Ringworlds are cool and all, but Niven Ringworlds. Those are the size of solar systems. And THEY are 𝘤𝘰𝘰𝘭.
A Niven Ring is actually two megastructures, an internal ring of orbital shades to simulate a day-night cycle, and an outer ring for habitation. It would be 600 million miles across and a million miles tall. The earth is 7,917 miles in diameter, for scale.
It would be so big that signals sent from one side of the ring to the other would take about an hour and a half to send and receive.
@starwall It's unstable though, right?
@RexfordGTugwell That's one of MANY challenges in building one of these. Comparatively to literal dyson spheres or shield-worlds though, they are considerably more stable. A significant and constant effort would need to be made to keep the system in check.
@starwall how does atmosphere hold to the surface & how do they keep away all the radiation without a magnetosphere
@vegetablegremlin A magnetosphere can be produced artificially using large enough electromagnets. The atmosphere is held down because the ring is spinning fast enough to simulate 1G of centripetal force, and there are walls on either side of the ring. A person standing on the ring would feel near normal Earth gravity.
Contrary to O'Neil Cylinders, this would require structural technology that is beyond our capabilities today. Just keeping the ring in once piece, and not flying apart under the massive strain of its spinning so fast would be impossible for any known chemical materials we have today. Maybe in the future we might have something strong enough.
That's not even mentioning the fact that building one of these would take far more mass than the solar system has to offer. All of the planets and asteroids dismantled wouldn't be enough to build one, massive amounts of mass would need to be imported from other systems, or siphoned off of the parent star itself.
@starwall Niven didn't initially realize that, unlike a Dyson Sphere, a Ringworld's orbit would be unstable. One of his readers pointed it out IIRC. So for the second book he introduced thrusters.