TheKardashev scale (Russian:шкала Кардашёва,romanized: shkala Kardashyeva) is a method of measuring acivilization's level oftechnological advancement based on the amount ofenergy it is capable of harnessing and using. The measure was proposed bySoviet astronomerNikolai Kardashev in 1964,[1] and was named after him.
Kardashev first outlined his scale in a paper presented at the 1964 conference that communicated findings on BS-29-76,Byurakan Conference in theArmenian SSR, which he initiated, a scientific meeting that reviewed the Sovietradio astronomy space listening program. The paper was titled "Передача информации внеземными цивилизациями" ("Transmission of Information by Extraterrestrial Civilizations").[1] Starting from a functional definition of civilization, based on the immutability ofphysical laws and usinghuman civilization as a model forextrapolation, Kardashev's initial model was developed. He proposed a classification of civilizations into three types, based on theaxiom ofexponential growth:
Under this scale, the sum of human civilization does not reach Type I status, though it continues to approach it. Extensions of the scale have since been proposed, including a wider range of power levels (Types 0, IV, and V) and the use of metrics other than pure power, e.g.,computational growth orfood consumption.[2][3]
In a second article, entitled "Strategies of Searching for Extraterrestrial Intelligence", published in 1980, Kardashev wonders about the ability of a civilization, which he defines by its ability to access energy, to sustain itself, and to integrate information from its environment.[4] Two more articles followed: "On the Inevitability and the Possible Structure of Super Civilizations" and "Cosmology and Civilizations", published in 1985 and 1997, respectively;[5][6] the Soviet astronomer proposed ways to detect super civilizations and to direct theSETI (Search for Extra Terrestrial Intelligence) programs. A number of scientists have conducted searches for possible civilizations, but with no conclusive results.[7] However, in part thanks to such searches, unusual objects, now known to be eitherpulsars orquasars, were identified.[8]
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 entitledTransmission of Information by Extraterrestrial Civilizations, published in 1964 first in Russian in the March–April issue of theAstronomicheskii Zhurnal,[1] then in English in the September–October 1964 issue of the Soviet Astronomical Journal.[1] 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.[1][9]
Acivilization known as "Type 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 1012watts (W). A civilization known as "Type 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, Earth's homestar's "output" at that time, predicted at 4 × 1026 W. Finally, a civilization known as "Type 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 1011 stars in the Milky Way galaxy, which involves harnessing power of up to an estimated 4 x 1037 W.[1]
Assuming the development ofradio, Kardashev predicted that in the following two decades (i.e. in the 1980s) it would be possible to build antennas of 100,000 m2 capable of detecting Type II and III civilizations. A Type 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.[1][10]
Kardashev then examined the characteristics of a transmission from an artificial source. He mentioned the two cosmic radio sources discovered in 1963 by theCalifornia Institute of Technology, CTA-21 andCTA-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 II and III civilizations would then be theGalactic 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 theAndromeda Galaxy, theMagellanic Clouds,M87, orCentaurus A. Kardashev concluded his paper by noting that the possible discovery of even the simplest organisms onMars would increase the likelihood that Type II civilizations exist in the galaxy.[1]
In 1980, Nikolai Kardashev published a second article entitledStrategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem,[4] in which he stated that:
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.
— Nikolai Kardashev, Strategies of Searching for Extraterrestrial Intelligence: A Fundamental Approach to the Basic Problem
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; theSolar 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;[11] 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.[4]
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 definecivilization on the basis of this universal characteristic, which allowedAleksandr 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".[4] 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."[4]
Civilization is therefore characterized by the quality of theinformation acquired by its operating program, and by theenergy 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,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.[4]
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 thiscommunication 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 thelaws 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.[4]
Kardashev then analyzed various models and hypotheses of the evolution of civilization. Answering the question of the Russian astronomerIosif Shklovsky, who in an article published in 1977 entitledPossibility 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 wholeUniverse, 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, orblack holes for example).[4]
However, such civilization activities require the use of abundant energy. According to thelaws of thermodynamics, an important part of this consumed energy must be converted into radiation of abolometric magnitude approximately equal to that of the radiation background surrounding the source. The spectral distribution of this intensity must be close to that of ablack 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 ofelectromagnetic radiation.[4]
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 "terrestrialchauvinism", 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., theSETI program) would be to observe the most powerful (and often the most distant) sources of radiation in space.[4]
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 theelectromagnetic spectrum. These sources could be significant or periodicmonochromatic signals from thegalactic center, from other galaxies or fromquasars and other exotic cosmic objects.[4]
Kardashev believed that the search should focus on themillimeter wavelength spectrum, close to the maximum intensity of thecosmic microwave background, rather than in the21-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 amegastructure (such as aDyson sphere), a radio telescope with a diameter larger than that of the Earth would have to be placed in orbital space.[4]
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 theUniverse and its evolution over a period of several billion years.[4]
In the articleOn 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 ofhypothetical 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 thelaws of physics are immutable, even if new laws are discovered in the future, they will not abolish those already known.[5]
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 spacemegastructures of great size, emitting a lot ofenergy andinformation, and existing for billions of years, while being compact enough to rapidly exchange large amounts of data between them.[5][6]
A supercivilization would thus create a technological structure of cosmic dimensions. As an example, Kardashev citesFreeman Dyson's megastructure, in the form of asphere of severalastronomical units in diameter. Other phenomena may indicate highly technological activities, such as artificially exploding stars or the changing of stellarorbits to store mass and energy.Giant molecular clouds also hold great potential forastroengineering. Kardashev even raises the possibility of a supercivilization reshaping the entire galaxy.[5][6]
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 constantangular velocity. According to him, the search for intelligent signals should be directed to the detection of such megastructures at the characteristic radiation (20 μm).Quasars or galactic centers can be excellent candidates to testify to the existence of a supercivilization since they emit stronginfrared radiation, which indicates a solid structure. The astronomer advises to look for these objects in awavelength 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.[5]
