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Do one or more extraterrestrial civilizations exist? Until recently, speculation about extraterrestrial races was confined either to [[science fiction]] or to innumerable anecdotal reports of "[[UFO|unidentified flying objects]]." These latter reports were once the subject of an investigation, known as [[Project Blue Book]], by the [[United States Air Force]].<ref>Anonymous, "[http://www.ufoevidence.org/topics/ProjectBlueBook.htm Project Blue Book]", ''[http://www.ufoevidence.org/ UFO Evidence.org]'', retrieved April 16, 2007</ref><ref>Anonymous, ''[http://www.bluebookarchive.org/ The Project Blue Book Archive]'', retrieved April 16, 2007</ref><ref>Fund for Unidentified Flying Object Research (FUFOR), ''[http://www.nicap.org/index.htm Official Site of the National Investigative Committee for Aerial Phenomena]'', Francis L. Ridge, editor and Webmaster, December 15, 1997 to present. Retrieved April 16, 2007.</ref><ref>Presumably the [[Union of Soviet Socialist Republics|Soviet]] Army Air Forces had their own version of Blue Book as well.</ref> But years after Blue Book wound down, a large cadre of scientists began to entertain seriously the notion that extraterrestrial civilizations might exist.

Do one or more extraterrestrial civilizations exist? Until recently, speculation about extraterrestrial races was confined either to [[science fiction]] or to innumerable anecdotal reports of "[[UFO|unidentified flying objects]]." These latter reports were once the subject of an investigation, known as [[Project Blue Book]], by the [[United States Air Force]].<ref>Anonymous, "[http://www.ufoevidence.org/topics/ProjectBlueBook.htm Project Blue Book]", ''[http://www.ufoevidence.org/ UFO Evidence.org]'', retrieved April 16, 2007</ref><ref>Anonymous, ''[http://www.bluebookarchive.org/ The Project Blue Book Archive]'', retrieved April 16, 2007</ref><ref>Fund for Unidentified Flying Object Research (FUFOR), ''[http://www.nicap.org/index.htm Official Site of the National Investigative Committee for Aerial Phenomena]'', Francis L. Ridge, editor and Webmaster, December 15, 1997 to present. Retrieved April 16, 2007.</ref><ref>Presumably the [[Union of Soviet Socialist Republics|Soviet]] Army Air Forces had their own version of Blue Book as well.</ref> But years after Blue Book wound down, a large cadre of scientists began to entertain seriously the notion that extraterrestrial civilizations might exist.

In 1961, astronomer Frank Drake developed a method for estimating of the number of extraterrestrial civilizations in the galaxy.  The Drake equation simply begins with the number of stars, then multiplies that number by a series of probabilities (probability that a star has planets, that a planet can support life, etc.) to obtain the quantity desired (number of populated planets, number of civilizations whose existence is detectable, etc.).

SETI ('''S'''earch for '''E'''xtra'''t'''errestrial '''I'''ntelligence)<ref>[http://www.seti.org/site/pp.asp?c=ktJ2J9MMIsE&b=178025 Home of the SETI Institute]</ref> is the name given to several government and privately-funded projects that over the years have searched for evidence of extraterrestrial civilizations.  This is done by listening via [[radiotelescope]] on a defined frequency band for any transmission having any semblance of order. The frequency band is one that, they believe, is the likeliest region in the [[electromagnetic spectrum]] for anyone to be sending a signal intended to cross interstellar, or even intergalactic, space.

In principle, the Drake Equation can provide an upper and lower bound for the number of extraterrestrial civilizations by setting upper and lower bounds for each probability factor, which can then be improved upon as better information becomes available. Because the number of stars in so huge, even the lower bound is often calculated to be a respectable number. However, a serious problem is that some of the probabilities are completely unknown, or even unknowable.

No definitive evidence exists for any form of extraterrestrial civilization. While the [[Project Blue Book]] investigators found a number of cases that they had to classify as "unknown," they were able to classify the bulk of the anecdotes as anything from outright hoaxes to misinterpretations of common weather features to misinterpretation of the sightings of ordinary aircraft.<ref>The Air Force might also have acted in a deceptive manner in certain isolated cases in which what the witnesses took for [[UFO]]s were actually secret experimental prototypes. Perhaps some of these prototypes exist today as the [[B-2]], [[F-117]], and other [[Stealth aircraft]].</ref> Neither has any [[Astronomy|astronomer]] or [[astronaut]] reported a definite sighting of, much less contact with, any carrier-like vessel that would have been capable of launching any of the alleged two-seater or similar small-crewed craft that various "witnesses" report having encountered. Nor has any [[physics|physicist]] yet suggested a method by which such a craft could have visited our [[solar system]], given the fixed speed limit set by the [[Special Theory of Relativity]]. Finally, the SETI project, for all their searching for a signal (even to recruiting civilians to participate in a "distributed computing" project to process the noise they have received from their radiotelescopes), have never isolated anything like a definite signal.

