"
The world is a hollow sphere, there are legends of a vast black cave with beautiful lights called stars deep below the ground we stand on. There are heretical legends that say people came from outside the world. But heresy brings death by fire."
The spheres seem to be a strange sport of a Tech Level 12^ society. Each sphere is close to 1,800 kilometers in radius. The inside of each working sphere has a biosphere composed of life forms that seem to originate from the Earth. The ancestral life forms seem to have been taken from the Earth in the
Pleistocene or
Placenzian periods. Humans and humanoids have been found within the spheres.
There seems to be an artificial gravity field. The direction of acceleration of free falling bodies (down) is out from the center of the spheres. The "Gravity" in the spheres is 0.897G. The air pressure at "Ground Level" is 18psi. There is a luminous effect at the center of each sphere which seems to be a hologram like thing. These are the source of light and warmth inside the spheres. They have cycles in the production of light and heat creating Day/Night and Seasonal cycles. They're also a major focus of study by scientists exploring the spheres.
None of the cultures in the spheres have a Tech Level above three. There are no fossil fuel deposits. Psi phenomena are far more common among the populations in the spheres than in the general human population. Another source of serious study.