Editing Kardashev scale (section)

==== Two strategies for searching for intelligent signals ====
Kardashev then analyzed various models and hypotheses of the evolution of civilization. Answering the question of the Russian astronomer [[Iosif Shklovsky]], who in an article published in 1977 and titled ''Possibility of the Intelligent Life in the Universe Being Unique'' found it strange that the "shock wave of intelligence" of a supercivilization had not yet reached the limits of the whole [[Universe]], Kardashev put forward two explanatory hypotheses. In the first, he postulated that it would not be useful for a supercivilization to expand the space it occupies in order to maintain its activity, and in the second, it is possible that a civilization, instead of dispersing itself in space, would rather continue its activities of information analysis in order to discover new fundamental laws (such as the exploration of the microcosm, or [[black hole]]s for example).<ref name="Kardashev-1980" />

However, such civilization activities require the use of abundant energy. According to the [[laws of thermodynamics]], an important part of this consumed energy must be converted into radiation of a [[Absolute magnitude|bolometric magnitude]] approximately equal to that of the radiation background surrounding the source. The spectral distribution of this intensity must be close to that of a [[black body]]. This would be a possible way to search for extraterrestrial civilizations. Such energy consumption would also require a large amount of solid matter for [[stellar engineering]] activities, which Kardashev called "cosmic miracles". In short, information about the possible existence of an extraterrestrial civilization would come in the form of [[electromagnetic radiation]].<ref name="Kardashev-1980" />

With regard to the fate of civilizations, Kardashev saw two concepts, from which two strategies for the search for extraterrestrial civilizations can be derived. The first, which he called "terrestrial [[chauvinism]]", is based on the principle that civilizations can only stabilize or perish at a level of development close to ours currently reached. The second, which he called the "evolutionary concept", holds that civilizations are capable of reaching higher levels of development than that of contemporary humanity. In the first case, the best search strategy using astronomical detection means (e.g., the [[Search for extraterrestrial intelligence|SETI]] program) would be to observe the most powerful (and often the most distant) sources of radiation in space.<ref name="Kardashev-1980" />

The observer will then be able to determine if they are natural emission sources, and only then can the search focus on objects with weaker radiation. In the second case, he recommended to search for new and powerful sources of radiation, especially in the poorly known regions of the [[electromagnetic spectrum]]. These sources could be significant or periodic [[Monochromatic radiation|monochromatic]] signals from the [[Galactic Center|galactic center]], from other galaxies or from [[quasar]]s and other exotic cosmic objects.<ref name="Kardashev-1980" />

Kardashev believed that the search should focus on the [[Submillimetre astronomy|millimeter wavelength spectrum]], close to the maximum intensity of the [[cosmic microwave background]], rather than in the [[Hydrogen line|21-centimeter band]] (which is the domain of investigation of the SETI program). According to Kardashev, in order to capture the significant radiation of an advanced civilization emitted by a [[megastructure]] (such as a [[Dyson sphere]]), a radio telescope with a diameter larger than that of the Earth would have to be placed in orbital space.<ref name="Kardashev-1980" />

Kardashev concluded by predicting that the search for extraterrestrial civilizations would lead to positive results in the [then] next decade, giving humanity access to a vast amount of information about the [[Universe]] and its evolution over a period of several billion years.<ref name="Kardashev-1980" />