Search for extraterrestrial intelligence 1

Search for extraterrestrial intelligence

Screen shot of the screensaver for SETI@home, a distributed computing project inwhich volunteers donate idle computer power to analyze radio signals for signs of

extraterrestrial intelligence

The search for extraterrestrialintelligence (SETI) is the collective namefor a number of activities undertaken tosearch for intelligent extraterrestrial life.SETI projects use scientific methods in thissearch. For example, electromagneticradiation is monitored for signs oftransmissions from civilizations on otherworlds.[][1] Some of the most well knownprojects are run by Harvard University, theUniversity of California, Berkeley, and theSETI Institute. Since the United Statesgovernment withdrew funding for SETIprojects in 1995, projects have beenprimarily funded by private sources.

There are great challenges in searching thecosmos for signs of intelligent life,including their identification and interpretation. SETI projects necessarily make assumptions to narrow the search,the foremost being that electromagnetic radiation would be a medium of communication for advanced extraterrestriallife.[2]

Radio experiments

Microwave window as seen by a ground based system. From NASA report SP-419: SETI– the Search for Extraterrestrial Intelligence

Many radio frequencies penetrate ouratmosphere quite well, and this led toradio telescopes that investigate thecosmos using large radio antennas.Furthermore, human endeavors emitconsiderable electromagnetic radiationas a byproduct of communicationssuch as television and radio. Thesesignals would be easy to recognize asartificial due to their repetitive natureand narrow bandwidths. If this istypical, one way of discovering anextraterrestrial civilization might be todetect non-natural radio emissionsfrom a location outside our SolarSystem.

Early work

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As early as 1896, Nikola Tesla suggested that radio could be used to contact extraterrestrial life.[3] In 1899 whileinvestigating atmospheric electricity using a Tesla coil receiver in his Knob Hill lab, Tesla observed repetitivesignals, substantially different from the signals noted from storms and Earth noise, that he interpreted as being ofextraterrestrial origin. He later recalled the signals appeared in groups of one, two, three, and four clicks together.Tesla thought the signals were coming from Mars. Analysis of Tesla's research has ranged from suggestions thatTesla detected nothing, he simply was misunderstanding the new technology he was working with,[4] to claims thatTesla may have been observing naturally occurring Jovian plasma torus signals. In the early 1900s, GuglielmoMarconi, Lord Kelvin, and David Peck Todd also stated their belief that radio could be used to contact Martians,with Marconi stating that his stations had also picked up potential Martian signals.[5]

On August 21–23, 1924, Mars entered an opposition closer to Earth than any time in a century before or since. In theUnited States, a "National Radio Silence Day" was promoted during a 36-hour period from the 21–23, with all radiosquiet for five minutes on the hour, every hour. At the United States Naval Observatory, a radio receiver was lifted 3kilometers above the ground in a dirigible tuned to a wavelength between 8 and 9 kilometers, using a "radio-camera"developed by Amherst College and Charles Francis Jenkins. The program was led by David Peck Todd with themilitary assistance of Admiral Edward W. Eberle (Chief of Naval Operations), with William F. Friedman (chiefcryptographer of the US Army), assigned to translate any potential Martian messages.[][6]

A 1959 paper by Philip Morrison and Giuseppe Cocconi first pointed out the possibility of searching the microwavespectrum, and proposed frequencies and a set of initial targets[7][8]

In 1960, Cornell University astronomer Frank Drake performed the first modern SETI experiment, named "ProjectOzma", after the Queen of Oz in L. Frank Baum's fantasy books.[9] Drake used a radio telescope 26 meters indiameter at Green Bank, West Virginia, to examine the stars Tau Ceti and Epsilon Eridani near the 1.420 gigahertzmarker frequency, a region of the radio spectrum dubbed the "water hole" due to its proximity to the hydrogen andhydroxyl radical spectral lines. A 400 kilohertz band was scanned around the marker frequency, using asingle-channel receiver with a bandwidth of 100 hertz. The information was stored on tape for off-line analysis. Hefound nothing of great interest, but has continued a pro-active involvement in the search for life beyond Earth for 50years.The first SETI conference took place at Green Bank, West Virginia in November 1961. The ten attendees wereconference organiser Peter Pearman, Frank Drake, Philip Morrison, businessman and radio amateur Dana Atchley,chemist Melvin Calvin, astronomer Su-Shu Huang, neuroscientist John C. Lilly, inventor Barney Oliver, astronomerCarl Sagan and radio astronomer Otto Struve. From the agenda points of the conference Drake derived the Drakeequation by multiplying the various factors that were discussed at the conference. The Drake equation is anestimation of how many planets in the Milky Way are inhabited by intelligent life forms.[]

The Soviet scientists took a strong interest in SETI during the 1960s and performed a number of searches withomnidirectional antennas in the hope of picking up powerful radio signals. Soviet astronomer Iosif Shklovskii wrotethe pioneering book in the field Universe, Life, Intelligence (1962), which was expanded upon by Americanastronomer Carl Sagan as the best-selling Intelligent Life in the Universe (1966).[]

The first Kraus-style radio telescope was powered up in 1963. It was 360 feet (110 m) wide, 500 feet (150 m) long,and 70 feet (21 m) high. In the March 1955 issue of Scientific American, John D. Kraus described a concept to scanthe cosmos for natural radio signals using a flat-plane radio telescope equipped with a parabolic reflector. Withintwo years, his concept was approved for construction by Ohio State University. With US$71,000 total in grants fromthe National Science Foundation, construction began on a 20-acre plot in Delaware, Ohio. This Ohio StateUniversity radio telescope was called Big Ear. Later, it began the world's first continuous SETI program, called theOhio State University SETI program.

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View of Arecibo Observatory in Puerto Rico with its300 m dish- the world's largest. A small fraction of its

observation time is devoted to SETI searches.

In 1971, NASA funded a SETI study that involved Drake, BernardOliver of Hewlett-Packard Corporation, and others. The resultingreport proposed the construction of an Earth-based radio telescopearray with 1,500 dishes known as "Project Cyclops". The price tagfor the Cyclops array was US$10 billion. Cyclops was not built,but the report[10] formed the basis of much SETI work thatfollowed.

The WOW! SignalCredit: The Ohio State University Radio Observatoryand the North American AstroPhysical Observatory

(NAAPO).

The OSU SETI program gained fame on August 15, 1977, whenJerry Ehman, a project volunteer, witnessed a startlingly strongsignal received by the telescope. He quickly circled the indicationon a printout and scribbled the phrase “Wow!” in the margin.Dubbed the Wow! signal, it is considered bysomeWikipedia:Avoid weasel words to be the best candidate for aradio signal from an artificial, extraterrestrial source everdiscovered, but it has not been detected again in several additionalsearches.[11]

In 1979 the University of California, Berkeley, launched a SETIproject named "Search for Extraterrestrial Radio Emissions fromNearby Developed Intelligent Populations (SERENDIP)".[] In 1986, UC Berkeley initiated their second SETI effort,SERENDIP II, and has continued with four more SERENDIP efforts to the present day. The latest incarnation of theSERENDIP project is SERENDIP V.v, a commensal all-sky survey using the Arecibo radio telescope began in June2009.

