June 15 (UPI) -- In a newly published paper, scientists have offered a narrower estimate range for the number of possible extraterrestrial civilizations lurking within our home galaxy.
Using the assumption that life evolves on alien planets similar to how it emerged on Earth, researchers determined there should be roughly 30 active communicating intelligent civilizations inside the Milky Way, according to a study published Monday in the Astrophysical Journal.
"There should be at least a few dozen active civilizations in our Galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth," lead researcher Christopher Conselice, professor of astrophysics at the University of Nottingham, said in a news release. "The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit."
To make a more precise estimate about the number of alien civilizations in the Milky Way, researchers relied on both a weak and hard limit. The weak limit is the time it takes for the evolution of intelligent civilizations, less than or approximately 5 billion years. Humans capable of long-distance communication emerged roughly 4.5 billion years after life began.
The hard limit is the metal content in sun-like stars. For a solar system to host intelligent life, scientists estimate the star must feature metal content equal to that of the sun.
"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," said first author Tom Westby, a Nottingham astrophysicist. "Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations in our galaxy."
As scientists acknowledged in their paper, there are other challenges -- besides the Astrobiological Copernican Limits -- facing intelligent civilizations and our ability to communicate with them.
In order for humans on Earth to make contact with an alien civilization, the faraway civilization must enjoy staying power. Humans have been capable of long-distance communication for roughly 100 years. If civilizations appear but don't last as long as humans -- if they blink in and out of existence -- we may never connect with them.
In order to communicate with one of the galaxy's intelligent civilizations, both humans and aliens need advanced communications technologies. According to the latest analysis, the average alien civilization would be 17,000 light-years away, complicating the sending and receiving of communication signals.
"Our new research suggests that searches for extraterrestrial intelligent civilizations not only reveals the existence of how life forms, but also gives us clues for how long our own civilization will last," 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," he said. "By searching for extraterrestrial intelligent life -- even if we find nothing -- we are discovering our own future and fate."