The vast majority of the alien civilizations that have ever flourished in our galaxy are probably dead. That is the extraordinary and discouraging conclusion of a study carried out by researchers at the California Institute of Technology and NASA’s Jet Propulsion Laboratory, which appeared just a few days ago on the arXiv prepublication server.
For their work, the scientists used an extended version of the famous Drake equation, which in 1961 tried to determine the probabilities of finding extraterrestrial intelligence in our galaxy and which after being popularized by Carl Sagan in his unforgettable series “Cosmos” has suffered, since then, numerous updates.
The new study, in effect, is much more practical than the original, telling us where and when life is most likely to occur in the Milky Way. But it also identifies what scientists consider to be the most important factor affecting their ability to survive: the tendency of intelligent creatures to self-annihilate. Using complex statistical models, the researchers found that the best time for intelligent life to emerge in the Milky Way was about 8 billion years after its formation and that many of these civilizations may have been “only” 13,000 light-years away. galactic center, just half the distance from Earth, where humans emerged about 13.5 billion years after the formation of the Milky Way.
Since Sagan’s time,” explains Jonathan H. Jiang, one of the study’s authors, “there has been a lot of research. In particular, from the Hubble and Kepler space telescopes, we have a lot of knowledge about the densities of gas and stars in the Milky Way, as well as about the rate of formation of new stars and planets and about the rate of occurrence of explosions of a supernova. In fact, we know of some of the numbers that were still a mystery in Sagan’s day.
In their work, the study authors analyzed a wide variety of factors capable of influencing the development of life, such as the prevalence of Sun-like stars with Earth-like planets, the frequency of supernovae emitting deadly radiation, the probability and the time required for intelligent life to evolve and, of course, the more than likely tendency of advanced civilizations to self-destruct. Taking all these factors into account, the researchers found that the probability that life-based on the elements we know will emerge and consolidate peaks some 13,000 light-years from the galactic center about 8 billion years after the formation of the planet.
The Earth, as has been said, is located about 25,000 light-years from the center of the Milky Way and human civilization arose almost 13.5 billion years after its birth. In other words, in terms of galactic geography, it is likely that the human is a “frontier civilization” and relatively late with respect to the bulk of the intelligent civilizations of the galaxy, which for the most part would be clustered around that band of 13,000 light-years of the center, where Sun-like stars are most abundant.
But the study, as has been said, also considered the factors that could have ended these civilizations, such as radiation exposure, the interruption of evolution due to an asteroid impact or other natural catastrophe, and, above all, the intelligent life’s tendency to self-annihilate, whether through climate change, technological advances, or war. All of the above suggests that most of the civilizations that still exist in the Milky Way are probably young. The rest would have “eradicated themselves,” so that most of the civilizations that once existed in the Milky Way would have irretrievably disappeared by their own self-destruction.
But how often do civilizations “commit suicide”? It is the most uncertain variable in the article, but also the most important when determining how widespread intelligent life can be outside our planet. According to the study, even an extremely low probability that a certain civilization will be annihilated at a certain time, for example, due to a nuclear holocaust or uncontrolled climate change, would mean that the vast majority of civilizations that have existed on the Way Milky would be gone forever.
“While no evidence explicitly suggests that intelligent life will eventually annihilate itself,” the researchers write, “we cannot a priori exclude the possibility of self-annihilation.” Without going any further, the possibility that war or climate change, among other scenarios, inevitably lead to the complete destruction of the human race is something that is already supported by numerous studies, such as Nick’s in 2002, Webb in 2011, Billings in 2018 or Sotos in 2019.
