The moment human beings walked out of the earth to see the vast universe, they began to think: Does alien civilization exist? As for the existence of extraterrestrial civilization, with the continuous development of human science and technology, there are more and more discussions.
Objectively speaking, there is no evidence to prove the existence of extraterrestrial civilization. The so-called “evidence” we have seen are actually false, even some people’s pranks. Even so, scientists do not deny the existence of extraterrestrial civilization. The main reason why we did not discover it is that the universe is too big and the suns between star systems are too far away, on average more than a few light-years.
Let’s take the small solar system as an example. There are eight planets, including the Oort Cloud, which has a diameter of 2 light years. According to the current detection data, the solar system has only one civilization, humans. Therefore, if we want to discover an alien civilization, we must at least go to the closest galaxy to us, the Biling Galaxy. Proxima Centauri is about 4.2 light-years away from us.
4.2 The distance of light-years is nothing in the universe, but for humans, it is an insurmountable gap. It will take at least tens of thousands of years for the fastest human aircraft to reach Proxima. Although the history of the birth of mankind has been millions of years, the time of civilization is not long. According to the earliest human civilization discovered so far is the Sumerian civilization in West Asia, it is only about 5,000 years away from us.
It can be seen that human civilization has only appeared for about 5,000 years, while the universe has a history of 13.8 billion years, and the Milky Way is also 10 billion years old. From the perspective of the time period, the probability of the existence of alien civilization is also extremely great. . Therefore, we cannot rule out the existence of alien civilizations, but we have not discovered it yet.
So how do we calculate the probability of the existence of an alien civilization? Around the 1960s, there was an astronomer Drake who proposed a very famous plan to search for extraterrestrial civilizations, which is known to many people as the search plan for extraterrestrial civilizations, referred to as SETI. The main application of this search plan is to search for signals of alien civilizations that may exist in the universe by means of radio exploration.
To this end, Drake also proposed a famous equation called: Drake’s equation. This equation adds eight factors to calculate how many possible alien civilizations there will be in the Milky Way galaxy through these eight factors. Through the formula in the picture, we have a simple analysis of these eight key factors. After the analysis, you will understand the probability of the existence of alien civilizations.
1. The proportion of stars with planetary systems. As we all know, the diameter of the Milky Way is at least 100,000 light-years, of which there are about 1,000-4,000 stars like the sun. Based on the Milky Way’s age of 10 billion years, an average of about 10 stars are born every year.
So how many planets exist among the hundreds of billions of stars? Theoretically speaking, every star should have a star system, with varying numbers of planets orbiting around it. We exclude that stars closer to the galactic center are unlikely to have a stellar system. On average, there should be at least three planets orbiting around other stars, and there are eight planets in the solar system. On average, there are three planets around each star, so the number of planets in the Milky Way can reach about one trillion.
2. The proportion of habitable planets in each planetary system. According to the current conditions for the birth of life on Earth, scientists believe that the position of a planet in the system is very important if a planet wants to give birth to life and complete a series of subsequent evolutions. We call this location a livable zone.
The so-called habitable zone is not far or close to the host star. Within this range, rocky planets can enjoy the appropriate light and heat brought by the star, liquid water can exist on the surface for a long time, and there must be a thick atmosphere. And a relatively strong magnetic field.
Only when the conditions of a habitable zone are met, planets can form a relatively excellent ecosystem, and an excellent ecosystem is very important for the birth of life. There may be some bad planets that can give birth to primitive life, but if you want to evolve intelligent life through long evolutionary evolution, then the planetary ecosystem must be excellent.
As we said earlier, there are at least trillions of planets in the Milky Way, some of which are rocky planets in the habitable zone. According to the point of view of the habitable zone model, the proportion of habitable planets may be between 1% and 10%.
3. The proportion of life on habitable planets. If the planet is in the habitable zone, it may not be able to become a life planet. We must know that there are also three planets in the habitable zone of the solar system, namely Venus, Earth and Jupiter, but the current life planet is only the Earth, while Venus and Mars are one of purgatory and the other a desert planet, and there is no life.
It can be seen that being in a habitable zone does not mean that life will be born. Some scientists believe that the origin of life is an accident, and there is only a very low probability that life will appear on planets in the habitable zone. Of course, some scientists believe that as long as the conditions for planets in the habitable zone are met and the planets are given enough time to evolve, they can become life planets.
4. The probability that a living planet will evolve into intelligent life. After a planet in the habitable zone becomes a living planet, it will take at least billions of years of evolution for life to eventually evolve into intelligent life. If various changes occur within this time, then the evolution of life will also end, and intelligent life cannot eventually evolve.
Scientists have speculated that Venus and Mars were also life planets long ago, and life was born and evolved. But later they all made changes, the ecological environment completely collapsed, and life disappeared. All, some scientists believe that life will evolve into a smart civilization is also an accidental event, the probability is extremely low, it may be less than 1%.
5. The probability of the development of intelligent life to scientific and technological civilization is very high. The common opinion of scientists is that as long as intelligent life is born, after a period of development, it will enter the era of civilization and embark on the development of science and technology. The road is basically certain. Even if this probability is not 100%, it can be as high as 90% or more.
6. The ratio of technological civilization to interstellar civilization: This scientist can’t give an answer. In theory, as long as a smart civilization embarks on the path of technological development, it is certain to become an interstellar civilization as long as enough time is given. The Milky Way has a history of 10 billion years. In such a long period of time, if many intelligent civilizations appeared and entered the age of technology, it should have become an interstellar civilization by now.
For an interstellar civilization, this distance of the Milky Way is nothing at all. They have enough time to find us and come to the earth, but why don’t we find anything? This is the Fermi paradox proposed by the famous physicist Fermi.
Based on the above description, we have added various conditions to the Drake equation. The number of intelligent civilizations in the galaxy should not be less than 100. This is only the most conservative estimate, and the actual situation may far exceed this. Among the more than 100 intelligent civilizations of this person, a considerable part of the civilization strength may far exceed human civilization, which means that they have already become interstellar civilizations.
Since there is interstellar civilization in the Milky Way, why didn’t it come to the solar system and come to the earth to come into contact with humans? There may be several reasons for this. One reason is that alien civilization has already become an interstellar civilization, and it also knows the existence of the earth and human beings. However, because our civilization strength is not even counted as a first-class civilization, they are not willing to contact us.
There is another possibility that the interstellar civilization of the Milky Way may have left the Milky Way long ago to explore more distant galaxies. This possibility is actually very high. We must know that the Milky Way is a huge galaxy to the solar system, but the Milky Way is still as small as dust to the universe. Even within the current observable range of human beings, the number of star coefficients such as the Milky Way will not be less than one trillion.
Mankind expects to be able to explore the entire galaxy, and for the advanced civilization of the galaxy that has long become an interstellar civilization, they have the strength to go out of the galaxy, and naturally they also hope to be able to explore more distant galaxies and explore the ultimate mystery of the universe. Therefore, when a civilization becomes an interstellar civilization, there is a high probability that it will not shrink into a galaxy, but will go out and explore the entire universe.
In any case, scientists believe that the probability of alien civilization is basically 100%, and we have not found anything. The main reason is that our strength is too low to be able to go out of the solar system to explore. If mankind’s scientific and technological prowess can go further, and the speed of the probe can reach sub-light speed, then galaxies near the solar system can be explored, and traces of alien civilization may be found at that time.