Editing Kardashev scale (section)

== Origin of the classification ==

=== First publication (1964) ===
[[File:KScale.svg|alt=A red dotted line that goes up from left to right.|thumb|upright=1.4|A projection of the Kardashev scale to 2040 based on data from the International Energy Agency World Energy Outlook]]
Kardashev presented for the first time a classification of civilizations according to the level of the rate of their energy consumption, or ability to harness power, in an article entitled ''Transmission of Information by Extraterrestrial Civilizations'', published in 1964 first in Russian in the March–April issue of the [[Astronomy Reports|Astronomicheskii Zhurnal]],<ref name=Kardashev-1964 /> then in English in the September–October 1964 issue of the Soviet Astronomical Journal.<ref name="Kardashev-1964"/> In this article, the scientist presents a calculation of the evolution of the power needs of humanity. Assuming that overall human power use will continue to increase, he calculated that the rate of energy consumption will cross specific mileposts. Kardashev proposed a typology of technological civilizations based on the evolutive attainment of the three power harnessing mileposts he described.<ref name=Kardashev-1964 /><ref>{{Cite book |last=Basalla |first=George |title=Civilized Life in the Universe: Scientists on Intelligent Extraterrestrials |year=2006 |publisher=Oxford University Press |isbn=978-0195171815 |pages=148–149 |language=en |chapter=Life in an Expanding Universe}}</ref>

A [[civilization]] known as "Type&nbsp;I" has achieved a technological level close to the one attained on earth at the time Kardashev’s article was submitted (December 1963), with a rate of energy consumption evaluated at about 4 x 10<sup>12</sup> [[watt]]s (W). A civilization known as "Type&nbsp;II" would surpass the first by fourteen orders of magnitude, matching the entire power emitted by the Sun in about 3,200 years, i.e, our home [[star]]’s “output“ at that time, predicted at 4 × 10<sup>26</sup> W. Finally, a civilization known as "Type&nbsp;III" reaches the milepost set in 5,800 years when humanity’s rate of energy consumption is predicted by the author to match the power emitted by the approximated 10<sup>11</sup> stars in our home [[galaxy]], the Milky Way, which involves harnessing power of up to an estimated 4 x 10<sup>37</sup> W.<ref name=Kardashev-1964/> 

Assuming the development of [[radio]], Kardashev predicted that in the following two decades (i.e. in the 1980s) it would be possible to build antennas of 100,000 m<sup>2</sup> capable of detecting Type&nbsp;II and III civilizations. A Type&nbsp;I civilization like that of earth would be able to receive the extraordinary energetic emissions of the other types of civilizations, which would supposedly be able to emit continuously.<ref name=Kardashev-1964/><ref name="Galántai-2003">{{Cite journal |last=Galántai |first=Zoltan |date=2003-09-07 |title=Long Futures and Type IV Civilizations |url=http://mono.eik.bme.hu/~galantai/longfuture/long_futures_article1.pdf |url-status=live |journal=Periodica Polytechnica, Social and Management Sciences |volume=12 |issue=1 |pages=83–89 |archive-url=https://web.archive.org/web/20230307020046/http://mono.eik.bme.hu/~galantai/longfuture/long_futures_article1.pdf |archive-date=2023-03-07}}</ref>

Kardashev then examined the characteristics of a transmission from an artificial source. He mentioned the two cosmic radio sources discovered in 1963 by the [[California Institute of Technology]], CTA-21 and [[CTA-102]] in particular, which would have characteristics close to those of a presumed artificial source. The most suitable region of the galaxy for observing Type&nbsp;II and III civilizations would then be the [[Galactic Center]], due to the high density of the stellar population it harbors. He then recommended that the search programs for such artificial sources should focus on other nearby galaxies, such as the [[Andromeda Galaxy]], the [[Magellanic Clouds]], [[Messier 87|M87]], or [[Centaurus A]]. Kardashev concluded his paper by noting that the possible discovery of even the simplest organisms on [[Mars]] would increase the likelihood that Type&nbsp;II civilizations exist in the galaxy.<ref name=Kardashev-1964/>[[File:Consommations énergétiques des trois types de l'échelle de Kardashev.svg|thumb|upright=2|alt=Three schematic representations: Earth, Solar System and Milky Way|Energy consumption in three types of civilization as defined by Sagan's extended Kardashev scale|center]]

