Bowl World

[Johnny Pneumatic]

In reading Niven's Ringworld I had an idea for another artificial structure, but much smaller. A "bowl world" about 1,000km in diameter that faces toward a sun. The structure would need to have thrusters or something to keep it always pointing toward its parent star throughout its year. The bowl is capped to keep the atmosphere from leaking out and it rotates in its axis to produce "gravity". The strength of "gravity" depends on where you are on the inside surface of the bowl world. At the axis it's zero g, near the edge it's 1.something g. Sound cool? Could something like this actually work?

[The Lone Ranger]

I dunno. Some sort of "bowl-world" would work quite well, but yours seems awfully large. I'd think it would be awfully hard to build something this size that wouldn't tear itself apart.

You calculate the acceleration caused by rotation by dividing the rotational velocity squared divided by the radius of the turn: A = v^2 / r .

Rearranging for the needed rotational velocity, we get: v^2 = A * r .

So, how fast would a dome with a radius of 500 kilometers have to rotate in order to generate an acceleration of one "G" at the edges? One "G" is an acceleration of 9.8 m/sec^2, and r would be 500,000 meters, so if I did my math correctly, the dome must rotate at over 2,200 meters/second. That's one complete rotation ever 24 minutes or so, if I did the math correctly. I'm no engineer, but my guess is that it'd be awfully tough to build a structure that size that rotates at that speed -- that wouldn't tear itself apart from the stress. I could be wrong, of course.

Cheers,

Michael

[livius drusus]

Cool thread, SkepticJ. :) Michael, by your calculations, what size do you think would be the biggest possible bowl world?

[Dingfod]

Wouldn't that depend upon what it is made of? I mean, something made of titanium-steel alloys wrapped with some unknown synthetic fibre is probably going to have a lot more integrity than something made of duct tape and popsicle sticks. Duct tape and popsicle sticks are what my world is made of, that's why it's falling apart all the time.

[The Lone Ranger]

Cool thread, SkepticJ. :) Michael, by your calculations, what size do you think would be the biggest possible bowl world?

Good question. The short answer is: I haven't a clue.

My guess is that, given how fast the thing would have to rotate, it'd be awfully difficult to build something like it with currently-available materials. Not impossible, I would guess, since we're only talking one "G" of force at the outer edges. But it's the shear forces that really get you, and those would probably be considerable for something rotating that fast. Even moderate shear forces will quickly destroy even the strongest structures.

We need an engineer in here!

Cheers,

Michael

[ceptimus]

Did someone call for an engineer? :yup:

I think the biggest problems would not be the forces due to rotation, but those caused by the 'atmosphere' and other fluids.

For a start the 'cap' to hold in the air couldn't be a flat plate; the forces on it would just be impossible. So really we're looking at a 'sphere world', but with one hemisphere transparent to let the sunlight through. Now whatever stresses occur on the 'living' side of the sphere would be more or less the same on the 'cap' side, but with the added problem that it has to be transparent.

Oceans, lakes and rivers are also a major problem. The artificial 'gravity' induced by the rotation means that water would run 'downhill' as far away from the spin axis as possible, so any ocean would necessarily be around the '1'g' rim, and would exist between the 'earth' and 'sky' sides.

Of course any soil, or other loose objects would also tend to be thrown to this 'rim' so unless stuff was nailed down, you are really looking at 'cylinder world'. rather than 'bowl world'.

Interesting idea though. I might post some more thoughts on this later.

[JoeP]

Interesting idea though. I might post some more thoughts on this later.
Thoughts? A blueprint will be fine, thanks.

[livius drusus]

Okay, what follows will be a series of really dense questions from a complete ignoramus. Forewarned is forearmed, as they say.

For a start the 'cap' to hold in the air couldn't be a flat plate; the forces on it would just be impossible. So really we're looking at a 'sphere world', but with one hemisphere transparent to let the sunlight through. Now whatever stresses occur on the 'living' side of the sphere would be more or less the same on the 'cap' side, but with the added problem that it has to be transparent.

Wouldn't a sphere have to have a core or do I just think that because Earth has one? If it is necessary, wouldn't that bring us back to a diskworld of sorts, since the nucleus would be uninhabitable?

Oceans, lakes and rivers are also a major problem. The artificial 'gravity' induced by the rotation means that water would run 'downhill' as far away from the spin axis as possible, so any ocean would necessarily be around the '1'g' rim, and would exist between the 'earth' and 'sky' sides.

Would lakes and rivers not be able to dot the inside, though, even if they flowed to an ocean along the perimeter?

Of course any soil, or other loose objects would also tend to be thrown to this 'rim' so unless stuff was nailed down, you are really looking at 'cylinder world'. rather than 'bowl world'.

Why a cylinder instead of a sphere? Wouldn't the same gravity operate in a sphere world with a transparent hemisphere as operates on earth? Or were you simply responding to SkepticJ's original ideation of the bowl world rather than elaborating on your counter?

