Lets talk about Niven’s Ringworld

 

TL;DR. Before we can start understanding my Dyson sphere conjecture, we need to understand Nivin’s Ringworld. There are technical details provided for the ring, many of which make sense with today’s knowledge, others require materials that we could not explain today, and some minor details are left unexplained. But in the end, things like Dyson spheres and ringworlds are more about the enigma they represent to the protagonist than they are about the actual structure.

This is Part 2 of my series on Dyson spheres. Part 1 is here. 

Larry Nivin wrote a series of science fiction novels set in his Known Space setting. The ringworld was a giant, ancient structure with a habitable surface area about three million times that of the Earth. To put that in perspective, the Star Wars Visual Encyclopedia states that the Star Wars universe has a total of 3.2 million worlds. So, Nivin’s ringworld has a habitable area on the order of that of the Star Wars universe.

Image curtesy: Eric M. Jones, CC BY-SA 4.0, via Wikimedia Commons.

What is it? Pretty much what it says on the tin. The ringworld is a ring of an unobtainium material called scrith which encircles a star and by rotating at just the correct speed anyone standing on the inner surface of the ring will experience a centrifugal force about equal to earth’s gravity. This is a Sci Fi megastructure of the first order, but there are a number of technical details worth considering.

Orbital Instability. If perfectly balanced and in a featureless universe, the ringworld will spin around its star without a problem forever. Unfortunately, we are not in a featureless universe and eventually something will give the ring a little nudge. Once this happens, the gravitational attraction of the star will start to pull the ring inward, and the entire system will collapse. This issue is easily corrected by having a system of active thrusters which can provide small correcting forces to keep the ring in place.

Day and Night. Constant sunlight will heat the surface of the ring making it uninhabitable. To counter this, an inner ring is placed between the star and the ringworld with shadow squares blocking the sun and creating artificial night. The squares are wired together, presumably with scrith, and rotate in a way that creates Earth-like day and night.

Retaining Atmosphere. Any gases placed on the inner surface of the ring will fall off the edge and flow outward into space. This is prevented by building up walls taller than the atmosphere on either edge. The rim-walls on Nivin’s ringworld are 1,000 miles tall. The good news is that on Earth our atmosphere has the bulk of its mass within 11 kilometers of the surface. Unfortunately, traces of the atmosphere extend much higher than that so over time, the atmosphere would bleed off.

Atmospheric Inertia. Additionally, the air will feel inertial which should be realized as a strong wind blowing in the opposite direction of rotation. I’ll be honest here, I don’t recall how Niven delt with this, and I couldn’t find an answer. But, by the time you can build a ringworld, this should be easy enough to fix. Simply having thin baffles between the rim-walls would likely go a long ways, but I’ll leave the specifics as an exercise for interested readers.

Physical Properties of Scrith. It is only a math/physics problem to calculate the strength needed for the ringworld to not fly as it rotates. And someone has done this and the conclusion is that the hull-metal scrith would need to bind together with roughly the strength of the strong nuclear force. Of course, there is nothing known to us that can even begin to do this, so we simple except the existence of this material and get on with the story.

 

Role of the Ringworld

What is the point of Niven’s ringworld? In his stories it is an enigma. Characters discover its existence and are compelled to explore it and its mysteries. It is a physical manifestation that current human existence does not know all that can and will be. There are things out there that we have yet to learn. There are goals out there that we have yet to achieve.

I would argue that the existence of the ringworld allows us to imagine a protagonist who is in a world which is technically advanced relative to that of the reader, but which still has mysteries or enigmas.

In Star Maker (1937), Olaf Stapledon explores his view of the ever-increasing complexity of civilization and the nature of intelligence. I don’t agree with his conclusion, but man do I respect his presentation. Along the way, Stapledon introduces us to civilizations that can easily build things such as a ringworld. In Niven’s stories the ring is simply an enigma to be investigated. A place on which an adventure can unfold.

In my next installment on Dyson spheres, I will introduce my idea for a sphere. Like Niven’s ringworld, it will have strengths and weaknesses. But it will allow us to imagine stories—modern stories—that are centered around the nature of humanity and how much there is still left to learn.