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, entitledRadioastron – a Radio Telescope Much Greater than the Earth.[12] For this supercivilization, the science of "cosmic ethnography" must be highly developed. However, the fact thatno contact has been made so far could be explained byethical considerations of these civilizations. Based on this principle, Kardashev sees only two possible evolutionary scenarios for a supercivilization: natural evolution andevolution after contact with other extraterrestrial civilizations. He considers more likely the scenario based on contact between two 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 theUniverse.[5]
Kardashev lists, in the form of investigative tools, six possible scenarios (summarized in a table at the end of his 1997 article)[12] that explain the evolution of a civilization. Each of the scenarios corresponds to aprobability, one or more objects to be observed, an adapted procedure, and, finally the possible consequences for our civilization:[5]
In the articleCosmology 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 thatlife on Earth is recent compared to theage of the Universe (8 × 109 years before theformation 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 × 109 years. Such civilizations can be observed in nearby regions, since the farther away we observe, the younger the objects are. Recent discoveries ofsources 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 thematter remains invisible or can only be inferred by the gravitational influence it produces.[6]
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 300K, which is characteristic of large structures of solid matter.[14] It would then be possible to detect structures belonging to Type II in our galaxy or in those nearby. Type III structures can also be observed at large cosmological distances. Kardashev recalls that a study was conducted on 3000 sources of theIRAS 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 theGalactic plane and in its center. Kardashev explains that only more powerful observations in theinfrared andsubmillimeter range can reveal possible artificial sources of radiation. He then refers to projects that he has proposed, in particular that of putting into orbit acryogenicspace telescope (theMillimetron Project).[6][15]
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 byEnrico Fermi when he formulated hisparadox: "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 bySebastian von Hoerner in 1975),[16] which is based on thehypothesis 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 theexpansion of the Universe is infinite, the number and lifetime of such supercivilizations are also infinite.[6]
The hypothetical classification, known as the Kardashev scale, distinguishes three stages in the evolution of civilizations according to the dual criteria of access andenergy consumption.[17][18] The purpose of this classification is to guide the search for extraterrestrial civilizations, particularly withinSETI, in which Kardashev participated,[19] and this on the assumption that a fraction of the energy used by each type is intended for communication with other civilizations. To make this scale more understandable, Lemarchand compares the speed at which a volume of information equivalent to 100,000 average-sized books can be transmitted across the galaxy. A Type II civilization can send this data using a transmission beam that lasts for only 100 seconds. A similar amount of information can be sent acrossintergalactic distances of about ten million light years, with a transmission time of several weeks. A Type III civilization can send the same amount of data to the entireobservable universe with a transmission time of 3 seconds.[17][20]
Kardashev's classification is based on the assumption of a growth rate of 1% per year. Kardashev believed that it would take humanity 3,200 years to reach Type II, and 5,800 years to reach Type III.[2] However, Dr.Michio Kaku believes that humanity must increase its energy consumption by 3% per year to reach Type I in 100–200 years.[21] These types are thus separated from each other by a growth rate of several billion.[2]
A civilization "close to the level currently achieved on Earth, with an energy consumption of ≈4×1019 erg/sec" (4×1012 watts).[1] A Type I civilization is usually defined as one that can harness all the energy that reaches its home planet from its parent star (for Earth, this value is about 2×1017 watts), which is about fourorders of magnitude higher than the amount currently achieved on Earth, with an energy consumption of ≈2×1013 watts by 2020. The astronomer Guillermo A. Lemarchand defined Type I as a level close to today's terrestrial civilization, with an energy capacity equivalent to Earth'ssolar irradiance, between 1016 and 1017 watts.[22]
A civilization capable of harnessing the energy radiated by its own large star – for example, by successfully completing aDyson sphere orMatrioshka brain – with an energy consumption of ≈4×1033 erg/sec.[1] Lemarchand defined such civilizations as being able to harness and channel the entire radiation output of their star. The energy consumption would then be comparable to the luminosity of theSun, about 4×1033 erg/sec (4×1026 watts).[22]
A civilization with energy on the scale of its owngalaxy, with an energy consumption of ≈4×1044 erg/sec.[1] Lemarchand defined civilizations of this type as having access to energy comparable to the luminosity of the entireMilky Way galaxy, about 4×1044 erg/sec (4×1037 watts).[22]
In accordance with the data available at the time, Kardashev did not go beyond a Type III civilization. However, new types (0, IV, V, and VI) have been proposed.
In 1973,Carl Sagan discovered Kardashev's work on the classification of civilizations.[23] He found that the differences between the types Kardashev identified were so great that they did not allow for the best possible modeling of the evolution of civilizations.[10] Consequently, Sagan proposes a more refined classification, still based on Kardashev's types, but integrating intermediate levels using the followinglogarithmicinterpolation formula:[24]
,
whereK is the Kardashev type of a civilization andW is the amount of power it uses, in watts. Thus, aType 1.1 civilization would be defined by a power of 1017 watts, while aType 2.3 civilization would be able to harness 1029 watts.
Moreover, the above formula could be used to extrapolate beyond Kardashev's original types. For example, aType 0 civilization, not defined by Kardashev, would control about 1 MW of power (equivalent to having around 100 campfires burning at any given time); on Earth, the emergence of Type 0 civilizations is roughly concurrent with therise of civilization in a general sense.[25]
Sagan estimated that, according to this revised scale, 1970s humanity would be Type 0.7 (about 10terawatts),[26] equivalent to 0.16% of the power available on Earth.[27] This level is characterized, according to him, by the ability to self-destruct, which he calls "technological adolescence".[20] In 2021, the totalworld energy consumption was 595.15exajoules (165,319 TWh),[28] equivalent to an average power consumption of 18.87 TW or a Kardashev rating of 0.73.[note 1][29]
Sagan also suggests that, for completeness, an alphabetical scale should be added to indicate the level ofsocial development, expressed in the amount of information available to the civilization. Thus, a Class A civilization would be based on 106bits of information (less than any recorded human culture), a Class B on 107, a Class C on 108, and so on. Humanity in 1973 would belong to the "0.7 H" class.[30] According to Sagan, the first civilization with which humanity would come into contact could be between "1.5 J" and "1.8 K"; a galactic supercivilization would be at the "3 Q" stage, while a federation of galaxies could be at the "4 Z" stage.[20] The information and energy axes are not strictly interdependent, so even a level Z civilization would not have to be Kardashev Type III.[30] Sagan believed that no civilization had yet reached level Z, speculating that so much unique information would exceed that of all the intelligent species in agalactic supercluster, and observing that the universe is not old enough to exchange information effectively over large distances.
