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CETI (Communication with Extraterrestrial Intelligence) is a branch of SETI research that focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. The best-known CETI experiment was the 1974 Arecibo message composed by Frank Drake and Carl Sagan.

CETI research has focused on four broad areas: mathematical languages, pictorial systems such as the Arecibo message, algorithmic communication systems (ACETI) and computational approaches to detecting and deciphering 'natural' language communication.


In the nineteenth century there were many books and articles about the possible inhabitants of other planets. Many people believed that intelligent beings might live on the Moon, Mars, and Venus; but since travel to other planets was not yet possible, some people suggested ways to signal the extraterrestrials even before radio was discovered.

Carl Friedrich Gauss suggested that a giant triangle and three squares, the Pythagoras, could be drawn on the Siberian tundra. The outlines of the shapes would have been ten-mile wide strips of pine forest, the interiors could be rye or wheat.
The Pythagoras.

Joseph Johann Littrow proposed using the Sahara as a blackboard. Giant trenches several hundred yards wide could delineate twenty-mile wide shapes. Then the trenches would be filled with water, and then enough kerosene could be poured on top of the water to burn for six hours. Using this method, a different signal could be sent every night.

Meanwhile, other astronomers were looking for signs of life on other planets. In 1822, Franz von Gruithuisen thought he saw a giant city and evidence of agriculture on the moon, but astronomers using more powerful instruments refuted his claims. Gruithuisen also believed he saw evidence of life on Venus. Ashen light had been observed on Venus, and he postulated that it was caused by a great fire festival put on by the inhabitants to celebrate their new emperor. Later he revised his position, stating that the Venusians could be burning their rainforest to make more farmland.

By the late 1800s, the possibility of life on the moon was put to rest. Astronomers at that time believed in the Kant-Laplace hypothesis, which stated that the farthest planets from the sun are the oldest--therefore Mars was more likely to have advanced civilizations than Venus. It was evident that Venus was perpetually shrouded in clouds, so the Venusians probably wouldn't be very good astronomers. Subsequent investigations focused on contacting Martians. In 1877 Giovanni Schiaparelli announced he had discovered "canali" ("channels" in Italian, and mistranslated as "canals") on Mars--this was followed by thirty years of Mars enthusiasm.

The inventor Charles Cros was convinced that pinpoints of light observed on Mars and Venus were the lights of large cities. He spent years of his life trying to get funding for a giant mirror with which to signal the Martians. The mirror would be focused on the martian desert, where the intense reflected sunlight could be used to burn figures into the martian sand.

Inventor Nikola Tesla mentioned many times during his career that he thought his inventions such as his Tesla coil, used in the role of a "resonant receiver", could communicate with other planets and even observed repetitive signals of what he believed were Extraterrestrial radio communications coming from Venus or Mars in 1899. However, these "signals" turned out to be terrestrial radiation.

Around 1900, The Guzman Prize was created; the first person to establish interplanetary communication would be awarded 100,000 francs under one stipulation: Mars was excluded because Madame Guzman thought communicating with Mars would be too easy to deserve a prize.

When the Martian canals proved illusory, it seemed that humans were alone in the solar system.

Mathematical and scientific languages


Published in 1953 by Lancelot Hogben describes a system for combining numbers and operators in a series of short and long pulses. In Hogben's system, short pulses represent numbers, while trains of long pulses represent symbols for addition, subtraction, etc.

Lincos (Lingua cosmica)

Lincos: Design of a Language for Cosmic Intercourse, published in 1960 by Hans Freudenthal, expands upon Astraglossa to create a general-purpose language derived from basic math and logic symbols.

Carl Sagan

The science fiction novel Contact by Carl Sagan explored in some depth how a message might be constructed to allow communication with an alien civilization, using the prime numbers as a starting point, followed by various universal principles and facts of mathematics and science. Sagan also wrote a non-fiction book on the subject.

Jack McDevitt

In his science fiction novel The Hercules Text, Jack McDevitt describes an extraterrestrial message based on powers of 2 as a starting point.

A language based on the fundamental facts of science

Published in 1992 by Carl Devito and Richard Oehrle, is similar in syntax to Astraglossa and Lincos but builds its vocabulary around known physical properties.

