Richard pressed his gold-rimmed glasses.

Sitting by the window, gazing out at the gloomy sky, he remembered that autumn two years ago. At that time, he was terminally ill, sitting on a bench outside the hospital building and fainting, and when he was pushed to the emergency room by a group of people, the sky was also cloudy, lead-gray, like a layer of indelible haze.

Richard didn't expect that he would survive like that.

And in such a weird way.

"What the hell am I doing now??anti-traversal?," Richard looked at the sparrows flying by outside the window, lost in thought.

His last memory as "Richard of Earth" is frozen in front of the operating room. After that, about half a year, he traveled through time and space, to a fantasy world of dragons, gods, and magic. Possessed as a small mercenary, relying on his own knowledge, he made some noise, and became a master for a while......

Seeing that life is about to go to glory, it has ushered in a strange end.

At that moment, he was about to escape from Ascension to Heaven when he was about to escape from the Ascension to Heaven when a strange, emotionless, female voice that seemed to be an electronic voice sounded in his ears.

- "Bug No. 132 fixed. ”

Richard lowered his head and looked at his slender white hands.

About a year and a half ago, when he opened his eyes again, he found that he had returned to Earth. But he is not the original Richard, but possessed by a man named Wang Ming.

This is a vegetative person who has been paralyzed for about a year due to a car accident that has caused severe brain damage.

Although he woke up through his body, Richard had no memory of "Wang Ming", and he had no impression of "Wang Ming's" indifferent parents, greedy girlfriends, and those drunken friends. Although, in the past year and a half, he has acted as Wang Ming and has become a rich second-generation college student.

Richard was sure he wasn't dreaming.

Because he turned out to be really dead, shortly after this awakening, he went to the cemetery and saw his grave. Everything he used to have is still in this world.

At this time, half a year later, as an orphan, almost all the traces left in the world have been ruthlessly polished away, like a wild goose stepping on the paws of slush and leaving only a lonely tombstone.

"It turned out that I didn't have parents, but I didn't expect that I have now, but it's the same as nothing. Richard laughed miserably twice at the thought of this.

At this moment, looking at the scenery outside the window through the glass, rows of "0" and "1" data flashed on the retina.

The strange movement only lasted for about a second or two, but it gave birth to a new change.

Richard's eyes widened, and his mouth was wide open enough to swallow a ripe pear.

At this moment, the window disappeared, the glass was gone, and what he had seen turned upside down, like a television set, from a gloomy light gray sky to a bright world that hung obliquely tomorrow at this moment.

What Richard saw when he turned his head at this moment was a huge sun hanging diagonally in the northwest corner of the sky, about three or four o'clock, about the size of several wheels, and it was extremely magnificent. Brilliant light, staining the sky on that side, a scene of burning clouds, layers of clouds as if on fire, burning.

Richard felt that what he was looking at at this time was by no means the earth, nor was it like the Roland world.

The sun in these two places was by no means as great and magnificent as he had seen at this moment.

However, Richard only looked at it for three or four blinks.

Having just recovered from the shock and was looking in other directions, Richard found himself sitting at the back of the classroom, in the second row of seats by the window.

"What's going on? I'm dazzled?" Richard had a big question mark in his mind.

Just as he was lost in thought again, a voice forcibly interrupted him.

"Now let's welcome Wang Ming's 20-minute lecture. In our interdisciplinary study, Wang Ming chose astronomy and science fiction, and his theme this time was 'The Three-Body Problem and the Fermi Paradox'. ”

It was a hoarse, middle-aged man's voice, who was none other than Wang Ming's university teacher.

As soon as the voice fell, in a burst of customary applause, some scattered eyes were cast on Richard, who was sitting in the back position, staring at the thin white boy.

Interrupted by this, Richard had no choice but to get up.

Leaving his seat, Richard strolled to the podium, bowed to the teacher who had retreated, and then leaned down in front of the computer embedded in the desk, moved the mouse for a while, and called up the PPT he had made.

Looking up at the more than forty classmates in front of him, Richard shook his head helplessly.

Sitting far back, he knew that half of the people here had cell phones hidden in their desks. But he only sighed, people who look at the scenery outside the window are not qualified to laugh at people who play with mobile phones.

Richard was actually serious this time.

The rich and varied life of the university seems to exclude only classes. Otherwise, it wouldn't make people more listless than they were in high school.

Bringing up the first page of the PPT, Richard pointed to the image behind him, covering half of the blackboard's projection screen, and spoke without being shy at all.

"Hello students, what I have brought this time is my recent learning experience. After learning some knowledge of science fiction literature, astronomy, and cosmic physics, I wrote this lecture. ”

He had a polite smile on his face, "The theme of this time is mainly to introduce the Fermi paradox, and to extend some things related to science fiction literature, and the entry point is the three-body problem." ”

"Everyone should know about the three-body problem, right?"

"Even if you don't know about the three-body problem, you should have some understanding of the 'law of the dark forest'. Moreover, this thing once swiped the post bar, Weibo, QQ group on a large scale, and once had terrible spread in various online forums. ”

"Especially when Da Liu won the award, it was even more overwhelming, like a plague ......"

At this moment, there was a burst of laughter at the back of the class.

