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Re: Thoughts about sphere worlds

The gravity of a shell is not precieved by objects within the shell. For this reason, the gravity you experience will grow less and less as you penetrate deeper and deeper into a body such as the Earth.

This is how black holes work. There are many, many stars with sufficient mass to become a black hole. However, they are too big and continue growing as they get hotter with age. It is the heat that pushed the mass of a star ourward from the nuclear reaction that occurs at or very close to its core. At some point a the fusion reactor at the center of the star runs out of fuel that it can fuse at the pressure exerted by the mass of the star pulled inward by its own gravity. At this point the star collaspes in on itself, as it is not producing enough heat to keep itself puffed up. When a sufficient amount of the stars mass gets compressed into a sufficiently small space then you will have a black hole.

At least, I'm pretty sure that's how that works. I am sure about the shell part.

From the outside, the shell will will be an immense amount of gravity. But if the outside surface is spinning, and it will be spinning much faster than the earth's orbital velocity, then at the equator one would be thrown off at around 1 G. In thruth it would be pretty damn hard to ladn on, you'd have to be on one wicked eliptic... though I could have the scale wrong.

Additionally, no human would be able to run or jump fast enough agaisnt the spin of the world to escape it and start floating. I believe, in order to get the 1 G, you'd have to be cranking damn fast.

You actually have some options, where radius and rpm are concerned, since the equation for relative centrifugal force goes like this.

RCF (in g forces) = 1.119x10^-5 x rpm^2 x radius (in cm)

hmm... that rpm is going to be troublesome... oh, centimeters, too... Yeah, the units in this equation are going to kill me.

In any case the gravity will definately be sufficient to keep the atmosphere pinned into the 'bowl' at the equator.

Kamog, that is an excellent solution for the "gradient gravity of a sphereworld" problem. Note, however, that you would need huge, ringworld-style walls between the rotating sections or the atmosphere would all flow downhill. Note also that when the plane formed by that ring does not bisect the star's center of gravity the ring is not in a 'stable orbit' the way a ringworld or solid sphereworld are Though the outer sphere could just provide a mounting point for these various rings, which I think you suggested. Remember that they would, however, be subjected to a pull away from the sphere and toward the star, and the 'ground' would have to be inclined to compensate.

[ November 26, 2003, 18:27: Message edited by: Loser ]

Re: Thoughts about sphere worlds

Quote:

Originally posted by Omnicron1:
ecosystems are directly dependent on the one way flow of energy into them from the sun to support life...there are a few instances of life without sun near heat vents and such but still a one way flow of energy and the earths core would cool if it were too much farther from the sun....sooo i assumed that even the farthest planets in the game werent beyond jupiter and not beyond saturn at the most by this it would not be an accurate graphic but if the solar systems in the game, despite the fact that even the farthest planets can support life, can in fact encompass pluto's orbit im sorry about my rant about the inaccuracies of the graphic but i now have to rant about the inaccuracies of the star graphic which is now faaaaaaaaaarrrrrrr too large (1000s of times our suns own mass and volume and too large to support itself making it a blackhole or very near to it)so some graphic is wrong....

The heat of the earth's core is currently thought to come from heavy radioactive elements decaying. It's 'mostly' iron, but not all iron! This energy will probably Last many millions of years yet. Jupiter emits two and a half times as much energy as it receives from the sun. This is probably from the sheer pressure of its size causing a little bit of fusion -- just not enough for it to ignite as a star by itself. It could also be from heavy radioactive elements in its core as well. It is presumed to have a rocky core. Jupiter's moons are heated from the sheer tidal force of gravity as they orbit, and so it is thought that Europa could have liquid water oceans under its ice crust.

So you see, there are all sorts of sources of energy other than direct solar radiation and all life needs is a source of energy. We have seen right here on earth that sunlight is not the only way to operate a metabolism.

Quote:

Originally posted by Omnicron1:

narf poit made good point about centriFugal force (someone said Centripetal and thats the opposite) not being a good artificial gravity...but he said that jumping would bring you back to the outside but Narf you were right to begin with because the rule about matter continuing in the same speed and direction would be negated by the jump if you had enough strength to jump from the centrifugal force then you turned the speed and direction around and you would float away from the "ground" which points out that this type of artificial gravity would not support a thick enough atmosphere because air is not dense enough to be significantly affected by centrifugal force..try spinning a balloon around really fast and see if it follows the same course as say a balloon of water...soo if this were the method of gravity it would be more than 1G if you wanted to breathe...

nother importante questione!! if you can move all the matter in many solar systems to cover a star why not sift out all those resources on the way... i can see getting lots of radiactives(energy from sun) or organics (grow real well if they can handle the constant sun) but minerals c'mon you built the place for god's sake!!!!

