There are over a billion stars in our own galaxy, the Milky Way, and most of the people on the Earth believe that there is some form of intelligent civilisation existing on other planets.
Obtaining good estimates of the number of possible extraterrestrial civilisations has, however, been very challenging. Are we the only living life form in the galaxy?
A new study by University of Nottingham, published in The Astrophysical Journal, has taken a new approach to this problem. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilisations within the Milky Way. They calculate that there could be over 30 active communicating intelligent civilisations in our home galaxy.
Professor of Astrophysics at the University of Nottingham Christopher Conselice, who led the research, explains, "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." Conselice also explains that, "The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit."
First author Tom Westby explains, "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.”
“The two Astrobiological Copernican Limits are that intelligent life forms in less than 5 billion years, or after about 5 billion years—similar to on Earth where a communicating civilisation formed after 4.5 billion years. In the strong criteria, whereby a metal content equal to that of the Sun is needed (the Sun is, relatively speaking, quite metal rich), we calculate that there should be around 36 active civilisations in our galaxy."
The research shows that the number of civilisations depends strongly on how long they are actively sending out signals of their existence into space, such as radio transmissions from satellites and television. If other technological civilisations last as long as ours, which is currently 100 years old, then there will be about 36 ongoing intelligent technical civilisations throughout our galaxy.
However, the average distance to these civilisations would be 17,000 light-years away, making detection and communication very difficult with our present technology. It is also possible that we are the only civilisation within our galaxy unless the survival times of civilisations like our own are long.
"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. 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,” said Professor Conselice.
“By searching for extraterrestrial intelligent life—even if we find nothing—we are discovering our own future and fate."