There’s a 0.0014% chance humans could invade another planet once we achieve interstellar travel.
A study suggests that the Milky Way may harbor around four potentially hostile alien civilizations capable of invading Earth if given the chance. This intriguing estimate comes from research conducted by Alberto Caballero, a doctoral student in conflict resolution at the University of Vigo in Spain, and is based on an extrapolation of human history. His findings, posted on the arXiv preprint database, propose that the odds of encountering hostile extraterrestrial beings might be higher than previously thought, though still very low.
Estimating the Odds of Alien Invasion
To predict the likelihood of meeting a hostile alien civilization, Caballero first examined human history, specifically focusing on invasions between 1915 and 2022. He found that 51 of the world’s 195 countries had launched invasions during this period, with the U.S. accounting for the most, having initiated 14. He then calculated the probability of invasion based on each country’s military spending, with the U.S. once again at the top, representing 38% of global military expenditure. By combining these factors, Caballero estimated a “human probability” of invading another inhabited planet to be 0.028%.
However, this percentage is based on the current state of human civilization, and Caballero notes that humans are still far from achieving interstellar travel. Using the Kardashev scale, which ranks civilizations based on their energy use, Caballero estimated that humans won’t become an interstellar (Type 1) civilization for another 259 years. By then, he predicts the probability of humans invading another planet would drop to 0.0014%, as humanity’s tendency toward conflict continues to decline.
What About Alien Civilizations?
Building on a 2012 study from the journal Mathematical SETI, which estimated there could be as many as 15,785 alien civilizations in the Milky Way, Caballero applied his probability model to predict how many of those civilizations could be hostile. He concluded that 0.22 of these Type 1 civilizations would likely be hostile toward humans, meaning the probability of encountering a dangerous alien civilization capable of interstellar travel is quite slim. When factoring in alien civilizations that, like modern humans, are not yet capable of interstellar travel, the number of potentially hostile neighbors rises to 4.42.
While this number might seem alarming, Caballero points out that even if these civilizations existed, they likely wouldn’t pose a significant threat to Earth because they, like us, lack the technology for interstellar invasion.
Small Risk, Big Implications
According to Caballero’s paper, the likelihood of humans contacting a hostile alien civilization is extremely small — much lower than the odds of a planet-killing asteroid hitting Earth. He estimates the probability of an extraterrestrial invasion is two orders of magnitude lower than the 1-in-100-million-year chance of a planet-destroying asteroid.
Despite the fascinating nature of this study, Caballero acknowledges its limitations. His model is based on a narrow slice of human history and assumes alien species will have similar values and brain structures to humans, which may not be the case. As Caballero admits, “We don’t know the mind of extraterrestrials.” While these calculations are speculative, the study offers an interesting thought experiment and highlights the long journey ahead in understanding alien civilizations.
Though it will likely be centuries before humanity encounters extraterrestrial life, studies like this spark valuable discussions on how we might interact with life beyond Earth.
