Seti
Seti
SETI is an organized effort to detect communications from intelligent beings somewhere in the universe besides Earth. Since radio astronomers first tuned into the skies, scientists have listened for an elusive radio signal that would confirm the existence of extraterrestrial intelligence. One of the major efforts that began during the last quarter of the twentieth century and has now continued into the twenty-first century is a project termed the Search for Extra-Terrestrial Intelligence (SETI). Over the years, the SETI project has evolved into a variety of programs utilizing research resources at a number of different facilities. A number of other programs have embraced at least part of the SETI concept and goals.
To search the entire universe is an impossibility for humans under current technological abilities. Consequently, to perform a search for intelligent life, certain assumptions had to be made by the scientific community. These primary assumptions are: Earth is not unique in its ability to support life, especially intelligent life like humans; the presence of water on a planet is necessary for intelligent life; extraterrestrial life will be most likely based on the element carbon; and a star similar to the sun is essential for extraterrestrial life to evolve. Based on these assumptions, SETI estimates that about 10% of the stars in the Milky Way galaxy are like the sun. Within around 100 light-years of Earth, there are about 1,000 of these sun like stars. Consequently, SETI scientists are concentrating muchof their efforts on these prime targets for intelligent life.
As of October 2006, only a fraction of the potential sources of radio signals have been thoroughly observed, and no signal definitively identified as extraterrestrial in origin. As of 2004, about 10% of the visible night sky has never been scanned for signals. Less than 50% of the visible sky had been briefly scanned more than once.
SETI is a term that encompasses several different groups and their efforts to seek out intelligent extraterrestrial life. The driving force behind these groups is the ancient human desire to understand the origin and distribution of life throughout the universe. As technology progresses, SETI have evolved from single project observations of the night sky to coordinated efforts in data analysis that, as of 2004, involved more than 5 million volunteers from around the globe (over 200 countries), who had collectively donated over 19 million years or collective computer CPU (central processing unit) time.
The concept of SETI began from the 1959 paper written by physicists Giuseppe Cocconi (1914–) and Philip Morrison (1915–2005) in which they suggested that interstellar communications would be best possible in the range of 1 to 10 gigahertz. Then, Cornell University professor and American astronomer and astrophysicist Frank Drake (1930–) founded the first SETI program in late 1959. Drake reinforced his idea of scanning the skies with his famous Drake equation. The Drake equation predicts the abundance of intelligent life within a certain galaxy.
(N = N * f(p) * n(e) * f(l) * f(i) * f(c) * f(L))
The first continuous SETI program revolved around Big Ear, the Ohio State University 360-feet 9 (110-m) wide, 500-feet (150-m) long, and 70-feet (20-m) high radio telescope that was constructed in Delaware, Ohio, in 1963.
The second major development of SETI took shape in the late 1960s when NASA (National Aeronautics and Space Administration) joined the program. NASA was minimally involved with the project, but spawned many SETI related programs. These programs included the Microwave Observing Project, Project Orion, the High Resolution Microwave Survey, Toward Other Planetary Systems. One of the most intensive SETI related programs NASA would initiate began in 1992, but the U.S. Congress cut funding for the program within one year. SETI projects now must rely on private funding, and SETI operates through the SETI Institute, a non-profit corporation.
Historically, scientists used several different methods for searching for extraterrestrial intelligence. The earliest method, and still most commonly used in present research, is the scanning of electromagnetic emissions. Radio waves are picked up by an array of radio telescopes and scanned for non-random patterns. More modern methods expand the search to other regions of the electromagnetic spectrum, including the infrared spectrum.