Sentinel, META, and BETAIn 1980, Carl Sagan, Bruce Murray, and Louis Friedman founded the U.S. Planetary Society, partly as a vehicle forSETI studies.In the early 1980s, Harvard University physicist Paul Horowitz took the next step and proposed the design of a spectrum analyzer specifically intended to search for SETI transmissions. Traditional desktop spectrum analyzers were of little use for this job, as they sampled frequencies using banks of analog filters and so were restricted in the number of channels they could acquire. However, modern integrated-circuit digital signal processing (DSP) technology could be used to build autocorrelation receivers to check far more channels. This work led in 1981 to a

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portable spectrum analyzer named "Suitcase SETI" that had a capacity of 131,000 narrow band channels. After fieldtests that lasted into 1982, Suitcase SETI was put into use in 1983 with the 26-meter Harvard/Smithsonian radiotelescope at Harvard, Massachusetts. This project was named "Sentinel", and continued into 1985.Even 131,000 channels weren't enough to search the sky in detail at a fast rate, so Suitcase SETI was followed in1985 by Project "META", for "Megachannel Extra-Terrestrial Assay". The META spectrum analyzer had a capacityof 8.4 million channels and a channel resolution of 0.05 hertz. An important feature of META was its use offrequency doppler shift to distinguish between signals of terrestrial and extraterrestrial origin. The project was led byHorowitz with the help of the Planetary Society, and was partly funded by movie maker Steven Spielberg. A secondsuch effort, META II, was begun in Argentina in 1990 to search the southern sky. META II is still in operation, afteran equipment upgrade in 1996.The follow-on to META was named "BETA", for "Billion-channel Extraterrestrial Assay", and it commencedobservation on October 30, 1995. The heart of BETA's processing capability consisted of 63 dedicated fast Fouriertransform (FFT) engines, each capable of performing a 222-point complex FFTs in two seconds, and 21general-purpose personal computers equipped with custom digital signal processing boards. This allowed BETA toreceive 250 million simultaneous channels with a resolution of 0.5 hertz per channel. It scanned through themicrowave spectrum from 1.400 to 1.720 gigahertz in eight hops, with two seconds of observation per hop. Animportant capability of the BETA search was rapid and automatic re-observation of candidate signals, achieved byobserving the sky with two adjacent beams, one slightly to the east and the other slightly to the west. A successfulcandidate signal would first transit the east beam, and then the west beam and do so with a speed consistent withEarth's sidereal rotation rate. A third receiver observed the horizon to veto signals of obvious terrestrial origin. OnMarch 23, 1999, the 26-meter radio telescope on which Sentinel, META and BETA were based was blown over bystrong winds and seriously damaged. This forced the BETA project to cease operation.

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MOP and Project Phoenix

Sensitivity vs range for SETI radio searches. The diagonal lines show transmitters ofdifferent effective powers. The x-axis is the sensitivity of the search. The y-axis on the

right is the range in light years, and on the left is the number of sun-like stars within thisrange. The vertical line labeled SS is the typical sensitivity achieved by a full sky search,such as BETA above. The vertical line labeled TS is the typical sensitivity achieved by a

targeted search such as Phoenix.[12]

In 1978, the NASA SETI program washeavily criticized by Senator WilliamProxmire, and funding for SETIresearch was removed from the NASAbudget by Congress in 1981,[13]

however, funding was restored in1982, after Carl Sagan talked withProxmire and convinced him of theprogram's value.[13] In 1992, the U.S.government funded an operationalSETI program, in the form of theNASA Microwave Observing Program(MOP). MOP was planned as along-term effort to conduct a generalsurvey of the sky and also carry outtargeted searches of 800 specificnearby stars. MOP was to beperformed by radio antennasassociated with the NASA Deep SpaceNetwork, as well as the 140-foot(43 m) radio telescope of the NationalRadio Astronomy Observatory atGreen Bank, West Virginia and the1,000-foot (300 m) radio telescope at the Arecibo Observatory in Puerto Rico. The signals were to be analyzed byspectrum analyzers, each with a capacity of 15 million channels. These spectrum analyzers could be groupedtogether to obtain greater capacity. Those used in the targeted search had a bandwidth of 1 hertz per channel, whilethose used in the sky survey had a bandwidth of 30 hertz per channel.

MOP drew the attention of the U.S. Congress, where the program was ridiculed[14] and canceled a year after itsstart.[13] SETI advocates continued without government funding, and in 1995 the nonprofit SETI Institute ofMountain View, California resurrected the MOP program under the name of Project "Phoenix", backed by privatesources of funding. Project Phoenix, under the direction of Jill Tarter, is a continuation of the targeted searchprogram from MOP and studies roughly 1,000 nearby Sun-like stars. From 1995 through March 2004, Phoenixconducted observations at the 64-meter Parkes radio telescope in Australia, the 140-foot (43 m) radio telescope ofthe National Radio Astronomy Observatory in Green Bank, West Virginia, and the 1,000-foot (300 m) radiotelescope at the Arecibo Observatory in Puerto Rico. The project observed the equivalent of 800 stars over theavailable channels in the frequency range from 1200 to 3000 MHz. The search was sensitive enough to pick uptransmitters with 1 GW EIRP to a distance of about 200 light years. According to Miss Tarter, in 2012 it costsaround "$2 million a year to keep SETI research going at the SETI Institute" and approximately 10 times that tosupport "all kinds of SETI activity around the world." [15]

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The SETI League and Project ArgusFounded in 1994 in response to the US Congress cancellation of the NASA SETI program, The SETI League, Inc. isa membership-supported nonprofit organization with 1,500 members in 62 countries. This grass-roots alliance ofamateur and professional radio astronomers is headed by executive director emeritus Prof. H. Paul Shuch, theengineer credited with developing the world's first commercial home satellite TV receiver. Many SETI Leaguemembers are licensed radio amateurs and microwave experimenters. Others are digital signal processing experts andcomputer enthusiasts.The SETI League pioneered the conversion of backyard satellite TV dishes 3 to 5 meters in diameter intoresearch-grade radio telescopes of modest sensitivity.[16] The organization concentrates on coordinating a globalnetwork of small, amateur-built radio telescopes under Project Argus, an all-sky survey seeking to achieve real-timecoverage of the entire sky. Project Argus was conceived as a continuation of the all-sky survey component of the lateNASA SETI program (the targeted search having been continued by the SETI Institute's Project Phoenix). There arecurrently 143 Project Argus radio telescopes operating in 27 countries. Project Argus instruments typically exhibitsensitivity on the order of 10−23 Watts/square metre, or roughly equivalent to that achieved by the Ohio StateUniversity Big Ear radio telescope in 1977, when it detected the landmark "Wow!" candidate signal.The name "Argus" derives from the mythical Greek guard-beast who had 100 eyes, and could see in all directions atonce. In the SETI context, the name has been used for radio telescopes in fiction (Arthur C. Clarke, "ImperialEarth"; Carl Sagan, "Contact"), was the name initially used for the NASA study ultimately known as "Cyclops," andis the name given to an omnidirectional radio telescope design being developed at the Ohio State University.

