# What is the probability of the existence of alien civilization? A formula tells us the answer

When human beings walk out of the earth and see the vast universe, they begin to think: does alien civilization exist? With the continuous development of human science and technology, there are more and more discussions about the existence of alien civilization.

Objectively speaking, there is no evidence to prove the existence of alien civilization. The so-called “evidence” we see is actually false, even some people’s pranks. Even so, scientists do not deny the existence of alien civilization. The main reason why we did not find it is that the universe is too big and the sun between the star systems is too far away, with an average of more than a few light years.

Let’s take the small solar system as an example. There are eight planets, including the Oort cloud, with a diameter of 2 light-years. According to the current exploration data, there is only one civilization in the solar system, so if we want to find an alien civilization, we should at least go to the nearest galaxy, biling galaxy. And the nearest star is about 4.2 light years away.

The distance of 4.2 light-years is nothing in the universe, but it is an insurmountable gap for human beings. It will take at least tens of thousands of years for the fastest human aircraft to reach Bilin. Although the history of human birth has been millions of years, the time of civilization is not long. According to the discovery of the earliest human civilization is the Sumerian civilization in Western Asia, which is only about 5000 years away from us.

From this, we can see that the time of human civilization is only about 5000 years, while the universe has a history of 13.8 billion years, and the Milky way has a history of 10 billion years since its birth. In terms of time cycle, the probability of the existence of alien civilization is also great. Therefore, we can not rule out the existence of alien civilization, but we have not yet found it.

So how do we calculate the probability of alien civilization? Around the 1960s, Drake, an astronomer, put forward a very famous plan to search for extraterrestrial civilization, which is known to many people as SETI. The main application of this search plan is to search for possible alien civilization signals in the universe through radio search.

Therefore, Drake also put forward a famous equation called Drake equation. Eight factors are added to this equation to calculate the probability of the existence of alien civilizations in the galaxy. Through the formula in the picture, we will make a simple analysis of the eight key factors. After the analysis, you will understand the probability of the existence of alien civilization.

1. The proportion of stars with planetary systems, we all know that the diameter of the Milky way is at least 100000 light-years, and there are about 1000-4000 stars like the sun. According to the galaxy’s 10 billion year age, about 10 stars are born every year.

So how many planets exist in hundreds of billions of stars? Theoretically speaking, every star should have a stellar system with different number of planets around it. We exclude those stars that are close to the silver center and are unlikely to have a stellar system. On average, there should be at least three planets around other stars, such as eight planets in the solar system. On average, there are three planets around each star, so the number of planets in the galaxy 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 if a planet wants to give birth to life and complete a series of subsequent evolution, the position of the planet in the system is very important. This location is called livable zone.

The so-called habitable zone is not far from or near the main star. Within this range, rocky planets can enjoy the light and heat brought by the star. Liquid water can exist on the surface for a long time, and there is a thick atmosphere and a relatively strong magnetic field.

Only when the habitable zone is satisfied, can the planet form an excellent ecosystem, which is very important for the birth of life. There may be some bad planets that can also give birth to primitive life, but if we want to evolve intelligent life after a long period of evolution, then the ecosystem of the planet must be excellent.

As we said earlier, there will be at least trillions of planets in the galaxy, some of which are rocky planets in the habitable zone. According to the habitable zone model, the proportion of habitable planets may be between 1% and 10%.

3. The proportion of livable planets with life, planets in the livable zone, may not be able to become living planets. You should know that there are three planets in the habitable zone of the solar system, namely Venus, earth and Jupiter. But at present, the only living planet is earth, while Venus and Mars are purgatory planets and desert planets, both of which have no life.

It can be seen that being in the livable zone does not mean that life will be born. Some scientists believe that the origin of life is an accidental event, and there is only a very low probability that planets in the habitable zone will have life. Of course, some scientists believe that as long as the conditions for habitable planets are met and enough time is given for planets to evolve, they can become living planets.

4. The probability of intelligent life evolving from a living planet. After a planet in the habitable zone becomes a living planet, it will take at least several billion years for life to evolve into intelligent life. If there are all kinds of changes in this period of time, the evolution of life will be terminated, and intelligent life cannot be evolved.

Venus and Mars, scientists speculate, may have been living planets a long time ago, as well as the birth and evolution of life. But later, they all made their own changes, the ecological environment collapsed completely, and life disappeared. Therefore, some scientists believe that it is also an accidental event for life to evolve into an intelligent civilization, and the probability is extremely low, which may be less than 1%.

5. The proportion of intelligent life developing into scientific and technological civilization is very high. The common view of scientists is that as long as intelligent life is born, then after a period of development, entering the era of civilization and embarking on the road of scientific and technological development is basically certain. Even if the probability is not 100%, it can be as high as 90%.

6. The proportion of scientific and technological civilization to interstellar Civilization: this scientist can not give an answer. Theoretically speaking, as long as an intelligent civilization embarks on the road of scientific and 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 time, if a lot of intelligent civilizations appeared and entered the era of science and technology, it should have become an interstellar civilization by now.

For an interstellar civilization, this distance of the galaxy is nothing at all. They have enough time to find us and come to earth, but why don’t we find anything? This is the Fermi paradox proposed by the famous physicist Fermi.

Based on the above, we add 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 be far beyond that. Among the more than 100 intelligent civilizations of this man, probably a considerable part of the civilization strength is far beyond human civilization, that is to say, they have already become interstellar civilization.

Since there is interstellar civilization in the galaxy, why didn’t you come to the solar system and the earth to contact with human beings? There may be several reasons for this. One reason is that the alien civilization has already become an interstellar civilization, and also knows the existence of the earth and human beings. However, due to our civilization strength, they are not willing to contact us.

There is also a possibility that the interstellar civilization of the galaxy may have left the galaxy long ago to explore more distant galaxies. This possibility is actually very high. You should know that the Milky way is a huge galaxy for the solar system, but the Milky way is still as small as dust for the universe. Even within the current human observable range, the number of galaxies such as the Milky way will not be less than one trillion.

Human beings are looking forward to exploring the entire galaxy. For the advanced civilization of the galaxy, which has already become an interstellar civilization, they have the strength to go out of the galaxy. Naturally, they also hope to explore more distant galaxies and explore the ultimate mystery of the universe. So, when a civilization becomes an interstellar civilization, it will probably not shrink into one galaxy, but go out and explore the whole universe.

In any case, scientists believe that the probability of the existence of alien civilization is basically 100%. We have not found anything, mainly because our strength is too low to go out of the solar system for exploration. If human science and technology can go further, and the speed of the detector can reach the speed of sub light, then we can explore the galaxies near the solar system, and then we may be able to find traces of alien civilization.

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