Using the assumption that intelligent life develops on exoplanets in a similar way as it does on Earth, a duo of researchers from the School of Physics and Astronomy at the University of Nottingham has obtained an estimate for the number of communicating extraterrestrial intelligent (CETI) civilizations within our Milky Way Galaxy. They calculate that there could be 36 active CETI civilizations in the Galaxy; the nearest is 17,000 light-years away and most likely hosted by a red dwarf star, likely far surpassing our ability to detect it for the foreseeable future, and making interstellar communication impossible.
“There should be at least a few dozen active CETI civilizations in our Galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth,” said Professor Christopher Conselice, senior author of the study.
“The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit.”
“The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life, whereby opinions about such matters vary quite substantially,” added Dr. Tom Westby, first author of the study.
“Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations 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 civilization formed after 4.5 billion years.
In the strong criteria, whereby a metal content equal to that of the Sun is needed, the authors calculate that there should be around 36 active CETI civilizations in the Milky Way.
They show that the number of civilizations depends strongly on how long they are actively sending out signals of their existence into space, such as radio transmissions from satellites, television, etc.
If other technological civilizations last as long as ours which is currently 100 years old, then there will be about 36 ongoing intelligent technical civilizations throughout our Galaxy.
However, the average distance to these civilizations 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 civilization within our Galaxy unless the survival times of civilizations like our own are long.
“Our new research suggests that searches for extraterrestrial intelligent civilizations not only reveal the existence of how life forms, but also give us clues for how long our own civilization will last,” Professor Conselice said.
“If we find that intelligent life is common then this would reveal that our civilization could exist for much longer than a few hundred years, alternatively if we find that there are no active civilizations 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.”
The team’s paper was published in the Astrophysical Journal.