If the universe is a "dark forest", why should we look for aliens?

Text ｜ Li Yuebai Jiang Xiaoyuan

Recently, news about UFO and external amino acids, such as the search for extraordinary life, frequently appeared on hot search.

Since 1960 astronomers Drake launched the first Seti (Search for Extra-Terrestric Intelligence) project in human history, it has been more than 60 years since searching for outdoor civilization) projects.

In the past 60 years, what efforts have humans have done in order to find aliens? What signals have been received? Why do scientists such as Drake and Carl Sagan are full of enthusiasm for finding aliens, but scientists such as Hawking and Brin strongly opposed it? After listening to Liu Cixin's interpretation of "Dark Forest", do you agree to find aliens?

Seti history -starting from a science fiction movie

In 1997, the United States released a science fiction movie called "Contact".

The heroine of the film is curious about the universe since she was a child, and she became an excellent celestial physicist.

She is committed to looking for alien Seti activities and devoted all her body and mind to this hopes.

One day at dumplings, Eri heard a special and wonderful regular signal in the headphones. After identifying, this signal came from the weaver actress of 26 light years from the earth. Humans finally received information from alien civilization.

Facing the vast universe, the curiosity of the same wisdom and seeking the natural heart of human beings.

The screenwriter of the "Macross" movie -American celestial physicist and science fiction writer Karl Sagan is one of the main sponsors of Seti in reality.

Karl Sagan's imagination and expectations for alien civilization are goodwill. His famous saying- "If there is only us in the universe, it will be too wasteful."

The main means of SETI are to receive electromagnetic waves from the universe through advanced equipment such as radio telescopes, and analyze the regular signals from it. I hope to discover alien civilization.

The principle of SETI's faith is that if the technology of alien creatures has reached a certain stage, they may use radio wave transmission information (such as television, radar, etc.) like us, so that trace radiation will be radiated from their lives. The planet leaked out.

In addition, aliens may consciously emit signals to the universe, hoping to communicate with other smart lives, and what we have to do is to identify the signal of alien civilization from the universe background full of radiation.

When it comes to Seti operations, Frank Drake is always mentioned. He is a more important pioneer than Kakar Sagan.

In 1960, American astronomer Drake launched the first Seti project in human history, the Ozma Plan. The name of Ozma's plan comes from the fairy tale "Green Wild Fairy".

Although Frank has a beautiful imagination of "Ozma", the plan operation has considerable problems.

First of all, Frank had only a radio telescope with a caliber of 26 meters (which was insignificant compared to the "China Sky Eye" 500 -meter -caliber spherical spherical radio telescope). Where should the telescope be directed to the entire sky?

The more critical question is, which frequency to monitor? When we use the radio, we know that if the frequency is not adjusted, it is impossible to receive the radio, and we can only hear noise.

But it is difficult for us to know which frequency of aliens choose to transmit signals.

In the end, Drake pointed the telescope at the star of the whale and the ε star of the Jiangbo seat. The situation of these two stars is similar to the sun, which is 10.5 light years and 12 light years from the earth.

In the choice of listening frequency, it was finally determined to be 1420.405 MM. Drake and other scientists agreed that this frequency is relatively special, and it is likely to be the first choice frequency of aliens to convey information to space, because this is the electromagnetic wave frequency emitted by the most hydrogen atoms in the universe, the vast majority of the vast majority Alien civilizations with radio telescopic technology can detect this frequency signal.

Drake's team monitored the two galaxies for about 150 hours. Except for receiving the signal of two aircraft launch, it did not intercept any information from aliens.

The first SETI experiment in human history failed.

After that, other larger SETI projects have been launched one after another, such as the "Big Ear" SETI program in Ohio launched in 1973, and the "Phoenix" Seti program launched in 1995.

From passive to active: send messages to aliens

Since the curiosity of other lives in the universe is the natural heart of human beings, there are always some "bolders" hoping to take more active measures. As early as Seti lasted for ten years, Sagan and others couldn't hold back.

How can we get in touch with alien civilization as soon as possible?

That is, actively send our information to space. "The mountain is not me, I will go to the mountain."

In 1972 and 1973, the United States launched two space detectors, "Pioneer 10" and "Pioneer 11". The main detection targets of these two detectors were Jupiter and Saturn, respectively.