Interesting idea though. I might post some more thoughts on this later.

I'm so hoping you do. :yup:

[Johnny Pneumatic]

I thought of another problem with my idea. The air pressure would be far to low at the part of the bowl where gravity is 1/1000th of a g and there would be no air pressure at all at the hub unless I'm mistaken. Not the kind of thing you want if you're an oxygen breathing creature. I guess a cylinder world with a transparent dome on one end is the way to go. I'm most interested in that this world has no night. Or it could if you wanted it to by having "glass" that can go almost or totally opaque. What amount of living space would a 1000km in diameter and 4,000km long cylinder have?

[Johnny Pneumatic]

Wouldn't a sphere have to have a core or do I just think that because Earth has one? If it is necessary, wouldn't that bring us back to a diskworld of sorts, since the nucleus would be uninhabitable?

No, you'd live on the inside surface of the ball. It'd be like a mini Dyson Sphere without a star in the core. Speaking of Dyson Spheres does this have it right? Is there anyway to make a Dyson Shell in real life? 1,000,000,000x Earth living space would be so cool. http://en.wikipedia.org/wiki/Dyson_sphere
Here are some other neat concepts.--> http://en.wikipedia.org/wiki/Space_fountain
http://en.wikipedia.org/wiki/Skyhook_%28structure%29

[The Lone Ranger]

Okay, just for fun I did some quick calculations. Someone please correct me if I've made any mathematical errors.

Since our hypothetical “world” generates “gravity” by spinning, what will be the rotational periods of different-sized worlds if they’re to generate a “gravity” equal to that at the earth’s surface? [This applies whether they’re spheres (though a sphere would experience the full one “g” of “gravity” only along the equator), disks, or cylinders.] Why I’m concerned about the rotational period will be clearer in a moment, but it has been bugging me. There just doesn’t seem to be any practical way to make the thing rotate with a period of 24 hours or thereabout.

Some examples might make this clearer.

If our world is only 1 kilometer in diameter, it will have a rotational period of just 45 seconds. You might get dizzy looking out the windows, considering how fast the stars will be whirling by.

If our world is 2 kilometers in diameter, its rotational period will be just over 1 minute.

If the world is really big, say 1,000 kilometers in diameter, it will still have a rotational period of less than 24 minutes.

A world that’s 1,000,000 kilometers in diameter would have to spin at the rather fast pace of 70,000 meters/second (that’s 70 kilometers per second), and would still take only 12.5 hours to complete a single rotation.

To get a world with approximately a 24-hour “day”, you’d need one almost 4 million kilometers in diameter, and it would have to rotate at about 140 kilometers per second. (A world 4 million kilometers in diameter would have a rotational period of approximately 24.9 hours.)


Why must our worlds spin so fast to generate a “gravity” force of only one “g”? After all, you can generate that much force in your car. You notice that the bigger the world is, the faster it must spin. I doubt anyone needs convincing that building a structure 4 million kilometers in diameter that rotates at a speed of 140 kilometers per second (making it much faster than any rocket we’ve yet to build) would be a monumental undertaking.

What matters is the radius of the turn. If the radius of your turn is only a few meters, you can generate a “g” of acceleration even at the comparatively slow speeds at which an automobile operates. But the bigger the radius of your turn, the faster you must be moving in order to generate that “g.” If you want to build a structure that generates one “g” of “gravity” at its surface and has a rotational period of roughly 24 hours, it’s going to have to be immense.


The more I think about it, the more ceptimus’ idea of a rotating cylinder makes a lot more sense than a rotating sphere or half-sphere. Think of Babylon 5 – by far the most practical-seeming space station that I’ve ever seen on television or in a movie.


Would lakes and rivers not be able to dot the inside, though, even if they flowed to an ocean along the perimeter?

You could have ‘em, to be sure, but you’d have to have some sort of mechanism to pump the water back “upstream,” or it’d eventually all wind up along the rim. Now a “world” the size of the one SkepticJ was originally suggesting might actually have cloud formation and rainfall, but I would think you’d still have to have a dedicated system to pump the water back toward the axis and away from the rim, since the clouds themselves would tend to migrate toward the rim.


Why a cylinder instead of a sphere? Wouldn't the same gravity operate in a sphere world with a transparent hemisphere as operates on earth? Or were you simply responding to SkepticJ's original ideation of the bowl world rather than elaborating on your counter?

A “world” that’s only 1,000 kilometers in diameter and consists almost entirely of empty space isn’t going to generate much gravity from its mass. The “gravity” would be produced by its spin. The “gravity” that’s created in this way is the same effect as when you go around a sharp turn in a car. Your body’s inertia resists the change in direction, and so you feel a “force” much like gravity. Think of it like this: imagine tying a ball to a string and spinning it above your head. You’ll easily be able to feel the ball trying to “pull away.” If the string breaks, the ball will immediately travel away from you in a straight line, since it’s no longer constrained to move in a circle.