In 2017, the total amount of information generated on theinternet was26 zettabytes (with an estimated 120 zettabytes in 2023),[31] equivalent to 0.73 R/S on Sagan's combined scale.[note 1]
InPhysics of the Future (2011), American physicistMichio Kaku examines the conditions for humanity to converge on a Type I planetary civilization. This convergence is based primarily on theknowledge economy. Kaku uses the Kardashev scale, but develops it by adding an additional stage: a Type IV civilization would be able to draw the energy it needs fromextragalactic radiation. By studying the evolution of technologies that have changed history (paper, theintegrated circuit), Kaku believes that humanity is moving toward a civilization of planetary dimensions, the "starting point" of which is theInternet.[32]
A Type I civilization consumespower on the order of thousands to millions of times our current planetary output, about 100 trillion trillion watts. It would have enough energy to manipulate the occurrence of certain natural phenomena, such asearthquakes orvolcanoes, and could build cities on theoceans. We can see the beginnings of a Type I civilization in the fact that a global language is developing (English), a global communication system is emerging (theInternet), a global economic system is in the making (the establishment of theEuropean Union), and even a globalized culture is standardizing humanity (mass media,television,rock music, andHollywood movies).[2] To achieve Type I, humanity must be able to communicate with the rest of the world and to focus on several areas: buildinginfrastructure to facilitate communication and cooperation,education,research and development, andinnovation, as well as building strong ties betweendiasporas and their countries of origin, and between migrants and non-migrants.[32] If development fails, it is likely that the world will not be able to achieve Type II. If these areas do not develop, Kaku predicts that humanity will sink into the "abyss":[32] an advanced civilization must grow faster than the frequency of occurrence ofextinction-level cosmic catastrophes, such ascomet or asteroid impacts. A Type I civilization should also be able to masterspace travel to deflect threatening objects. It would also have to anticipate the onset ofice ages and modify the climate long before they occur to avoid them.[2]
In addition, in his booksHyperspace andParallel Worlds, Michio Kaku has discussed a Type IV civilization that could harness "extragalactic" energy sources such asdark energy.[33]
InEntering Space: Creating a Spacefaring Civilization,Robert Zubrin suggests another form: his definition of a Type I civilization is described as one that has achieved full mastery of the resources of its planet (global), a Type II of its solar system (interplanetary), and a Type III would have unleashed the full potential of the galaxy (starfaring civilization). Metrics other than pure energy consumption have also been proposed.[3]
He ponders the possibility of a Type IV civilization, one that would dominate the universe, noting that there are limits to how minds can connect and interact on a galactic or intergalactic basis. As an example, he mentions that communication from theGalactic Center of theMilky Way galaxy to its edge would take about 50,000 years (sincenothing can travel faster than light, according to our understanding of physics).[34][3]
The astronomerJohn D. Barrow of theUniversity of Sussex has hypothesized that there are other stages beyond Type III. These Type IV, V, or even VI civilizations would be able to manipulate cosmic structures (galaxies, galactic clusters, superclusters) and even escape theBig Crunch through holes in space.[2]
Barrow also proposes an "anti-Kardashev scale": he observes that humans have found it more cost effective to extend their ability to manipulate their environment to smaller and smaller scales rather than to larger and larger ones. He, therefore, proposes a reverse classification, from Type I-minus to Type Omega-minus:
In Impossibility: The Limits of Science and the Science of Limits (1998), Barrow proposes a scale ranging from "BI" to "BVI", with an ultimate stage he calls "BΩ", the former characterized by the possibility of manipulating one's environment, while the latter allows for the modification ofspacetime.[36]
Zoltan Galántai recognizes the important role that Kardashev's classification has played in the SETI program, but he believes that another scale is possible, without using energy consumption, by resorting to miniaturization. The hypothesis of Donald Tarter, researcher at SETI, is that a civilization based onnanotechnology would not need an ever-increasing amount of energy. A Type I civilization that masters local space travel could colonize its planetary system and even theOort cloud without needing an amount of energy that would make it Type II.[23] This scale loses its meaning beyond Type II, since it is impossible to predict the evolution of civilizations over long distances in a galactic colonization process. Finally, the Kardashev scale is the product of an era of insufficient scientific knowledge, which considered the possibility of stellar objectCTA-102 as an artificial Type III source, whereas today we know that it is agalactic nucleus.[23]
In another article, Zoltan Galántai suggests considering another scale, no longer based on energy consumption, but on a civilization's ability to survive natural and cosmic disasters. Type I would describe a civilization capable of surviving a local natural disaster, like theAnasazi. A Type II civilization would have the means to withstand a regional or continental disaster, and finally Type III could face a global disaster such as anasteroid's impact, asupervolcano's eruption, or anice age. Beyond the first three types are civilizations that have scattered throughout the galaxy. The Type IV civilization would still be vulnerable to some cosmic threats, while the Type V civilization would be technically immortal, as no cosmic catastrophe could reach it.[23] The Kardashev scale can be a relevant tool for preventing catastrophes, whether human or natural, according to Richard Wilson, who relates this scale to the power of destruction, inTNT. A Type I civilization would use 25megatons of equivalent TNT per second, a Type II civilization 4 × 109 times more (4 billion hydrogen bombs per second), while a Type III civilization would use 1011 times more.[27]
According to Carl Sagan, Type I should be reached around 2100.[32]
Physicist and futuristMichio Kaku has suggested that, if humans increase their energy consumption at an average rate of 3 percent per year, they could reach Type I status in 100–200 years, Type II status in a few thousand years, and Type III status in 100,000 to a million years.[37]
PhysicistFreeman Dyson has calculated that Type I should be reached in about 200 years,[38] while Richard Carrigan has estimated that the Earth is just four-tenths of the way to Type I on the Sagan scale. If Type I is reached soon (in the year 3000 forRichard Wilson),[39] it would be accompanied by profound social upheavals, but also by a significant risk of self-destruction.[39]
According to Per Calissendorff, energy consumption cannot be the main parameter to explain the transition from one type to another. Civilizations must have the means to maintain their growth rate despite climatic conditions and major natural disasters, even on the cosmic scale. A civilization moving towards Type II must have masteredspace travel,interplanetary communication, stellar engineering, andclimate. It must also have developed a planetary communication system, such as theInternet.[18] For Michio Kaku, the only serious threat to a Type II civilization would be the explosion of a nearbysupernova, while no known cosmic catastrophe would be capable of wiping out a Type III civilization.[2]