SETI@homeSETI@home was conceived by David Gedye along with Craig Kasnoff and is a popular volunteer distributedcomputing project that was launched by the University of California, Berkeley, in May 1999. It was originallyfunded by The Planetary Society and Paramount Pictures, and later by the state of California. The project is run bydirector David P. Anderson and chief scientist Dan Werthimer. Any individual can become involved with SETIresearch by downloading the Berkeley Open Infrastructure for Network Computing (BOINC) software program,attaching to the SETI@home project, and allowing the program to run as a background process that uses idlecomputer power. The SETI@home program itself runs signal analysis on a "work unit" of data recorded from thecentral 2.5 MHz wide band of the SERENDIP IV instrument. After computation on the work unit is complete, theresults are then automatically reported back to SETI@home servers at UC Berkeley. By June 28, 2009, theSETI@home project had over 180,000 active participants volunteering a total of over 290,000 computers. Thesecomputers give SETI@home an average computational power of 617 teraFLOPS.[17] In 2004 radio sourceSHGb02+14a was an interesting signal but was quickly shown to have a natural source.[][18]

As of 2010, after 10 years of data collection, SETI@home has listened to that one frequency at every point of over67 percent of the sky observable from Arecibo with at least 3 scans (out of the goal of 9 scans), which covers about20 percent of the full celestial sphere.[19]

Allen Telescope ArrayThe SETI Institute has been collaborating with the Radio Astronomy Laboratory at UC Berkeley to develop aspecialized radio telescope array for SETI studies, something like a mini-cyclops array. The array concept is namedthe "Allen Telescope Array" (ATA) (formerly, One Hectare Telescope [1HT]) after the project's benefactor PaulAllen. Its sensitivity will be equivalent to a single large dish more than 100 meters in diameter. The array is beingconstructed at the Hat Creek Observatory in rural northern California.[]

The full array is planned to consist of 350 or more Gregorian radio dishes, each 6.1 meters (20 ft) in diameter. These dishes are the largest producible with commercially available satellite television dish technology. The ATA was planned for a 2007 completion date, at a very modest cost of US$25 million. The SETI Institute provides money for

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building the ATA while UC Berkeley designs the telescope and provides operational funding. Berkeley astronomerswill use the ATA to pursue other deep space radio observations. The ATA is intended to support a large number ofsimultaneous observations through a technique known as "multibeaming", in which DSP technology is used to sortout signals from the multiple dishes. The DSP system planned for the ATA is extremely ambitious. The first portionof the array became operational in October 2007 with 42 antennas. Completion of the full 350 element array willdepend on funding and the technical results from the 42-element sub-array.CNET published an article and pictures about the Allen Telescope Array (ATA) on December 12, 2008.[20][21]

In April 2011, the ATA was forced to enter "hibernation" due to funding shortfalls. Regular operation of the ATAwas resumed on December 5, 2011.[][22]

SETI NetSETI Net is a private search system created by a single individual. It is closely affiliated with the SETI League and isone of the project Argus stations (DM12jw).The SETI Net station consists of off-the-shelf, consumer-grade electronics to minimize cost and to allow this designto be replicated as simply as possible. It has a 3-meter parabolic antenna that can be directed in azimuth andelevation, an LNA that covers the 1420 MHz spectrum, a receiver to reproduce the wideband audio, and a standardPC as the control device and for deploying the detection algorithms.The antenna can be pointed and locked to one sky location, enabling the system to integrate on it for long periods.Currently the Wow! signal area is being monitored when it is above the horizon, but all search data are collected andmade available on the internet archive.SETI Net started operation in the early 1980s as a way to learn about the science of the search, and has developedseveral software packages for the amateur SETI community. It has provided an astronomical clock, a file manager tokeep track of SETI data files, a spectrum analyzer optimized for amateur SETI, remote control of the station from theinternet, and other packages.

Realized Interstellar Radio Message projectsIn 1974, a largely symbolic attempt was made at the Arecibo Observatory to send a message to other worlds. It wassent towards the globular star cluster M13, which is 25,000 light years from Earth. The first Interstellar RadioMessage (IRM), the "Arecibo Message", was transmitted in November 1974 from Arecibo Radar Telescope. FurtherIRMs Cosmic Call, Teen Age Message, Cosmic Call 2, and A Message From Earth were transmitted in 1999, 2001,2003 and 2008 from Evpatoria Planetary Radar.Additional information on messages sent outward from Earth at: Communication with Extraterrestrial Intelligence,Active SETI, List of interstellar radio messages.

Paper projectsA large number of paper projects also exist. For example, directed by Douglas Vakoch at the SETI Institute inMountain View, California, the Interstellar Message Composition Project is charged with designing messages thatcould presumably be sent to extraterrestrials that convey basic scientific or mathematical principles, as well ashuman altruism. Vackoch's idea is to send a message of reciprocal altruism because hopefully any extraterrestrialswould reciprocate with a reply back.Vakoch has founded "Encoding Altruism", a workshop that started in 2003 in Paris that brings togetheranthropologists, philosophers, physicists, astronomers, theologians, musicians, and artists to address the challenge ofcommunicating with extraterrestrials in a language and syntax that would be intelligible to an alien civilization.Vakoch's most recent research is highlighted through the Greater Good Science Center, University of California,Berkeley.

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Optical experimentsWhile most SETI sky searches have studied the radio spectrum, some SETI researchers have considered thepossibility that alien civilizations might be using powerful lasers for interstellar communications at opticalwavelengths. The idea was first suggested by R. N. Schwartz and Charles Hard Townes in a 1961 paper published inthe journal Nature titled "Interstellar and Interplanetary Communication by Optical Masers". In 1983, Townes, oneof the inventors of the laser, published a detailed study of the idea in the US journal Proceedings of the NationalAcademy of Sciences. Most SETI researchers agreed with the idea.[citation needed]

The 1971 Cyclops study discounted the possibility of optical SETI, reasoning that construction of a laser system thatcould outshine the bright central star of a remote star system would be too difficult.Some SETI advocates, such as Frank Drake, have suggested that such a judgment was too conservative; early21st-century humans have no means of knowing how a superior technology is communicating or wouldcommunicate, and negative results may simply mean humans are making the wrong searches.[citation needed]

There are two problems with optical SETI. The first problem is that lasers are highly "monochromatic", that is, theyemit light only on one frequency, making it troublesome to figure out what frequency to look for.However, according to the uncertainty principle, emitting light in narrow pulses results in a broad spectrum ofemission; the spread in frequency becomes higher as the pulse width becomes narrower, making it easier to detect anemission.The other problem is that while radio transmissions can be broadcast in all directions, lasers are highly directional.This means that a laser beam could be easily blocked by clouds of interstellar dust, and Earth would have to cross itsdirect line of fire by chance to receive it.Optical SETI supporters have conducted paper studies[23] of the effectiveness of using contemporary high-energylasers and a ten-meter focus mirror as an interstellar beacon. The analysis shows that an infrared pulse from a laser,focused into a narrow beam by such a mirror, would appear thousands of times brighter than the Sun to a distantcivilization in the beam's line of fire. The Cyclops study proved incorrect in suggesting a laser beam would beinherently hard to see.Such a system could be made to automatically steer itself through a target list, sending a pulse to each target at aconstant rate. This would allow targeting of all Sun-like stars within a distance of 100 light-years. The studies havealso described an automatic laser pulse detector system with a low-cost, two-meter mirror made of carbon compositematerials, focusing on an array of light detectors. This automatic detector system could perform sky surveys to detectlaser flashes from civilizations attempting contact.In the 1980s, two Soviet researchers conducted a short optical SETI search, but turned up nothing. During much ofthe 1990s, the optical SETI cause was kept alive through searches by Stuart Kingsley, a dedicated British researcherliving in the US state of Ohio.Several optical SETI experiments are now in progress. A Harvard-Smithsonian group that includes Paul Horowitzdesigned a laser detector and mounted it on Harvard's 155 centimeter (61 inch) optical telescope. This telescope iscurrently being used for a more conventional star survey, and the optical SETI survey is "piggybacking" on thateffort. Between October 1998 and November 1999, the survey inspected about 2,500 stars. Nothing that resembledan intentional laser signal was detected, but efforts continue. The Harvard-Smithsonian group is now working withPrinceton University to mount a similar detector system on Princeton's 91-centimeter (36-inch) telescope. TheHarvard and Princeton telescopes will be "ganged" to track the same targets at the same time, with the intent being todetect the same signal in both locations as a means of reducing errors from detector noise.The Harvard-Smithsonian group is now building a dedicated all-sky optical survey system along the lines of thatdescribed above, featuring a 1.8-meter (72-inch) telescope. The new optical SETI survey telescope is being set up atthe Oak Ridge Observatory in Harvard, Massachusetts.

