The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
Extraterrestrial life or alien life is life which does not originate from Earth. No extraterrestrial life has yet been conclusively detected. Such life might range from simple forms such as prokaryotes to intelligent 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 is known as astrobiology.
The Fermi paradox is the discrepancy between the lack of conclusive evidence of advanced extraterrestrial life and the apparently high likelihood of its existence. As a 2015 article put it, "If life is so easy, someone from somewhere must have come calling by now."
The Kardashev scale is a method of measuring a civilization's level of technological advancement based on the amount of energy it is capable of using. The measure was proposed by Soviet astronomer Nikolai Kardashev (1932–2019) in 1964 and was named after him.
Extraterrestrial intelligence, or non-human intelligence, refers to hypothetical intelligent extraterrestrial life. No such life has ever been proven to exist in the Solar System except for humans on Earth, and its existence on other star systems is still speculative. 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.
The Gods Themselves is a 1972 science fiction novel written by Isaac Asimov, and his first original work in the science fiction genre in fifteen years. It won the Nebula Award for Best Novel in 1972, and the Hugo Award for Best Novel in 1973.
The mediocrity principle is the philosophical notion that "if an item is drawn at random from one of several sets or categories, it's more likely to come from the most numerous category than from any one of the less numerous categories". The principle has been taken to suggest that there is nothing very unusual about the evolution of the Solar System, Earth's history, the evolution of biological complexity, human evolution, or any one nation. It is a heuristic in the vein of the Copernican principle, and is sometimes used as a philosophical statement about the place of humanity. The idea is to assume mediocrity, rather than starting with the assumption that a phenomenon is special, privileged, exceptional, or even superior.
The Stars, Like Dust is a 1951 science fiction mystery book by American writer Isaac Asimov.
The concept of self-replicating spacecraft, as envisioned by mathematician John von Neumann, has been described by futurists and has been discussed across a wide breadth of hard science fiction novels and stories. Self-replicating probes are sometimes referred to as von Neumann probes. Self-replicating spacecraft would in some ways either mimic or echo the features of living organisms or viruses.
The City and the Stars is a science fiction novel by British writer Arthur C. Clarke, published in 1956. This novel is a complete rewrite of his earlier Against the Fall of Night, Clarke's first novel, which had been published in Startling Stories magazine in 1948 after John W. Campbell, Jr., editor of Astounding Science-Fiction, had rejected it, according to Clarke.
In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth required an improbable combination of astrophysical and geological events and circumstances.
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, similar 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, in which humanity is being subjected to experiments, with Earth serving as a giant laboratory.
The Great Filter is the idea that in the development of life from the earliest stages of abiogenesis to reaching the highest levels of development on the Kardashev scale, there is a barrier to development that makes detectable extraterrestrial life exceedingly rare. The Great Filter is one possible resolution of the Fermi paradox.
First contact is a common science fiction theme about the first meeting between humans and extraterrestrial life, or of any sentient species' first encounter with another one, given they are from different planets or natural satellites. The theme allows writers to explore such topics such as xenophobia, transcendentalism, and basic linguistics by adapting the anthropological topic of first contact to extraterrestrial cultures.
An Earth analog, also called an Earth analogue, Earth twin, or second Earth, is a planet or moon with environmental conditions similar to those found on Earth. The term Earth-like planet is also used, but this term may refer to any terrestrial planet.
The Voyager Golden Record contains 116 images and a variety of sounds. The items for the record, which is carried on both the Voyager 1 and Voyager 2 spacecraft, were selected for NASA by a committee chaired by Carl Sagan of Cornell University. Included are natural sounds, musical selections from different cultures and eras, spoken greetings in 59 languages, human sounds like footsteps and laughter, and printed messages from President Jimmy Carter and U.N. Secretary-General Kurt Waldheim.
The cultural impact of extraterrestrial contact is the corpus of changes to terrestrial science, technology, religion, politics, and ecosystems resulting from contact with an extraterrestrial civilization. This concept is closely related to the search for extraterrestrial intelligence (SETI), which attempts to locate intelligent life as opposed to analyzing the implications of contact with that life.
In astrobiology and planetary astrophysics, the galactic habitable zone is the region of a galaxy in which life might most likely develop. The concept of a galactic habitable zone analyzes various factors, such as metallicity and the rate and density of major catastrophes such as supernovae, and uses these to calculate which regions of a galaxy are more likely to form terrestrial planets, initially develop simple life, and provide a suitable environment for this life to evolve and advance. According to research published in August 2015, very large galaxies may favor the birth and development of habitable planets more than smaller galaxies such as the Milky Way. In the case of the Milky Way, its galactic habitable zone is commonly believed to be an annulus with an outer radius of about 10 kiloparsecs (33,000 ly) and an inner radius close to the Galactic Center.
The theorized habitability of red dwarf systems is determined by a large number of factors. Modern evidence indicates that planets in red dwarf systems are unlikely to be habitable, due to their low stellar flux, high probability of tidal locking and thus likely lack of magnetospheres and atmospheres, small circumstellar habitable zones and the high stellar variation experienced by planets of red dwarf stars, impeding their planetary habitability. However, the ubiquity and longevity of red dwarfs could provide ample opportunity to realize any small possibility of habitability.
"The Immortals" is the eleventh episode of the American documentary television series Cosmos: A Spacetime Odyssey. It premiered on May 18, 2014, on Fox, and aired on May 19, 2014, on National Geographic Channel. The episode was written by Ann Druyan and Steven Soter, and directed by Brannon Braga. The episode explores the possibility of the interstellar spread of life and possible alien encounters. The episode also presents the hypothesis of panspermia, where the origin of life is attributed to comets or asteroids carrying radiation-resistant organisms.
