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Billions of years ago, an extremely advanced civilization created an artificial world. Whether it is a ringworld, a shellworld, or something more isn't really relevant. This world's crust has a depth of a couple kilometers, but it does not have any resources other than soil and stone in it.

The original civilization moved its possessions to the world: houses, cars, ships, weapons, etc.

Due to the nature of this world, resource extraction is impossible (unless the resource is biological in origin). Mining is basically impossible.

Would it be possible for civilizations to recycle those materials for billions of years after the disappearance of the original civilization? Or would said materials disintegrate into nothing over time? How would an economy in this recycling world function?

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  • $\begingroup$ There has never been a civilization on Earth to last more than about 3,000 years (and that upper bound has been reached only once). There has never been a civilization on Earth which survived only on recycling. The point being that nobody has the faintest idea about how to imagine a civilization lasting billions of years, or how to structure a society to survive only on recycling. $\endgroup$ – AlexP Jun 1 at 19:58
  • $\begingroup$ See en.wikipedia.org/wiki/Biomining. It demonstrates that there are methods to re-concentrate even highly dispersed elements and molecules in a fashion that they become usable raw materials again. It may be highly inefficient but, given no other option, it's not impossible to do. $\endgroup$ – GrumpyYoungMan Jun 1 at 22:22
  • $\begingroup$ you will have huge swaths of empty hull exposed as erosion moves soil down hill. $\endgroup$ – John Jun 1 at 23:01
  • $\begingroup$ The elements are still there, but it'll take effort to concentrate them. Is it worth it, for the civilisation in your story? It'll naturally concentrate over time by the action of wind and water, eventually to mining-feasible levels. $\endgroup$ – Anon Jun 2 at 7:22
  • $\begingroup$ It's no different from mining qn asteroid, if it cintains the stuff u like u mine if it is not then not, why the question, matter does not disentegrate on thosetime scales, the planet u are on is the proof, soo why the question $\endgroup$ – MolbOrg Jun 2 at 11:56
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As already stated by Empedocles

For it is impossible for anything to come to be from what is not, and it cannot be brought about or heard of that what is should be utterly destroyed

If a material can be recycled or not depends on the material. Metals and glass are already widely recycled in our world (iron scrap is routinely added to the smelting load, aluminum is actually cheaper to recycle than to purify from alumina and so on) without any degradation in their performance.

Recycled plastic, on the other hand, tend to show poorer mechanical behavior. However to recycle certain materials mined materials might still be necessary. Take iron: to reduce the iron oxide into iron, coke has the advantage of providing both the energy and the reducing environment. Doing without it possible but not necessarily as convenient.

Some materials are harder if not impossible to recycle: take ceramic or concrete, for example: they can be reused for some other scope, but not for their original one.

And don't forget that, in order to recycle, you still need an energy source capable of providing the needed energy.

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  • $\begingroup$ To recycle plastic one can always burn it, capture the CO2, synthesize artificial petroleum and use it as a feed stock... And no need to recycle ceramics -- the question says they have "rocks". $\endgroup$ – AlexP Jun 1 at 20:03
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Entropy always wins.

No recycling is 100% efficient. That tiny sacrifice to entropy with each iteration will gradually eat away at your starting materials. The % loss of material with each recycle iteration will determine how long you can keep it working for any given material.

What opposes entropy (on a local level; yes just on a local level) is biology. In an ancient world without raw materials, what could keep going is the circle of life. People get by well with just animal and plant materials. Many millions of years later I think that is how things would be.

For keeping the life cycle going over this sort of time frame on an artificial world, you would need to make sure though that there was not some secret dead end for a vital nutrient - for example over the millenia all of the calcium or all of the sulfur is gradually accumulating in sediments at the bottom of the ocean, and the plants are gradually weaker for the lack of what they need.

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Intelligent creators

In order to build this place, the creators must have had massive industrial capacity, and this problem is one they could have foreseen. So, what to do about it?

Increase the concentration/recovery with passive mechanisms. Use gravel traps and leaching systems to intentionally recover the elements, and concentrate them for re-use. Set up energy collectors hovering over a star with the sole purpose of energy-mass conversion or fusion plants (perhaps both) to enrich the world with metals over time, probably in pre-purified form. Subsequent civilisations might neglect the maintenance, but that'll only make the task harder, not impossible.

If you can plan a project this large, you can plan for the long haul. Including stellar evolution. Entropy wins in the end, but as long as you can leech from another system (the star), you can continue to bribe Maxwell's Demon to separate them.

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