GURPS Ringworld 1,000,000 AD

[DoctorRomulus]

I used an Alderson Disc as the basis for a fantasy world I put together years ago. But thus far I’ve only exploited an area about .001% of it.

[Tom Kalbfus]

Originally Posted by Fnord-Fnairlane

The required tensile strength of a proposed "ringworld material" is roughly equal to that of the strong nuclear force.

Last time: you cannot build a ringworld out of baryonic matter in the standard solid matter phase. It is many, many orders of magnitude too weak.

Something like stabilised single-molecule neutronium is roughly what you need to build a ringworld. Making the baseplate thicker simply makes the problem worse.

Your not listening. If you pile enough baryonic matter in the outer nonrotating ring, you will achieve sufficient inward force to counter the outer centrifugal force of the middle ring and thus hold it in place. I don't know how much matter this will require. The outside limit will be to have it such that the outer ring weight under Solar Gravity equals the mass of the middle ring, this assumes that the outer ring has no tensile strength at all, it could be a pile of loose rubble on a tray for instance! I do think the outer ring will have some tensile strength, especially if it is made out of carbon nanotubes.

[Tom Kalbfus]

Originally Posted by DoctorRomulus

I used an Alderson Disc as the basis for a fantasy world I put together years ago. But thus far I’ve only exploited an area about .001% of it.

Precisely what is an Alderson Disc?

[DoctorRomulus]

Originally Posted by Tom Kalbfus

Precisely what is an Alderson Disc?

Basically it's a megastructure that resembles a huge LP record or cd-disc with a sun in it's center. My disc has radius of about 500,000,000 miles and is about 5000 miles thick but honeycombed so as to give it an "underworld".

[Tom Kalbfus]

Originally Posted by DoctorRomulus

Basically it's a megastructure that resembles a huge LP record or cd-disc with a sun in it's center. My disc has radius of about 500,000,000 miles and is about 5000 miles thick but honeycombed so as to give it an "underworld".

Does it rotate? If it does, you have sort of a problem as the disk becomes a verticle wall. If it doesn't then the Sun's gravity pulls you toward it. How does the thing hold onto an atmosphere?

[DoctorRomulus]

Originally Posted by Tom Kalbfus

Does it rotate? If it does, you have sort of a problem as the disk becomes a verticle wall. If it doesn't then the Sun's gravity pulls you toward it. How does the thing hold onto an atmosphere?

It does rotate and it's inner wall is where Mercury whould be in our universe while it's outer edge is where the asteroids would be in ours. The outer edge has a perimeter wall on it which helps keep the atmospher in that and the surface gravity of the disc itself. Floating between the "sun" and the inner wall is a series of panels which cast a shadow across the disc giving it a day and a night as they rotate around the "sun"

[Tom Kalbfus]

Originally Posted by DoctorRomulus

It does rotate and it's inner wall is where Mercury whould be in our universe while it's outer edge is where the asteroids would be in ours. The outer edge has a perimeter wall on it which helps keep the atmospher in that and the surface gravity of the disc itself. Floating between the "sun" and the inner wall is a series of panels which cast a shadow across the disc giving it a day and a night as they rotate around the "sun"

Rotating a disk won't hold someone to the disk, he'll slide along it until he hits a wall. Also if it rotates like a record, the pull of force would be proportional to the distance from the Sun. Only at the vary edge of the disk would the gravity be anywhere near 1 G, that is unless the disk is so thick and massive that it possesses its own gravity. A ringworld is easier to envision, its surface is beneath your feet rather than a giant wall that ascends vertically toward the Sun.

Actually the Ringworld has walls to hold in its atmosphere, they don't stretch all the way to Mercury's orbit, but I suppose they could, most of that height would be unnecessary for holding in the atmosphere though.

On the other hand, if the disk stretches almost all the way to the sun, it could serve as an anchor for the ringworld. 500 million miles is too great a distance however, you'd want it going only to 93 million miles if you want something living on the ringworld's surface.

[DoctorRomulus]

Well it does have it's own gravity and the world is about 5000 miles thick.
And as for the area I wanted to be able to have all kinds of environments on it's surface. The thing however does exist in a quasi-magical pocket universe where you might say there are a few "extra" laws of physics which allow for such a structure anyway.

Originally Posted by Tom Kalbfus

Rotating a disk won't hold someone to the disk, he'll slide along it until he hits a wall. Also if it rotates like a record, the pull of force would be proportional to the distance from the Sun. Only at the vary edge of the disk would the gravity be anywhere near 1 G, that is unless the disk is so thick and massive that it possesses its own gravity. A ringworld is easier to envision, its surface is beneath your feet rather than a giant wall that ascends vertically toward the Sun.

Actually the Ringworld has walls to hold in its atmosphere, they don't stretch all the way to Mercury's orbit, but I suppose they could, most of that height would be unnecessary for holding in the atmosphere though.

On the other hand, if the disk stretches almost all the way to the sun, it could serve as an anchor for the ringworld. 500 million miles is too great a distance however, you'd want it going only to 93 million miles if you want something living on the ringworld's surface.

[CraigR]

Originally Posted by Tom Kalbfus

Your not listening. If you pile enough baryonic matter in the outer nonrotating ring, you will achieve sufficient inward force to counter the outer centrifugal force of the middle ring and thus hold it in place. I don't know how much matter this will require.

It would, by definition, have to be enough mass to balance against the middle ring's mass + outward spin, using the star's distance-diminished gravity well to supply the weight. This mass, tens of thousands of miles thick, would far exceed the mass of the sun. The weight pressing down would have one of two effects:
(1) It would either collapse in on itself, as in a neutron star (unlikely as the pressure would be released perpendicular to the plane of the ring), OR
(2) a nuclear fusion reaction would result, cooking the inner ring and tearing itself apart as the whole mess becomes a group of new stars, possibly falling in to the center star.

Piling on baryonic matter will not work. Jupiter's size only works because it is just 1/6 the density of Earth. It's a big gas bubble, held spherical by gravity.

[Tom Kalbfus]

I just got the GURPS Ice Age Download. I think I'll make it the default setting for the Ringworld. Basically everything that's true in the Ice Age book applies to the surface of the Ringworld. That is the rule.

What happened is that the ringworld "banestormed"/Downloaded/replicated some Ice Age creatures, Cro-Magnons, Neanderthals, and Archaic Homo Sapiens onto the Ringworld's surface along with all sorts of attendant animals belonging to the Pleistocene epoc, most of the ringworld floor is covered with that.

75% of everything on the ringworld is this TL0 Pleistocene.
(About 2,250,000 Earths worth of Ice Age Creatures)

18.75% of the ringworld inhabitants are at TL1
(about 562,500 Earths worth of bronze age civilizations

4.69% are at TL2
(140,625 Earths worth of Iron Age civilizations)

1.17% are at TL3
(35,156 Earths worth of middle age kingdoms)

0.293% are at TL4
(8,789 Earths worth of Gunpower age nations)

0.0732% are at TL5
(2,197 Earths worth of Industrial Age societies)

0.0549% are at TL6
(1,648 Earths worth of Automobile age societies)

0.0412% are at TL7
(1,235 Earth's worth of nuclear age civilizations)

0.0309% are at TL8
(927 Earths worth of information age civilizations

0.0232% are at TL9
(695 Earths worth of fusion age civilizations)

And that's it, everything more advanced is an artifact from the Type 2 civilization
One Earth is at TL 6

Another is at TL 7

And a third is at TL 8