Chapter 426

After listening to Zhang Yuan's story, Lin Xuanxuan was silent for a long time and suddenly said, "the feelings between you boys are often more pure. If I were you, I would have cried... "

A star drifted from the light mass behind, drew a complex curve and transferred to the light mass ahead. This is because the spacecraft is sailing at high speed.

"The relationship in our dormitory is not very harmonious. You know, there are always small frictions between girls. If a girl's private life is chaotic, the whole dormitory will be polluted. Everyone forms their own small groups. I don't know how complicated it is. "

"I haven't heard you talk about it."

Lin Xuanxuan said: "actually, it's nothing. It's all over... Finally, close to graduation, we had a break up meal, and then they dispersed. All the old and new hatred disappeared. There's no more chance to get together. "

Zhang Yuan said, "it's no pity. In fact, the relationship between people is not as close as expected. Sometimes you don't bother to go to parties. One or two friends are enough in a lifetime. "

Lin Xuanxuan thought for a moment, "Hey, yes, what are their names? I can't remember them! What's more, I can't even remember my mother's face. "

"I can't remember what my father looks like... I can only remember it by looking at photos." Zhang Yuan sighed.

They were so silent for a while.

Lin Xuanxuan asked again: "... Would you cry if I suddenly died?"

"What are you crying for?" Zhang Yuan smiled and said, "death is a new beginning. This reincarnation is over, and a new life will start again. It doesn't make much sense to miss the past. "

"I can only wish you happiness in the new world and live your next life!"

Lin Xuanxuan was surprised and then smiled: "I wish you a bright future in the future world!"

……

In the last few years, Zhang Yuan has been working at the observatory. He is mainly responsible for teaching primary and junior high school students how to use astronomical telescopes and how to distinguish the planets in the universe, including the direction of the sun and the direction of Gliese 581. These are the former mother stars, where humans were born or developed here.

"If one day you become captain, you will be miserable if you can't find your way home!"

This job is very easy, there is not much workload, and it is full and happy every day.

A clever little girl asked, "Grandpa Zhang, how should navigation in the universe be positioned? The Milky way is moving and everything is moving. How should we determine the position of our spacecraft? "

"Even planes on the planet need navigation. How can spaceships navigate? Long distance navigation must be accurate enough! "

Faced with this problem, Zhang Yuan thought for a while and drank a mouthful of water: "it's very simple. There are three good ways in total."

"First, use accelerometers and gyroscopes, that is, inertial navigation system. By measuring the acceleration and angular velocity at each moment, the velocity and displacement of the aircraft can be calculated by integration. However, the disadvantages of inertial navigation are also obvious: the longer the time, the greater the error, so it is only suitable for short range and auxiliary positioning. "

"The second method uses the relative position of known celestial bodies to locate and observe the surrounding stars, and simultaneous equations. But as you said, everything is moving, and the distance measured by spectrum changes from time to time, which is difficult to measure very accurately. "

"Method 3: navigation through a fixed radio signal source is also the method we use now. There are a large number of pulsars in the universe, which periodically emit electromagnetic pulses. As long as multiple pulsars are observed to form a pulsar timing array, it is a natural deep space network, that is, the so-called "Galactic positioning system."

"If you think pulsars inside the Milky way are moving, resulting in a certain degree of error, you can even observe pulsars outside the Milky way, 100 million light-years away!"

"Such a distant planet, we can directly think of it as static."

Zhang Yuan played several images of pulsars on the screen. These pulsars are equivalent to man-made satellites that constantly send signals to the outside world.

These students, faced with real complex knowledge, were stunned one by one.

The girl asked, "if we go out of the Milky way and sail across the river system, how should we position ourselves?"

Zhang Yuan replied, "there is a phenomenon called rapid radio burst. It is speculated that the signal source of these high-energy millisecond flashes is very huge, which may come from outside the Milky way. Maybe one day, they will become lighthouses for human beings to travel across galaxies. It is speculated that the signal source of these high-energy millisecond flashes is very huge, which may come from outside the Milky way. Maybe one day, they will become lighthouses for human beings to travel across the river system. "

"Crossing the river system?!"