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The University of California, Berkeley, home of SERENDIP and SETI@home, is also conducting optical SETIsearches. One is being directed by Geoffrey Marcy, an extrasolar planet hunter, and involves examination of recordsof spectra taken during extrasolar planet hunts for a continuous, rather than pulsed, laser signal. The other Berkeleyoptical SETI effort is more like that being pursued by the Harvard-Smithsonian group and is being directed by DanWerthimer of Berkeley, who built the laser detector for the Harvard-Smithsonian group. The Berkeley survey uses a76-centimeter (30-inch) automated telescope at Leuschner Observatory and an older laser detector built byWerthimer.

Gamma-ray burstsGamma-ray bursts (GRBs) are candidates for extraterrestrial communication. These high-energy bursts are observedabout once per day and originate throughout the observable universe. SETI currently omits gamma ray frequencies intheir monitoring and analysis because they are absorbed by the Earth's atmosphere and difficult to detect withground-based receivers. In addition, the wide burst bandwidths pose a serious analysis challenge for modern digitalsignal processing systems. Still, the continued mysteries surrounding gamma-ray bursts have encouraged hypothesesinvoking extraterrestrials. John A. Ball from the MIT Haystack Observatory suggests that an advanced civilizationthat has reached a technological singularity would be capable of transmitting a two-millisecond pulse encoding1×1018 bits of information. This is "comparable to the estimated total information content of Earth's biosystem-genesand memes and including all libraries and computer media."[24]

Probe SETI and SETA experimentsThe possibility of using interstellar messenger probes in the search for extraterrestrial intelligence was first suggestedby Ronald N. Bracewell in 1960 (see Bracewell probe), and the technical feasibility of this approach wasdemonstrated by the British Interplanetary Society's starship study Project Daedalus in 1978. Starting in 1979,Robert Freitas advanced arguments [25][26][27] for the proposition that physical space-probes are a superior mode ofinterstellar communication to radio signals. See Voyager Golden Record.In recognition that any sufficiently advanced interstellar probe in the vicinity of Earth could easily monitor ourterrestrial Internet, Invitation to ETI was established by Prof. Allen Tough in 1996, as a Web-based SETI experimentinviting such spacefaring probes to establish contact with humanity. The project's 100 Signatories includesprominent physical, biological, and social scientists, as well as artists, educators, entertainers, philosophers andfuturists. Prof. H. Paul Shuch, executive director emeritus of The SETI League, serves as the project's PrincipalInvestigator.In a 2004 paper,[28] C. Rose and G. Wright showed that inscribing a message in matter and transporting it to aninterstellar destination can be enormously more energy efficient than communication using electromagnetic waves ifdelays larger than light transit time can be tolerated. That said, for simple messages such as "hello," radio SETI couldbe far more efficient .[29] If energy requirement is used as a proxy for technical difficulty, then a solarcentric Searchfor Extraterrestrial Artifacts (SETA) [30] may be a useful supplement to traditional radio or optical searches.[31][32]

Much like the "preferred frequency" concept in SETI radio beacon theory, the Earth-Moon or Sun-Earth librationorbits [] might therefore constitute the most universally convenient parking places for automated extraterrestrialspacecraft exploring arbitrary stellar systems. A viable long-term SETI program may be founded upon a search forthese objects.In 1979, Freitas and Valdes conducted a photographic search of the vicinity of the Earth-Moon triangular libration points L4 and L5, and of the solar-synchronized positions in the associated halo orbits, seeking possible orbiting extraterrestrial interstellar probes, but found nothing to a detection limit of about 14th magnitude.[] The authors conducted a second, more comprehensive photographic search for probes in 1982[33] that examined the five Earth-Moon Lagrangian positions and included the solar-synchronized positions in the stable L4/L5 libration orbits,

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the potentially stable nonplanar orbits near L1/L2, Earth-Moon L3, and also L2 in the Sun-Earth system. Again noextraterrestrial probes were found to limiting magnitudes of 17–19th magnitude near L3/L4/L5, 10–18th magnitudefor L1/L2, and 14–16th magnitude for Sun-Earth L2.In June 1983, Valdes and Freitas[34] used the 26 m radiotelescope at Hat Creek Radio Observatory to search for thetritium hyperfine line at 1516 MHz from 108 assorted astronomical objects, with emphasis on 53 nearby starsincluding all visible stars within a 20 light-year radius. The tritium frequency was deemed highly attractive for SETIwork because (1) the isotope is cosmically rare, (2) the tritium hyperfine line is centered in the SETI waterholeregion of the terrestrial microwave window, and (3) in addition to beacon signals, tritium hyperfine emission mayoccur as a byproduct of extensive nuclear fusion energy production by extraterrestrial civilizations. The wideband-and narrowband-channel observations achieved sensitivities of 5–14 x 10−21 W/m²/channel and 0.7-2 x 10−24

W/m²/channel, respectively, but no detections were made.

Search for Physical TechnosignaturesBesides directed messages by alien civilizations, another way of detecting their presence is the search for physicaltechnosignatures.Advanced techniques could be used to uncover signs of alien technology, industrial activity or Megascaleengineering.It is possible that even a civilisation at the same technology level as human beings might be detectable in this wayand the presence more advanced civilisations may be more detectable.

SETI's search for Dyson spheresA Dyson Sphere, constructed by life forms not dissimilar to humans, who dwelled in proximity to a Sun-like star,made with materials similar to those available to humans, would most likely cause an increase in the amount ofinfrared radiation in the star system's emitted spectrum. Hence, Dyson selected the title "Search for Artificial StellarSources of Infrared Radiation" for his published paper.[] SETI has adopted these assumptions in their search, lookingfor such "infrared heavy" spectra from solar analogs. As of 2005[35] Fermilab has an ongoing survey for suchspectra by analyzing data from the Infrared Astronomical Satellite (IRAS).[36][37] Identifying one of the manyinfra-red sources as a Dyson Sphere would require improved techniques for discriminating between a Dyson Sphereand natural sources.[38] Fermilab discovered 17 potential "ambiguous" candidates of which four have been named"amusing but still questionable".[39] Other searches also resulted in several candidates, which are howeverunconfirmed.[40]

As of October 2012 astronomer Geoff Marcy, one of the pioneers of the search for extrasolar planets, was givenresearch grant to search data from Kepler telescope, with the aim of detecting possible signs of Dyson Spheres[41]

Artificial Light and Heat emissionsSome astronomers including Avi Loeb of the Harvard-Smithsonian Center for Astrophysics and Edwin Turner ofPrinceton University (2011) have proposed that stable night light such as those emanating from cities, industry andtransport networks on Earth could be detectable and indicate the presence of ETI using artificial light.[42][43] Theseapproaches make the assumption that radiant energy generated by civilisation would be clustered and can thereforebe detected reasonably easily.A more recent approach focuses on detecting artificially infrared radiation emissions. A 250 foot telescope proposedin 2013 at a cost of US$1 billion, "Colossus" aims to detect civilisations passively through infrared heat signals.[44]

However signals detected are unlikely be conclusive. For example NASA's 2012 "Black Marble" experiment showed that significant stable light and heat sources on Earth originate from uninhabited areas and are naturally occurring (such as steady burning wildfires of Western Australia's deserts).[45] Extraterrestrial lightning, aurora, combustion

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and other natural phenomenon such as volcanoes may also be misidentified as being the activity of an ETI. Inaddition, this approach is somewhat anthropocentric as it assumes that such an ETI uses the visible spectrum likehumans do. Focusing on the visible spectrum technique would be unlikely to detect ETIs that use, for example,infrared or sonar for communication and navigation. To counter this, signals could be monitored at differentwavelengths and for predictable patterns that would exclude a natural explanation.

