Qualitative classification of extraterrestrial civilizations
Valentin D. Ivanov, Juan Carlos Beamin, Claudio Caceres, Dante Minniti
aa r X i v : . [ phy s i c s . pop - ph ] M a y Astronomy&Astrophysicsmanuscript no. class˙13 c (cid:13)
ESO 2020May 29, 2020
Qualitative classification of extraterrestrial civilizations
Valentin D. Ivanov , Juan Carlos Beam´ın , Claudio C´aceres , , and Dante Minniti , European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei M¨unchen, Germany N´ucleo de Astroqu´ımica y Astrof´ısica, Instituto de Ciencias Qu´ımicas Aplicadas, Facultad de Ingenier´ıa, Universidad Aut´onomade Chile, Av. Pedro de Vald´ıvia 425, Santiago, Chile Departamento de Ciencias F´ısicas, Facultad de Ciencias Exactas, Universidad Andr´es Bello, Av. Fernandez Concha 700, LasCondes, Santiago, Chile N´ucleo Milenio Formaci´on Planetaria – NPF, Universidad de Valpara´ıso, Av. Gran Breta˜na 1111, Playa Ancha, Casilla 5030,Valpara´ıso, Chile Vatican Observatory, V00120 Vatican City State, Italy 0000-0002-7064-099X!lsReceived 2 November 1002 / Accepted 7 January 3003
ABSTRACT
Context.
The interest towards searches for extraterrestrial civilizations (ETCs) was boosted in the recent decades by the discovery ofthousands of exoplanets.
Aims.
We turn to the classification of ETCs for new considerations that may help to design better strategies for ETCs searches.
Methods.
This study is based on analogies with our own biological, historical, technological and scientific development. We take abasic taxonomic approach to ETCs and investigate the implications of the new classification on ETCs’ evolution and observationalpatterns. Finally, we use as a counter-example to our qualitative classification the quantitative scheme of Kardashev and we considerits implications on the searches for ETCs.
Results.
We propose a classification based on the abilities of ETCs to modify their environment and to integrate with it: Class 0 usesthe environment as it is, Class 1 modifies the environment to fit its needs, Class 2 modifies itself to fit the environment and Class 3 ETCis fully integrated with the environment. Combined with the classical Kardashev’s scale our scheme forms a 2-dimensional schemefor interpreting the ETC properties.
Conclusions.
The new framework makes it obvious that the available energy is not an unique measure of ETCs’ progress, it maynot even correlate with how well that energy is used. The possibility for progress without increased energy consumption implies alower detectability, so in principle the existence of a Kardashev Type III ETC in the Milky Way can not be ruled out. This reasoningweakens the Fermi paradox, allowing for the existence of advanced, yet not energy hungry, low detectability ETCs. The integrationof ETCs with environment will make it impossible to tell apart technosignatures from natural phenomena. Therefore, the most likelyopportunity for SETI searches to find advanced ETCs is to look for beacons, specifically set up by them for young civilizationslike ours (if they would want to do that remains a matter of speculation). The other SETI window of opportunity is to search forETCs at technological level similar to ours. To rephrase the famous saying of Arthur Clarke, su ffi ciently advanced civilizations areindistinguishable from nature. Key words.
