In a recent paper at Physics ArXiv, Alberto Caballero, a PhD student in conflict resolution at the University of Vigo in Spain, has calculated that there are, perhaps, four civilizations in our galaxy that are both intelligent and evil.

A natural response has been “only four? Not counting us?”

The estimate got quite a bit of media attention. To arrive at it, Caballero began by reviewing the history of conflicts on Earth:

To reach his estimation, Caballero first counted the number of countries that invaded other countries between 1915 and 2022. He found that a total of 51 of the world’s 195 nations had launched some sort of invasion during that period. (The U.S. sat at the top of the list, with 14 invasions tallied in that time.) Then, he weighted each country’s probability of launching an invasion based on that country’s percentage of the global military expenditure. (Again, the U.S. came top with 38% of global military spending.)

Brandon Spektor, “4 hostile alien civilizations may lurk in the Milky Way, a new study suggests” at Space.com (June 2, 2022)

According to his model, if we average the probability of one civilization invading another, we come up with a probability of humans invading another planet’s civilization of only 0.14% by the time we can engage in serious travel to other planets, which he sees as more than two and a half centuries off at least. But— here’s the hitch — there are believed to be millions of habitable planets. One 2012 paper at Mathematical Seti estimates 15,785 intelligent civilizations.

Using this figure — and noting that the probability of invasion decreases with technological advancement — he concluded that very few advanced civilizations (Kardashev Scale 1 type) would attack us but that a little over four (4.42) would, based on human history, be malicious toward us if we landed and they were where we are now.

Stephen Hawking did not think it would end well for us:

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.”

Jason Koebler, “There Are 4 ‘Malicious Extraterrestrial Civilizations’ in Milky Way, Researcher Estimates” at Vice Motherboard (May26, 2022)

At Futurism, Noor Al-Sabai puts the question in perspective:

Part thought experiment and part game theory, Caballero’s admittedly out-there paper is also interesting because of the way he reached his conclusions: by using a formula that takes into consideration how technologic advances seem to make civilizations less likely to invade one another.

By using known data about the ways humans have historically invaded each others’ territories and comparing it to the number of assumed habitable exoplanets in the Milky Way, this alien-focused conflict resolution researcher deduced that although there could be up to four hostile alien civilizations in our galaxy, Earth is vastly more likely to be destroyed by an asteroid than to be invaded by bloodthirsty aliens.

Noor Al-Sibai, “Study: There May Be as Many as Four Evil Civilizations in Our Galaxy” at Futurism (June 1, 2022)

In fact, the Breakthrough team has proposed caution in attempting to contact extraterrestrials and some, like Stony Brook astrophysicist Paul Sutter, encourage us to look for biosignatures (evidence of life) rather than technosignatures (evidence of technology).

Caballero discussed his own approach at some length with a writer at Vice:

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.”

Jason Koebler, “There Are 4 ‘Malicious Extraterrestrial Civilizations’ in Milky Way, Researcher Estimates” at Vice Motherboard (May 26, 2022)

He also admits to wanting to send a message of sorts:

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.

Jason Koebler, “There Are 4 ‘Malicious Extraterrestrial Civilizations’ in Milky Way, Researcher Estimates” at Vice Motherboard (May26, 2022)

One way of looking at it: The native Americans had no idea what they were getting into when Europeans started showing up with swords, guns, cannon — hard metal weapons, generally. That probably meant that they made many decisions that were not in their best interests (but they couldn’t have known that with no forewarning). If, as Caballero suggests, we consider a number of possibilities in advance, we would be better prepared, on the off chance anything did happen.

Here’s Caballero’s Abstract:

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 once we become a Type-1 civilization in the Kardashev Scale capable of nearby interstellar travel. The estimation is based on the world’s history of invasions in the last century, the military capabilities of the countries involved, and the global growth rate of energy consumption. Upper limits of standard deviations are used in order to obtain the estimated probability of extraterrestrial invasion by a civilization whose planet we send a message to. Results show that such probability is two orders of magnitude lower than the impact probability of a planet-killer asteroid. These findings could serve as a starting point for an international debate about sending the first serious interstellar radio messages to nearby potentially habitable planets.

You may also wish to read: New study on why aliens never phone, never write, never visit. Planetary scientists suggest that civilizations follow a trajectory in which there is only a short window of time to look for intelligent extraterrestrial civilizations. If Wong and Bartlett are right, WE may only have a short window of time to look for intelligent extraterrestrial civilizations.