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It was the year 1950. In Los Alamos, New Mexico, the best cafeteria conversation of all time took place. The physicist Enrico Fermi, eating with his colleagues Emil Konopinski, Edward Teller and Herbert York, asked: “Where is everyone?” The Fermi paradox was born. What does Fermi’s paradox say If our galaxy, the Milky Way, contains between 100,000 and 400,000 million stars, many of them thousands of years older than the Sun. Yes, by extension, we are surrounded by a huge number of exoplanets. Yes, as we know today, The rocky planets are common in the habitable zone of other solar systems. Why have we not found any evidence of extraterrestrial life? That is the essence of one of the most disturbing problems of modern science: Fermi’s paradox. From the abundance of worlds, intelligence and technology should have emerged capable of colonizing the galaxy or at least sending detectable signals. A flagrant contradiction between the high probability that there is intelligent life in other places and the absolute lack of evidence: a cosmic silence that persists in our telescopes and explorations. Until today we have not seen a convincing proof of visits, or artificial signals from other civilizations. The Milky Way is old: it is 13,000 million years old. A species capable of making interstellar “slow” trips would suffice to colonize it in less than 100. But we still do not see its mega -structures. And what is worse, we still do not detect its radio transmissions. Or they are extraordinarily rare civilizations, or do not exist. What is the difference with Drake’s equation Fermi’s paradox is an empirical observation that was born from an informal conversation. To give it structure and mathematics, astronomer Frank Drake proposed in 1961 the Drake equation: a probabilistic formula that tries to estimate the number of technologically advanced civilizations and with the ability to communicate that there should be in our galaxy. The equation multiplies a series of factors, such as the rate of stars, the number of planets per star and the fraction of planets that could develop life. Statistics are overwhelmingly favorable. Drake’s formula serves to give meaning to the search for extraterrestrial lifefeeding our statistical hope. But while Drake’s equation tells us that there should be someone out there, Fermi’s paradox asks us why we haven’t found anyone. This contradiction is actually the heart of Fermi’s question. It is not a formal theory, but a line of argument that forces us to ask ourselves why the universe seems so empty. And perhaps the best possible tribute to Enrico Fermi, astronomers are still looking for answers to their question 75 years later. Who was Enrico Fermi Known as the “Architect of the Atomic Bomb”, it was an Italo-American physicist who received the Nobel Prize in Physics in 1938 for his works on induced radioactivity. Fermi was a key figure in the Manhattan project, the program that developed the first nuclear bomb during World War II. He directed the construction of the Chicago Pile-1, the world’s first artificial nuclear reactor. His team achieved the first self -sustained nuclear reaction in 1942. Born in 1901, he died of cancer at age 53, shortly after formulating Fermi’s paradox. The question “Where is everyone?” He emerged during a lunch with his colleagues in the National Laboratory of Los Alamos. Despite the informal nature of the conversation, the depth of the question and the authority of those who raised it gave it a weight that has endured 75 years, becoming a pillar of thought about extraterrestrial life. Responses to Fermi’s paradox Image | Jiang et al. (CC By-C-SA 4.0) Throughout these decades, scientists, philosophers and astronomers have proposed innumerable hypotheses to resolve Fermi’s paradox. These responses can be grouped into three great families of hypotheses. Smart life is extremely rare. Maybe the simplest and desolate solution. It suggests that there is a “great filter”, a barrier or a series of barriers extremely difficult to overcome so that living beings appear, evolve or come to expand through the galaxy. It may be the conditions for life to arise, they are so incredibly specific that they only occur once, here on earth. It may be to move from simple microorganisms to complex and multicellular life, it is the true bottleneck. Or intelligence like ours may not be an inevitable consequence of evolution. Or maybe, as the Apocalypse clock From the bulletin of atomic scientists, technological civilizations tend to self -destruct before being able to expand through the galaxy, either by a nuclear war, by climate changes or by pandemics. In any case, Humans do not usually succeed In our apocalyptic predictions. They exist, but we cannot detect them. There are many hypotheses to explain our lack of contact. A recent one NASA funded study I found the simplest. The space is so great and we have been observing it so little, that it is normal for us to continue without clues: “Fermi’s paradox is a very large extrapolation from a very local observation. You could look out the window and conclude that bears do not exist because you don’t see any.” Perhaps its technology is undetectable. They may not need to build mega -structures as Dyson spheres that would be visible to us. They could use energy sources that we don’t even understand. Maybe they have decided to enter hibernation and are asleep. As the summation hypothesis says, it is possible that are waiting for the cosmos to cool Within billions of years to maximize their computational capabilities. And his communications? As the astrophysician Amri Wandel postulates, our radio signs have only traveled about 100 light years. Any response would take the same to return. We might need between 400 and 50,000 years for a first contactassuming that someone who is listening to answer. But first they would have to find our needle in the haystack. They exist, but they deliberately avoid us. The most disturbing hypotheses propose that other more advanced civilizations know our existence, but have decided … Read more