Pictorial messages

Pictorial communication systems seek to describe fundamental mathematical or physical concepts via simplified diagrams sent as bitmaps. These messages assume that the recipient has similar visual capabilities (weak assumption) and can understand basic math and geometry (strong assumption because both are prerequisites for building the optimal shape for a radio or optical telescope). A common critique of these systems is that they assume a shared understanding of special shapes, which may not be the case with a species with substantially different vision, and therefore a different way of interpreting visual information.

Pioneer probes

The two Pioneer plaques were launched on Pioneer 10 and Pioneer 11 in 1972 and 1973, depicting the location of the Earth in the galaxy and the solar system, and the form of the human body.

Voyager probes

Launched in 1977, the Voyager probes carried two golden records that were inscribed with diagrams depicting the human form, our solar system and its location. Also included were recordings of pictures and sounds from Earth.

The Arecibo message

The Arecibo message, transmitted in 1974, was a 1679 pixel image with 73 rows and 23 columns. It shows the numbers one through ten, the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus, the formulas for the sugars and bases in the nucleotides of DNA, the number of nucleotides in DNA, the double helix structure of DNA, a figure of a human being and its height, the population of Earth, a diagram of our solar system, and an image of the Arecibo telescope with its diameter.

Cosmic Call messages

The Cosmic Call messages consisted of few digital sections - "Rosetta Stone", copy of Arecibo Message, Bilingual Image Glossary, the Braastad message, as well as text, audio, video and other image files submitted for transmission by everyday people around the world. The "Rosetta Stone" was composed by Stephane Dumas and Yvan Dutil and represents a multi-page bitmap that builds a vocabulary of symbols representing numbers and mathematical operations. The message proceeds from basic math to progressively more complex concepts, including physical processes and objects (such as a hydrogen atom). The message is designed with noise resistant format and characters, which make it resistant to alteration by noise. These messages were transmitted in 1999 and 2003 from Evpatoria Planetary Radar under scientific guidance of Alexander L. Zaitsev. Richard Braastad coordinated the overall project.

Stars to which messages were sent, are the following:

Name Designation HD Constellation Date sent Arrival date Message
16 Cyg A HD 186408 Cygnus May 24 , 1999 November 2069 Cosmic Call 1
15 Sge HD 190406 Sagitta June 30 , 1999 February 2057 Cosmic Call 1
HD 178428 Sagitta June 30 , 1999 October 2067 Cosmic Call 1
Gl 777 HD 190360 Cygnus July 1 , 1999 April 2051 Cosmic Call 1
Hip 4872 Cassiopeia July 6 , 2003 April 2036 Cosmic Call 2
HD 245409 Orion July 6 , 2003 August 2040 Cosmic Call 2
55 Cnc HD 75732 Cancer July 6 , 2003 May 2044 Cosmic Call 2
HD 10307 Andromeda July 6 , 2003 September 2044 Cosmic Call 2
47 UMa HD 95128 Ursa Major July 6 , 2003 May 2049 Cosmic Call 2

Multi-modal messages

Teen-Age Message

The Teen-Age Message, composed by Russianmarker scientists (Zaitsev, Gindilis, Pshenichner, Filippova) and teens, was transmitted from the 70-m dish of Evpatoria Deep Space Center to six Sun-like stars on August 29 and September 3 and 4, 2001. The message consists of three parts:

Section 1 represents a coherent-sounding radio signal with slow Doppler wavelength tuning to imitate transmission from the Sun's center. This signal was transmitted in order to help extraterrestrials detect the TAM and diagnose the radio propagation effect of the interstellar medium.

Section 2 is analog information and represents musical melodies, performed on the Theremin. This electric musical instrument produces a quasi-monochromatic signal, which is easily detectable across interstellar distances. There were seven musical compositions in the 1st Theremin Concert for Aliens.

Section 3 represents a well-known Arecibo-like binary digital information: the logotype of the TAM, bilingual Russian and English Greeting to Aliens, and Image Glossary.

Stars to which the message was sent are the following:

Name HD designation Constellation Date sent Arrival date
197076 Delphinus August 29 , 2001 February 2070
47 UMa 95128 Ursa Major September 3 , 2001 July 2047
37 Gem 50692 Gemini September 3 , 2001 December 2057
126053 Virgo September 3 , 2001 January 2059
76151 Hydra September 4 , 2001 May 2057
193664 Draco September 4 , 2001 January 2059

Cosmic Call 2 (Cosmic Call 2003) message

The Cosmic Call-2 message contained text, images, video, music, the Dutil/Dumas message, a copy of the 1974 Arecibo message, BIG = Bilingual Image Glossary, the AI program Ella, and the Braastad message.