Even more serious is that the equation presumes that there is a possibility, however small, of life beginning and evolving.

However, one of the most well-accepted scientific laws, the [[law of biogenesis]] says that life only comes from life, which means that it cannot come from non-life.

Furthermore, scientific observations are that evolution itself is impossible, as evolution requires ''increasing'' genetic [[information]], whereas observations show that living things ''lose'' genetic information.<ref>Wieland, Carl, [http://www.creationontheweb.com/content/view/431/ The evolution train’s a-comin’], ''Creation'' 24(2):16–19, March 2002.</ref>

The two questions that most speculators raise regarding extraterrestrial civilizations are mainly whether:

==The Drake Equation==

In 1961, astronomer Frank Drake developed a method for estimating of the number of extraterrestrial civilizations in the galaxy.  The Drake Equation simply begins with the number of stars, then multiplies that number by a series of probabilities (probability that a star has planets, that a planet can support life, etc.) to obtain the quantity desired (number of populated planets, number of civilizations whose existence is detectable, etc.).

# Such a civilization might somehow communicate with, or visit, or even attempt to invade and conquer, the earth.

In principle, the Drake Equation can provide an upper and lower bound for the number of extraterrestrial civilizations by setting upper and lower bounds for each probability factor, which can then be improved upon as better information becomes available.  Because the number of stars in so huge, even the lower bound is often calculated to be a respectable number. However, a serious problem is that some of the probabilities are completely unknown, or even unknowable.  For example, the probability of life emerging on a planet is a meaningless concept if life is created directly by God and not by some naturalistic process.

# Humans, in their further-ranging exploration of space, will eventually encounter, trade with, or go to war with, such civilizations.

In addition to Blue Book, NASA has maintained [[Project SETI]] (for '''S'''earch for '''E'''xtra'''t'''errestrial '''I'''ntelligence).<ref>[http://www.seti.org/site/pp.asp?c=ktJ2J9MMIsE&b=178025 Home of the SETI Institute]</ref> This search consists mainly of listening by [[radiotelescope]] on a defined frequency band for any transmission having any semblance of order. This frequency band is one that, they believe, is the likeliest region in the [[electromagnetic spectrum]] for anyone to be sending a signal intended to cross interstellar, or even intergalactic, space.

If any of the probabilities appearing in the equation is zero, then the number of extraterrestrial civilizations of course goes to zero. This is a serious problem if one relies only on naturalistic explanations of the genesis of life.  One of the most well-accepted scientific laws, the [[law of biogenesis]] says that life only comes from life, which means that it cannot come from non-life.  Furthermore, scientific observations are that evolution itself is impossible, as evolution requires ''increasing'' genetic [[information]], whereas observations show that living things ''lose'' genetic information.<ref>Wieland, Carl, [http://www.creationontheweb.com/content/view/431/ The evolution train’s a-comin’], ''Creation'' 24(2):16–19, March 2002.</ref>

 

No definitive evidence exists for any form of extraterrestrial civilization. While the [[Project Blue Book]] investigators found a number of cases that they had to classify as "unknown," they were able to classify the bulk of the anecdotes as anything from outright hoaxes to misinterpretations of common weather features to misinterpretation of the sightings of ordinary aircraft.<ref>The Air Force might also have acted in a deceptive manner in certain isolated cases in which what the witnesses took for [[UFO]]s were actually secret experimental prototypes. Perhaps some of these prototypes exist today as the [[B-2]], [[F-117]], and other [[Stealth aircraft]].</ref> Neither has any [[Astronomy|astronomer]] or [[astronaut]] reported a definite sighting of, much less contact with, any carrier-like vessel that would have been capable of launching any of the alleged two-seater or similar small-crewed craft that various "witnesses" report having encountered. Nor has any [[physics|physicist]] yet suggested a method by which such a craft could have visited our [[solar system]], given the fixed speed limit set by the [[Special Theory of Relativity]]. Finally, the SETI project, for all their searching for a signal (even to recruiting civilians to participate in a "distributed computing" project to process the noise they have received from their radiotelescopes), have never isolated anything like a definite signal.

== Extraterrestrial Life in Science Fiction ==

== Extraterrestrial Life in Science Fiction ==