As of 2006, the University of California at Berkeley hosts the most widespread SETI effort in history. Berkeley projects include SETI@Home (a distributed computing project), Search for Extraterrestrial Radio Emissions at the Nearby Developed Intelligent Populations (SERENDIP), Optical SETI, and Southern SERENDIP. SETI@Home collects its data in the background of the Arecibo Radio Observatory and relays it back to the laboratory in Berkeley. The data is, then, divided into work units where it is sent out to the personal computers of volunteers throughout the world. These personal computers scan the data for candidate signals. If a candidate signal appears, it is relayed back to Berkeley, where the signal is checked for data integrity. Finally, the lab removes radio interference and scans the data for final candidates. The Berkeley faction of SETI will be expanding their efforts with the Allen Telescope Array (ATA, formerly known as the One Hectare Telescope) designated specifically for this research. The array will be equivalent to a single large dish over 328 feet (100 meters) on a side. As of 2006, about one-fifth of the antennas have been completed.
Project Phoenix, also run by the SETI Institute, concentrates on obtaining signals from targeted areas within the Milky Way galaxy. The focused Phoenix receiver can amass radio energy for longer periods of time and with greater sensitivity than previous SETI radio-telescopes, allowing for faster and more precise analysis. The search is able to search the galaxy out to about 200 light-years.
Although only a small fraction of the sky has been scanned, so far, SETI initiatives have not confirmed a signal from an extraterrestrial source that is conclusive proof of an extraterrestrial intelligence. A few strong and unexplained signals have intrigued SETI scientists; the most well known was received in 1977 at the Ohio State Radio Observatory. None of the signals have ever repeated.
On August 15, 1977, astronomer Jerry Ehman was going through the computer printouts of Big Ear, when he discovered the reception of what remained throughout the twentieth century as the best candidate for a signal that might be classified as a sign of extraterrestrial intelligence. Excited, Ehman scribbled, “WOW!” on the printout and forever after the signal became known as the “WOW!” signal.
Despite repeated attempts to reacquire the signal, the fact that the signal was never again recorded, makes many astronomers, including Ehman, skeptical about the origins of the “WOW!” signal. If it were an intentional signal, astronomers argue, the sending civilization would have repeated it—or something like it—many times. A number of SETI experts now assert the “WOW!” signal was, perhaps, a mere reflection of a signal from the Earth off an orbiting satellite.
In March 2003, researchers with the SETI@Home (which was started in May 1999 so that any individual could download its software and participate in SETI research) distributed computing project, the largest computation in human history, announced that the 150 highest probability candidate signal sources would be systematically reexamined by the Arecibo telescope in Puerto Rico. The candidate signals were identified over a four-year period during which SET@Home participants donated more than one million years of computing time.
The final stellar countdown phase of the SETI@Home project will attempt to further discriminate between signals that are random noise or terrestrial interference and those that might be of extraterrestrial origin. The signals of highest investigative interest were evaluated by several factors, including the number of times the radio source was detected, strength of signal, apparent proximity of origin to known and observable stars, and the type of star and/or presence of known planets near the apparent source of the signal.
As of 2005, the International Academy of Astronautics (IAA) created the SETI: Post-Detection Science and Technology Task Group in order to advise and consult on matters pertaining to extraterrestrial intelligence. In the early years of the twenty-first century, several countries, including the United States have been sending spacecraft to planets within the solar system. They are also observing the evolution of the universe with telescopes on Earth and orbiting in space. In 2005, for example, NASA’s Spitzer Space Telescope found gaseous chemicals around a star that is only 375 light-years from Earth. These chemicals could likely form protein and DNA (deoxyribonucleic acid), some of the ingredients for the building blocks of life as found on Earth.
As scientists explore the universe with equipment on Earth and with spacecraft sent into the solar system, humans are learning more and more about how the universe develops. The Milky Way galaxy is an average galaxy within the universe, however, it appears to be rich in possibilities for intelligent life. Whether intelligent life exists elsewhere than on Earth is still a question to be answered. As of October 2006, SETI has not confirmed any discovery of communications from intelligent life forms from outer space.
See also Astronomical unit; Astronomy; Astrophysics; Cosmology; Radio astronomy.
