The Concentration City

"The Concentration City" is a dystopian short story by British author J. G. Ballard, first published (as "Build-Up") in the January 1957 issue of New Worlds.

It has been reprinted in the Ballard collections Billennium and Chronopolis, and - under its revised title - in The Disaster Area. It appears in volume one of The Complete Short Stories of J. G. Ballard.

Setting
The story is set in the City, an unimaginably vast three-dimensional urban space (essentially an arcology with no outside.) The City comprises its inhabitants' entire universe, with streets and buildings stretching indefinitely in all directions - including vertically, on Levels spaced every eighty feet. Its total population is incalculable, and apparently stable; cubic space is in high demand, with a dollar per cubic foot as the median valuation. While there is no serious material deprivation, there are slums; more seriously, there are also rumored "dead zones" which have been walled off from the rest of the City, and where urban decay is allowed to run rampant.

The structure is densely-built, with very few open areas, such as arenas and stadiums; the only remnants of nature are scattered in small gardens and zoos, containing a few samples of plants and wildlife (the protagonist's home County of thirty million can boast of having one tree.) The City supposedly dates from an unspecified "Foundation," three hundred billion years ago; the only independent confirmation of its age is that the animal life in its zoos has been evolutionarily shaped by its environment (with birds that are not only flightless but have lost their pectoral girdles, to which wings would have been attached.) The general population is concerned with day-to-day existence, which resembles that of a large American city in the 1950s, and never speculates what might lie beyond the endless urban expanse; it is generally assumed that the City simply goes on forever.

Plot
The narrative follows Franz M., a twenty-year-old physics student who has come to fixate on the concept of "free space" - the notion that there must somewhere be an end to the City, to be followed by some sort of void - a concept that his best friend Gregson has a difficult time even conceptualizing. Franz has recurring dreams of flight or levitation in such a space, and experiments with building crude fireworks-propelled gliders, limited by the fact that aerodynamics is a relatively obscure theory. At any rate, Franz concludes that this approach is a dead end, as there is - aside from closed construction zones - no empty space large enough to trial a device large enough to carry a human. He resolves to learn for himself whether the city has an edge - and whether there is free space beyond it - by traveling in one direction for as long as possible, to which end he boards an extremely high-speed Supersleeper train propelled through an evacuated tube by rockets. After ten days of westbound travel, he has made it from his native 298th Local Union (with its eleven trillion inhabitants) up through increasingly grandiose layers of political subdivisions which culminate in a "755th Greater Metropolitan Empire," with the total implied total population of the part of the City he has transited being at least 1027 people. On the tenth day, Franz suddenly notices that the Supersleeper's direction is now - without ever having reversed course - listed as eastbound. His incredulous reaction draws the attention of the railway authorities, who revoke his ticket and ship him back to his point of origin. In his home neighborhood, during an interrogation by a sympathetic police psychologist, Franz glances at a calendar and discovers that it is the day of his initial departure on the Supersleeper.

Relationship with other works
Similar concepts can be found in other works of speculative fiction, in which several distinct types of "infinite cities" appear:
 * Trantor - a planet-spanning ecumenopolis from Isaac Asimov's Foundation novels
 * Diaspar - a sealed, self-contained city-state that endures for a billion years in Arthur C. Clarke's The City and the Stars
 * The City - a finite-but-unbounded megastructure larger than the Solar System in Tsutomo Nihei's manga Blame!