# Creating a Matryoshka Shell world: temperature regulation

In a galaxy far far away, during a fit of inspiration for a super massive marvel of technology, the Imperator dedicates an astounding 10% of energy and materials from his civilization's dyson sphere and solar materials processing units to attempt an innovative (and possibly insane) plan to create a matryoshka world. By attempting a massive 3d printing of multiple world shells, the leader hopes to create many planetary shells within each other.

So the first problems appear, heat regulation.

If you don't want to bake the inner shells nor freeze the outer shell, how do you process heat (or a lack thereof) upward or downward between different shells?

Is this really as simple as putting a bunch of massive vents or would it require more than that?

Edit: To be more specific about what is Habitable for this civilization there should be no extended periods of heat above 40 degrees C nor below -5 degrees C.

Edit 2: Septerra Core is a good analog for the world I'm creating. It is a video game with a similar world. But it does not have a ton of information on how the heat is regulated within the world shells. In addition, the shells don't fully cover the other shells allowing light (and heat) to go into lower shells and heat to be radiated upwards. In this constructed world there would be no such gaps. Shell 1 receives all the light from the star and radiates all the heat from every other shell below. Assuming that's how that works (I don't do a lot of science).

Edit 3: This created planet is put in a convenient location near the star enough to get energy put into it and in orbit around the star. But to clarify, this question is primarily concerned with how to regulate waste heat production created from within the shells to keep the lower shells and upper shells in a habitable state.

Edit 4: I have dispensed with a majority of backstory to just get the question at hand answered.

https://en.wikipedia.org/wiki/Kardashev_scale

• Try watching this: youtube.com/… – Thucydides Nov 9 '18 at 23:28
• I watched almost all of this video and I'm entirely confused as to how it relates to my question. The video does go into waste heat but it deals with nothing about how to regulate the temperature so that different layers are habitable. Again, it's great for Matryoshka Brains but my question pertains to another megastructure. Could you go over the areas where this video that would help me with my question? I did go through and watch the series video on shell worlds which does mention worlds I'm talking about but it doesn't go very in depth. – GuidingOlive Nov 10 '18 at 0:06
• As many posters have suggested, the purpose of the Matryoshka Brain is to use the temperature differentials between each layer as a Carnot engine to power the next. In terms of temperature, essentially you pick an orbit and calculate the effective temperature of an object exposed to sunlight there (if the centre is a star like the Sun, then at 1AU, you have our temperature. The heat radiating from the layer below provides the heat energy to power the next level. Layers corresponding to Venus, Earth and Mars would likely be where a carbon based life would prefer to live. – Thucydides Nov 10 '18 at 0:28
• So if I'm getting you correctly use the center layer of this created world like a managed plasma ball then determine the distance to enter habitability for my civilization and the distance at the maximum end of that. And there's no need for additional regulation? What about the energy getting put into it from the star (let's say at a distance of 1 AU)? Would that affect the calculations? Having a central core plasma generator producing energy expanding out and the sun putting energy in? – GuidingOlive Nov 10 '18 at 0:53
• The solar radiation falling on the outer surface will affect how efficiently that layer can be used to radiate into space (the dark side will obviously be more efficient at radiating heat than the illuminated side). I'm not clear why you believe that using an artificial plasma ball will be more efficient than simply englobing the Sun with multiple shells, but if that is your plan, then the "brain" should be built near the orbit of Neptune to limit outside insolation. – Thucydides Nov 10 '18 at 1:15

You do want to freeze the outer shells and bake the inner shells. That is the entire point of a Matryoshka Brain. The entire point is to be able to create a multi-stage Carnot engine with a massive number of stages, and an incredibly high efficiency. This will implicitly call for hot inner shells and cold outer shells.

The one thing you don't do is put massive vents to let the heat out. If you do that, you aren't getting work out of your difference in heat. You pass all the heat through heat engines.

