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There are four hostile alien civilizations in the Milky Way

By: April Carson

The Milky Way may be home to millions of potentially inhabitable planets, according to new research published in the preprint repository arXiv, and about four of them may contain malevolent alien civilizations that would attack Earth if they could.

The new study, which has not yet been subjected to peer review, asks a peculiar question: What are the chances that humans might one day communicate with a hostile alien race that could invade Earth? To answer it, the authors first had to come up with a definition for a "hostile" alien race.

"A hostile extraterrestrial civilization is one that has the ability and motivation to attack Earth," they wrote in the study. "We use the term 'attack' to include any action that an extraterrestrial civilization might take that would have a negative impact on the long-term survival of humankind."

To address this, sole author Alberto Caballero — a doctoral student in conflict resolution at the University of Vigo in Spain — started by looking back at human history before looking outward to space.

"This paper endeavors to offer a prediction of the incidence of hostile extraterrestrial civilizations by extrapolating the likelihood that we, as a human species, would attack or invade an inhabited exoplanet," Caballero added in the report.

Caballero, who isn't an astrophysicist, has published a study on the notorious Wow! signal — a possible indication of extraterrestrial life -— in the peer-reviewed International Journal of Astrobiology.

In the new paper, Caballero argues that humans have a long and bloody history of aggression, which suggests that extraterrestrial lifeforms might be similarly inclined. He points to a number of factors that could increase the likelihood of hostility, including scarce resources, religious differences, and a desire to colonize new territory.

To assess his claim, Caballero started by tallying the number of countries that invaded other nations between 1915 and 2022. He discovered that during that time, 51 of the world's 195 countries had launched some sort of invasion. (The United States was at the top of the list, with 14 invasions recorded in that period.) Then he weighted each country's likelihood of launching an invasion based on its share in global military spending. (Again, the United States was at the top with 38% of global military expenditure.)

After collecting data on the possible involvement of each country in an extraterrestrial invasion, Caballero divided the total by all of Earth's nations to generate what he calls "the current human probability of extraterrestrial civilization invasion."

According to this theory, the chance that humans will invade another inhabited planet is 0.028%. However, according to Caballero, this figure refers to current human civilization — and humans aren't yet capable of interstellar travel. Using the Kardashev scale to calculate how long it will take for humanity to reach a given level of technological development, Caballero determined that interstellar travel won't be possible for another 259 years if current rates of technological progress remain constant - a period known as the Kardashev scale.

Assuming that the frequency of human incursions continues to fall at the same rate as it has done over the previous 50 years (minus 1.15 percent per year on average, as stated in Caballero's paper), then when we become an interstellar, or Type 1, civilization 259 years from now, humans have a 0.0014% likelihood of attacking another planet.

That may appear to be a miniscule chance — and it is, until you consider the millions of potentially habitable planets in the Milky Way. Caballero's final calculation was based on a 2012 paper published in the journal Mathematical SETI, in which researchers predicted that as many as 15,785 alien civilizations might cohabit with humans across the galaxy. If even a fraction of those civilizations are slightly more belligerent than ours, well, the Milky Way could be a very dangerous place.

According to Caballero, just less than one of the Type 1 civilizations — 0.22, or roughly 22% — would be hostile toward people who make contact. When you take into account civilizations that, like modern humans, are not yet capable of interstellar travel, the amount of malicious neighbors rises to 4.42 , according to Caballero.

"I don't include the 4.42 civilizations in my paper because 1) we don't know if all galaxies have civilizations like us... 2) since we lack the technology to go to their planet, a civilization like us would not be a danger to another one," Caballero said.

It's a lot easier to imagine an asteroid colliding with Earth than it is five hostile alien civilizations. Caballero also said that the chance of humans coming into contact with one of these malevolent civilizations — and then being subjugated by them — is incredibly remote.

According to Mr. Kaku, the probability of an alien civilization receiving our message and mounting an invasion is... "It's about two orders of magnitude less probable than a planet-killer asteroid collision," he wrote in his paper, adding that planet-killing asteroids, like the one that killed the dinosaurs, are 1-in-100-million-year occurrences.

However, the author acknowledges that his model has limitations. The invasion probability is calculated on a very limited section of human history, and it makes numerous assumptions about our species' future development. The hypothesis also assumes that alien intellect will have brain structures, values, and feelings of compassion comparable to humans, which may not be the case. Caballero told Vice that the model also presumes that aliens will have brains with characteristics similar to those of humans.

"I did the paper just on the basis of what we know right now," he added. "We have no idea what aliens' minds are like."

This is not the first time that scientists have looked at the possibility of hostile alien civilizations. In 2015, a group of researchers from Cornell University published a paper that argued that advanced alien civilizations are likely to be warlike and expansionist.

The new study provides a more detailed look at the potential for hostility among aliens, and it underscores just how little we know about the possibility of intelligent life elsewhere in the universe.

The study was originally published on Live Science.

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About the Blogger:

April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on

To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav



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