The physicist Enrico Fermi He asked himself the same as many inhabitants of the earth: "Where is everyone?"However, there are many specialists who answer this question with the help of science.
>We are too far away. According to this explanation, our extraterrestrial life does not reach us by a matter of distance. The nearest star to Earth is four light years away (it would take 40,000 years to travel there with spaceships that look like today and man only exists for 10,000).
>The aliens do not live on the surface. Thanks to the probes that revealed that the underground oceans of cold and inhospitable worlds are a potential home for life forms, this theory took strength. The "aliens" can live wherever there is underground water (safe for radiation, toxic atmospheres and supernova explosions too close).
>Excess baggage. Perhaps it is not so easy to make a journey through space: what would happen if a civilization were to live in a super-earth, with a crushing gravity, at least ten times higher than ours? There is research that confirms that differences in gravity in space can seriously affect the possibility of contact with extraterrestrials.
>The aliens are machines. Artificial intelligence is developing on earth. Shostak, futurist and director of the Intelligent Life Search Institute (SETI) is of the opinion that, in other civilizations, this progress has caused biological beings to cease to exist. In this case we must not only search for habitable worlds, but also attractive places for machines (full of energy).
>They have destroyed themselves. We do not have a hopeful future on our planet: pollution, damage to the environment and climate change seem to lead to destruction. There are people who believe that this happened to the extraterrestrials. Astrophysicist Adam Frank designed a mathematical model to try to answer this question. Taking into account available and known energy sources, four scenarios of social evolution simulated. Three of the four led to a collapse and most of the population disappeared.
>The universe is too unstable. Asteroids, dying stars, supernova's, volcanic eruptions and other phenomena can cause the destruction of humanity.
>We are extraterrestrials. There are theories that people are intelligent beings from space. This is panspermie, according to which certain microbes traveled through asteroids from other worlds.
>Life is stranger than we think. We could be the only ones if the earth were the only one with its conditions that enable the development of intelligent life. In the development of civilization, the sun has been influenced in the habitability zone of the Milky Way, safe from the galactic core. Moreover, the presence of a planet as gigantic as Jupiter is the key, which by its gravity keeps us from the impact of waste and asteroids, for example.
>What if we are unable to listen to them? Most intelligent life search systems follow stars that look like the sun. But they may not be what we are looking for or they send out imperceptible signals to us, perhaps with the help of frequencies or codes that would make us go unnoticed.
>They are not very communicative. Maybe they do not share mathematics, or their mathematical language (not to mention the literal) is incompatible with ours. Maybe their physiology or their way of thinking prevents them from communicating with us. There are theories in which there is the possibility that the aliens observe us without intervening, because they do not want to do more than study us.