People standing on the inside of the rotating sphere would feel the same effect. Because the sphere is spinning, the people are moving with a certain speed. But their mass makes their bodies “want” to move in a straight line. If the sphere suddenly disappeared, that’s exactly what would happen – the unfortunate people would find themselves flying outward in straight lines. (Assuming there are no objects nearby that’re big-enough to generate a significant gravitational field and so alter their motion.)

Anyway, the people and other objects on the inside surface of the sphere will feel “pulled” outward. Fortunately, the hull of the sphere will prevent that from happening, and the force they feel pulling them will feel exactly like gravity. What might be disorienting is that what feels like “up” will be toward the center of the sphere, and what feels like “down” will be toward the outside. If the sphere has windows, you could stand on one and look “down” to see the sun and stars “beneath” your feet.



The earth is a sphere of course (approximately), but its gravity is generated by its mass, not by its spin. Indeed, since we’re standing on the outside of the planet, the earth’s spin is, in effect, generating a force which if it were strong enough, would fling us off into space. (The earth would have to be spinning a lot faster for that to happen!) On the other hand, if the earth’s rotation were to stop, we’d all find ourselves weighing a bit more, since the spin-generated force would no longer be opposing gravity.

Consider a rotating sphere like the earth. The earth completes one rotation every 24 hours. But the earth’s diameter at the equator is almost 8,000 miles, meaning that a point on the equator travels about 24,000 miles during a complete rotation, but if you’re standing a few feet away from the North or South Pole, the earth’s diameter is only a few feet, and so you’d travel only a few feet in 24 hours. (If the earth were a perfect sphere, and you were standing 5 feet from the North Pole, the diameter of the earth where you were standing would be about 10 feet, meaning that its circumference at that point would be only about 30 feet – you don’t have to move very fast to cover 30 feet in 24 hours.) So, a point on the earth’s equator is moving at about 1,000 miles per hour, while the poles don’t have any rotational velocity at all. This is why space agencies like to launch rockets as close to the equator as possible. The rockets get a “boost” in speed from the earth’s rotation – the closer to the equator, the greater the boost.



As ceptimus points out, there would be some real problems with life inside a spherical “world” that generates gravity by its spin. Since the equator is moving fastest, that’s where the “gravity” would be the strongest. So everything that wasn’t secured would tend to migrate toward the equator. If you walked from the equator toward one of the poles, you’d grow progressively lighter as you approached the pole. Theoretically, at the pole itself you’d be weightless. You could easily launch yourself into the air, but getting back down again might be a real problem. (I’d imagine that in such a world, people would be forbidden to approach the rotational axis too closely.)


Building your world as a rotating cylinder makes a lot more sense, as it would immediately solve a lot of the problems that a sphere would pose. For instance, though you’d still be weightless along the axis of rotation, you wouldn’t be able to walk to it. Nor would you have the problem of your weight changing as you move along the habitable portion of the structure. Nor would soil, water, and other loose matter migrate to one region.



I thought of another problem with my idea. The air pressure would be far to low at the part of the bowl where gravity is 1/1000th of a g and there would be no air pressure at all at the hub unless I'm mistaken.

I would think that this would depend greatly on the size of the structure. The air would have a tendency to flow toward the equator in a spherical structure of sufficient size, which could become a real problem for those living any distance away from the equator. Building your world in the form of a disk (though most of it would be uninhabitable) or better-yet a cylinder would solve that problem. My guess is that if your world were a hollow sphere 1,000 km in diameter, there would indeed be almost no air pressure at the poles.


I guess a cylinder world with a transparent dome on one end is the way to go. I'm most interested in that this world has no night. Or it could if you wanted it to by having "glass" that can go almost or totally opaque. What amount of living space would a 1000km in diameter and 4,000km long cylinder have?

Well, assuming it’s hollow and uncompartmented, a cylinder of such size would have a volume of about 3,141,590,000 cubic kilometers. That’s quite a lot of space, but most of it would be near-vacuum. (You could get around this by putting air in under pressure, so that even the axis has plenty of air, but then the air pressure at the ground is going to be considerably higher.)

A better measure would be surface area, since just-about everyone’s going to be living along the inside surface anyway. A cylinder of this size would have a surface area of about 14,137,155 square kilometers – a fair bit of land, to be sure.


It strikes me that even if you make it really big, you’d probably want to compartmentalize this thing to some extent. I assume that any society that could build such a thing would have sufficiently sophisticated scanners and weaponry to detect and deflect a meteoroid large-enough to pose a threat, but still, what if one gets through? You don’t want the whole world to depressurize because one meteor got through while somebody was napping, and it happened to hit near the equator. Worse yet, you don’t want some nutcase to open an airlock and kill everyone. Compartmentalization means that damage to one part of the world doesn’t have to doom everyone. Plus, if you wanted to maximize the living space, you could fill the entire volume of the cylinder. People living and working in compartments close to the axis would enjoy low-gravity conditions, while those living close to the surface would have normal gravity. You could always have a few really big compartments to function as parks or other recreational areas.

