Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. Physical messages like that of the

Pioneer plaque The Pioneer plaques are a pair of gold-anodized aluminum plaques that were placed on board the 1972 ''Pioneer 10'' and 1973 ''Pioneer 11'' spacecraft, featuring a pictorial message, in case either ''Pioneer 10'' or ''11'' is intercepted by inte ...

may also be considered an active SETI message. Active SETI is also known as METI (Messaging to Extra-Terrestrial Intelligence). The term METI was coined by Russian scientist Alexander Zaitsev, who proposed a subtle distinction between Active SETI and METI: In 2010, Douglas A. Vakoch from

SETI Institute The SETI Institute is a not-for-profit research organization incorporated in 1984 whose mission is to explore, understand, and explain the origin and nature of life in the universe, and to use this knowledge to inspire and guide present and futu ...

, addressed concerns about the validity of Active SETI alone as an experimental science by proposing the integration of Active SETI and Passive SETI programs to engage in a clearly articulated, ongoing, and evolving set of experiments to test various versions of the Zoo Hypothesis, including specific dates at which a first response to messages sent to particular stars could be expected. On 13 February 2015, scientists (including Douglas Vakoch, David Grinspoon, Seth Shostak, and

David Brin Glen David Brin (born October 6, 1950) is an American scientist and author of science fiction. He has won the Hugo,American Association for the Advancement of Science discussed Active SETI, and whether transmitting a message to possible intelligent

extraterrestrials Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...

in the

Cosmos The cosmos (, ) is another name for the Universe. Using the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos, and understandings of the reasons for its existence and significance, are studied in ...

was a good idea. That same week, a statement was released, signed by many in the SETI community including

Berkeley SETI Research Center The Berkeley SETI Research Center (BSRC) conducts experiments searching for optical and electromagnetic transmissions from intelligent extraterrestrial civilizations.The New York Times ''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...

''.

Rationale for METI

In the pape
Rationale for METI
transmission of the information into the Cosmos is treated as one of the pressing needs of an advanced civilization. This view is not universally accepted, and it does not agree to those who are against the transmission of interstellar radio messages, but at the same time are not against SETI searching. Such duality is calle
The SETI Paradox

Radio message construction

The lack of an established

communications protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchr ...

is a challenge for METI. While trying to synthesize an Interstellar Radio Message (IRM), Extraterrestrials will first deal with a physical phenomenon and, only after that, perceive the information. At first, ET's receiving system will detect the radio signal; then, the issue of extraction of the received information and comprehension of the obtained message will arise. Therefore, above all, the constructor of an IRM should be concerned about the ease of signal determination. In other words, the signal should have maximum openness, which is understood here as an antonym of the term security. This branch of signal synthesis can be named anticryptography. To this end, in 2010, Michael W. Busch created a general-purpose binary language, later used in the

Lone Signal Lone Signal was a crowdfunded active SETI project designed to send List of interstellar messages, interstellar messages from Earth to a possible extraterrestrial civilization. Founded by businessman Pierre Fabre and supported by several entreprene ...

project to transmit crowdsourced messages to extraterrestrial intelligence. Busch developed the coding scheme and provided Rachel M. Reddick with a test message, in a blind test of decryption. Reddick decoded the entire message after approximately twelve hours of work. This was followed by an attempt to extend the syntax used in the

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 hailing message.
Also characteristics of the radio signal such as wavelength, type of polarization, and modulation are considered. Over galactic distances, the interstellar medium induces some scintillation effects and artificial modulation of electromagnetic signals. This modulation is higher at lower frequencies and is a function of the sky direction. Over large distances, the depth of the modulation can exceed 100%, making any METI signal very difficult to decode.