Algorithmic messages

Algorithmic communication systems are a relatively new field within CETI. In these systems, which build upon early work on mathematical languages, the sender describes a small set of math and logic symbols that form the basis for a rudimentary programming language that the recipient can run on a virtual machine. Algorithmic communication has a number of advantages over static pictorial and mathematical messages, including: localized communication (the recipient can probe and interact with the programs within a message, without transmitting a reply to the sender and then waiting years for a response), forward error correction (the message might contain algorithms that process data elsewhere in the message), and the ability to embed proxy agents within the message. In principle, a sophisticated program when run on a fast enough computing substrate, may exhibit complex behavior and perhaps intelligence.


CosmicOS, designed by Paul Fitzpatrick at MITmarker, describes a virtual machine that is derived from lambda calculus.

Logic Gate Matrices

Logic Gate Matrices (a.k.a. LGM), developed by Brian McConnell, describes a universal virtual machine that is constructed by connecting coordinates in an n-dimensional space via math and logic operations, for example: (1,0,0) <-- (OR="" (0,0,1)="" (0,0,2)).="" Using="" this="" method,="" one="" can="" describe="" an="" arbitrarily="" complex="" computing="" substrate="" as="" well="" the="" instructions="" to="" be="" executed="" on="" it.=""></-->

Natural Language Messages

This research focuses on the event that we receive a signal / message that is either not directed at us (eavesdropping) or one that is in its natural communicative form. To tackle this difficult but probable scenario, methods are being developed that will first detect if a signal has intelligent-like structure, categorize the type of structure detected and then decipher its content: from its physical level encoding and patterns to the parts-of-speech, which encode internal and external ontologies (Elliott, 2004; Elliott, Atwell & Whyte, 2001).

Primarily, this structure modeling focuses on the search for generic human and inter-species language universals to devise computational methods by which language can be discriminated from non-language and core structural syntactic elements of unknown languages can be detected (Elliott & Atwell, 2000). Aims of this research include: contributing to the understanding of language structure and the detection of intelligent language-like features in signals, to aid the search for extraterrestrial intelligence (Elliott, 2002a; Elliott 2002b).

The problem goal is therefore to separate language from non-language without dialogue, and learn something about the structure of language in the passing. The language may not be human (animals, aliens, computers...), the perceptual space can be unknown, and we cannot assume human language structure but must begin somewhere. We need to approach the language signal from a naive viewpoint, in effect, increasing our ignorance and assuming as little as possible (Elliott, Atwell & Whyte, 2000; Elliott, 2007).

CETI researchers

  • Frank Drake (SETI Institute): SETI pioneer, composed the Arecibo message with Carl Sagan
  • Dr John Elliott (SETI Research UK): research into developing strategies, which are based on receiving a 'natural' language message, that look at developing algorithms to detect if an ET signal has intelligent-like structure and if so, then how to decipher its content. Author of many papers in this area and a contributor to SETI's book on interstellar communication. Other contributions include message design and construction; member of: International Academy of Astronautics, SETI Permanent Study Group; International Task Group for the Post-detection identification of unknown radio signals.
  • Laurence Doyle (SETI Institute): studies animal communication, and has developed statistical measures of complexity in animal utterances as well as human language.
  • Stephane Dumas: developed Cosmic Call messages, as well as a general technique for generating 2-D symbols that remain recognizable even if corrupted by noise.
  • Yvan Dutil: developed Cosmic Call messages with Stephane Dumas.
  • Paul Fitzpatrick (MITmarker): developed CosmicOS system based on lambda calculus
  • Brian McConnell: developed framework for algorithmic communication systems (ACETI) from 2000-2002.
  • Marvin Minsky (MITmarker AI researcher): first proposed the idea of including algorithms within an interstellar message.
  • Carl Sagan (deceased): co-authored the Arecibo message, and was heavily involved in SETI throughout his life.
  • Douglas Vakoch (SETI Institute): studies CETI and has published numerous articles, as well as an upcoming book from MIT Press about interstellar communication.
  • Alexander Zaitsev (IRE, Russia): composed Teen Age Message with Boris Pshenichner, Lev Gindilis, Lilia Filippova, et al., composed Bilingual Image Glossary for Cosmic Call 2003 Message, Scientific Manager of transmitting from Evpatoria Planetary Radar the Cosmic Call 1999, the Teen Age Message 2001, and the Cosmic Call 2003.

