Why artificial gravity is not possible?

[DaveC426913]

As has been hinted at earlier in the thread, generating the field is * easier.

Where?

The energy moving an asteroid-sized space station around to generate a gravitational field of 9.8 m/s is going to be several orders of magnitude less than accellerating and decellerating a mass equivilent to planet Earth wherever you want to go.

Sorry -point of order- we're mixing up ideas. My suggestion was that an asteroid-sized space station would be big enough to create sufficient real gravity (but less than Earth's gravity). If the intent is to create gravity equivalent to 9.8ms^2, then that's different.

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

1] Tell me why you are convinced that it would take "several orders of magnitude less energy" to produce 1g by way of an EMF than it would to simply move around an Earth-sized body. I am not convinced it would.


2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

 

[spikenigma]

Where?

Post 16, but then he went on to talk about micro-blackholes, so perhaps not!

Sorry -point of order- we're mixing up ideas. My suggestion was that an asteroid-sized space station would be big enough to create sufficient real gravity (but less than Earth's gravity). If the intent is to create gravity equivalent to 9.8ms^2, then that's different.

A space station is easier since you don't have to move it nor power your artificial gravity - whether you need to rotate it or not. I was thinking of a starship.

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

1] Tell me why you are convinced that it would take "several orders of magnitude less energy" to produce 1g by way of an EMF than it would to simply move around an Earth-sized body. I am not convinced it would.

I'll say from the outset that I am in no way qualified in the field we are talking about to provide calculations on this, and would happily accept them from anybody who cares to have a go in the thread.

My view is based on this:

http://www.sciencedaily.com/releases/2006/03/060325232140.htm - beware popular science magazine

http://esamultimedia.esa.int/docs/gsp/Experimental_Detection.pdf - experimental paper

Which produced a gravitomagnetic field 100 millionths that of Earth.

Obviously, the field scales up geometrically based on speed of rotation, strength of magnetic field, size of super-conductor, charge of super-conductor etc...

However, back-of-the envelope below and assuming it scales up linearly to give a fair minimum:

Let's say (perhaps erroneously) that this small lab uses a tenth of the LHC's annual 800,000 Megawatt hours running this specific experiment constantly - so 80'000 Mwh or 2.88x10^14 joules. Multiply by 10^9 is 2.88x10^23 J annually for an Earth-strength field.

CharlesP (https://www.physicsforums.com/archive/index.php/t-63459.html) seems to suggest that moving the Earth to any appriciable degree would take approximately 4.18 x 10 ^15 joules every 10 seconds for a billion years in one megaton bombs. A total of 1.3x10^31 J to move the Earth. To say nothing of deceleration or damage to the body.

2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

You'd still need to move it, would the extra-terristial mining, manufacture and moving of this body take less than 2.88x10^23 J annually? - in the null case my point still stands

 

[nismaratwork]

Why would a ship not have a rotational habitat area around a central axis?

 

[DaveC426913]

Why would a ship not have a rotational habitat area around a central axis?

Have you been following the thread? We're looking for alternate forms of artificial gravity. A centrifuge is only one method and it has its drawbacks.

 

[DrGreg]

So let's set some benchmarks. I'll go with yours. We want to make our space station have gravity of 1 Earth g.

...

2] You wouldn't actually need an Earth mass body. We feel 1g because we are ~4000mles from the gravitational point source. A smaller, denser and much less massive body would accomplish the same thing. It should be calculable how small a mass you'd need.

Dickfore has already covered this in post #7, but here's another way of putting it. A planet of half the Earth's radius but the same density would have half the surface gravity (it turns out), so to maintain the same gravity you'd have to double the density. There's a maximum density that would be possible with ordinary matter, so that puts a (pretty large) limit on the minimum sized planet with 1 g surface gravity. This makes this method practically infeasible, at least until we find a way of creating a tame mini black hole.

