The alien? Once there were, now they are all extinct!
Aliens do not contact us simply because they are extinct. This is the original hypothesis formulated by astrobiologists at the Australian National University to explain the difficulty of finding signs of life in the universe despite its teeming with potentially habitable planets.
In 1950, while working in the Los Alamos laboratories, Enrico Fermi took part in a conversation with some colleagues, including Edward Teller, during lunch in the laboratory canteen. The conversation was about a recent UFO sighting reported in the press, about which a satirical cartoon made fun.
The conversation continued on various related topics, until suddenly, during lunch, Fermi exclaimed “Where is everybody? ”.
Yeah, where is everyone? If aliens exist, why haven't they contacted us yet?
To the numerous hypotheses formulated to answer this question, we add that formulated by astrobiologists at the Australian National University in Canberra.
According to the theory, presented in the journal Astrobiology (https://doi.org/10.1089/ast.2015.1387), the lack of signals from ET is not due to the low probability of life forming on planets. The most primitive life forms, once they appear, are very fragile: "this is why we think that they rarely manage to evolve quickly enough to survive rapidly changing environmental conditions", explains Aditya Chopra.
"To make a young planet habitable, life forms must be able to regulate greenhouse gases, such as carbon dioxide, in order to maintain stable surface temperatures," continues the researcher. This is what happened on Earth and probably failed on other planets. Just think, for example, of Mars and Venus: 4 billion years ago they too could have conditions favorable to the birth of life. After 1 billion years, however, the climate on Venus became too hot and that of Mars too cold to guarantee the survival of any life forms that appeared in the meantime, which could therefore have become extinct.
In light of this hypothesis, the universe could be seen as a cosmic 'cemetery'. For Charley Lineweaver, of the Institute of Planetary Sciences of the Australian university, "most of the fossils present in the universe could belong to forms of now extinct microbial life, not to more complex and multicellular life forms, such as dinosaurs or our hominid ancestors."
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