So, If I'm trying to make a borderline-isekai (trapped in an MMORPG world anime) setting, I might as well just make the game mechanics more real, like invisible walls, everywhere.
The world of Underdown used to be a nice place until... something happened. Now everyone has to live under 200 meters of graphene-reinforced UHMWPE and SAM2x5-630 composite plates, crammed into the elaborate cavern system, known as the Underdown (roll credits).
Such a nice location has many disadvantages, especially when used as the last beacon of civilization (sorry, that's 4chan). Today, I wanted to focus on the basic question of Underdown's size.
But first, basic information about the tech-level and the Barrier:
The Barrier:
- [Irrelevant Data Removed]
- [Irrelevant Data Removed]
- Nanomachines in the stratosphere (slightly above the ozone layer) collect all the sunshine with a 40% efficiency and send it to Underdown, so we dodged the Second Law of Thermodynamics.
The technology:
- Despite looking high-medieval, the society actually has access to modern day (and slightly better) technology.
- Magic is also a form of technology, which should explain why it's so inept and can only shine in terms of healing (complete regeneration, hyper-effective disinfectant), infiltration, sabotage, intel-gathering, manufacture, and Megumin-grade explosions, given time (and propane).
- Food can also be easily be produced using magic.
Now, let's name the factors we need to consider in Underdown's size:
- Population: Cramming the entire Pathfinder Bestiary 1 into a tiny cave, and trying to provide the preferred habitat (swamps, jungles, a bloody lava lake) for them is hard.
Let's assume 1 million individuals, who all have the same needs as an average adult human (Why? I put a hard cap on living creatures, both in terms of size and resilience to the elements, and dragons, with the size of Big Jake, are the maximum in both terms, but still, fail to outperform polar bears). Remember, this is a permanent home for them, let it be at least a bit comfy.
- Construction materials: I'm more forgiving with that, after all, the absolute madman who built the place started using boron carbide and alumina instead of concrete halfway through. And because MMCs are widespread in this world.
So how big would Underdown (area and height (because the birds)) have to be to meet all the criteria, given the best construction materials, and all the energy in the planet? Of course, only if it can be built at all.