On a hot summer afternoon, there are only a few dozen students sitting in the lecture hall that can accommodate hundreds of people. If it is a compulsory course such as advanced mathematics and English, or a professional course for graduate school entrance examination, it is by no means such a scene. In order to hear more clearly, get more points when you are admitted to graduate school, and even leave a good impression on your future mentors, those who look well-dressed and gentle and elegant will grab their seats with vigour, which will make even the small traders and vendors who are used to grabbing the territory of the vegetable market feel ashamed.

And now this kind of scene can only show one problem: this class is not a course for graduate school entrance examinations.

This is indeed the case. Not only is it not a graduate course, but it is not even a final exam course, it is just an elective course.

Of course, electives are also required to earn credits. However, comparatively speaking, it is too easy to mix up the credits of elective courses. As long as you save some face for the teacher, half of the students can usually come to the class, and the teacher will not get along with the students. In the end, the teacher collected the lecture fee, and the students got the credits, and everyone was happy.

Electives and electives are not the same, though. Some popular electives, such as Japanese, are also going to be squeezed. At the moment, this door is obviously the unpopular among the unpopular. On the podium, an old professor with gray hair was reading from the book unhurriedly. The students opposite him were more colorful: some were reading other books, some were playing with their mobile phones, some were dozing with their heads buried in books, and some were flirtatious.

The name of this course is: Quantum Mechanics.

Sometimes college is just that's a spoof. Elective courses were supposed to be free for students to choose. But there are some courses that no one chooses, so what should I do, the teacher will not be able to collect the lecture fee. Therefore, it is necessary to divide the quota, and there must be n students in each major to take M major. The result of this is just like now, dozens of people studying finance, accounting, and physical education are facing a professor who teaches quantum mechanics. Then in addition to being in a daze, it is understandable to do some underground work.

The old professor didn't seem to care about playing the piano to the cow, and he enjoyed the lecture very much. Today, however, the students seem to have gone too far, and there are so few of them that they are less than a quarter. Looking at these lawless guys, the old professor smiled slightly and raised his voice a little: "The students who didn't come today are afraid that they will regret it." ”

As soon as these words came out, everyone in the classroom couldn't help but shiver: It's not good, name it!

If you don't name names, the consequences are quite serious. If you usually take a roll call in class and your final exam score is a little worse, the teacher will usually give you a boost, and the reason is very simple: usually take a few more classes, give the teacher face, and the teacher will give you face. But if the roll call doesn't arrive, it will become a key object of care, and if you don't pass the exam, you will have to pay for it again.

For such a major matter, the students did not dare to take it lightly. Anyone who skips class has already said hello to his buddies or sisters in the same dormitory: "Help me say yes when you call me!" ”

But today's situation is special, there are too few people coming, and it can't be a person who shouts seven or eight times, which is too fake.

Just when everyone was nervous, the old professor smiled with satisfaction: "Don't be nervous, everyone, I'm not naming names." I mean, the topic that we're going to talk about next is very interesting. It's not just fun, it's also fun. Not only is it fashionable, but it is also very high-end, and I have never told them about my doctoral students. This high-end is not to say how difficult it is, on the contrary, for students with understanding, it is as simple as drinking a glass of boiled water. Therefore, if any student can understand, I will consider recommending him to study for a master's degree and a doctorate. Students who didn't come to class had to miss it, but it's a pity, it's a pity. ”

The old professor's words have whetted the appetite of most people. Of course, there are also a few dead pigs who are not afraid of boiling water and muttered: "Brother, it's good to graduate with this grade, it doesn't matter if you're interesting or not, whether it's high-end or not." It's better to sleep for a while, and have to work on the dungeon all night. ”

The old professor seemed to see the disdain of these people, but he still said quite confidently: "Today, let's discuss the crossing. ”

At this moment, even those two hundred and five were in good spirits. These are all fans of time-traveling novels, don't look at the class and get sleepy as soon as you pick up the textbook, and watch "Xun Qin" with candles lit when the lights go out in the middle of the night, and one of them doesn't even know that his hair is burning.