Atmospheric AnalysisAtmospheric analysis of planet (by means such as powerful spectroscopy) may reveal ETI activity. Similartechniques are currently used to indirectly study the atmospheres of objects in the Solar System as well as transitingthose of extrasolar objects. Atmospheric chemistry could be analysed for complex chemicals that may by thebyproducts of technology.Atmospheric emissions from industry on Earth including Nitrogen dioxide and Chlorofluorocarbons are detectablefrom space.[46] Artificial pollution may therefore be detectable on extrasolar planets. Though there remains apossibility of mis-detection, for example the Atmosphere of Titan has detectable signatures of complex chemicalsthat are similar to what on Earth are industrial pollutants, though obiously not the byproduct of civilisation.[47]

SETI has proposed searching for artificial atmospheres created by planetary engineering to produce habitableenvironments for colonisation by an ETI.[48] Similarly the signatures of a terraformed Martian environment (byintroducing complex warming gases) might be detectable from outside the Solar System. Likewise neighbouringplanets with strong similarities in atmospheric breathing gas composition could indicate an ETI's expansion withinits home system, particularly if complex gases were also present. For example, a fully terraformed Mars (and Venus)would likely have unexpectedly similar concentrations of oxygen and nitrogen to the Earth which could beobservable from outside the Solar System and deduced when taking into account the respective planetary properties(age, mass, distance from the Sun) to be artificial.

Asteroid miningTraces of targeted asteroid mining on asteroids and comets could also be utilized for the search of ETI.[49]

Search for Extraterrestrial Starships or StarprobesRobert Zubrin has pointed out that interstellar vehicles have the potential to be detectable from scores and evenhundreds of light years.[50]

Fermi paradoxItalian physicist Enrico Fermi suggested in the 1950s that if technologically advanced civilizations are common inthe universe, then they should be detectable in one way or another. (According to those who were there,[51] Fermieither asked "Where are they?" or "Where is everybody?")The Fermi paradox can be stated more completely as follows:

The size and age of the universe incline us to believe that many technologically advanced civilizations mustexist. However, this belief seems logically inconsistent with our lack of observational evidence to support it.Either (1) the initial assumption is incorrect and technologically advanced intelligent life is much rarer than webelieve, or (2) our current observations are incomplete and we simply have not detected them yet, or (3) oursearch methodologies are flawed and we are not searching for the correct indicators.

Possible explanations for the paradox suggest, for example, that while simple life may well be abundant in the universe, intelligent life may be exceedingly rare. In 2000, Peter Ward, professor of Biology and of Earth and Space Sciences at the University of Washington authored a book claiming the Rare Earth hypothesis. In short, the theory claims that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely

Search for extraterrestrial intelligence 12

combination of astrophysical and geological events and circumstances. This hypothesis contradicts the principle ofmediocrity, which SETI takes as an assumption.Another suggestion, made by astrophysicist Ray Norris in 2000[52] (and subsequently by Allen Tough[53]) was thatgamma-ray burst events are sufficiently frequent to sterilize vast swaths of galactic real-estate. This idea wassubsequently popularized by physicist Arnon Dar, and described in the show Death Star on PBS Nova.[54]

Science writer Timothy Ferris has posited that since galactic societies are most likely only transitory, an obvioussolution is an interstellar communications network, or a type of library consisting mostly of automated systems.They would store the cumulative knowledge of vanished civilizations and communicate that knowledge through thegalaxy. Ferris calls this the "Interstellar Internet", with the various automated systems acting as network "servers".If such an Interstellar Internet exists, the hypothesis states, communications between servers are mostly throughnarrow-band, highly directional radio or laser links. Intercepting such signals is, as discussed earlier, very difficult.However, the network could maintain some broadcast nodes in hopes of making contact with new civilizations.Although somewhat dated in terms of "information culture" arguments, not to mention the obvious technologicalproblems of a system that could work effectively for billions of years and requires multiple lifeforms agreeing oncertain basics of communications technologies, this hypothesis is actually testable (see below).Another scenario is that it is not the civilisation itself that is transitory, rather it is the interest in exploring space thatis transitory. A civilisation with technology that has advanced a mere century beyond ours might be capable ofbiological and cybernetic projects way beyond what we can envision today. The attraction of manufacturing theirown lifeforms and living in virtual worlds of their own design may dwarf any of the inclinations to explore spacethat we would expect them to have.An alternate hypothesis is that evolutionary pressures in many environments favor species which rapidly consumeavailable resources once they achieve dominance. By the time they have achieved sufficient technology to come tothe notice of other civilizations, they are already well on their way to exhausting the resources of their host planet.Therefore the time period available for communication is finite, and very small compared with planetary timescales.Once a planet's finite resources are exhausted no further species on that planet can develop advanced technology.Another problem is the vastness of space. Despite piggybacking on the world's most sensitive radio telescope,Charles Stuart Bowyer said, the instrument could not detect random radio noise emanating from a civilization likeours, which has been leaking radio and TV signals for less than 100 years. For SERENDIP and most other SETIprojects to detect a signal from an extraterrestrial civilization, the civilization would have to be beaming a powerfulsignal directly at us. It also means that Earth civilisation will only be detectable within a distance of 100 lightyears.[55]

Post detection disclosure protocolThe International Academy of Astronautics (IAA) has a long-standing SETI Permanent Study Group (SPSG,formerly called the IAA SETI Committee), which addresses matters of SETI science, technology, and internationalpolicy. The SPSG meets in conjunction with the International Astronautical Congress (IAC) held annually atdifferent locations around the world, and sponsors two SETI Symposia at each IAC. In 2005, the IAA established theSETI: Post-Detection Science and Technology Taskgroup (Chairman, Professor Paul Davies) "to act as aStanding Committee to be available to be called on at any time to advise and consult on questions stemming from thediscovery of a putative signal of extraterrestrial intelligent (ETI) origin." It will use, in part, the Rio Scale[56] toevaluate the importance of releasing the information to the public.[57]

When awarded the 2009 TED Prize SETI Institute's Jill Tarter outlined the organisation's "post detection protocol".[58] During NASA's funding of the project, an administrator would be first informed with the intention of informing the United States executive government. The current protocol for SETI Institute is to first internally investigate the signal, seeking independent verification and confirmation. During the process, the organisation's

Search for extraterrestrial intelligence 13

private financiers would be secretly informed. Once a signal has been verified, a telegram would be sent via theCentral Bureau for Astronomical Telegrams. Following this process, Tarter says that the organisation hold a pressconference with the aim of broadcasting to the public. SETI Institute's Seth Shostak has claimed that knowledge ofthe discovery would likely leak as early as the verification process.[59]

However the protocols mentioned apply only to radio SETI rather than for METI (Active SETI).[60] The intention forMETI is covered under the SETI charter "Declaration of Principles Concerning Sending Communications withExtraterrestrial Intelligence".The SETI Institute does not officially recognise the Wow! signal as of extraterrestrial origin (as it was unable to beverified). The SETI Institute has also publicly denied that the candidate signal Radio source SHGb02+14a is ofextraterrestrial origin[61][62] though full details of the signal, such as its exact location have never been disclosed tothe public. Although other volunteering projects such as Zooniverse credit users for discoveries, there is currently nocrediting or early notification by SETI@Home following the discovery of a signal.Some people, including Steven M. Greer,[63] have expressed cynicism that the general public might not be informedin the event of a genuine discovery of extraterrestrial intelligence due to significant vested interests. Some, such asBruce Jakosky[64] have also argued that the official disclosure of extraterrestrial life may have far reaching and as yetundetermined implications for society, particularly for the world's religions.

