NationMaster - Encyclopedia: Fermi's Paradox

The Fermi paradox is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence of contact with such civilizations. Image File history File links Download high resolution version (217x664, 17 KB)I took the image from http://www. ... Image File history File links Download high resolution version (217x664, 17 KB)I took the image from http://www. ... Arecibo Observatory This is the message with color added to highlight its separate parts. ... The Arecibo Observatory in Puerto Rico, currently used by the SETI project in the search for extraterrestrial life Extraterrestrial life is life that may exist and originate outside the planet Earth, the only place in the universe currently known to support life. ...

The extreme age of the universe and its vast number of stars suggest that extraterrestrial life should be common. Considering this with colleagues over lunch in 1950, the physicist Enrico Fermi is said to have asked: "Where are they?"^[1] Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exist in the Milky Way galaxy, evidence such as probes, spacecraft or radio transmissions has not been found. The simple question "Where are they?" (alternatively, "Where is everybody?") is possibly apocryphal, but Fermi is widely credited with simplifying and clarifying the problem of the probability of extraterrestrial life. ... Enrico Fermi (September 29, 1901 â€“ November 28, 1954) was an Italian physicist most noted for his work on the development of the first nuclear reactor, and for the development of quantum theory. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Î“Î±Î»Î±Î¾Î¯Î±Ï‚ (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... A von Neumann probe is a specific example of a hypothetical concept based on the work of Hungarian-born American mathematician and physicist John von Neumann. ... A spacecraft is a vessel, craft or device designed to operate beyond the surface of the Earth in outer space. ... Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of visible light. ...

There have been attempts to resolve the Fermi Paradox by locating evidence of extraterrestrial civilizations, along with proposals that such life could exist without human knowledge. Counterarguments suggest that intelligent extraterrestrial life does not exist or occurs so rarely that humans will never make contact with it. The Arecibo Observatory in Puerto Rico, currently used by the SETI project in the search for extraterrestrial life Extraterrestrial life is life that may exist and originate outside the planet Earth, the only place in the universe currently known to support life. ...

A great deal of effort has gone into developing scientific theories and possible models of extraterrestrial life and the Fermi paradox has become a theoretical reference point in much of this work. The problem has spawned numerous scholarly works addressing it directly, while various questions that relate to it have been addressed in fields as diverse as astronomy, biology, ecology and philosophy. The emerging field of astrobiology has brought an interdisciplinary approach to the Fermi paradox and the question of extraterrestrial life. A giant Hubble mosaic of the Crab Nebula, a supernova remnant. ... Biology (from Greek Î’Ã¬Î¿ meaning life and Î›oÎ³Î¿Ï‚ meaning the study of, see below) is the study of life. ... Ernst Haeckel coined the term oekologie in 1866. ... Socrates (central bare-chested figure) about to drink hemlock as mandated by the court. ... This article or section is missing references or citation of sources. ...

Basis of the paradox

The Fermi paradox is a conflict between an argument of scale and probability, and a lack of evidence. A more complete definition could be stated thus: Spatial scale provides a shorthand form for discussing relative lengths, areas, distances and sizes. ... Probability is the extent to which something is likely to happen or be the case[1]. Probability theory is used extensively in areas such as statistics, mathematics, science, philosophy to draw conclusions about the likelihood of potential events and the underlying mechanics of complex systems. ... Evidence has several meanings as indicated below. ... For other uses, see Definition (disambiguation). ...

The first aspect of the paradox, "the argument by scale", is a function of the raw numbers involved: there are an estimated 250 billion (2.5 x 10¹¹) stars in the Milky Way and 70 sextillion (7 x 10²²) in the visible universe.^[2] Even if intelligent life occurs on only a minuscule percentage of planets around these stars, there should still be a great number of civilizations extant in the Milky Way galaxy alone. This argument also assumes the mediocrity principle, which states that Earth is not special, but merely a typical planet, subject to the same laws, effects, and likely outcomes as any other world. Some estimates using the Drake equation (see below) support this argument, although the assumptions behind those calculations have themselves been challenged. To help compare orders of magnitude this page lists dimensionless numbers between 109 and 1012. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Î“Î±Î»Î±Î¾Î¯Î±Ï‚ (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ... To help compare orders of magnitude this page lists dimensionless numbers between 1021 and 1024. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... The mediocrity principle is the notion in the philosophy of science that there is nothing special about Earth, and by implication the human race. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... The eight planets and three dwarf planets of the Solar System. ... The Drake equation (also known as the Green Bank equation or the Sagan equation) is a famous result in the speculative fields of xenobiology, astrosociobiology and the search for extraterrestrial intelligence. ...

The second cornerstone of the Fermi paradox is a rejoinder to the argument by scale: given intelligent life's ability to overcome scarcity, and its tendency to colonize new habitats, it seems likely that any advanced civilization would seek out new resources and colonize first their star system, and then surrounding star systems. As there is no evidence on Earth or anywhere else of attempted alien colonization after 13 billion years of the universe's history, either intelligent life is rare or assumptions about the general behavior of intelligent species are flawed. In economics, scarcity is defined as a condition of limited resources, where society does not have sufficient resources to produce enough to fulfill unlimited subjective wants. ... Habitat (from the Latin for it inhabits) is the place where a particular species lives and grows. ... It has been suggested that this article or section be merged with Colonialism. ...

Several writers have tried to estimate how fast an alien civilization might spread through the galaxy. There have been estimates of anywhere from 5 million to 50 million years to colonize the entire galaxy; a relatively small amount of time on a geological scale, let alone a cosmological one.^[3] Even if colonization is impractical or undesirable to an alien civilization, large scale exploration of the galaxy is still possible; the means of exploration and theoretical probes involved are discussed extensively below. The Arecibo Observatory in Puerto Rico, currently used by the SETI project in the search for extraterrestrial life Extraterrestrial life is life that may exist and originate outside the planet Earth, the only place in the universe currently known to support life. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang. ...

Related concepts

Drake equation

While numerous theories and principles attend to the Fermi paradox, the one most closely related is the Drake equation. It was formulated by Dr. Frank Drake in 1960, a decade after the objections raised by Enrico Fermi, in an attempt to find a systematic means to evaluate the numerous probabilities involved in alien life. The speculative equation factors: the rate of star formation in the galaxy; the number of stars with planets and the number that are habitable; the number of those planets which develop life and subsequently intelligent communicating life; and finally the expected lifetimes of such civilizations. The Drake equation (also known as the Green Bank equation or the Sagan equation) is a famous result in the speculative fields of xenobiology, astrosociobiology and the search for extraterrestrial intelligence. ... Professor Frank Drake Frank Drake (born May 28, 1930, Chicago, Illinois) is an American astronomer and astrophysicist. ... Year 1960 (MCMLX) was a leap year starting on Friday (the link is to a full 1960 calendar). ... Enrico Fermi (September 29, 1901 â€“ November 28, 1954) was an Italian physicist most noted for his work on the development of the first nuclear reactor, and for the development of quantum theory. ... Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ...

The Drake equation has been used by both optimists and pessimists, with varying results. Dr. Carl Sagan, for example, suggested as many as one million communicating civilizations in the Milky Way in 1966, though he later suggested that the number could be far smaller.^[4] Other published estimates from Frank Tipler place the value at just one—i.e., human beings are the only extant intelligent life.^[5] Carl Edward Sagan (November 9, 1934 â€“ December 20, 1996) was an American astronomer, astrobiologist, and highly successful science popularizer. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Î“Î±Î»Î±Î¾Î¯Î±Ï‚ (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ... Frank J. Tipler is a professor of mathematical physics at Tulane University, New Orleans, physicist, theologian and cornucopian philosopher. ...

