The communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence (SETI) that focuses on composing and deciphering interstellar messages that theoretically could be understood by another technological civilization. The best-known CETI experiment of its kind was the 1974 Arecibo message composed by Frank Drake.
There are multiple independent organizations and individuals engaged in CETI research; the generic application of abbreviations CETI and SETI (search for extraterrestrial intelligence) in this article 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 that arise in many scenarios of interplanetary communication.
On 13 February 2015, scientists (including Douglas Vakoch, 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. 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". On 28 March 2015, a related essay was written by Seth Shostak and published in The New York Times.
History In the 19th century, many books and articles speculated about the possible inhabitants of other planets. Many people believed that intelligent beings might live on the Moon, Mars, and/or Venus.
Since travel to other planets was not possible at the time, some people suggested ways to signal extraterrestrials even before radio was discovered. Carl Friedrich Gauss is often credited with an 1820 proposal 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, whereas the interiors could be filled with rye or wheat.
Joseph Johann Littrow proposed in 1819 to use the Sahara as a sort of 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 Paula 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 previously been observed on the dark side of 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.Cattermole, P., & Moore, P. (1997). Atlas of Venus. Cambridge University Press.
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 oldesttherefore Mars was more likely to have advanced civilizations than Venus.Owen, T. C. (2001) "Solar system: origin of the solar system", Encyclopædia Britannica, Deluxe CDROM edition 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 enthusiasm about the possibility of life on Mars. Eventually the Martian canals proved illusory.
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 be used to communicate with other planets,. and that he even had observed repetitive signals of what he believed were extraterrestrial radio communications coming from Venus or Mars in 1899. These "signals" turned out to be terrestrial radiation, however.
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.
Mathematical and scientific languages
Lincos (Lingua cosmica)
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. Several researchers have expanded further upon Freudenthal's work. A dictionary resembling Lincos was featured in the Carl Sagan novel Contact and its film adaptation.
Astraglossa Published in 1963 by Lancelot Hogben, "Astraglossa" is an essay describing 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.
Carl Sagan In the 1985 science fiction novel Contact, Carl Sagan explored in some depth how a message might be constructed to allow communication with an alien civilization, using prime numbers as a starting point, followed by various universal principles and facts of mathematics and science.
Sagan also edited a nonfiction book on the subject. An updated collection of articles on the same topic was published in 2011.Vakoch, Douglas. Communication with Extraterrestrial Intelligence. SUNY Press, 2011, 500 pgs.
A language based on the fundamental facts of science Published in 1992 by Carl Devito and Richard Oehrle, A language based on the fundamental facts of science is a paper describing a language similar in syntax to Astraglossa and Lincos, but which builds its vocabulary around known physical properties.
Busch general-purpose binary language used in Lone Signal transmissions In 2010, Michael W. Busch created a general-purpose binary language ; later used in the Lone Signal project 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. Name Designation Constellation Date sent Arrival date Message Gliese 526 HD 119850 Boötes 2013-07-10July 10, 2013 2031Lone Signal
Pictorial messages
Pictorial communication systems seek to describe fundamental mathematical or physical concepts via simplified diagrams sent as bitmaps. These messages necessarily assume that the recipient has similar visual capabilities and can understand basic mathematics and geometry. A common critique of pictorial systems is that they presume 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 might be misinterpreted as a weapon firing.
Pioneer probes Two etched plaques, known as the Pioneer plaques, were included aboard the Pioneer 10 and Pioneer 11 spacecraft when they launched in 1972 and 1973. These were the idea of astronomers Eric Burgess and Sagan, with contributions from Drake, Linda Salzman, and Jon Lomberg. The plaques depict the specific location of the Solar System within the galaxy and the Earth within the Solar System, as well as the form of the human body.
Voyager probes Launched in 1977, the Voyager probes carried two golden records that were inscribed with diagrams similar to the Pioneer plaques, depicting the human form, the Solar System, and its location. Also included were recordings of images and sounds from Earth. While the motivating factor originated from Voyager project manager John R. Casani, the idea of formatting it as a record was the work of Sagan, Drake, Salzman, Lomberg and their colleagues.
Arecibo message The Arecibo message, transmitted in 1974, was a 1,679-pixel bitmap created by Drake that, when properly arranged into 73 rows and 23 columns, shows the numbers one through ten; the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus; the formulas for the sugars and bases that make up the nucleotides of DNA; the number of nucleotides in the human genome; the double helix structure of DNA; a simple illustration of a human being and its height; the human population of Earth; a diagram of the Solar System; and an illustration of the Arecibo telescope with its diameter.
Cosmic Call messages The Cosmic Call messages consisted of a few digital sections – "Rosetta Stone", a copy of the Arecibo Message, the Bilingual Image Glossary, and the Braastad message – as well as text, audio, video, and other image files submitted for transmission by people around the world. The "Rosetta Stone" was composed by Stéphane 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 was designed with a noise-resistant format and characters that make it resistant to alteration by noise. These messages were transmitted in 1999 and 2003 from Evpatoria Planetary Radar in Ukraine under the scientific guidance of Alexander L. Zaitsev. Richard Braastad coordinated the overall project.
Star systems to which the messages were sent include the following:
Name Designation HD Constellation Date sent Arrival date Message 16 Cyg A HD 186408 Cygnus May 24, 1999 November 2069Cosmic Call 1 15 Sge HD 190406 Sagitta June 30, 1999 February 2057Cosmic Call 1 HD 178428 Sagitta June 30, 1999 October 2067Cosmic Call 1 Gl 777 HD 190360 Cygnus July 1, 1999 April 2051Cosmic Call 1 Hip 4872 Cassiopeia July 6, 2003 April 2036Cosmic Call 2 HD 245409 Orion July 6, 2003 August 2040Cosmic Call 2 55 Cnc HD 75732 Cancer July 6, 2003 May 2044Cosmic Call 2 HD 10307 Andromeda July 6, 2003 September 2044Cosmic Call 2 47 UMa HD 95128 Ursa Major July 6, 2003 May 2049Cosmic Call 2
Multi-modal messages
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 Evpatoria Deep Space Center in Ukraine to six star systems resembling that of the Sun 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.