CriticismAs various SETI projects have progressed, some have criticized early claims by researchers as being too "euphoric"or "optimistic". For example, Peter Schenkel, while remaining a supporter of SETI projects, has written that "[i]nlight of new findings and insights, it seems appropriate to put excessive euphoria to rest and to take a moredown-to-earth view ... We should quietly admit that the early estimates—that there may be a million, a hundredthousand, or ten thousand advanced extraterrestrial civilizations in our galaxy—may no longer be tenable."[] CliveTrotman presents some sobering but realistic calculations emphasizing the timeframe dimension.[65]

SETI has also occasionally been the target of criticism by those who suggest that it is a form of pseudoscience. Inparticular, critics allege that no observed phenomena suggest the existence of extraterrestrial intelligence, andfurthermore that the assertion of the existence of extraterrestrial intelligence has no good Popperian criteria forfalsifiability.[66]

In response, SETI advocates note, among other things, that the Drake Equation was never a hypothesis, and so neverintended to be testable, nor to be "solved"; it was merely a clever representation of the agenda for the world's firstscientific SETI meeting in 1961, and it serves as a tool in formulating testable hypotheses. Further, they note that theexistence of intelligent life on Earth is a plausible reason to expect it elsewhere, and that individual SETI projectshave clearly defined "stop" conditions. Many detractors have not considered the collection and processing of data,the first order of business, and the refining of those data streams, in the case of SETI through algorithm optimization.To justify SETI projects does not require an acceptance of the Drake equation. Science proceeds through hypothesis.If one were to only take what was at face value observable, many scientific phenomena never would have beendiscovered.The search for extraterrestrial intelligence is not an assertion that extraterrestrial intelligence exists or are visitingEarth, and conflating the two can be seen as a straw man argument. There is an effort to distinguish the SETIprojects from UFOlogy, the study of UFOs, which many consider to be pseudoscience. In Skeptical Inquirer, MarkMoldwin argued that the important differences between the two projects were the acceptance of SETI by themainstream scientific community and that "[t]he methodology of SETI leads to useful scientific results even in theabsence of discovery of alien life."[67]

Some in the UFO community, such as nuclear physicist Stanton Friedman, are highly critical of the search and say it is unscientific. Friedman has writen that "if aliens are indeed visiting, then the Radio Telescope Search for ET

Search for extraterrestrial intelligence 14

signals would seem a useless exercise and might indicate the SS [SETI specialists] have been on the wrong track allalong". He has challenged SETI specialists to debate the issues, with no takers so far.[68] Examples of objections toSETI include questioning energy requirements as well as why advanced civilizations would use radio.

Active SETIActive SETI, also known as messaging to extraterrestrial intelligence (METI), consists of sending signals into spacein the hope that they will be picked up by an alien intelligence. Physicist Stephen Hawking, in his book A BriefHistory of Time, suggests that "alerting" extraterrestrial intelligences of our existence is foolhardy, citing mankind'shistory of treating his fellow man harshly in meetings of civilizations with a significant technology gap. He suggests,in view of this history, that we "lay low".The concern over SETI was raised by the science journal Nature in an editorial in October 2006, which commentedon a recent meeting of the International Academy of Astronautics SETI study group. The editor said, "It is notobvious that all extraterrestrial civilizations will be benign, or that contact with even a benign one would not haveserious repercussions" (Nature Vol 443 12 Oct 06 p 606). Astronomer and science fiction author David Brin hasexpressed similar concerns.[69]

Richard Carrigan, a particle physicist at the Fermi National Accelerator Laboratory near Chicago, Illinois, suggestedthat passive SETI could also be dangerous in the style of computer viruses.[70] Computer security expert BruceSchneier dismissed this possibility as a "bizarre movie-plot threat".[71]

To lend a quantitative basis to discussions of the risks of transmitting deliberate messages from Earth, the SETIPermanent Study Group of the International Academy of Astronautics adopted in 2007 a new analytical tool, the SanMarino Scale.[72] Developed by Prof. Ivan Almar and Prof. H. Paul Shuch, the scale evaluates the significance oftransmissions from Earth as a function of signal intensity and information content. Its adoption suggests that not allsuch transmissions are equal, and each must be evaluated separately before establishing blanket international policyregarding active SETI.[citation needed]

However, some scientists consider these fears about the dangers of METI as panic and irrational superstition; see, forexample, Alexander L. Zaitsev's papers.[73][74]

Results of extraterrestrial contact for humanityA part of the search for extraterrestrial intelligence involves the analysis of the implications of extraterrestrial contactfor humanity, culturally, scientifically, technologically, and socially. Numerous contact scenarios have been createdby scientists who are involved in the search for extraterrestrial intelligence in order to better contextualize what mayeventually occur when humanity is contacted by an extraterrestrial species. These studies reveal that the result ofextraterrestrial contact will be strongly governed by the benevolence or malevolence of an extraterrestrialcivilization, how advanced it is technologically, and whether or not such a species sends robotic probes to contacthumanity, as opposed to radio signals from a centralized source,[][][] as well as biological similarities and differencesbetween humanity and the extraterrestrial species.[]

Malevolent civilizations, as speculated by Dr. Michio Kaku (2009) and Robert Freitas (1978) independently, maypossess resources which can destroy humanity with little effort on the part of the extraterrestrial civilization and withlittle chance at resistance.[][] Supporting the view of aggression, Seth Shostak, a senior astronomer at the SETIInstitute, speculates that the finite quantity of resources in the galaxy[] and the "explorer" nature of any civilizationwould cause it to be aggressive in the same way that human explorers have been historically.[]

However, these views have been disputed by, among others, the late Carl Sagan, who speculated that any technologically advanced extraterrestrial civilization would be advanced ethically as well, and would not be aggressive, and that humanity would, due to the extraterrestrial civilization's technological prowess, reciprocate this non-aggression.[] Corroborating this view, a study conducted by James W. Deardorff states that only a small

Search for extraterrestrial intelligence 15

percentage of extraterrestrial civilizations may be aggressive.[] Such civilizations may use various methods in orderto help humanity, such as immediate actions to avert catastrophe (i.e. creating computer glitches in nuclear-weaponssystems on the eve of global nuclear conflagration) or long-term mitigation of risks which may destroy humanitybefore true technological cooperation.[]

Extraterrestrial civilizations may also have specific implications for various aspects of humanity against a backdropof these broad contact scenarios. In particular, religion may undergo various degrees of change, from areinterpretation of religious texts by theologians to accommodate the new discovery[] to a complete reinvention ofreligion, with extraterrestrials bringing humanity into an all-encompassing cosmic faith.[]