Different from the previous series of "pioneers", No. 10 and 11 will fly out of the solar system with inertia after completing the detection task and to the depths of the universe.

What's more special is that both detectors have a special item -gifts from humans to aliens.

Photo of the author of the pioneer gold -plated aluminum plate

This "gift" is essentially a very light gold -plated aluminum plate. It was jointly designed by Karl Sagan and Frank Drake. It was written by Sagan's wife and tried to introduce our civilization to the aliens with a painting. And our planet.

The most aimless purpose in the picture is the image of human beings of a man and two naked earth. Men have done a "beckoning" action, expressing friendship in human limbs.

There is a rectangular pattern next to the male, which represents the outline of the pioneer detector. The main purpose is to compare the size of the human body relative to the detector.

The upper left corner of the picture is engraved with a self -spinning image in a hydrogen atom, which conveys the degree of understanding of human civilization for the micro -world.

The radioactive pattern on the left indicates that the pulse signal cycle of the 14 pulse stars in the Milky Way, the length of the lines in the pattern represents the distance between these pulse stars to the solar system.

Once the alien understands this image, it can infer the launch time of the detector, and you can also find the specific location of the solar system in the galaxy.

This gift has completely exposed our coordinates.

Humans took the initiative to "give gifts" to space more than once.

In August and September 1977, the United States launched two aerospaces, "Traveler No. 1" and "Traveler 2", each with a copper -plated laser records on each of them. The life of the record is expected to reach 1 billion years.

This record accommodates 115 pictures, 35 kinds of nature's voice, nearly 60 types of world -language greetings, 27 world -renowned music, and so on.

Among the nearly 60 kinds of greetings include Chinese Mandarin and Minnan, Cantonese, and Wu language. The month of the Chinese Guqin song "Flowing Water" performed by Guan Pinghu was selected.

Today, the pioneers have lost contact on the 10th and 11th, and the time to receive the information is 2003 and 1995, respectively. We only know that the spacecraft has reached the speed of escape and will leave the solar system forever.

In September 2013, NASA, USA announced that Traveler No. 1 had flew out of the solar system and entered the interstellar space. Traveler No. 2 was close to the boundary of the solar system.

But the nuclear batteries of travelers No. 1 and No. 2 are about to fail to lose contact with us forever.

While "pioneers" and "travelers" send gifts to space, Drake and Sagan did another thing -actively transmit radio positioning signals on space emitted by electric telescopes. It is regarded as "active Seti".

The first "active SETI" operation of human beings occurred in 1974. Drake launched a 16,79 bit information with Ares Bowang glasses at 25,000 light years away from the earth. Essence

The "Alecybo Information" mainly contains seven parts of the content, which is carefully written by Drake and Sagan. It uses the most basic digital expression elements to use the element group to form a molecular formula. Strict logical relationship.

However, many people doubt whether aliens can decipher the information. After all, aliens may have a completely different thinking pattern from the Earth, or they are completely different from us.

However, even if human beings can really receive a reply from the "M13 ball -shaped star group", it is at least 50,000 years later.

Since the launch of "Alecybo Information", human beings have conducted three larger "active Seti" operations, namely "Universe Call 1999" (Russia), "Youth Information" (Russia), and "Copy Call 2003". (Russia, the United States, Canada).

The amount of information and launching power of the latter three times are far greater than the "Arecybo Information" in 1974.

In fact, whether it is shouting to the universe with radio telescope, or sending the spacecraft carrying the earth information into space, both are tried to actively contact the civilization of the earth. This behavior is also called Meti - " Send information to MESSAGE to the Extra Terrestric Intelligence.

Its ideas are that the reason why aliens have not appeared because they do not know the existence of human beings. If we actively send the earth to the universe, the aliens will contact us after receiving it.

Controversy: Do you want to send the signal actively

Internationally, Meti is a controversial event, and many well -known people oppose Meti.

Martin Ryl, an expert in British Astronomy, is one of the earliest people who oppose Meti.

He warned that any creature of aliens may be full of malicious and hungry, and the initiative to contact it may cause the killing of the body.