Extraterrestrial intelligence – Astrobiology – History and philosophy of astronomy
1. Introduction
At a fundamental level the search for extraterrestrial civiliza-tions (ETCs) is motivated by scientific curiosity. We wantto understand how intelligent life and intelligence arise andevolve, to compare biologies, histories and social structuresthat have developed completely independently from each other.Undoubtedly, there are potential risk from the contact with anETC (Neal 2014), but there are also indications that it may havea stimulating e ff ect on the humanity (Kwon & Bercovici 2017).On a long run, the transfer of new knowledge from fundamentalsciences to industry is likely to induce a fast economic growthand on pure psychological level we will have – for the first time –a truly external scale to measure ourselves and our achievementsup. However, all these promising prospects ultimately requirea successful search for extraterrestrial intelligence (SETI). TheSETI programs in the last half a century have been fruitless. Onepossibility is that the Universe is empty, but the commonly found Send o ff print requests to : V. Ivanov, e-mail: [email protected] ingredients of – at least our form of – life cast some doubts onthis hypothesis. Another option is that the ETCs are extremelyrare. Therefore, the success is just a matter of time and increasedsensitivity of the techniques we are already applying. Withoutlisting all the possibilities for the silentium universi , let us con-sider the possibility that our search strategies may be wrong.Indeed, some time ago Bradbury et al. (2011) pointed at somecaveats in our strategies: SETI mostly remains an e ff ort isolatedfrom the wider astronomical and astrobiological studies, and theSETI proponents refuse to adopt a broader multidisciplinary ap-proach and to consider important criticism.So far the dominant SETI approach, going back to Cocconi& Morrison (1959), relies (i) on the willingness of ETCs to bedetected or (ii) on their unwillingness or failure to control theirown energy waste (that we could detect). In the former case weare searching for radio beacons set up with the purpose to be vis-ible to other ETCs and in the latter – for the emission that wouldleak into space in the course of regular radio communications.The transfer of the searches to other ranges of the electromag-netic spectrum does not make a fundamental di ff erence (Fabian1977; Wright et al. 2014b).
1. D. Ivanov: Classification of extraterrestrial civilizations
Kardashev (1964) evaluated the feasibility of these ap-proaches in radio and as a by-product developed a quantitativescheme to measure the stage of an ETC’s advancement via thetotal amount of energy they have at their disposal. Undoubtedly,Kardashev’s classification is still useful for SETI because it helpsto define benchmark energy capabilities of the ETCs and fromthese to set up sensitivity requirements for the SETI equip-ment. However, recent years brought up some new considera-tions. For example, Benford et al. (2010b,a) argued about cost-optimized means of interstellar communication, and proposedsome strategies to that e ff ect (see more arguments for cost-saving in Davies & Wagner 2013). Kardashev (1964) had nottaken these into account. He implicitly makes the assumptionthat unlimited resources are available to the ETCs, allowingunconstrained growth of the energy production and consump-tion, at least up to galactic scale. Furthermore, the estimates ofKardashev are upper limits that give the maximum energy avail-able for interstellar communication for the given level of ETCdevelopment.Our historic and modern experience can hardly support un-constrained growth. Therefore, it is compelling to re-examinethe ETC classification as a guiding tool for SETI strategies,aiming to optimize them and to arrive to a new priority scalefor the di ff erent search methods. The next section reviews theKardashev’s classification and its implications. Section 3 de-scribes a new quantitative scale proposed here, and the finalSection 6 sumarizes this work.
2. Quantitative classification: Kardashev’s scale
Kardashev (1964) introduced a classification scheme for ETCsbased on the energy, available to them. This is a quantitative ap-proach, well-justified in the context of that study, aimed to deter-mine the technical feasibility of the communication between civ-ilizations. He considered an isotropic radio emission, and esti-mated that transmitting with a data rate of 3 × bits sec − at dis-tance of ∼ × erg s − ,comparable to the total solar luminosity.Kardashev (1964) concluded that the transmitting power isthe controlling parameter of the data rate and covered distance.This prompted him to build a classification of ETCs based on theenergy in their disposal: – Class I – an ETC in possession of all energy of its planet or ∼ × erg s − – Class II – an ETC in possession of all energy