=== Second publication (1980) ===

==== Towards an energetic definition of civilization ====
In 1980, Nikolai Kardashev published a second article entitled ''Strategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem,''<ref name="Kardashev-1980">{{Cite journal |last=Kardashev |first=Nikolai S. |date=1980 |title=Strategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem |url=http://www.bigear.org/CSMO/HTML/CS07/cs07p36.htm |url-status=live |journal=Cosmic Search |volume=2 |issue=7 |pages=36–38 |bibcode=1980CosSe...2...36K |archive-url=https://web.archive.org/web/20230727035448/http://www.bigear.org/CSMO/HTML/CS07/cs07p36.htm |archive-date=2023-07-27}}</ref> in which he stated that:{{Blockquote|text=Detection and studies of extraterrestrial civilizations constitute a problem of immense significance for the progress of humanity and for its culture and philosophy. The discovery of intelligent life in the Universe would provide a guideline to the possible development of our civilization over astronomical time spans.|author=Nikolai Kardashev|title=Strategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem}}

[[File:Annual_world_primary_energy_consumption.svg|alt=A broken line in blue goes, from left to right, from the bottom to the top|thumb|upright=2|A graph of world [[World energy supply and consumption|primary energy consumption]] in 2011 according to the BP ''Statistical Review'']]
According to the Soviet astronomer, the Earth's civilization would be too young to be able to contact another civilization that would certainly be more advanced; the [[Solar System]] is too young with its five billion years, and the first ancestors of today's man appeared only 6 million years ago at the earliest;<ref>{{Cite journal |last=Begun |first=David R. |date=2010-10-21 |title=Miocene Hominids and the Origins of the African Apes and Humans |url=https://www.annualreviews.org/doi/10.1146/annurev.anthro.012809.105047 |journal=Annual Review of Anthropology |language=en |volume=39 |issue=1 |pages=67–84 |doi=10.1146/annurev.anthro.012809.105047 |issn=0084-6570 |doi-access=}}</ref> the oldest celestial objects are between 10 and 14 billion years old; it is clear that the other civilizations are incomparably older than the human civilization. Therefore, the knowledge of these civilizations must be greater than Earth's, and, he reasoned, they must surely be aware of what humans are doing.<ref name="Kardashev-1980" />

Kardashev believed it is probable that the present state of Earth's civilization is only one of the stages through which civilizations pass during their evolution. It is thus possible to define [[civilization]] on the basis of this universal characteristic, which allowed [[Aleksandr Lyapunov]] to define life as "a highly stable state of matter, which uses information encoded by the states of individual molecules to produce maintaining reactions", which Kardashev calls the "functional definition of civilization".<ref name="Kardashev-1980" /> He therefore suggests thinking of civilization as a "highly stable state of matter capable of acquiring, making abstract analysis of, and utilizing information to obtain qualitatively new information about its environment and about itself, to improve its capabilities of gathering new information for producing sustaining reactions."<ref name="Kardashev-1980" />

Civilization is therefore characterized by the quality of the [[information]] acquired by its operating program, and by the [[energy]] required to implement these functions. By "information about its environment and about itself", Kardashev specified that it is data about organic or inorganic nature, [[science]], [[technology]], [[economy]], [[culture]], [[The arts|arts]], etc. From this definition, he proposed a diagram representing the interactions between a civilization and its environment, and enumerated a number of scientific problems arising from these interactions with the information available in the Universe.<ref name="Kardashev-1980" />

From this definition, Kardashev drew three conclusions. The first postulated that because of the vast and unlimited set of activities required by scientific problems, the period during which civilizations must transmit and communicate is necessarily long, even unlimited. On the other hand, since our present development covers only a negligible fraction of this [[Interstellar communication|communication phase]], Kardashev hypothesized the high improbability that we will meet "brothers in intelligence" who are at the same stage of evolution as are we. After all, highly advanced civilizations know and use the [[Scientific law|laws of physics]] to a degree that we have yet to suspect. Kardashev asserted that "this last point should be taken into account in the research programs of extraterrestrial civilizations" and concluded that it is very likely that our present state is only one of the stages through which every civilization passes during its evolution.<ref name="Kardashev-1980" />

