A little girl in her early twenties, her grandfather is a university professor, her father went to Silicon Valley to start a company, her family environment is superior, and she goes to a prestigious university, such a little girl is somewhat domineering. Everyone else said so, and Yu Shan felt that it was a little bad for him not to say it again.

So he organized the language and said, "Well, I'm a science fiction lover myself, I've read a lot, and I've recently conceived a story. ”

"Yo, great writer! Eh, what do you write about science fiction? ”

"No, this hasn't been written yet, it's still being conceived. This story is about time travel......"

Before Yushan finished speaking, the little girl was happy: "Ah, talking about crossing, I like crossing the most." Eh, did you write about the Qing Dynasty or the Tang Dynasty? If it was the Qing Dynasty, you would have written the fourth elder brother away, the most annoying fourth, I am the eighth master. ”

Yu Shan blinked...... It's all a mess. After carefully thinking about the little girl's words for a long time, Yu Shan suddenly couldn't cry or laugh, feeling that this girl was still a lover of clean clothes.

"Well, it's not the Qing Dynasty or the Tang Dynasty."

The little girl frowned: "That's the Republic of China?" Tsk, the Republic of China is boring, and most of the beautiful men who can be counted are traitors. ”

Hey, this sour and refreshing directly made Yu Shan speechless.

"Huh? What are you glaring at me for, do you continue? ”

I say...... What else am I talking about?

Yu Shan endured his tiredness, said that his encounter was a novel, and replaced the characters with symbolic pronouns. When he finished speaking, the little girl waited a few seconds and said, "Finished?" What kind of story is this without a beginning or an end? What are you trying to express? ”

"I'm only halfway through the idea, and now there's a problem." Yu Shan said angrily: "Didn't you find a problem with the logic of the space-time gate?" ”

"Oh, oh." The little girl finally remembered that she had to solve the problem by herself. She thought about it, found a pen and paper to list a few of Yu Shan's questions, and began to think.

After thinking about it for a long time, the little girl's eyes lit up and said, "I thought of it...... Hey, when you're innovative, it's still a stalk that people use. "While talking, I picked up a brush and brushed a notebook and drew more than a dozen strokes." Uncle, do you know what it means to be bound by the world line? ”

"What is the world line?"

"The world line is closed." The little girl turned the book upside down, pointed to the graffiti on the notebook and said, "There is a cartoon called the Gate of the Stone of Destiny...... Well, you haven't seen it. Let me tell you this, the so-called world line closure is the setting of this cartoon. To put it simply, there is only one world, but there are countless possibilities in the world, do you know this? ”

Yu Shan shook his head: "I don't understand." ”

"What stupid!" The little girl pointed to the graffiti and said, "Look, this is the model of the world line constriction." It is inevitable to go from the vertex to the end, but there can be an infinite number of paths from the vertex to the end. ”

"Still don't get it, like?"

"I think about it...... Let's just talk about your dog-stepping, theory. Let's say you used to go out in the morning, and an hour later, now you step on a dog or while shopping. At this time, you travel back in time and space back to when you went out in the morning. Because you know that walking will step on dogs and, so you take the bus, and when you get off the bus, you step on the dog and again. And then you shuttle countless times, and every time, no matter what mode of travel you choose, you will end up stepping on dogs, dogs, and. The cause is predestined, the result is predestined, but the process can be infinite. Got it? ”

Yu Shan said: "I kind of understand...... You're a typical causalism. Huh? No, what does that have to do with the story I just told? As mentioned in the story, the world changes dramatically every time the protagonist comes back. ”

The little girl blinked and said, "Why is it okay?" Every time the protagonist looks back, his friend is either dead or suddenly disappears, which is the doomed result. ”

"Huh?"

The little girl thought for a moment and said: "I don't know if the protagonist's friend is the Great Demon King, and his existence will affect the law of cause and effect, so the world has wiped him out." ”

What is this? Yu Shan felt that if he continued to talk to the little girl, he would definitely take himself into the ditch. So he shook his head with a wry smile, intending to end the topic.

At this moment, the front door opened, and Professor Zhang, dressed in sportswear, pushed the door in. As soon as he entered the door, Professor Zhang greeted first: "Xiaoyu is here?" Waiting, aren't you? I'm used to this, and I have to do tai chi for a while at this point every day, and I feel uncomfortable when I don't move. ”

Yu Shan, who had already gotten up, hurriedly said, "I just arrived, so I'm bothering you." ”

Professor Zhang waved his hand and said to the little girl with a stiff face: "Jinxuan, I heard you shout about dogs and from afar, why does the girl's family talk so vulgarly?" ”

Zhang Jinxuan pouted and said aggrievedly: "Grandpa, why are you as indiscriminately wronged as my father?" I missed a day of class and came back to accompany you. ”

Professor Zhang pointed to the little girl's nose and said, "Are you embarrassed to say it?" I came back on Friday until now, and if I don't catch you up, won't you leave tonight? ”

"That can't be, there is Ma Zhe tomorrow morning, and the old lady is not easy to talk."

