In 1937 Olaf Stapledon described the concept of artificial biospheres constructed by advanced extraterrestrial civilizations in his science fiction novel "Star Maker." About 20 years later physicist Freeman Dyson formulated the idea that very advanced ET civilizations may construct large artificial shells around their parent star. These so-called "Dyson Spheres" would be capable of capturing all of the star's energy for use by these civilizations. Advanced civilizations are divided into three major classes by the exo-biology community. Type I civilizations have the capability to communicate using electromagnetic radiation and have a basic understanding of the laws of physics. They have an energy capability equal to the solar insulation on Earth (between 1016 and 1017 watts). A Type II community has the capability of constructing Dyson Spheres and can initiate interstellar travel and space colonization. Their societal lifetimes are long, ranging from 1000 to 100,000 years. The Galactic civilizations or Type III societies have energy resources on the order of their entire galaxy (about 1044 ergs/sec). They have very long lifetimes on the order of the main sequence lifetime of their sun. They are effectively the "immortals" among the galactic communities. The "Dyson Sphere" constructing civilizations would rank at the late evolutionary stages of Type II societies in the transition phase to Type III communities. The giant biosphere would most likely be constructed from dismantled planets within the solar system of the advanced civilization. According to Dyson, a large shell could be constructed around the central star using the mass of a planet like Jupiter. If the radius of the Dyson sphere is taken to be 1 astronomical unit (1 AU = the mean distance between the earth and the sun) it's volume would be 4*pi*R^2*S, where R is the radius of the sphere (1 AU) and S thickness. A shell or layer of rigidly built objects with a diameter of 10^6 moving in orbits about the parent sun would require approximately 100,000 objects to complete the spherical enclosure. Radiating at a temperature of 300 Kelvin this Dyson sphere would be a powerful source of infrared radiation. Using Wein's law, given by Lambda=0.29T-1, the emitted radiation peaks at approximately 9.7 microns (in the infrared region of the EM spectrum). Attempts to detect Dyson Spheres using the IRAS (Infrared Astronomical Satellite) sky survey data are currently underway.
Mark Elowitz
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