Error correction

In METI research, it is implied that any message must have some redundancy, although the exact amount of redundancy and message formats are still in great dispute. Using ideograms, instead of binary sequence, already offers some improvement against noise resistance. In faxlike transmissions, ideograms will be spread on many lines. This increases its resistance against short bursts of noise like radio frequency interference or interstellar scintillation. One format approach proposed for interstellar messages was to use the product of two prime numbers to construct an image. Unfortunately, this method works only if all the bits are present. As an example, the message sent by

Frank Drake Frank Donald Drake (May 28, 1930 – September 2, 2022) was an American astrophysicist and astrobiologist. He began his career as a radio astronomer, studying the planets of the Solar System and later pulsars. Drake expanded his interests t ...

from the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

in 1974 did not have any feature to support mechanisms to cope with the inevitable noise degradation of the interstellar medium. Error correction tolerance rates for previous METI messages * Arecibo Message (1974): 8.9% (one page) * Evpatoria message (1999): 44% (23 separate pages) * Evpatoria message (2003): 46% (one page, estimated)

Examples

The 1999

Cosmic Call Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music * "Cosmic", a song by Kylie Minogue from the album '' X'' * CosM.i.C, a member of ...

transmission was far from being optimal (from our terrestrial point of view) as it was essentially a monochromatic signal spiced with a supplementary information. Additionally, the message had a very small modulation index overall, a condition not viewed as being optimal for interstellar communication. * Over the 370,967 bits (46,371 bytes) sent, some 314,239 were “1” and 56,768 were “0”—5.54 times as many 1's as 0's. * Since

frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather ball ...

modulation scheme was used, most of the time the signal was on the “0” frequency. * In addition, “0” tended to be sent in long stretches (white lines in the message).

Realized projects

These projects have targeted stars between 17 and 69 light-years from the Earth. The exception is the

Arecibo message The Arecibo message is an interstellar radio message carrying basic information about humanity and Earth that was sent to the globular cluster Messier 13 in 1974. It was meant as a demonstration of human technological achievement, rather than a ...

, which targeted

globular cluster M13 Messier 13 or M13, also designated NGC 6205 and sometimes called the Great Globular Cluster in Hercules or the Hercules Globular Cluster, is a globular cluster of several hundred thousand stars in the constellation of Hercules. Discovery and v ...

, approximately 24,000 light-years away. The first message to reach its destination was the Altair (Morimoto - Hirabayashi) Message, which likely reached its target in 1999. *

The Morse Message (1962) The Morse Message was a series of brief radio messages in Morse code that were transmitted from the Evpatoria Planetary Radar (EPR) complex and directed to the planet Venus in 1962. The message consisted of three words, all encoded in Morse code ...

(1974) *

1 (1999) *

Teen Age Message The Teen Age Message (TAM) was a series of interstellar radio transmissions sent from the Yevpatoria Planetary Radar to six solar-type stars during August–September 2001. The structure of the TAM was suggested by Alexander Zaitsev, Chief Sci ...

(2001) *

2 (2003) *

Across the Universe "Across the Universe" is a song by the English rock band the Beatles. It was written by John Lennon and credited to Lennon–McCartney. The song first appeared on the 1969 various artists' charity compilation album ''No One's Gonna Change Our W ...

(2008)
Hello from Earth
(2009) *

Wow! WideOpenWest (doing business as WOW!) is the sixth largest cable operator in the United States with their network passing 3,248,600 homes and businesses. The company offers landline telephone, cable television, and broadband Internet services ...

Reply (2012) *

(2013) *

A Simple Response to an Elemental Message A Simple Response to an Elemental Message (ASREM) was an Interstellar Radio Message (IRM) consisting primarily of 3775 worldwide responses to this initiative's posed question; "''How will our present, environmental interactions shape the future?' ...

(2016)

Transmissions

Below is a table of messages sent and target/destination stars, ordered chronologically by date of sending:

Controversy

Active SETI has been criticized due to the perceived risk of revealing the location of the Earth to alien civilizations, without some process of prior international consultation. Notable among its critics was Stephen Hawking, and scientist and science fiction author

David Brin Glen David Brin (born October 6, 1950) is an American scientist and author of science fiction. He has won the Hugo,Liu Cixin Liu Cixin (, pronounced ; born 23 June 1963) is a Chinese science fiction writer. He is a nine-time winner of China's Galaxy Award and has also received the 2015 Hugo Award for his novel '' The Three-Body Problem'' as well as the 2017 Lo ...

