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Neocatastrophism
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.〔Cirković MM, Vukotić B. (2008). Astrobiological phase transition: towards resolution of Fermi's paradox.
Orig Life Evol Biosph. 38(6):535-47. PMID 18855114〕〔Ćirković M.M. (2009). ( Fermi's paradox: The last challenge for copernicanism? ) Serbian Astronomical Journal 178:1-20 〕〔Cirkovic, M. M. Vukotic, B. (2009). (Astrobiological Landscape and Neocatastrophism. ) Publications of the Astronomical Observatory of Belgrade,86:193-19〕 It is proposed as an explanation of Fermi's paradox since it provides a mechanism which would have delayed the otherwise expected advent of intelligent beings in the local galaxy nearby to Earth. This is an avenue to explain why none so far have been detected by humans.
==The problem==
It is estimated that Earth-like planets in the Milky Way started forming 9 billion years ago, and that their median age is 6.4 ± 0.7 Ga.〔Lineweaver C.H. (2001). (An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect. ) Icarus, 151:307-313 .〕 Moreover, 75% of stars in the galactic habitable zone are older than the Sun.〔Lineweaver CH, Fenner Y, Gibson BK. (2004). (The galactic habitable zone and the age distribution of complex life in the Milky Way. ) Science. 303(5654):59-62. PMID 14704421〕 This makes the existence of potential planets with evolved intelligent life more likely than not to be older than that of the Earth (4.54 Ga). This creates an observational dilemma since interstellar travel, (even of the "slow" kind that is nearly within the reach of present Earth technology) could in theory, if this had arisen elsewhere, take from only 5 million to 50 million years to colonize the galaxy.〔Crawford, I.A., ("Where are They? Maybe we are alone in the galaxy after all" ), '' Scientific American,'' July 2000, 38-43, (2000)〕 This leads to a conundrum first posed in 1950 by the physicist Enrico Fermi in his namesake paradox: "Why are no aliens or their artifacts physically here?"〔Webb S. (2002). ''If the universe is teeming with aliens, where is everybody? Fifty solutions to the Fermi paradox and the problem of extraterrestrial life''. Copernicus Books (Springer Verlag)〕
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