==== 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" />

=== Third publication (1985) ===

==== Discovering supercivilizations ====
In the article ''On the Inevitability and the Possible Structure of Supercivilizations'' published in 1985, Kardashev evokes the possible scenarios and the means of investigation available to humanity for the detection of [[Extraterrestrial hypothesis|hypothetical extraterrestrial supercivilizations]]. The Soviet astronomer reminds us that we search for these supercivilizations on the basis of our own development criteria, and that predictions are possible only for extraterrestrial worlds close to our technological level, the others being beyond our intellectual representation. Nevertheless, it seems useful to him to conceive models of supercivilizations based at the same time on imagination and on our present scientific knowledge. Since the [[Scientific law|laws of physics]] are immutable, even if new laws are discovered in the future, they will not abolish those already known.<ref name=Kardashev1985/>

According to Kardashev, theoretical models of supercivilizations must meet two basic assumptions. The first is that the range of supercivilization activities that obey the laws of physics is limited only by natural and scientific constraints, while the second is that the evolution of supercivilization activities cannot be interrupted or limited by intrinsic, inherent contingencies, such as large-scale social conflicts. For Kardashev, unlike other scientists, supercivilizations cannot self-destruct or retrogress. According to these principles, there must exist in space [[megastructure]]s of great size, emitting a lot of [[energy]] and [[information]], and existing for billions of years, while being compact enough to rapidly exchange large amounts of data between them.<ref name=Kardashev1985 /><ref name="Kardashev-1997"/>

A supercivilization would thus create a technological structure of cosmic dimensions. As an example, Kardashev cites [[Freeman Dyson]]'s megastructure, in the form of a [[Dyson sphere|sphere]] of several [[astronomical unit]]s in diameter. Other phenomena may indicate highly technological activities, such as artificially exploding stars or the changing of stellar [[orbit]]s to store mass and energy. [[Molecular cloud|Giant molecular clouds]] also hold great potential for [[Astronomical engineering|astroengineering]]. Kardashev even raises the possibility of a supercivilization reshaping the entire galaxy.<ref name=Kardashev1985 /><ref name="Kardashev-1997"/>

Then he evokes the theoretical and mathematical possibility of the existence of a megastructure in the form of a disk rotating on itself at a constant [[Angular frequency|angular velocity]]. According to him, the search for intelligent signals should be directed to the detection of such megastructures at the characteristic radiation (20 μm). [[Quasar]]s or galactic centers can be excellent candidates to testify to the existence of a supercivilization since they emit strong [[infrared]] radiation, which indicates a solid structure. The astronomer advises to look for these objects in a [[wavelength]] range from a few microns to a few millimeters. Large intelligent structures can also be detected by the fact that they screen or reflect the surrounding radiation.<ref name=Kardashev1985 />

==== Possible scenarios for the evolution of supercivilizations ====
{{See also|Potential cultural impact of extraterrestrial contact}}
Kardashev believes that it is very likely that a supercivilization has already detected and observed humanity through cosmic-sized telescopes. He discusses this in a 1997 article on the subject, entitled ''Radioastron – a Radio Telescope Much Greater than the Earth''.<ref name="Kardashev-1997-2">{{Cite journal |last=Kardashev |first=Nikolai S. |date=1997-12-01 |title=Radioastron – a Radio Telescope Much Greater than the Earth |url=https://doi.org/10.1023/A:1007937203880 |journal=Experimental Astronomy |language=en |volume=7 |issue=4 |pages=329–343 |doi=10.1023/A:1007937203880 |bibcode=1997ExA.....7..329K |issn=1572-9508 |s2cid=118639223}}</ref> For this supercivilization, the science of "cosmic ethnography" must be highly developed. However, the fact that [[Fermi paradox|no contact has been made so far]] could be explained by [[Zoo hypothesis|ethical considerations of these civilizations]]. Based on this principle, Kardashev sees only two possible evolutionary scenarios for a supercivilization: natural evolution and [[Potential cultural impact of extraterrestrial contact|evolution after contact with other extraterrestrial civilizations]]. He considers more likely the scenario based on contact between two civilizations highly developed technologically and culturally advanced civilizations; this scenario, which he calls the "Urbanization Hypothesis", would result in the regrouping and unification of several civilizations within a few compact regions of the [[Universe]].<ref name=Kardashev1985 />