If you want to minimize this effect, keep the layers all in middle-range orbital distances. The sun produces a fixed amount of energy per second. If you have a larger inner radius, that energy is distributed wider, making it easier to manage the heating. Likewise, small outer radii help minimize cooling into space.

However, you'll have to look at how efficient you want to be. The efficiency of a Carnot engine, multi-stage or single-stage, is goverened by the ratio of the temperature of the cold sink to the heat sink. If your inner layer isn't really close to the sun (getting hot), it limits your maximum efficiency.

• This is an excellent answer for a Matryoshka Brain (en.wikipedia.org/wiki/Matrioshka_brain) as far as I can tell. However, my question isn't about Matryoshka Brains but rather Matryoshka Worlds or Habitats. It is about temperature regulation between different shells of a created world where people would live on the surface of each world shell. An analogue to this would be the Video Game Septerra Core where there are seven World Shells with continents passing over continents that are below them leading inward to the core. How would you suggest I clarify my question? – GuidingOlive Nov 8 '18 at 19:02
• Ahh. How much temerature differential can you accept from the first layer to the last? – Cort Ammon Nov 8 '18 at 19:07
• I will add that in, for common habitability of arachnids specifically spider like beings. Don't want to be too humanistic with this group. – GuidingOlive Nov 8 '18 at 19:12
• @GuidingOlive Septerra core already answers your question. The upper shells are a desert, the top being a polar desert, the second being a desert, and the bottom being a warm dark jungle with plants competing for the little light available and the heat coming from the lava on the core itself. – Trevor D Nov 8 '18 at 19:34

This has been said in some of the comments to the answers, but no one has stated it outright:

Why does a civilization capable of producing a Dyson Sphere require this boondoggle?

If it's a vanity project, because the Imperator wants to build one, sure, no problem. But the inner (or outer, depending on star type) surface of a Dyson sphere can be arranged to be at a distance from the star that makes it habitable. If it is so arranged, you have a surface area equivalent to five hundred and fifty million Earths.

Population pressure will not be a problem for at least 25 generations, assuming no population control. (Assuming doubling of population per generation, with one earth's worth of people to start.)

It's an impossibly vast space to fill... and, importantly, vs. the elaborate shell-game that is the proposed planet, they've already built one.

Gravity could potentially be a problem if you're living on the inside, or with certain kinds of star, but this could be overcome with sufficient engineering, provided your civilization has access to some remarkable materials (which they would have to have anyway).

• Why do they need it? As you said, they already built the Dyson sphere. What if they built it 25 or 26 generations ago. They've had all those generations of "We'll never use up all this space" to take away all interest on the part of the population to control their reproduction, so that might be why the government has had no luck on putting the brakes on overpopulation. They've filled their Dyson sphere and are still going. (Breeding like Energizer bunnies.) It reminds me of computer hard drives, when bigger ones came out and we all thought, I'll never need this much space--until we did. – Cadrac Nov 9 '18 at 15:05
• @Cadrac - If they've filled the surface area of 500M Earths, a seven layer planet won't do anything for their population problem. – jdunlop Nov 9 '18 at 15:59
• At this point it's becoming painfully obvious that I'm not going to get an answer on thermal regulation without fully changing the backstory. So how do we make this a better question to get an answer toward? Is this a Class I civilization? Why does it matter why they're creating this contraption? What do I need to reframe to get an answer that works toward the thermal regulation between layers of a matyroshka shell world? – GuidingOlive Nov 9 '18 at 16:57
• @GuidingOlive - Just make it a Culture level question. A civilization capable of harnessing all the energy from a star is not going to need this construct, so it has to be a "want". Eliminate all the context of "needing more living space", and you're fine. This civilization (or its supreme ruler, or their religion) wants to build an impractical shell-world. – jdunlop Nov 9 '18 at 19:27

The upper shells are a desert, the top being a polar desert, the second being a warmer windy desert, and the bottom being a warm dark jungle with plants competing for the little light available and the heat coming from the lava on the core itself. There is not much water on shell 7 but the moisture is high because water falling from the higher shells turns to mist and steam on the lower shells.

