Tell me about the idea that mugged you in the night and wouldn't let you go
 When explorers found out that Earth was flat after all, they mounted expeditions beyond the edge to climb the gears of Heaven.
 Some brought back stars and pieces of the sun and installed them on towers, to grant their cities eternal day.
 Others stayed. Their houses adorn the steel beams that carry the sun and watch down onto earth, which now looks like the night sky once did.
The ideas quickly became too many to pour into a coherent twitter thread, so I'll bloviate here instead. How is this world different from ours? It is flat, it is finite (beyond the beams that carry sun, moon and stars, there is nothing), and stars are small and easily tamed.
After the first explorers, there are now two "interesting" civilizations: The sky settlers and the star tamers.
The Sky Settlers
They are the descendants of the explorers who have chosen to stay among the stars. The gears and spokes of heaven are gargantuan indeed and have plenty of surface. Which is hard but not impenetrable and dust has accumulated in places, so settlements and some species of moss and lichen cling to them. It is a very austere environment, but the view is great and some of the planets even habitable. They trade stars with the surface in exchange for soil, ropes and other rarities, and it is rumored they have been working on their own artificial stars, and machines to cross the distances without a harness.
The Star Tamers
They have stolen stars from the sky and built giant receptacles (generally towers called pharos [plural the same as singular]) in their cities to carry them. This has various ramifications:
PS: Mechanical suns can't melt steel beams
published: Feb 10 2016.
epistemic status: subjunctive.
- Obviously, eternal day. The manufacturing sector is all over it (this is not a world with electrical light), as are some farmers (mostly of high value crops, space lit by the pharos is still a limited resource).
- Sleepless citizens. For this, various remedies are found: Whole quarters put up sun screens at night, or a city will have a moving screen that revolves around the star once a day to simulate a night. Or you simply get thick curtains.
- What makes or breaks a proper city is the presence of a star. They become very coveted items, and it is not unheard of for one to be stolen after a lost war and reerected elsewhere. They are pretty much indestructible though. Transporting one takes serious gear, but it is possible.
- Time is now within the reach of human manipulation and becomes political. Clocks power the screens and mirrors of a pharos and make time instead of measuring it, everything is fine as long as the citizens' sleep cycles can cope with it. A clock's precision becomes kind of obsolete. Different city quarters get more or less light at different times depending on how rich they are (and conversely their value is determined by the amount of light they receive). Sometimes, citizens move to other cities that have more accomodating sleep rhythms (an hour or two can make quite a difference). Also you can now get jetlag from walking a kilometer into one of the city's other timezones.
- Light subscription: Manufactures have no use for the night and settle next to the pharos or sign mirror contracts to get a small part of the star's output in their general direction.
- In a pinch, the energy output of a pharos can be used against an approaching/besieging army. This makes sieges look very different from what we're used to. Armies advance under sunscreens, fortifications don't grant attackers a bit of shadow, and traitors that smash the mirrors at the pharos are in high demand.
- Communication: The world is flat and the pharos are high. You can divert parts of its output for semaphore signaling between cities. Not very high bandwidth, but it's enough for troop movements and trade tickers.
- If these people make it into the silicon age, they either won't have a global (diskal) timezone database, or it will be a nightmare of conflicting calendars and clocks to which our current implementation doesn't nearly compare.
- This looks a lot like an interstellar civilization by now! Only without those meddlesome planet killer weapons that are the logical consequence of travelling at significant fractions of c.
- There are some oddball cities: One is a fleet of ships anchored around a tiny volcanic island. They have figured out basic weather manipulation and use their pharos to redirect storms. Another is rumored to exist under the earth, near its roots, sequestered from our civilization.
- Energy flow works a bit differently in this world. There is no open space as such to lose warmth to, the edge of the world just bleeds energy while sun and stars produce it from nowhere. Bringing those stars with their non-negligible energy output down to earth seriously altered the diskal climate and the effects are ongoing.