At the same time, Ryr also wrote a letter to the International Astronomy Federation, calling on the promulgation of the international ban, specifically aimed at those on the earth who tried to contact the aliens or actively send signals to him.

Another big man who opposes Meti is Stephen Hawking. In 2010, Hawking's screenwriter and produced a set of documentary "Knowing the Universe with Hawking" and aired on the US exploration channel.

There are three episodes of the documentary, including the entire episode of the alien problem with a full episode.

Hawking said that thinking in purely mathematics, light can draw the conclusions of aliens in terms of numbers. The form of alien life should be diverse, and it does not rule out the possibility of evolving the possibility of threatening intelligent creatures that can threaten humans. These creatures may have learned the secrets of longevity, exhausted the resources of the mother star, embarked on the path of conquering the universe, and even use the energy of the star level to tear the space directly and make the wormhole reaching the predetermined target to plunder.

Humans actively seeking contact with aliens are very dangerous. Once the aliens come to the earth, it may be like Columbus discovered the American continent. It is of course not a good thing for the local Indians.

Also opposed to METI is David Brin. He is an American physicist and is famous for writing science fiction.

For why the aliens can't be contacted so far, Brin proposed an interesting theory called "big silence".

"If the high -level extraterrestrial life chooses to silence, shouldn't we choose the same practice as them? Or at least a little watched? It is likely that they are silent because they know something we don't know. "

Bollinger believes that there may be some dangers and rules that humans do not know in the universe that have led to the occurrence of "big silence". At present, the more wise strategy is to adopt Seti without Meti.

Different from the malicious inferring of Ryl, Hawking and others, the supporters of Meti such as Carl Sagan and Satself have a considerable positive prediction on the results of contact.

Satselff believes that the alien civilization world with more advanced technology must be "civilization", and they will show us -also to show friendship and love as the rare wisdom in the universe.

Satselfa even believes that aliens will teach us knowledge and experience to save humans from the crisis of nuclear weapons, wars and environmental pollution.

It is not only an adventure, but it is also very necessary. It will play a role in the development and continuity of human civilization.

In Liu Cixin's sci -fi "Three Body", Chinese scientist Ye Wenjie is also an enthusiastic supporter of the outside civilization. After being arrested, she had such a conversation with the interrogation officer on the earth:

(The following text is taken from Liu Cixin's "Three Body Ⅰ")

"Questioner: Do you know the three -body civilization?

Ye Wenjie: I do n’t understand. The information we get is very limited. In fact, the true and detailed appearance of the three -body civilization, except for the core personnel of the advent of three -body information, are not clear.

Questioner: Then why do you have such expectations for it and think that they can transform and improve human society?

Ye Wenjie: If they can come to our world across the interstellar, it means that their science has developed to a considerable level. A society with such a clear science must have a higher level of civilization and morality.

Questioner: Do you think this conclusion is scientific itself? "

The final question of the interrogator can be regarded as the best refutation of those scientists who are looking forward to alien civilization to act as the savior.

Think of how Westerners who have advanced technology treat backward Indians and Africans, it is not difficult to conclude that there is no positive relationship between the degree of the brightness of technology and the level of civilization and morality.

"Don't talk to aliens."

Is there an alien in the universe?

In 1961, at the Observatory near the Green Coast in the United States, Drake presided over the first academic seminar for outbound civilization search, and he and the young Karl Sagan proposed the famous "Drake formula" (also known as it is also called it Sagan formula) is used to estimate the number of high civilizations in the Milky Way.

In mathematics, the Drake Formula (N = R × FP × NE × FL × Fi × FC × L) shows that the probability of aliens in the universe is very high.

The earth is just one of the 8 planets that rotate around the sun. The sun is just one of more than 200 billion stars in the galaxy. If the entire universe is looking at, the galaxy is only one of more than 100 billion galaxies.

Even if there is only one human in the Galaxy (that is, the so -called N value is equal to 1), in more than 100 billion galaxies, we can no longer be arrogant.

This is what Hawking said, "Thinking with my mathematics mind, you can get the conclusion of aliens from the figure."

"But where are they?"

In the summer of 1950, after breakfast on one day, Fermi also expressed such doubts. If aliens exist, they should have appeared. Due to Fermi's huge reputation, it passed through the question and became a famous "Fermi paradox".

