What "problem" do theoretical megastructures "solve"?

By “megastructure” I’m referring to any number of theoretical man made habitats common in science fiction and speculative science. Usually in scales of hundreds, thousands or even millions of miles. These may include (but not limited to):

Bernal spheres (tiny by comparison, at only a few miles across)
O’Neil cylanders
Halos (small ring world orbiting a planet instead of having a star at the center)
Globus Cassus (hollowing out the Earth into a shell the diameter of Saturn)
Ring worlds
Disk worlds
Dyson spheres (encasing a star with a giant sphere)
Matrioshka brains (bunch of Dysons spheres inside each other, acting like a giant computer calculating the question to life, the universe & everything)
So my question is, what problems do any of these giant structures “solve”?

Environmental? Most of them require literally tearing planets apart and reconstructing them into new shapes. Not great for the environment.

Sure, a Dyson sphere can capture all the energy from a star. And you’ll probably need every Gigawatt of it to construct a sphere the radius of the solar system.

So other than as interesting set pieces for science fiction stories, what good are these things?

Well, the alleged ability to capture all of a star’s energy aside, such worlds would lack basic resources, require an amazing level of ability to move and reshape matter and a more permanent ability to defend it from outside threats such as asteroids and comets.

Oh sure, allegedly you remove all of those, strip the Oort cloud for your materials, but things move, stars move, there’s a lot of stuff floating around between stars and eventually you’re still going to have random shit striking it from outside your host star’s area.

And as was worked out with the Ringworld, eventually all of your terrain would wear down by weather to flatness and swamps.

So I guess the only two I can think of are “more space for population” and “collecting more solar energy”. Given the horrendous energy required to build it in the first place, I can’t see it being cost effective.

It should be noted that the origianal Dyson ‘shell’ (and the “gauze of light traps” from Olaf Stapledon’s Star Maker which preceded it) were a large mass of individual habitats or solar collectors rather than a unified megastructure. These make sense from the standpoint of maximizing the collection of energy from a central star and providing a distributed habitat for a civilization to occupy. A large megastructure such as Niven’s Ringworld has obvious disadvantages such as indefensibility, the potential for a single system failure or instability to have catastrophic consequences, et cetera. A Matryoshka ‘brain’ has the additional advantage of being able to moderate energy gradients (as opposed to the Ringworld whose ‘scrith’ material resists all electromagnetic radiation, and would require some heat exhaust mechanism to prevent excessive heat accumulation) and could be used to power a giant computational network, but again suffers from being a delicate and indefensible structure if you are concerned about other alien species attacking (as the xenophobic Pak certainly would be).

The benefit of smaller habitats such as Bernal spheres and the like is that they maximize habitable surface area per unit mass and provide a relatively defensible and/or mobile place to house a population. They also don’t suffer from the many problems and inherent instabilities of planets, including direct exposure to solar and cosmic radiation, meterorites, uncontrolled weather events due to energy gradients and Coriolis forces, and seismic activity. Such habs can be carefully moderated and the destruction of one or a few from natural hazards or attack is essentially inconsequential in the overall scheme of things. Such habs could potentially even be used as an interstellaral vessel with enough additional resources and an external power source.


Any moreso than on Earth?

Presumably, if you have that level of teraforming tech in the first place, you could just “remodel” the surface every couple millenia like you’re renovating kitchen cabinets.

That’s what I was thinking. But is it better to just terriform a bunch of shitty planets into habitible ones instead of creating one giant megastructure?

Imagine living on a Ringworld (or Diskworld or Dyson Sphere) the size of Earth’s orbit. A city on the opposite side is still a 240 million mile flight or train ride away. Even traveling at Earth’s escape velocity (25,000 mph), it would still take a year to get there along the surface.

Plate tectonics.

Yes. Here, new “earth” is arising all the time, coming up from the core. On the ringworld, eventually all the topsoil would erode, leaving bare scrith.

