly kill the unwary.

Whilst this will work well for providing gravity to insulating objects, there may be some oddities as charge moves around conductive objects (such as crew members)

*Force may in fact be of order 1g at 10 meters.

Edited January 16, 2014 by Kermunist
Added more disadavantages

[K^2]

With the potential difference between floor and ceiling at, say, 2MV,and they are 2m apart, we have 10^6V/m.

Erm... Humans are conductors. That means electric field inside human body is zero, and it's going to be 2MV between crewman's head and the ceiling. Average adult male height is 1.8m. That makes it 2MV/20cm = 10MV/m, which is more than 3x the dielectric strength of dry air. Air is going to undergo electric breakdown, like a miniature lightning, and your contraption just started frying the crew.

But even if you get rid of that particular issue, human bodies are still conductors. How are you planning to keep all this charge distributed evenly through the body in this strong of a field? Or keep everyone perfectly insulated?

Anyways, if you want to use electromagnetism, go with diamagnetic levitation.

[Kermunist]

I wouldn't take my post too seriously. All the disadvantages I listed are in fact very understated (possibly that's a rather British sense of humor?), and the scheme is completely impossible for human sized objects: any attempt to implement it would be a deathtrap.

That said, I don't think the ceiling is going to discharge into the crew that much. A strong insulating layer would prevent it, and the head charge is never going to be anywhere near as strong or as close to the roof as the feet charge is to the floor. It's going to have to be a very tough carpet.

More problems:

The electrostatic repulsion also applies to any other objects that are charged. Drop your pen? It's now shooting away at high speed. You can't have an uncharged pen, as it will get a charge when you touch it.

The point you raise about keeping the charge distributed is a good one, and I was trying to hint at it in disadvantage 4. In the static case, the charge will redistribute towards the feet, so they will feel more 'gravity' than the rest of you. Probably most of your body will be in zero G, as most of the charge is in your feet. If you try and move, the charge redistributes. I haven't tried to work out if that would produce lethal currents, but vigorous waving of the left arm would probably be ill-advised.

Corona discharge will slowly bleed off charge, it will collect on the floor (on the surface of the insulating carpet) and reduce the electric field. You will have to periodically move this back onto the crew/other objects you wish to have gravity.

If you have an uncharged visitor, they will stick lightly to the floor or ceiling (van der waals force) until they touch someone, then the discharge will probably kill both of them.

Also, diamagentic levitation is cool, but doesn't scale up very well either. I have never been able to levitate more than a few drops of water, and I am very glad I didn't have to pay the electricity bill for that.

Edited January 16, 2014 by Kermunist
correct a physics error

[K^2]

That said, I don't think the ceiling is going to discharge into the crew that much. They may have zero electric field inside, but they have a huge surface charge. If the charge is free, it will move around so that their head is at the same potential as the air around it, which is below the breakdown potential (but not by much, hence the corona discharge)

Nope. Same reason lightning strikes tall objects. The physics of it is pretty straight forward too. The mobile charges are precisely what makes the field inside zero. And the voltage drop along any path is the integral of the electric field along that path. Since inside the body that field is zero, it the entire difference is going to result in the field between the head and the ceiling.

Coronal discharge happens when the object is small compared to the distance, so charges moving to the top do not change the electric field by much. Then you get something like Saint Elmo's fire around the person's head. But if the charges moving makes a difference between 2m of path and 20cm of path, that's going to result in a proper breakdown.

[Dispatcher]

Gravity generators? Just gather mass; lots of mass. A substitute? Centripetal force by rotating something ins such a way as to yield desirable results.

[Kermunist]

Nope. ...

Argh! You caught me. I realized it was wrong and edited it out within minutes, but I was too slow. I still maintain that the carpet is going to take more of a beating than the ceiling liner though (and the whole idea is patently ridiculous of course).

[Kilmeister]

Why bother with the ship? Just attach the engines to your home planet.

A few minor engineering problems aside this should actually work. Plus we've already constructed the crew quarters and a have a solar powered life support system. Just need some engines and a rather large fuel source and we're GTG!

[TheDarkStar]

A few minor engineering problems aside this should actually work. Plus we've already constructed the crew quarters and a have a solar powered life support system. Just need some engines and a rather large fuel source and we're GTG!

The main downside is that there probably isn't enough room in the universe for any fuel source short of a huge amount of antimatter or an Alcubierre drive. Antimatter has its own downsides, and if you use an Alcubierre drive, you might as well just use a large centrifuge for people and other things that need gravity, and send anything else necessary simply sealed in a container, without worrying about the large portion of the planet that you (probably) don't need.

[Brotoro]

Until you discover a method of grabbing hold of space-time and bending it into the shape you want (without needing a high density of mass/energy) you aren't going to get fancy artificial gravity like you see on Star Trek.

[shynung]

Gravity is a natural force, so can we artificially create it, of course we can.

The only stopping point is we don't actually know how to do it short of accelerating objects or rotating them.

Ah, you're right. It is, indeed, artificial gravity. That's one big oversight I just made.

However, that raises another question: Is gravity and acceleration exactly the same phenomenon? If not, why can we artificially create it by accelerating things (either by thrust or rotation)?

In fact, what IS gravity? What causes them? How do they work? Is it possible for its processes to be replicated? If so, how?

Before these questions can be answered, I am not sure whether artificial gravity as depicted in sci-fi movies will actually be possible at all.

