Dyson sphere

A heartfelt tribute to Freeman Dyson

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(...) Dyson is too modest.
Richard Carrigan⁽⁸⁾

The search for extraterrestrial life has, as I already written, some illustrious founding fathers: Enrico Fermi and his paradox; Giuseppe Cocconi and Philip Morrison and their 1959 proposal to use radio astronomy to search for extraterrestrial signals of intelligent origin⁽¹⁾; Frank Drake with his famous equation, and therefore with the Ozma project⁽²⁾, so called for the queen of the imaginary land of Oz, a very distant place, difficult to reach and populated by exotic beings, a kind of proto-SETI, project that Drake helped to found and launch.
Another important contribution to the quest of intelligent signal in the universe come from Freeman Dyson^{(3, 8)}:

If extraterrestrial intelligent beings exist and have reached a high level of technical development, one by-product of their energy metabolism is likely to be the large-scale conversion of starlight into far-infrared radiation. It is proposed that a search for sources of infrared radiation should accompany the recently initiated search for interstellar radio communications.⁽³⁾

Dyson, taking our solar system as a model, observed how the mass of Jupiter, if distributed with spherical symmetry on a double orbit compared to that of the Earth, would have been 2 tons per square meter thick:

A shell of this thickness could be made comfortably habitable, and could contain all the machinery required for exploiting the solar radiation falling onto it from the inside⁽³⁾

It was this observation that prompted science fiction writers to coin the expression "Dyson spheres", described as real spheres built around a star, although the idea of ​​a similar technology was suggested to Dyson reading in 1945 the novel Star maker (1937) by Olaf Stapledon⁽⁸⁾.

Fractal Dyson Sphere by Steve Bowers

Classifing civilization

In his great modesty, Dyson has always believed that the spheres that bear his name should instead be named Stapledon spheres or clouds. In any case, the discovery of signals of this kind of technology should allow us to classify a possible extraterrestrial civilization in the type 2 on a scale of three stage proposed by the Russian astronomer Nikolai Kardashev^{(8, 4)}. Following Kardashev, intelligent civilizations can be classified according to the kind of resources they manage to manipulate, starting from type 1 (manipulation of planetary resources), type 2 (control of stellar energies), type 3 (management of resources galactic). If in this classification our civilization has not yet reached the first level of development, it is also quite evident that the Dyson spheres are a level 2 technology, because a level 3 technology should be particularly evident.
The technology proposed by Dyson, however, is not a hollow sphere: however rotating, it is gravitationally unsustainable, destined to collapse under its own weight due to stellar gravity. So the astronomer imagined a more plausible cloud of objects inhabited in orbit around the star, dense enough to absorb solar radiation but with carefully calculated orbits so as not to collide. Such a system was named by Dyson artificial biosphere, anticipating the idea behind the Biosphere 2 project.

Alien survival experiment

This is a project born between 1984 and 1991 and actually built at north of Tucson in Arizona by the private company Space Biospheres Ventures. The first mission, which began on September 26, 1991 with a "crew" of eight people employed for two years to live in a controlled environment designed to support their survival through self-reliance. Basically the idea of ​​the experiment was to understand the sustainability of an environment whitout most of the bilogical variety present on Earth, the main biosphere, and the chances of survival of human beings in a situation therefore very similar to what could be encountered on a different planet from ours.
Various aspects were therefore studied: from the production of food to the food diet, without forgetting the management of pets, the disposal and recycling of waste and the internal dynamics of the group of "settlers". Particularly interesting in the articles that I (fairly quickly) read^{(5, 6, 7)} are a couple of apparently superficial observations on the beneficial effects on the mood of lush and varied vegetation and on a diet designed to be not only nutritionally complete but sufficiently variable. If in our view as inhabitants of the Earth they are fairly trivial observations, for possible space colonists, as we can see studing astronauts on ISS, they constitute the difference between the success or defeat of the colonization of an alien planet.

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1. Giuseppe Cocconi, & Philip Morrison (1959). Searching for Interstellar Communications Nature, 184 (4690), 844-846 doi:10.1038/184844a0 ↩
2. F. Drake, "How can we Detect Radio Transmissions from Distant Planetary Systems?", Sky and Telescope, 19, 140 (1959) ↩
3. Freeman J. Dyson (1960). Search for Artificial Stellar Sources of Infrared Radiation Science, 131 (3414), 1667-1668 doi:10.1126/science.131.3414.1667 ↩↩↩
4. N. Kardashev, "Transmission of Information by Extraterrestrial Civilizations" (in Russian), Astronomicheskii Zhurnal, 41, 282 (1962), English translation, Soviet Astronomy AJ, 8, 217 (1964). ↩
5. Nelson, M., Finn, M., Wilson, C., Zabel, B., van Thillo, M., Hawes, P., & Fernandez, R. (1999). Bioregenerative recycling of wastewater in Biosphere 2 using a constructed wetland: 2-year results Ecological Engineering, 13 (1-4), 189-197 doi:10.1016/S0925-8574(98)00099-8 (pdf) ↩
6. Bruno D.V. Marino, & H.T. Odum (1999). Biosphere 2: Introduction and research progress Ecological Engineering, 13 (1-4), 3-14 doi:10.1016/S0925-8574(98)00088-3 (pdf) ↩
7. Silverstone, S., & Nelson, M. (1996). Food production and nutrition in Biosphere 2: Results from the first mission September 1991 to September 1993 Advances in Space Research, 18 (4-5), 49-61 doi:10.1016/0273-1177(95)00861-8 (pdf) ↩
8. Freeman J. Dyson, & Richard Carrigan (2009). Dyson sphere Scholarpedia, 4 (5) doi:10.4249/scholarpedia.6647 ↩↩↩↩