of its star or ∼ × erg s − – Class III – an ETC in possession of all energy of its galaxyor ∼ × erg s − The first Class is the easiest to comprehend, because it im-plies a technological level close to the present-day Earth’s. Thehumanity itself is approaching this level of energy consumption.Right now we are still limited mostly to the Earth’s fossil fueland atomic energy from some radioactive elements; the renew-able sources of energy are still underutilized, but their contribu-tion in the total energy budget of our civilization is increasing.The second Class is more hypothetical. Kardashev (1964)gives as an example the Dyson sphere (Dyson 1960). Such a structure is unstable against collapse, as pointed by many authors(e.g. Su ff ern 1977). This problem can be addressed without call-ing for speculative technology or physics by breaking the sphereinto a swarm of individual elements often called Dyson swarm.Each of these elements is not unlike the space habitats proposedby O’Neill & Kraus (1979), but they must be quite numerous toprovide a covering factor close to unity, so nearly the entire en-ergy of the star is captured – as required by the definition of theClass II ETC.Dyson (1960); Kardashev (1964); Sagan & Walker (1966)realized that the most prominent signature of both the ETCs’energy metabolism and of the Dyson sphere would be the in-frared (IR) radiation and a number of searches for stars withIR excesses have been carried out since, mainly at stars onthe main sequence that are long-lived and are not expected toshow IR excess, all with negative results (Slysh 1985; Tilgner &Heinrichsen 1998; Timofeev et al. 2000; Jugaku & Nishimura2004; Carrigan 2009; Wright et al. 2014b; Gri ffi th et al. 2015;Osmanov 2016). Searches in the optical have also been consid-ered by Osmanov & Berezhiani (2018) who predicted anoma-lous variability of the sphere’s structure due to oscillations.Zackrisson et al. (2018) argued that a Dyson sphere with acovering factors less than unity can be recognized as a sub-luminous source, as long as an accurate parallax measurementis available. They searched for such object combining the Gaia
Data Release 1 (Gaia Collaboration et al. 2016) with the RadialVelocity Experiment (RAVE; Kunder et al. 2017) and found afew stars with lower intrinsic luminosity than expected for theirspectral Class and with no detectable IR excess. However, alter-native explanations such as unseen companions that might com-promise the astrometric solutions or gray dust can not be fullyexcluded.The last Class in the Kardashev’s classification is the mostspeculative and our current technology gives little clues how anETC could capture and utilize the energy of an entire galaxy.One option is a simple quantitative expansion of Class II ETCs,populating a galaxy with multiple Dyson spheres, whose totalnumber is comparable to that of the stars in the galaxy. Similarlyto the sphere-enshrouded stars, the galaxy will become fainterand redder and move away from the usual scaling relations suchas the Tully-Fisher relation. Following this argument, Zackrissonet al. (2015) set an upper limit of ≤ ffi th et al. (2015)searched for ETCs with large energy supplies, mostly by meansof the Wide-field Infrared Survey Explorer (WISE; Wright et al.2010). They identified some unusual objects, none of them fullymatches the expected signatures of Class III ETCs. The authorsconverted the obtained observational limits into limits on theETCs’ energy supply. Other teams also failed to detect Class IIIETCs (Annis 1999; Garrett 2015; Olson 2017)A possible explanation for the lack of detections is suggestedby Lacki (2019), who investigated the observational conse-quences if only a fraction of the stars is enshrouded. Presumablyit is easier to build Dyson spheres around low-mass stars thanaround hot high-mass stars for which the habitability zone is fur-ther out. The model predicts no detectable e ff ects if the limit isclose to the Solar Class stars; it must be raised up to ∼
30 L
S un tomake the presence of Dyson spheres apparent.Lacki (2016) considers an alternative to the classical Dysonspheres – enshrouding the entire galaxies with artificial dust thatwould turn them e ff ectively into black boxes, bright only in themicrowave spectral region. He searched the Planck
Catalog of
2. D. Ivanov: Classification of extraterrestrial civilizations
Compact Sources (Planck Collaboration et al. 2016), with nega-tive result.Although the last two Class are purely hypothetical, theKardashev’s classification gained foothold in the ETC studiesbecause of its convenience and the straightforward quantitativeparameterisation. In his excellent review, ´Cirkovi´c (2015) showswith multiple examples that the scale had a strong e ff ect on themany SETI searches over the last five decades, on the strate-gies that these projects have adopted, and on the interpretationof their results.
