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This is an accepted version of this page This is the latest accepted revision, reviewed on 15 January 2025. Problem of the lack of evidence for alien life despite its apparent likelihood This article is about the absence of clear evidence of extraterrestrial life. For a type of estimation problem, see Fermi problem. Enrico Fermi (Los Alamos 1945) The Fermi paradox is the discrepancy between ...
The anthropic principle, also known as the observation selection effect, is the proposition that the range of possible observations that could be made about the universe is limited by the fact that observations are only possible in the type of universe that is capable of developing intelligent life. Proponents of the anthropic principle argue ...
The firstborn hypothesis is a special case of the Hart–Tipler conjecture (the idea that the lack of evidence for interstellar probes is evidence that no intelligent life other than humanity exists in the universe) which asserts a time-dependent curve towards discovery. [1]
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. [1] [2] The Great Filter is one possible resolution of the Fermi paradox.
The Rare Earth hypothesis argues that planets with complex life, like Earth, are exceptionally rare.. 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 ...
The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence. [1] [2] Extraterrestrial life forms might, for example, choose to allow contact once the human species has passed certain technological, political, and/or ethical standards.
Rare Earth was succeeded in 2003 by the follow-on book The Life and Death of Planet Earth: How the New Science of Astrobiology Charts the Ultimate Fate of our World, also by Ward and Brownlee, which talks about the Earth's long-term future and eventual demise under a warming and expanding Sun, showing readers the concept that planets like Earth ...
f i = the fraction of planets with life that go on to develop intelligent life (civilizations). f c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space. L = the length of time for which such civilizations release detectable signals into space. [6] [7]