According toPhilip T. Metzger, humanity has reached Type I, but faces an energy challenge. In his 2011 paperNature's Way of Making Audacious Space Projects Viable, he states that the Earth'snon-renewable energy sources are nearly exhausted;natural gas will be depleted by 2020–2030,coal by 2035,uranium by 2056, whileoil production peaked in 2006–2008.[40]Nuclear energy cannot fully meet the world's energy needs (it represented only 6% in 2011). In addition, renewable energy cannot meet the growing demand for energy. Most of the minerals used by humans are in danger of becoming scarce; 11 minerals are already classified as having passed their peak production. For Metzger, humanity must therefore undertake a "100-year project" aimed at building a spacecraft ("100 Year Starship") capable of accessing the vast energy resources of theSolar System.[40] For Metzger, it is even probable that if extraterrestrials coveted the energy resources of our Solar System, they would not look for them on Earth, but on the variousasteroids andplanetoids.Robotics is the only way to access so many dispersed resources, and humanity should embark on a second long-term project, which Metzger calls the "robotsphere", that would begin with the energetic exploitation of theMoon (estimated at 2.3 × 1013J/year). This first step would make it possible to reach Type II in 53 years. Then the robotsphere (self-replicating andself-learning automated probes) would extend to the rest of the Solar System. Current advances inartificial intelligence suggest that the foundations of a robotsphere could be reached early in the next century, beginning in 2100. Metzger sees eight benefits for humanity in building the 100 Year Starship, including zero launch costs because the spacecraft will be built in space by robots that can do so with little human assistance (drastically reducing manufacturing costs), the creation of a Solar System-wide economy, and the use of resources from celestial objects and possiblyterraforming them.[40]
Viorel Badescu [ro] andRichard Cathcart have studied the possibility that a Type II civilization could use a 450 million kilometer device to directsolar radiation and thus be able to impart a kinetic motion to its star that deviates it from its usual trajectory by about 35 to 40parsecs,[41] allowing it, among other things, to capture itsenergy and navigate the galaxy.[42][41]
For Claude Semay, "a Type II civilization could be detected at great distances (by what is called "astro-technical leakage"),[verification needed] provided that it is not located in a region of the galaxy that is too distant from us, or that it does not occupy a location that is obscured from us by clouds of gas or dust".[43]
A Type III civilization should be detectable because of the large amount of radiation captured on a galaxy-wide scale. Calissendorff suggests using 75% of the total light emitted by a galaxy to determine that a Type III civilization uses manyDyson spheres. If only three or four of these spheres occupy the galaxy, it does not necessarily mean that the civilization has reached Type III, and it may still be in transition;[18] however, such civilizations may remain beyond the reach of our understanding and instruments. Sagan believes that the nearest Type III civilization is at an average distance of 10,000 light-years from us, but that it is not interested in classical radio transmissions, being of a different technological level. Only small, low-level civilizations could communicate with us.[26]
Semay observes that "a Type III civilization should not be confused with what science fiction writers call a 'galactic empire'", knowing that it can only exist ifinterstellar travel is achieved. Semay argues that there is no evidence that this will ever be possible.[43] Based on Dyson's calculations, Semay believes that such a journey would take three centuries, with an average distance between stars of about 7 light years. Overall, the speed of the colonization front, which ranges from 4 × 10−4 to 5 × 10−3 light-years per year, would result in humanity spreading throughout the galaxy in a period of 16 to 200 million years.[43] "A Type III civilization, having thus "domesticated" its galaxy by building a large number of Dyson spheres, would be detectable over intergalactic distances of several million light-years."[43]
A Type III civilization could theoretically live inside asupermassive black hole, in a stable periodic orbit, which would make it completely undetectable, according to V. I. Dokuchaev.[44]
Zoltan Galántai notes that neither Kardashev nor Sagan thought to extend the scale and define a Type IV (which would use the energy of an entire universe). They simply did not envision a civilization capable of manipulating its environment on the largest possible scale (about 14 billionparsecs).[10] The concept of a Type IV supercivilization approaches divine possibilities, enabling the creation of, and travel through,alternate universes of such a civilization's own design,[10] although the latter possibility is reserved for a Type V civilization by Carrigan.[24] The fraction of energy captured by a civilization capable of powering itself on a black hole could also be used to classify civilizations.[45]
According to Kardashev, the most important parameters to define the existence of a civilization are three: the presence of very powerful energy sources, the use of non-standard technologies, and the transmission of significant amounts of information of various kinds through space.[46]
Kardashev's classification is based on the hypothesis that an advanced civilization uses significant energy, which implies that it must be de facto detectable over long distances, as summarized by Zoltan Galántai.[23] For Kardashev, the limit of a civilization's energy consumption is originally located in the region of theelectromagnetic spectrum from 106 to 108 Hz, which allows two observations related tothermodynamics. First, all the energy consumed is inevitably converted into heat. Second, this energy can only be dissipated in the form of radiation scattered in space. These two findings are the pillars of Kardashev's theory that cosmic objects with strong radiation could be artificial sources.[46] He also considered the possibility of detecting an artificial source by emphasizing thespectral line ofhydrogen in its use fornuclear fusion.[47]
Dutil and Dumas consider several physical limits to continuous energy production, such asphotosynthesis (about 10TW), climate (about 127 TW), andsolar flux (174,000 TW). The only inexhaustible source of energy that can sustain a civilization for over several billion years, isdeuterium (used innuclear fusion).[48] The sustainability of a civilization must therefore involve "strict control of the exploitation of available resources"; this difficulty in exceeding energy limits may explain the fact that the vast majority of civilizations fail to engage in a space colonization project.[48]
Astrophysicist Makoto Inoue and economist Hiromitsu Yokoo have explored the possibility that a Type III civilization could extract energy from asupermassive black hole (SMBH). The captured energy could meet the extraordinary needs of a civilization that requires about 4 × 1044 erg/s.[45] The energy would be captured in the form of radiation emitted by the matter rushing into the star, by means of collectors located within theaccretion disk. These collectors are similar to Dyson spheres. The overflow, as well as the waste of the civilization, would be redirected towards the black hole. A fraction of this energy, directed as ahigh-powered beam, could be useful for space travel. A galactic club of civilizations could transmit the energy through networks within the galaxy. Within the various central power stations that make up the network, power transmission is periodically switched between transmitter and receiver, according to the galactic rotation. To be efficient, this network should be located at the center of the galaxy.[45]