The plants have to give off their own light to attract insects to pollinate, making the bottom shell glow to people on shell 5 and 6. Shell 3 becomes a temperate zone, located high enough to get sun, but low enough to get extra water from the above 2 shells.

Shell 5 will likely have the most people, as they are able to mine the core rather easily for resources, collect water from upper shells easily, and still collect enough sunlight for farming.

Shell 3 will have less access to resources, but stronger farming. This means shell 4 will probably become a trade hub between shell 5 and 3.

You want to insulate the outside layer and let heat through to the inside layer.

The outside layer is going to have a temperature dominated by the cold of space, at something like -270C. It's really cold. Heat is going to constantly flow through it. You need to make sure that the energy from 1 star can pass through this layer at a rate which preserves the -5C minumum you mention. This will likely involve controlling the conductivity of the outside shell, and possibly even putting insulation on it.

You'll want to do similar for the inside layer. It is going to face the star all day, so it will get much hotter than our environment does today with its transitions between day and night. You'll probably also need to put insulation here, but we may approach that differently.

The real trick is to get the thermal resistance of the inner shells low. Think of it like 7 layers of copper sandwiched in styrofoam. No matter how you heat or chill the outside layers of the stryofoam, the 7 layers conduct heat quickyl from one to ther other, so they are all relatively similar in temperature.

I would choose to do this by erecting giant fresnel lenses over the inner layer which focus a large fraction of the light through relatively small holes in the the layer. If you covered 50% of the area this way, only 50% of the light would fall on the inner layer (the part that was not covered). The remaining light could go through holes, which would cause the inner layer to look like a giant constelation of stars, with each hole providing some of the sun's light to the next layer. This would let you rapidly move heat from one layer to another without wasting large amounts of surface area. It also means you can have natural light on the second and third layers, which is a nice perk.

• Now we're cooking. However this is still a little too star centric. Should I clarify more that this world isn't covering my dyson sphere? This is a world that is constructed on an orbit around the star that does not collide with any other major celestial body nor alter orbits significantly from any other world. Or would it be better suited being a world covering the dyson sphere? Granted the empire's homeworld would have to be migrated onto that world lest they all freeze in the absence of a star to heat them. – GuidingOlive Nov 8 '18 at 20:24
• Wait... you have a fully functioning Dyson sphere, and a mere planetary-sized world is going to relieve your population pressures? – Cort Ammon Nov 8 '18 at 20:28
• Several planetary-sized worlds, one inside the other but yes. Look, I'm not a scientist I'm a writer. This civilization has built a functioning dyson sphere (maybe it runs at like 1% efficiency) and is far from its next solar neighbor (in a manner like we are). Its population has been utilizing rotating habitats but a larger scale solution is needed. Currently it claims (and has reasonable claim over) its solar system. But its more band-aid then it is relief. – GuidingOlive Nov 8 '18 at 20:36
• I'd say the right answer is "the engineers put the additional habitation wherever it is convenient." It depends on their construction. But I would note that if you lived on 3 Earthlike worlds, and you had a dyson sphere that runs at 1% efficiency and you consume that 1% on the planets, that's $1.276\cdot10^{24} W$ of power to dissipate per planet. Currently the sun provides Earth $1.74\cdot10^{17} W$ of power. Your three planets each need to be sinking almost $10,000,000$ times more heat into space than the Earth does today! That's some incredible engineering capabilities. – Cort Ammon Nov 8 '18 at 20:41
• If you're a Kardashev Class II civlization, you're basically obliged to live distriuted across either a dyson sphere or similarly massive collection of structurse or across the galaxy, or you'll never dissiapate all that waste heat. It's just too much energy for a handful of planets. – Cort Ammon Nov 8 '18 at 20:42