A world with a somewhat old-fashioned cosmology.The world is flat. The continents are arranged roughly as on a Mercator map (although Greenland is of course much smaller.). A thousand miles of sea east of far Siberia and west of Alaska, there arises a continuous line of mountains twenty miles high. This wall of mountains encircles the world. Beyond it is another three thousand miles of sea. This sea is apparently bottomless and inhabited by vast monsters. Beyond that is a wall of white alabaster, rising fifty miles from the sea. It supports the blue dome of heaven.Radiological studies indicate the world is perhaps 50,000 years old. It is widely accepted that someone created it, although the nature of the Creator remains in dispute. Recent genetic studies indicate that humanity was created in Africa and spread out from there, although some remain huffily convinced of the Multiple Creations theory of human history.The moon and planets emerge from under the Outer Sea and sink under it when they set. The sun emerges from a great pair of brazen doors set just above the waters, which open and close with a metallic clash that can be heard from the Encircling Mountains. The sun and moon are each perhaps a hundred miles across. The stars simply appear when the sun descends and travel complex paths right under the vault: they are currently understood as being somehow generated or projected from the material of the vault rather than being individual moving bodies.Air extends only a small distance up above the earth, various forms of weightless and cold or fiery Aethers filling the greater bulk of the volume beneath the vault of heaven. (This is fortunate since otherwise atmospheric pressures would crush everything flat).Since the world's surface is flat, the rays of the sun do not arrive at the poles at as an acute an angle as they do in our world. There is no Antarctic continent, but Greenland is as habitable as OTL Norway and actually pretty green in the summer, and supports some 23 million people, mostly of British descent (The Vikings didn't make it past Iceland, given the wider north Atlantic). Siberia and Canada are also more pleasant.Since the first rockets made it over the Encircling Mountains in the 1950s and showed humanity the ultimate extent of the world, the debate has raged about how far humanity should go in exploring God's creation. The debate has continued as the Outer Seas were surveyed, and as fliers landed on the fairly narrow strip atop the Alabaster Wall, landed on the Moon and Planets, and took a close look at the Firmament, and there was some _serious_ outrage when an exploratory rocket actually hit the top of the Firmament.No harm was done: the material of which the Firmament is made seems to be virtually indestructible, as are the Gates of the Sun, and the Alabaster Wall. The cloudy crystal of the Moon, the yellow-gold crystal of Venus, the red crystal of Mars – these seems less impervious, although multiple diamond drills were used up to get some nearly microscopic samples of the Moon on the second expedition (the first expedition did not go well: the Moon's surface is almost frictionless, and the first lunar lander kept sliding off the Moon). So far, studies of these samples, and those obtained by automated probes to the planets, seem to indicate that whatever the celestial bodies are made of, it does not seem to be made of atoms.The Sun is of course too hot to get anywhere near, and various efforts to get a good look past the Gates of the Sun have failed due to the heat and light of the sun burning out any instrumentation: about all that can be told is that there is a square-walled tunnel extending some ways back, but that is about all: the Gates do not remain open long enough to make a run for it once the sun has moved far enough away. (What exactly the sun is remains uncertain: some scientists suggest it is not so much a thing in itself but some sort of link or channel to some fiery other space. Fusion is a theoretical process outside of bombs).If going up is blocked by the Vault, going down is blocked by water. Using atomic weapons to create sufficiently powerful vibrations in the earth for sonar-type measurements, scientists have determined that the Encircling Mountains actually encircle a partially water-filled basin: earth underlies the inner seas, and extends downwards some five hundred miles, but below that there is water, with the earth apparently supported on a great number of vast pillars. The Outer Seas are connected with this Great Deep, and presumably of equal depth: how deep is unknown, since the most ingeniously reflected and counter-reflected wave vibrations can't resolve things more than a few thousand miles down. In any event, water pressures as one descends soon grow far too high for even the sturdiest of submersibles. There is some talk of developing a solid metallic probe with no internal voids, but the technology remains speculative.There are a great many curious voids and apparently flows of liquids through the interior of the earth, water and fiery gasses and molten rock: some suggest that these resemble some sort of vast circulatory system, and that the Earth is alive in some sense: others see a vast mechanism, while others look at the impossibly vast caverns below the reach of current mining technology and mutter of Hell and Sheol.Travel above the atmosphere is somewhat complicated by the fact that the gravity field is constant in all places: there is no way to "orbit" and no such thing as "escape velocity." This is to some extent offset by the fact that the aether, although weightless, is substantial enough to provide support for large enough wing surfaces.Native Americans in this un-curved world never reached the Americas by way of Siberia, but by island-hopping managed