Resources
BOOKS
Bova, Ben. Faint Echoes, Distant Stars: The Science and Politics of Finding Life Beyond Earth. New York: William Morrow, 2004.
McConnell, B. Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations. O’Reilly and Associates, 2001.
PERIODICALS
Korpela, E. “SETI@Home—massively distributed computing for SETI.” Computing in Science and Engineering Magazine. Volume: 3 Issue: 1 (2001):78-83.
OTHER
University of California. “SETI@Home.” <http://setiathome.berkeley.edu/> (accessed October 25, 2006 ).
SETI Institute. “Homepageof SETI Institute.” <http://www.seti.org/site/pp.asp?c=ktJ2J9MMIsE> (accessed October 25, 2006 ).
Lee W. Lerner
SETI
SETI
Of all the scientific efforts to find life in space, none has potential consequences as profound as SETI, the Search for Extraterrestrial Intelligence. SETI researchers are trying to uncover other civilizations whose technical sophistication is at a human level or higher.
While science fiction routinely describes face-to-face encounters with intelligent aliens, it may be that we will never actually meet extraterrestrials. Building fast rockets capable of carrying living cargo to the stars is a formidable, perhaps even impossible, challenge. The amount of energy required to hurl a craft the size of the space shuttle at even half the speed of light is enormous—equivalent to the energy required to keep New York City running for 10,000 years.* This is a problem of physics, not technology.
On the other hand, there are ways to reach other civilizations without interstellar travel. In 1959 Philip Morrison and Giuseppe Cocconi, two physicists at Cornell University, made a simple calculation to determine how far away a good radio receiver and a large antenna could detect our most powerful military radar transmitters. To their surprise, the answer turned out to be light-years—typical of the distances to the stars. Morrison and Cocconi realized that while interstellar rocketry was hard, interstellar communication by radio was easy. They suggested that other galactic civilizations might be discovered by simply eavesdropping on their radio traffic.
The Search for Extraterrestrial Intelligence
Within months, Frank Drake, a young radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, tried to do just that. He was unaware of the work of the two Cornell physicists but had independently thought of the same idea. For several weeks in the spring of 1960, Drake pointed an 85-foot antenna (a radio telescope) at two Sun-like stars, Tau Ceti and Epsilon Eridani, tuning his receiver up and down the dial near 1,420 megahertz (MHz). This particular frequency was chosen because it is truly a universal radio channel. Hydrogen gas, which drifts and swirls through the immense spaces between the stars, naturally emits some radio noise at 1,420 MHz. Drake believed that every sophisticated society in the cosmos would know of this hydrogen hiss, and consequently it would make sense to broadcast interstellar hailing signals near this sweet spot on the dial.
Drake's Project Ozma was the first modern SETI search. By the early twenty-first century, about seventy others were undertaken. One of the most ambitious was the NASA SETI program, which ultimately became known as the High Resolution Microwave Survey. NASA got into SETI slowly, beginning in the 1970s with a technical study of the equipment and strategy required for a serious search. In the fall of 1992, sufficient equipment had been built to start the listening. However, very shortly thereafter, the U.S. Congress stopped all NASA SETI efforts. The rationale for canceling this research was to reduce federal spending during an era of large budget deficits.
SETI work continued, however, funded in the United States by private donations. Most of these projects have been radio experiments, of the type pioneered by Drake. The SETI Institute, in California, runs the most sensitive search, known as Project Phoenix. Various large radio telescopes, including the king-sized 305-meter (1,000-foot) antenna at Arecibo, Puerto Rico, have been used by Project Phoenix to carefully examine the neighborhoods of nearby, Sun-like stars. Other projects, such as the University of California, Berkeley's SERENDIP experiment, sweep the sky in an attempt to survey greater amounts of cosmic real estate. While more of the heavens are examined, the sensitivity in any given direction is lower. Some of the SERENDIP data have been distributed on the Web for processing at home with a screen saver program known as SETI@home.
