There Are 4 ‘Malicious Extraterrestrial Civilizations’ in Milky Way, Researcher Estimates

Back-of-the-napkin math assuming aliens are like humans suggests there are only a few evil alien societies in our galaxy, which is good news for everyone.
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Stephen Hawking famously said sending messages from Earth into deep space could get human civilization destroyed: “If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn’t turn out very well for the Native Americans.”

Hawking’s words have often been used to discourage the practice of METI, which is Messaging Extraterrestrial Intelligence. But how many “malicious” alien civilizations are there? And what are the chances any message we sent into our own galaxy would be received by an evil alien civilization? There is precious little research on this topic, and very few scientists have even posited a guess.


A new thought experiment attempts to at least venture a guess in hopes that other scientists will begin to take METI more seriously, and will try to determine how dangerous it actually is to try to contact alien civilizations.

According to this paper, which the author admits has “some limitations,” there are roughly four “malicious extraterrestrial civilizations” in the Milky Way, and we could likely send out 18,000 interstellar messages to different exoplanets in our galaxy and the probability of ensuring our own destruction would still be about the same as Earth being hit by a “global catastrophe asteroid.” 

The paper—which hasn't been peer-reviewed—is called “Estimating the Prevalence of Malicious Extraterrestrial Civilizations" and was written by Alberto Caballero, a PhD student in conflict resolution at the University of Vigo in Spain and the author of a separate study published in Cambridge University’s peer-reviewed International Journal of Astrobiology earlier this month that attempted to analyze where the famous WOW! Signal originated

Caballero says he had to make some assumptions that make it very difficult to know if his calculations are correct. To do the study, he researched how many external “invasions” there have been on Earth over the last 50 years, meaning countries that invade other countries. He then took that data and applied it to the number of known and estimated exoplanets, and potentially habitable exoplanets, based on Italian SETI scientist Claudio Maccone's estimate that there could be as many as 15,785 civilizations in the Milky Way. (The basic idea—extending Earthbound ideas of conflict into outer space—will be familiar to fans of sci-fi fare such as The Expanse.)


Caballero concludes that the probability of a hostile alien race invading Earth is low—very low. "The probability of extraterrestrial invasion by a civilization whose planet we message is, therefore, around two orders of magnitude lower than the probability of a planet-killer asteroid collision," which is already a one-in-100-million-years event, he writes in the paper. 

He also said that there is likely fewer than one malicious extraterrestrial civilization in the Milky Way that has also mastered interstellar travel, which would make them a so-called “Type 1” civilization.

“0.22 Type-1 civilizations (capable of nearby interstellar travel), and 4.42 civilizations if all of them were like humanity (we aren't a Type 0 yet),” he said. “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 (below Type-0), 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 (we will reach that technology once we become a Type-1).”

Caballero told Motherboard in a phone call that, as society has become more advanced, there have been fewer invasions, suggesting to him that alien civilizations capable of destroying Earth would be less interested in actually doing so as they progress technologically. 

“I did the paper based only on life as we know it. We don’t know the mind of extraterrestrials. An extraterrestrial civilization may have a brain with a different chemical composition and they might not have our empathy or they might have more psychopathological behaviors,” he said. “I found this way to do [the study], which has limitations, because we don’t know the mind of what aliens would be like.”

“I think unfortunately it’s still quite a secret topic, no one seems to be willing to talk about it,” he added. “There’s this fear of being afraid to send messages out there, but there’s very little research on whether it’s actually dangerous to do.”

Caballero understands that this isn’t necessarily the most sophisticated science, but said he hopes that by putting a number out there, he can start a conversation about whether it’s actually risky to send messages into space. 

“The fact that the estimated probability of extraterrestrial invasion is two orders of magnitude lower than that of a planet-killer asteroid collision should open the door to the next step, which is having an international debate to determine the conditions under which the first serious interstellar radio or laser message will be sent to a nearby potentially habitable exoplanet,” he wrote.