to reach the Encircling Mountains, where in spite of wars with the Unipeds and the Blemmyes they created various nations of their own in the harsh but habitable foothills. (The Vikings also reached the Encircling Mountains by going north, but Ultima Thule is colder and rather less hospitable place than the *Amerindian lands which go south to past the OTL Equator. The *Amerindians are in this world called, of course, East Indians.).The Americas were uninhabited when Europeans arrived: given the lack of a "great circle route", it was a good deal further from Europe to Greenland. Fortunately for colonists lacking a native hand up with corn and so on, the Creator provided several useful local plants and a rich variety of mega-fauna which made colonization easier. Still, the Spanish American nations, without locals to till the soil or dig up gold and silver, were settled rather more slowly than OTL, and have a rather different political history. Due to the lack of local labor, the population tends to be rather more African, ethnically, than OTL, and there are several "African nations" on the continent as well as in the Caribbean. (And I shan't even mention Evil Pseudo-CSA Greater Argentina). On the other hand, the Empire of Brazil is no further from Africa than it is OTL, and in our world never had a dense and easily exploitable native rural population: if a bit smaller, it is otherwise similar to OTL.The inhabitants of this world's United States have no blood on their hands (well, aside from that of slaves). Colonized initially a bit more slowly than OTL US due to greater travel distances, its population is not as great as in our world, and in defending freedom and democracy it has often leaned on the support of its northern neighbor, mighty Canada.The Encircling Mountains in the east were reached by Europeans in the 1700s when the Russians followed the island chains east for furs. The long, narrow habitable strip (rarely more than 20 miles wide) between un-farmable slopes and the sea is divided up into various former British and Russian colonies for a length of 7,000 miles, south to the point where the Monster Empire blocked further East Indian expansion, north to the fringes of Greater Norden territory. Less biologically vulnerable than the Amerindians of our world (the Monster Races carried a variety of diseases which kept their immune systems active), the locals in a number of places retain their own languages and religions, and the states tend to be more "East Indian" and less white and Mestizo than the Latin American nations of OTL: total population is about 40 million, divided into some thirty smallish states.The northern Encircling Mountains are part of the Scandinavian federation of Greater Norden, a fairly important middling-sized state in this world. The western ones were colonized by the United States of Columbia in the final stages of Manifest Destiny. The Monster Races survive mostly in the south, which was not colonized until the 19th century and avoided a flood of colonists, although there are enclaves and protectorates in US territory. The Unipeds, Blemmyes, Cynocephalids, and those guys with the really big ears have small, shaky independent states in the south nowadays.History was roughly similar to OTL (the locals would probably say something about predestination) until the Age of Discovery, and has followed some parallels since. In spite of the lack of gravitational orbits to inspire a Newton, a Scientific Revolution still took place, and Europe as OTL industrialized and came to (for a while) dominate the globe. Germany unified, tried to conquer Europe twice, and was beaten twice. (Although the Jews managed to avoid any particularly unpleasant experiences in the process). Russia had a revolution and instituted a socialist dictatorship, although in this world it was a Christian socialist dictatorship. Japan, the long way around from America, never got into a war with the United States of Columbia, although it was eventually largely driven from the East Asian mainland by Russian-backed insurrection.The Philippines weren't on the way to anywhere and weren't colonized until modern times (by the French): they are currently part of the remaining Japanese Co-Prosperity Sphere. The US has never been that interested in the Chinese and never really cared that much that much of East Asia went Socialist (currently India, Japan and Australia are allied to contain further expansion of the Proletarian Menace in East Asia).Due to the lack of transpolar flight routes, the USC and the USCR remained less capable of directly striking at each other than OTL for a while: Europe remained the main staging force for any attack on the Soviet heartland for a while, and the US-European alliance was closer than OTL due to the greater need for military cooperation.The Cold War has largely faded, with the Russians moving to a less socialist and more religious-nationalist outlook and withdrawing from Turkestan and some parts of Europe: although the Chinese state remains relatively radical, it is far away and its current missile technology is unable to hit Western Europe or the Americas. Let the Japs and the Indians handle them, most Americans feel. (There was no Vietnam War in this world).Siberia is less Russian in this world, having supported considerably larger native populations when the Czars moved east: no less than four of the seventeen Soviet Republics are ethnically dominated by Siberian peoples.Japan also still rules Taiwan and parts of OTL Indonesia, along with some Pacific islands. (The Polynesians moved east until they reached the Encircling Mountains and got stuck through with arrows by the "East Indians."Sub-Saharan Africa, where the slave trade was even more extensive than OTL (to make up for those missing Amerindians), is