China News Service, June 21 (BBC) Chinese network published an article saying that British astrophysicists recently published research papers saying that there may be at least 36 similar, active, Smart civilization with advanced technology. How is the number "the Milky Way galaxy may have 36 alien civilizations" calculated? Are there any aliens? Is earth really a lonely planet?

On July 22, 2019, local time, a simulation map released by the Instituto de Astrofisica de Canarias, Spain, described the merger of the galaxy's ancestral galaxies with the dwarf galaxy Gaia-Enceladus about 10 billion years ago ( Left), and the current scene of the Milky Way (right).

formula

Whether an alien civilization like Earth exists and whether the Earth is a lonely planet in the Milky Way, this ancient question has concrete speculation numbers for the first time, which is one step closer to the answer.

Astrophysics professors Christopher Conselice and Tom Westby of the University of Nottingham in the UK published their research papers on the website of Astrobiology (April 2020) and Astrophysics. June 2020).

　　The paper mentioned that "the Milky Way may have 36 alien civilizations". So, how is this number calculated?

　　To explore how many other planets in the Milky Way may have similar Earth civilizations, the main tool so far is the Drake formula, which was proposed by astronomer Frank Drake in 1961.

　　This formula contains 7 factors, and the number of intelligent civilization planets with communication capabilities that may exist in the Milky Way is calculated based on these factors. To perform the calculation, all factors must first be determined.

　　These factors range from the average number of stars born in the Milky Way every year, the proportion of these stars that can form terrestrial planets, to how long it takes for an earth-like civilization to produce the ability to send detectable communication and communication information to space.

　　In 2013, Sara Seager, an astrophysicist at the Massachusetts Institute of Technology (MIT) in the United States, proposed her formula to calculate how many planets with detectable life might be discovered in the next few years.

　　The factors of this formula include the number of observable stars, how many of them are surrounded by planets, how many of them can be observed, and so on.

　　Siegel’s formula does not involve whether extraterrestrial life is intelligent, whether it can use radio transmission signals, etc.; she is concerned about whether the number of life on the planet is enough to change the chemical composition of the planet’s atmosphere, just like the atmosphere of the earth. . This combination of chemical components is similar to human fingerprints. The analysis of the atmosphere can detect whether there is life on that planet and in what form.

The NASA announced on December 20, 2011 that the Kepler space telescope had discovered two planets of similar size to the earth for the first time. They are also the smallest terrestrial planets found in solar-like star systems to date.

Soft underbelly

　　But why haven't these two tools come up with meaningful calculation results so far? The key is that the factors that make up the formula are mostly unknown.

　　Stuart Clark, author of "The Big Questions: The Universe", pointed out in the book that the main purpose of Drake's formula is to provide an idea, a framework.

　　Because only one of the seven factors necessary for formula calculation is known, that is, how many new stars form each year, a calculation result generally accepted by the astronomy community is an average of 7 per year.

　　The other factors in the Drake formula are currently unknown and difficult to determine.

　　The fatal weakness of Siegel's formula is the same as that of Drake's formula. The values ​​of many factors cannot be determined and there is not much value in quantitative calculation, but both of them help people sort out their ideas.

Recently, the international academic journal Nature-Astronomy recently published an online astronomy research paper saying that the birth of stars in the Milky Way may be due to the periodic "close contact" of the Milky Way with the neighboring human dwarf galaxy.

Suppose

　　Astrophysicists Consells and Westby of the University of Nottingham have proposed new ideas based on the Drake formula, or adjusted the formula with new factors and assumptions, and reached a conclusion The meaningless span of "between 100 million" is more specific.

　　The sun is a star. Planets that revolve around stars, such as the earth, can form life under certain conditions.

　　Their calculations are based on a set of assumptions. First, suppose that the formation and evolution of intelligent life on the other planets in the Milky Way are similar to the civilization of the earth. Then the life will naturally appear after billions of years after the planet is born, and then continue to evolve.

　　According to the Copernican principle of astrobiology, everything can happen from the chemical reaction to the formation of the planet if the necessary conditions are met.

　　Assuming that the formation of intelligent life has scientific laws, rather than random, random, irregular, or unique, then according to the calculation of the Consells team, the result is "at least 36", that is, there may be at least 36 galaxies with the earth Civilizations are similar to active, alien civilizations with communication capabilities.

Data Map: The researchers have drawn a fine three-dimensional map of the Milky Way. The latest three-dimensional map shows that the Milky Way galaxy is curly S-shaped as a whole, which is the warped structure described by astronomers.

Copernicus limit

　　This calculation process uses Astrobiological Copernican Limits (Astrobiological Copernican Limits).

　　Copernicus was a Polish priest, astronomer, mathematician, medical scientist, and doctor of law in the European Renaissance of the 15-16th century. He proposed the heliocentric theory (the sun is the center of the universe, and the earth revolves around the sun), leaving the great book "celestial bodies" "Operation Theory" completely changed the human universe view.

　　The Copernicus limit known as astrobiology is divided into strong limit and weak limit. Weak limit refers to that at least 5 billion years after the formation of a planet, intelligent life may occur. For example, the intelligent life of the earth may occur at most 5 billion years ago, or at any time after that.

　　Under the weaker hypothesis of the loose Copernicus theory, the Consells team calculated that there are currently at least 928 alien intelligent civilizations in the Milky Way. This means that more civilizations exist at a closer distance, and it takes about 700 years to detect each.

　　The strong limit includes a series of very strict qualifications; according to the strong limit assumption, life appears between 4.5 billion and 5.5 billion years after the formation of the Earth-like planets in the Milky Way, the process refers to the earth. Based on this, it is calculated that the number of smart civilization planets in the galaxy that may currently have communication skills is about 4 to 211, of which the most likely value is 36.

　　Concellis pointed out that this is a conservative estimate. Because there is also a set value in their calculations, that is, the time when the earth civilization began to send radio signals to the universe, so far about 100 years.

　　Because extraterrestrial civilizations are at least 17,000 light-years away from the earth, the one-on-one contact and communication between the earth and the aliens will have to wait at least as long as 6120 years, if the earth civilization can continue to that day.

　　However, they pointed out in the paper: "The search for extraterrestrial intelligent civilization not only reveals the existence of life forms, but also provides clues as to how long our own civilization will last. Even if we get nothing, we are also exploring our own future and destiny. "

Back to reality

　　Dr. Oliver Shorttle, an expert at the University of Cambridge in the UK, believes that there are many setting factors in the latest formula that are too vague and require careful analysis and clear definition, otherwise the extrapolated results are of little significance.

　　In an interview with the Guardian, he pointed out that these factors include how the life on earth first appeared? Also, how many of the Earth-like planets that are considered suitable for survival are truly capable of nurturing intelligent life and civilization.

　　Professor Andrew Coates of the Mullar Space Science Laboratory at University College London acknowledges that the assumptions and projections of the Consells team are reasonable, but at least the current efforts to find alien civilization In view, it is more realistic to focus on the solar system planets closer to the earth.

　　Efforts in this area include the Exomars 2022 Mars landing and exploration program in cooperation with the European Space Agency and Russia, and plans to explore the moon of Jupiter and Saturn in the future.