Where is everybody?

During a lunch break in 1950, Italian physicist Enrico Fermi, famous for creating our first nuclear reactor, asked a casual question. Where is everybody? He referred to the aliens who, given that the earth is part of a young planetary system compared with the rest of the universe should already have visited us. The contradiction between the lack of evidence for extraterrestrial civilizations and their high probability became known as the Fermi paradox or the Great Silence. 

Fermi wasn’t the first to ask this question. Already in 1933, Russian rocket scientist Konstantin Tsiolkovsky noted that people deny the presence of intelligent beings on other planets because if they existed, they would have visited earth and would have given us some sign of their existence. A firm believer in the possibility of space travel and extraterrestrial life, he went on to suggest the zoo hypothesis. It speculates that mankind is not yet ready for higher beings to contact us, so they refrain from it to allow for natural evolution. The zoo hypothesis suggests that there’s a legal policy present amongst a collection of advanced extraterrestrial civilizations which necessitates the isolation of civilizations at Earth-like stages of development. Without a hegemonic power, random civilizations would make contact, which makes the possibility of a crowded universe with clearly defined rules more plausible. 

The zoo hypothesis is an appealing answer to the Fermi paradox. Our universe is incredibly vast and old. One estimate says the universe spans 92 billion light-years in diameter and is about 13.82 billion years old. When it took at least 3.5 billion years for intelligent life to evolve on earth, this opens up the possibility for ancient extraterrestrial civilizations on other planets in the universe. Imagine what you could do with a half-a-billion-year head start. If the oldest civilization in the Milky Way, which has 200-400 billion stars, enjoyed a 100-million-year time advantage over the next oldest civilization it could have the power to monitor and control the emergence of every civilization that follows within its sphere of influence. And technology like interstellar travel. It could be that we are the first civilization to evolve towards this stage. However, it seems unlikely.

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