See also


  1. .
  2. Ley, Willy. Rockets, Missiles, and Space Travel (revised). New York: The Viking Press (1958)
  3. Sagan, Carl. Communication with Extraterrestrial Intelligence. MIT Press, 1973, 428 pgs.
  4. Передача и поиски разумных сигналов во Вселенной

  • Braastad, Richard, The Extraterrestrial Sermons,
  • Dumas, Stepane. The 1999 and 2003 messages explained,
  • Dutil, Dumas, ACTIVE SETI PAGE,
  • Elliott, J. (2007) A Post-Detection Decipherment Matrix: Acta Astronautica, Journal of the International Academy of Astronautics Elsevier Science Ltd, England, AA2853.
  • Elliott, J. (2004) 'Unsupervised Discovery of Language Structure in Audio Signals, Proceedings of IASTED International Conference on Circuits, Signals and Systems, (CSS 2004), Clearwater Beach, Florida, USA
  • Elliott, J. (2002b) 'The filtration of inter-galactic objets trouvés and the identification of the Lingua ex Machina hierarchy', Proceedings of World Space Congress: The 53rd International Astronautical Congress, pp. IAA-02-IAA.9.2.10.
  • Elliott, J. (2002a) 'Detecting languageness', Proceedings of 6th World Multi-Conference on Systemics, Cybernetics and Informatics (SCI 2002), vol. IX, pp. 323-328.
  • Elliott, J, Atwell, E & Whyte, B. (2001) 'First stage identification of syntactic elements', An extraterrestrial signal in Proceedings of IAC '2001: the 52nd International Astronautical Congress, pp. IAA-01-IAA.9.2.07
  • Elliott, J and Atwell, E. (2000) 'Is anybody out there: the detection of intelligent and generic language-like features', Journal of the British Interplanetary Society, Vol. 53, pp. 13-22. ISSN: 0007-084X.
  • Elliott, J, Atwell, E & Whyte, B. (2000) 'Increasing our ignorance of language: identifying language structure in an unknown signal', in Daelemans, W (ed.) Proceedings of CoNLL-2000: International Conference on Computational Natural Language Learning, pp. 25-30 Association for Computational Linguistics
  • Martin, Martin C. 1991 SETI Puzzle, posted to sci.crypt, sci.astro,, rec.arts.sf-lovers and rec.puzzles.
  • Communication with Alien Intelligence, 1985, Marvin Minsky,
  • Devito, C. and Oerle, R. A Language Based on the Fundamental Facts of Science, Journal of the British Interplanetary Society, 1990, Vol 43, pp. 561-568
  • EllaZ Systems,
  • Freudenthal H 1960 Lincos: Design of a Language for Cosmic Intercourse. North-Holland, Amsterdam.
  • Hogben, Lancelot. Science in Authority. New York: W. W. Norton (1963)
  • Ley, Willy. Rockets, Missiles, and Space Travel (revised). New York: The Viking Press (1958)
  • McConnell, Brian S. 2001 Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations. O'Reilly, Cambridge, MA
  • McConnell, Brian S. 2002 Algorithmic Communication with ETI & Mixed Media Message Composition
  • McConnell, Brian S at al, 2006?, Between Worlds, SETI Institute/MIT Press
  • Minsky, Marvin, talk given at Communication With Extraterrestrial Intelligence (CETI), Proceedings of a conference held at the Byurakan Astrophysical Observatory, Yerevan, USSR, 5-11 September, 1971. Edited by Carl Sagan. Cambridge, MA: The Massachusetts Institute of Technology, 1973., p.ix
  • Morrison, P. "Interstellar Communication." Bulletin of the Philosophical Society of Washington, 16, 78 (1962). Reprinted in A. G. W. Cameron, ed., Interstellar Communication.
  • Team Encounter, Cosmic Call 2003,
  • Zaitsev, A. Teen-Age Message,
  • Zaitsev, A. Interstellar Radio Messages ( in English, in Russian)
  • Zaitsev, A. Messaging to Extraterrestrial Intelligence (METI), [110020]

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