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The zoo hypothesis is one of many theoretical explanations for the Fermi paradox. The hypothesis speculates as to the assumed behavior and existence of technically advanced extraterrestrial life and the reasons they refrain from contacting Earth. One interpretation of the hypothesis argues that intelligent alien life intentionally ignores Earth to allow for natural evolution and sociocultural development. The hypothesis seeks to explain the apparent absence of extraterrestrial life despite its generally accepted plausibility and hence the reasonable expectation of its existence. Aliens might, for example, choose to allow contact once the human species has passed certain technological, political, or ethical standards. They might withhold contact until humans force contact upon them, possibly by sending a spacecraft to planets they inhabit. Alternatively, a reluctance to initiate contact could reflect a sensible desire to minimize risk. An alien society with advanced remote-sensing technologies may conclude that direct contact with neighbors confers added risks to oneself without an added benefit. ==Assumptions== The zoo hypothesis assumes first that a large number of alien cultures exist, and second that these aliens have great reverence for independent, natural evolution and development. In particular, assuming that intelligence is a physical process that acts to maximize the diversity of a system's accessible futures,〔A. D. Wissner-Gross, "(Causal entropic forces )", ''Physical Review Letters'' 110, 168702 (2013).〕 a fundamental motivation for the zoo hypothesis would be that premature contact would "unintelligently" reduce the overall diversity of paths the universe itself could take. These ideas are perhaps most plausible if there is a relatively universal cultural or legal policy among a plurality of extraterrestrial civilizations necessitating isolation with respect to civilizations at Earth-like stages of development. In a Universe without a hegemonic power, random single civilizations with independent principles would make contact. This makes a crowded Universe with clearly defined rules seem more plausible.〔Soter, S. (2005). Astrobiol. Mag. 17 Oct ("SETI and the Cosmic Quarantine Hypothesis" )〕 If there is a plurality of alien cultures, however, this theory may break down under the uniformity of motive concept because it would take just a single extraterrestrial civilization to decide to act contrary to the imperative within our range of detection for it to be abrogated, and the probability of such a violation increases with the number of civilizations.〔Crawford, I.A., "Where are They? Maybe we are alone in the galaxy after all", Scientific American, July 2000, 38–43, (2000).()〕 This idea, however, becomes more plausible if all civilizations tend to evolve similar cultural standards and values with regard to contact much like convergent evolution on Earth has independently evolved eyes on numerous occasions,〔Kozmik, Z.; Ruzickova, J.; Jonasova, K.; Matsumoto, Y.; Vopalensky, P.; Kozmikova, I.; Strnad, H.; Kawamura, S. et al. (Jul 2008). "Assembly of the cnidarian camera-type eye from vertebrate-like components". ''Proceedings of the National Academy of Sciences of the United States of America'' 105 (26): 8989–8993.()〕 or all civilizations follow the lead of some particularly distinguished civilization . . . the first civilization.〔Bracewell, R. (1982). Pre-emption of the Galaxy by the First AdvancedCivilization, Pergmon Press, Oxford.()〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「zoo hypothesis」の詳細全文を読む スポンサード リンク
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