 

[nismaratwork]

Have you been following the thread? We're looking for alternate forms of artificial gravity. A centrifuge is only one method and it has its drawbacks.

We covered all the possibilities from miniature black holes to magnetic fields that would fricassee your nervous system. I would say the same conclusion is the substitution of the pseud-force for another. Did you read Spike's post? He specifically compared a rotation STATION with a ship, and I was pointing out that a ship need not lack a centrifugal component... do you have an alternative suggestion?

 

[DaveC426913]

... that puts a (pretty large) limit on the minimum sized planet with 1 g surface gravity. This makes this method practically infeasible...

Agreed. My point was simply that some EM force-field powerful enough to create a gravity well would likely use an equivalent amount of energy as it would take to throw a planet around. IMO.

 

[SkepticJ]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Nearer term, just use two centrifuges spinning in opposite directions, or a smaller, high speed flywheel spinning counter to the rotation of the centrifuge. That'll take care of the pesky gyroscopic effects of the centrifuge(s).

You just have to live with the Coriolis effect, but if you make your wheel with a big enough diameter, at least it won't make the occupants sick when they move their heads around.

 

[DaveC426913]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Gravity serves other purposes than keeping our bones strong. It keeps our feet on the floor and the butcher knife on the countertop. Either of those floating around a room can be bad. Both of those floating around a room can be double plus bad.

 

[Chronos]

Gravitational fields are carried by integer spin particles, EM fields are the product of a half spin particle.

 

[Ich]

Gravitational fields are carried by integer spin particles, EM fields are the product of a half spin particle.

Even and odd numbers, not integer and half.

 

[nismaratwork]

The best thing to do, in the long run, will be to alter our biology to where lack of gravity won't weaken us. That, or become machines without the weaknesses of meat.

Nearer term, just use two centrifuges spinning in opposite directions, or a smaller, high speed flywheel spinning counter to the rotation of the centrifuge. That'll take care of the pesky gyroscopic effects of the centrifuge(s).

You just have to live with the Coriolis effect, but if you make your wheel with a big enough diameter, at least it won't make the occupants sick when they move their heads around.

https://www.physicsforums.com/showpost.php?p=2781702&postcount=12

Yep, I agree.

DaveC: Not just objects which can be dangerous in 1g; liquids can become very hazardous or at least a terrible mess, and of course there is the issue of bacterial growth in microgravity.

 

[DaveC426913]

...of course there is the issue of bacterial growth in microgravity.

What effect does microgravity have on bacterial growth?

[EDIT] I can see it impeding bacterial growth, but I got the impression you were suggesting growth would become problematic for occupants. I could be misinterpreting.

[EDIT EDIT] Oh yeah. Impaired bacterial growth in our bodies could negatively impact our health.

 

[nismaratwork]

What effect does microgravity have on bacterial growth?

[EDIT] I can see it impeding bacterial growth, but I got the impression you were suggesting growth would become problematic for occupants. I could be misinterpreting.

[EDIT EDIT] Oh yeah. Impaired bacterial growth in our bodies could negatively impact our health.

Re: Edit Edit: Exactly!

 

[SkepticJ]

Gravity serves other purposes than keeping our bones strong. It keeps our feet on the floor and the butcher knife on the countertop. Either of those floating around a room can be bad. Both of those floating around a room can be double plus bad.

Magnets, gecko-like adhesive, velcro, clips, straps, bungee cords . . . can all secure things you don't want floating around when you're not using them.

Zero gravity is so much more useful. You get http://www.kschroeder.com/my-books/sun-of-suns/engineering-virga" that way.

You can manufacture novel materials in zero gee because liquids of different densities don't separate. You can grow large, perfect crystals without the constraint of gravity. Though with molecular manufacturing, these would probably be obsolete reasons for manufacturing materials in zero gee.

 

[DaveC426913]

Magnets, gecko-like adhesive, velcro, clips, straps, bungee cords . . . can all secure things you don't want floating around when you're not using them.

