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New Study: Our Galaxy Could Contain 36 Intelligent Extraterrestrial Civilizations

The Milky Way is seen over a “nuraghe” (tower-fortresses) on the island of Sardina, Italy, July 7, 2018. (Stefano Rellandini/Reuters)

In the spirit of considering unexpected things that could happen in 2020, I bring more out-of-the-box science news. According to a new study in the Astrophysical Journal, the Milky Way Galaxy (i.e., ours) could contain around 36 intelligent extraterrestrial civilizations (in addition to — or perhaps not including — our own).

That is actually the low-end number, in a sense. The study presents different estimates based on different criteria; more-rigorous conditions for the emergence of life mean fewer likely intelligent civilizations. As a press release announcing it elaborates:

First author Tom Westby explains: “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. 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 Sun is relatively speaking quite metal rich), we calculate that there should be around 36 active civilizations in our Galaxy.”

The research shows 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.

When exploring the corresponding “weak criteria” — i.e., less strict conditions for the emergence of life on other planets — the study increases that estimate to more than 900.

This study also reckons with two of the most famous concepts one encounters in assessing the possibility of extraterrestrial life, both named after famous scientists: the Drake equation (of Frank Drake) and the Fermi paradox (of Enrico Fermi). The Drake equation is an early attempt to calculate how many existing, intelligent civilizations could exist in the Milk Way. But, as the Astrophysical Journal study’s authors note, “many of its terms are unknowable and other methods must be used to calculate the likely number of communicating civilizations.” They use new data and new methods to try to fill in the gaps. 

The study’s authors have less time for the Fermi paradox, which they fairly define in this way: “the supposedly surprising failure to detect evidence of extraterrestrial intelligence after decades of searching.” They resolve the paradox simply by noting how little of space we have actually explored. 

It’s interesting, then, that this study dovetails somewhat with another possible solution for the Fermi paradox: that civilizations advanced enough to communicate through space (which our present civilization has only been for about a hundred years) quickly develop the capacity to destroy themselves (and do). As the authors put it: “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.” 

Well, let’s hope not. But even if it’s not universal, self-destruction is not the only reason we haven’t encountered our galactic neighbors yet. There’s also the fact of the vastness of space, and the limitations (without an ansible) of communication. The study goes into detail about how close another civilization could feasibly be to us, and, from there, how long we both would have to coexist for mutual communication to be possible. Indeed, in the study’s “most optimistic case,” another such civilization would be

approximately 1030 [light years] away, therefore the time required for two-way communication rises to around 2060 [years]. Indeed, if the average lifetime of civilizations is in fact less than 1030 [years], then their average separation becomes too great to allow any communication between neighbors before the species becomes extinct . . .

In other words: Intelligent life may be out there, but both of us may fail to last long enough to exchange so much as a “hello.” Which is a shame, because there’s bugger all down here on earth.

For what it’s worth, the study does not consider the possibility of imminent (or ongoing!) extraterrestrial visitation, a potential failure of imagination given the course of 2020 so far.


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