Air is matter just like any other matter. Other than the different viscosity, what you are seeing with the balloons is the relative proportional difference of friction to weight. The air inside a balloon weights very little compared toa similar volume of water, so the friction of the surface it is sitting on, or even the air outside of it, will stop it much more quickly than the water balloon. There is no reason that air moving in the right direction would not be held by centrifugal force as well as water or solid material. The problem is that air will be heated by the sunlight/radiation hitting it and tend to get 'knocked' out into space. This happens to planets too, and earth would have far less atmosphere if it didn'thave a strong magnetosphere to help contain the atmosphere. Mars has almost completely lost its atmosphere, which may have been almost like earth's a billion or more years ago. As with all other technical problems in SciFi engineering, you'd have to imagine a new technology (super-magnets that Last for millions of years?) to keep the atmosphere in yours Ringworld.

Re: Thoughts about sphere worlds

I was about to come back and point out that the heat at the Earth's core was because of the manner in which the Earth formed (radioactive elements? Sure!) or the pressure it suffers under its own mass subject to its own gravity.

But I see that the Baron has already covered this.

Re: Thoughts about sphere worlds

infallibility is a bore and everyday is a learning experience but i still don't think centrifugal force could hold down an atmosphere as for all other statements granted i was wrong... but no one touched the statement about the economic ramifications of such a project...

if you could overcome all the inherent engineering problems with building a sphere world why when your moving this many solar systems worth of matter around this sun don't you sift out the important parts? I think the only thing you should be able to extract from ringworlds and sphereworlds are organics, population and energy which is everything but minerals i guess what im saying here is why on earth are you mining resources from something you built?! I think looking at the real cost of one of these things it'd be more efficient to build a huge close-formation satellite field around the star to gather its energy...If it ever gets built it will be more a monument of achievement (tower of Pisa or Lady Liberty) than a useful source of resources though it'd be great place to stick all those naggy scientist characters!!

military strategms of a sphere world... If you can somehow manage the intense heat of the star that a sphereworld would generate>>then when someone attacks you why dont you just aim that crap in their general direction....... more food for thought

also i want to give a hand to all the great minds assembled here i've taken 5 AP courses including AP Calculus and AP Chemistry and i could neer have carried on such engaging and fascinating conversations and everyone has good points...even when they prove me wrong!! http://forum.shrapnelgames.com/images/icons/tongue.gif

Re: Thoughts about sphere worlds

Quote:

Originally posted by Loser:
The gravity of a shell is not precieved by objects within the shell. For this reason, the gravity you experience will grow less and less as you penetrate deeper and deeper into a body such as the Earth.


Gravity applies inside a shell, but if you're inside, the shell's gravitation comes from all sides, so some of it cancels out some of the rest. It then depends on where you are within the shell, and whether the shell is of uniform density or not. A Dyson sphere's own gravity would be a major factor in its engineering.

Quote:

...From the outside, the shell will will be an immense amount of gravity. But if the outside surface is spinning, and it will be spinning much faster than the earth's orbital velocity, then at the equator one would be thrown off at around 1 G.


Naturally. If you design the spin so interior objects have a 1G acceleration towards the inside, then objects on the outside will fly off at 1G. On a ringworld, or the equator of a sphereworld with no scifi artificial gravity on the equator.

Quote:

In thruth it would be pretty damn hard to ladn on, you'd have to be on one wicked eliptic... though I could have the scale wrong.


Certainly it'd a much simpler problem than assembling the contraption in the first place.

Try flying through a docking port and landing on the inside.

Quote:

Additionally, no human would be able to run or jump fast enough agaisnt the spin of the world to escape it and start floating. I believe, in order to get the 1 G, you'd have to be cranking damn fast.


Try jumping off the Earth (no offense; I only suggest it because I'm sure you won't succeed) - it's exactly the same amount of difficulty - that's the point.

PvK

Re: Thoughts about sphere worlds

Quote:

Originally posted by Omnicron1:
...
about centriFugal force (someone said Centripetal and thats the opposite) not being a good artificial gravity...

See for example THIS page about "Centrifugal" vs. "Centripetal", which says, in part:

Quote:

For those who don't know, when you are in a rotating space colony, your feet exert a centrifugal force on the floor, whereas the floor exerts a centripetal force on your feet. Hence, artificial gravity as regards a force on your body is a centripetal force. They're equal and opposite forces of the same phenomenon. Your feet exert the centrifugal force onto the floor of a rotating space colony.



PvK

Re: Thoughts about sphere worlds

As for economic aspects, yes Omicron, I imagine, as I more or less said before, that if you can move the matter from many solar systems to one in order to build a Dyson sphere, and build it and get it to work, then I tend to think there would be many other more practical and/or interesting things you could have done with your time and energy. As you say, resource extraction is a much smaller task than the above.

PvK

Re: Thoughts about sphere worlds

i don't remember who wrote it.

Re: Thoughts about sphere worlds

Quote:

Originally posted by gregebowman:
but there's a series by David Brin that involves intelligent dolphins using space suits. I just can't remember the name of the series, however.

Check out "Startide Rising" about the dolpins. "SunDiver" had a scene of a human in a dolpin suit, but only swimming. IMHO one of the best current authors.

Check out Larry Nivien short story "Bigger than Worlds" in "A Hole in Space". It starts at a colony ship, then ends with covering over a galaxy and filling it with air. Then people just swim around (Maybe using those suits).