Active SETI

In the paper 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 are called The SETI Paradox.

The lack of an established communications protocol is a challenge for METI.

First of all, while trying to synthesize an Interstellar Radio Message (IRM), we should bear in mind that 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,[8] later used in the Lone Signal project[9] to transmit crowdsourced messages to extraterrestrial intelligence.[10] Busch developed the coding scheme and provided Rachel M. Reddick with a test message, in a blind test of decryption.[8] Reddick decoded the entire message after approximately twelve hours of work.[8] 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 hailing message.[11]

Also characteristics of the radio signal such as wavelength, type of polarization, and modulation have to be 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.

These projects have targeted stars between 17 and 69 light-years from the Earth. The exception is the Arecibo message, which targeted globular cluster M13, 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.[12]

• The Morse Message (1962)[13]
• Arecibo message (1974)
• Cosmic Call 1 (1999)
• Teen Age Message (2001)
• Cosmic Call 2 (2003)
• Across the Universe (2008)
• Wow! Reply (2012)[14]
• Lone Signal (2013)
• A Simple Response to an Elemental Message (2016)

Below is a table of messages sent and target/destination stars, ordered chronologically by date of sending:[15][16][17][18][19]

Active SETI has been heavily 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, particularly in his article "expose."[21]

However, Russian and Soviet radio engineer and astronomer Alexander L. Zaitsev has argued against these fears.[22][23] Indeed, Zaitsev argues that we should consider the risks of not attempting to contact extraterrestrial civilizations.[24]

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[25] adopted in 2007 a new analytical tool, the San Marino Scale.[26] Developed by Prof. Ivan Almar and Prof. H. Paul Shuch, 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.[27]

In 2015, João Pedro de Magalhães 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."[28]

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."[29]

One proposal for a 10 billion watt interstellar SETI beacon was dismissed by Robert A. Freitas Jr. to be infeasible for a pre-Type I civilization, such as humanity, on the Kardashev scale.[30] 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.[31] 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.[32]

• METI (Messaging Extraterrestrial Intelligence) – Organisation that conducts active SETI
• SETIcon – Public conventions on the search for extraterrestrial intelligence

• Interstellar Radio Messages
• ActiveSETI.org
• active-seti.info
• Making a Case for METI
• Self-Decoding Messages
• Should We Shout Into the Darkness?
• Error Correction Schemes In Active SETI
• The Evpatoria Messages
• Encounter 2001 Message
• Zaitsev, Alexander L. (2011). "METI: Messaging to Extra Terrestrial Intelligence". Searching for Extraterrestrial Intelligence. The Frontiers Collection. pp. 399–428. doi:10.1007/978-3-642-13196-7_21. ISBN 978-3-642-13195-0.
• The Pros and Cons of METI from Centauri Dreams
• Zaitsev, Alexander (2012). "Classification of interstellar radio messages". Acta Astronautica. 78: 16–19. Bibcode:2012AcAau..78...16Z. doi:10.1016/j.actaastro.2011.05.026.
• Lone Signal