A ringworld would be a good solution to a population problem, but I can’t see it being built in reality. If you “built” it conventionally, it would take the lifetime of the universe (well, a bit of exaggeration) to complete. Even if it was built totally by autonomous machines being fed pure raw material, it would still take centuries to build. And that’s just the bare structure, with no details.

If you have the power to generate the raw material, move it around, cannibalize planets, and build the thing, and fill it with an atmosphere, you don’t need to build one, because you’re not in that desperate a situation yet. By the time a civilization go to the poiint it needed one, it probably is too late to actually build it.

Plus, economically speaking, it would take so much power and so much material that whatever catastrophe caused you to think a ringworld was the only solution could most likely have been solved using that power in other means. Overpopulation? Just make smaller orbiting habitats. Or move to other planets. or practice birth control. or have a war.

The only way I could imagine a species building a ringworld was hubris. It sure would be cool to have.

As Stranger pointed out, this isn’t going to be a gigantic ball-world simulating surface. A Dyson Sphere is just a system of collecting all the energy a sun creates. This doesn’t mean a thin hard shell with continents and houses on the inside. It means some insane amount of wispy solar panels enclosing the star, the energy output of which is used for some unfathomable purpose, and the creators of the shell live in whatever habitats they see fit. A ball-world with the atmosphere exposed to space is pretty vulnerable to all sorts of mishaps, so the shell builders live in space habitats of all sorts, and if a couple million of them get destroyed in some disaster they just rebuild and move on.

The “problem” is that a solar system only contains so much matter, and a sun only produces so much energy. So a civilization will have to live within those limits, and no farther. Or they run into fundamental limits earlier than that. Since we don’t detect millions upon millions of star-mass objects radiating in the infra-red, it seems pretty likely that if there are any alien Dyson shells out there they aren’t that common. They can’t be dark matter, since they’d be baryonic MACHOS and now we think dark matter has to be non-baryonic WIMPS.

So, a civilization progresses and starts using the resources of their home planet and eventually uses all resources on their planet, expands off their planet and starts using the resources in their solar system, and eventually uses all resources in their solar system. The end result of “using all resources in their solar system” is something like a Dyson shell or swarm. It isn’t going to be a solid sphere, because that wouldn’t actually work. At any rate, at the scales we’re talking about there’s no such thing as “solids”. Even on just a planetary scale planets aren’t solid, that’s why they’re spherical.

As I recall, the Pak built the Ringworld to shield their breeder population from the radiation effects of the galactic core explosion (implosion?). The Ringworld was oriented so that the line of sight to the galactic core was blocked by the impermeable scrith floor. Very long-term planning.

How can you have a non-solid, “swarm” Dyson sphere? If it isn’t solid, then the individual parts must be orbiting the star, yes? But then objects above or below the Dyson sphere’s equator would be on inclined orbits that cross each other. It’d just be non-stop Kessler syndrome. I suppose you could have different inclinations at different distances, and a lot of really accurate station-keeping, but it just seems prone to a lot of very high-speed collisions to me.

I feel like the smaller habitats (Bernel spheres, Taurus rings, etc) serve an actual purpose in the event there is an economic need to have tens of thousands of humans (or whoever) permentently in space for long periods of time. They also don’t require grinding up every planet in the solar system into unobtanium or maguffinite.

I don’t buy into the “we need to colonize other planets / build space habbitats to save the human race”. Most problems where the solution requires putting thousands of people on another planet can be solved by just building whatever you were going to put them in, right here on Earth. Only more cheaply.

a) Isn’t another term for “galactic core implosion” “supermassive black hole at the center of every galaxy”?

b) Is that sort of radiation explosion/implosion even a thing?

c) It’s a Ringworld, not a Diskworld. So shouldn’t one side be facing the galactic core at any given time?

You have a varied list there, so the answer is they solve different problems. Some are for energy collection, some could be used to solve an issue with habitation or with orbital insertion and some (the last one) is for a large digitized collective if I’m recalling correctly. Some would be stepping stones to colonizing the solar system and exploitation of its resources, perhaps ensuring all our eggs aren’t in the same basket, perhaps getting us ready for the next step as a multi-system race. To move up on the Kardashev scale we’d inevitably have to do some of them in some fashion.