's trilogy of novels The Three Body Problem highlights the potential dangers of METI. However, Russian and Soviet radio engineer and astronomer Alexander L. Zaitsev has argued against these concerns. Zaitsev argues that we should consider the risks of not attempting to contact extraterrestrial civilizations, since the knowledge and wisdom an ETI could impart to us would save us from humanity's self-destructive tendencies. To lend a quantitative basis to discussions of the risks of transmitting deliberate messages from Earth, the SETI Permanent Study Group of the International Academy of Astronautics adopted in 2007 a new analytical tool, the

San Marino Scale The San Marino Scale is a suggested scale for assessing risks associated with deliberate transmissions from Earth aimed to possible extraterrestrial intelligent life. The scale evaluates the significance of transmissions from Earth as a function ...

. Developed by Prof. Ivan Almar and Prof.

H. Paul Shuch H. Paul Shuch (born May 23, 1946) is an American scientist and engineer who has coordinated radio amateurs to help in the search for extraterrestrial intelligence (SETI). Shuch, an aerospace engineer, microwave technologist, and radio amateur ...

, the San Marino Scale evaluates the significance of transmissions from Earth as a function of signal intensity and information content. Its adoption suggests that not all such transmissions are created equal, thus each must be evaluated on a case-by-case basis before establishing blanket international policy regarding Active SETI. In 2012, Jacob Haqq-Misra, Michael Busch, Sanjoy Som, and Seth Baum argued that while the benefits of radio communication on Earth likely outweigh the potential harms of detection by extraterrestrial watchers, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI. In 2015,

João Pedro de Magalhães Joao Pedro Lourenco Rocha De Magalhaes is a Portuguese microbiologist. He studies aging through both computational and experimental approaches. His ultimate goal is to cure human aging. In 1999, he obtained his degree in Microbiology from Escola ...

proposed transmitting an invitation message to any extraterrestrial intelligences watching us already in the context of the Zoo Hypothesis and inviting them to respond. By using existing television and radio channels, de Magalhães argued this would not put us in any danger, "at least not in any more danger than we are already if much more advanced extraterrestrial civilizations are aware of us and can reach the solar system." Douglas Vakoch, president of METI, argues that passive SETI itself is already an endorsement of active SETI, since "If we detect a signal from aliens through a SETI program, there’s no way to prevent a cacophony of responses from Earth."

Beacon proposals

One proposal for a 10 billion watt interstellar SETI beacon was dismissed by

Robert A. Freitas Jr. Robert A. Freitas Jr. (born 1952) is an American nanotechnologist. Career In 1974, Freitas earned a bachelor's degree in both physics and psychology from Harvey Mudd College, and in 1978, he received a Juris Doctor (J.D.) degree from Santa Clar ...

to be infeasible for a pre-Type I civilization, such as humanity, on the

Kardashev scale The Kardashev scale (Russian: Шкала Кардашева, ''Shkala Kardasheva'') is a method of measuring a civilization's level of technological advancement based on the amount of energy it is able to use. The measure was proposed by Sovie ...

. However, this 1980s technical argument assumes omni-directional beacons which may not be the best way to proceed on many technical grounds. Advances in consumer electronics have made possible transmitters that simultaneously transmit many narrow beams, covering the million or so nearest stars but not the spaces between. This multibeam approach can reduce the power and cost to levels that are reasonable with current mid-2000s Earth technology. Once civilizations have discovered each other's locations, the energy requirements for maintaining contact and exchanging information can be significantly reduced through the use of highly directional transmission technologies. A 2018 study estimated a 1 to 2 megawatt infrared laser focused through a 30 to 45 meter telescope could be seen from about 20,000 light years away.