Under what conditions is the existence of aliens possible

American astronomers have calculated different scenarios for the emergence of extraterrestrial civilizations and concluded that they should be extremely rare, but at the same time able to establish contact with a person from anywhere in the Galaxy, says an article published in the electronic library arXiv.org

“In May 1961, President Kennedy announced that the US would send people to the moon and bring them back in the next 10 years, a dream that was fulfilled in July 1969, filling one of the important pages in the history of space exploration. That nothing like that happened in other corners of the universe and that’s why we have been thinking for a very long time about what Enrico Fermi was saying – where all these aliens were gone? “- write Jorge Soriano and his colleagues from the City University of New York, (USA).

More than half a century ago, the American astronomer Frank Drake developed a formula for calculating the number of civilizations in the galaxy with which contact is possible, trying to assess the chances of finding extraterrestrial intelligence and life.
The physicist Enrico Fermi, in response to a sufficiently high estimate of the chances of interplanetary contact by Drake’s formula, formulated the thesis, which is now known as the Fermi paradox: if there are so many alien extraterrestrials, why does humanity not observe any of their tracks? This paradox scientists have tried to solve in many ways, the most popular of which is the hypothesis of the “unique Earth”.

It says that for the emergence of intelligent beings, unique conditions are necessary, in fact, a complete copy of our planet. Other astronomers believe that we can not communicate with aliens because the galactic civilizations either disappear too quickly for us to notice them, or because they actively hide the fact of their existence from humanity.
Soriano and his colleagues decided to find out why we have not yet come across brothers in the mind, having calculated various versions of their evolution and time of existence.

In these calculations, scientists relied on two simple things – not all inhabited planets can become a haven for intelligent life, and the average time of their existence can vary greatly, depending on the frequency of gamma-bursts, supernova explosions and other galactic cataclysms, capable of destroying life on A single planet.
Guided by these ideas, scientists have tried to reconcile the Fermi paradox and Drake’s formula, having calculated such scenarios of extraterrestrial existence that would correspond to that and other idea. For this, the scientists added two new parameters to the Drake formula – the proportion of “intelligent” civilizations that have interstellar communication facilities and the time of their existence.

As these calculations show, reasonable, but invisible alien civilizations really could or may exist in our Galaxy, but their share among the total number of intelligent aliens will be extremely small – about 0.5%. This significantly complicates their search and explains why we do not observe them today.

At the same time, the existence of these civilizations can be quite large – about 300 thousand years – and therefore they could in principle be able to establish contact with humanity from anywhere in the galaxy if they knew about its existence. The search for their tracks, as Soriano and his colleagues believe, will be possible only in the future, when a greater number of Earth “twins” and full analogues of our planet will be discovered by the heirs of NASA’s modern space telescopes.