This parameter is one of the most undetectable in the Universe due to the fact that solid matter structures are at low temperatures and emit weak radiation. Their luminosity, which is difficult to observe, also makes it impossible to observe them with telescopes. Likewise, we cannot detect them by theirgravitational effects.[46] However their existence can be detected by analyzingwavelengths between 8 and 13 microns, corresponding to surface temperatures of 300 K. A hypotheticalDyson sphere could thus be detected,[24] provided that the observation is made from space. Locally, the significant dip in luminosity that would result from a giant Dyson sphere (or "Fermi bubble") would allow the detection of a Type III civilization.[24]
Amegastructure like a Dyson sphere could be the result of a technology based onself-replicating probes, as those imagined byvon Neumann. A Type III civilization would have the means to disperse a significant number of these spheres throughout the galaxy, which would have the effect of attenuating the light emitted by the galaxy.[18] Kaku also considers this to be the most efficient method of colonizing space. For example, a galaxy 100,000 light years in diameter would be explored in half a million years.[2]Paul Davies has suggested that a civilization could colonize the galaxy by scattering miniature probes, no larger than the palm of a hand, usingnanotechnology. This thesis is realistic, he explains, because it is obvious that the technology is becoming increasingly miniaturized and proportionally less expensive.[2]
Type II megastructures would be easier to detect. This would be the case of aDyson sphere used as a "stellar engine",[49] as well as the contribution of heavy elements.[24] Similarly, "Shkadov thrusters", which would produce a lateral thrust of 4.4parsecs on their star by reflecting solar radiation through a structure made of mirrors, would be observable objects. This device would break the symmetry of solar radiation and counteractgravitational forces, allowing a Type II civilization to move its home solar system through space.[50][49] Drake and Shklovski have also considered the possibility of "seeding" a star (Stellar salting) by artificially adding extremely rare elements such astechnetium orpromethium. Such an intervention in a star's composition would be detectable.[24]
It is still possible that humanity could discover traces of lost Type I, II, or III civilizations. The search for material traces of such civilizations (e.g. Dyson spheres or stellar engines), an "interesting alternative" to the conventional SETI program, lays the foundation for a "cosmic archaeology" according to Richard A. Carrigan. Efforts to detect intelligence markers in the atmospheres ofexoplanets (such asfreon,oxygen, or evenozone, residues of biotic activity according toJames Lovelock's research)[24] are one of the most promising avenues. A civilization watching its star die (as ared giant, for example) could have tried to prolong its existence through megastructures that should be detectable.[24] The possible traces could be nuclear remnants, to be sought within thespectral types going fromA5 toF2 according to Whitmire and Wright.[51] It could also be a change in theisotopic ratio, due to a stellar engine, or an unusual spectral modulation in the composition of the star.[24]
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According to Kardashev, the transmissions of an extraterrestrial civilization (whatSERENDIP is looking for) can be divided into two types. On the one hand, there can be an exchange of information between highly developed civilizations or civilizations at similar stages of evolution. On the other hand, the transmission of information can be aimed at raising the level of other less developed civilizations. If supercivilizations do exist, the transmissions of the first type must remain inaccessible to our observation because they must be unidirectional and not be directed toward theSolar System. Conversely, those of the second type must be easily detectable by our listening devices.[46]
A signal of artificial origin should contain more than 10 and less than 100bits. The latter would be of two types: transient and stable. Several criteria allow us to distinguish a signal of artificial origin from others. First, the optimal region of the spectrum to host artificial signals is the one where the temperature of thecosmic microwave background is the lowest.[46] Second, artificial sources must have a minimum angular size. The presence of suspicious data in other regions of the spectrum (such ascircular polarization, radio and optical frequencies,[52] orX-ray emissions) can confirm that it is an intelligent transmission. Two sources among those studied have parameters close to those expected: 1934-63 and3C 273B.[46]
For L. M. Gindilis, there are two criteria for a signal to be called artificial: one related to the artificial nature of the source and the other related to a particular radiation, intentionally designed to ensure communication and facilitate detection.[53] Only Type II or III civilizations can communicate usingisotropic transmissions that allow omnidirectional reception. In a 1 MHz band (which requires about 1024 watts), detection of signals from a Type II civilization is possible up to 1,000light-years away, while signals from a Type III civilization are detectable virtually throughout theobservable Universe.[53] However, building an omnidirectional transmitter powerful enough to transmit over a range of 1,000 light years would take several million years. According to V.S. Troitsky, the energy required and the limitations in its production would be two obstacles to completing this project in a reasonable time.[54]
For Zoltan Galántai, we would not be able to distinguish between an intelligent extraterrestrial signal and a signal of natural origin. Therefore, he does not believe that Type II, III or even IV civilizations can be detected. Even if humanity reaches Type IV, it will not be able to detect another supercivilization of a similar level, and we will consider their changes in the universe to be the result of natural causes. Thus, there may be many Type IV civilizations in the universe, but none of them will be able to detect the others. Moreover, the dimensions of the universe make these supercivilizations like islands far from the others, which Dyson defines as a "Carroll Universe".[10]
For Alexander L. Zaitsev, the radio transmission of interstellar messages (IRM) is the most likely method used by civilizations. Planetaryradio telescopes and those installed onasteroids would make it possible to listen to the many messages that could be sent to us.[55] In 2007, theSETI program analyzed the only television frequencies sent by a Type 0 civilization, notesMichio Kaku. Therefore, our galaxy may have communications from Type II and III civilizations, but our listening devices can only detect Type 0 messages.[2]
From 1962, Kardashev was a member of aSETI research group at theSternberg Astronomical Institute in Moscow. In 1964, he organized the firstSoviet conference on the possibility of extraterrestrial civilizations, which was held at the Byurakan astrophysical observatory inArmenia.[56] This national conference was held in response to the American seminar known as theGreen Bank conference of 1961, which was held at theGreen Bank observatory in the United States.[57] It brought togetherradio astronomers with the aim of "finding rational technical and linguistic solutions to the problem of communication with an extraterrestrial civilization that is more advanced than the Earth's civilization". Kardashev presented his classification, while Troitskii announced that it was possible to detect signals from other galaxies.[58]