Critics of the Drake equation claim that since the variables cannot yet be determined with any real confidence, estimating the number of extraterrestrial civilizations based on it is methodologically flawed, a criticism which the wide divergence in estimates seems to support. Assigning meaningful values to the Drake equation factors will require empirical data, collection of which is still preliminary.

Rare Earth hypothesis

The Rare Earth hypothesis attempts to resolve the Fermi paradox by suggesting that Earth is not typical, but unusual, and perhaps even unique. This is a rejection of the mediocrity principle. While a unique Earth has had historical support on philosophical or religious grounds, the Rare Earth Hypothesis deploys quantifiable and statistical arguments in support of the theory that multicellular life is exceedingly rare in the universe because Earth-like planets are themselves exceedingly rare. Supporters argue that many improbable coincidences have converged to make complex life on Earth possible.^[6] In planetary astronomy and astrobiology, the Rare Earth hypothesis asserts that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological events and circumstances. ... The mediocrity principle is the notion in the philosophy of science that there is nothing special about Earth, and by implication the human race. ... A hypothesis (from Greek ) is a suggested explanation of a phenomenon or reasoned proposal suggesting a possible correlation between multiple phenomena. ... For Wikipedia statistics, see m:Statistics Statistics is the science and practice of developing human knowledge through the use of empirical data expressed in quantitative form. ... This article is about the tv programme Life on Earth. ...

Insofar as the Rare Earth Hypothesis privileges Earth-life and its process of formation, it is a variant of the anthropic principle. The Anthropic Principle notes that the universe seems uniquely suited to the development of human intelligence and that any variation in any one of a myriad of universal constants would make the development of intelligent life more difficult. This philosophical stance opposes not only mediocrity, but the Copernican principle more generally, which suggests there is no privileged location in the universe. In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such... The mediocrity principle is the notion in the philosophy of science that there is nothing special about Earth, and by implication the human race. ... The Copernican principle is the philosophical statement that no special observers should be proposed. ...

Opponents dismiss both Rare Earth and the anthropic principle as tautological — if a condition must exist in the universe for human life to arise, then the universe must already meet that condition, as human life exists — and as an unimaginative argument. According to this analysis, the Rare Earth hypothesis confuses a description of how life on Earth arose with a uniform conclusion of how life must arise.^[7] While the probability of the specific conditions on Earth being widely replicated may be low, complex life may not require exclusively Earth-like conditions in order to evolve (see Evolving the Alien: The Science of Extraterrestrial Life and Alternative biochemistry for further information). In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such... Within the study of logic, a tautology is a statement containing more than one sub-statement, that is true regardless of the truth values of its parts. ... The universe from a speculative theoretical physicists point of view can be described as the sum of all matter and energy that exists and the space-time in which they are located and in which all events occur or could occur. ... The argument from ignorance, also known as argumentum ad ignorantiam or argument by lack of imagination, is a logical fallacy in which it is claimed that that a premise is true only because it has not been proven false, or that a premise is false only because it has not... Evolving the Alien: The Science of Extraterrestrial Life (second edition publised as What Does a Martian Look Like? The Science of Extraterrestrial Life) is a book about xenobiology by biologist Jack Cohen and mathematician Ian Stewart. ... Alternative biochemistry is the biochemistry of alien life forms that differ radically from those on earth. ...

Resolving the paradox empirically

One obvious way to resolve the Fermi paradox would be to find conclusive evidence of extraterrestrial intelligence. Various efforts to find such evidence have been made since 1960, and several are ongoing. As human beings do not have interstellar travel capability, such searches are being carried out at great distances and rely on careful analysis of very subtle evidence. This limits possible discoveries to civilizations which alter their environment in a detectable way, or produce effects that are detectable at a distance, such as radio emissions. Non-technological civilizations are very unlikely to be detectable from Earth in the near future (though microbial life may be deduced in the Solar System). Year 1960 (MCMLX) was a leap year starting on Friday (the link is to a full 1960 calendar). ... Interstellar space travel is unmanned or manned travel between stars, though the term usually denotes the latter. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... This article is about the Solar System. ...

One difficulty in searching is avoiding an overly anthropomorphic viewpoint. Conjecture on the type of evidence likely to be found often focuses on the types of activities that humans have performed, or likely would perform given more advanced technology. Intelligent aliens might avoid these "expected" activities, or perform activities totally novel to humans. An anthropomorphic character Anthropomorphism, also called personification anthropomorphism, is the attribution of human characteristics and qualities to nonhuman beings, inanimate objects, or natural or supernatural phenomena. ... In mathematics, a conjecture is a mathematical statement which appears likely to be true, but has not been formally proven to be true under the rules of mathematical logic. ...

Radio emissions

Radio technology and the ability to construct a radio telescope are presumed to be a natural advance for technological species^[8] theoretically creating effects that might be detected over interstellar distances. Sensitive observers of the solar system, for example, would note unusually intense radio waves for a G2 star due to Earth's television and telecommunication broadcasts. In the absence of an apparent natural cause, alien observers might infer the existence of terrestrial civilization. The radio telescope at Arecibo. ... The radio telescope at Arecibo. ... The Arecibo Observatory is located approximately 9 miles south-southwest from Arecibo, Puerto Rico (near the extreme southwestern corner of Arecibo pueblo). ... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of radio receiver used in astronomy. ... This article is about the search for extra-terrestrial intelligence. ... Project Ozma was a pioneering SETI experiment started in 1960 by Cornell University astronomer Frank Drake, at the National Radio Astronomy Observatory at Green Bank, West Virginia. ... Project Phoenix is a SETI project: a search for extraterrestrial intelligence by listening for radio signals. ... This article is about the search for extra-terrestrial intelligence. ... ATA Dish Size Scale The Allen Telescope Array (ATA), formerly known as the One Hectare Telescope (1hT), is a joint effort by the SETI Institute and the Radio Astronomy Laboratory at the University of California, Berkeley to construct a radio interferometer that will be dedicated to astronomical and simultaneous search... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of radio receiver used in astronomy. ... This article is about the astronomical object. ...

Therefore, the careful searching of radio emissions from space for non-natural signals may lead to the detection of alien civilizations. Such signals could be either "accidental" byproducts of a civilization, or deliberate attempts to communicate, such as the Communication with Extraterrestrial Intelligence's Arecibo message. A number of astronomers and observatories have attempted and are attempting to detect such evidence, mostly through the SETI organization, although other approaches, such as optical SETI also exist. CETI (Communication with Extraterrestrial Intelligence, or more correctly METI, Messaging to Extraterrestrial Intelligence) is a branch of SETI research that focuses on composing and deciphering messages that could theoretically be understood by another technological civilization. ... Arecibo Observatory This is the message with color added to highlight its separate parts. ... This article is about the search for extra-terrestrial intelligence. ... This article is about the search for extra-terrestrial intelligence. ...

Several decades of SETI analysis has not revealed any main sequence stars with unusually bright, or meaningfully repetitive radio emissions, although there have been several candidate signals: on August 15, 1977 the "Wow! signal" was picked up by The Big Ear radio telescope. It lasted for only 72 seconds, and has not been repeated. In 2003, Radio source SHGb02+14a was isolated by SETI@home analysis, although it has largely been discounted by further study. There are numerous technical assumptions underlying SETI that may cause human beings to miss radio emissions with present search techniques; these are discussed below. August 15 is the 227th day of the year in the Gregorian Calendar (228th in leap years), with 138 days remaining. ... For the album by Ash, see 1977 (album). ... The Wow! signal was a strong narrowband radio signal detected by the astrophysicist Jerry R. Ehman on August 15, 1977 while working on a SETI project at the Big Ear radio telescope of The Ohio State University. ... The Big Ear was a radio telescope located on the grounds of the Ohio Wesleyan Universitys The Perkins Observatory from the 1960s to 1998 when it was disassembled. ... SHGb02+14a is a radio emitted frequency. ... SETI@home (SETI at home) is a grid computing (distributed computing in the projects own terminology) project using Internet-connected computers, hosted by the Space Sciences Laboratory, at the University of California, Berkeley, in the United States. ...