Indeed, in just 300 years since the first industrial revolution, human beings have boarded the moon and launched many satellites and spacecraft. Among them In space, if there is another civilization that is similar to our intelligence and the speed of development, but it is 100 million years ago, their colonial rule should have already spread throughout the Galaxy.

Many scientists and science fiction writers in the world have tried to answer this question. Among them, the eye -catching explanation is the following:

The first explanation is that alien civilization has existed, but they have died before they have developed to interstellar colonization, for example, because of nuclear war, environmental pollution, and irresistible disaster. The thinking that this explanation brings us is how long can "civilization" survive? Is the current development of human beings unsustainable? Will we face the same destiny soon after?

The second explanation is that we are the only smart civilization in the galaxy.

Even if there are more advanced civilizations in other galaxies, their forces cannot reach the galaxy at present.

In this way, it means that human beings are the races that are most likely to develop into type II civilizations.

If this historical mission is successfully completed, our descendants will freely shuttle in the interstellar, and eventually establish a huge galaxy, a human galaxy in the galaxy.

The third explanation is that alien civilization exists, but they deliberately do not let us discover it.

The earth is a "laboratory" of aliens, and even the "zoo". They silently observed us and attempted to know what a civilization that will eventually become unprepared and spontaneous.

Therefore, no matter how much Seti and Meti are carried out in humans.

In addition to the above three explanations, there are many wonderful explanations.

In recent years, Chinese writer Liu Cixin put forward another answer in "Three Body II "-" Dark Forest "law. This explanation is inherited from David Brin's "great silence", but it is more refined and more distressed.

Liu Cixin's "Dark Forest" law is based on two basic axioms and two important concepts.

Two basic axioms are:

First, survival is the first need for civilization.

Second, civilization is growing and expanding, but the total amount of material in the universe remains unchanged.

The two important concepts are:

First, suspense chain.

Because the universe is very huge, the distance between civilization and civilization is very far away, and because the speed of light cannot be surpassed, it is impossible to establish effective communication and mutual trust between the different civilizations of the universe, which leads to the emergence of the "suspicion chain".

For example, human beings want to communicate with a 100 light -year -old civilization, from sending messages to receiving echo for at least 200 years.

How can we know what happened in 200 years? What is the credibility of their echo and their attitudes? Since effective communication cannot be established, we cannot confirm whether alien creatures are good or malicious.

Even if we believe that they are goodwill, we cannot know whether we are good -faith or malicious in their eyes.

Such a "suspicion chain" can extend to infinite length, and the result is that any civilization cannot trust another civilization.

2. Technical explosion

Human civilization has a history of 5,000 years, while modern technology has been developed within 300 years. From the perspective of time scale, this is not development at all, but an explosion.

Similarly, such a "technical explosion" may occur in any civilization, but I do not know when it will happen.

Therefore, even if the technical level of the alien race we contacted is far behind us, they may occur at any time, and quickly surpass us, and even threatened us!

These two basic principles and important concepts outline the cosmic picture scene:

The various civilizations in the universe must fight for their first targets with their own survival. They cannot trust another civilization and cannot ensure that they are in the leading position of technology.

In this way, let you know my existence, and the second, let you continue to exist, is dangerous for "I".

This is the reason why the "Dark Forest" of the universe, and it is also the reason why the alien civilization collective "big silence".

"The universe is a dark forest. Each civilization is a hunter with guns. He sneaks in the forest like a ghost, gently pulls away the branches that block the road, and strives to prevent the footsteps from making a sound. Be careful, because there are hunters who sneak like him everywhere in the forest. If he finds other lives, whether it is a hunter or a devil or a devil, whether it is a delicate baby or a faltering old man ... only what he can do is to do. One thing: shoot out. In this forest, others are hell, a eternal threat, and any life that exposes its existence will be destroyed quickly. This is the picture of the cosmic civilization. Explanation. "

Overall, Liu Cixin's warning to us is:

"Don't talk to aliens."

(The author Li Yuebai is a doctor of science and technology, the librarian of the Qianxuesen Library of Shanghai Jiaotong University, and Jiang Xiaoyuan is a professor of chair at the Marxist College of Shanghai Jiaotong University)

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