h a l f b a k e r yOn the one hand, true. On the other hand, bollocks.
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Could several of these be placed inside a
cosmic scale engine block ? I think
topographical models of the earth, with
countries mapped on in this form already
exist. |
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// The tilted axis would also have to be rectified, amongst other concerns |
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I don't disbelieve you, but could you explain why? Also, what are your other concerns? |
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The 'corners' of the cylinder would be like
very high-altitude mountains - it might be
hard to breathe there. Also, gravity would
be non-perpendicular to the surface. |
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Basically a celestial kebab spit then? |
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A cylindrical planet would have the same climate everywhere except at the ends, and if tilted, the climate would be cooler everywhere, not just at the ends. There would also be a gravitational problem, but this could be solved by varying the density along the axis, as if the ends are made of osmium and the equator of lithium, or perhaps hollowed out towards the centre and solid all the way through at the ends. |
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//Also, gravity would be non-perpendicular to the surface.//
I'm not disputing this, but I can't figure out why it would be so. I figure the centroid of a cylinder would still be .... hmmm.
So are you saying that - screw diets, just move further away from the equator? |
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// you are not eliminating the problem of some parts of the earth being closer to the sun |
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The difference in the distance from the sun between the pole furthest from it and the point on the earth closest to it is less than 0.006%. The difference in temperature is primarily caused by the angle of the surface to the sun, which dilutes the energy it receives per unit area according to the cosine of the angle (Or maybe ArcTan, I can't be bothered thinking about it). You would have to angle it if it was in Earth orbit or else it would be hotter than the tropics, which are at an angle also. You could have a series of these worlds at different orbits, and angle differently them to achieve optimum temperatures at the different distances from the sun. |
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The non-perpendicular gravity issue is one I hadn't considered, thanks for nineteenthly's suggested solution. |
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The optimum surface area I would guess is for a "square" cylinder (Height = diameter). A different proportion could be chosen to control rotational speed if that cannot be altered another way. |
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Rama, while a great book and concept, is very different from this. |
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Either, Lt_Frank. I wouldn't mind doing it to this world, except we'd see the mass extinction of a lot of species that have adapted to temperate and colder climates. |
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I think that doing any globe-spanning action should really be tried out and proven on another world before we try it on ours, to be sure that it will work. |
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<rant> which is why I think that, while we don't know the effect of emissions on the atmosphere, we should really terraform another world, see what massive emissions do to that, and then decide how much CO2 etc this world can sustain. <\rant> |
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Non perpendicular gravity is going to be a major problem. From a gravitational perspective the surface of your cylinder world is going to be a valley with the bottom at the equator. Stuff is going roll "downhill" until a sphere is reformed. |
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Even modifying the density is probably not going to completely solve the problem. Since your cylinder is going to have to have zero density at the equator. |
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Think of this thought experiment. Instead of a solid cylinder, you have two dense spheres that are touching at one point. Now enclose those spheres in a thin shell from the equator of one to the equator of the other (looking like a pressurized tank). Now imagine you are standing at the exposed pole of one sphere. As you walk toward the equator, you experience flat land. The gravity is always perpendicular the surface you are walking on. You reach the equator and start walking on the cylinder. Because you are walking away from the surface of the first sphere, it will feel like you are walking uphill. But as you continue, the force from the other sphere will take more and more effect until you feel like you are walking downhill to the other sphere. |
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Ok, maybe this could work. Because you could squash the two spheres together to a degree where the "Hill" effect of two spheres is balanced by the "Valley" effect of a homogeneous cylinder. |
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Yep, as [Galbinus_Caeli] rightly states, any world with a gravity non perpendicular to the surface due to non spherical configuration will tend to accrete back towards the spherical ideal. |
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Every time a grain of sand falls, it will fall towards the centre and away from the poles, air, water and any free-flowing matter will move itself towards the centre - you're going to end up with a sphere - any other configuration (with the exception of hollow ones, using centripetal force to keep things stuck to the outer wall) will tend towards a spherical ideal, because that's the only stable form there is for large gravitational objects. |
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[Zen Tom] A sphere is the only gravitational stable configuration /at rest/ Add some motion in there and you can get a number of different configurations. From oblate spheroids (like this one we are sitting on) to separate bodies orbiting a common center like Alpha Centauri |
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If the cylinder was short and squat, and rotated fast enough, it would maintain it's shape, something like a discus if you could keep it from flying apart under centrifugal forces. But as pointed out by [hippo], what you would end up with is an airless surface as gravity pulled the atmosphere to the poles where it would assume a blister-like shape. |
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// with the exception of hollow ones,
using centripetal force to keep things
stuck to the outer wall // the inner wall,
surely? I am working on a contraption
exploiting this right now. |
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//As you walk toward the equator, you
experience flat land. The gravity is always
perpendicular the surface you are walking
on.// [Galbinus Caeli] Since the center of