In addition to the religious problems which may arise, Michaud (2006) and Othman (2011) speculate thatextraterrestrial contact may cause problems for global foreign relations, causing global political divisiveness over theinvolvement of radio astronomers worldwide in post-detection processes[] and over which bodies represent humanityas a whole in the wake of contact, as well as how, with what content, and whether a message should be sent in replyto what has been received from extraterrestrial intelligence.[] On a larger scale, Harrison (2000) has speculated that,as humanity builds relations with an extraterrestrial civilization, humanity may be given an invitation to a "GalacticClub" with numerous other civilizations.[]

As well as political implications, extraterrestrial contact may have scientific implications as well. Extraterrestrialcivilizations may, as Harrison (2002) speculates, cause a profound technological and societal impact of a magnitudemuch greater than the Industrial Revolution of the late-eighteenth to nineteenth centuries, and extraterrestrial life ingeneral may give us knowledge of extraterrestrial biochemistry.[] However, extraterrestrial civilizations, if they knowterrestrial biology and its weaknesses and are malevolent, may conduct biological warfare by means of pathogensand invasive species completely unknown to the Earth previously.[]

References[6] Prepare for Contact (http:/ / www. lettersofnote. com/ 2009/ 11/ prepare-for-contact. html). Letters of Note (2009-11-06). Retrieved on

2011-10-14.[7] http:/ / www. coseti. org/ morris_0. htm[8] http:/ / www. bigear. org/ vol1no1/ interste. htm[9] "Science: Project Ozma," Time, Apr. 18, 1960 (http:/ / www. time. com/ time/ magazine/ article/ 0,9171,874057,00. html) (web version

accessed 17 September 2010)[11] Robert H. Gray, The Elusive WOW: Searching for Extraterrestrial Intelligence 2012, Palmer Square Press, Chicago. 242 pages. ISBN

978-0-9839584-4-4.[13] Garber, Stephen J., Searching for Good Science: the Cancellation of NASA's SETI Program (http:/ / history. nasa. gov/ garber. pdf), Journal

of the British Interplanetary Society, 52, pp. 3-12, 1999[19] Alan M. MacRobert. "SETI Searches Today" (http:/ / www. skyandtelescope. com/ resources/ seti/ 3304561. html?page=5& c=y). Sky and

Telescope (2010?).[20] Terdiman, Daniel. (2008-12-12) SETI's large-scale telescope scans the skies | Geek Gestalt – CNET News (http:/ / news. cnet. com/

8301-13772_3-10121889-52. html). News.cnet.com. Retrieved on 2011-10-14.[21] Rendering of 350 image – Photos: Searching the heavens for life – CNET News (http:/ / news. cnet. com/ 2300-11397_3-6248324-1.

html?tag=mncol). News.cnet.com (2008-12-12). Retrieved on 2011-10-14.[22] http:/ / www. seti. org/ node/ 905[35] http:/ / en. wikipedia. org/ w/ index. php?title=Search_for_extraterrestrial_intelligence& action=edit[38] Dyson sphere at Scholarpedia (http:/ / www. scholarpedia. org/ article/ Dyson_sphere)[41] http:/ / newscenter. berkeley. edu/ 2012/ 10/ 05/ grants-help-scientists-explore-border-between-science-science-fiction/[42] http:/ / www. upi. com/ Science_News/ 2011/ 11/ 03/ SETI-search-urged-to-look-for-city-lights/ UPI-89301320361336/ #ixzz2HRkOcctY[43] Extrasolar Planets: Formation, Detection and Dynamics Rudolf Dvorak, page 14 John Wiley & Sons, 2007[44] http:/ / www. space. com/ 21480-extraterrestrial-civilization-heat-seeking-telescope. html[45] http:/ / www. nasa. gov/ mission_pages/ NPP/ news/ aus-fires. html[46] http:/ / www. esa. int/ Our_Activities/ Observing_the_Earth/ Satellite_sniffs_out_chemical_traces_of_atmospheric_pollution[47] http:/ / www. space. com/ 21470-saturn-moon-titan-haze-cassini. html[48] Alien Hairspray May Help Us Find E.T. (http:/ / www. space. com/ 18624-alien-life-search-hairspray. html) Charles Q. Choi, SPACE.com

26 November 2012

Search for extraterrestrial intelligence 16

[49] Evidence of asteroid mining in our galaxy may lead to the discovery of extraterrestrial civilizations (http:/ / smithsonianscience. org/ 2011/04/ evidence-of-asteroid-mining-in-our-galaxy-may-lead-to-the-discovery-of-extraterrestrial-civilizations/ ) smithsonianscience.org; AsteroidMining: A Marker for SETI? (http:/ / www. centauri-dreams. org/ ?p=17357) centauri-dreams.org; Duncan Forgan, Martin Elvis:ExtrasolarAsteroid Mining as Forensic Evidence for Extraterrestrial Intelligence (http:/ / arxiv. org/ abs/ 1103. 5369)@ arxiv.org, (Retrieved2011-04-07)

[50] (http:/ / articles. adsabs. harvard. edu/ full/ 1995ASPC. . . 74. . 487Z)[58][58] Jill Tarter speech 2009 TED Prize acceptance[59][59] Coast to Coast AM interview February 24, 2000[60] Pope, Nick What to do if we find extraterrestrial life? Who gets notified? Do we reply? Experts are already arguing (http:/ / www. msnbc.

msn. com/ id/ 39675346/ ns/ technology_and_science/ t/ what-do-if-we-find-extraterrestrial-life/ #. TsthMz3z3BI) msnbc.com 10/18/2010[63] Vance, Ashlee SETI urged to fess up over alien signals (http:/ / www. theregister. co. uk/ 2006/ 07/ 31/ signals_seti/ ) The Register 31st July

2006[64] Siegel, Lee [The Meaning of Life http:/ / nai. nasa. gov/ news_stories/ news_print. cfm?ID=138] NASA July 6, 2001

Further reading• McConnell, Brian; Chuck Toporek (2001). Beyond Contact: A Guide to SETI and Communicating with Alien

Civilizations. O'Reilly. ISBN 0-596-00037-5.• Perelmuter, J.M. (2006). The Sinusoidal Spaghetti. iUniverse. ISBN 0-595-41713-2.• MJ Carlotto (2007). "Detecting Patterns of a Technological Intelligence in Remotely Sensed Imagery" (http:/ /

spsr. utsi. edu/ articles/ markjbis2007. pdf). J British Interplanetary Society 60: 28–39.• John B Campbell (2006). "Archaeology and direct imaging of exoplanets" (http:/ / eprints. jcu. edu. au/ 1027/ 1/

S1743921306009392a. pdf). In C. Aime & F. Vakili. Proceedings of the International Astronomical Union.Cambridge University Press. pp. 247 ff. ISBN 0-521-85607-8.

• Frank White: The Seti Factor – How the Search for Extraterrestrial Intelligence Is Changing Our View of theUniverse and Ourselves. Walker & Company, New York 1990, ISBN 978-0-8027-1105-2

• David W. Swift: Seti Pioneers — Scientists Talk about Their Search for Extraterrestrial Intelligence. Univ. ofArizona Press, Tucson 1993, ISBN 0-8165-1119-5

• P.Morrison, J.Billingham, J.Wolfe: The search for extraterrestrial intelligence-SETI. NASA SP, Washington1977, online (http:/ / history. nasa. gov/ SP-419/ sp419. htm)

• Brian MacConnell: Beyond contact – a guide to SETI and communicating with Alien civilizations. O'Reilly,Beijing 2001, ISBN 0-596-00037-5.