Direct planetary observation

Detection and classification of exoplanets has come about out of recent refinements in mainstream astronomical instruments and analysis. While this is a new field in astronomy—the first published paper claiming to have discovered an exoplanet was released in 1989—it is possible that planets which are likely to be able to support life will be found in the near future. Direct observational evidence for the existence of life may eventually be observable, such as the absorption spectrum of chlorophyll. Other detectable biotic signatures include methane and oxygen and, for advanced civilizations, trace industrial gases such as freon.^[9] More obvious evidence of an alien technological civilization requires precise imaging (see right). Download high resolution version (2400x1200, 534 KB)Composite image of the Earth at night, created by NASA and NOAA. NASA Description: This image of Earth’s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). ... Download high resolution version (2400x1200, 534 KB)Composite image of the Earth at night, created by NASA and NOAA. NASA Description: This image of Earth’s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS). ... Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. ... A materials absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. ... Chlorophyll gives leaves their green color Space-filling model of the chlorophyll molecule Chlorophyll is a green photosynthetic pigment found in most plants, algae, and cyanobacteria. ... Methane is a significant and plentiful fuel which is the principal component of natural gas. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Freon is a trade name for a group of chlorofluorocarbons used primarily as a refrigerant. ...

Exoplanets are rarely directly observed (the first claim to have done so was in 2005) rather their existence is inferred based on effects caused in their orbiting a star. Currently, the size and orbit of an exoplanet can be deduced. This information, along with the stellar classification of its sun, and educated guesses as to its composition based on its size and comparisons to studied bodies, allows for rough approximations of the planetary environment. In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ...

The methods for exoplanet detection are not likely to deduce Earth-like life at present, given that most exoplanets discovered are Jupiter mass or larger. As of 9 October 2006, 210 extrasolar planets have been discovered^[10] - 159 in single-planet systems and 51 planets in 21 multiple-planet systems. Any planet is an extremely faint light source compared to its parent star. ...

Alien constructs

Probes, colonies, and other artifacts

As noted, given the size and age of the universe, and the relative rapidity at which dispersion of intelligent life can occur, evidence of alien colonization attempts might plausibly be discovered. Additionally, evidence of "unbeinged" exploration in the form of probes and information gathering devices may await discovery. A von Neumann probe is a specific example of a hypothetical concept based on the work of Hungarian-born American mathematician and physicist John von Neumann. ... A Bracewell probe is a hypothetical concept for an autonomous interstellar probe dispatched for the express purpose for communication with (an) alien civilization(s). ...

Some theoretical exploration techniques such as the Von Neumann probe could exhaustively explore a galaxy the size of the Milky Way in as little as half a million years, with relatively little investment in materials and energy relative to the results. If even a single civilization in the Milky Way attempted this, such probes could spread throughout the entire galaxy. Evidence of such probes might be found in the solar system—perhaps in the asteroid belt where raw materials would be plentiful and easily accessed.^[11] A von Neumann probe is a specific example of a hypothetical concept based on the work of Hungarian-born American mathematician and physicist John von Neumann. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Î“Î±Î»Î±Î¾Î¯Î±Ï‚ (Galaxias), sometimes referred to simply as the Galaxy), is a barred spiral galaxy of the Local Group. ... Image of the main asteroid belt between the orbits of Mars and Jupiter. ...

Another possibility for contact with an alien probe—one that would be trying to find human beings—is an alien Bracewell probe. Such a device would be an autonomous space probe whose purpose is to seek out and communicate with alien civilizations (as opposed to Von Neumann probes, which are usually described as purely exploratory). These were proposed as an alternative to carrying a slow speed-of-light dialogue between vastly distant neighbors. Rather than contending with the long delays a radio dialogue would suffer, a probe housing an artificial intelligence would seek out an alien civilization to carry on a close range communication with the discovered civilization. The findings of such a probe would still have to be transmitted to the home civilization at light speed, but an information-gathering dialogue could be conducted in real time.^[12] A Bracewell probe is a hypothetical concept for an autonomous interstellar probe dispatched for the express purpose for communication with (an) alien civilization(s). ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation in a vacuum, not just visible light. ... Hondas humanoid robot AI redirects here. ...

Since the 1950s direct exploration has been carried out on a small fraction of the solar system and no evidence that it has ever been visited by alien colonists, or probes, has been uncovered. Detailed exploration of areas of the solar system where resources would be plentiful—such as the asteroids, the Kuiper belt, the Oort cloud and the various planetary ring systems—may yet produce evidence of alien exploration, though these regions are also massive and difficult to investigate. There have been preliminary efforts. The SETA (Search for Extraterrestrial Artifacts) and SETV (Search for Extraterrestrial Visitation) projects^[13] have attempted to locate evidence within the solar system. There have also been attempts to signal, attract, or activate Bracewell probes in Earth's local vicinity, including by scientists Robert Freitas and Francisco Valdes.^[14] Many of the projects that fall under this umbrella are considered "fringe" science by astronomers and none of the various projects have located any artifacts. 253 Mathilde, a C-type asteroid. ... Artists rendering of the Kuiper Belt and hypothetical more distant Oort cloud. ... This image is an artists rendering of the Oort cloud and the Kuiper Belt. ... The existence of extraterrestrial life remains hypothetical though human beings continue to search Extraterrestrial life is life that may exist and originate outside the planet Earth. ... A Bracewell probe is a hypothetical concept for an autonomous interstellar probe dispatched for the express purpose for communication with (an) alien civilization(s). ... Robert A. Freitas Jr. ...

Should alien artifacts be discovered, even here on Earth, they may not be recognizable as such. The products of an alien mind and an advanced alien technology might not be perceptible or recognizable as artificial constructs. Exploratory devices in the form of bio-engineered life forms created through synthetic biology would presumably disintegrate after a point, leaving no evidence; an alien information gathering system based on molecular nanotechnology could be all around us at this very moment, completely undetected. Clarke's third law suggests that an alien civilization well in advance of humanity's might have means of investigation that are not yet conceivable to human beings. Synthetic biology is a new area of research that combines science and engineering in order to design and build novel biological functions and systems. ... It has been suggested that Molecular engineering be merged into this article or section. ... Arthur C. Clarke formulated the following three laws of prediction: // Origins Clarkes Law, later the first of the three laws, was proposed by Arthur C. Clarke in the essay Hazards of Prophecy: The Failure of Imagination, in Profiles of the Future (1962). ...

Advanced stellar scale artifacts

In 1959, Dr. Freeman Dyson observed that every developing human civilization constantly increases its energy consumption, and theoretically, a civilization of sufficient age would require all the energy produced by its sun. The Dyson Sphere was the thought experiment solution that he derived: a shell or cloud of objects enclosing a star to harness as much radiant energy as possible. Such a feat of astroengineering would drastically alter the observed spectrum of the sun, changing it at least partly from the normal emission lines of a natural stellar atmosphere, to that of a black body radiation, probably with a peak in the infrared. Dyson himself speculated that advanced alien civilizations might be detected by examining the spectra of stars, searching for such an altered spectrum.^[15] Image File history File links Dyson_Sphere_Diagram. ... Image File history File links Dyson_Sphere_Diagram. ... A cut-away diagram of an idealized Dyson shell â€” a variant on Dysons original concept â€” 1 AU in radius A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure. ... A cut-away diagram of an idealized Dyson shell â€” a variant on Dysons original concept â€” 1 AU in radius A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure. ... Kardashev scale projections ranging from 1900 to 2100. ... An Alderson disk (named after Dan Alderson, its originator) is an artificial astronomical megastructure, like Nivens Ringworld or a Dyson sphere. ... A Matrioshka Brain is a hypothetical megastructure, based on the Dyson sphere, of immense computational capacity. ... // A stellar engine is a class of hypothetical megastructures which use a stars radiation to create usable energy. ... Freeman John Dyson (born December 15, 1923) is an English-born physicist and mathematician, famous for his work in quantum mechanics, nuclear weapons design and policy, and for his serious theorizing in futurism and science fiction concepts, including the search for extraterrestrial intelligence. ... A cut-away diagram of an idealized Dyson shell â€” a variant on Dysons original concept â€” 1 AU in radius A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure. ... In philosophy, physics, and other fields, a thought experiment (from the German Gedankenexperiment) is an attempt to solve a problem using the power of human imagination. ... Astroengineering is the construction of megastructures in space by technologically advanced beings. ... Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of matter and its properties by investigating light, sound, or particles that are emitted, absorbed or scattered by the matter under investigation. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Different stars have different atmospheres. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... Image of two girls in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ...

