“...... But for some reason, they are all silent, and even many people in our supposed small, inconspicuous little planet think that they are unique. ”

"Scholars in some related fields have also put forward the concept of polymorphic civilization based on some knowledge. For example, a Type 1 civilization can control all the resources in the planet, and a Type 2 civilization can control all the resources in the star system, and so on. Among them, there is also a kind of 'Dyson sphere' device, that is, a device artificially created to cover the stars at the center of the galaxy with a close distance, reaching 50% or even more, in order to obtain more energy. But the strange thing is that we haven't found a device like the Dyson sphere once. ”

"So, friends of the universe, where are they?"

"This is the 'Great Silence', this is the Fermi Paradox!"

"After everyone understands the Fermi paradox, let's take a look at "The Three-Body Problem". Take a look at the law of the dark forest it proposes for this, an explanation of the Fermi paradox. ”

Richard cut the original page.

At this time, there was a discussion in the classroom. Seeing some classmates and showing some incredible expressions, he suddenly felt that his efforts had not been in vain.

Teacher Wang, who was wearing glasses on the side, suddenly coughed twice, making the classroom quiet again.

He stared at the projection on the screen with amusement.

Richard continued: "The law of the dark forest, the interpretation of Fermi's paradox, is 'everyone deliberately does not speak up'. ”

It likens the universe to a dark and dangerous forest, where all civilizations are loners with guns and need to be constantly wary of others. Others are dangers, others are hells, others are abysses. If you expose your traces, you will immediately usher in a devastating blow, so in order to survive, you must hide yourself!"

Richard pointed to the text on the curtain, "This is probably the darkest solution to Fermi's paradox." ”

Soon, Richard heard some scattered rebuttals - "I feel!", "This is too dark!", "Hey, you're done listening", he smiled.

He shook his head with a smile, and then continued: "We see that this passage is actually a conclusion. The characters in the book deduce it based on premises, such as 'chain of suspicion', 'technological explosion', and the acquiescence that 'there are many civilizations in the universe', 'the total amount of matter in the universe is constant', 'survival is the first law of civilization', and 'the speed of light is irreversible'. ”

"From these premises, it is established that 'communication between civilizations is extremely difficult', 'there is competition between civilizations due to the limitation of the total amount of matter', and 'attack is simpler and less expensive than communication', and further conclusions are drawn here: 'If there are a million civilizations in the universe and find an exposed target, 900,000 civilizations may ignore it, 90,000 of the remaining 100,000 will go to probe, and the last 10,000 hunters, one or two will definitely make a choice - shoot at that location and try it'. ”

"In short, the content of this law of the dark forest has a whole set of logic in the book. Richard concluded.

He changed a new page of PPT, "However, everyone has to pay attention to it, this is the logic and truth in the book, not reality." For example, in one book, it is said that 'science is eternal, art is useless', but in another book, it becomes 'art is immortal, science is useless'. What is pursued is only self-consistency, that is, the truth in the default background of the book, which is different from the reality of our real world. ”

This page of the new PPT has a line written - "Reality's interpretation of Fermi's paradox".

Finally, let's introduce the various explanations of the scientific community's paradox. Here I would like to remind you that there is no answer to the Fermi paradox, and I am afraid that ten scientists in related fields will give ten answers, and a hundred will give a hundred answers. Here are some of the most famous answers and explanations. ”

"First of all, there is a screening mechanism, the so-called big filter. ”

"It believes that even though the universe is incomparably vast, there are many planets that could give birth to civilization. But whether these planets can give birth to life and civilization needs to pass through one level after another, and these levels are the big filters. ”

"Taking our earth as an example, the birth of life may have to go through these stages, such as 'the birth of complex organic macromolecules such as amino acids', 'the emergence of cellular organs', 'the birth of multicellular life', 'the differentiation of brains and other thinking organs', 'the emergence of intelligent life', 'the gradual evolution of civilization', and so on. ”

"Maybe every level we've passed has been a big filter. ”

"If other planets encounter levels that they can't get through, or if they take a very long time, they may not be able to develop a civilization. ”

"Similar to the big filter, there is also a concept mentioned in the previous introduction. ”

"That is, the earth is rare. ”

"After all, from the perspective of carbon-based organisms like us, the ecological environment of the earth is too friendly. We are on a moderately sized terrestrial planet, the Earth's orbit is still in the habitable zone of water, there is a well-developed magnetic field, an atmosphere, and a large brother like Jupiter to shield us from meteorite attacks. Probably the most unique point is the moon. As a satellite, it is a bit of a big anomaly compared to the Earth. ”

"And the type of life that the universe automatically produces is just carbon-based life similar to ours. Then, there is no doubt that we are extremely rare, such as the widespread existence of binary star systems, it is difficult to give birth to such an environment as ours. ”

Both of these interpretations are about the same point of view, that is, civilization and life are rare. Even though there are hundreds or thousands of times more stars in the universe than there are grains of sand on Earth, they are not as many as we think. ”

There is also an important theory that speaks of this view. ”

That is, the first civilizations in the Earth's universe. ”

Richard has a new page.

He looked up and saw that everyone in the class was fascinated.

I couldn't help but smile, and subconsciously turned around to check the projection behind me.

However, at this moment, the retina of his eye appeared again with data composed of "0" and "1".

Flashes faster and more in number!

When Richard was still in shock, the sun hanging obliquely appeared in his eyes again!