Professor Zhang began to blow her beard and stare at her, and the little girl playfully stuck out her tongue, winked at Yu Shan, and ran upstairs with a smoke: "I'll go upstairs and pack my things." ”

As soon as the person left, Professor Zhang's face immediately turned warm, and he said, "This girl!" Only then did he sit on the side of Yu Shan. The old professor copied the graffiti notebook and frowned: "What kind of ghost is this?" ”

"Oh, that's what your granddaughter described to me...... Forehead...... Worldline closure model. ”

"What model?"

Yes, Yu Shan is now learning and selling, and told Professor Zhang the worldline tightening model that the little girl just talked about. After that, I talked about the set of my own stupid little girl.

After hearing this, Professor Zhang nodded and said, "Xiaoyu, what do you want to ask?" Is it intended that the novel you conceive is logically self-consistent, or is it ......"

Yu Shan said: "In addition to logical self-consistency, I also want to know whether there is a realistic theoretical basis for this setting. ”

Professor Zhang smiled: "Xiaoyu, this is difficult for me." Time travel, even Hawking didn't understand whether it could be realized, do you think I, a retired professor, could figure it out? After a pause, he added: "But if you want to consider the logic and self-consistency, I can help the staff officers." ”

While speaking, Professor Zhang picked up the pen on the coffee table, turned a page in the notebook, and drew a tree root with a brush. One backbone, countless branches. Yu Shanxin said, sure enough, it is an ancestor and grandson, and this painting skill is definitely passed down from generation to generation.

"This is a model I drew based on your description. The past is certain, and the future is endless. The main reason for the uncertainties in the future is the protagonist's impact on the past. In your story, the first four time you traveled through time and space all fit this model. ”

Yu Shan hurriedly nodded and said, "That's right, it changed the fifth time." ”

"Well, you're trying to explain the new changes with quantum theory, and in doing so, you're overturning the model that you built in the first four times. Because according to quantum theory, there are too many choices in this world at any moment, and maybe after the first shuttle back, the third world war broke out. ”

Professor Zhang laughed, and Yu Shan also smiled bitterly.

"So, I think you should reimagine it and unify the fifth shuttle with the previous ones."

"Professor," Yu Shan interjected, "that's exactly what I've come to you for, for the fifth time...... It's a good story and can't be given up. ”

"That's right...... That's going to be hard. The old professor asked curiously, "Is it necessary for you to be so rigorous in writing a novel?" ”

Yu Shan felt a little embarrassed to be taught by others, so he had to say to himself: "I'm a little bit obsessive-compulsive. ”

"Let me think about it...... Since it cannot be abandoned, it is necessary to maintain the unity of the model. You can start with the butterfly effect, where the protagonist has an impact on the past that will surely carry over into the future. Some of these influences are uncontrollable, anyway, you're writing a novel, isn't it self-consistent for you to start here and improve the logic? ”

Yu Shan nodded first, and then began to ponder on his own. The chaotic memory caused him to not believe his memory, and he could only rely on objective evidence to trace everything that had happened on this timeline. According to Sun Qiang's description, he embarked on the road of business because of Qiao Si. So who is Joss influenced by, and who is he affected by in turn?

He was pondering it, and Professor Zhang said again: "Solve this problem, let's talk about other questions." Xiaoyu, according to the idea you described, after each shuttle, the protagonist will jump from a timeline to a new timeline. And the jump is through a space-time gate, right? I think you can start with the space-time gate to explain the disappearance of the protagonist's friend. ”

"How?"

"Can it be explained that everyone who passes through the space-time gate will be marked by the space-time gate? And then, whether he travels through the space-time gate or not, will he jump to a new timeline? You see, that's pretty well explained. The hero's friend died in the past in the original time and space, and the result can no longer be changed. Therefore, after the jump, the hero's friends will disappear out of thin air. ”

"Is that okay?" Yu Shan's eyes widened.

The old professor spread his hands, his face full of embarrassment: "I, an old man, have a limited imagination, and there is only so much I can think of." ”

Looking at the embarrassed look of the old professor, what else could Yu Shan say besides thanks? He felt a little impulsive about his trip. First of all, Professor Zhang, who is engaged in theoretical physics, will definitely not believe that his story is true. It's like asking an atheist to tell a ghost story, no matter how wonderful the story is, you must be tired of telling it.

With resistance, can you still expect people to use existing theories to think and describe the phenomena in the story?

It can't be said that this visit was fruitless, on the contrary, Yu Shan had a lot of thoughts in his mind. He wanted to go to the cemetery and see if Joss's grave had changed; I want to find out what Xu Hui, Yang Rui, and Ding Dakan have become in the new timeline; I want to look up Joss and find out what changed Joss.

In the mess of thoughts, a lot of thoughts came to him, thoughts about the gate of yesterday.