3. Qualitative classification of ETCs
The main motivation to re-examine the existing ETC classifi-cation is the question how a hypothetical ETC would use theavailable energy beyond the somewhat brute force approach ofemitting it in space or blowing things up and building artificialspace habitats. In practical terms, we propose to measure thisquality of use as the level of interaction with the Universe.We can turn to the humanity’s own scientific and technolog-ical progress, to trace the capabilities to manipulate matter: me-chanical – chemical – atomic – nuclear – etc. One can only spec-ulate what the next levels will be – Adams & Laughlin (1997)mention the annihilation of CDM particles as a possibility. Thisis similar to the ETC classification scheme of Barrow (1999),who uses as metrics the level of manipulation of the microworld.However, we can generalize further, combining these interac-tions into a single process – of modifying our environment. Thehumanity entered this stage the moment the first tool was used.From this prospective the next step will be to start modify-ing ourselves, to match the environment. The modern medicineis on the verge of this transition – from curing organisms to up-grading them. It is one step form the gene therapies that pre-vent a fetus from developing some dangerous diseases to im-proving it. Indeed, the CRISPR-Cas9 (clustered regularly inter-spaced short palindromic repeats) technique for gene editing hasrecently been improved to allow simultaneous editing of multi-ple genes (Jinek et al. 2012; Strecker et al. 2019; Camps et al.2019), bringing both medical and commercial applications ofgene therapies within closer reach.Is modifying ourselves an improvement over modifying theenvironment? – Yes, for a number of reasons. First, because we,as a product of semi-random evolution, are far from optimal forall the environments, even here on the Earth. We have evolvedfor a short life in small groups, in the savannah. As a result, ourbrains have insu ffi cient computing capabilities for the modernlife when we have to complete complex tasks that require func-tioning within large diverse groups. One of the unfortunate con-sequences is that resort to typecasting – a major reason for theproblems we face with various biases in the connected globalvillage of today (Kahneman 2011, and the references therein).Vast areas of Earth’s surface near the poles and the oceans aremarginally accessible to us.Next, our bodies wear out quickly and by age of 50-60 westart facing problems with such basic components as bones, vi-sion and hearing. As of 2011 about 0.2-0.3% of people needhip joint replacement and 0.1-0.2% – knee replacement at somepoint of their lives (Wengler et al. 2014), and those numbers areincreasing (Kremers et al. 2015). In some countries eight in tenpeople wear glasses by age of 20 and the fraction has been risingfor ages, correlating with reading and education (Williams et al.2015; Morgana et al. 2018). These are just a few easy problems,we are not discussing here the most serious ones such as cancerand various genetic disorders. A major argument for improving ourselves is to boost ouradaptability – an important advantage in a world of nearly infi-nite environmental variety. We can not tolerate the entire rangeof temperatures and pressures without major protection mea-sures even on our home planet, let alone live on any of the otherplanets in the solar System or potentially – on any exoplanet.Last but not least, adopting the strategy to modify ourselvesremoves the need to achieve consensus about how the environ-ment could be changed and our civilization has a remarkablypoor record on agreement, as the two world wars in the last cen-tury demonstrate.We can bracket these two stages of ETC evolution. At thelow-end, we extent of the term civilization to include wild ani-mals that generally use the environment as it is. However, this isnot always the case. First, in a broad sense any animal modifiesthe environment – e.g. just because of its metabolism, and sec-ond, there are well known examples of animal tool use (Goodall1964; Van Lawick-Goodall 1971; McGrew 1974, among others)which underlines the point that the new classes that we are aboutto introduce are not discrete bins but represent a part of a contin-uous sequence.At the high-end side we speculate that the boundary betweenthe environment and one’s self would eventually be diluted inthe process of self-improvement to the point of merging the two.This is a natural consequence if we assume that the ultimate goalof the intelligence is to spread, which in more speculative termsmay imply converting all the matter in the Universe into think-ing matter (but see Sandberg et al. 2017, for a reasoning whyan advanced civilization may prefer to stay dormant during thepresent cosmological era).To underline, we use here the level of interactions with mat-ter and the degree of integration of ourselves