While many are going to hate this, I’m going to link some videos from this channel that discuss a lot of these. This is the main link to IA’s megastructures series. It’s a lot, and these are relatively long videos, but he discusses exactly what you are asking, and if you can get past his speech impediment it’s really good stuff, IMHO and FWIW and all that.

One thing you could do is create a bunch of mega-structure habitats to transplant eco systems and species to. Or, this could allow (along with stuff like Arcologies) vast amounts of the Earth to be allowed to go back to it’s (changed) natural state or at least to allow for a lot more room for whatever species are left or we recreate. Also, they don’t have to tear up THIS planet…most of the things on your list there would only require us to harvest and exploit things like asteroids and other debris. Sure, you could use some of the planets (say Mercury) for material to build bigger, or go really out there and lift material directly from the sun or the large gas giants, but you wouldn’t necessarily have to do that and certainly wouldn’t initially.

Watch the video on Dyson Spheres, but others have answered this…you don’t really need to create a perfect sphere around the sun to take advantage (i.e. something like the Dyson Swarm already mentioned).

Yes, you first have a ring of objects all co-orbiting in the same orbit. Then you add another ring at a different inclination and distance, then another and another. Yes, this means station keeping.

But you can’t have a “solid” sphere either, because the forces the “solid” sphere will be subjected to are many orders of magnitude greater than the forces holding steel beams or carbon fiber or diamond together. At least in Niven’s Known Space they already had a dozen or so types of unobtanium so it’s not a stretch to add in another flavor to build the Ringworld out of.

The only plausible continuos structure would be an extremely thin membrane that isn’t orbiting the sun but is held up by light pressure. How you make a solar collector out of such a material is left as an exercise for the reader.

Their lifespan is far longer than a planet revolving around a sun. A manmade megastructure can last for endless trillions of years.

Isaac Arthur speculates that manmade spheres around a black hole can keep human civilization around for 10^100 years. In our solar system, our planet will become uninhabitale in 10^10 years.

For a planet to be habitable would require a combination of different parameters (proximity from star, axial tilt not too extreme, gravity within a certain range, atmospheric composition, large mass of surface water, liquid core, stable biosphere, et cetera) that are difficult to achieve. And planets are not stable over the long term (millions of years); the climate, seismology, and external hazards could too easily cause a hundred thousand year project reforming the surface and atmosphere of a planet to habitability to revert to an inhabitable state. (Indeed, there is a school of thought within xenobiology that if extraterrestrial life is common it likely arises on moons of jovian planets with liquid subsurface oceans that are well protected from solar and cosmic radiation, and are not sensitive to variable output of their central star or stars.)

But the real reason to build habs is to better utilize resources. Earth-like planets are particularly wasteful in terms of both energy and materials. Of the vast wealth of iron, copper, nickel, platinum, gold, and other precious materials, not to mention natural fissile isotopes, we can only access those in a very shallow layer of the crust; the rest provide essentially no benefit other than mass to produce surface gravity. ‘Dismantling’ the Earth in some hypothetical fashion gives complete access to the mantle and core materials.

I’m not sure why that is a problem, or indeed, why you would limit travel to Earth escape speed. Niven’s Ringworld has a surface area of 1.6 x 10[SUP]15[/SUP] km[SUP]2[/SUP], or about the equivalent of three million Earths. It is large enough to support thousands of conventional terrestrial civilizations that could be sufficiently dispersed to never have physical contact. But every part of the structure is within at most seventeen light-minutes away by radio or laser. (Longer, I suppose, if you are communicating using ‘land’ lines, but still not more than half an hour.) If you are looking for space to house a population in a terrestrial environment and have the technomagical capability to produce materials with unrealistically high tensile strength, it makes sense from a optimum material utilization standpoint. Of course, such a structure is pretty much completely indefensible (solar plasma lasers aside) and subject to any number of instabilities. One of the hypotheses about the Ringworld origin is that it was specifically designed to leave the galaxy and travel, taking its star with it, to escape the coming explosion in the galactic core.