Making one end of the cylinder transparent and keeping it pointed at the local sun would work so long as the cylinder’s mostly empty space. You could have the “window” be shuttered or go opaque to generate any day/night cycle you wanted. However, it seems to me that it would be just as efficient to put smaller windows in the outer hull, which could be shuttered/unshuttered at will to let in or keep out light. This would work well if the interior is mostly empty space.

As the calculations above suggested, people living near the surface wouldn’t be able to enjoy anything like a normal 24-hour day from the world’s rotation, unless the world is truly immense. Having “sunrise” and “sunset” occur every 20 minutes or so would doubtless be a bit distracting.

Of course, if the interior volume is mostly occupied, then only the people living near the surface are going to have a chance to see natural light in any event, and the vast majority of people inhabiting this place are going to have to rely on artificial light.




Dyson spheres are a fascinating idea, but my impression is that the general consensus is that it’s an unlikely thing for anyone to build. Where would you get the tremendous mass of materials to build such a thing? We’re talking about something that would require building materials much stronger than diamond, and would still probably outweigh the earth itself by orders of magnitude. A “ringworld” would be enough trouble to build; a Dyson sphere would be much harder.


Cheers,

Michael

[Scotty]

Always fun to speculate.

How about, instead of just one "bowl" shapped structure, you had two, connected together by a VERY STRONG monofiliment string. The two would counterweight each other, spinning, thus creating the gravity that way (more than one string of course, hundreds, thoustands, millions to hold them together)

Now, how much distance between required to make them spin and create gravity at an acceptable level and have a resonable amount of living space? How big are the "bowls", are they not completely hemispherical, maybe like contact lenses in curve?

Would the atmosphere hold in with that spin without a "top" to the structure?

On another weird note, could you use an artifically created "black hole" to create gravity....? Dangerous pasttime? :) How small can you make a stable black hole (if there is such a thing)?

Plus, they should have made within the Star Trek universe a Ring World, and stationed people there (or the Dyson's Sphere they had, although I think the imagery on a Ring World would be more specatular). That would have made an interesting show, better than Enterprise.

There you go. :D Too bad I can barely add and subtract....or spell.

-Scott

[ceptimus]

Regarding the atmosphere height, if we want to replicate Earth atmosphere and Earth gravity, then we simply have to note that the Earth's atmosphere only extends about 60 miles up. So if the structure is on the 1000 mile scale or more, then the reduction in gravity will be pretty small over the first 60 miles or so and the atmosphere will be held in without the need for a 'cap'.

The two 'saucer worlds' connected by a rope or ropes is a neat idea. You could look 'up' at the people living on the other saucer - it would be like moon gazing here on Earth, but much more interesting.

[The Lone Ranger]

On another weird note, could you use an artifically created "black hole" to create gravity....? Dangerous pasttime? :) How small can you make a stable black hole (if there is such a thing)?


I'm not sure how practical the artificial black hole would be as a gravity source. First of all, how would you confine such a thing? I suppose if you could somehow get enough matter together in the right place and put it into a nice, stable orbit around a star, that's a good start. Now, you need to (somehow) compress that matter 'til you get a black hole. Once you've got a black hole, you could theoretically build your world around it. But boy! It'd have to be perfectly balanced, and the consequences of making even a tiny error in your calculations would be catastrophic! (I'd think that you could partially counter this danger by placing rocket thrusters on your world that could continually reposition it so that it doesn't get drawn into the hole.)

The problem with a black hole is that unless it's something like the mass of an entire planet (and if you have the technology to manipulate that much matter, and to compress it to infinite density, why are you building black holes instead of ringworlds?), the gravitational gradient is going to be something fierce.

Suppose you build your world around a stable black hole of such mass that those standing 10 kiometers away from the hole will feel a gravity of 1 g. Someone standing 20 kilometers away would feel only 1/4 g. Someone standing 30 kilometers away would feel only 1/9 g, and so on.

If you built your world as a shell around the hole, some 1,000 kilometers in diameter, you'd have a mini Dyson sphere or ringworld. (Only the habitable surface would be facing away from the black hole, not toward it.) Such a thing might work if you had a sufficiently massive black hole. I wouldn't think there'd be enough of a gravitational gradient between 1,000 kilometers from the hole and 1,100 kilometers from the hole that you'd need to worry too much about the atmosphere escaping.

The point here is that you'd need to make (or find) a fairly massive black hole, one that's the size of a planet. (And since such things almost certainly don't form naturally, we'd need to have the technology to somehow create a black hole that massive.) It'd still be an awfully small black hole on the scale of such things though, which brings up the radiation problem.