Since then, several other theoretical stellar-scale megastructures have been proposed (see links above), but the central idea remains that a highly advanced civilization — Type II or greater on the Kardashev scale — could alter its environment enough as to be detectable from interstellar distances. In science fiction and speculative (or exploratory) engineering, a megastructure is an enormous self-supporting artificial construct. ... Kardashev scale projections ranging from 1900 to 2100. ...

However, such constructs may be more difficult to detect than originally thought. Dyson spheres might have different emission spectra depending on the desired internal environment; life based on high-temperature reactions may require a high temperature environment, with resulting "waste radiation" in the visible spectrum, not the infrared.^[16] Additionally, a variant of the Dyson sphere has been proposed which would be difficult to observe from any great distance. A Matrioshka Brain is a series of concentric spheres, each radiating less energy per area than its inner neighbour. The outermost sphere of such a structure could be close to the temperature of the interstellar background radiation, and thus be all but invisible. A Matrioshka Brain is a hypothetical megastructure, based on the Dyson sphere, of immense computational capacity. ...

There have been some preliminary attempts to find evidence of the existence of Dyson spheres or other large Type-II or Type-III Kardashev scale artifacts that would alter the spectra of their core stars but optical surveys have not located anything. Fermilab has an ongoing program to find Dyson spheres,^[17] but such searches are preliminary and incomplete as yet. A cut-away diagram of an idealized Dyson shell â€” a variant on Dysons original concept â€” 1 AU in radius A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure. ... Kardashev scale projections ranging from 1900 to 2100. ... Fermilabs Tevatron Robert Rathbun Wilson Hall Fermi National Accelerator Laboratory (Fermilab), located in Batavia near Chicago, Illinois, (Google Sat Map) is a U.S. Department of Energy national laboratory specializing in high-energy particle physics, operated for the Department of Energy by the Universities Research Association (URA). ...

Explaining the paradox theoretically

Certain theoreticians accept that the apparent absence of evidence proves the absence of extraterrestrials and attempt to explain why. Others offer possible frameworks in which the silence may be explained without ruling out the possibility of such life, including assumptions about extraterrestrial behaviour and technology.

They do not exist ...

The simplest explanation is that the human species is alone in the galaxy. Several theories along these lines have been proposed, explaining why intelligent life might be either very rare, or very short lived.

... and they never did

Those who believe that extraterrestrial intelligent life does not exist in the galaxy argue that the conditions needed for life—or at least complex life—to evolve are rare or even unique to Earth (see Rare Earth Hypothesis section above). While some have pointed out that complex life may evolve through other mechanisms than those found specifically here on Earth, the fact that in the extremely long history of life on the Earth only one species has developed a civilization to the point of being capable of space flight and radio technology seems to lend more credence to the idea of technologically advanced civilization being a rare commodity in the universe. For other uses, see Life (disambiguation), Lives (disambiguation) or Living (disambiguation), Living Things (disambiguation). ...

For example, the emergence of intelligence may have been an evolutionary accident. Geoffrey Miller proposes that human intelligence is the result of runaway sexual selection, which takes unpredictable directions. Geoffrey Miller Geoffrey Miller is a widely recognised evolutionary psychologist, whose work is in the tradition of scientists such as Richard Dawkins, Daniel Dennett, and Steven Pinker. ... Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right. ...

Another theory along these lines is that even if the conditions needed for life might be common in the universe, that the formation of life itself, a complex array of molecules that are capable simultaneously of reproduction, the creation or extraction of all base components that it uses to build itself, from the environment, and of obtaining energy in a form that it can use to maintain the reaction (or the initial abiogenesis on a potential life-bearing planet), might ultimately be very rare even if worlds that might have the proper initial conditions for life might be common. For other uses, see Life (disambiguation), Lives (disambiguation) or Living (disambiguation), Living Things (disambiguation). ... This article focuses on the history of the theory of abiogenesis (the spontaneous generation of life from non-living sources). ...

... because an inhospitable universe destroys complex intelligent life

Another possibility is that life can and does arise elsewhere, but events such as ice ages, impact events, or other catastrophes prevent complex life forms from evolving. Even if initial conditions for the development of life are not unique to Earth, it may be that on most worlds such events routinely and periodically destroy such life. Even if a "benign local environment" might exist on some world long enough for intelligent life to finally arise, such life might also be exterminated by cosmological events (such as supernovae, or gamma ray bursts) suddenly sterilizing previously hospitable regions of space.^[18] Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ... Artists impression of a major impact event. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... In astronomy, gamma-ray bursts (GRBs) are flashes of gamma rays that last from seconds to hours, the longer ones being followed by several days of X-ray afterglow. ...

... because it is the nature of intelligent life to destroy itself

Technological civilizations may usually or invariably destroy themselves before or shortly after developing radio or space flight technology. Possible means of annihilation include nuclear war, biological warfare or accidental contamination, nanotechnological catastrophe, or a Malthusian catastrophe after the deterioration of a planet's ecosphere. This general theme is explored both in fiction and in mainstream scientific theorizing. Indeed, there are probabilistic arguments which suggest that humanity's end may occur sooner rather than later (see Doomsday argument). In 1966 Sagan and Shklovskii suggested that technological civilizations will either tend to destroy themselves within a century of developing interstellar communicative capability or master their self-destructive tendencies and survive for billion-year timescales.^[19] Self-annihilation may also be viewed in terms of thermodynamics: insofar as life is an ordered system that can sustain itself against the tendency to disorder, the "external transmission" or interstellar communicative phase may be the point at which the system becomes unstable and self-destructs.^[20] Nuclear War is a card game designed by Douglas Malewicki, and originally published in 1966. ... For the use of biological agents by terrorists, see bioterrorism. ... Grey goo refers to a hypothetical end-of-the-world scenario involving molecular nanotechnology in which out-of-control self-replicating robots, deliberately designed and built in a way known to be dangerous, consume all living matter on Earth while building more of themselves (a scenario known as ecophagy). ... A Malthusian catastrophe, sometimes known as a Malthusian check, Malthusian crisis, Malthusian dilemma, Malthusian disaster, Malthusian trap, or Malthusian limit is a return to subsistence-level conditions as a result of agricultural (or, in later formulations, economic) production being eventually outstripped by growth in population. ... Ecosphere has several different meanings: In astronomy an ecosphere is an imaginary shell of space surrounding stars where conditions are such that life might survive. ... The Doomsday argument (DA) is a probabilistic argument that claims to predict the future lifetime of the human race given only an estimate of the total number of humans born so far. ... Carl Edward Sagan (November 9, 1934 â€“ December 20, 1996) was an American astronomer, astrobiologist, and highly successful science popularizer. ...