[Themohawkninja]

Ah, you're right. It is, indeed, artificial gravity. That's one big oversight I just made.

However, that raises another question: Is gravity and acceleration exactly the same phenomenon? If not, why can we artificially create it by accelerating things (either by thrust or rotation)?

In fact, what IS gravity? What causes them? How do they work? Is it possible for its processes to be replicated? If so, how?

Before these questions can be answered, I am not sure whether artificial gravity as depicted in sci-fi movies will actually be possible at all.

Gravity acts on objects by pulling objects towards each other. Every object with gravity causes acceleration (hence how gravitational attraction works), but not all acceleration is gravity.

Unless you really want to get into a debate about how gravity is derived from density, which is related to mass, which is affected by velocity, which is similar to acceleration... all acceleration isn't gravity.

[randomness5555]

Magnetic shoes. What? It's cheap and it can be done... though you would have to be carefull where you stand so you dont break any sensitive equipment

[TheDarkStar]

Ah, you're right. It is, indeed, artificial gravity. That's one big oversight I just made.

However, that raises another question: Is gravity and acceleration exactly the same phenomenon? If not, why can we artificially create it by accelerating things (either by thrust or rotation)?

In fact, what IS gravity? What causes them? How do they work? Is it possible for its processes to be replicated? If so, how?

Before these questions can be answered, I am not sure whether artificial gravity as depicted in sci-fi movies will actually be possible at all.

You should probably see something that K^2 has written about this or look it up, but GR (pretty sure it's not special relativity) describes gravity as "warped" or "bent" space-time, and it ends up being basically the same as acceleration.

Edit: Note that if you are in an enclosed space and don't test for tidal forces, it is impossible to tell whether you are accelerating at a certain rate or under gravity of the same amount.

Edited January 17, 2014 by TheDarkStar

[shynung]

You should probably see something that K^2 has written about this or look it up, but GR (pretty sure it's not special relativity) describes gravity as "warped" or "bent" space-time, and it ends up being basically the same as acceleration.

Edit: Note that if you are in an enclosed space and don't test for tidal forces, it is impossible to tell whether you are accelerating at a certain rate or under gravity of the same amount.

Then, is it true that gravity and acceleration are basically different phenomenons that produces the same effect? In this case, gravity producing acceleration, that is felt by humans by having themselves being stuck to a specific surface? (forgive my grammar)

If so, for the purposes of artificial gravity generation, I see no viable means to generate it other than simulating it using acceleration.

And I think it's safe to say that the 'gravity' produced by that acceleration is a simulated one, as it does not involve using plenty of mass (other than the spacecraft itself and its occupants, which only produces gravity at negligible levels).

[K^2]

Then, is it true that gravity and acceleration are basically different phenomenons that produces the same effect? [...]

And I think it's safe to say that the 'gravity' produced by that acceleration is a simulated one, as it does not involve using plenty of mass.

Not really. Gravity, as in the force of gravity, is just an artifact of acceleration. The force you are experiencing while standing on the surface of the planet is exactly the same as the force you are experiencing while standing inside a centrifuge. In both cases, the force of (artificial) gravity is a fictitious force arising due to accelerated frame of reference, and in both cases, what is actually important is the real force with which ground pushes against your feet. Even the equations you'd use to derive the force of gravity in General Relativity can be applied to a centrifuge, and you will get correct answers.

The difference between the artificial gravity we can make with acceleration and gravity of the massive bodies is a bit more subtle. If I have a centrifuge, and I attach my coordinate system to it, then I have to introduce a centrifugal force and a Coriolis force to explain motion of the objects inside. But that's just a "bad" choice of coordinates. I can always chose an inertial coordinate system, say, from perspective of an observer floating outside of a rotating space station, and describe everything without using centrifugal force. The normal force supporting artificial weight of objects in the station, in this case, is just there to provide centripetal acceleration of the objects. F=ma, and nothing else.

With gravity, I can always choose such a coordinate system locally. A space station in orbit of the planet is in effective free-fall, and therefore, I can attach a coordinate system to it and call it my inertial system. But no matter how I try, I can't come up with a coordinate system that's inertial everywhere once I have massive bodies involved.

There is formal way to describe all of it, and it has to do with symmetries of space-time, but the important bit is that while there are very important distinctions between gravity of large bodies and artificial gravity we can make, the force of gravity and the force of artificial gravity are absolutely equivalent in every way.

[shynung]

There is formal way to describe all of it, and it has to do with symmetries of space-time, but the important bit is that while there are very important distinctions between gravity of large bodies and artificial gravity we can make, the force of gravity and the force of artificial gravity are absolutely equivalent in every way.

I have to admit, this is probably one of the strangest facts I have ever encountered.

The force exerted by a massive object, via a curvature of space-time, is absolutely equivalent to the force exerted by either a linearly or centripetally accelerated, man-made object, in every way?

What a weird universe we live in.

[ZetaX]

Why do you find simplicity weird¿ Wouldn't it be more weird if there are lots and lots of complicated laws that are not similiar at all¿ Or no "laws" at all, whatever that means...

Reminds me of: "Then again, there were lots of physicists who thought that quantum mechanics was weird, instead of quantum mechanics being normal and them being weird".

[nhnifong]

If the only reason we need "gravity" on spacecraft in the first place is human bone and muscle degeneration, then trying to create artificial gravity is a bit of an over-engineered solution. It could be solved with something as simple as suit with elastic bands, or with drugs and gene therapy to take another angle.