The other thing about black holes is that -- if Hawking is right -- they radiate. The smaller they are, the greater the gravitational gradient they create near the event horizon. (For a galaxy-mass black hole, the gravitational gradient near the event horizon is so small that you might cross the event horizon and so become trapped forever without even knowing it; for star-sized or smaller black holes, this isn't a problem, because the radiation they emit would make them hard to miss, even if the tidal forces they generate didn't tip you off.) Ironically then, the smaller the black hole, the more energy it should radiate. In a way, this is convenient, because you might be able to capture that energy and put it to use. On the other hand, something that's putting out lots of gamma radiation isn't something you necessarily want to be too close to. All the more so because -- again, if Hawking is correct -- small-mass black holes would have a nasty tendency to release their last bits of energy all at once, in the form of a rather powerful explosion.

The upshot is that the smaller a black hole is, the less stable it is.


Cheers,

Michael

[squian]

As ceptimus points out, there would be some real problems with life inside a spherical “world” that generates gravity by its spin. Since the equator is moving fastest, that’s where the “gravity” would be the strongest. So everything that wasn’t secured would tend to migrate toward the equator. If you walked from the equator toward one of the poles, you’d grow progressively lighter as you approached the pole. Theoretically, at the pole itself you’d be weightless. You could easily launch yourself into the air, but getting back down again might be a real problem. (I’d imagine that in such a world, people would be forbidden to approach the rotational axis too closely.)
I doubt anyone could approach the rotational axis. At least not on foot. The artificial gravity pushes things away from the rotational axis. As such, it would be like walking up an ever increasing slope.

Think about trying to walk up a half-pipe at a skate park. The farther from the center of the half-pipe the steeper the incline until you just cannot walk forward anymore and each step starts to make you slip downward. Even if the downward force is reduced with each step from the center, it still pulls in the same direction.

On the other hand, maybe a combination of stairs and ladders would allow a person to travel to the axis.

Making one end of the cylinder transparent and keeping it pointed at the local sun would work so long as the cylinder’s mostly empty space. You could have the “window” be shuttered or go opaque to generate any day/night cycle you wanted. However, it seems to me that it would be just as efficient to put smaller windows in the outer hull, which could be shuttered/unshuttered at will to let in or keep out light. This would work well if the interior is mostly empty space.

You could do without shutters and still have a day and night cycle. As an experiment, take a toilet paper tube (or similar household cylindrical item) and point it at a lamp so you can see the lamp through the tube. If you tilt the tube slightly, you see a shadow cast from the lip of the tube onto the inside. If the tube rotates around the center, you can see how the shadow moves over the surface. The end closest to the sun has longer days while the back of the tube may have permanent night.

At the "warm end" (pointing at the sun), the night sky would be lit up by reflected light from the daylight side. You could also look out the end to see the stars. I can imagine looking up at a blue sea that sparkles with reflected sunlight and seeing the stars twinkling next to it. My what a scene that would be.

The big question might be why build something like that? If one could overcome the challenges of finding a material that would not fly apart from the stress, keeping the object at sufficient rotational velocity, and controlling it so it does not fly into the sun (or something else), then there is still the question of whether it wouldn't be easier to do something else. For example, if you need to move so much materials into space, maybe it's easier to push some asteroids or even planets closer to the sun (since moving closer is easier than moving farther out) and just live on that. Of course, if it were easy enough to do, maybe it would be done for the simple artistry of it all.

[Johnny Pneumatic]

big question might be why build something like that? If one could overcome the challenges of finding a material that would not fly apart from the stress, keeping the object at sufficient rotational velocity, and controlling it so it does not fly into the sun (or something else), then there is still the question of whether it wouldn't be easier to do something else. For example, if you need to move so much materials into space, maybe it's easier to push some asteroids or even planets closer to the sun (since moving closer is easier than moving farther out) and just live on that. Of course, if it were easy enough to do, maybe it would be done for the simple artistry of it all.

But you wouldn't lift the materials off Earth. Lets say humans want to build one of these. We'd mine asteriods for the metals, build a space fountain or elevator on Titan to hold up the pipeing for pumping the natural gas oceans up to a giant orbiting space station. Nanites would convert the hydrocarbons to nanotubes, resins and other polymers. The hydrogen that is used to power the station's and transport craft's fusion reactors comes from Jupiter's atmosphere. A nanotube cable dangles down into the atmosphere from a very high stationary orbit. On the end of the cable is pumps and pressure spheres that are filled with the hydrogen. The spheres then ride up the ribbon on electromagnetic tracks to the orbiting space station to be fired from rail guns to escape Jupiter's gravity and are caught by a rotating tether to slow it back down and then the hydrogen gas is loaded into ships for their fuel.