with the environ-ment as near synonymous, because the latter follows from theformer: historically, once our technological capabilities allowedit, we tried to modify the environment, e.g. moving from naturalcaves to purpose build housing; we are already willing to acceptmodifying our kind as long as it is seen as upgrading, even if it isethically questionable – the tendency for selective abortions offemale fetuses in East Asia proves it (Hesketh et al. 2011).Summarizing, we propose a new ETC classification scheme,containing the following three categories: – Class 0 : the environment is used as is (animals) – Class 1 : we modify the environment (clothes, buildings) – Class 2 : we modify ourselves to fit the environment (geneti-cally improved humans) – Class 3 : we merge with the environment, converting the deadmatter in the Universe into thinking matterThroughout this paper we denote the new classes with Arabicnumerals, including fractional classes such as 0.5, 1.3, 2.8, etc.For clear separation for the Kardashev classes we use Romannumerals, although there are strong arguments for fractionalKardashev classes as well (see the discussion in ´Cirkovi´c 2015).The proposed new ETC scale is less strict than the classicalKardashev’s scale, as the example given above of tool use byanimals suggests. Furthermore, some of the modifications to theenvironment that we apply right now can also be interpreted asmodifications of ourselves – although this example is far fromthe genetic manipulations mentioned earlier, a hand watch and apair of binoculars are modifications of the environment, but theycan also be though of as removable implants aimed to improvethe internal time keeping and the eyesight of average humans.However, the eye glasses or lenses despite being removable im-
3. D. Ivanov: Classification of extraterrestrial civilizations plants, aim to cure a disease, not to advance our capabilities andtherefore are not indications of self-upgrade.Some notions of the ideas proposed here can be found inthe works of Kecskes (1998, 2013) who considered a classifi-cation scheme adding to the energy resources the complexity ofETCs’ transport, communication and other resources. In anotherrelevant work Nunn et al. (2014) considered the historic path ofthe humanity and concludes that it may have reached the pointof creating an environmental utopia that removes the stimuli foroptimal health, but stops short of asking the question what is thenext step after that utopia – a question that we address with ourETC classification scheme.The two classifications – Kardashev’s and the new one wepropose – can be combined to form a single 2-dimensionalscheme that describes the ETC’s progress with two parameters:the quantity of the available energy and the quality of its use.Figure1 demonstrates this scheme with a few examples. Theapproximate locations of the humanity throughout history areshown on the upper panel: the first tool-making illustrates themastering of the mechanical energy, the discovering of fire – thewidespread use of chemical energy, and our present day stateis characterized by use of atomic energy and an incomplete useof the entire energy available on our planet. Dyson sphere build-ing civilization and a conventional pan-galactic supercivilization(e.g. one that expands though its home-galaxy by means of mul-tiple Dyson spheres) are also shown. Presumably, the two lastexamples have not achieved the level of self-modification thatcharacterizes our Class 3 ETC; we describe such civilizationswith the word terraforming with quotation marks to underlineour wider interpretation: adjusting the environmental conditionto ones needs in general, not necessarily on a planetary surface.The bottom panel shows the Earth animals, with an o ff setfrom the pure Class 0 to account for the tool usage, e.g. bychimpanzees. The present-day humanity spans the regions ofusing and modifying the environment, but stops short of theself-modifications. Barring major catastrophic events, we willprobably reach that level of technology in the foreseeable future.Again, we mark the loci of Dyson sphere builders and terraform-ing pan-galactic supercivilization, and we add a hypothetical civ-ilization that has converted its host galaxy into a computationalenvironments – the heat losses of such ETCs can potentiallybe detected by the WISE searches (e.g., Wright et al. 2014a,among others). The largest, all encompassing class of civiliza-tions is that of the adaptable, self-modifying ones. Changing theparadigm from physical change of environment to biological oreven post-biological modification and optimization of the livingorganisms changes the energy requirements. Indeed, the biolog-ical or computational research do not pose high energy demand.Our framework opens up a particularly interesting possibility –a self-modifying civilization that does not need vast amounts ofenergy because it is fully adaptable to the environment.