For Kardashev, "in the next 5 to 10 years, all the sources of radiation with the largest observable flux, in all the regions of theelectromagnetic spectrum, will have been discovered and studied", the sensitivity of the listening devices having indeed reached their technical limits. According to him, the entire electromagnetic spectrum will be known and, consequently, the list of the objects that could be artificial sources could thus be extended. The search for artificial signals will then have to concentrate on objects of maximumluminosity or radiation belonging to a certain region of the spectrum, but also on objects of significant mass, and on those that represent the essence of matter in the Universe. As early as 1971, Kardashev considered that this observation requires the preparation of a plan of listening and analysis, which will allow the success of the search for extraterrestrial civilizations. Humanity will then be able to solve the "main dilemma", as it was stated byEnrico Fermi.[46] This dilemma is, according to the Soviet astronomer, is certainly connected with our lack of information and knowledge.[46][59]
Kardashev believes that a research project likeOzma is incapable of detecting a Type I civilization (an idea also promoted by Kaplan in 1971),[60] and that SETI should instead focus on searching for intense radio signals that could emanate from active Type II or III civilizations.[23] To prove the effectiveness of this approach, Kardashev therefore turned his attention to two radio sources discovered by theCalifornia Institute of Technology, nicknamed CTA-21 andCTA-102. Subsequently, Gennadii Borisovich Sholomitskii then used the Russian astronomical research station to study the data from CTA-102.[57] He found that thisradio source is characterized by its variability. Kardashev then considered that this could be an indication of an artificial emission source, albeit of rather short life span.[56]
The knowledge of these hypothetical supercivilizations must fit into a wide range ofphysical laws that contain the entirety of our current knowledge, since the technical and scientific developments of mankind can be considered as an inevitable and necessary stage in the process of the evolution of acivilization. Based on this principle, Kardashev proposes to define several concepts applicable to extraterrestrial civilizations.[46] The physical laws, which are universal, can be used as a common basis for understanding other civilizations and, in particular, allow us to develop an objective research program.[46]Michio Kaku also believes that the evolution of civilizations obeys the "iron laws of physics" and in particular thelaws of thermodynamics, those of stable matter (baryonic matter) and those ofplanetary evolution (probability of occurrence of natural or cosmic catastrophes).[2] Theanthropic principle also makes it possible to predict the sociological characteristics at the basis of any civilization.[61]
However, these universal laws are not the only parameters to consider. Zoltan Galántai explains that "it is impossible to calculate the future of the Universe over long periods of time without including the effects of life and intelligence", a position close to that ofFreeman Dyson.[19] Taking into account these two phenomena, the universal physical laws and theintelligence resulting from life, defines a "physicaleschatology", as Galántai puts it. This approach began in the 1970s with the work of Kardashev, and then physical eschatology gradually interested a number of scientists and thinkers, notes Dyson.[19]
Observation of the development ofliving organisms shows that they are characterized by the tendency to store a maximum amount ofinformation, both about the environment and about themselves. This information then leads to an abstract analysis, which plays an important role in the development of life forms. Thus, Kardashev defines civilization from a functional perspective as "a state of very stable matter capable of acquiring, abstractly analyzing and applying information in order to extract data about the environment and itself, in order to develop survival reactions ".[46] However, thisfunctional definition of civilization implies that it cannot have agoal or end, since it is based on the principle of accumulating more and more information. Taking up von Hoerner's categories, Kardashev sees four possible scenarios for the development of civilizations:
However, he refuses to see these as inevitable ends. But the assumption that the only limit to the development of a civilization can be the existence of a finite amount of information, in all areas, is also false, since it is highly improbable that information in the Universe is infinite.[46] Given these twohypotheses, Kardashev argues that there is no universal civilization (supercivilization) because highly developed civilizations lose interest in space exploration. In any case, and despite the problem of the end of civilizations, he concludes, in the light of his functional definition of the advanced civilization, that the latter must use mass and energy on fantastic scales. According to him, there is no reason to denounce the hypothesis that theexpansion of the Universe would not be an effect of the intelligent activity of a supercivilization.[46]
Kardashev poses the following question: "Is it possible to describe the development of a civilization in general terms over large cosmological periods?" Now many of the fundamental parameters that characterize the development of civilization on Earth aregrowing exponentially. In the field of energy, astronomer Don Goldsmith estimated that the Earth receives about one billionth of the Sun's energy, and that humans use about one millionth of it.[2] So we consume about one millionth of a billionth of the Sun's total energy. Since human expansion is exponential, we can determine how long it will take for humanity to go from Type II to Type III according toMichio Kaku.[2]
Thus, the rate of development of our own world remains the only criterion forextrapolating the state of civilizations older than humanity.[46] The same is true for social values and basic needs according to Ashkenazi.[62] Therefore, the time to double technical knowledge is about ten years, and to double energy output, available reserves, and population is about 25 years. Two scenarios are then possible: spatial expansion or energy stagnation, the latter being possible only for 125 years, according to Kardashev, using the following relationship:
where is the number of years, is a parameter that increases annually as a function of and of according to and, a growth rate.
If, then humanity's energy consumption will exceed the incident solar power (1.742 × 1017W) after 240 years, the total power of theSun (3.826 × 1026W) after 800 years, and that of the Galaxy (7.29 × 1036W) after 1,500 years.[note 2][46] Based on this calculation, Zuckerman estimates the number of civilizations that could exist in ourgalaxy at 10,000.[63] Kardashev concludes that the current exponential growth is a transitional phase in the development of a civilization, and that it is inevitably limited by natural factors. In fact, he believes that the requiredmass andenergy will continue to grow exponentially for another 1,000 years.[46] Civilization is thus defined by an exponential rate of increase. Humanity as a model for thinking about the development of extraterrestrial civilizations has its limitations, which can be truly overcome by amultidisciplinary approach according to the work of Kathryn Denning.[64]
In 1963, Nikolai Kardashev and Gennady Borissovich Sholomitskii studied theCTA 102radio source on the 920 MHz band from theCrimea Deep Space Station, looking for signs of a Type III civilization.[65] CTA 102 had been discovered by Sholomitskii a year earlier, and Kardashev quickly saw it as a possible artificial source to study in order to validate his classification. The observation lasted until February 1965, and on April 12, Sholomitskii announced to the press (via the RussianITAR-TASS) that Soviet astronomers had discovered a signal that could be of extraterrestrial origin. On April 14, he gave a conference in Moscow where he repeated his announcement; but by November 1964, two American astronomers had identified CTA 102 as aquasar, and their publication definitively closed the "CTA 102 case".[66] It was the study of this source that had led to the Byurakan conference in 1964.[67]