Additional radio SETI experiments are being carried out in Australia (Southern SERENDIP), Argentina (META II), and Italy. Starting in the late twentieth century, another approach to SETI has gained a number of adherents: so-called optical SETI. Rather than tuning the dial in search of persistent, artificial signals, ordinary telescopes (with mirrors and lens) are outfitted with special detectors designed to find very short (less than a billionth of a second) laser pulses from distant worlds.
The Probability of Success
So far, no confirmed extraterrestrial signals—either radio or optical—have been found by SETI scientists. What are the chances that the aliens will ever be found? In 1961 Drake summarized the problem with a simple formula that predicts the number of galactic civilizations that are broadcasting now. Known as the Drake Equation, the computation is simply a product of factors bearing on the existence of intelligence. These factors include the number of galactic stars capable of supporting life, the fraction of such stars with planets, the number of planets in a solar system on which life evolves, the fraction of inhabited worlds where intelligence appears, and the lifetime of a broadcasting society. While we still do not know many of these factors, some scientists contend that the recent evidence for extrasolar planets and the growing suspicion that biology might be a common phenomenon have increased the chances for finding intelligence among the stars.
SETI scientists have made plans to greatly expand their search during the first two decades of the twenty-first century. The SETI Institute will build the Allen Telescope Array, a large grouping of small antennas that will be used for full-time searching. A world consortium of radio astronomers is considering the construction of a radio telescope a kilometer in size, a gargantuan instrument that could also be used for SETI. Optical SETI experiments are already increasing in number and sophistication.
In light of this rapid improvement in experimental technique, some scientists are optimistic that a signal will be found in the early decades of the twenty-first century. If so, the consequences would be dramatic. If we can ever successfully find and decode any message accompanying the signal, we might learn something of the knowledge and culture of other galactic beings, most likely from a society technologically far more advanced than our own. Even if we never understand or reply to an interstellar message, simply knowing that we are not the only "game" in town—let alone the most interesting game—would give us new and valuable perspective.
see also Extrasolar Planets (volume 2); Life in the Universe, Search for (volume 2); Why Human Exploration? (volume 3).
Seth Shostak
Bibliography
Cocconi, Giuseppe, and Philip Morrison. "Searching for Interstellar Communications." Nature 84 (1959):844.
Davies, Paul. Are We Alone? Philosophical Implications of the Discovery of Extraterrestrial Life. New York: Basic Books, 1996.
Dick, Steven. J. Life on Other Worlds. Cambridge, UK: Cambridge University Press,1998.
Drake, Frank D., and Dava Sobel. Is Anyone out There? New York: Delacorte Press,1992.
Goldsmith, Donald, and Tobias C. Owen. The Search for Life in the Universe. Reading, MA: Addison-Wesley, 1992.
Harrison, Albert. After Contact: The Response to Extraterrestrial Life. New York: Plenum,1997.
Regis, Edward, Jr., ed. Extraterrestrials: Science and Alien Intelligence. Cambridge, UK:Cambridge University Press, 1985.
Shostak, Seth. Sharing the Universe: Perspectives on Extraterrestrial Life. Berkeley, CA:Berkeley Hills Books, 1998.
*At half the speed of light, travel time to Alpha Centauri, the nearest star system, would take nine years.
SETI
SETI
Since radio astronomers first tuned into the skies, scientists have listened for an elusive radio signal that would confirm the existence of extraterrestrial life. One of the major efforts in the last quarter of the twentieth century was a project termed the Search for Extraterrestrial Intelligence (SETI). Over the years the SETI project evolving into a variety of programs utilizing research resources at a number of different facilities. A number of other programs have embraced at least part of the SETI concept and goals. As of May 2003, only a fraction of the potential sources of radio signals have been thoroughly observed, and no signal definitively identified as extraterrestrial in origin. As of February 2003, nearly 10% of the visible night sky had never been scanned for signals. Less than 50% of the visible sky had been briefly scanned more than once.