4. Implications for our notion of ETCs
The new classification proposed here is deeply rooted on hu-manity’s own evolution and may be biased in ways that can notbe evaluated as long as we only know of one intelligent species– our own. Therefore, we assume that the lessons we learn fromthe humanity’s evolution and history are – at least to some degree– typical for at least some ETCs. The most obvious advantage ofour scheme is the novel way of thinking about the ETC: we ac-knowledge that the parametric space that SETI searches need tocover can not be described with a single parameter as Kardashev(1964) proposed. We introduce the question of how the available
Level of interaction with matter T o t a l a v a il a b l e e n e r g y MechanicalChemicalAtomic . . . Sub-quark? . . . . . . ETC mergingwith matter?Class IClass IIClass IIIpresent-daydiscovering firefirst tool-making H u m a n i t y Dyson sphere builders"Terraforming" pan-galactic supercivilizationIntegration with the environment T o t a l a v a il a b l e e n e r g y Class 0: useenvironmentas it is Class 1:modifyenvironment Class 2:modifythemselves Class 3:merge withenvironment Class IClass IIClass IIISelf-adapting pan-galacticbiological civilizationNot-energy-hungrypan-galactic "invisible"civilization"Computational" galaxyAnimalsHumanityDyson sphere builders"Terraforming" pan-galactic civilization
Fig. 1.
Two-dimensional classification of the ETCs.
Top:
Thehorizontal axis expresses the capabilities of an ETC to interactwith its environment. The vertical axis quantifies the amount ofenergy available to them, as defined by the classical Kardashev’sscale.
Bottom:
Generalized two-dimensional classification. Thehorizontal axis shows the level of integration with the environ-ment. The approximate locations of the humanity throughouthistory and of a few hypothetical civilizations are shown andlabeled. For details see Sec. 3.energy is used and what is its impact on the interaction with thematter in the Universe.First, our classification scheme address in a new way theimportant question of detectability – the ultimate strength ofKardashev’s work that was developed exactly to address this is-sue in the particular context of radio communications. Recently,Lingam & Loeb (2019) concluded that the probability of de-tecting advanced ETCs’ technosignatures may be two ordersof magnitude lower than of detecting biosignatures from prim-itive life. It is worth to remember that all SETI projects haveexplored an exceptionally low fraction of the Milky Way para-metric space that can be inhabited by ETCs – only 10 − –10 − (Wright et al. 2018). The realization that the footprint of an ETCand its detectability – both dominated mainly by the energy –may not scale up with the available energy, makes this estimateoptimistic.
4. D. Ivanov: Classification of extraterrestrial civilizations
Another point, underlined by the new framework is that thetwo classifications – Kardashev’s and the one proposed here –are not directly correlated. In other words, the available amountof energy does not necessarily mean a more sophisticated inter-action with matter and closer integration with the environment.The Kardashev classes are separated by vast 11-12 orders ofmagnitude but the humanity – estimated to be using still onlyabout 70% of the energy at the disposal of a Class I civiliza-tion ( ´Cirkovi´c 2015) – does not seem too far from reaching theadequate biotechnological development to improve itself and tointegrate with the environment. This is easy to understand if wekeep in mind that the biological research is not as energy inten-sive as the nuclear physics, as pointed above.Furthermore, it is uncertain whether we can expect that moreavailable energy would only scale up our ability to modify theenvironment. In other words, we still lack the understandingwhether the building of a Dyson sphere is just a matter ofhaving more powerful mining equipment and heavier rocketsor of some speculative technologies like nano-machines, self-replicators, etc (see the discussion in Armstrong & Sandberg2013). In the former case the total amount of available energymay play a role, but in the latter – less so, hereby removing anycorrelation between the two ETC scales described here.These ideas are not entirely new among the SETI commu-nity. Indeed, the two-pointed arrow in his Fig. 1 of ´Cirkovi´c(2015) acknowledges the possibility, that the complexity is notdirectly related to the available energy.The third direct consequence from the broader considerationof ETCs’ properties proposed here is the invalidation of the ob-vious statement that a Class III ETC does not exist