However, there is a larger issue than just security or stability in the concept. A spacefaring species with a command of physics to construct such a megastructure would likely also have the knowledge and means to convert their physical form to something more robust to the space environment, obviating the need for giant habitats and the wasteful resources to keep an organic body alive and functional. Why waste energy and material resources making a delicate habitate when they could be better put to collecting and storing energy directly, and maximize the processing and storage capability of information? Terraforming planets, constructing habitats, and so forth makes little sense in the grand scheme of civilization if the goal is to propagate knowledge and ensure the survival of future sapience. Outside of a nostalgia for the organic form (and it is indeed inconvenient and even embarrassing in countless ways) there is no particular reason not to evolve away from a delicate biochemical organism which requires a delicate balance of environmental conditions and nutrients to remain functional. Even if converting the human brain and central nervous system to computational hardware is not feasible (and there are good neurophysiological reasons to believe this might be so) at least getting rid of external dependencies on atmosphere and nutrients for respiration and metabolism would make ‘humans’ far more robust and reduce requirements for habitation, and is not nearly as technologically demanding as building giant habitable rings around a star or planet.


In the case of “Ringworld” in particular, Niven decided the builders had to be his already introduced Pak to answer some of the objections you raised. They have a biological imperative to protect their breeder stage, which means they can’t mutate them into spacefaring form, because then they wouldn’t smell right. Of course this is all working backwards from “Ringworld exists” premise, and then authorwanking reasons it could exist.

Well no, it would eventually erode down to the average depth of the soil/rock placed on top of the scrith.

Although even that probably isn’t technically correct, because you’d have losses due to changes in form (solid soil to food to some portion gas, etc) and gains due to infall of dust.

And if there were two different cultures capable of this sort of megaforming and they went to war, they’d both be more than familiar with moving planetary masses around, which makes both sides vulnerable.

You need four immense, immortal elephants and an even larger turtle for that.

The Ringworld was edge-on to the core. Assuming the radiation is emanating from a point source (or close enough to one given the distance) the side facing the core is shielded by the side nearer the core.

Whether or not such radiation is really a thing, it is necessary to explain a number of occurrences in Known Space.

One thing I see is that you could do it in smaller increments. The megastructures don’t have to be complete. Making an entire planet habitable is a larger undertaking.

The other is that you could just make things be exactly what you need, and not have all that waste material. Most of the planet is not useful to humans for any purpose. There’s all that material below us that isn’t doing anything. Or, at least, if it is doing something, we could do it more efficiently.

It’s just like with how “natural” medicine is less efficient than when we isolate compounds and even modify them to be more like what we want. When we have complete control, we can make sure all of it is going towards our purpose.

I love Niven’s stories, and I’m always drawn to and fascinated by the Pak, even though I have to suspend quite a bit of disbelief.

Ringworld is especially a problem. I happen to be re-reading just now. I don’t think he was thinking of Pak when he first wrote it, but with hominids aboard, it’s hard to come to any other conclusion. I just can’t get past this problem with them as the Ringworld engineers. By reports, the Pak were essentially restricted to a planet near the core and local environs, as described in ‘Protector’, managing to launch one colonization effort to the spiral arm (us) and one rescue effort (plus follow-on invasion fleets, again implying that "our’ colony was the one sure bet they knew about). No FTL.

And suddenly, a giant engineering project is found out in our neck of the woods? And while they were at it, they mapped out the worlds of ‘Known Space’ and built replicas in their Great Ocean, even going so far as to populate the maps with indigenous fauna (some of which would be quite dangerous to breeders)? If they were so thick and busy in ‘Known Space’ and they had breeders along, why isn’t every habitable world filled with Pak (or at least evolved Pak breeders?

So I suspend my disbelief…