Communication with extraterrestrial intelligence

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Communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence 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. There are multiple independent organizations and individuals engaged in CETI research; the abbreviations CETI and SETI alone should not be taken as referring to any particular organization (such as the SETI Institute).

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. There remain many undeciphered writing systems in human communication, such as Linear A, discovered by archeologists. Much of the research effort is directed at how to overcome similar problems of decipherment which arise in many scenarios of interplanetary communication.

On 13 February 2015, scientists (including David Grinspoon, Seth Shostak, and David Brin) at an annual meeting of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea.[1][2] That same week, a statement was released, signed by many in the SETI community, that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent".[3] On 28 March 2015, a related essay was written by Seth Shostak and published in the New York Times.[4]


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.[5]

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 would not be very good astronomers. Subsequent investigations focused on contacting Martians. In 1877 Giovanni Schiaparelli announced he had discovered "canali" ("channels" in Italian, which occur naturally, and mistranslated as "canals", which are artificial) 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[6][7] 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.[8]

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

Mathematical and scientific languages[edit]

Lincos (Lingua cosmica)[edit]

Published in 1960 by Hans Freudenthal, Lincos: Design of a Language for Cosmic Intercourse, expands upon Astraglossa to create a general-purpose language derived from basic mathematics and logic symbols.[9] Several researchers have further expanded upon Freudenthal's work. A Lincos-like dictionary was featured in the Carl Sagan novel Contact and film adaptation.


Published in 1963 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.[10]

Carl Sagan[edit]

In 1985, 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 edited a non-fiction book on the subject,[11] which has been updated in 2011.[12]

A language based on the fundamental facts of science[edit]

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.[13]

Busch general-purpose binary language used in Lone Signal transmissions[edit]

In 2010, Michael W. Busch created a general-purpose binary language[14] later used in the Lone Signal project[15] to transmit crowdsourced messages to extraterrestrial intelligence (METI). This was followed by an attempt to extend the syntax used in the Lone Signal hailing message to communicate in a way that, while neither mathematical nor strictly logical, was nonetheless understandable given the prior definition of terms and concepts in the Lone Signal hailing message.[16]

Name Designation Constellation Date sent Arrival date Message
Gliese 526 HD 119850 Boötes 2013-07-10July 10, 2013 2031 Lone Signal

Pictorial messages[edit]

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 mathematics 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. For instance, an arrow representing the movement of some object could be interpreted as a weapon firing.

Pioneer probes[edit]

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[edit]

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[edit]

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[edit]

The Cosmic Call messages consisted of a 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 mathematics 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:[17]

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[edit]

Teen-Age Message[edit]

Main article: Teen Age Message

The Teen-Age Message, composed by Russian scientists (Zaitsev, Gindilis, Pshenichner, Filippova) and teens, was transmitted from the 70-m dish of Yevpatoria 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 representing 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. The 14 minute analog transmission of the theremin concert would take almost 50 hours by digital means; see The First Musical Interstellar Radio Message.

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:[17]

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[edit]

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[edit]

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 mathematics 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,[citation needed] 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 MIT, describes a virtual machine that is derived from lambda calculus.

Logic Gate Matrices[edit]

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 mathematics 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 as the instructions to be executed on it.[clarification needed]

Natural language messages[edit]

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.[18][19]

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.[20] 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.[21][22]

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.[23][24]

SETI scientist Laurance Doyle explains that the slope of a line that represents individual tokens in a stream of tokens can indicate whether the stream contains linguistic or other structured content. If the line angles at 45°, the stream contains such content. If the line is flat, it does not.[25][26]

SETI researchers[edit]

  • 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.[18][19][20][21][22][23][24]
  • 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 (MIT): developed CosmicOS system based on lambda calculus
  • Brian McConnell: developed framework for algorithmic communication systems (ACETI) from 2000-2002.
  • Marvin Minsky (MIT AI researcher): Believes that aliens may think like humans because of shared constraints, permitting communication.[27] 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, Scientific consultant for A Message From Earth project.

[28] [29][30][31]

  • Michael W. Busch: (Lone Signal) created the binary encoding system for the ongoing Lone Signal hailing message.
  • Jacob Haqq Misra: (Lone Signal) is the Chief Science Officer for the ongoing Lone Signal active SETI project.

Connections with Interspecies Communication[edit]

John C. Lilly worked on teaching dolphins English (successful with rhythms, not with understandability, given their different mouth/blowhole shapes) and identifying whether extraterrestrial signals contain communication.

Laurance Doyle compares the complexity of cetacean and human languages to help determine if a specific signal from space is complex enough to represent a message that needs to be decoded.

Brenda McCowan studies signal complexity of humpback whales and extraterrestrial signals.

Robert Freitas has used density of brain processing (Sentience Quotient) to compare the difficulty of communicating with animals, including cetaceans, and extraterrestrials.