SETI is a term that encompasses several different groups and their efforts to seek out intelligent extraterrestrial life. The driving force behind these groups is the ancient human desire to understand the origin and distribution of life throughout the Universe. As technology progresses, SETI have evolved from single project observations of the night sky to coordinated efforts in data analysis that, as of February 2003, involved more than four million volunteers from around the globe, who had collectively donated more than 1,327,600 years or collective computer CPU time .
Cornell University professor Frank Drake founded the first SETI program in late 1959. Drake reinforced his idea of scanning the skies with his famous Drake Equation. The Drake equation predicts the abundance of intelligent life within a certain galaxy .
The second major development of SETI took shape in the late 1960s when NASA joined the program. NASA was minimally involved the project, but spawned many SETI related programs. These programs included the Microwave Observing Project, Project Orion, the High Resolution Microwave Survey, Toward Other Planetary Systems, and more. One of the most intensive SETI related programs NASA would initiate began in 1992, but Congress cut funding for the program within a year. SETI projects now must rely on private funding, and SETI operates through the SETI Institute, a nonprofit corporation.
Historically, scientists used several different methods for searching for extraterrestrial intelligence. The earliest method, and still most commonly used in present research, is the scanning of electromagnetic emissions. Radio waves are picked up by an array of radio telescopes and scanned for non-random patterns. More modern methods expand the search to other regions of the electromagnetic spectrum , including the infrared spectrum .
As of 2003, the University of California at Berkeley hosts the most widespread SETI effort in history. Berkeley projects include SETI@Home (a distributed computing project), Search for Extraterrestrial Radio Emissions at the Nearby Developed Intelligent Populations (SERENDIP), Optical SETI, and Southern SERENDIP. SETI@Home collects its data in the background of the Arecibo Radio Observatory and relays it back to the lab in Berkeley. The data is then divided into workunits and sent out to the personal computers of volunteers throughout the world. These personal computers scan the data for candidate signals. If a candidate signal appears, it is relayed back to Berkeley, where the signal is checked for data integrity. Finally, the lab removes radio interference and scans the data for final candidates. The Berkeley faction of SETI will be expanding their efforts with the Allen Telescope Array (formerly known as the One Hectare Telescope) designated specifically for this research.
Project Phoenix, also run by the SETI Institute, concentrates on obtaining signals from targeted areas within our galaxy. The focused Phoenix receiver can amass radio energy for longer periods of time and with greater sensitivity than previous SETI radiotelescopes, allowing for faster and more precise analysis.
Although only a small fraction of the sky has been scanned, so far, SETI initiatives have not confirmed a signal from an extraterrestrial source that is conclusive proof of an extraterrestrial intelligence. A few strong and unexplained signals have intrigued SETI scientists; the most well known was received in 1977 at the Ohio State Radio Observatory. None of the signals have ever repeated.
On August 15, 1977, astronomer Jerry Ehman was going through the computer printouts of an earlier SETI-like project run by Ohio State University (dubbed, "Big Ear"), when he discovered the reception of what remained throughout the twentieth century as the best candidate for a signal that might be classified as a sign of extraterrestrial intelligence. Excited, Ehman scribbled, "WOW!" on the printout and forever after the signal became known as the "WOW!" signal.
Despite repeated attempts to reacquire the signal, the fact that the signal was never again recorded, makes many astronomers, including Ehman, skeptical about the origins of the "WOW!" signal. If it were an intentional signal, astronomers argue, the sending civilization would have repeated it—or something like it—many times. A number of SETI experts now assert the "WOW!" signal was, perhaps, a mere reflection of a signal from Earth off an orbiting satellite .
In March 2003, researchers with the SETI@Home distributed computing project, the largest computation in human history, announced that the 150 highest probability candidate signal sources would be systematically reexamined by the Arecibo telescope in Puerto Rico. The candidate signals were identified over a four year period during which SET@Home participants donated more than a million years of computing time.