From a Darwinian perspective, self-destruction is a paradoxical outcome of evolutionary success. The evolutionary psychology that developed during the competition for scarce resources over the course of human evolution has left the species subject to aggressive, instinctual drives to consume resources, increase longevity, and to reproduce — in part, the very motives that lead to the development of technological society. It seems likely that intelligent extraterrestrial life would evolve subject to similar conditions and thus face the same possibility of self-destruction. It has been suggested, for instance, that a successful alien species will be a superpredator, as is Homo sapiens.^[21] Evolutionary psychology (abbreviated ev-psych or EP) is a theoretical approach to psychology that attempts to explain certain mental and psychological traitsâ€”such as memory, perception, or languageâ€”as evolved adaptations, i. ... This snapping turtle is trying to make a meal of a Canada goose, but the goose is too wary. ... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ...

... because it is the nature of intelligent life to destroy others

Another possibility is that intelligent species beyond a certain point of technological capability will destroy other intelligence as it appears. The idea that someone, or something, is destroying intelligent life in the universe is well explored in science fiction, for instance. The primary motive would be perceived competition for an aggressive, expansionist species. In 1981, cosmologist Edward Harrison also pointed out that such behaviour would be an act of prudence: an intelligent species that has overcome its own self-destructive tendencies would view any other species bent on galactic expansion as a kind of virus.^[22] Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... 1981 (MCMLXXXI) was a common year starting on Thursday of the Gregorian calendar. ...

Violent extermination of other civilizations is not an unrealistic goal. The concept of self-replicating spacecraft need not be limited to exploration or communication, but can be applied to aggression (see Berserker probe). Even if a civilization who created such machines were to disappear, the probes could outlive their creators, destroying civilizations far into the future. A von Neumann probe is a specific example of a hypothetical concept based on the work of Hungarian-born American mathematician and physicist John von Neumann. ...

While it appears plausible that intelligent life tends to suppress other intelligent life, the idea can be criticized as continuing to beg the question at the heart of the Fermi Paradox: if intelligence destroys upstart intelligence, why is humanity still here? One might suggest that alien intelligences are so far advanced that ours is too insignificant to destroy. (see below, and technological singularity) Begging the question, in modern popular usage, is often used synonymously for raising the question. However the original meaning is quite different: it described a type of logical fallacy (also called petitio principii) in which the evidence given for a proposition as much needs to be proved as the proposition... When plotted on a logarithmic graph, 15 separate lists of paradigm shifts for key events in human history show an exponential trend. ...

It would also not explain why we have not seen such a destroyer, hunters often do not hid themselves from their prey.

... because God created humans alone

Although not a testable scientific explanation, the belief that a God or gods has placed humanity as the only intelligent life in the universe is widespread through cultures and history. Tenets of the Judeo-Christian tradition can be interpreted to position human beings as unique in the universe and have created ambivalent ideas regarding the question of alien life.^[23] While not necessarily an outcome of the Rare Earth Hypothesis, like Rare Earth it is a variant of the anthropic principle, which in this case becomes teleological: the universe has to be this way, or it was designed to be this way, for the express purpose of creating human intelligence. In science and the philosophy of science, falsifiability, contingency, and defeasibility are roughly equivalent terms referring to the property of empirical statements that they must admit of logical counterexamples. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence on Earth of biochemistry, carbon-based life, and eventually human beings to observe such... Teleology is the philosophical study of purpose (from the Greek teleos, perfect, complete, which in turn comes from telos, end, result). ...

They do exist ...

It may be that technological extraterrestrial civilizations exist, but that human beings cannot communicate with them because of various constraints: problems of scale or of technology; because their nature is simply too alien for meaningful communication; or because human society refuses to admit to evidence of their presence.

... but communication is impossible due to problems of scale

Intelligent civilizations are too far apart in space to communicate Image File history File links Download high resolution version (1900x1425, 138 KB) Terrestrial Planet Finder - Infrared interferometer concept source: http://photojournal. ... Image File history File links Download high resolution version (1900x1425, 138 KB) Terrestrial Planet Finder - Infrared interferometer concept source: http://photojournal. ... The National Aeronautics and Space Administration (NASA) is an agency of the United States Government, responsible for that nations public space program. ... Terrestrial Planet Finder - Infrared interferometer concept The Terrestrial Planet Finder (TPF) is a plan by NASA for a telescope system that would be capable of detecting extrasolar terrestrial planets. ...

It may be that non colonizing technologically capable alien civilizations exist, but that they are simply too far apart for meaningful two-way communication.^[24] If two civilizations are separated by several thousand light years, it is very possible that one, the other, or both cultures may become extinct before meaningful dialogue can be established. Human searches may be able to detect their existence, but communication will remain impossible because of distance. This problem might be ameliorated somewhat if contact/communication is made through a Bracewell probe. In this case at least one partner in the exchange may obtain meaningful information. This theory is similar to another known as 'Divine Quarantine', which suggests that some form of God purposely sets different instances of life so far from one another that they could never contact each other and thus never destroy one another through purposeful or inadvertent interaction. A light-year or lightyear, symbol ly, is a unit of length. ... A Bracewell probe is a hypothetical concept for an autonomous interstellar probe dispatched for the express purpose for communication with (an) alien civilization(s). ... This article discusses the term God in the context of monotheism and henotheism. ...

Given the length of time that intelligent life has existed on Earth or is likely to exist (see discussion above), the "window of opportunity" for detection or contact might be quite small. Advanced civilizations may periodically arise and fall throughout our galaxy, but this may be such a rare event, relatively speaking, that the odds of two or more such civilizations existing at the same time are low. There may have been intelligent civilizations in the galaxy before the emergence of intelligence on Earth, and there may be intelligent civilizations after its extinction, but it is possible that human beings are the only intelligent civilization in existence now. The term "now" is somewhat complicated by the finite speed of light and the nature of spacetime under relativity (see Relativity of simultaneity). Assuming that an extraterrestrial intelligence is not able to travel to our vicinity at faster-than-light speeds, in order to detect an intelligence 1,000 light-years distant, that intelligence will need to have been active 1,000 years ago. NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light-years in diameter and approximately 60 million light-years distant. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation in a vacuum, not just visible light. ... In physics, spacetime is a mathematical model that combines three-dimensional space and one-dimensional time into a single construct called the space-time continuum, in which time plays the role of the 4th dimension. ... The relativity of simultaneity is the dependence of the notion of simultaneity on the observer. ... Faster-than-light (also superluminal or FTL) communications and travel are staples of the science fiction genre. ...

There is a possibility that archeological evidence of past civilizations may be detected through deep space observations — especially if they left behind large artifacts such as Dyson spheres — but this seems less likely than detecting the output of a thriving civilization. A cut-away diagram of an idealized Dyson shell â€” a variant on Dysons original concept â€” 1 AU in radius A Dyson sphere (or shell as it appeared in the original paper) is a hypothetical megastructure. ...

A special case of this is that humans may well be the first intelligent life in the galaxy. This is often dismissed as a result of two factors: the idea that if there was going to be any other intelligent life, it would exist by now, and the tendency on the part of scientists to try to avoid anthropocentrism. Unlikely though it may be, it is still a possibility. Anthropocentrism (Greek Î¬Î½Î¸ÏÏ‰Ï€Î¿Ï‚, anthropos, human, ÎºÎÎ½Ï„ÏÎ¿Î½, kentron, center), or the human-centered principle, refers to the idea that humanity must always remain the central concern for humans. ...

Many assumptions about the ability of an alien culture to colonize other stars are based on the idea that interstellar travel is technologically feasible. While the current understanding of physics rules out the possibility of faster than light travel, it appears that there are no major theoretical barriers to the construction of "slow" interstellar ships (see Project Daedalus, Project Orion, and Project Longshot). This idea underlies the concept of the Von Neumann probe and the Bracewell probe as evidence of extraterrestrial intelligence. For other uses, see Faster than the speed of light (disambiguation). ... An artists conception of the British Interplanetary Society design for Project Daedalus Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society to design a plausible interstellar unmanned spacecraft. ... An artists conception of the NASA reference design for the Project Orion spacecraft powered by nuclear propulsion. ... Project Longshot is a design for an interstellar spaceship, an unmanned probe intended to fly to Alpha Centauri powered by nuclear pulse propulsion. ... A von Neumann probe is a specific example of a hypothetical concept based on the work of Hungarian-born American mathematician and physicist John von Neumann. ... A Bracewell probe is a hypothetical concept for an autonomous interstellar probe dispatched for the express purpose for communication with (an) alien civilization(s). ...

