Extraterrestrial life, sometimes colloquially referred to as alien life, is hypothetical life that may occur outside Earth and which did not originate on Earth. Such life might range from simple forms comparable to prokaryotes, to intelligent beings and even sapient beings, possibly bringing forth civilizations that might be far more advanced than humanity. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life in all its forms is known as astrobiology, the multidisciplinary field that investigates the deterministic conditions and contingent events with which life arises, distributes, and evolves in the universe.
Extraterrestrial intelligence refers to hypothetical intelligent extraterrestrial life. The question of whether other inhabited worlds might exist has been debated since ancient times. The modern form of the concept emerged when the Copernican Revolution demonstrated that the Earth was a planet revolving around the Sun, and other planets were, conversely, other worlds. The question of whether other inhabited planets or moons exist was a natural consequence of this new understanding. It has become one of the most speculative questions in science and is a central theme of science fiction and popular culture.
A humanoid is a non-human entity with human form or characteristics. The earliest recorded use of the term, in 1870, referred to indigenous peoples in areas colonized by Europeans. By the 20th century, the term came to describe fossils which were morphologically similar, but not identical, to those of the human skeleton.
Ian Nicholas Stewart is a British mathematician and a popular-science and science-fiction writer. He is Emeritus Professor of Mathematics at the University of Warwick, England.
Grey aliens, also referred to as Zeta Reticulans, Roswell Greys, or Grays, are purported extraterrestrial beings. They are frequent subjects of close encounters and alien abduction claims. The details of such claims vary widely, but typically Greys are described as being human-like with small bodies with smooth, grey-colored skin; enlarged, hairless heads; and large, black eyes. The Barney and Betty Hill abduction claim, which purportedly took place in New Hampshire in 1961, popularized Grey aliens. Precursor figures have been described in science fiction and similar descriptions appeared in early accounts of the 1948 Aztec UFO Hoax and later accounts of the 1947 Roswell UFO incident.
Jack Cohen, FRSB was a British reproductive biologist also known for his science books and involvement with science fiction.
The extraterrestrial hypothesis (ETH) proposes that some unidentified flying objects (UFOs) are best explained as being physical spacecraft occupied by extraterrestrial life or non-human aliens, or non-occupied alien probes from other planets visiting Earth.
The Science of Discworld is a 1999 book by novelist Terry Pratchett and popular science writers Ian Stewart and Jack Cohen. Three sequels, The Science of Discworld II: The Globe, The Science of Discworld III: Darwin's Watch, and The Science of Discworld IV: Judgement Day, have been written by the same authors.
Xenoarchaeology, a branch of xenology dealing with extraterrestrial cultures, is a hypothetical form of archaeology that exists mainly in works of science fiction. The field is concerned with the study of the material remains to reconstruct and interpret past life-ways of alien civilizations. Xenoarchaeology is not currently practiced by mainstream archaeologists due to the current lack of any material for the discipline to study.
The Science of Discworld III: Darwin's Watch (2005) is a book set on the Discworld, by Terry Pratchett, Ian Stewart and Jack Cohen. It is the sequel to The Science of Discworld and The Science of Discworld II: The Globe.
The zoo hypothesis speculates on the assumed behavior and existence of technologically advanced extraterrestrial life and the reasons they refrain from contacting Earth. It is one of many theoretical explanations for the Fermi paradox. The hypothesis states that alien life intentionally avoids communication with Earth to allow for natural evolution and sociocultural development, and avoiding interplanetary contamination, similarly to people observing animals at a zoo. The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence. A variant on the zoo hypothesis suggested by the former MIT Haystack Observatory scientist John Allen Ball, is the laboratory hypothesis, where humanity is being subjected to experiments, with Earth being a giant laboratory.
An extraterrestrial or alien is any extraterrestrial lifeform; a lifeform that did not originate on Earth. The word extraterrestrial means "outside Earth". The first published use of extraterrestrial as a noun occurred in 1956, during the Golden Age of Science Fiction.
Alien Planet is a 2005 docufiction TV special created for the Discovery Channel. Based on the 1990 book Expedition by the artist and writer Wayne Barlowe, Alien Planet explores the imagined extraterrestrial life of the fictional planet Darwin IV in the style of a nature documentary. Although closely following Barlowe's depiction of Darwin IV, Alien Planet features a team of scientists and science fiction figures discussing Darwin IV as if it had actually been discovered. Among the people featured are Michio Kaku, Stephen Hawking, Jack Horner, James B. Garvin and George Lucas.
Barlowe's Guide to Extraterrestrials is a science fiction book by artist Wayne Barlowe, with Ian Summers and Beth Meacham. It contains Barlowe's visualizations of different extraterrestrial life forms from various works of science fiction, with information on their planetary location or range, biology, and behaviors, in the style of a real field guide for animals. It was nominated for an American Book Award and for the 1980 Hugo Award for Best Related Work.
Edison's Conquest of Mars is an 1898 science fiction mashup novel by American astronomer and writer Garrett P. Serviss. It was written as a sequel to Fighters from Mars, an unauthorized and heavily altered version of H. G. Wells's 1897 story The War of the Worlds. It has a place in the history of science fiction for its early employment of themes and motifs that later became staples of the genre.
Wheelers is a hard science fiction novel written by English mathematician Ian Stewart and reproductive biologist Jack Cohen. The book was originally released in hardcover form in the year 2000, and a more common paperback printing was begun in 2001. It has enjoyed modest commercial success and is perhaps best known for its conceptions of alien zoology and intelligence—hallmarks of Cohen's work as a consultant on exobiology for books, movies, and television.
The Science of Aliens is a touring exhibition that launched at the London Science Museum in October 2005. It was developed by a company called The Science of... set up by The Science Museum and Fleming Media. Two versions of the exhibition are touring venues around the world.
The War of the Worlds is a science fiction novel by English author H. G. Wells, first serialised in 1897 by Pearson's Magazine in the UK and by Cosmopolitan magazine in the US. The novel's first appearance in hardcover was in 1898 from publisher William Heinemann of London. Written between 1895 and 1897, it is one of the earliest stories to detail a conflict between mankind and an extra-terrestrial race. The novel is the first-person narrative of both an unnamed protagonist in Surrey and of his younger brother in London as southern England is invaded by Martians. The novel is one of the most commented-on works in the science fiction canon.
Speculative evolution is a genre of speculative fiction and an artistic movement focused on hypothetical scenarios in the evolution of life, and a significant form of fictional biology. It is also known as speculative biology and it is referred to as speculative zoology in regards to hypothetical animals. Works incorporating speculative evolution may have entirely conceptual species that evolve on a planet other than Earth, or they may be an alternate history focused on an alternate evolution of terrestrial life. Speculative evolution is often considered hard science fiction because of its strong connection to and basis in science, particularly biology.
The Zoologist's Guide to the Galaxy. What Animals on Earth Reveal about Aliens – and Ourselves is a 2020 popular science book by the Cambridge University zoologist Arik Kershenbaum. It discusses the possible nature of life on other planets, based on the study of animal life on Earth.