[squian]

Even if we do not lift the materials from Earth, we are "lifting" them from somewhere in the sense that it takes energy to extract the materials and energy to move pull them out of any source of gravity. However it's done, it doesn't come for free. It just seems like there should be some purpose to creating an artificial world.

For example, if the tube world has an artificial light source instead of a sun, it can go places as a traveling world-ship. Presumably, we could do the same with a bowl world-ship as well.

But if it's just more room we need, why not push something closer to the sun and make it more Earth-like?

[Johnny Pneumatic]

Do you have any idea how much energy it would take to move a planet closer to a sun?! I think putting a lot of super green house gases into a far out planet's atmosphere would be more efficient than moving trillions of trillions of metric tons of rock and metal(a planet) closer to a star to warm it up.
How warm would Venus be if it were in Mars's orbit? A cylinder world would have advantages over living on Earth. No hurricanes, earthquakes, floods, volcanos, tidal waves, freak ice storms, tornados etc. A perpetual food growing season would be nice. Although if your civilization can build one of these you'd already have advanced nanotech so your food could be made by nanites from the raw chemical elements into whatever you want to eat that day. Or you might even be mostly machine by that point and wouldn't eat in the same manner that we do anymore.

[JoeP]

I haven't put any thought into these suggestions, but damn, this is an interesting thread.

[The Lone Ranger]

Do you have any idea how much energy it would take to move a planet closer to a sun?! I think putting a lot of super green house gases into a far out planet's atmosphere would be more efficient than moving trillions of trillions of metric tons of rock and metal(a planet) closer to a star to warm it up.


I could be wrong, but I'm guessing that squian's point is that it would be a lot easier to move an asteroid or two nearer the sun and use those to build an artificial world than to build one from scratch, especially if you'd otherwise have to get the raw materials out of Earth's (or any other planet's) gravity well.

You could put domes on an asteroid, so as to provide both living space and to allow for the growing of plants for food and oxygen. Of course, an asteroid wouldn't have much gravity, which might be a problem for some. 'Course, you could partially hollow it out, build your living quarters on the inside, and then spin it for "gravity."

How warm would Venus be if it were in Mars's orbit? A cylinder world would have advantages over living on Earth. No hurricanes, earthquakes, floods, volcanos, tidal waves, freak ice storms, tornados etc. A perpetual food growing season would be nice. Although if your civilization can build one of these you'd already have advanced nanotech so your food could be made by nanites from the raw chemical elements into whatever you want to eat that day. Or you might even be mostly machine by that point and wouldn't eat in the same manner that we do anymore.

Terraforming Mars seems like it might be a real possibility for the not-entirely-distant future. With a thick-enough atmosphere containing sufficient quantities of carbon dioxide, it should be able to support human life. (Heck, even now, with an atmosphere that's 100 times less-dense than the Earth's, Mars' surface temperature has been known to soar to a balmy 20 degrees Fahrenheit during the Martian summer.)



Cheers,

Michael

[Johnny Pneumatic]

Would the angular momentum of the cylinder world be canceled out if it was connected to a structure that was connected to another cylinder world spinning in the opposite direction at the same speed? You'd want to cancel or reduce the angular momentum as much as you could so you wouldn't waste energy forcing it to point at a sun throughout the orbital year.

[Johnny Pneumatic]

You don’t want the whole world to depressurize because one meteor got through while somebody was napping......Compartmentalization means that damage to one part of the world doesn’t have to doom everyone........As the calculations above suggested, people living near the surface wouldn’t be able to enjoy anything like a normal 24-hour day from the world’s rotation, unless the world is truly immense. Having “sunrise” and “sunset” occur every 20 minutes or so would doubtless be a bit distracting..........We’re talking about something that would require building materials much stronger than diamond.

That would screw with the great view the place would have, and that all places on it could have perpetual day. Why not have a foam that would absorb the kinetic energy of an impact and would seal back on its own until nanites can repair the damage. Anything that would truely be a threat would be destroyed by lasers or pushed out of an impact course by robotic craft years before it would hit. They wouldn't have a day night cycle unless the borosilicate glass dome could go mostly opaque on command. The sun would always be in the same spot in the sky. You wouldn't see the other stars living in it. Just like you don't see any other stars during the day on Earth. The Sun's brightness is to great. You wouldn't be able to see the stars at night(if the engineers chose to have night) because the glass would be like welding glass or darker. So you couldn't be disoriented by these things because you wouldn't see it.

How strong is diamond anyway? A common misconception is that diamond is really hard to break. It isn't, it's just hard. Diamonds are the hardest known natural material. You can break a diamond by whacking it with a hammer and you can burn it by heating it high enough to.

[Johnny Pneumatic]

What would the glass dome on the end of ceptimus's cylinder world look like? Would it curve like a contact lens or be a full hemisphere? Whatever the shape it'd need to be subdivided into hundreds of millions of panes supported by a lattice of support members. Something like a bucky dome, but much more subdivided. Let's keep this thread going.

