What’s a Ringworld?

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Ringworld is a classic science fiction novel by Larry Niven about a massive ring-shaped colony equal to the length of Earth’s orbit, with artificial gravity provided by rapid rotation. The term “ringworld” now refers to any artificial construct exceeding a hundred kilometers in at least one dimension. The structure requires a material with a tensile strength equal to the atomic nucleus, and Larry Niven said it was an intermediate step between a planet and a Dyson sphere. The Ringworld is a fascinating thought experiment and an interesting sci-fi plot device.

Ringworld is a 1970 science fiction novel by Nebula and Hugo Award winner Larry Niven. It is considered a classic of the genre. In the years since the novel’s publication, the term “ringworld” has come to refer to its namesake in the novel: a massive ring-shaped colony equal to the length of the entire Earth’s orbit. Its width was 1 million miles, 125 times wider than the diameter of the Earth. Its circumference is given as 6×108 miles, as a surface area was about 300 million times the size of Earth. Artificial gravity was provided by rapidly rotating the ring. Throughout history, every planet in the solar system has been taken apart and used to build the Ringed World.

A ringworld is a perfect example of a megastructure in science fiction; informally, an artificial construct exceeding a hundred kilometers in at least one dimension. The megastructures aren’t entirely science fiction — at least two already exist on Earth as of the early 21st century: the 3,947-mile-long (6,352 km) Great Wall of China and the Philippine Cordillera Terraced Rice Fields, a 10,360-square-kilometre (4,000-square-mile) ) ) agricultural complex. In science fiction, the word often refers to something suspended in space.

Running physics numbers on the ringworld structure has long been an interest of sci-fi geeks and extreme engineering enthusiasts. In the novel, it is stated that 20 masses of Jupiter’s energy must be expended just to spin the ring fast enough to simulate 1 g of gravity through centrifugal force. Calculations by physicists have found this to be right. To prevent the ring from separating due to centrifugal force, a foundation material with a tensile strength approximately equal to the atomic nucleus would be needed. In the novel, this material is called scrith. The only known material with a tensile elongation equal to scrith is neutronium which makes up neutron stars. If neutronium could somehow be formed into a ring, it would still be likely to collapse down to its own gravity.

Larry Niven said his ring world was an intermediate step between a planet and a Dyson sphere; an artificial sphere that completely encloses a star. Building one could take hundreds of thousands of years, if it could ever be built.
Most people discussing the Ringworld object consider it a fascinating thought experiment and an interesting sci-fi plot device. Small-scale ringworlds are featured in the Halo computer game series.




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