But Earth is 100 times more likely to be destroyed by an asteroid than invaded by aliens.
According to new research submitted to the preprint database arXiv, the Milky Way has millions of potentially habitable planets, with around four of them harboring evil alien civilizations that would conquer Earth if they could.
The new paper, which has yet to be peer-reviewed, presents an unusual question: What are the odds that humanity may one day contact a hostile alien civilization capable of invading our planet?
To answer this, the study’s sole author, Alberto Caballero, a doctoral student in conflict resolution at Spain’s University of Vigo, began by looking back at human history before looking out to the stars.
“This paper attempts to provide an estimation of the prevalence of hostile extraterrestrial civilizations through an extrapolation of the probability that we, as the human civilization, would attack or invade an inhabited exoplanet,” Caballero wrote in the study.
(Caballero is not an astrophysicist, but he has published a study on the infamous Wow! signal — a potential sign of extraterrestrial life — in the peer-reviewed International Journal of Astrobiology.)
To reach his estimation, Caballero first counted the number of countries that invaded other countries between 1915 and 2022. He discovered that 51 of the world’s 195 nations launched some type of invasion during that time span. (At the time, the United States led the list with 14 invasions.) Then he weighted each country’s probability of launching an invasion based on its share of global military spending. (Again, the U.S. came out on top with 38% of global military spending.)
Caballero then summed up each country’s individual probability of instigating an invasion and divided the total number of countries on Earth to arrive at what he calls “the current human probability of invasion of an extraterrestrial civilization.”
The current probability of humanity invading another inhabited planet are 0.028 percent, according to this model. However, that possibility, according to Caballero, applies to the current stage of human civilization – and humans are not now capable of interstellar travel. Caballero predicted, using the Kardashev scale — a system that categorizes how evolved a civilisation is based on its energy expenditure — that if current rates of technological advancement continue, interplanetary travel would be impossible for another 259 years.
Assuming that the frequency of human invasions continues to decline at the same rate as it has over the last 50 years (an average of minus 1.15 percent per year, according to Caballero’s paper), the human race has a 0.0014 percent chance of invading another planet when we potentially become an interstellar, or Type 1, civilization 259 years from now.
That may appear to be a small chance — and it is — until you multiply it by the millions of possibly habitable planets in the Milky Way. For his final calculation, Caballero turned to a 2012 paper published in the journal Mathematical SETI, in which researchers predicted that as many as 15,785 alien civilizations could theoretically share the galaxy with humans.
Caballero estimated that only 0.22 of the Type 1 civilizations would be hostile to humans who made contact with them. However, when civilizations that, like modern humans, are not yet capable of interstellar travel are included, the number of malicious neighbors rises to 4.42, according to Caballero.
“I don’t mention the 4.42 civilizations in my paper because 1) we don’t know whether all the civilizations in the galaxy are like us… and 2) a civilization like us would probably not pose a threat to another one since we don’t have the technology to travel to their planet,” Caballero told Vice News.
Four hostile alien powers doesn’t seem like much to be concerned about. Furthermore, the probability of humans contacting one of these malicious civilizations and being invaded by them is vanishingly unlikely, according to Caballero.
“The probability of extraterrestrial invasion by a civilization whose planet we message is… around two orders of magnitude lower than the probability of a planet-killer asteroid collision,” he wrote in his paper — adding that planet-killing asteroids, like the one that doomed the dinosaurs, are 1-in-100-million-year events.
Caballero’s study is an intriguing thought experiment, although the author admits that his model has limits. The invasion likelihood is based on a very short slice of human history, and it makes numerous assumptions about our species’ future progress. The model also assumes that alien intelligence will have human-like brain compositions, values, and empathy, which may or may not be the case, according to Caballero.
“I did the paper based only on life as we know it,” he said. “We don’t know the mind of extraterrestrials.”
And it appears that it will be at least a few hundred years before we do.v