In 1975 and 1976, the American astronomersFrank Drake andCarl Sagan searched atArecibo for signs of Type II civilizations in four galaxies of theLocal Group:M33,M49,Leo I andLeo II.[68][69] The year before, the two men had sentmankind's first message toM13.[70] The results were published as "The Search for Extraterrestrial Intelligence" inScientific American in May 1975.[71]
In 1976, Kardashev, Troitskii, and Gindilis used theRATAN-600 radio telescope in the North Caucasus to search for signals from Type II or III civilizations in theMilky Way and other nearby galaxies.[69] The radio telescope was built in 1966 under the supervision of Gindilis to listen at centimeter wavelengths.[67]
In 1987,Tarter, Kardashev, and Slysh used theVLA to detect possible infrared sources near the galactic center from theIRAS telescope catalog. All three were looking for evidence of hypotheticalDyson spheres. The objects turn out to beOH/IR type stars.[69][72]
A small-scale search for possible Type III sources was conducted by James Annis in 1999 and published in theJournal of the British Interplanetary Society under the title "Placing a limit on star-fed Kardashev type III civilizations".[73] An astrophysicist atFermilab (US), Annis studied a sample of 31 galaxies, bothspiral andelliptical, using theTully-Fisher diagram, in which theabsolute magnitude is a function of the galaxies' rotational speed. Annis suggested that 75% of the least luminous objects (i.e., those with a decrease in absolute magnitude of 1.5 compared to the diagram) could be considered as possible candidates. However, no object with this characteristic is observed in his survey.[18][43] On the other hand, Annis uses the available astronomical data to estimate the probability that a Type III civilization could exist. He shows that the average time that could allow for the emergence of such a civilization is 300 billion years, so none can exist in our present Universe.[74]
Per Calissendorff conducted a study on a sample of spiral galaxies from two databases: 4,861 from theSpiral Field I-band (SFI++ catalog compiled by Springob et al. in 2005) and 95 from that of Reyes et al. in 2011.[18] The same procedure was followed as in Annis, but the sample of galaxies used is 80 times larger than that used in the Annis study.[18] Some sources were classified as "lopsided": they appearasymmetric in shape, meaning that one side of thegalactic disc is more massive and less luminous than the other. This characteristic, according to Calissendorff, could be an indication that the galaxy is home to a civilization that has placed Dyson spheres in its main part. This can be explained by the fact that the colonization starts from one side of the galactic disk, making it appear darker and leading a distant observer to believe that the core has moved to that same side.[18] On the other hand, a galaxy hosting Dyson spheres should be characterized by a significant source of far-infrared radiation.[18] The fact remains that a Type III civilization can consume energy through a Dyson sphere without surrounding a star. Indeed, suchmegastructures could also extract energy from ablack hole, according to the study by Inoue and Yokoo (2011). However, such a structure would not reduce the luminosity of an observed galaxy.[18] Calissendorff's study concludes that 11 of the sources analyzed (out of a catalog of 2,411 galaxies, or 0.46%) show possible evidence of a Type III civilization. Searching for objects that obscure 90% of the light leaves only one source remains that meets the criteria.[18] These positive sources show a lowredshift (so they are old, about 100 million years), which is consistent with possible Type III civilizations, that could have flourished only in the early past.[18] To have a better chance of detecting Type III artificial sources, Calissendorff suggests taking several photographs in a row, fast enough to fix the movement of turbulence in the atmosphere, applying differentphotometric filters and looking for dark areas (the case of a Dyson sphere being assembled by a Type II civilization), or analyzing the infrared spectrum of galaxies. A much larger sample of objects should be studied.[18]
In 2015, a study of galactic mid-infrared emissions concluded that "Kardashev Type III civilizations are either very rare or do not exist in thelocal Universe".[75]
In 2016, Paul Gilster, author of the Centauri Dreams website, described a signal apparently coming from the starHD 164595 as requiring the power of a Type I or Type II civilization, if produced by extraterrestrial lifeforms.[76] In August 2016, however, it was discovered that the origin of the signal was most likely a military satellite orbiting the Earth.[77]
According to Kardashev, humanity's ignorance of the physical possibilities of communication through space is great.[46] Only a negligible fraction of theelectromagnetic spectrum as an existing source of information in the universe is known.[46] Thus, of the 89% of information that humans lack, 42% concerns the range from 109 to 1014 Hz (centimetric, millimetric, submillimetric and infrared waves) and 25% concerns the range from 1015 to 1018 Hz (ultraviolet radiation and X-rays).[46] Kardashev distinguishes two categories of listening areas: objects emitting in a broad frequency spectrum and objects emitting on the contrary in a narrowspectral line, the second category posing much more theoretical problems than the first, while being central, both forastrophysics and for the search for extraterrestrial civilizations.[46]
Despite advances in astrophysics, the available information is still insufficient to prove the absence of supercivilizations, based on the inability to observe signs of activity. However, because of the possibility that there areplanetary systems much older than the Solar System, and considering that cosmic objects such asquasars could be products of supercivilization activity, a detailed program of listening and searching for intelligent signs remains valid. This program includes:[46]
According to Kardashev, only aradio interferometer with a base, either of the order of or larger than the diameter of theEarth, placed in orbital space, would allow listening to centimetric and decimetric frequencies.[46] Once a set of unusual sources has been selected, the next step is to look for significant content in the radiations from these objects.[46] In 1998, Nikolai Kardashev, S. F. Likhachev, and V. I. Zhuravlev proposed twoSETI space projects to detect artificial sources: theMillimetron project (an orbiting observatory with a 10-meter diameter mirror) and theVLBI optical telescope (for interferometric synthesis of ultraviolet, optical, and infrared images).[78]
ForSamuil Aronovich Kaplan, "the most reliable criterion" remains the smallangular diameter of the radio source. Thewavelength of 21 cm, privileged since 1959, according to the study of Cocconi and Morrison, is not the only listening region. Kaplan, in 1971, also mentioned the radio region of the spectrum, characterized by thehydroxyl radical (OH). For Livio, the means of detection should focus onglobular clusters, the regions most likely to harbor planets similar to the Earth.[24]
For Guillermo A. Lemarchand, extraterrestrial civilizations should not use an omnidirectional transmitter. Instead, they should look for signals of weak information, intermittent and unidirectional. They will certainly need to useinterferometry to inspect planetary systems where life might appear. From Earth, it would be possible to pick up such signals at distances of up to35 + (t_f - 2000) / 2, wheret_f is the observation date in years, knowing thatt_f ≥ 2000.[20] However, there are many techniques for transmitting an interstellar message, ranging frombosons toparticles and evenantiparticles.[22]
An artificial source located in theaccretion disk of asupermassive black hole would be undetectable by the beams used to transmit the collected energy. In fact, the probability of detecting a beam of onemicronarc-second is less than 10−23. Moreover, the energy emitted by the black hole would not allow detection of the energy used by the Type III civilization. On the other hand, thespecular reflection system of the radiation could be detected by the shadow it casts on the accretion disk.[45]