[ceptimus]

Would the angular momentum of the cylinder world be canceled out if it was connected to a structure that was connected to another cylinder world spinning in the opposite direction at the same speed? You'd want to cancel or reduce the angular momentum as much as you could so you wouldn't waste energy forcing it to point at a sun throughout the orbital year.
Yes. But it might not be worth the trouble. By applying a force at right angles to the cylinder's spin axis, you could make it precess, like a gyroscope, and it wouldn't take a lot of force to make it precess through one cycle each year, and so keep the transparent end of the cylinder pointing at the sun.

[ceptimus]

What would the glass dome on the end of ceptimus's cylinder world look like? Would it curve like a contact lens or be a full hemisphere? Whatever the shape it'd need to be subdivided into hundreds of millions of panes supported by a lattice of support members. Something like a bucky dome, but much more subdivided. Let's keep this thread going.
When I wrote about that, I was thinking of a complete hollow sphere, with one half of it transparent. I hadn't imagined any support members - I was thinking of smooth glass, plastic (or transparent aluminium or other metal :yup: )

I thought of that shape as the best one to hold in the gas pressure of the atmosphere, but I was wrong. As we have seen, with a large spinning bowl, sphere or cylinder where we replicate Earth atmosphere and gravity, all the air will be centrifuged out to the outside, and if we go more than 50 or 60 miles from the outside towards the spin axis, it will be an almost perfect vacuum.

So on a large rotating system more than a few hundred miles across, you don't need a complete dome to hold the air in - you only need an inturned lip or rim about 50 miles 'high' and after that you can just leave a big hole. :D

It would be a cool place to live. but I think living, as we do, on the outside of a giant ball with no lid to hold in the air is even cooler!

[The Lone Ranger]

I'm trying to imagine how the sky would look if you lived in a great big cylindrical world like that.

If it were pointing right at the sun, then the sun should be in the middle of the "sky" -- that is, right in the middle of the dome (or hemidome, or whatever you'd call it). Obviously, it would never be directly overhead to anyone in the cylinder, no matter where they were standing.

So, from the perspective of someone standing on the inside of the cylinder, would the sky look blue toward the horizon, fading toward black as you looked toward the center of the dome and the sun? Or would the overhead atmosphere be thick enough to scatter sunlight such that the sky looks blue everywhere? That would be my guess, though the sky would probably redden somewhat as your shift your gaze toward the horizon.

It seems to me that if you're looking down the axis of the world (if we're talking about a world that's hundreds of miles long), you'd be looking through enough atmosphere for the sky to be perceptibly reddened, and it would become bluer as you look toward the sun (and consequently, through less air). Of course, that would depend on where you are in the world. Someone standing at the far edge of a 500-mile-long world would be looking through nearly 500 miles of atmosphere when looking at the sun, and the sky would surely be quite red. Someone standing at the near edge would be looking through a lot less air, and so would probably see a blue sky.

An astute observer should be able to tell where in the world any photograph was taken from the color of the sky, or so it seems to me.

Thoughts?


Cheers,

Michael

[livius drusus]

I think that's super, super cool.

[pescifish]

There are quite a few considerations of artificial worlds in both science fiction and physical science. A quick Google on "hollow sphere" and "artificial world" got me a pretty good reference
http://encyclopedia.thefreedictionary.com/Artificial%20world

Check out the article on Dyson spheres (http://encyclopedia.thefreedictionary.com/Dyson%20sphere).

[Johnny Pneumatic]

If someday, somehow a Dyson shell could be made that would be so kick ass. The living space of a billion earths. Generating the gravity is the problem though. Using the space fountain idea it looks like to me it maybe could be supported against the star's gravity. There is a super strong material(600 times stronger than steel), but it's going to remain in the labs until the cost of making it comes down. $300 dollars per gram isn't cheap. http://en.wikipedia.org/wiki/Carbon_nanotube

[Johnny Pneumatic]

I found a painting of a bowl world while I was looking for art of artificial worlds. Here it is--> http://www.gsoftnet.us/graphics/Sharu.jpg I didn't find any cylinder worlds but there is some ringworld art if you do a Google image search for it. Looks like I should paint a cylinder world in a few years after I've had some lessons.

[ceptimus]

I'm trying to imagine how the sky would look if you lived in a great big cylindrical world like that.

If it were pointing right at the sun... <snip>
I think you're right about the 'permanent sunset' effect, IF you make that 'pointing right at the sun' assumption. But why make that assumption? Things are much more interesting if you don't...

Assume the spin axis lies in the orbital plane of the world, but does not point at the the sun, but always in the same direction, say at some distant 'pole star'. Now we get day and night, and also seasons!