It is possible, however, that present scientific knowledge cannot properly gauge the feasibility and costs of such interstellar colonization. Theoretical barriers may not yet be understood and the cost of materials and energy for such ventures may be so high as to make it unlikely that any civilization could afford to attempt it. This possibility has been examined in terms of percolation theory: colonization efforts may not occur as an unstoppable rush, but rather as an uneven tendency to "percolate" outwards, within an eventual slowing and termination of the effort given the enormous costs involved and the fact that colonies will inevitably develop a culture and civilization of their own. Colonization will thus occur in "clusters," with large areas remaining uncolonized at any one time.^[25] In mathematics, percolation theory describes the behavior of connected clusters in a random graph. ... It has been suggested that this article or section be merged with Colonialism. ...

Humanity's ability to detect and comprehend intelligent extraterrestrial life has existed for only a very brief period—from 1937 onwards, if the invention of the radio telescope is taken as the dividing line—and Homo sapiens is a geologically recent species. The whole period of modern human existence to date (about 200,000 years) is a very brief period on a cosmological scale, a position which changes little even if the species survives for hundreds of thousands of years more. Thus it remains possible that human beings have neither been searching long enough to find other intelligences, nor existed long enough to be found. The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of radio receiver used in astronomy. ... Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... This article does not cite its references or sources. ...

One million years ago there would have been no humans for alien emissaries to meet. For each further step back in time, there would have been increasingly fewer indications to such emissaries that intelligent life would develop on Earth. In a large and already ancient universe, a space-faring alien species may well have had many other more promising worlds to visit and revisit. Even if alien emissaries visited in more recent times, they may have been misinterpreted by early human cultures as supernatural entities. Look up Supernatural in Wiktionary, the free dictionary. ...

This hypothesis is more plausible if alien civilizations tend to stagnate or die out, rather than expand. However, "the probability of a site never being visited, even [with an] infinite time limit, is a non-zero value".^[26] Thus, even if intelligent life expands elsewhere, it remains statistically possible that terrestrial life will go undiscovered.

Artificial radio waves emitting from Earth have only propagated since first broadcasts made by Popov, Marconi and Tesla in 1895. This would mean that as of 2006, only intelligent extraterrestrial life within 55 light years would have been able to receive the signal and manage to send a reply back to Earth. Or perhaps first and subsequent signals were too weak to be received, and detection may have only been possible at the beginning of the space age, in 1957. In that case, only aliens within 24 light years would have been able to communicate back to earth. With time, the number of potential alien planets within reach increases. Alexander Popov (1859-1905) Alexander Stepanovich Popov (Russian: ÐÐ»ÐµÐºÑÐ°Ð½Ð´Ñ€ Ð¡Ñ‚ÐµÐ¿Ð°Ð½Ð¾Ð²Ð¸Ñ‡ ÐŸÐ¾Ð¿Ð¾Ð²) (March 4/16 1859 - January 13/December 31 1905/6) was a Russian physicist who publicly demonstrated the transmission of radio waves (but did not apply for a patent for this invention). ... Guglielmo Marchese Marconi, GCVO (25 April 1874-20 July 1937) was an Italian inventor, best known for his development of a practical radiotelegraph system, which served as the foundation for the establishment of numerous affiliated companies worldwide. ... Nikola Tesla (1856-1943)[1] was a world-renowned Serbian inventor, physicist, mechanical engineer and electrical engineer. ...

... but communication is impossible for technical reasons

There are some assumptions that underlie the SETI search programs that may cause searchers to miss signals that are present. For example, the radio searches to date would completely miss highly compressed data streams (which would be almost indistinguishable from "white noise" to anyone who did not understand the compression algorithm). Extraterrestrials might also use frequencies that scientists have decided are unlikely to carry signals, or use modulation strategies that are not being looked for. "Simple" broadcast techniques might be employed, but sent from non-main sequence stars which are searched with lower priority; current programs assume that most alien life will be orbiting Sun-like stars.^[27] This article is about the search for extra-terrestrial intelligence. ... White noise spectrum White noise( ) is a random signal (or process) with a flat power spectral density. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... A solar twin is the informal name for a star with characteristics similar to our own Sun. ...

The greatest problem is the sheer size of the radio search needed to look for signals, the limited amount of resources committed to SETI, and the sensitivity of modern instruments. SETI estimates, for instance, that with a radio telescope as sensitive as the Arecibo Observatory, Earth's television and radio broadcasts would only be detectable at distances up to 0.3 light years.^[28] Clearly detecting an Earth type civilization at great distances is difficult. A signal is much easier to detect if the signal energy is focused in either a narrow range of frequencies (Narrowband transmissions), and/or directed at a specific part of the sky. Such signals can be detected at ranges of hundreds to tens of thousands of light-years distance.^[29] However this means that detectors must be listening to an appropriate range of frequencies, and be in that region of space to which the beam is being sent. Many SETI searches go so far as to assume that extraterrestrial civilizations will be broadcasting a deliberate signal (like the Arecibo message), in order to be found. The Arecibo Observatory is located approximately 9 miles south-southwest from Arecibo, Puerto Rico (near the extreme southwestern corner of Arecibo pueblo). ... A light-year or lightyear, symbol ly, is a unit of length. ... Narrowband (narrow bandwidth) refers to a signal which occupies only a small amount of space on the radio spectrum -- the opposite of broadband or wideband. ... Arecibo Observatory This is the message with color added to highlight its separate parts. ...

Thus to detect alien civilizations through their radio emissions, Earth observers either need more sensitive instruments or must hope for fortuitous circumstances: that the broadband radio emissions of alien radio technology are much stronger than our own; that one of SETI's programs is listening to the correct frequencies from the right regions of space; or that aliens are sending focused transmissions such as the Arecibo message in our general direction.

Civilizations only broadcast detectable radio signals for a brief period of time

It may be that alien civilizations are detectable though their radio emissions only for a short time period, reducing the likelihood of spotting them. There are two possibilities in this regard: civilizations outgrow radio through technological advance or, conversely, resource depletion cuts short the time in which a species broadcasts.

The first idea, that civilizations advance beyond radio, is based in part on the "fiber optic objection": the use of broadcast technologies for the long-distance transmission of information is fundamentally wasteful of energy and bandwidth, as broadcasts typically radiate in all directions evenly and large amounts of power are needed. Human technology is currently moving away from broadcast for long-distance communication and replacing it with wires, optical fibers, narrow-beam microwave and laser transmission. Most recent technologies that employ radio, such as cell phones and Wi-Fi networks, use low-power, short-range transmitters to communicate with numerous fixed stations that are themselves connected by wire or narrow beam radio. Television, as developed in the mid-twentieth century, employs transmitters with strong narrow-band carrier signals that are perhaps the most detectable human signals at stellar range; however digital television is replacing this technology and uses wide-band spread spectrum modulation with much lower carrier power. It is argued that these trends will make the Earth much less visible in the radio spectrum within a few decades. Hypothetically, advanced alien civilizations evolve beyond broadcasting at all in the electromagnetic spectrum and communicate by principles of physics we don't yet understand. Thus it seems plausible that other civilizations would only be detectable for a relatively short period of time between the discovery of radio and the switch to more efficient technologies. Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by total internal reflection. ... Wikibooks has more about this subject: Marketing Note: broadcasting is also a term for hand sowing. ... In communications, transmission is the act of transmitting electrical messages (and the associated phenonomena of radiant energy that pass through media). ... This article or section does not cite its references or sources. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) wavelengths, but relatively short for radio waves. ... A LASER (from the acronym of Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. ... Mobile phones from various years Several mobile phones A mobile or cellular telephone is a long-range, portable electronic device for personal telecommunications over long distances. ... Official Wi-Fi logo Wi-Fi is a brand originally licensed by the Wi-Fi Alliance to describe the underlying technology of wireless local area networks (WLAN) based on the IEEE 802. ... Digital television (DTV) is a telecommunication system for broadcasting and receiving moving pictures and sound by means of digital signals, in contrast to analogue signals in analogue (traditional) T.V. It uses digital modulation data, which is digitally compressed and requires decoding by a specially designed television set or a... Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ...