The final "stellar countdown" phase of the SETI@ Home project will attempt to further discriminate between signals that are random noise or terrestrial interference and those that might be of extraterrestrial origin. The signals of highest investigative interest were evaluated by several factors, including the number of times the radio source was detected, strength of signal, apparent proximity of origin to known and observable stars, and the type of star and/or presence of known planets near the apparent source of the signal.
See also Astronomical unit; Astronomy; Astrophysics; Cosmology; Radio astronomy.
Resources
books
McConnell, B. Beyond Contact: A Guide to SETI and Communicating with Alien Civilizations. O'Reilly and Associates, 2001.
Sagan, Carl. Project Haystack: The Search for Life in the Galaxy (Life in the Universe Series). Seti Institute, Teacher Ideas Pr., 1997.
periodicals
Korpela, E. "SETI@Home—Massively Distributed Computing for SETI." Computing in Science and Engineering Magazine. Volume: 3 Issue: 1 (2001):78-83.
other
"SETI: Searching for Life." Sky and Telescope [cited February 13, 2003]. <http://skyandtelescope.com/resources/SETI/>.
Lee W. Lerner
SETI
SETI
SETI (The Search for Extraterrestrial Intelligence) is a term that encompasses several different groups and their efforts to seek out intelligent extraterrestrial life. The driving force behind these groups is the ancient human desire to understand the origin and distribution of life throughout the Universe. As technology progresses, SETI efforts move from the study of extraterrestrial rocks and meteors towards scanning the skies for a variety of signal types.
Cornell University professor Frank Drake founded the first SETI program in late 1959. Drake reinforced his idea of scanning the skies with his famous Drake Equation. The Drake Equation predicts the abundance of intelligent life within a certain galaxy.
The second major development of SETI took shape in the late 1960s when NASA joined the program. NASA was minimally involved the project, but spawned many SETI related programs. These programs included the Microwave
Observing Project, Project Orion, the High Resolution Microwave Survey, Toward Other Planetary Systems, and more. One of the most intensive SETI related programs NASA would initiate began in 1992, but Congress cut funding for the program within a year. SETI projects now must rely on private funding, and SETI operates through the SETI Institute, a non-profit corporation.
Historically, scientists used several different methods for searching for extraterrestrial intelligence. The earliest method, and still most commonly used in present research, is the scanning of electromagnetic emissions. Radio waves are picked up by an array of radio telescopes and scanned for non-random patterns. More modern methods expand the search to other regions of the electromagnetic spectrum , including the infrared spectrum.
As of 2002, the University of California at Berkeley hosts the most widespread SETI effort in history. Berkeley projects include SETI@Home, SERENDIP, Optical SETI, and Southern SERENDIP. SETI@Home collects its data in the background of the Arecibo Radio Observatory and relays it back to the lab in Berkeley. The data is then divided into workunits and sent out to the personal computers of volunteers throughout the world. These personal computers scan the data for candidate signals. If a candidate signal appears, it is relayed back to Berkeley, where the signal is checked for data integrity. Finally, the lab removes radio interference and scans the data for final candidates. The Berkeley faction of SETI will be expanding their efforts with the Allen Telescope Array (formerly known as the One Hectare Telescope) designated specifically for this research.
Project Phoenix, also run by the SETI Institute, concentrates on obtaining signals from targeted areas within our galaxy. The focused Phoenix receiver can amass radio energy for longer periods of time and with greater sensitivity than previous SETI radio telescopes, allowing for faster and more precise analysis.
Although only a small fraction of the sky has been scanned, so far, SETI initiatives have not confirmed a signal from an extraterrestrial source that is conclusive proof of an extraterrestrial intelligence. A few strong and unexplained signals have intrigued SETI scientists; the most well known was received in 1977 at the Ohio State Radio Observatory. None of the signals have ever repeated.