Astrobiology, is a scientific field within the life and environmental sciences that studies the origins, early evolution, distribution, and future of life in the universe by investigating its deterministic conditions and contingent events. As a discipline, astrobiology is founded on the premise that life may exist beyond Earth.
The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way Galaxy.
Extraterrestrial life, alien life, or colloquially aliens, 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 humans. 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 search for extraterrestrial intelligence (SETI) is a collective term for scientific searches for intelligent extraterrestrial life, for example, monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets.
Frank Donald Drake was an American astrophysicist and astrobiologist.
Extraterrestrial intelligence (ETI) refers to hypothetical intelligent extraterrestrial life. No such life has ever been observed to exist. 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.
Jill Cornell Tarter is an American astronomer best known for her work on the search for extraterrestrial intelligence (SETI). Tarter is the former director of the Center for SETI Research, holding the Bernard M. Oliver Chair for SETI at the SETI Institute. In 2002, Discover magazine recognized her as one of the 50 most important women in science.
The SETI Institute is a not-for-profit research organization incorporated in 1984 whose mission is to explore, understand, and explain the origin and nature of life in the universe, and to use this knowledge to inspire and guide present and future generations, sharing knowledge with the public, the press, and the government. SETI stands for the "search for extraterrestrial intelligence".
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, and subsequently human intelligence, required an improbable combination of astrophysical and geological events and circumstances. According to the hypothesis, complex extraterrestrial life is an improbable phenomenon and likely to be rare throughout the universe as a whole. The term "Rare Earth" originates from Rare Earth: Why Complex Life Is Uncommon in the Universe (2000), a book by Peter Ward, a geologist and paleontologist, and Donald E. Brownlee, an astronomer and astrobiologist, both faculty members at the University of Washington.
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 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 extraterrestrial 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.
The communication with extraterrestrial intelligence (CETI) is a branch of the search for extraterrestrial intelligence (SETI) that focuses on composing and deciphering interstellar messages that theoretically could be understood by another technological civilization. The best-known CETI experiment of its kind was the 1974 Arecibo message composed by Frank Drake.
Neocatastrophism is the hypothesis that life-exterminating events such as gamma-ray bursts have acted as a galactic regulation mechanism in the Milky Way upon the emergence of complex life in its habitable zone. It is one of several proposed solutions to the Fermi paradox since it provides a mechanism which would have delayed the advent of intelligent beings in local galaxies near Earth.
Active SETI is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are predominantly sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message. Active SETI is also known as METI.
Metalaw is “the entire sum of legal rules regulating relationships between different races in the universe.” It is a concept of space law closely related to the scientific Search for Extraterrestrial Intelligence (SETI). The idea is an elaboration of Immanuel Kant's Categorical imperative "Act only according to that maxim whereby you can at the same time will that it should become a universal law."
The Eerie Silence: Renewing Our Search for Alien Intelligence is a 2010 popular science book by Paul Davies, chair of the SETI: Post-Detection Science and Technology Taskgroup of the International Academy of Astronautics. The Eerie Silence explores the possibilities of intelligent extraterrestrial life, and its potential consequences.
Talking About Life: Conversations on Astrobiology is a non-fiction book edited by astronomer Chris Impey that consists of interviews with three dozen leading experts on the subject of astrobiology. The subject matter ranges from the nature and limits of life on Earth to the current search for exoplanets and the prospects of intelligent life in the universe. The book was published as a hardcover by Cambridge University Press in 2010.
The Hart–Tipler conjecture is the idea that an absence of detectable Von Neumann probes is contrapositive evidence that no intelligent life exists outside of the Solar System. This idea was first proposed in opposition to the Drake equation in a 1975 paper by Michael H. Hart titled "Explanation for the Absence of Extraterrestrials on Earth". Assuming that the probes traveled at 1/10 the speed of light and that no time was lost in building new ships upon arriving at the destination, Hart surmised that a wave of Von Neumann probes could cross the galaxy in approximately 650,000 years, a comparatively minimal span of time relative to the estimated age of the universe at 13.7 billion years. Hart’s argument was extended by cosmologist Frank Tipler in his 1981 paper entitled "Extraterrestrial intelligent beings do not exist".