The question then becomes: if the default state for where you want most things to be is not floating around, then why create a method for each individual thing? You set your environment for the default, not the exception.

Zero gravity is so much more useful. You get http://www.kschroeder.com/my-books/sun-of-suns/engineering-virga" that way.

No you don't; you get exactly the same amount of living space. We have invented these things called floors.

You can manufacture novel materials in zero gee because liquids of different densities don't separate. You can grow large, perfect crystals without the constraint of gravity. Though with molecular manufacturing, these would probably be obsolete reasons for manufacturing materials in zero gee.

Yeah, yeah. Perfect crystals. That old hackneyed thing is dragged out every time someone talks about uses for zero g. If zero g were so incredibly useful, someone in the last half century would have come up with more than one or two examples.

Fine, make your engineering things in zero-g. Does that mean the whole station should be in zero-g?

The same argument could be made for vacuum. Lots of things need to vacuum for their manufacture.

We should fill our space station with vacuum so that the materials are taken care of, and any silly old thing that actually needs oxygen can carry an air cannister on its back...


Feelin' kinda b*tchy today...

 

[SkepticJ]

The question then becomes: if the default state for where you want most things to be is not floating around, then why create a method for each individual thing? You set your environment for the default, not the exception.

Using adhesive patches is that much of a hassle? I'd gladly trade having to stick things "down" on any surface I choose for being able to fly freer than a bird.

In any case, it's not an all or nothing proposition. If gravity is more convenient, then use a centrifuge for those locations. Bathrooms, kitchens, and workshops could have gravity, the rest could go without. Those places needn't even have the gravity of Earth, just enough so things don't go floating around -- say 1/10th, or less, of a gee.

No you don't; you get exactly the same amount of living space. We have invented these things called floors.

I respectfully disagree. When you can use each wall and ceiling as you can the floor, you clearly have five times the usable surface area.

Without gravity, there's no need for space-wasting stairwells and elevator shafts. Hardly any structural support would be needed; skyscraper-sized buildings could have frameworks as substantial as a camping tent.

The taller a skyscraper, the more of its structure goes to holding itself up than providing usable space. That's why we don't make skyscrapers with brick anymore. Steel will eventually reach its limits, then we'll have diamond, then what? Theoretically you could hold a building up like http://en.wikipedia.org/wiki/Space_fountain" to any height, but it would be a dang-expensive building to keep upright.

Yeah, yeah. Perfect crystals. That old hackneyed thing is dragged out every time someone talks about uses for zero g. If zero g were so incredibly useful, someone in the last half century would have come up with more than one or two examples.

Perhaps we simply haven't thought of the uses yet. Imagine the first person to discover how to make glass. They clearly didn't think of lenses, window panes, fiber optic cables, fiberglass composites, fiberglass insulation, or even glass containers. All they saw was fused sand under what was their campfire.

 

[Jesvant]

It IS possible, you have to rotate the ship about its horizontal axis to create a force that holds the astronauts to the circular hull/floor of the ship

 

[nismaratwork]

It IS possible, you have to rotate the ship about its horizontal axis to create a force that holds the astronauts to the circular hull/floor of the ship

Did you just not read the last four pages? Did you even read the last four POSTS?!

 

[DaveC426913]

I respectfully disagree. When you can use each wall and ceiling as you can the floor, you clearly have five times the usable surface area.

Without gravity, there's no need for space-wasting stairwells and elevator shafts. Hardly any structural support would be needed; skyscraper-sized buildings could have frameworks as substantial as a camping tent.

The taller a skyscraper, the more of its structure goes to holding itself up than providing usable space. That's why we don't make skyscrapers with brick anymore. Steel will eventually reach its limits, then we'll have diamond, then what? Theoretically you could hold a building up like http://en.wikipedia.org/wiki/Space_fountain" to any height, but it would be a dang-expensive building to keep upright.

All excellent points. I had not thought of the structural angle. Conceded.