Seeing that the atmosphere in the classroom was lively and the goal was achieved, the old professor couldn't help but feel secretly proud in his heart, and continued to say: "It's very popular to travel novels and TV series now, right?" So let me ask you a question first: what is crossing? ”

A big brother who usually never raised his hand jumped up on the ground and shouted: "Traveling through time and space is time travel, returning to the past from the present!" ”

The old professor smiled with satisfaction and motioned for the overexcited buddy to sit down: "Very good." So, I now ask the second question: how to cross? ”

There was no movement in the classroom. After a while, the benevolent brother stood up: "Teacher, do you really believe that you can cross over?" ”

The classroom burst into laughter. The old professor didn't laugh, but said seriously: "Yes, I believe that I can really cross over." And I'm already planning to devote all the rest of my life to researching time-traveling. ”

The classroom was silent again. Without waiting for everyone to come back to their senses from their surprise, the old professor turned around and drew two dots on the blackboard, and continued to ask, "Please tell me, what is the shortest distance between these two dots?" ”

Everyone didn't understand how the old professor could suddenly shift the topic from time travel to plane geometry. After a while, a girl timidly said, "The distance between two points is the shortest." ”

The old professor shook his head: "You're not entirely right. Why? Because you think these two dots are on this board. So if I tell you now that this is not a blackboard, but a piece of paper, would the result be different? ”

The girl frowned and thought for a while, shook her head and said, "Teacher, does this have anything to do with whether it's a blackboard or paper?" The distance hasn't changed! ”

The old professor sighed and said, "It seems that the students' thinking is a bit rigid. There is a big difference between a blackboard and a paper. The chalkboard is hard and the paper is soft. ”

At this time, the boy who jumped up just now seemed to suddenly realize: "I understand, teacher!" If these two dots are on a soft piece of paper, then I can fold the paper in half and the two dots will be directly next to each other! ”

The old professor was as if he had discovered a bosom friend, and suddenly became excited: "You said it so well! The definition of crossing you just mentioned is not perfect. Let me talk about my definition of time travel: using the distortion of time and space to jump from one space-time node to another, this is called time-travel. The two points I just gave are the simplest kind of crossing. Of course, both blackboards and paper are flat and two-dimensional. If three-dimensional space can also be distorted, then we can teleport. Theoretically, as long as we can distort space reasonably, we can reach any part of the universe in an instant! ”

Without waiting for everyone to react, the old professor continued: "Let us continue to expand our thinking, from three dimensions to four dimensions. What is the fourth dimension? ”

At this time, some students woke up like a dream: "It's time!" ”

The old professor nodded with satisfaction: "That's right, it's time!" You may have the feeling that time is forever moving forward, like a ray or an axis. Now I ask you to imagine: the timeline can be distorted under certain conditions, like a piece of paper. Then, when this axis is bent to a certain extent, we can go back to a certain point in time. ”

A big brother who listened like an idiot couldn't help but ask, "So how can we make space and time warp?" ”

The old professor said: "That's a good question, this is also the core question of crossing: how to cross? Actually, it's very simple to twist something and give it enough force. It's the same with distorting space and time, when a force is strong enough to distort space-time. In a distorted space-time, a 'bridge' will suddenly appear or persist to allow us to take a shortcut from one point of time and space to another. The scientific community calls this 'bridge' a 'wormhole'. Regarding space-time distortion and wormholes, this is also the essence of quantum mechanics, which we will talk about in the next class, and we will leave the class now. ”

Only then did everyone realize that it was time to get out of class unconsciously, and they couldn't help but sigh: it turned out that a seemingly boring course could make students who couldn't play the professional eight poles listen to it with relish, which is the charm of quantum mechanics.

As everyone got up and left the lecture hall, only one of the aliens was still sitting upright, looking thoughtful. The old professor saw it in his eyes and thought in his heart: "What is he thinking?" Maybe he had something in mind? Is this a manufacturable material? ”

So he didn't alarm the classmate, and quietly approached his seat and looked carefully.

It didn't matter if I looked at it, I almost didn't make the old professor angry.

Dare to love this benevolent brother has a bit of Zhang Fei Zhang Yide's ability, and he actually fell asleep with his eyes open, and the little snoring at the moment is beautiful!

The old professor was excited in vain, and after recognizing the true face of this product, he couldn't help but be furious, and slammed the table: "Wake up, wake me up!" Did you come to sleep in class? ”

This benevolent brother reacted quite quickly, and immediately jumped up like a spring and shouted: "Here! ”

The old professor really crooked his nose: "Do you think I've been calling names?" Well, what's your name! ”

Only then did the sleeping god come to his senses and figure out the situation. In the laughter of everyone, he suddenly looked like a punctured balloon, shorter by more than three points, and it took a long time to burst out a few words: "I... I... It's called You Jian..."