The Milky Way is home to millions of potentially habitable planets, and around four of these could harbor extraterrestrial civilizations that might invade Earth if given the chance, a new study suggests.
The author of this research, Alberto Caballero, a PhD candidate in conflict resolution at the University of Vigo in Spain, began by reflecting on human history before looking to the stars.
“This paper attempts to provide an estimate of the prevalence of hostile extraterrestrial civilizations through a probabilistic extrapolation of whether we, as a human civilization, would attack or invade a habitable extraterrestrial planet.” Caballero wrote in the study.
Description of an alien spacecraft contacting our planet.
Although Caballero is not an astrophysicist, he has published research on the Wow signal—an apparent indicator of extraterrestrial life—in the International Journal of Astrobiology.
To achieve his estimates, Caballero first cataloged the number of countries that invaded others between 1915 and 2022. He found that a total of 51 out of the 195 countries in the world had engaged in some form of invasion during that period. The United States topped the list, with 14 invasions counted at that time.
From this, Caballero added the individual probability of each country instigating an invasion, then divided the total by the number of countries on Earth, arriving at what he describes as the current probability of humanity invading an extraterrestrial civilization.
According to this model, the current rate of humanity invading another habitable planet is 0.028%. However, Caballero noted that this probability pertains to the current state of human civilization—and humans currently lack the capability for interstellar travel.
If the current rate of technological progress continues, interstellar travel will not be achievable for another 259 years, Caballero stated.
Assuming the frequency of human invasions continues to decline during that time, at the same rate as invasions have decreased over the past 50 years, then humanity has a 0.0014% chance of invading another planet when we might achieve interstellar civilization in approximately 259 years from now.
Caballero concluded that the number of potential hostile neighbors increases to 4.42 when considering civilizations similar to modern humans that currently lack the ability for interstellar travel.
The four extraterrestrial planets are not particularly concerning, as the likelihood of humans encountering one of these hostile civilizations—and subsequently being invaded by them—is very low.
He further explained that cataclysmic asteroid impacts, like the one that caused the extinction of the dinosaurs, are events that occur once every 100 million years.
