The Fermi Paradox, named after the Italian physicist Enrico Fermi, refers to an apparent contradiction: the expectation that intelligent life must be commonplace in a galaxy with billions of solar systems and the complete lack of observational evidence. Discussing UFOs and the prospects of alien civilisations in 1950, Fermi reportedly summed up the contradiction with the observation “but where are they?” Or words to that effect.
Researchers at the University of Nottingham may have come up with an explanation. Using the Earth-Sun system as a model for the chemistry, temperature and other conditions that gave rise to intelligent life – humanity – over similar timescales, they calculate there should be about three dozen communicating civilisations across the galaxy.
“There should be at least a few dozen active civilisations in our galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth,” said Nottingham astrophysics professor Christopher Conselice. “The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit.”
Said Tom Westby, first author of a paper in The Astrophysical Journal: “The classic method for estimating the number of intelligent civilisations relies on making guesses of values relating to life, whereby opinions about such matters vary quite substantially. Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilisations in our galaxy.”
Considering stars with metal content similar to the Sun’s and a roughly 5-billion-year timescale similar to the time needed by humanity to reach its current level of technology, the researchers conclude there should be about 36 “active civilisations” across the Milky Way.
As for Fermi’s famous question, the researchers say the average distance between those civilisations would be about 17,000 light years, making detection and communication extraordinarily difficult using current technology.
And, of course, it’s also possible that humanity is alone.
“Our new research suggests that searches for extraterrestrial intelligent civilisations not only reveals the existence of how life forms, but also gives us clues for how long our own civilisation will last,” says Conselice.
“If we find that intelligent life is common then this would reveal that our civilisation could exist for much longer than a few hundred years. Alternatively, if we find that there are no active civilisations in our galaxy it is a bad sign for our own long-term existence. By searching for extraterrestrial intelligent life — even if we find nothing — we are discovering our own future and fate.”