Communication with extraterrestrial intelligence
Communication with extraterrestrial intelligence or CETI, is a branch of the search for extraterrestrial intelligence 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 in this article should not be taken as referring to any particular organization.
CETI research has focused on four broad areas: mathematical languages, pictorial systems such as the Arecibo message, algorithmic communication systems, 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 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.
In June 2020, astronomers from the University of Nottingham reported the possible existence of over 30 "active communicating intelligent civilizations" in our own Milky Way galaxy, based on the latest astrophysical information.
History
In the 19th 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.Since travel to other planets was not possible at that time, some people suggested ways to signal the 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, the interiors could be 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 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 oldesttherefore Mars was more likely to have advanced civilizations than Venus. Subsequent investigations focused on contacting Martians. In 1877 Giovanni Schiaparelli announced he had discovered "canali" on Marsthis was followed by thirty years of Mars enthusiasm. 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 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.
Arrival (film)
In 2016, McGill University Linguistics Professor, Jessica Coon, spoke with Business Insider about how 2016 sci-fi blockbuster, Arrival, properly portrayed how humans might actually communicate with aliens. To create this language, film producers consulted with Wolfram Research Founder and CEO, Stephen Wolfram – creator of the computer programming language known as the Wolfram Language – and his son, Christopher. Together, they helped analyze approximately 100 logograms that ultimately served as the basis for the alien language utilized throughout the film. This work, along with many other thoughts with regard to artificial intelligence communication has been documented in an interview published by Space.com. During production, Wolfram's personal copy of Lincos: Design of a Language for Cosmic Intercourse was also on set.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. 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 | July 10, 2013 | 2031 | Lone Signal |
Pictorial messages
Pictorial communication systems seek to describe fundamental mathematical or physical concepts via simplified diagrams sent as bitmaps. These messages presume that the recipient has similar visual capabilities and can understand basic mathematics and geometry. A common critique of these 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 could be interpreted as a weapon firing.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 images 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 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. The message is 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 under scientific guidance of Alexander L. Zaitsev. Richard Braastad coordinated the overall project.Star systems 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 Russian scientists 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.
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 First Theremin Concert for Aliens. The 14-minute analog transmission of the theremin concert would take almost 50 hours by digital means; see .
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.
Star systems 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 mathematic 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, forward error correction, 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
CosmicOS, designed by Paul Fitzpatrick at MIT, describes a virtual machine that is derived from lambda calculus.Logic Gate Matrices
Logic Gate Matrices, 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: <-- ). Using this method, one may describe an arbitrarily complex computing substrate as well as the instructions to be executed on it.Natural language messages
This research focuses on the event that we receive a signal or message that is either not directed at us or one that is in its natural communicative form. To tackle this difficult, but probable scenario, methods are being developed that first, will detect if a signal has structure indicative of an intelligent source, categorize the type of structure detected, and then decipher its content: from its physical level encoding and patterns to the parts-of-speech that encode internal and external ontologies.Primarily, this structure modeling focuses on the search for generic human and inter-species language universals to devise computational methods by which language may be discriminated from non-language and core structural syntactic elements of unknown languages may be detected. 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.
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, the perceptual space may be unknown, and we cannot presume 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.
If a sequence can be tokenized, that is, separated into "words", an unknown human language may be distinguished from many other data sequences by the frequency distribution of the tokens. Human languages conform to a Zipfian distribution, while many other data sequences do not. It has been proposed that an alien language also might conform to such a distribution. When displayed in a log-log graph of frequency vs. rank, this distribution would appear as a somewhat straight line with a slope of approximately -1. SETI scientist Laurance Doyle explains that the slope of a line that represents individual tokens in a stream of tokens may 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.
CETI researchers
- Frank Drake : SETI pioneer, composed the Arecibo message.
- Dr John Elliott: 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 : 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 : developed CosmicOS system based on lambda calculus
- Brian McConnell: developed framework for algorithmic communication systems from 2000–2002.
- Marvin Minsky : Believes that aliens may think similarly to humans because of shared constraints, permitting communication. First proposed the idea of including algorithms within an interstellar message.
- Carl Sagan: co-authored the Arecibo message and was heavily involved in SETI throughout his life.
- Douglas Vakoch : studies CETI and has published numerous articles, as well as an upcoming book from MIT Press about interstellar communication.
- Alexander Zaitsev : 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.
- Michael W. Busch: created the binary encoding system for the ongoing Lone Signal hailing message.
- Jacob Haqq Misra: is the chief science officer for the ongoing Lone Signal active SETI project.
Interspecies communication