A different argument is that resource depletion will soon result in a decline in technological capability. Human civilization has been capable of interstellar radio communication for only a few decades and is already rapidly depleting fossil fuels and grappling with the problem of peak oil. It may only be a few more decades before energy becomes too expensive, and the necessary electronics and computers too difficult to manufacture, for societies to continue the search. If the same conditions regarding energy supplies hold true for other civilizations, then radio technology may be a short-lived phenomenon. Unless two civilizations happen to be near each other and develop the ability to communicate at the same time it would be virtually impossible for any one civilization to "talk" to another. The Hubbert peak theory, also known as peak oil, is an influential theory concerning the long-term rate of conventional oil production and depletion. ...

Critics of the resource depletion argument point out that an energy-consuming civilization is not dependent solely on fossil fuels. Alternate energy sources exist, such as solar power which is renewable and has enormous potential relative to technical barriers.^[30] For depletion of fossil fuels to end the "technological phase" of a civilization some form of technological regression would have to invariably occur, preventing the exploitation of renewable energy sources. Coal rail cars in Ashtabula, Ohio Fossil Fuels are hydrocarbons, primarily coal, fuel oil or natural gas, formed from the remains of dead plants and animals. ... Solar power describes a number of methods of harnessing energy from the light of the sun. ... The end of civilization or the end of the world are phrases used in reference to human extinction scenarios, doomsday events, and related hazards which occur on a global scale. ... Renewable energy is defined as energy derived from resources that are regenerative or for all practical purposes can not be depleted. ...

Another possibility is that technological civilizations invariably experience a technological singularity and attain a posthuman (or postalien) character. Theoretical civilizations of this sort may have altered drastically enough to render communication impossible. The intelligences of a post-singularity civilization might require more information exchange than is possible through interstellar communication, for example. Or perhaps any information humanity might provide would appear elementary. Because of this they do not try to communicate, any more than human beings attempt to talk to ants. When plotted on a logarithmic graph, 15 separate lists of paradigm shifts for key events in human history show an exponential trend. ... Posthuman Future by Michael Gibbs A posthuman or post-human is a hypothetical future being whose capabilities so radically exceed those of present humans as to be no longer human by current standards. ...

Even more extreme forms of post-singularity have been suggested, particularly in fiction: beings that divest themselves of physical form, create massive artificial virtual environments (see Matrioshka brain), transfer themselves into these environments through mind transfer, and exist totally within virtual worlds, ignoring the external physical universe. Surprisingly early treatments, such as Lewis Padgett's short story Mimsy were the Borogroves (1943), suggest a migration of advanced beings out of the presently known physical universe into a different and presumably more agreeable alternate one. A Matrioshka Brain is a hypothetical megastructure, based on the Dyson sphere, of immense computational capacity. ... In transhumanism and science fiction, mind transfer (also referred to as mind uploading or mind downloading, depending on ones point of reference), whole body emulation, or electronic transcendence refers to the hypothetical transfer of a human mind to an artificial substrate. ... Lewis Padgett was the pseudonym of Henry Kuttner, usually working with his wife C. L. Moore. ...

One version of this perspective, which makes predictions for future SETI findings of transcension "fossils" and includes a variation of the Zoo hypothesis below, has been proposed by singularity scholar John Smart^[31] They also may be as far superior to us as we are to ants, not being able to communicate meaningfully. (See Also Sentience Quotient) John Smart is a developmental systems theorist whose interests include accelerating change, computational autonomy, evolutionary development, and the technological singularity. ... The Sentience Quotient concept was invented by Robert A. Freitas Jr. ...

... and they choose not to communicate

This idea is most plausible if there is a single alien civilization within contact range, or there is a homogenous culture or law amongst alien civilizations which dictates that the Earth be shielded. If there is a plurality of alien cultures, however, this theory may break down under the uniformity of motive flaw: all it takes is a single culture or civilization to decide to act contrary to the imperative for it to be abrogated, and the probability of such a violation increases with the number of civilizations.^[32] In astrobiology, the Uniformity of Motive theory suggests that any civilization in the universe would go through similar technological steps in their development. ...

It is possible that the belief that alien races would communicate with the human species is a fallacy, and that alien civilizations may not wish to communicate, even if they have the technical ability. A particular reason that alien civilizations may choose not to communicate is the so-called Zoo hypothesis: the idea that Earth is being monitored by advanced civilizations for study, or is being preserved in an isolated "zoo or wilderness area".^[33] The zoo hypothesis is one of a number of suggestions that have been advanced in response to the Fermi Paradox, regarding the apparent absence of evidence in support of the existence of advanced extraterrestrial life. ... It has been suggested that Logical fallacy be merged into this article or section. ...

The motivation may be ethical (encouraging humanity's independent development) or strategic (aliens wish to avoid detection and possible destruction at the hands of other civilizations). These ideas are similar to the Prime Directive of the "United Federation of Planets" in the fictional Star Trek television series. This possibility has caused some to speculate that humanity needs to pass a certain ethical, technological or social boundary before being allowed to make contact with existing advanced alien civilizations. To meet Wikipedias quality standards, this article may require cleanup. ... This article is about the Star Trek franchise. ...

Another possibility is that human theoreticians have underestimated how much alien life might differ from that on Earth. Alien psychologies may simply be too different to communicate with, and realizing this, they do not make the attempt (see: They're Made Out Of Meat). It is also possible that the very concept of communication with other species is one which they cannot conceive. Human mathematics, language, tool use, and other cornerstones of technology and communicative capacity may be parochial to Earth and not shared by other life.^[34] Using Earth as an example, it is possible to conceive of dolphins evolving intelligence, but such an intelligence might have difficulty developing technology (and particularly key aspects of our sort of technology, for example fire and electricity). See also technological singularity above. Euclid, Greek mathematician, 3rd century BC, known today as the father of geometry; shown here in a detail of The School of Athens by Raphael. ... A modern hammer is directly descended from ancient hand tools A tool or device is a piece of equipment that most commonly provides a mechanical advantage in accomplishing a physical task. ... When plotted on a logarithmic graph, 15 separate lists of paradigm shifts for key events in human history show an exponential trend. ...

Most scenarios for communication with other civilizations rest upon the assumption that these other races share our scientific curiosity and our desire to make contact. This may be incorrect. It is entirely possible that, for cultural reasons of its own (such as a religious taboo, xenophobia, or simple indifference), an alien society may have no desire to talk to others even if it has the technical capability. Look up xenophobia in Wiktionary, the free dictionary. ...

Finally, there is the possibility that an intelligent alien species may believe itself to be alone in the universe. This is hardly out of the question, as there are many here on Earth who believe the same thing. Of course, such speculations about alien psychology and culture are far beyond the ability of science to evaluate. This would assume that they are not even looking for other things beside ETI.

... and they are here unobserved

It may be that intelligent alien life forms not only exist, but are already present here on Earth. They are not detected because they do not wish it, human beings are technically unable, or because societies refuse to admit to the evidence.

