Let’s Talk Dyson Spheres

 

 So once upon a time I wrote a story set on a Dyson sphere. It hasn’t been published yet, but it did win a contest. I’ll write more about that in another post, but before I can write about the role of Dyson spheres in stories, we need to talk a little bit about the spheres themselves.

There is a nice Wikipedia article on Dyson spheres that explains the basics better than I can, so if you’re not at least passingly familiar with them, I would recommend you start there. And you might want to also read up on the Kardashev scale of interstellar civilizations—you just need to know the types, we’re going to talk about what we think Type 3 civilizations can and cannot do. Or at least what stories we’re willing to tell about them.

Three Types of Dyson spheres

I would like you to recognize three kinds of fictional Dyson spheres. I’ve given them the cleaver names of Type 1 to Type 3.

Type 1 Dyson sphere. This is the sphere described in Dyson’s original 1960 Science paper. It is a thin structure with a total mass approximately equal to the mass of Jupiter. This thin structure completely encloses a star, capturing the majority of the stars radiated energy—letting escape only a characteristic electromagnetic signature. Dyson originally proposed that anyone using radio telescopes to search for intelligent life, should look for this signature.

Type 1 spheres can be expanded to include the Dyson swarm. This is when a vast number of thin panels are deployed in orbits around a star completely enclosing it and having the same effect as if it were a single solar panel.

Type 2 Dyson sphere. Here we leave proposed megastructures and the needs of radio astronomy and turn our thoughts to imagining extremely advanced civilizations. Freeman Dyson is said to have been inspired for his notion of the Type 1 Dyson sphere by Olaf Stapledon’s 1937 novel Star Maker.

In this story, our protagonist is afforded the opportunity to witness increasingly sophisticated civilizations. Spoilers, he goes from Kardashev 0 to well past Kardashev 3. Near the middle of this natural hierarchy of civilizations, two galaxies each achieve their own, near utopian Kardashev 3 civilizations. In one, the many species of intelligent life have developed the ability to create artificial planets. The artificial worlds are the idyllic homes to their many people. And they keep adding more and more artificial worlds orbiting their central stars until these worlds absorb all of its light. Basically, a Dyson swarm of inhabitable worlds.

In the story, the first galaxy takes such a star and bends its course such that it will act as a generation ship taking their emissaries to the other galaxy. That trip doesn’t go as expected, but I won’t spoil it for you.

Let’s call these a Type 2 Dyson sphere. It is not just a solar power collector beaming energy to its builder, it is a living place. Millions of artificial worlds, countless forms of life. It is a storyteller’s dream.

Type 3 Dyson sphere. In Star Trek: The Next Generation season 6, episode 4, Relics, our heroes encounter another type of Dyson sphere. This one has a flat interior surface on which people can live. Everywhere you stand, the sun is directly above you, and you have nearly endless habitable surfaces extending in all directions. By my calculation a sphere built at the same radius as the Earth to the sun (1 AU) would have around 550 million times the surface area of the Earth. It would be an unimaginably vast space.

The Gravity of the Situation. The problem with a Type 3 Dyson sphere is, of course, one of gravity. In undergraduate physics most people meet the Shell theorem, once more Wikipedia has a detailed explanation [https://en.wikipedia.org/wiki/Shell_theorem], but unfortunately, they get rather technical. In brief, it is an “undergraduate physics class exercise” level of difficulty to show that a hollow sphere of uniform density exerts no gravitational force on objects inside it. The mass of the shell that is near you exerts a strong force pulling you towards it, which is exactly canceled by the weaker force of the rest of the shell.

So, some hypothetical aliens could build such a shell, but they couldn’t walk around on the inside of it. Not in an Earth-like way. Certainly, no atmosphere would stick to it. It would just be a surface in space. This is fine for a Type 1 sphere, but a deal-breaker for a Type 3. Star Trek doesn’t have this problem since, from Day 1, they have always postulated some technology which artificially creates gravity. Just assume that technology is built on the outside of the shell. It then pulls everything down at 1 g. Everything works and they go on with their story.

Others think about Larry Niven’s Ringworld [https://en.wikipedia.org/wiki/Ringworld]. Here centrifugal force creates an artificial gravity. The ring is rotating at a speed such that anyone standing on it feels a downward force similar to that of gravitational attraction. If you spin a ring, everyone standing on it will have about the same artificial gravity. But if you spin a sphere, those on the equator will experience the maximum artificial gravity, and as you move towards the poles, this force will decrease.

Of course, none of these ideas talk about the material strengths needed to hold these things together—current science fiction gets a free pass on material science—we just don’t talk about that.

Why do we care? I assert there are strong social forces in the modern culture demanding that we stop imagining big or different or better. For example, Wikipedia tells us that Dyson spheres are often referred to as a “type of plot device known as a Big Dumb Object”. Note that “dumb” is a diminutive of “stupid”. People who use this phrase are not only saying that any discussion of the whole idea of things like Dyson spheres are not only stupid, but a special child-like stupid—it’s dumb.

I adamantly disagree that we stop imagining big or different or better. I am a scientist. I work in a field called bioinformatics. One of the largest problems I see in my discipline is the lack of imagination of so many of the people trying to work in the field. Problem solving requires imagination and conversation.

We all have limits to our knowledge. Instead of embracing encounters with this limit as exciting opportunities, some people build logical boxes—“No, this tool does that task and that task alone. You cannot use it in other ways.” In bioinformatics there is a whole community of researchers who view the field as being composed of tools which do a thing, and each tool does that thing unerringly. Their job, they think, is to put these things together in a chain, or pipeline, to solve the problem at hand. They don’t imagine that things might not be as they understand them. (And let me assure you, hardly any of the tools in bioinformatics work unerringly. Understanding what they do is critical to getting the right answer.)

One purpose of story is to let us imagine how things can be and not just how they currently are. We selectively ignore some problems in science fiction, but we attack others. We don’t worry about the required material strength of the Ringworld but it is essential that it has a known mechanism for creating gravity. But these attacks are kind of silly, they frequently reflect the rigid mental roadblocks of the attackers, which they use as bulwarks against the limits of their own understanding.

Moving forward. It is no secret that I wrote a novel set in a Type 3 Dyson sphere of my own design. The purpose of this post is to set the groundwork for me to write the next post in which I will present a conjecture that there may be a solution to the issue of gravity on the inner surface of such a Dyson sphere. I whether or not my conjecture turns out to be correct, it doesn’t really matter. Instead, I want the readers to suspend disbelief and focus on the other science that we do know to be observable and think about its implications.

I thought I should review some basics of ringworlds before jumping into my Dyson sphere. My ringworld post is here.