Extraterrestrial life or alien life is life which may occur outside of Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might range from simple forms such as prokaryotes to intelligent beings, possibly bringing forth civilisations that might be far more advanced than humanity.[1][2][3] The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology. Speculation about the possibility of inhabited worlds outside the planet Earth dates back to antiquity. 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.[4] In his first-century poem De rerum natura (Book 2:1048–1076), the Epicurean philosopher Lucretius predicted that humanity would find innumerable exoplanets with life-forms similar to, and different from, the ones on Earth, and even other races of man.[citation needed] Pre-modern writers typically assumed extraterrestrial "worlds" are inhabited by living beings. William Vorilong, in the 15th century, acknowledged the possibility that Jesus could have visited extraterrestrial worlds to redeem their inhabitants.[5] Nicholas of Cusa wrote in 1440 that Earth is "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. He theorised all extraterrestrial bodies could be inhabited by men, plants, and animals, including the Sun.[6] 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.[7] The writings of these individuals demonstrate interest in extraterrestrial life has existed throughout history, although only recently have humans have had any means of investigating it.[citation needed] 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. Depending on the category of search, methods range from the analysis of telescope and specimen data[8] to radios used to detect and transmit communications.[citation needed] The concept of extraterrestrial life, and particularly extraterrestrial intelligence, has had a major cultural impact, especially extraterrestrials in fiction. Science fiction has communicated scientific ideas, imagined a wide range of possibilities, and influenced public interest in and perspectives on extraterrestrial life. One shared space is the debate over the wisdom of attempting communication with extraterrestrial intelligence. Some encourage aggressive methods to try to contact intelligent extraterrestrial life. Others – citing the tendency of technologically advanced human societies to enslave or destroy less advanced societies – argue it may be dangerous to actively draw attention to Earth.[9][10]