There may be more than 30 intelligent alien civilizations living on planets across the Milky Way, a study has found. By simplifying assumptions about the requirements of life, researchers were able to give a “solid estimate” for how many other intelligent extraterrestrials exist within our host galaxy.
In a study published in The Astrophysical Journal, researchers led by Christopher Conselice, from the U.K.’s University of Nottingham, examined limits for intelligent life. This included the age of the planet and the composition of their host star. Assumptions were made on what we understand about intelligent life on Earth—that it took about five billion years to get us to the point we are at now and that the environment is rich in metals.
“The idea is looking at evolution, but on a cosmic scale,” he said in a statement. “We call this calculation the Astrobiological Copernican Limit.” Their calculations showed there should be 36 planets in the Milky Way with intelligent civilizations.
This, they say, is the lower limit that is based on the average lifetime of a civilization being around 100 years. This assumption was made based on humans having only mastered radio communication around a century ago.
They say these 36 hypothetical civilizations are spread evenly across the galaxy, the closest would be around 17,000 light years away. One light year is around 5.88 trillion miles. Radio waves travel at the speed of light, so any radio communication sent from Earth would take 17,000 years to reach that civilization, ” making interstellar communication impossible,” the team wrote.
“Furthermore, the likelihood that the host stars for this life are solar type stars is extremely small and most would have to be M-dwarfs, which may not be stable enough to host life long timescales,” they said.
Findings showed that even in the “most optimistic case” the closest intelligent civilization would be approximately 1,030 light years away. This is still too far for “two-way communication,” which would take 2,060 years.
“Indeed, if the average lifetime of civilizations is in fact less than 1,030 years, then their average separation becomes too great to allow any communication between neighbors before the species becomes extinct,” they said.
While communicating with intelligent civilizations across the galaxy may not be feasible, the researchers say we could learn from their existence. By understanding how long other lifeforms may have lasted, it could provide clues about the fate of our own species.
The researchers say that while extinction events are difficult to predict, they do occur on Earth on a fairly regular basis. In terms of intelligent life, they say it is more likely that “a civilization’s self-destruction is more likely to occur than a natural extinction.”
“Perhaps the key aspect of intelligent life, at least as we know it, is the ability to self-destroy,” the team said. “As far as we can tell, when a civilization develops the technology to communicate over large distances it also has the technology to destroy itself and this is unfortunately likely universal. On Earth, two immediately obvious possibilities are destruction by weapons and through climate change creating an uninhabitable environment.”
Conselice said that if we are to find intelligent life is common in the galaxy, then it would help to show that mankind could sustain itself for far 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.”
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