Perhaps we simply haven't thought of the uses yet.

Then you don't get points for it.


1] You can't submerge hoomans in an environment on spec, in the hopes that we'll think of reasons for it.
2] You do that kind of thing in your labs, not in your living spaces.

Imagine if we had the same l9ine of thought for vacuum. (Bah, humans can just wear helmets all day. Think of the discoveries we might make! )

 

[tbwhel]

It might be worth while to mention here that there are other methods of inducing a gravitational like state the does not require rotation or extreme mass. One possible alternative would be an industrial alternative (ex: incorporating metal into clothing in such a way as to have a similar effect to gravity on earth. ) Another possibility is the idea that gravity is at it's heart a magnetic attraction. if you could generate enough of the right polarity you might be able to produce an gravitational field. another option, though probably less feasible than the first or second, would have to do with how you would power an inter stellar or long travel ship. The ships would have to be huge in order to house a large enough garden to produce sufficient oxygen. best way to power such a large structure in space would be a fusion reaction. Space would greatly help with the heat issues that stop fusion from being feasible on a planet and a sufficient reaction could be fairly heavy in mass, almost like a mini sun. just some thoughts to keep in mind. there is no point in saying something isn't possible, after all discovery means proving someone else wrong. Einstein was a great man but at some point someone will prove him wrong somehow.

 

[DaveC426913]

One possible alternative would be an industrial alternative (ex: incorporating metal into clothing in such a way as to have a similar effect to gravity on earth. )

How does incorporating metal into one's clothing induce a gravity-like effect?

Anothero possibility is the idea that gravity is at it's heart a magnetic attraction.

No it isn't.

if you could generate enough of the right polarity you might be able to produce an gravitational field.

How does this follow?

another option, though probably less feasible than the first or second, would have to do with how you would power an inter stellar or long travel ship. The ships would have to be huge in order to house a large enough garden to produce sufficient oxygen. best way to power such a large structure in space would be a fusion reaction. Space would greatly help with the heat issues that stop fusion from being feasible on a planet and a sufficient reaction could be fairly heavy in mass, almost like a mini sun. just some thoughts to keep in mind. there is no point in saying something isn't possible, after all discovery means proving someone else wrong. Einstein was a great man but at some point someone will prove him wrong somehow.

Hrm, so you're saying a spaceship that has a big enough mass will have its own gravity. Well, kind of more like and asteroid than a spaceship then. The more massive it is, the less it can maneuver like a spaceship (and the harder it is to get it up to speed). There's a diminishing returns thing there.

 

[Mech_Engineer]

People keep mentioning putting a "mini black hole" at the center of the ship in this thread, but I don't think the conventional definition of a black hole allows for the possibility of a "small" one (isn't the critical mass required to create a black hole much larger than the Earth or even our Sun?).

On another note, I did hear about the "metal in clothes" idea and thought it was a good one (previous poster didn't explain it very well). Basically if you have a floor full of electromagnets, and a person has metal in a sort of a jump suit. You could simulate 1G by utilizing a properly-powered magnetic field and strategically distributed metal and/or magnets in the astronaut's suit.

 

[DaveC426913]

(isn't the critical mass required to create a black hole much larger than the Earth or even our Sun?).

Well, a natural one yeah. But don't think that would apply to BH technology.

On another note, I did hear about the "metal in clothes" idea and thought it was a good one (previous poster didn't explain it very well). Basically if you have a floor full of electromagnets,

Ah. That was the missing piece.

 

[cjameshuff]

It might be worth while to mention here that there are other methods of inducing a gravitational like state the does not require rotation or extreme mass. One possible alternative would be an industrial alternative (ex: incorporating metal into clothing in such a way as to have a similar effect to gravity on earth. )

Metal weights might be useful in low gravity...it's unclear how this would work in freefall.

Another possibility is the idea that gravity is at it's heart a magnetic attraction. if you could generate enough of the right polarity you might be able to produce an gravitational field.

