The question of whether humans are alone in the universe or not fueled our ideas, including the  world's best minds. The lack of extraterrestrial evidence, and yet a high probability that it exists, has still astounded experts. But maybe aliens have already found us and are intentionally hiding, say extraterrestrial observers.
Messaging Extraterrestrial Intelligence (METI) researchers have suggested that aliens could hold people in a "galactic zoo" without being open-minded. Avoid triggering Pandemonium on Earth.
Scientists of all disciplines gathered in a Paris science museum to explore a 1950s puzzle known as the Fermi paradox.
Although it's a worrying thought, more and more scientists believe that it's been an alien all the time here and humanity has not recognized it.
Jean-Pierre Rospars, Honorary Research Director of the National Institute of Agricultural Research, said: "It is likely that extraterrestrials will impose a galactic quarantine because they recognize it. It would be culturally disturbing if we learned something about it.
"Cognitive development on Earth shows random features, while also following o predictable paths.
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"We can expect the repeated, independent occurrence of intelligent species in the universe, and we should expect to see more or less similar forms of intelligence everywhere under favorable conditions.
"There is no reason to believe that man has reached the highest possible cognitive level.
"Higher levels could evolve on Earth in the future and be reached elsewhere.
And the scientists say humanity must be more direct to make contact.
Dr Douglas Vakoch, President of METI, draws the analogy of a zoo animal that suddenly ejects primes with its hoof.
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Such an unexpected and extreme action would certainly trigger an observer response.
Dr. Vakoch said, "Aliens may observe humans on Earth in much the same way we observe animals in the zoo.
" How can we make the galactic zookeepers show themselves? "
And this request could be radio signal transmissions to nearby stars
This has been attempted on numerous occasions in recent decades, when scientists for the first time made a deliberate message into space using the Arecibo Radio Telescope in Puerto Rico.
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What is the Fermi paradox?
The Italian physicist Enrico Fermi asked in 1
The Fermi paradox addresses a contradiction in astronomy. summarized as: If extraterrestrial life and even intelligent extraterrestrial civilizations are not only likely but most likely, then why has none of us contacted?
Are there biological or sociological explanations for this "Great Silence"