in the MilkyWay (Hart 1975). Our searches of such advanced ETCs rely onthe concept of detecting their heat leaks (e.g. Wright et al. 2014b;Gri ffi th et al. 2015), on the observational consequences from thecontrolled disintegration of galaxies for resources (Tipler 2003),or on searches for megastructures (Wright et al. 2016). The newclassification scheme allows for the existence of quiet advancedcivilizations that may co-exist with us, yet remain invisible toour radio, thermal or transit searches. The implicit underlyingassumption of Hart (1975) is that the hypothetical ETC is in-teracting with the matter on a similar level as us. We can noteven speculate if it is possible to detect a heat leak or a transitingstructure build by an ETC capable of interacting with the matterat sub-quark level, but the answer is more likely negative and notbecause that ETC would function according to some speculativephysics laws, but because such an ETC would probably be vastlymore e ffi cient than us controlling its energy wastes and minimiz-ing its construction projects. Would such an advanced ETC evenneed megastructures and vast astroengineering projects?It is also unlikely the on-going SETI project would success-fully detect the Kardashev Class II stellivorous ETC describedby Vidal (2016). Indeed, Heidmann & Klein (1991) noted that asuccessful SETI search requires a match between the technologyof the transmitting and receiving sides.These consideration cast some doubts on the popular pes-simistic conclusions about the lack of ETCs (e.g. Lacki 2016)(although some concerns for a Great Filter intrinsic to all civi-lizations appears to be still valid (e.g. Sotos 2019).Summarizing, the new framework leads to questioning thecommon assumption that progress is equivalent to ascending theladder of energy consumption from Class I to III, as suggestedby Dyson (1960) even before Kardashev came up with his clas-sification. Indeed, an ETC can – as our own history shows it– progress from purely mechanical modification of its environ- ment to more complex manipulation on chemical, atomic, nu-clear, etc. levels that allow it to achieve larger impacts and moreimportantly, impacts that were not possible earlier with the sim-pler levels of interaction. However, this is not necessarily ac-complished by an ever increasing energy consumption – the bio-sciences show it, and the opposite notion is probably a bias, dueto the fact that astronomers and physicists akin to Kardashev,Dyson and Sagan have been leading the SETI research, and theycome armed with the idea that progress is embodied by a morepowerful accelerator or radio transmitters.The final and the most important consequence from the newframework is the weakening of the Fermi Paradox (Hart 1975)– if ETCs’ progress does not always imply higher energy con-sumption and waste, then progress also does not imply higherdetectability of the ETCs. This explanation of the Fermi paradoxopposes the usual conclusion for the rarity of ETCs. In fact, theymay be common, but the low cross-section of ours and their levelof interaction with the Universe would account for the silentiumuniversi .
5. Predictions and implications for the SETIstrategies
The SETI programs search for ETC’s technosignatures – tracesof advanced technologies. On the other hand, the searches forlife at the crossing of the modern astronomical and biologicalresearch look for products form the natural life cycle (not neces-sarily advanced to the level of civilization, never mind how ill-defined this level may be; Des Marais et al. 2002; Seager et al.2005; Segura et al. 2005; Scalo et al. 2007). However, the dis-tinction between bio- and technosignatures may not be clear-cut.Raup (1992) considered hypothetical animals that communicatewith radio waves. Indeed, the electric squids and rays (e.g. Raup1992) use electricity, and direct electricity generation by bio-logical systems have been demonstrated Tanaka et al. (2016).Therefore, signatures we commonly consider part of the techno-logical realm, may actually evolve naturally. For simplificationwe will exclude this possibility from the following discussion,but we remind the reader that the most fundamental assumptionsof SETI are not simple and straightforward.What does this new ETC classification scheme mean forthe definition of future SETI projects? – Wittingly or not, thesearches so far have been fine-tuned to detect civilizations ofKardashev Types II and III, but only ones that follow the samemore-is-better philosophy as we do. The mechanistic transfer ofthis power hungry reasoning across a range of available energylevels wider than 25 orders of