Self-explanatory languages like Lincos have been tried with radio waves to extraterrestrials, but not sound waves or other signals on earth. They assume recipients patient enough to analyze repetitive mathematical signals to understand the content, and may assume note-taking ability such as opposable thumbs.

See also[edit]


  1. ^ Borenstein, Seth (of AP News) (13 February 2015). "Should We Call the Cosmos Seeking ET? Or Is That Risky?". New York Times. Retrieved 14 February 2015. 
  2. ^ Ghosh, Pallab (12 February 2015). "Scientist: 'Try to contact aliens'". BBC News. Retrieved 12 February 2015. 
  3. ^ Various (13 February 2015). "Statement - Regarding Messaging To Extraterrestrial Intelligence (METI) / Active Searches For Extraterrestrial Intelligence (Active SETI)". University of California, Berkeley. Retrieved 14 February 2015. 
  4. ^ Shostak, Seth (28 March 2015). "Should We Keep a Low Profile in Space?". New York Times. Retrieved 29 March 2015. 
  5. ^ Cattermole, P., & Moore, P. (1997). Atlas of Venus. Cambridge University Press.
  6. ^ Seifer, Marc J. (1996). "Martian Fever (1895-1896)". Wizard: the life and times of Nikola Tesla: biography of a genius. Secaucus, New Jersey: Carol Pub. p. 157. ISBN 978-1-55972-329-9. OCLC 33865102. 
  7. ^ "Tesla at 75". Time (magazine) 18 (3). July 20, 1931. p. 3. .
  8. ^ Ley, Willy. Rockets, Missiles, and Space Travel (revised). New York: The Viking Press (1958)
  9. ^ Freudenthal H, ed. (1960). Lincos: Design of a Language for Cosmic Intercourse. Studies in Logic and the Foundations of Mathematics (Book 28). North-Holland, Amsterdam. ISBN 978-0-444-53393-7. 
  10. ^ Hogben, Lancelot (1963). Science in Authority. New York: W. W. Norton. ISBN 1245639935. 
  11. ^ Sagan, Carl. Communication with Extraterrestrial Intelligence. MIT Press, 1973, 428 pgs.ISBN 0262191067
  12. ^ Vakoch, Douglas. Communication with Extraterrestrial Intelligence. SUNY Press, 2011, 500 pgs.
  13. ^ Devito, C. and Oerle, R (1990). "A Language Based on the Fundamental Facts of Science". Journal of the British Interplanetary Society 43: 561–568. PMID 11540499. 
  14. ^ Busch, Michael W.; Reddick, Rachel M. "Testing SETI Messages Design". Astrobiology Science Conference 2010. Archived from the original (PDF) on July 1, 2013. ; Busch, Michael W.; Reddick, Rachel. M. "Testing SETI Messages (Extended version)". Archived from the original (PDF) on June 30, 2013. 
  15. ^ "Lone Signal - Encoding". Retrieved 7 July 2013. 
  16. ^ Chapman, Charles R. "Extending the syntax used by the Lone Signal Active SETI project". Archived from the original on August 13, 2013. 
  17. ^ a b Передача и поиски разумных сигналов во Вселенной
  18. ^ a b 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. 
  19. ^ a b Elliott, J, Atwell, E & Whyte, B. (2001). "First stage identification of syntactic elements, An extraterrestrial signal". Proceedings of IAC 2001: the 52nd International Astronautical Congress: AA–01–IAA.9.2.07. 
  20. ^ a b 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 53: 13–22. ISSN 0007-084X. 
  21. ^ a b Elliott, J. (2002a). "Detecting languageness". Proceedings of 6th World Multi-Conference on Systemics, Cybernetics and Informatics (SCI 2002) IX: 323–328. 
  22. ^ a b 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: IAA–02–IAA.9.2.10. 
  23. ^ a b 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. 
  24. ^ a b Elliott, J. (2007). "A Post-Detection Decipherment Matrix: Acta Astronautica, Journal of the International Academy of Astronautics Elsevier Science Ltd, England, AA2853". 
  25. ^ Freeman, David (March 5, 2012). "'Through The Wormhole' Host Morgan Freeman: 'We Can't Be' Alone In The Universe (VIDEO)". Huffington Post. Retrieved 25 May 2013. 
  26. ^ "Through the Wormhole: Information Theory : Video : Science Channel". Discovery Communications. Retrieved 25 May 2013. 
  27. ^ Minsky, Marvin (April 1985). "Communication with Alien Intelligence". BYTE. p. 127. Retrieved 27 October 2013. 
  28. ^ Zaitsev, Alexander (2002-03-18). "A Teen-Age Message to the Stars". Retrieved 2012-08-21. 
  29. ^ Zaitsev, A (5 Oct 2006). "Interstellar Radio Messages ( in Russian)". 
  30. ^ Zaitsev, A (August 29, 2001). "Messaging to Extraterrestrial Intelligence (METI)". 
  31. ^ Alexander Zaitsev (2011). "Clasificación de Mensajes de Radio Interestelares".