Gravity's clearly not electromagnetic. The second sentence boils down to "if you could generate a gravitational field you could generate a gravitational field". The only apparent ways to do so involve enormous amounts of mass and/or energy, and would be quite a bit more inconvenient than rotation.

another option, though probably less feasible than the first or second, would have to do with how you would power an inter stellar or long travel ship. The ships would have to be huge in order to house a large enough garden to produce sufficient oxygen. best way to power such a large structure in space would be a fusion reaction. Space would greatly help with the heat issues that stop fusion from being feasible on a planet and a sufficient reaction could be fairly heavy in mass, almost like a mini sun.

Space would not directly help with the heat issues...while vacuum would provide good insulation for cryogenic systems for superconducting magnets, it also provides good insulation for the radiator you're trying to dispose of waste heat through. You might manage a reaction chamber open to space without chamber walls needed to exclude atmosphere, but this would "solve" the problem by throwing away the energy produced by the reactor. And I would hope that such a spacecraft could use less than a planetary mass of fusion fuel. Note that even an Earth mass of fuel under any believable pressure would have a radius much greater than Earth itself, and thus a lower surface gravity than Earth. Heating the whole thing up until it starts fusing as you suggest only makes it worse.

Again, carting around a planet with you isn't a good solution. Artificial mini-suns aren't any better. You'd be better off using a fusion drive to accelerate constantly, which only requires impractical amounts of fuel and improbably high reaction rates.

just some thoughts to keep in mind. there is no point in saying something isn't possible, after all discovery means proving someone else wrong. Einstein was a great man but at some point someone will prove him wrong somehow.

That's not what discovery means, not everything thought to be true will be proven wrong, and not everything conceivable is possible.

At present, there aren't any apparent ways to produce gravitational fields without lots of mass and energy. The odds of such a way being found and being simpler than just spinning the craft to simulate gravity are rather slim.

 

[DaveC426913]

Metal weights might be useful in low gravity...it's unclear how this would work in freefall.

Yah. I wasn't sure if he meant for the extra weight or for the ferro-magneticity.

 

[cjameshuff]

Yah. I wasn't sure if he meant for the extra weight or for the ferro-magneticity.

Yeah...I've seen magnets and metal suggested, but it really wouldn't work very well. Aside from the inconvenience of having to avoid long moving conductors and pick materials so things "weigh" the right amount, ferromagnetic materials don't just fall toward magnets, they become magnetized and stick to other ferromagnetic things. Your clothes will stick to the furniture, to random objects, to themselves, to other people's clothes...

 

[mheslep]

People keep mentioning putting a "mini black hole" at the center of the ship in this thread, but I don't think the conventional definition of a black hole allows for the possibility of a "small" one (isn't the critical mass required to create a black hole much larger than the Earth or even our Sun?).

See http://en.wikipedia.org/wiki/Schwarzschild_radius" . Mass of the sun collapsed to a black hole has radius of 3 km, black hole w/ mass of the Earth would have a radius of 9mm, and so on, down even to atomic dimensions as I understand it.

 

[nismaratwork]

See http://en.wikipedia.org/wiki/Schwarzschild_radius" . Mass of the sun collapsed to a black hole has radius of 3 km, black hole w/ mass of the Earth would have a radius of 9mm, and so on, down even to atomic dimensions as I understand it.

I think his point was that the energy required to crush something without using an enormous mass in a state of natural collapse, would be VAST. How this is any more of hurdle than moving a black hole and having even the notion of a fail-safe system... I have no idea.

Like dynamos and flywheels and other such means of storing energy, I think we've all learned that maintaining massive amounts of energy output is as dangerous as sitting next to a dynamo whipping around at some ridiculous speed. Unless a low-energy way of manipulating the fabric of spacetime, or the discovery of some naturally portable ultra-dense material (certainly not a description for any flavor of degenerate matter) artificial gravity isn't happening.

