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BDO of the Day: Orbitsville

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Today’s Big Dumb Object (BDO) is Orbitsville, the Dyson sphere appearing in the eponymous novel by Bob Shaw and its sequels. I gave a brief review of the first two in a recent post.

Orbitsville is a traditional Type II Dyson sphere of the sort that made Dyson regret his association with them: made of a thin shell (“only a few centimeters thick”, later upped to 8cm) of magic material (“ylem”), magically radiating no heat or other energy from its central sun, with an environment magically clinging to the inside of the shell in violation of the shell theorem.

Orbitsville is the name used by its discoverers, but it is officially called Lindstromland, then later Optima Thule, by the wider human society. Human explorers first detected Orbitsville because it does have the expected amount of gravity for a Dyson shell enclosing a sun. Its reported diameter is “some 320,000,000 kilometers”, giving it a radius of “just over” 1 AU. Its outer surface is described as perfectly smooth (yet with “a reasonable index of friction”), perfectly spherical, and impervious to all forces possessed by humanity, which got there with a faster-than-light drive based on some invented post-Einsteinian physics.

The sphere rotates at 70,000 kilometers an hour at the equator, which is not the tangential acceleration required to produce gravity (4 million kph); at some point the humans note that the gravity is, instead, “synthetic”. The sphere blocks all radio signals with a (magical) dampening field, as well as the humans' interstellar drive (apparently not by magic but only for lack of the interstellar dust it uses for fuel). The explorers prove able to travel inside the sphere by more primitive means such as airplanes and the like.

The inside surface is “625,000,000 times the total surface of Earth”, which the characters estimate is about “equivalent to five billion Earths” worth of usable land (since most of the area of the Earth isn’t useful, whereas most of Orbitsville is). A rotating shade structure around the sun—a “globular filigree of force fields”, which even the author put in scare quotes—produces both seasons and alternating bands of day and night.

The sphere has a single circular opening at the equator, plus more blocked openings discovered and reopened later in the story. The first opening is about a kilometer in diameter and is protected by a (magic) force field through which a person (or a ship) can pass.

The sphere appears to be a classic abandoned BDO, with several species unrelated to the builders having come across it over time and settled within. More details about the builders and the apparent abandonment are revealed in the sequel, but BDO-wise we only get the added detail that there are 207 openings at the equator spaced about five million miles apart, plus a ring of 173 in the northern hemisphere and 168 in the southern hemisphere; all “vary a little in sizing and spacing”.

The first sequel is, frustratingly, mainly set mainly on Earth, but there is some BDO action at the end, and Orbitsville does loom over the human race thematically for the entire series. Earth was overpopulated with a constant stream of emigrants heading to its one colony world when humanity found Orbitsville, which becomes their new destination. Even in the first book, the characters voiced dark suspicions about the ultimate purpose of the BDO and the risk of humanity’s devolving to a primitive agricultural level within it as many races had apparently done before. But such misgivings don’t slow the exodus one bit; by the second book the Earth is nearly abandoned, and the true purpose of the BDO is revealed.

I didn’t find the notion that vast croplands would turn humanity back into subsistence farmers particularly convincing, but that’s not for any want of effort on the author’s part. His theory is at least superior to that of other authors who project our current interests and lifestyles onto a BDO setting infinitely, perpetually, and thoughtlessly.

The third book is harder to find and I haven’t read it yet, but reviews indicate that there isn’t much more there about the BDO qua BDO.