mass of your double sphere system is at
the point of contact, the gravity would
*not* be perpendicular to the surface. |
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[placid] True! I was thinking of the special case of standing at the pole. |
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As you walk toward the equator you gravity will make it feel as though you are walking UP a hill. This sensation will continue until you reach the midpoint of the connecting cylinder. |
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[Galbinus Caeli] Ok, I see. Although I think
that the sensation would be one of
downhill rather than uphill. |
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Mathematical challenge: model a non-spherical solid with uniform density that has gravity perpendicular to its entire surface OR prove that it cannot exist. |
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Advanced challenge: if this cannot exist, what non-spherical solid has the largest percentage of it's surface area meeting the above criteria? |
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[placid], Yeah, you are right. Downhill from pole to the equator, Then uphill from the equator to halfway across the cylinder, then downhill to the equator of the second sphere, then uphill again to from the equator to the pole. |
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All of which says that no matter how you distribute the mass, you are going to have areas of non perpendicular gravity somewhere on the surface. |
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Anaximander, a student of Thales, beat to you this idea by about 2500 years. He said of the Earth: "Its curious shape is that of a cylinder[8] with a height one-third of its diameter. The flat top forms the inhabited world, which is surrounded by a circular oceanic mass." (link) |
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Would a donut shaped ring satisfy [wagster]'s challenge? |
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The center of gravity would have to be circular, in the center of the ring... |
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Now that I think about it, that seems absurd :P |
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The larger and thinner the donut was, the more it would work. I suspect that a donut with infinite circumference but finite cross-section would satisfy the conditions, but I can't prove it. |
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What about a cylinder made of separated components? Instead of a single cylinder, a hollow cylinder of asteroids rotating together kept apart by magnets. |
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//donut with infinite circumference but finite cross-section would satisfy // yep, it would, because with infinite circumference you can ignore the far-away parts. It then becomes the same as an infinitely long cylinder, which also satisfies the conditions except for at the ends, and since there are none, it works fine. Distribution of sunlight is a problem, though. |
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So is building it in a finite universe, out of finite resources. Not to mention the problem of setting a firm finish date to the project. |
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I think people are making the incorrect assumption that the the gravitational attraction exerted by an object is towards its centre of gravity. The centre of gravity of the earth-moon system is out in space, but you don't fall off the earth when the moon is overhead. Nonetheless, towards the equator would be downhill, as has been pointed out. |
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[spidermother] You are mixing up the Earth/Luna system with the Pluto/Charon system. The center of mass for the former is well within the mass of the Earth (though the earth does wobble.) Check out the wikipedia entry for "Center of Mass" |
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Gravity follows the inverse square law. Increase the distance by 10, decrease the gravitional force by 100. |
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This is an idea from that one scifi series..
that gene roddenberry series about that
ship that goes around trying to save the
"commonwealth" or something. |
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How would you light the thing? |
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Even if the rock the planet was composed of was strong enough to support what would effectively be enormous mountains at high latitudes, the sea would still flow down to a sphere (approximately - actually an ellipsoid because of the planet's rotation). So you'd end up with deep water all round the equator, and none anywhere else. The atmosphere would do the same, give or take a few miles... |
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//How would you light the thing?// - Candles. |
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//Not to mention the problem of setting a firm finish date to the project.// |
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Has anyone ever actually <i>believed</i> a "firm finish date" (or a "budget") for any project bigger than the washing-up? Or even for the washing-up, for that matter... |
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Just give it a date of "tiistai 10. huhtikuuta 1998". It's firm and it's Finnish. |
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I've brought in a building project on budget before, and I'm about to do it again. Of course I'll never bring it in on time *and* on budget. That would be silly. |
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Ah, the universal law of construction: |
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Fast, cheap, nice - pick any two. |
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Or as my architect put it, "Sounds like you want to be in the middle of the cost, time, quality triangle." |
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The trick is not in the execution phase [wagster]. You have to get things going your way from the very beginning by choosing "appropriate" budgets and schedules. |
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I'm trying. As my other half will attest. |
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I didn't say nothing ever comes in on time or on budget. I questioned whether anyone ever believed they would. |
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Obviously these things can happen by accident occasionally! :-) |
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The trick to coming in on budget is to oversize the budget *before* you start. |
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[nuke hobo] Indeed - by a big enough margin to cover contingencies and errors of estimation, but by a small enough margin (very likely negative) that you don't price yourself out of the contrick. The latter issue is of course the key. |
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However, in the context this arose in, the probability of producing a finite budget that would cover eventualities is zero... |
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