External links• Search for Extra-Terrestrial Intelligence (http:/ / setiathome. berkeley. edu/ )• The eerie silence (http:/ / physicsworld. com/ cws/ article/ indepth/ 41816) Expanding the parameters of the

search for technological and evolutionary footprints of extrasolar civilizations, beyond only radio signals.(Physics World). Mar 2, 2010.

• Series of 90 videos of SETI Talks, by setiinstitute on YouTube (http:/ / www. youtube. com/ setiinstitute)• Passage of radiation through wormholes of arbitrary shape by R. A. Konoplya, and A. Zhidenko (http:/ / arxiv.

org/ abs/ 1004. 1284)• Project Dorothy (http:/ / www. nhao. jp/ ~narusawa/ oseti/ project-dorothy. html)• The SETI Challenge, a series of decoding challenges (http:/ / seti. matthen. com)• Is it true that there could be intelligent life out there? (http:/ / www. physics. org/ facts/ sand-et. asp,) physics.org

page about SETI• "SETI: Astronomy as a Contact Sport - A conversation with Jill Tarter" (http:/ / www. ideasroadshow. com/

issues/ jill-tarter-2013-04-19), Ideas Roadshow, 2013

Article Sources and Contributors 17

Article Sources and ContributorsSearch for extraterrestrial intelligence  Source: http://en.wikipedia.org/w/index.php?oldid=559255411  Contributors: .:Ajvol:., 2T, 5 albert square, A bit iffy, A2Kafir, A876, Acoma Magic,Adam McMaster, Adreamsoul, Againme, Ahoerstemeier, Akerans, Alansohn, Albert.a.jackson, Aldebaran66, Ale jrb, Altaïr, Amalas, Amaury, AmazeStar, Amy1r4e3, Andre Engels,Andrewpmk, Andy M. Wang, Andypp123, Arb, ArchonMagnus, ArnoldReinhold, Asparagus, AstroMark, Ati3414, Axeloide, B1atv, BD2412, Backslash Forwardslash, BatteryIncluded, Beland,Benzband, Bermy88, Between My Ken, Bevo, Bgwhite, Billy9999, Blelbach, Bongwarrior, Borgx, Braincricket, Breno, Brentt, Brews ohare, Brianporter, BruceSwanson, Bruguiea, BryanDerksen, Bryan Seecrets, Bubba73, C S, CWenger, Cadillac, Caleb rosenberg, Caliga10, Caltas, CanadianLinuxUser, Cantanchorus, Caper13, Capricorn42, Carbuncle, Carmichael, Causa sui,CelticJobber, Chairboy, Chill doubt, Chris the speller, Chris55, ChrisBianchi, Chzz, Cimon Avaro, Closedmouth, Cnmirose, Codemonkey, Coffee, Conversion script, Craig Baker, Crakkpot,Crum375, Cyfal, DVdm, Dane 1981, Daniel, Danielmfonseca, Danjoseofluzon, Danlibbo, Dariusz Peczek, Darkwand, David Be, David Haslam, David J Johnson, David.Mestel, DavidCary,Davidcannon, DeadEyeArrow, Debresser, Deglr6328, Derek Ross, Derekbd, Dethme0w, Discospinster, Djcunning, Dmol, Doc Perel, Doc richard, Docame, DrStrangedlove, DrTorstenHenning,Draytonian, Drbogdan, DreamGuy, Drseti, Dumoren, Dusty777, E23, ESkog, Ebthi2012, Eilthireach, Eleassar, Ellmist, Ellywa, Eloquence, Emax0, Emijrp, Emw, Eric Kvaalen, Eric-Wester,Eschbaumer, Eshuy, EvenGreenerFish, Exeunt, Eye.earth, Eyreland, FWL.A.M.F., Fabartus, Fashionslide, Faturita, FayssalF, Fdp, Fehler, Ferkelparade, Fethers, Fountains of Bryn Mawr,Fraggle81, Furrykef, GL, Gabbe, Gabenowicki, Gadgetball, Gaius Cornelius, Galactic drifter seti, Gamaliel, Gap9551, Geimas5, Geoffrey.landis, Geraldo Perez, Giftlite, Giordanobrunoburning,Giuliopp, Glennpicker, Gogo Dodo, Golbez, Graham87, Grant Gussie, Gravitophoton, Gregfitzy, Grizzly, GyroMagician, Gzkn, Hadal, Hamiltondaniel, Hamiltonstone, Havermayer, Headbomb,Hede2000, I5bala, ID4EVER, II MusLiM HyBRiD II, Ice Cold Beer, Icek, Ihardlythinkso, Impi, Imran, Infrogmation, Ingolfson, Insanity Incarnate, Iridescent, Irishguy, Ixfd64, J.delanoy, JFMephisto, JNW, JaGa, Jacob.husted, Jacob1207, James McBride, Jamesslot3, Jan Arkesteijn, JayEsJay, Jellyfisho, Jemecki, Jetblack101, Jiang, Jimaginator, Jimp, Jjhat1, Jni, John, John D. Croft,John of Reading, JohnBlackburne, Johntex, JonHarder, Jondel, Jonstewartwiki, Jonverve, Joseph Dwayne, Jurystar, KG4SGP, KGyST, Kafziel, Kalidasa 777, Katalaveno, Keilana, Kent Witham,Kerowren, Kevin Baas, Kfitzner, Kingpin13, Kingturtle, Kinhull, Kirrages, Kjkolb, KnowledgeOfSelf, Kosebamse, Koyaanis Qatsi, Kubigula, Kuralyov, LAgurl, Lackey, Lb.at.wiki,LeDiableBrun, Leda74, Leeroy SD, Leon7, Lexor, Liam langan, Lifeboatpres, Lightmouse, LilHelpa, Loadmaster, Looxix, LordBleen, Lorenzarius, LouScheffer, Lowellian, Lradrama, M.nelson,MER-C, METIfan, MadGuy7023, Mani1, Manwithbrisk, Maradona01, Marc9510000, Marcika, Marcus Brute, MarkusJ, Marskell, Marvinandmilo, Marwo, Materialscientist, Maurice Carbonaro,Mayumashu, Mbecker, Melly42, Mereda, Michael A. White, Michael Hardy, Michael T. 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Image Sources, Licenses and ContributorsFile:SETI@home Multi-Beam screensaver.png  Source: http://en.wikipedia.org/w/index.php?title=File:SETI@home_Multi-Beam_screensaver.png  License: unknown  Contributors:Namazu-tronFile:TerrestrialMicrowaveWindow.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:TerrestrialMicrowaveWindow.jpg  License: Public Domain  Contributors: Philip Morrison, JohnBillingham, John WolfeFile:Arecibo Observatory Black and White.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Arecibo_Observatory_Black_and_White.jpg  License: Public Domain  Contributors:NASAFile:Wow signal.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Wow_signal.jpg  License: Public Domain  Contributors: Credit: The Ohio State University Radio Observatory andthe North American AstroPhysical Observatory (NAAPO).File:NASA-SETI-Sensitivity.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:NASA-SETI-Sensitivity.jpg  License: Public Domain  Contributors: John H. Wolfe, Robert E. Edelson,John Billingham, R. Bruce Crow, Samuel Gulkis, Edward T. Olsen, Bernard M. Oliver, Allen M. Peterson, Charles L. Seeger, Jill C. Tarter.

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