magnitude could be why thesesearches fail. The searches for Dyson spheres and swarms, al-though relatively easy with the present technology, also seemless than promising. Somewhat more productive strategy maybe to search for biosignatures, because that would accompanylife regardless from the technological development (Lingam &Loeb 2019). However, as discussed earlier, we can not fully relyeven on the biosignatures, because an advanced ETC can (pre-sumably) easily modify itself to survive beyond the limitationsof its original habitability limitations.The possibilities of self-modification and for further inte-gration of ETCs with their environment destroys the very ideaof separating natural and artificial phenomena and by definitionmakes it impossible for us to detect with confidence any tech-nosignatures, because – rephrasing A. C. Clarke – any advancedETC will be indistinguishable from nature. This idea of indistin-
5. D. Ivanov: Classification of extraterrestrial civilizations guishability has been discussed earlier in Cirkovic (2018) . Thisprocess of technological development and optimization is di ff er-ent from the natural evolution of techno-like signatures proposedby Raup (1992).Undoubtedly, these arguments would be well understood byETCs that have attained the levels of progress discussed here.Therefore, they would set up beacons to emit clearly artificialsignals – on the condition (addressing this major question is be-yond the scope of this work) that they still wish to communicatewith less advanced counterparts such as us.These arguments do not close the possibility to find ETCs atsimilar level to ours, but given the limited energy resources avail-able to those ETC, such SETI programs are limited to smallerspace volume that can be searched with any hopes for success.Concluding, the new framework implies two strategies forSETI: – Search for ETCs similar to us, for their radio radars and com-munications, for laser beacons and laser-powered interstellarprobes, etc. – Search for highly advanced ETCs (that have retained interestin their younger / simpler counterparts) for their energy e ffi -cient Benford beacons, rare / unstable element / isotope dopedstars and white dwarfs, modulated / coordinated variables, etc.
6. Summary and conclusions
A classification for ETCs based on their level of interaction andintegration with the environment is proposed. It can be combinedwith the classical Kardashev’s scale to form a 2-dimensionalscheme for interpreting the ETC properties. The new frame-work makes it obvious that the available energy is not an uniquemeasure of ETCs’ progress, it may not even correlate withthe quality of use of that energy. Furthermore, the possibilityfor progress without increased energy consumption implies alower detectability, so in principle the existence of a KardashevType III ETC in the Milky Way can not be excluded. This rea-soning weakens the Fermi paradox, allowing for the existence ofadvanced, but energy quiet ETCs.The integration of ETCs with environment will make it im-possible to tell apart the technosignatures from natural phenom-ena. Therefore, the only hope for future SETI searches to find ad-vanced ETCs is to look for beacons, intentionally set up by them,to be found by the backward civilizations like ours. It remains amatter of speculation if advanced ETCs would be interested tocommunicate with us. The other SETI window of opportunity isto search for ETCs at approximately our technological level.This new proposal is not a criticism of the Kardashev (1964).He carried out this work with the specific goal to estimatethe feasibility of interstellar radio communications and, natu-rally, it was used to evaluate the detectability of ETCs in radio.Undoubtedly, the Kardashev’s scale will continue to be impor-tant for defining the sensitivities of SETI searches that utilizethe strategies relying on communication leaks or communica-tion beacons.
Acknowledgements.
We thank the referees for the comments that helped to im-prove the paper and for pointing at the number of relevant works in the field ofbiology. We thank M.S. for the helpful discussions. D.M. acknowledges supportfrom the BASAL Center for Astrophysics and Associated Technologies (CATA)through grant AFB 170002, and Proyecto FONDECYT No. 1170121. CC ac-knowledges support from DGI-UNAB project DI-11-19 / R. The same idea can also be found in the 1971 essay
The NewCosmogony by Polish writer and philosopher Stanislaw Lem. It canbe found in the collection
A Perfect Vacuum (trans. by M. Kandel),Northwestern U. Press, 1999, pp. 197227.
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