![]() ![]() Life may have emerged independently at many places throughout the universe, as it arose on Earth roughly 4.2 billion years ago through chemical processes. The chemistry of life may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the universe was only 10–17 million years old. This argument is embodied in the Copernican principle, which states that Earth does not occupy a unique position in the Universe, and the mediocrity principle, which states that there is nothing special about life on Earth. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking it would be improbable for life not to exist somewhere other than Earth. This hypothesis relies on the vast size and consistent physical laws of the observable universe. Įxtraterrestrial life, such as microorganisms, has been hypothesized to exist in the Solar System and throughout the universe. Planetary habitability in the Solar SystemĪstronomers have discovered stars in the Milky Way galaxy that are almost 13.6 billion years old. Others-citing the tendency of technologically advanced human societies to enslave or wipe out less advanced societies-argue that it may be dangerous to actively call attention to Earth. Some encourage aggressive methods to try to contact intelligent extraterrestrial life. ![]() One shared space is the debate over the wisdom of attempting communication with extraterrestrial intelligence. Over the years, science fiction has communicated scientific ideas, imagined a wide range of possibilities, and influenced public interest in and perspectives on extraterrestrial life. The concept of extraterrestrial life, and particularly extraterrestrial intelligence, has had a major cultural impact, especially extraterrestrials in fiction. Depending on the category of search, methods range from the analysis of telescope and specimen data to radios used to detect and send communication signals. Since the mid-20th century, active research has taken place to look for signs of extraterrestrial life, encompassing searches for current and historic extraterrestrial life, and a narrower search for extraterrestrial intelligent life. The writings of these thinkers show that interest in extraterrestrial life existed throughout history, but it is only recently that humans have had any means of investigating it. Descartes wrote that there was no means to prove that the stars were not inhabited by "intelligent creatures," but their existence was a matter of speculation. He theorized that all extraterrestrial bodies could be inhabited by men, plants, and animals, including the Sun. Nicholas of Cusa wrote in 1440 that the Earth was "a brilliant star" like other celestial objects visible in space, which would appear similar to the Sun from an exterior perspective due to a layer of "fiery brightness" in the outer layer of the atmosphere. William Vorilong, in the 15th century, acknowledged the possibility that Christ could have visited extraterrestrial worlds to redeem their inhabitants. Pre-modern writers typically assumed that extraterrestrial "worlds" would be inhabited by living beings. In his first century poem De rerum natura code: lat promoted to code: la (Book 2:1048–1076), the Epicurean philosopher Lucretius predicted that we would find innumerable exoplanets with life-forms similar to, and different from, the ones on Earth, and even other races of man. ![]() Multiple early Christian writers discussed the idea of a "plurality of worlds" as proposed by earlier thinkers such as Democritus Augustine references Epicurus's idea of innumerable worlds "throughout the boundless immensity of space" (originally expressed in his Letter to Herodotus) in The City of God. Speculation about the possibility of inhabited "worlds" outside the planet Earth dates back to antiquity. The science of extraterrestrial life is known as astrobiology. The Drake equation speculates about the existence of sapient life elsewhere in the universe. ![]() Such life might range from simple forms like prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more advanced than humankind. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Robotic exploration of the Solar System (image: Curiosity rover on Mars)Įxtraterrestrial life, colloquially referred to as alien life, is life that may occur outside of Earth and which did not originate on Earth.Listening for extraterrestrial signals indicating intelligence (image: Allen array).The search for extrasolar planets (image: Kepler telescope).Some major international efforts to search for extraterrestrial life. ![]()
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