Kardashev lists, in the form of investigative tools, six possible scenarios (summarized in a table at the end of his 1997 article)<ref name="Kardashev-1997-2" /> that explain the evolution of a civilization. Each of the scenarios corresponds to a [[probability]], one or more objects to be observed, an adapted procedure, and, finally the possible consequences for our civilization:<ref name=Kardashev1985 />

# The scenario of a large unification of civilizations over an extent of one to ten billion light-years with concentration in a certain region has a probability of 60%. These civilizations are to be searched for in the most powerful [[quasar]]s and in the [[galactic bulge]], at a radiation level higher than 10<sup>38</sup> watts, in the wavelengths from 10 μm to 1&nbsp;cm, as well as in the other regions of the spectrum. This is to detect megastructures or signals with a wavelength of 1.5&nbsp;mm<ref>{{Cite journal |last=Kardashev |first=Nikolai S. |date=1979 |title=Optimal wavelength region for communication with extraterrestrial intelligence: λ = 1.5 mm |url=https://www.nature.com/articles/278028a0 |journal=Nature |language=en |volume=278 |issue=5699 |pages=28–30 |bibcode=1979Natur.278...28K |doi=10.1038/278028a0 |issn=1476-4687 |s2cid=4341965}}</ref> and omnidirectional emission up to 21&nbsp;cm. In the event of contact, humanity would see progress in all areas of society in order to join this supercivilization; it is also expected that an [[Ethnography|ethnographic]] conservatory would be created on Earth.
# The scenario of a unification on the scale of the [[Open cluster|galactic cluster]] has only a 20% probability of realization. Kardashev advises to observe the [[Virgo Cluster|Virgo cluster]] (especially [[Messier 87|M87]]) and other clusters in a similar way as in the first scenario. The consequences for humanity are the same as in the first scenario.
# The scenario of a unification on the scale of galaxies has only a 10% probability. To confirm it, we must study the galactic centers, both of the [[Milky Way]] and of neighboring galaxies (such as [[Andromeda Galaxy|M31]], [[Triangulum Galaxy|M33]]), according to a procedure similar to that of the first scenario. The consequences for humanity are the same as in the first scenario.
# The scenario of a complete [[Space colonization|colonization of space]] has no probability of being realized according to Kardashev because if it were realizable then "they" would already be on Earth; yet this is not the case. However, in the case of a contact, the consequences on humanity are the same as in the first scenario.
# This scenario assumes that all civilizations would have destroyed themselves before any contact. Kardashev estimates the probability of this to be 10%. Humanity should be able to detect ancient megastructures in the vicinity of the [[List of nearest stars and brown dwarfs|nearest stars]]. As a result, no contact with humanity can take place.
# The last scenario suggests that we are the first or the only ones in the Universe. Kardashev estimates its probability at 10%. Only [[Astrobiology|exobiology]] can confirm or falsify such a scenario. We can imagine a potential [[First contact (science fiction)|contact]] in the distant future, and then the consequences would be similar to those of the other five scenarios.

=== Fourth publication (1997) ===
[[File:CMB Timeline75.jpg|alt=Color illustration. An object resembling a truncated trumpet has white spots on its surface.|thumb|upright=2|According to the [[Standard Model|standard model]] describing the [[Expansion of the universe|expansion of the Universe]] since the [[Big Bang]], there may be planets older than the Earth, capable of harboring supercivilizations.]]
In the article ''Cosmology and Civilizations'' published in 1997, Kardashev reiterates the need to carefully observe astronomical objects with strong radiation in order to detect supercivilizations. However, the discovery of a civilization at a stage of development similar to ours is unlikely. The existence of such supercivilizations is made possible by the fact that [[History of life|life on Earth]] is recent compared to the [[Age of the universe|age of the Universe]] (8 × 10<sup>9</sup> years before the [[Formation and evolution of the Solar System|formation of the Solar System]]). He then examines the conditions for the appearance of life on cosmological time scales. Assuming the rate of evolution of life on Earth and considering the age of the Universe, it is reasonable to assume that a civilization could have reached our level of technological development in 6 × 10<sup>9</sup> years. Such civilizations can be observed in nearby regions, since the farther away we observe, the younger the objects are. Recent discoveries of [[Gamma ray|sources of intense radiation]] deadly to life show that life could have flourished under cover for the time necessary for its appearance and maintenance. Another argument for the possibility of a very old supercivilization is that most of the objects that could be megastructures have not yet been discovered and mapped. In addition, 95% of the [[Dark matter|matter remains invisible]] or can only be inferred by the gravitational influence it produces.<ref name="Kardashev-1997">{{Cite journal |last=Kardashev |first=Nikolai S. |date=1997-03-01 |title=Cosmology and Civilizations |url=https://doi.org/10.1023/A:1000837427320 |journal=Astrophysics and Space Science |language=en |volume=252 |issue=1 |pages=25–40 |bibcode=1997Ap&SS.252...25K |doi=10.1023/A:1000837427320 |issn=1572-946X |s2cid=117792321}}</ref>

