The age-old question, of whether we are alone in the universe, has now got a new answer.
Whilst previous estimates of the number of intelligent civilizations have ranged from zero to billions, a study by researchers at the University of Nottingham, UK, has suggested that, under strong criteria, there could be 36 active lifeforms in our galaxy alone. By revising the famous Drake equation to include new data and fewer unknowns, the team was able to make a “solid attempt” at calculating how many Communicating Extra-Terrestrial Intelligent (CETI) civilizations there may be.
“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,” lead author Tom Westby of the University of Nottingham, said in a statement. “Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations in our galaxy.”
To make these new estimations, Westby and co-author Professor Christopher Conselice, also from the University of Nottingham, utilized knowledge of the only intelligent life-from we know about – us. Using what is known as the Astrobiological Copernican Principle (that Earth is not special), the researchers made the assumption that an Earth-like planet found in the habitable zone of a suitable star will form life in a similar timeframe to Earth (around 5 billion years), and will have been actively sending out signals for as long as we have (around 100 years).
By doing so, they eliminated several of the terms used in the Drake Equation that have proved impossible to establish, such as the fraction of suitable planets on which life actually appears (fl), and the fraction of civilizations that develop a technology that releases detectable signs of their existence into space (fc). Their findings have been published in The Astrophysical Journal.
Since Dr Frank Drake’s formulation of the equation in 1961, our knowledge of star formation and planetary systems has also greatly improved. Armed with new and better data on our galaxy’s star formation history and the characteristics of exoplanets, the team could calculate the number of CETI civilizations in our galaxy according to “weak” criteria (has a stellar system age greater than 5 billion years old, and low stellar metallicity), all the way to “strong” criteria (has a stellar system age between 4.5 and 5.5 billion years old, and high stellar metallicity).
“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 civilizations in our galaxy,” Westby said.
This all sounds extremely promising, but here comes the big “but”. Even if these civilizations were communicating, the average distance to them would be around 17,000 light-years, meaning that it would take SETI at least 3,060 years to detect a signal. At the rate our planet is going, we will probably not live long enough to make such a detection. However, in the slim possibility that we were ever able to find other CETI civilizations, this would spell good news for Earth’s existence.
“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,” Professor Conselice said in a statement. “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.”