politically carved up pretty differently: penetration of the interior and mastery of its diseases occurred earlier, due to that need for slaves, and "modernization" set in generations before OTL. As a result, in spite of Cold War hijinks, the continent is generally richer and more developed than in our world, and also more Christianized.Black people have also had it better off in that evolutionary theory never caught on in this world, for obvious reasons: although some have tried to dismiss Africans as a separate, inferior creation, or invoked the curse of Ham, a basic biological inferiority has never been attributed to blacks with anything like the OTL consensus from the late 19th to early 20th centuries. (Not that it saved the US of this world from its own civil war over slavery).Canada has a population and economy roughly comparable to that of Germany OTL. It has its own nuclear arsenal and the world's deepest mining operations (they really want to know what's in that 20-mile wide cave 300 miles below Ottowa).Satellite communications are of course impossible, but the Aether layers act like the terrestrial magnetosphere, in that they can be used to reflect down radio messages to areas on the Earth's surface thousands of miles away. (And of course the range of a radio tower atop a high peak is pretty impressive given the lack of line-of-sight problems in a world sans curvature).The Monster Races are a puzzlement, and some consider them to be "rough drafts" for the creation of humanity. Since the expansion of the US to the western Encircling Mountains, a large number of dog-headed men and other oddities have achieved US citizenship, although social prejudices remain a serious problem. (Especially in California). So far, Sweden is the only country that allows human-Monster marriage.Since Muslims, Jews and Christians all share roughly the same mythology about the nature of the World, there is a greater willingness to accept the notion of a common "religious tradition" and a bit more interfaith tolerance. (Although of course the Hindus, with their florid and overblown mythical geography, get a bit of a hard deal, with western Monotheists either denying their having received revelation in the first place or suggested that tropical fevers and oriental opium fantasies had led them to forget the simple, obvious nature of the world).The real argument in this modern and rational age is over the nature of the creator - between those who believe in an imminent and transcendent Creator and the "great engineer" crowd, who tend to take that "created in his own image" thing a bit too seriously and suggest God is simply a race of superior humanoid beings who manufactured the world for some unknown purpose. In a world which can be crossed by rocket from one end to another within a few hours, the Creator doesn't seem as big as He/She/It used to be, and this world's equivalent of science fiction writers indulge in all sorts of elaborate fantasies about what might lie beyond the observable universe.Worries about the Wrath of God have been exacerbated by the facts that 1. Although geology shows there was no global Great Flood, there have been some local ones of scale hard to explain, and 2. Close-up photographs of the surface of the Vault of Heaven show thin lines that might be doors. (Some also mention the Tower of Babel, but this is poo-poohed by historical linguists that feel it is solidly proven that linguistic variety existed well before 1900 BC, and archeologists feel that it is also pretty much proven that the Tower of Babel collapsed under its own weight at 550-600 feet, much less than 1% of the way to the Vault.)Still, governments in most places have successfully overridden religious hostility to excessive Creation-poking, but recent events have caused consternation and temporarily put a freeze on any new exploratory activity beyond the Encircling Mountains or above the airy atmosphere.The Japanese Empire, on January 12, 2011, set off a thermonuclear device at the base of the Vault of Heaven. Helicopters quickly brought in a team in anti-radiation gear to examine the results, and the first radio reports indicated that finally something had overcome the seeming invulnerability of the Vault and the Wall: over an area of about a square mile, where the central fireball had burned, there were innumerable tiny (from microscopic to a few millimeters) pittings in the material of the Vault and the upper surface of the Wall, and their luminous blue and white colors seemed darkened.Further data was not obtained, since around the time the first reports were transmitted people noted a curious little luminous patch, like a cloud, some ways up the side of the Vault. No telescopes were looking at the area where it appeared, so the exact manner and timing of its appearance remain unknown. As people watched, the cloud rapidly descended: telescopic examination showed a white, luminous mass, slowly changing its shape, cloud-like but more cohesive than a cloud, some tens of miles in diameter and lit up by constant internal flashes of light. It reached the location of the atomic test within five minutes: although one of the Japanese helicopters made it into the air, it failed to get far enough away to avoid being enveloped.The "cloud" descended to the Wall-Vault joint, where it hovered for an hour, emitting frequent light flashes: finally, in a series of particularly bright flashes, it vanished entirely – leaving no trace of the reported damage, or of any of the helicopters.The question as to what it has been continues to rage: neither the "Avenging Angel" crowd nor the "Automatic Repair Mechanism" crowd is giving an inch. What is definite is that a very serious damper has been put on any talk of finding out what lies beyond the Vault of Heaven…