Our galaxy can be home to about four potentially hostile civilizations, says researcher Alberto Caballero.
Not one, but as many as four extraterrestrial civilizations with the will and technological ability to invade Earth could be lurking in the Milky Way, the galaxy in which we live. That is the conclusion reached by the Spanish researcher Alberto Caballero, from the University of Vigo, in a study that has just appeared on the ‘arXiv’ preprint server.
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Among the papers that, in the absence of real contacts, try to deduce the probable number of alien intelligences ‘out there’, Caballero’s study approaches the question from a totally different perspective: What is the probability that, one day, humans can contact a hostile civilization capable of invading Earth? And to answer the question, Caballero decided to take a look at human history.
“This paper -writes the author- attempts to provide an estimate of the prevalence of hostile extraterrestrial civilizations through an extrapolation of the probability that we, as a human civilization, would attack or invade an inhabited exoplanet.”
Looking for clues in human history
To make his estimate, the researcher, who also recently published another study on the famous Wow! in ‘International Journal of Astrobiology’, he first counted the number of countries that, from 1915 to 2022, invaded other neighboring countries. And he discovered that, in that time, 51 of the 195 nations of the world had carried out or attempted an invasion, the first of all the United States, which during that period carried out no more and no less than 14 invasions. He then weighted each country’s probability of launching an invasion based on that country’s percentage of global military spending (again, the US ranked first with 38% of global military spending).
From there, Caballero added up each country’s individual probability of instigating an invasion, then divided the sum by the total number of countries on Earth, ending up with what he describes as “the current probability of humans invading an alien civilization.”
According to the model, the current probability of humans invading another inhabited planet is 0.028%. However, writes Caballero, that probability refers to the current state of human civilization, and humans are currently not capable of interstellar travel. If current rates of technological advance continue, interstellar travel could be possible within 259 years, Caballero calculated using the Kardashev scale, a system that rates how advanced a civilization is based on its energy expenditure.
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Slim odds
But the frequency of human invasions has greatly decreased over the last 100 years and assuming it continues that way, by the time we reach the stars 259 years from now our probability of invading another inhabited planet will have dropped to 0.0014%. It seems little, but if we multiply it by the millions of potentially habitable planets in the Milky Way we will see that the figure increases.
For his final calculation, Caballero turned to a study published a few years ago in the journal ‘Mathematical SETI’, according to which there should be 15,785 extraterrestrial civilizations in the Milky Way. If we take that number for granted and extrapolate human behavior from the last century, it turns out, according to Caballero, that at least one of those Type 1 civilizations would be hostile to humans who make contact. But if we also take into account the ‘evil’ civilizations that have not yet developed interstellar travel, as is the case with ours, then the number will grow to 4.22 possible hostile civilizations.
In short, it seems that we have little reason to worry. In fact, apart from being very few, the chances that we will come into contact with some of these ‘dangerous’ civilizations is extremely small. According to the researcher, about two orders of magnitude lower than the probability of a collision with a planet-destroying asteroid like the one that wiped out the dinosaurs, something that happens only once every 100 million years.
About Caballero
Alberto Caballero is a Spanish astronomer and science communicator. Born in Edinburgh in 1991, he spent part of his childhood in the capital of Scotland until his family moved to the Spanish city of Vigo, on the north-Atlantic west coast of the country. Caballero studied Criminology at the University of Santiago de Compostela, in Spain. However, he already became interested in astronomy at a young age, and in 2017 he created The Exoplanets Channel, a YouTube channel that he uses for scientific communication and to present his research to the general public.
Two years later, in 2019, he started coordinating more than 30 astronomical observatories worldwide under the Habitable Exoplanet Hunting Project. Lately, Caballero has been trying to draw profits obtained from day trading – one of his hobbies – to fund the search for extraterrestrial intelligence, a branch of science that does not receive any public financial support.
