In the mid-1950s, physicist Enrico Fermi posed a question to his colleagues: "Where are they?" Everyone understood that he was referring to other extraterrestrial civilizations. Your question continues unanswered today.
The paradox of Fermi is the contradiction between the high probability of not being alone in the Universe, and the absence of any trace of extraterrestrial life.
Earth does not seem to have anything special for life to have evolved in it. It is a normal planet of a normal solar system, in a normal galaxy. In the universe there are millions of planets with the same characteristics as Earth. Life must have evolved in many other places.
At some time and place, civilizations had to exist much more advanced than ours. The universe is almost 14 billion years old. It is enough time for the first-star settlers to develop the technology needed to explore and colonize the galaxy. One only has to think about what we have achieved in less than 200,000 years, since our species was born.
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Source: astronomy.com
Credits: Kurzgesagt – In a Nutshell