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Or, technically, a civilization near the core of a planet.

In this question I will describe some aspect of my design, and you may comment on the realism of these aspects and add improvements, or point out something I am not aware of.

The Planet

The planet will be a rocky planet, possibly tidally locked to its star so as to reduce the effect of rotation on the world within.

I am not sure what effect a major satellite would have on a civilization inside a planet, so there will be none for now.

The planet will either be too small or too old to have volcanic activities, and the layers above the level of the civilization will be solid. This also means the planet probably don't have a strong magnetic field, but this would seem trivial to a civilization living under many kilometers of rock. The core, however, is still hot enough to emit light and heat.

And just so you know, the world built here is supposed to be a bleak, end-of-time sort of place, so the "star" about which the planet revolves is probably a black-hole or something dark and useless like that.

The architecture of the civilization

This is where things get a bit crazy. See diagram below (not to scale): pictures are worth a thousand words...this question is getting long I hope the diagram is sufficiently self-explanatory. That being said, a few significant note with this design:

  1. The support structure must be made from something that has a melting point higher than the temperature of the core's surface
  2. Either the core is quite solid, so as to be able to handle the weight of the supports, or that the rocky crust is quite solid, and the support structure can anchor itself securely on the inner surface of the crust without putting too much weight on the core
  3. The idea here is that the civilization derives its power from the light and heat coming out of the core, this means that the support probably wouldn't enclose the core completely, unless it is transparent (to permit the output of light).
  4. There must be some way that the excess heat is disposed of. My idea so far is that the universe itself has gotten quite cold at this point, so the conduction of heat into the crust and its later radiation into space should suffice.

Life in this world

The social aspect of this world is trivial at this point, however, life on the "residential area" would have the following major features:

  • Gravity will be like the gravity felt around a planet the size of the core, since inside a even hollowed sphere, the spherical shell's own gravity is balanced out at every point. Also, because the planet is designed to be tidally locked, the effect of centrifugal force, or the illusion of it, will be quite small, I hope.
  • If the core is bright enough to shine like a sun, sunlight will seem to shine from beneath the floor.
  • Major building project will be difficult, because a lack of raw material (it will probably be a bad idea to excavate the rock from the crust, but what do I know?)

That concludes my design so far. At this point, I don't see any major problem beside some numbers' game balancing the melting point of the support and the temperature of the core, but if you see any, or have improvements for the design, I would really like to hear.

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    $\begingroup$ Thanks to shell theorem your supports does not need to be that strong. And I advise having only 4 of them. Sadly, this is far from a full answer. $\endgroup$ – Mołot Dec 19 '16 at 19:16
  • $\begingroup$ This sounds like a low-mass planet like Mars or possibly smaller. If was a Moon-mass body the chances of constructing a core habitat might be better. This does mean a low-gravity environment for its inhabitants. $\endgroup$ – a4android Dec 20 '16 at 7:46
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No, it is not.

The crust of a planet gets pretty massive shake ups as the tectonic plates move. Even on a planet with relatively stable plates you're still going to experience a LOT of forces at those depths. The pressure and heat you're subjected to also grow exponentially as you descent towards the core.

Humanity has not been able to descent much further down than a kilometer or so, before the technical complications, and instability of the tunnels simply become too dangerous and/or expensive to overcome.

For you to dig down to tens of kilometers, isolate the molten core of a planet, and build a scaffold to hold the rest of the bulk of the planet up around you is simply preposterous.

If you are able to go to this length of effort simply to "keep warm", you're better off simply building a dyson sphere around your Sun, and siphoning off it's energy to heat your atmosphere.

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  • $\begingroup$ Well-informed answer, but here are a few objections: 1 I am not sure how much tectonic movement there will be if there are not molten magma moving underneath the plates. In fact, I wouldn't call it plates if they were parts of a solid body of rock. 2 What humanity can do today is not that important to the question, even if it's difficult to create such a structure, some hand-wave will do. 3 stars may have shorten lifespans then geothermic cores, also, there may not be suitable stars near by. $\endgroup$ – Luna Dec 19 '16 at 22:34
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    $\begingroup$ Also, you mentioned complications in digging deep on Earth, can you specify what these complications are? And just so we don't go too far off topic, the question focuses on the maintenance of the proposed structure, not its creation or the intentions behind its design $\endgroup$ – Luna Dec 19 '16 at 22:40
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A major problem with your concept is thermodynamic.

If the core of the world is hot enough to glow it is going to be pretty hot.

At least >525 °C and for reference the earth's core is 3,000 - 5,400 °C, so yes it would glow.

However, the problem is that the rock layer above the hot core is going to be only slightly cooler than the core. The temperature profile would follow a gradient from hottest at the core to the lowest at surface radiating heat into space, the heat has no where else to go but up. So your Rocky crust would be just as hot as the core (and would also glow) making your habitable region between the 2 regions nearly the same temperature, which isn't very habitable.

A mega structure level refrigeration system in place to move heat out of the region above the core to the surface could possibly fix this, but it would be pretty huge and require an amazing level of technical ability. At this level of engineering you're basically replacing your planet with an artificial structure. Your civilization would likely be better off and it would be easier to just build the artificial structure (A Dyson sphere).

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