At the thought of so many natural lighthouses in the universe, all the students yearned and couldn't help looking out of the window.

It's too far to cross the river system!

"Grandpa Zhang, there's another question. Why are integers as many as even numbers?"

After a while, a little fat man who had just entered junior high school asked again.

His name is Wang Tiantian. I don't know where he heard about this knowledge. He asks almost everything, whether it's astronomy, geography, mathematics, chemistry.

Children worship power. Knowledge is power. In their eyes, Zhang Yuan is the most knowledgeable person, and he is still the old captain. He has a gentle temper and can basically answer all the contents. You can even play with computers here, so there are always many children gathered at the observatory.

"This problem is too complicated!" Zhang Yuan laughed and it was too difficult to talk about infinity with children of this age.

After pondering for a while, he said, "do you think there are more points on the 1 cm line segment or more points on the 2 cm line segment?"

"Of course... There are more points on the 2 cm line segment! 2 cm is longer than 1 cm. Shouldn't there be more points on it! " The little fat man looked nervous. It's not a very simple problem

If you answer wrong, you'll lose face.

The surrounding students also thought that, however, there were several smart ones who tilted their heads and didn't speak.

Zhang Yuan said with a smile, "have you learned function once?"

"Of course I did."

"Then, the image of y = √ 3x can be drawn?"

This image is very simple. It is a straight line at an angle of 60 degrees from the x-axis.

Zhang Yuan intercepted 1 cm on the x-axis of the abscissa, and the corresponding oblique section was exactly 2 cm. He said with a smile: "according to this function image, the points on the abscissa correspond to the points on the oblique line one by one. From (0, 0) to (1, √ 3), it is exactly 2 cm. The coordinates of each X-axis can correspond to one by one. "

"You say there are more points on the 2 cm line segment. Where are the more points?"

"If we can't find it, we can only think that there are as many points on the 1 cm line segment as on the 2 cm line segment, right?"

The little fat man looked unconvinced to find those missing points, but he couldn't find them

In the end, they launched a mass offensive and set up fallacies, such as "whether the 0.9 cycle is equal to 1", but in the end, they can only be very unwilling to lose the battle.

"Can't find it, ha ha!"

Zhang Yuan gloated: "in fact, according to our theory, one-to-one correspondence is a very important means. There are as many points on a one centimeter line segment as on a two centimeter line segment; According to one method, there are as many points on a centimeter as on a piece of paper, that is, on a plane.

"Even one centimeter points are as many as points on such a large curved surface as the Kunlun Mountain spacecraft, and even points in the whole space... Even any point in high-dimensional space, which can be mapped one by one in some ways."

"That is, there are as many points on a one centimeter line segment as in the whole universe!"

"Ah?" Not only the little fat man, but also a large number of students behind him exclaimed.

They never thought that such a small section could be compared with the whole universe. Isn't it incredible?

Let these children show a surprised expression and sigh about the mystery of the universe, which has become a great pleasure for Zhang Yuan.

Zhang Yuan said with a smile, "but infinity can also be divided into size. The set of natural numbers is mathematically called alev 0, which is the smallest infinity."

"The smallest infinity?"

"The number of points on a line segment, that is, the infinite set formed by real numbers, is called alev 1."

"... all possible mathematical functions: the number of continuous and discontinuous functions is called alev 2."

"I see, and alev 3, alev 4, alev 5!" The little fat man shouted, as if he had found something full of power.

Students of this age are always so secondary 2. They have gained a little knowledge and can show off in front of their peers.