With a world of the size we've discussed, the cylinder has to spin about one revolution every half-hour so that would be the length of a 'day'.

Twice each year, the world's axis (either the north or south pole) would point straight at the sun, as you described and the sun would be on the horizon. At the pole nearest the sun it would be a very bright sun, and at the distant pole, it would be very dim, or even totally dark, if the cylinder is long enough for the atmoscylinder to attenuate the sunlight down to nothing. But even at the bright end, it would be very cold, as the sun would only strike the ground at a very oblique angle.

So these 'axis points at the sun' times would correspond to winter. The people living near the poles would get alternating 'bright winters' and 'dark winters'. Those living near the 'equator' would get middling winters, each time. but the sun would be on the northern horizon in odd-numbered winters, and the southern horizon on even-numbered ones.

At the two times each year when the axis was at right angles to the sun direction would be summer. There would be a brief 'eclipse' of a few days when the opposite side of the world blocked out the sun, at midsummer, but either side of that you would get days and nights of 15 minutes each.

I would write more about spring and fall, but my dinner is going cold...

[Johnny Pneumatic]

What would the climate be like if the cylinder world didn't have seasons other than a perpetual summer using the gyroscopic presession you talked about to keep the single transparent end pointed at the sun? I'm thinking the world could have much more carbon dioxide than earth's atmosphere does. Maybe ten or more times. The whole world would be very tropical and nice wouldn't it? I'm thinking that if a civilisation went to the trouble of making one of these it might be so they could escape having seasons. If you want seasons live on an northern or southern continent on an aqua planet that has an axial tilt somewhat like earth. Could a planet precess in the manner you decribed, so as to always point its axis of rotation toward its parent star? What would the weather be like on a earth sized oblate spheroid planet(sorry Hal Clement) that has an axial tilt close to ours? How flat could a planet get by spinning fast before it went so fast that it was unsafe and fly apart?

[Johnny Pneumatic]

I'm thinking the sky would look blue pretty much all over inside the cylinder, because the sun would be in the glassless hole hundreds of miles "above" the atmosphere. Thus even 4,000km in the back of the tube the sun would beam in above most of the atmosphere....maybe. Somebody correct me. :blush:

[The Lone Ranger]

That would be true only if the cylinder's really wide compared to its length; only that way would you be looking through only the 60 miles or so of atmosphere that's right overhead.

If the cylinder's much longer than it is wide, then the angle will be a shallow one (probably a very shallow one, if the cylinder's a lot longer than its diameter) when you're looking right at the sun, and so most of your line of sight will be through air. The way to get around this is to make the cylinder's diameter comparable to its length, so that the angle relative to the "ground" isn't so acute when you look at the sun, no matter where you are in the cylinder.


I did a quick sketch that may make it clearer. In the top "world" the observer is standing at point A, near the far edge of a cylinder world that's much longer than it is wide. The world is pointed right at the sun. The blue line overhead represents the atmosphere. Notice that the observer's line of sight is almost entirely through atmosphere. [The top half of the cylinder world has been omitted for clarity.]

The second world has a diameter that's actually greater than its length (again, the top half is omitted for clarity), so it's more of a ringworld than a cylinder world. In this world, even to an observer at the far end of the world (point B), the sun is close-enough to overhead that you aren't looking through too much atmosphere when you look at it.


So, the observer in World B should see a blue sky. The observer in World A most-definitely won't.

Cheers,

Michael

[Johnny Pneumatic]

ceptimus's world is 1,000km in diameter and 4,000 long. It'd be a lot closer to your bottom drawing than the top. I'd like to live in one, all by myself except for friends and lovely nude women. :blush:

[ceptimus]

The sun on the Lone Ranger's diagram is too close to the world, for it to be accurate scale. It doesn't affect the point he made however.

If you model our sun with an orange, then the earth is a millimetre sized grain, about 20 metres away. Space is big! On the same scale the nearest stars (other oranges) would be about 10,000 kilometres away.

So when the cylinder world's axis is pointing at the sun it's more like this (though this is nowhere near scale either)

_
/ \
= | |
\_/Gosh that looks ugly! :guilty:

[The Lone Ranger]

The sun on the Lone Ranger's diagram is too close to the world, for it to be accurate scale. It doesn't affect the point he made however.


Yeah, I know, but I figured that if I'd drawn it anywhere near scale, the world would have been only a pixel or so in size and the sun would have been several meters away -- kinda hard to fit within the size limitation of attachments.


If you model our sun with an orange, then the earth is a millimetre sized grain, about 20 metres away. Space is big! On the same scale the nearest stars (other oranges) would be about 10,000 kilometres away.
That's one of my favorite mental exercises. It's simply astonishing to think how far away even the "closest" celestial objects are! Space is 99.999999999% empty, and whole galaxies can pass right through each other with few or no collisions between the hundreds of billions of stars that make them up.

Cheers,

Michael