It is not unreasonable that a life form intelligent enough to travel to Earth would also be sufficiently intelligent to exist here undetected. In this view, the aliens have arrived on Earth, or in our solar system, and are observing the planet, while concealing their presence. While it seems unlikely that alien observers could move amongst the general population undetected for any great length of time, such observation could be conducted in a number of other ways that would be very difficult to detect. For example, a complex system of microscopic monitoring devices constructed via molecular nanotechnology could be deployed on Earth and remain undetected, or sophisticated instruments could conduct passive monitoring from elsewhere. It has been suggested that Molecular engineering be merged into this article or section. ...

Many UFO researchers and watchers argue that society as a whole is unfairly biased against claims of alien abduction, sightings, and encounters, and as a result may not be fully receptive to claims of proof that aliens are visiting our planet. Others use complex conspiracy theories to allege that evidence of alien visits is being concealed from the public by political elites who seek to hide the true extent of contact between aliens and humans. For example, it is also possible that human beings do in fact interact with many alien cultures, but that Earth functions as a kind of prison colony, with the aid of memory wipes. Scenarios such as these have been depicted in popular culture for decades. The Abduction Phenomenon is as umbrella term used to describe a number of kidnap individuals--sometimes called abductees--usually for medical testing or for sexual reproduction procedures. ... For other uses, see Conspiracy theory (disambiguation). ... Popular culture, or pop culture, (literally: the culture of the people) consists of widespread cultural elements in any given society. ...

... and they are communicating, but not via radio waves

Given that alien civilizations are thousands or millions of years more advanced than us, there is no reason to assume that they still communicate using electromagnetic radiation. It seems rather foolhardy of us to assume that extremely advanced aliens would still be patronising a technology that we discovered barely 100 years ago. Moreover radio waves are too slow to be of any use at cosmic distances. Presumably they use exotic methods such as quantum entanglement or any hitherto undiscovered fundamental phenomena. Communication with electromagnetic radiation may span just a small window of time on a civilization's history, before they move onto more advanced forms of communication.

A related series of views consider that alien entities have been communicating with humans throughout history, but utilizing methods and technologies that are non-electromagnetic in nature, perceivable via what are conventionally known as altered states, which are outside most people's experience or imagination. "Signals" are arriving, but only a few individuals perceive them, and then rarely and possibly in a distorted manner. Accounts of communication have perhaps been reported in ancient religious texts (accounting for the wide variety of anecdotal reports of angels, demons, and so on) but have been dismissed or overlooked. Religious is a term with both a technical definition and folk use. ... The Annunciation - the Angel Gabriel announces to Mary that she will bear Jesus (El Greco, 1575) An angel is an ethereal being found in many religions, whose duties are to assist and serve God. ... The demon Satan In folklore, mythology, and religion, a demon is a supernatural being that is generally described as an evil spirit, but is also depicted to be good in some instances. ...

As an example: if the human brain utilizes quantum mechanical processes in its operation (as theorized by Roger Penrose, Stuart Hameroff, and others) then it may be open to receiving some form of nonlocal "psychic" communication, perhaps using quantum entanglement. It has been proposed that some accounts of mystics, shamans, schizophrenics, and channelers may be such "garbled" communications, transmitted by non-human intelligences in this manner. According to quantum mechanics the transfer of information in the context of information theory is not possible using quantum nonlocal correlations. However, supporters of the idea of this form of communication idea believe that this may explain the "garbled", associative, and inspirational nature of the "messages" recorded in the world's religious and anthropological history. This idea also explains the evident absence of space travel, which is unnecessary to the community of alien intelligence communicating via this medium. Fig. ... Sir Roger Penrose, OM, FRS (born 8 August 1931) is an English mathematical physicist and Emeritus Rouse Ball Professor of Mathematics at the Mathematical Institute, University of Oxford and Emeritus Fellow of Wadham College. ... Stuart Hameroff, MD, is an anesthesiologist and professor at the University of Arizona known for his promotion of the scientific study of consciousness, and his speculative theories of the mechanisms of consciousness. ... Nonlocality in quantum mechanics, refers to the property of entangled quantum states in which both the entangled states collapse simultaneously upon measurement of one of their entangled components, regardless of the spatial separation of the two states. ... A psychic is a person who is able to experience extra-sensory perception, such as clairvoyance, psychometry, and precognition, or who has other paranormal abilities such as psychokinesis. ... Mysticism (ancient Greek mysticon = secret) is meditation, prayer, or theology focused on the direct experience of union with divinity, God, or Ultimate Reality, or the belief that such experience is a genuine and important source of knowledge. ... The shaman is an intellectual and spiritual figure who is regarded as possessing power and influence on other peoples in the tribe and performs several functions, primarily that of a healer ( medicine man). The shaman provides medical care, and serves other community needs during crisis times, via supernatural means (means... Schizophrenia is a man made illness, caused by the implanting of electronics in the ear, to cause the person to hear voices. ... Channeling can refer to Channeling (physics) Channeling (mediumistic), a term used in reference to the process of receiving messages or inspiration from invisible beings or spirits This is a disambiguation page â€” a navigational aid which lists pages that might otherwise share the same title. ... Fig. ... In physics, the principle of locality is that distant objects cannot have direct influence on one another: an object is influenced directly only by its immediate surroundings. ... A bundle of optical fiber. ...

However, the theories of Penrose, Hameroff, and others are not universally accepted, and have met with skepticism, nor has it yet been shown that quantum mechanical effects are required for consciousness to occur. Fig. ...

Another useful example of a theoretical means of communication that would appear so very alien to most people's way of thinking, that it would most likely be misinterpreted or dismissed outright, is the controversial proposals of Terence McKenna that the psychoactive drugs psilocybin and/or Dimethyltryptamine (DMT) is an alien technology, "seeded" here on Earth by non-human intelligence, as part of a "biological communication strategy", in order to alter the perceptive processes of the human mind so that it may receive messages being transmitted to us. Terence Kemp McKenna (November 16, 1946 â€“ April 3, 2000) was a writer and philosopher. ... Psilocybin (also known as psilocybine), is a psychedelic alkaloid of the tryptamine family. ... DMT is a three-letter acronym (TLA) which may stand for Desoxymethyltestosterone Digital Monetary Trust Dimethyltryptamine Discrete multitone modulation Discrete monitor timing (a VESA standard for computer displays) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

Contents

Basis of the paradox

Related concepts

Drake equation

Rare Earth hypothesis

Resolving the paradox empirically

Radio emissions

Direct planetary observation

Alien constructs

Probes, colonies, and other artifacts

Advanced stellar scale artifacts

Explaining the paradox theoretically

They do not exist ...

... and they never did

... because an inhospitable universe destroys complex intelligent life

... because it is the nature of intelligent life to destroy itself

... because it is the nature of intelligent life to destroy others

... because God created humans alone

They do exist ...

... but communication is impossible due to problems of scale

... but communication is impossible for technical reasons

... and they choose not to communicate

... and they are here unobserved

... and they are communicating, but not via radio waves

See also

References

Suggested reading

External links

Contents

Basis of the paradox GA_googleFillSlot("encyclopedia_square");

Related concepts

Drake equation

Rare Earth hypothesis

Resolving the paradox empirically

Radio emissions

Direct planetary observation

Alien constructs

Probes, colonies, and other artifacts

Advanced stellar scale artifacts

Explaining the paradox theoretically

They do not exist ...

... and they never did

... because an inhospitable universe destroys complex intelligent life

... because it is the nature of intelligent life to destroy itself

... because it is the nature of intelligent life to destroy others

... because God created humans alone

They do exist ...

... but communication is impossible due to problems of scale

... but communication is impossible for technical reasons

... and they choose not to communicate

... and they are here unobserved

... and they are communicating, but not via radio waves

See also

References

Suggested reading

External links

Basis of the paradox