Zhang Yuan said with a smile: "yes, it can extend infinitely upward... However, it is difficult for you to find the specific meaning of higher dimension infinity in reality, which can only become a string of symbols on paper. Moreover, the difficulty in mathematics is whether there is an infinity whose number is greater than alev 0 and smaller than alev 1? This problem is called the continuum hypothesis. "

"Although the continuum hypothesis is a hypothesis, it can never be proved or denied. It has been there alone for nearly 4000 years and has not been solved yet."

"Why?" Wang Tiantian asked again, is the world too strange.

A problem has not been solved for 4000 years. He's a little excited

Zhang Yuan laughed again: "that's another story, called Godel's incomplete theorem! The history of mathematics is another magnificent process. There are many problems that cannot be solved in the world! "

……

Time passes day by day. As aging continues, the body is getting worse day by day.

Even on the journey to the observatory, he felt very tired, but he still insisted on working and answering questions for the children, which can be said to be the greatest pleasure after friends withered one by one.

On this day, the doctor who specially examined his body showed a very sorry look. She said very carefully: "old captain, your physical condition has reached the standard of entering the virtual world."

"I'll type a report for you, and your wife has reached the standard. At the end of this month, if you like... "

"So... Really live long enough." Zhang Yuan nodded and sighed, "there's nothing unwilling. Let me say goodbye to this era."

On August 29, 5812, Zhang Yuan, the first captain of the Kunlun Mountain fleet, was about to leave the world.

The salute lit up briefly in the starry sky and disappeared silently.

At present, 90% of the population is in hibernation and there is no need to wake up specially. The remaining 10% of the sober population all spontaneously carried out this farewell ceremony.

Many production activities in Kunlun Mountains have also stopped, and the school has a one-day holiday, and Zhang Yuan can afford such an honor.

"Do you have anything else to say?" Said the doctor.

Countless seeing off descendants are looking at him, expecting him to say something, or encouragement, or something else. There are some old people who are constantly wiping their tears. This time, he is not the last one to go.

"No, everyone is fine. Move on." Zhang Yuan smiled and said, "the future still depends on you."

Several staff members helped him up from the wheelchair and lay down.

The hibernation warehouse is like a soft Simmons. It's very comfortable to lie down. Zhang Yuan turns his head and looks around.

A former friend, colleague, is saying goodbye to him.

It seems that there are few.

This feeling is very subtle. Zhang Yuan is not afraid of death, but at this moment, he still has a feeling of breathlessness.

He suddenly remembered——

When he was very young, the moment he understood what death was about, he squatted in the corner and cried.

"Can I not die?" Zhang Yuan asked with tearful eyes.

"What does immortality mean?" His father Zhang Qiming replied.

"Just... Always alive."

"Oh, you mean... You want to live forever." Facing this problem, Zhang Qiming pondered for a long time and said solemnly, "I think it's better to die. People can't live forever. "

Young Zhang Yuan couldn't accept this answer for a moment, although many of his father's answers were inexplicable.

Zhang Qiming said, "I think you are likely to imagine that the time period of eternal life is too short. Immortality means infinity. One hundred years, ten thousand years, one hundred million years, or even ten billion years are no different from infinity and zero. "

"In the eyes of the real immortals, the universe may be hot and quiet in a second, that is, all the happiness you feel on earth has only existed for a very short time. Then comes the long, lonely time in the vast open universe. No material, no company. "

"Until waiting for the faint big bang in the quantum sea to restart a new era. But how long will it take? "

"Human beings may not be able to endure this loneliness, or their thinking form may become another species, or they may stop thinking... I think it's better to stop thinking and choose death." Zhang Qiming looked at the blue sky, touched Zhang Yuan's head and said solemnly.

Even the young Zhang Yuan didn't understand what his father was talking about

I don't know why, before leaving the world, Zhang Yuan thought of this dialogue.

Maybe, a dead hero is a good hero.

Just... How lonely

Among the flowers, Zhang Yuan vaguely heard bursts of crying. I don't know who is crying.

Confused, he soon lost consciousness.

……

One era ended and another began.

Human beings will not stop their steps. This great journey continues

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