For hundreds of millions of years, Earth has been home to an incredible variety of life, including human beings, who are the only known species to have developed truly advanced technology. If that’s the case, then the rest of the galaxy has no right to exist. How many alien advanced civilizations might we expect to find in the Milky Way?
According to research presented in The Astrophysical Journal, the approximate answer to the second question is 36. No need to swear allegiance to any alien overlords just yet; this is only a statistical estimate, not a declaration that we have discovered three dozen civilizations in the galaxy.
The study’s findings are hypothetical, but it does use novel measurements and methodologies to estimate the number of alien societies in the Milky Way that are capable of interstellar messaging (a class of civilizations known as CETI).
Authors Tom Westby and Christopher Conselice, both astronomers from the University of Nottingham, state that “one of the oldest questions that humans have asked is whether our existence—as an advanced intelligent species—is unique” in the paper.
Since there is no way to model the distribution of the potential population of civilizations across the Galaxy, the team remarked, “Of course—from a statistical perspective—this is one of the most challenging problems in science, since all we can do is attempt to learn from a single known data point (ourselves).”
Scientists before Westby and Conselice have attempted to answer this difficult topic by putting limits on the number of CETI worlds in the Milky Way. The famous astronomer Frank Drake, who developed the Drake equation in 1961, is considered the progenitor of this practice. Considerable variables, like the galaxy’s star formation rate and the expected longevity of a technologically evolved civilization, are accounted for in Drake’s probabilistic thought experiment, which explains the conditions that might influence the galactic population of intelligent aliens.
According to the study, Westby and Conselice propose an updated version of the Drake equation that incorporates recent research from “various branches of modern astronomy.” For instance, over the past two decades, thousands of exoplanets have been discovered in alien star systems; Westby and Conselice included statistics on the likelihood that these planets orbit their stars in the habitable zone, where liquid water can exist. The origin of complex life on Earth, which took around 4.5 billion years, was another area of study for the group.
The number of CETI populations in the Milky Way that can be predicted by the pair’s findings ranges from four at the low end to 211 at the high end, with 36 being the most likely figure.
Even if their estimate is true, Westby and Conselice warn, CETI worlds may be too far away from Earth for contact, so this large number may not be good news for alien enthusiasts. If there are 36 civilizations in the galaxy that could communicate with us, on average they would be 17,000 light years from Earth, making a discussion between us impossible for at least 34,000 years.
It’s possible that some of these hypothetical cultures will happen on Earth at a distance that makes interplanetary communication easier. If we want to communicate with aliens who are only 1,000 light-years away, we’ll need to make sure our own civilization lasts another two millennia.
According to the calculations of Westby and Conselice, if the average lifespan of civilizations is less than 1,030 years, then the average distance between them becomes too wide to allow any communication between neighbors before the species falls extinct.
“The lifetime of civilizations in our Galaxy is a big unknown within this and is by far the most important factor in the CETI equation we develop, as it was for the Drake equation,” they said.
In other words, if we humans are serious about making contact with aliens in the future, we need to be just as committed to protecting Earth’s habitability for future generations as we are to discovering new human settlements elsewhere in the Milky Way.