As for powerful magnets, I'm not sure what the effect of magnets placed all over the body, strong enough to simulate your weight (in terms of down-force on the deck) would have, long term. We're not talking about some fridge magnet that doesn't penetrate a few sheets of paper... and this all takes place in a station or ship where magnetic interference with electronics would be very bad.

In space, nobody can hear you scream... unless you haven't finished venting atmosphere and they're right next to you...

Gravity, if Einstein was even MODERATELY right, and really he seems to have hit the mark... well, gravity is just out of our league when it comes to production, but detection... that has promise.

 

[DaveC426913]

Like dynamos and flywheels and other such means of storing energy, I think we've all learned that maintaining massive amounts of energy output is as dangerous as sitting next to a dynamo whipping around at some ridiculous speed.

And yet, even today, this is part of the day-to-day life of every person in the civilized world.

It is simply a matter of the sliding scales of what's "a lot" and what's "safe".

well, gravity is just out of our league when it comes to production

...for now.

 

[nismaratwork]

And yet, even today, this is part of the day-to-day life of every person in the civilized world.

It is simply a matter of the sliding scales of what's "a lot" and what's "safe".


...for now.

It's true, but I was using that as a small example of what it would be to live in some kind of artificially altered spacetime. There's one machine you don't want to break, especially during acceleration!

As for the "for now"... well sure, but reasonably I'd expect our extinction long before we had the kind of energy to play with. That doesn't make me right of course, but really, where would you place your bets?... humanity blasting to Alpha Centauri with artificial gravity... or humanity blasting each other to alpha centauri in a more metaphorical manner.

 

[DaveC426913]

It's true, but I was using that as a small example of what it would be to live in some kind of artificially altered spacetime. There's one machine you don't want to break, especially during acceleration!

Tell cro magnon we think nothing of flinging ourselves, babes-in-arms, 8 miles in the air at 500mph.

As for the "for now"... well sure, but reasonably I'd expect our extinction long before we had the kind of energy to play with. That doesn't make me right of course, but really, where would you place your bets?... humanity blasting to Alpha Centauri with artificial gravity... or humanity blasting each other to alpha centauri in a more metaphorical manner.

That's a completely different ball of worms.

 

[p1ayaone1]

Where's the thread to discuss removing gravity from where it is, rather than creating it where it isn't? Fascinating read here though.

 

[nismaratwork]

Tell cro magnon we think nothing of flinging ourselves, babes-in-arms, 8 miles in the air at 500mph.

That's amazing, but if there's a giant graph with "flint napping" at the bottom left, and "FTL or Artificial Gravity" at the far right, my feeling is that "flight" and other wonders of the modern age fall nowhere near the far right of that graph. It's amazing that we fly, but even the cro magnon saw birds in flight directly overhead... where's the equivalent for gravity?

That's a completely different ball of worms.

You're right.


p1ayaone1: What you've said is not a meaningful statement, or rather, it's so generic as to be meaningless. Gravity isn't some finite resource... it's the curvature of spacetime... you don't "move it around". You COULD move an enormous mass from one place to another, but presumably iif the tech exists to induce gravity, the tech exists to shield against it... otherwise it would be kind of dangerous tech don't you think?

 

[DaveC426913]

That's amazing, but if there's a giant graph with "flint napping" at the bottom left, and "FTL or Artificial Gravity" at the far right, my feeling is that "flight" and other wonders of the modern age fall nowhere near the far right of that graph. It's amazing that we fly, but even the cro magnon saw birds in flight directly overhead... where's the equivalent for gravity?

The point in question was: 'who wants to loiter near a huge source of energy that could go off if it failed'.

The answer being: we do it all the time. We get around in vehicles that, if they fail, will make us (and everyone near us) very, very dead. Yet we do it because we have grown up with the technology and are comfortable enough with its safety record to consider the risk minimal.

There is no 'absolute' in safety-comfort; it is entirely relative to our familiarity.