Active SETI

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 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, 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 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 including Berkeley SETI Research Center and published in ''The New York Times''.

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 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 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 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.

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 from the Arecibo Observatory 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 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 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, 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.

* The Morse Message (1962)
* Arecibo message (1974)
* Cosmic Call 1 (1999)
* Teen Age Message (2001)
* Cosmic Call 2 (2003)
* Across the Universe (2008)

Hello from Earth
(2009)
* Wow! Reply (2012)
* Lone Signal (2013)
* A Simple Response to an Elemental Message (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'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. 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.

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."

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

See also

* Communication with extraterrestrial intelligence
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* SETI@home
*Wow! signal

References

External links

Interstellar Radio Messages

ActiveSETI.org


active-seti.info





Should We Shout Into the Darkness?

Error Correction Schemes In Active SETI

The Evpatoria Messages


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The Pros and Cons of METI from Centauri Dreams
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Lone Signal

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