According to Kardashev, it is essential to focus our search tools on new objects radiating at a wavelength of a few microns to a few millimeters, and at a temperature of 3 to 300 [[Kelvin|K]], which is characteristic of large structures of solid matter.<ref>{{Cite journal |last=Lemarchand |first=Guillermo A. |date=1995 |title=Detectability of Extraterrestrial Technological Activities |url=http://www.coseti.org/lemarch1.htm |url-status=live |journal=SETIQuest |volume=1 |issue=1 |pages=3–13 |archive-url=https://web.archive.org/web/20230307020046/http://www.coseti.org/lemarch1.htm |archive-date=2023-03-07}}</ref> It would then be possible to detect structures belonging to Type&nbsp;II in our galaxy or in those nearby. Type&nbsp;III structures can also be observed at large cosmological distances. Kardashev recalls that a study was conducted on 3000 sources of the [[IRAS]] catalog from the four directions of the sky. Two temperature bands were targeted: from 110 to 120 K and from 280 to 290 K. The analysis showed that the 110–120 K sources are clustered in the [[Galactic plane]] and in its center. Kardashev explains that only more powerful observations in the [[infrared]] and [[Submillimetre astronomy|submillimeter]] range can reveal possible artificial sources of radiation. He then refers to projects that he has proposed, in particular that of putting into orbit a [[Cryogenics|cryogenic]] [[space telescope]] (the ''Millimetron Project'').<ref name="Kardashev-1997" /><ref>{{Cite journal |last1=Gromov |first1=V. |last2=Kardashev |first2=N. |date=2001 |title=Sensitivity evaluation of submillimeter interferometer Earth – space telescope Submillimetron |url=https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2001LIACo..36...99G&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf |url-status=live |journal=Liège International Astrophysical Colloquia |volume=36 |pages=99–102 |bibcode=2001LIACo..36...99G |archive-url=https://web.archive.org/web/20230807060637/https://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2001LIACo..36...99G&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf |archive-date=2023-08-07}}</ref>

According to Kardashev, these results, combined with those of other research on the age of certain cosmic objects, suggest that civilizations dating from 6 to 8 billion years ago may exist in our galaxy. It is likely that they have long since discovered our own civilization, a hypothesis that could answer the question posed by [[Enrico Fermi]] when he formulated his [[Fermi paradox|paradox]]: "Where are they?". Without the discovery of artificial sources, however, Shklovsky's theory that civilizations self-destruct as a result of large-scale social conflicts would be proven. Kardashev mentions another hypothesis that, in his opinion, is capable of explaining the dynamics of the supercivilizations: the "feedback effect" (theorized by [[Sebastian von Hoerner]] in 1975),<ref>{{Cite journal |last=von Hoerner |first=Sebastien |date=1975 |title=Population Explosion and Interstellar Expansion |url=https://library.nrao.edu/public/memos/spln/SPLN_76_20b.pdf |url-status=live |journal=Journal of the British Interplanetary Society |volume=28 |pages=691–712 |bibcode=1975JBIS...28..691V |archive-url=https://web.archive.org/web/20230807060637/https://library.nrao.edu/public/memos/spln/SPLN_76_20b.pdf |archive-date=2023-08-07}}</ref> which is based on the [[hypothesis]] that at a high technological level, civilizations tend to converge rather than to isolate themselves. The distance between supercivilizations could then be determined by half the time of the technological evolution of the oldest civilization, which would be about 3 to 4 billion years. On the other hand, this supercivilization may not have been present in our galaxy for a long time. Kardashev concludes by saying that since the [[Expansion of the universe|expansion of the Universe]] is infinite, the number and lifetime of such supercivilizations are also infinite.<ref name="Kardashev-1997" />