In Liu Cixin's short science fiction novel "Rural Teacher", the earth, as a planet with a 3C-class civilization, is at the top of the first spiral arm, and it is also the most desolate area in the galaxy.
Although this is the setting and plot of the novel, according to the current human cognition, the earth is only a "drop in the ocean" in the vast galaxy. Therefore, finding whether there are still alien civilizations in the Milky Way has become the goal of scientists' exploration.
▲ Picture from: NASA
Not long ago, in a new paper published on the arXiv preprint by Alberto Caballero of the University of Vigo in Spain, there is a bold prediction: In our galaxy, there may well be four "malicious alien civilizations lurking. ". And some of these civilizations may be technologically similar to humans, but not yet capable of interstellar travel.
At the end of 2020, Alberto Caballero also submitted a paper on the arXiv preprint on the origin of the "WOW!" signal, which was detected by the Big Ear radio telescope at Ohio State University in 1977 and appears to come from the constellation Sagittarius direction.
▲ Picture from: OSURO
Alberto Caballero mentioned that the "WOW!" signal is considered the best candidate for SETI radio signals that we have found with telescopes (SETI is a collective name for all groups searching for extraterrestrial civilizations, which are dedicated to receiving advanced equipment such as radio telescopes) Electromagnetic waves coming from the universe and analyzing them, hoping to discover alien civilizations).
▲ Picture from: OSURO
In Alberto Caballero's recent paper speculating that there are "malicious alien civilizations" in the Milky Way, there is actually no specific evidence in space to confirm this idea, but by inference.
In this paper, Alberto Caballero's inference is as follows, using the probability of attacking or invading an inhabited exoplanet if human civilization reaches the Kardashev level of interstellar travel in the vicinity of a Type I civilization. Invasion probability of "malicious alien civilization".
▲Image from: arXiv
The Kardashev scale mentioned here is a measure of the technological sophistication of a civilization, based on how much energy a civilization can use to communicate with exoplanets. Type I among them indicates that the civilization is the master of planetary energy, meaning that it can dominate the combined energy of the planet and surrounding satellites.
To extrapolate, Alberto Caballero collated countries that had invaded other countries between 1915 and 2022 and found that a total of 51 countries had launched some type of invasion during this period.
▲Image from: arXiv
After calculating the weighted probability of invasion for each country (the probability of invasion for each country is weighted according to its percentage of global military spending), and taking into account that there are 195 official countries on Earth, and considering that malicious civilizations do constitute Threat, Alberto Caballero concluded that there is about a 0.028% chance of an alien civilization invading Earth.
In addition, the article also mentioned that humans are expected to become a type I civilization with interstellar travel capabilities in about 259 years, and it is estimated that the probability of the earth civilization invading another civilization at that time is 0.0014%.
▲ Picture from: BenQ
These inferences are currently unverifiable, but Alberto Caballero also said that the probability of a malicious civilization invading the Earth is extremely low, probably similar to the probability of an asteroid collision causing a global catastrophe.
Interestingly, he also mentioned why SETI has not made serious attempts to send radio messages to potentially habitable exoplanets.
▲ Picture from: Unsplash
The reason there is no international debate on the possibility of doing so is because there is widespread concern in the scientific community that the messages sent out could be accessed by malicious alien civilizations. Such civilizations may be more advanced than our own, and may be interested in exploiting our planet's resources by force.
Humans who have been yearning to get out of the earth and eager to see the universe are still too "fragile" at present, but even so, although they are afraid of being disadvantaged, the pace of exploring space will not stop. Perhaps in the future, human beings can really achieve interstellar travel, get out of the "Blue Star" and go to deep space.
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