Some people even put down their phones and looked around.

"The core setting of the Three-Body Problem, that is, this key 'law of the dark forest', once set off a wave of discussion on the Internet. ”

Richard continued to speak, and then clicked on the second page of PPT, he pointed to the row of text, "The above is the law of the dark forest, which is the most common content when it is spread on the Internet." On this side, it describes the universe as a dark forest in which civilizations stalk like hunters with guns. They need to guard each other and try not to leave any traces of detection, because if someone else finds out, they will be killed by cold bullets that come out of nowhere. Others are hell, others are eternal threats, and any civilization and life that exposes its existence will soon be wiped out. ”

"I think everyone must be familiar with the content here. ”

But people who are not early fans of the three-body problem may not know that it has been illuminated into a series of influences. Because the picture of the universe outlined here is dark and terrifying, many people who watch this paragraph alone are very repulsed by it, and they have also set off rounds of online battles for this reason. Recalling the memories of the past, a smile flashed across Richard's mouth.

"The Three-Body Problem is a book worth reading, if you don't want to read the book, it is recommended to find a speed reading video, the story here is very interesting. ”

"And the starting point of our theme this time is 'Hessian's Law'. ”

Hesse's law is an explanation of Fermi's paradox. In fact, one of the implicit premises of the establishment of Hesse's law described in the book is a terrible thing revealed by Fermi's paradox. ”

"What is the Fermi paradox?"

Although this question is as simple as arithmetic in elementary school for those who understand science fiction literature and pay attention to astronomy. But here, I still have to introduce it to people who don't know. ”

Richard skillfully clicked on the third page of the PPT, and in this page, there were only eight big words - "Do you know how big the universe is?"

The page opened, and there was a small commotion in the classroom.

Richard's university teachers all glanced at the PPT.

The third page is followed by the fourth page.

This is a vast map of the starry sky, although there is no text, but after the foreshadowing of the previous question, it has a different meaning.

"When you were a child, did you ever think about the question, how many stars are there in the sky?"

Richard suddenly laughed elegantly, "Although when we were young, we only saw a gray sky at night, and I am afraid that we can only see the starry sky for a while in remote rural areas." But at least in TV and movies, when I see this charming starry sky, I always think about the question - how many stars are there in the sky?"

"The answer is now somewhat certain: there are about 7,000 stars that we can observe with the naked eye under a clear night sky. ”

"Being able to observe these stars is only a tiny part of the Milky Way. In a diagram, it's about just a red dot on this nebula. ”

PPT turned to page five.

It was a spiral-shaped map of a nebula, with Richard pointing to a red dot on it.

"The Milky Way is about 10 to 120,000 light-years in diameter, and the stars here are about 100 billion to 400 billion. That's a staggering number. ”

He paused deliberately.

I clicked on the next page of ppt.

"And putting the Milky Way into the universe is like putting the solar system into the Milky Way. Scientists used to estimate the observable universe at about 100 billion to 200 billion, but now in cutting-edge research, this number has increased tenfold. ”

"Here, we all count by the smallest number. There are 100 billion galaxies in the universe, and there are 100 billion galaxies in the Milky Way, so the observable universe contains stars such as the sun. ”

On the seventh page that Richard clicked on, there was only one number - "100,0000,0000,0000,0000,0000,0000".

"This number, which is 10 to the 22nd power, has greatly exceeded the amount of sand on Earth. And that's just counting the stars, or according to the smallest number. ”

When talking about this, Richard was very bizarre to find that there were many people staring at the PPT on the projector, and some people were amazed.

Teacher Wang on the side also showed the same curious expression, as if listening to it with relish.

"We can give such an analogy here, every grain of sand on the earth corresponds to dozens or hundreds of stars in the universe. ”

It is in this context that the Fermi paradox is proposed. ”

"Is this a star n times more than the sand in the Ganges, really giving birth to only the earth, a world with life?"

Richard points out the PPT on page 8.

Here is a calculation formula.

"The life form we know is only us. If you do, you usually know what carbon-based life, silicon-based life. On this side, without considering other life forms at all, only taking the form of life on earth as the standard, the number of life forms that are rigorously searched, and finally calculating the planets that may give birth to life, are very terrifying. ”

"And if we go down one level, we don't think about the universe, just count the Milky Way, it's very scary by the order of magnitude. Planets where life is likely to exist are measured in billions. ”

"Then the question arises again, where are these relatives of the universe?"

"The fastest speed of human current detectors is close to 1/10,000th of the speed of light. Even if we stand still, at this level of civilization, if we continue to launch outward, it is possible that within a certain period of time, it will spread throughout the galaxy. ”

"But the age of the earth is less than 5 billion years. During this time, we have developed such a civilization. The entire universe is more than 10 billion years old. ”

"Unfortunately, to date, we haven't received a single contact from the stars. It's not even sure where another planet with life might be?"

"At present, after mankind entered the modern civilization and established a scientific system, the development speed of civilization is increasing day by day. It could be upside down in just twenty or thirty years. If this is the case with civilizations that preceded humans, then it is not surprising that they will have much more technology than we do. ”

"Detectors, contact information, and other things should have been all around us for a long time. But why, so far, we haven't found any traces?"

"This is the Fermi paradox!"