How many extraterrestrial civilizations are in the galaxy? Scientists figured out the answer: 36!

  Highlights tracking

  Recently, in a paper published in the "Astrophysics" magazine, astrophysicists Tom Westby and Christopher J. Consells of the University of Nottingham in the United Kingdom estimated the extraterrestrial civilization in the galaxy. Quantity: There may be at least 36 alien civilizations with radio communication capabilities similar to the earth civilizations in the Milky Way.

  The existence of extraterrestrial civilizations in the universe has always been a hot topic, and some believe it, and others remain skeptical. What about astronomers? Do they believe in the existence of extraterrestrial civilization? Do you already have more scientific "evidence"?

  Why are humans not alone?

  Speaking from the "Copernican Principle"

  There is a famous "Copernicus principle" in astronomy-the position of the earth in the universe is not special. Sometimes it is stated that the observer anywhere in the universe will see the same large-scale structure image as we have seen, which has been confirmed by many astronomical observations. Further, some people think that life is not special in the universe, which is the "Copernicus Principle of Astrobiology". Although so far people have not really found life outside the department, many astronomers have affirmed this "principle". Because it is being supported by more and more indirect observation data.

  Through astronomical observations, people found that there are at least 200 billion stars in the Milky Way, and the total number of galaxies in the universe is more than hundreds of billions! Among them, the planets are also not uncommon. Since the first exoplanet was discovered by humans in 1995, more than 4,100 have been discovered in just over 20 years. Based on these data, people have been able to estimate with reasonable certainty that the probability of the existence of terrestrial planets in the habitable zone around the stars in the Milky Way is about 19%, which means that planets like Earth have at least 40 billion. If human civilization is unique, then the probability of the existence of civilization is less than one part in 40 billion, which violates the "small probability event principle" in probability theory. Therefore, astronomers can conclude that there must be other civilizations in our galaxy.

  Of course, there is a problem that needs attention here, that is, the direct data source of the "Copernicus Principle of Astrobiology" is only one, that is, the earth. Extrapolation based on a single data is very risky, so the above conclusions are not absolute. Although it is not entirely possible to determine how many parameters need to be considered at present, in terms of probability, a small probability cannot be matched by a large cardinality, so astronomers will be confident that it is correct.

  36 territorial civilizations?

  There are 3 qualifications

  Because there is only one data point for the earth, astrophysicists Tom Westby and Christopher J. Consells of the University of Nottingham in the United Kingdom used the formation environment and history of the earth to limit the formation conditions of extraterrestrial civilizations and inferred " The number of "exchangeable civilizations" (civilizations that have mastered radio communication technology).

  First of all, because the birth time of earth civilization should be about 5 billion years, the age of the parent star where the extraterrestrial civilization is located must be greater than 5 billion years. Secondly, it should be born on a rocky planet as large as Earth and located in a habitable zone around the stars. Third, this stellar system must have enough heavy elements, such as iron, copper and other metal elements, otherwise it will not be able to develop terrestrial civilization.

  Therefore, they gave a method for calculating the number of communicable civilizations in the galaxy—N=N*·fL·fHZ·fm·(L/t′). Among them, N* is the total number of stars in the Milky Way; fL is the proportion of stars over 5 billion years old; fHZ is the proportion of stars with a suitable planetary system; fm is the proportion of stars with enough metal elements; L is the exchangeable civilization The average life span is the average time from civilization's ability to carry out radio communication to its demise; t'is the average usable time of (smart) life evolution. Taking the earth as an example, it can be estimated as the average of the period from 5 billion years after the star formation to today. For example, for a terrestrial planet system with a current age of 8 billion years, the life time available for its evolution is 3 billion years.

  According to the latest observation data, and the restriction conditions are divided into 12 levels according to the strength and weakness, they came to the following conclusion: There are 36 civilizations like the earth in the Milky Way.

  Alien that has evolved for 5 billion years?

  There is still a lot of uncertainty

  The researchers believe that they have given the lower limit of the number of Earth-like civilizations in the Milky Way, and further calculated that the closest Earth-like civilization to us should not exceed 17,000 light-years. However, the formula given in the article makes people wonder: Compared with the Drake formula, some parameters in this formula may not be independent. For example, the average metal abundance and average age of stars in the Milky Way, that is, fL and fm may not be independent variables. Although the correlation is small, it may have no effect on the results. Similarly, fHZ may not be related to other parameters, and their probabilities are directly related. The multiplication may not be completely accurate, and the researchers have not conducted further analysis in this article. In addition, the text shows t′=48±550 million years, which means that civilizations born on terrestrial planets in the Milky Way have an average evolution time of nearly 5 billion years. If this is the case, then there will be a large number of extraterrestrial civilizations in the galaxy that have evolved billions of years more than us! Their level of civilization will be unimaginable.

  In short, there is still a lot of uncertainty in estimating how many extraterrestrial civilizations, in the future people will definitely give more accurate estimates as the observation data increases.

  (The author is a researcher at the Beijing Planetarium)