A Type III civilization using a "Fermi bubble" would be detectable by the fact that it decreases the luminosity of a region of the galaxy. An infrared observation would make it possible to highlight it, especially inelliptical galaxies, Annis suggests.[24]
The quasar3C 9 is cited by Kardashev as early as 1971.[46] The study of the quasar3C 273 shows that it has a solid structure. Other quasars (3C 279,3C 345, 3C 84) have properties close to those expected from an artificial source, especially since the emissions are powerful in the intermediate region of the spectrum (between radio and optical frequencies).[46] Quasars are potential artificial sources, especially since their age corresponds to the technical possibilities of supercivilizations. Radio sources at the center of galaxies can also be artificial sources, according to Kardashev, even if in 2013 they were proven to be supermassive black holes. In 1971, Kardashev believed that the objects most likely to be artificial sources could be discovered in the [then] next few years.[46]
The extraordinary periodicity ofpulsar emissions was already considered an artificial source in 1968 byAntony Hewish, the discoverer of the first pulsar (CP 19019). The press of the time nicknamed this object "LGM-1" (for "little green men"), following the clumsiness of Hewish, who did not wait for the necessary verifications. Kaplan, in 1971, removed the pulsar from the list of objects that could be a source of artificial origin.[60]
In 2011, James and Dominic Benford examined the possibilities that exist to distinguish pulsars from possible artificial sources emitting intelligent signals, such as: bandwidth (signals of about 100 MHz could be artificial), pulse length (to reduce costs, the pulse should be short) and frequency (about 10 GHz, also for economic reasons). Theradio source PSR J1928+15 (observed in 2005 near the Galactic disk, at a frequency of 1.44 GHz, atArecibo) could be of extraterrestrial origin. James and Dominic Benford consider three scenarios in which the cost factor is taken into account. If the source is cost-optimized, it belongs to a civilization of Type 0.35 (the Earth being of Type 0.73).[note 1] If it is not cost-optimized and operates with a small antenna, the Type is 0.86. With a large antenna, it would be from a Type 0.66. Using this cost/efficiency method, it can be estimated that low-intensity sources may be the most prevalent, but also the most difficult to observe.[79]
William I. Newman andCarl Sagan believe that the growth of energy consumption alone cannot describe the evolution of civilizations; it is also necessary to considerpopulation growth, and in particular the fact that it can be limited by the transport capacity of interplanetary means of travel. They conclude that there can be no ancient civilizations of galactic dimensions, nor galactic empires, although the possibility of networks of colonized worlds (of about 5 to 10 planets) is strong.[80]
The scale theorized by Kardashev was born in the geopolitical context of theCold War, in which energy had supreme value.[27] According to Guillermo A. Lemarchand, a physicist at the University of Buenos Aires, there are four arguments against Kardashev's classification:[20]
For the British meteorologistLewis Fry Richardson, author of a statistical study on mortality (published inStatistics of Deadly Quarrels, 1960), man's aggressiveness does not allow us to predict alife span that will allow humanity to reach more evolved stages. He estimates that man's violentimpulses will destroy the social order over a period of 1000 years. Moreover, mankind will probably be destroyed withweapons of mass destruction within a few centuries at the most.[20]
PaleobiologistOlev Vinn has suggested that Kardashev’s idea may itself reflect a relatively crude phase of our technological development, rather than a universal principle. He points instead to the possibility of technological minimalism, in which highly advanced societies seek to maximize effectiveness while minimizing energy use. Rather than pursuing ever-increasing levels of power consumption, such civilizations might focus on optimization, efficiency, and extreme miniaturization. Mastery of quantum-scale engineering could allow them to perform complex functions using only negligible amounts of energy. A sufficiently advanced technological society might also choose to separate its technological systems from the surrounding environment. Viewed from interstellar distances, such a world could appear pristine—supporting a flourishing natural biosphere, with little or no visible trace of industry or artificial modification[82].
Transhumanists Paul Hughes and John Smart explain the absence of signals from a Type III civilization with two hypotheses: either it has self-destructed or it has not followed the trajectory described by Kardashev.[23] The growth of energy consumption should lead to a climate crisis, whichYvan Dutil andStéphane Dumas set at 1W/m2 of theEarth or 127TW for the entire planet. At a growth rate of 2% per year, an industrial civilization should stop growing quite early in its history (after a few centuries).[48] In summary, the impossibility of sustainably securing energy resources may explain the absence of Type II and III civilizations.[48]
For Zoltan Galántai, it is not possible to imagine a civilization project that spans centuries (like aDyson sphere) or even millions of years, unless one imagines a thought and anethic different from ours, within the reach of an ancestral civilization. He therefore proposes to classify civilizations according to their ability to carry out large-scale civilization projects over the long term.[23]
Finally, forFreeman Dyson, communication and life can continue forever in anopen Universe with a finite amount of energy; intelligence is therefore the only fundamental parameter for a civilization to survive in the very long term, and energy is then no longer what defines it, a thesis he develops in his article "Time Without End: Physics and Biology in an Open Universe".[83]
There are many historical examples of human civilization undergoing large-scale transitions, such as theIndustrial Revolution. The transitions between Kardashev scale levels could potentially represent similarly dramatic periods of social upheaval, as they involve exceeding the hard limits of the resources available within a civilization's existing territory. A common speculation[95] is that the transition from Type 0 to Type I could carry a strong risk of self-destruction, since in some scenarios there would be no room for further expansion on the civilization's home planet, as in aMalthusian catastrophe.
For example, excessive energy consumption without adequate heat removal could plausibly render the planet of a Type I approaching civilization unsuitable for the biology of thedominant life forms and their food sources. Using Earth as an example, ocean temperatures above 95 °F (35 °C) would endanger marine life and make it difficult, if not impossible, for mammals to cool to temperatures suitable for theirmetabolism. Of course, thesetheoretical speculations may not become problems, possibly through the application of futureengineering andtechnology. Also, by the time a civilization reaches Type I, it may have colonized other planets or establishedO'Neill-type colonies, so that waste heat could be distributed throughout the star system.
The limitations of biological life forms and the evolution of computer technology may lead to the transformation of the civilization throughmind uploading andartificial general intelligence in general during the transition from Type I to Type II, leading to adigitized civilization.
{{citation}}: CS1 maint: work parameter with ISBN (link)I would suggest Type 1.0 as a civilization using 1016 watts for interstellar communication; Type 1.1, 1017 watts; Type 1.2, 1018 watts, and so on. Our present civilization would be classed as something like Type 0.7.
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