extraterrestrial intelligence
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What is extraterrestrial intelligence?
Extraterrestrial intelligence refers to hypothetical life beyond Earth capable of thinking and purposeful activity. The principle of mediocrity suggests that the processes leading to intelligent life on Earth could occur throughout the cosmos.
The search for extraterrestrial intelligence (SETI) involves looking for radio signals or optical flashes from other star systems that would indicate the presence of extraterrestrial intelligence. So far, these searches have been fruitless, but success would have an enormous scientific and cultural impact.
The existence of extraterrestrial intelligence is a subject of great interest, with some people eagerly seeking evidence and others denying its possibility. The probability of finding advanced technical civilizations depends on many factors.
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Why do scientists think extraterrestrial intelligence might exist?
The belief in potential extraterrestrial intelligence stems from the principle of mediocrity, suggesting that the conditions and evolution of our solar system are not exceptional. This implies that planets capable of supporting life are common, and on such planets, life will emerge and evolve into intelligent species due to natural selection.
The Drake equation estimates the number of signaling worlds in the Milky Way Galaxy, considering factors like the rate of star formation, the fraction of stars with planetary systems, and the likelihood of intelligent life arising and transmitting signals.
Observations made by the Kepler satellite have identified numerous Earth-sized planets within habitable zones, where liquid water could exist. Furthermore, projects such as the Search for Extraterrestrial Intelligence (SETI) actively scan for electromagnetic signals that may indicate extraterrestrial communication.
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How do scientists search for extraterrestrial intelligence?
Scientists search for extraterrestrial intelligence (SETI) by looking for electromagnetic signals, specifically radio or light, that could be beamed to Earth from other worlds. These signals could be unintentional or sent as deliberate beacons. SETI projects involve targeted searches of nearby Sun-like stars and systematic surveys covering all directions.
Radio SETI experiments scan the sky, using receivers tuned to the microwave band near 1,420 megahertz, the frequency of natural emission from hydrogen. Optical SETI projects search for light pulses using sensitive photomultiplier tubes attached to conventional mirror telescopes.
The Allen Telescope Array, jointly built by the SETI Institute and the University of California, is designed for continuous SETI observations. Additionally, projects like SETI@home use volunteers' computers to analyze data for signals.
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What is the SETI program, and what does it do?
The Search for Extraterrestrial Intelligence (SETI) is an ongoing effort focused on finding intelligent extraterrestrial life by detecting nonrandom patterns in electromagnetic signals from space, particularly in the radio and visible-light regions. SETI projects scan the sky for signals and examine nearby Sun-like stars, using radio telescopes to identify narrowband signals that differ from natural emissions.
Although no confirmed extraterrestrial signals have been found, the SETI program continues to evolve with projects like the Allen Telescope Array and initiatives such as Breakthrough Listen, which surveys a million nearby stars.
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What kinds of evidence would show extraterrestrial intelligent life exists?
Evidence of extraterrestrial intelligent life could take various forms. The discovery of physical artifacts, direct encounters, or the detection of signals would serve as proof that thinking beings exist on other worlds.
The Search for Extraterrestrial Intelligence (SETI) program focuses on detecting nonrandom patterns in electromagnetic signals, especially in the radio and visible-light regions, which would likely be sent deliberately or inadvertently by technologically advanced beings. SETI efforts involve targeted searches of nearby Sun-like stars and systematic surveys covering all directions.
Other methods include analyzing light reflected from exoplanet atmospheres for gases like oxygen or methane, which indicate biological activity. Also, sending physical artifacts is another communication technique, because radio waves tend to disperse, whereas physical artifacts retain their information in compact form and are more likely to be readable when they arrive at their destination.
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How might discovering extraterrestrial intelligence change life on Earth?
The discovery of extraterrestrial intelligence (ETI) could significantly alter life on Earth, though the exact nature of that change remains speculative.
Discovering ETI would unite a wide range of scientific disciplines and could lead to viewing ourselves as citizens of the universe rather than members of tribes. The detection of ETI would have utmost scientific significance, even if the life form discovered is not human-like. The search for extraterrestrial intelligence (SETI) brings unity to a wide range of scientific disciplines.
Alternatively, failure to find any evidence of life beyond Earth would highlight the importance of protecting the diversity of life on our planet.
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extraterrestrial intelligence, hypothetical extraterrestrial life that is capable of thinking, purposeful activity. Work in the new field of astrobiology has provided some evidence that evolution of other intelligent species in the Milky Way Galaxy is not utterly improbable. In particular, more than 4,000 extrasolar planets have been detected, and underground water is likely present on Mars and on some of the moons of the outer solar system. These efforts suggest that there could be many worlds on which life, and occasionally intelligent life, might arise. Searches for radio signals or optical flashes from other star systems that would indicate the presence of extraterrestrial intelligence have so far proved fruitless, but detection of such signals would have an enormous scientific and cultural impact.
(Read Carl Sagan’s Britannica entry on extraterrestrial life.)
Argument for extraterrestrial intelligence
The argument for the existence of extraterrestrial intelligence is based on the so-called principle of mediocrity. Widely believed by astronomers since the work of Nicolaus Copernicus, this principle states that the properties and evolution of the solar system are not unusual in any important way. Consequently, the processes on Earth that led to life, and eventually to thinking beings, could have occurred throughout the cosmos.
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The most important assumptions in this argument are that (1) planets capable of spawning life are common, (2) biota will spring up on such worlds, and (3) the workings of natural selection on planets with life will at least occasionally produce intelligent species. To date, only the first of these assumptions has been proven. However, astronomers have found several small rocky planets that, like Earth, are the right distance from their stars to have atmospheres and oceans able to support life. Unlike the efforts that have detected massive, Jupiter-size planets by measuring the wobble they induce in their parent stars, the search for smaller worlds involves looking for the slight dimming of a star that occurs if an Earth-size planet passes in front of it. The U.S. satellite Kepler, launched in 2009, found thousands of planets, more than 20 of which are Earth-sized planets in the habitable zone where liquid water can survive on the surface, by observing such transits. Another approach is to construct space-based telescopes that can analyze the light reflected from the atmospheres of planets around other stars, in a search for gases such as oxygen or methane that are indicators of biological activity. In addition, space probes are trying to find evidence that the conditions for life might have emerged on Mars or other worlds in the solar system, thus addressing assumption 2. Proof of assumption 3, that thinking beings will evolve on some of the worlds with life, requires finding direct evidence. This evidence might be encounters, discovery of physical artifacts, or the detection of signals. Claims of encounters are problematic. Despite decades of reports involving unidentified flying objects, crashed spacecraft, crop circles, and abductions, most scientists remain unconvinced that any of these are adequate proof of visiting aliens.
Searching for extraterrestrial intelligence
Artifacts in the solar system
Extraterrestrial artifacts have not yet been found. At the beginning of the 20th century, American astronomer Percival Lowell claimed to see artificially constructed canals on Mars. These would have been convincing proof of intelligence, but the features seen by Lowell were in fact optical illusions. Since 1890, some limited telescopic searches for alien objects near Earth have been made. These investigated the so-called Lagrangian points, stable locations in the Earth-Moon system. No large objects—at least down to several tens of metres in size—were seen.
SETI
The most promising scheme for finding extraterrestrial intelligence is to search for electromagnetic signals, more particularly radio or light, that may be beamed toward Earth from other worlds, either inadvertently (in the same way that Earth leaks television and radar signals into space) or as a deliberate beacon signal. Physical law implies that interstellar travel requires enormous amounts of energy or long travel times. Sending signals, on the other hand, requires only modest energy expenditure, and the messages travel at the speed of light.