What he saw was no longer a blackboard and a projection screen of light and shadow, but a magnificent sky of burning clouds, and near the northwest corner, a huge sun hung diagonally in the sky.

Suddenly, a twisted black line climbed up the magnificent background.

The red sun, as big as a urn, appeared on the radiant surface, and a twisted and winding, slanting black thick line appeared upward.

Richard felt that the thick black line that climbed up to the sky and blocked the red sun, and the strange way of twisting, was very similar to the way he saw snakes swimming in the water when he was a child.

Just as his eyes widened again, it was all back to normal.

The blackboard and projection screen re-entered his eyes.

Richard blinked a few times and realized that everything was back to normal, as if he had just been hallucinating. In the afterglow of his gaze, he glanced at the classmates below, who were all staring at him in surprise, and suddenly felt a pressure.

But after coughing twice, he still took over the conversation loudly and said calmly.

"Everyone knows the concept of the speed of light, the light year. Because of the limitation of the speed of light, when we observe other planets, we receive this series of information from them a long time ago. For example, a planet a light year away, we see it a year ago. ”

"This has had an impact on the observations we have made. But because of this, we have an unexpected gain. ”

In other words, we can receive the message of the universe's past. ”

"As far as I know, through high-tech equipment such as the Hubble Telescope, we have detected more than 10 billion light-years away. ”

"They are also messages from the dawn of the universe more than 10 billion years ago. ”

According to this, astronomers and cosmic physicists have gradually grasped many secrets of the birth and development of the universe. ”

Richard was calm.

Through the peripheral vision of his eyes, he observed that the students in the class had ignored his "mistake" just now.

Maybe they thought it was just a moment he couldn't remember.

"If the earth is still used as the standard, then it can be said that the environment in the early universe was extremely unfriendly to life. ”

"Stellar activity is so intense that it's all terrible radiation like gamma-ray bursts. ”

"After all, the heavy elements that we need must have to be violently stellar activities such as supernova explosions to give birth to some. The most abundant elements in the universe are light elements such as hydrogen and helium, similar to heavy elements such as gold and silver, which are as extremely scarce on a planetary scale. ”

"Although the earth was born relatively late, it is a comparison of the entire universe. If you look at rocky planets, they are still very young. ”

"This may have contributed to the fact that our humans may be the first civilizations in the universe. ”

Richard had already pressed the penultimate page in the PPT at this time.

At the moment, perhaps because the content of his lecture is relatively fresh, the whole classroom seems relatively silent.

"You can find that the above three explanations are all inclined to the explanation that 'life and civilization are rare even on a cosmic scale'. Moreover, they are interpreted from different aspects and do not contradict each other. It is highly probable that the birth of life will be limited to a very small number of planets, or it may be subject to a major filter, and that it will develop later and at a lower level than we do. ”

If this is the case, the Fermi paradox can be solved. ”

"If civilizations are rare and sparsely distributed, and most of them are not as developed as ours, the 'Great Silence' brought about by this Fermi paradox is perfectly reasonable. ”

The second type of explanation is inclined to these high-level civilizations, although they exist in large numbers, but for various reasons, they have not contacted us, or they have sent out contacts, and they have indeed left a lot of movement, but due to the low level of our earth, they cannot accept it for the time being. ”

"Like the law of the dark forest, it says that civilization is afraid of the danger of being exposed, and deliberately hides itself. ”

"The latter 'is sent, but we can't receive it, or we can't interpret it,' can be interpreted from the medium of the message. Geomagnetic waves, like those used by the Earth, have problems with energy consumption and fading, and do not travel far in the universe. If it's really aliens, maybe they're using higher-end gravitational waves. ”

"There is another category, which means that we have less time to explore, after all, it has only been a few hundred years since the development of modern civilization. Or maybe aliens have already been to Earth, but at that time human beings were not yet born, or the level of civilization was not advanced, which is also very likely. ”

The last category is more inclined towards conspiracy theories. ”

Richard clicked on the last page.

"Let's say we're isolated, in an alien experiment. Or they have already mastered the earth, decorating this side as a park, making fun of us, deliberately leaving us unaware. And those who have already been contacted, but for some reason, the government deliberately lied to us. ”

"There are some of the weirdest ones, such as we are like the Matrix, the whole world is illusory, simulated and naturally not felt. ”

In short, the Fermi paradox is still an unsolved mystery for now. ”

After Richard talked about this side, he had already taken control of the mouse and turned off the PPT.

"That's what I'm going to cover today. ”

When Richard went down, something very surprising happened - a round of applause rang out in the classroom!

(Maybe someone guessed it.) That's right, the core of the book is an explanation of Fermi's paradox! O(╥_╥)o, originally planned to write a science fiction book with it, but the plan couldn't keep up with the changes, and this time it had to be sacrificed to save the book. ）

After some more time, about 3:30 p.m., Richard's final class was over.

The moment he walked out of the teaching building with his textbooks, he deliberately looked up at the sun for a while.

Therefore, at this moment, the position of the sun's tilt is roughly similar to the position of the sun he saw during his previous "accident".

"Hallucinations, perhaps?" Richard shook his head at one end.

At this moment, an inexplicable voice came from his ears.

It was a wonderful, emotionless, cold, machine-like female voice that Richard felt familiar to Richard. Because, when he returned to Earth this time, it had sent it out once.

That time it was - "Bug 132 fixed. ”

And this time it rang in his ears again.

"Your past life is over, and now it's mine—save your world, and save yourself......"