Zhang Yang

After the lightning and thunder, the rain outside the window eased considerably.

The fluorescent lights steadied and stopped flickering.

The hundreds of Rhine Cat eyes reflecting the lightning softened as well, as if the terror of a moment ago had been nothing but a joke.

"Hey, hey."

Qin Feng was the first to break the silence:

"You're kind of scaring yourself here, aren't you? It's good to be cautious, but there's really no need to take it too far."

"If you're afraid after every step you take, you'll never make any progress."

"Come to think of it, this is just like those mysterious numbers from before. It's all baseless delusion, even bordering on paranoia."

Jiang Ran smiled.

"I didn't say it was definitely the case. It was just a guess."

"And the only reason I have so many concerns is that we can't find answers to these two questions in front of us, right?"

Sigh.

Questions that couldn't be proven or disproven were the most irritating. Jiang Ran was torn and couldn't make up his mind.

Cheng Mengxue looked from one of them to the other.

She cautiously raised her hand.

"Um..."

The two looked over. Cheng Mengxue pointed at the blackboard with her index finger.

"Since Teacher Zhang Yang has discussed Worldline Theory in class, and we first heard the term Worldline Jump from him..."

"[Why don't we ask Teacher Zhang Yang about these two questions?]"

Jiang Ran blinked.

Then he looked back at the blackboard.

Worldline Jump...

His gaze settled on the term.

It was true. He hadn't come up with it himself. Teacher Zhang Yang had used it in a general education class called Parallel Worlds and Worldline Theory.

He'd simply felt that the term described his situation perfectly, so he'd used it when explaining the problem to Cheng Mengxue.

Teacher Zhang Yang was well-known at the university.

Not because he was particularly outstanding himself, but because his teacher was renowned. The old academician was one of the most experienced and capable members of the Dragon Country Academy of Sciences.

As the old academician's last graduate student, Teacher Zhang Yang had returned to his alma mater, Donghai University, after earning his doctorate. He'd only become a graduate advisor this year.

Come to think of it, Teacher Zhang Yang had been in contact with some of the top minds in physics. He probably knew a lot about cutting-edge theories that hadn't been made public yet.

Cheng Mengxue was right.

Since they were completely at a loss, they might as well ask Teacher Zhang Yang, who was more knowledgeable, experienced, and qualified than they were.

"Little Xue has a point."

Jiang Ran stood up.

"The problems we're dealing with happen to align with Teacher Zhang Yang's field of research."

"He discussed the concept of [Worldline Jump] in class. It's only a theoretical hypothesis, but since we can't find answers ourselves, we might as well hear his thoughts. We might even make an unexpected discovery."

"Of course, we still have to keep this confidential. We can't tell him about the Spacetime Bulletin, the Positron Cannon, or our experiments. We'll only ask hypothetical questions about what he covered in class."

Qin Feng agreed.

"Teacher Zhang Yang is highly accomplished, and he studied under an academician from the Dragon Country Academy of Sciences. He might really have some insights."

"Then it's settled."

Jiang Ran opened his phone and checked his timetable.

"Teacher Zhang Yang doesn't have a general education class tomorrow, but he does have a specialized course in the School of Physics. We can catch him after class and ask him then."

The next day.

The three of them arrived early at the School of Physics building to wait.

After Teacher Zhang Yang's specialized course ended and the students had trickled out, the three approached the podium and explained why they'd come.

"Oh, heh heh heh."

Teacher Zhang Yang smiled as he unscrewed his thermos.

"I'm so glad you came to see me. I've always thought the students in my general education classes were only there to earn credits. Not many pay attention... And plenty of them treat my class like a science fiction novel."

"I never expected there'd actually be students who listened and thought about what I said. That's wonderful, just wonderful. I'm truly glad to see the three of you. So, what would you like to ask? I don't have another class after this, so we can have a good chat right here."

Just as Qin Feng had said, Teacher Zhang Yang was a kind person.

Cheng Mengxue raised her hand first.

"Teacher Zhang, we're very interested in the concept of [Worldline Jump] that you discussed before. There are also some things we don't understand."

"Oh? What don't you understand?"

"It's about the process of the jump—that is, what happens at the moment the worldline changes... We don't quite understand it."

Cheng Mengxue proceeded step by step, rather than jumping straight to the point.

"Oh, I see. That is a little complicated."

Zhang Yang took a sip of tea and screwed the lid back onto his thermos.

"After all, I teach you a general education class, not a specialized course, so I didn't go into it in much depth. Since you're so interested, I'll explain it again."

He picked up a piece of chalk and drew a straight line on the blackboard. Then he split the end of the line into two branches, one above the other, and extended them into two parallel lines.

"To make this easier to understand, I'll use my own life as an example."

Teacher Zhang Yang pointed to the first line.

"This line represents my life from birth to age eighteen. When I was eighteen, I failed the university entrance exam for the first time. At that point, I had two choices in life."

"The first choice was to repeat my final year of high school and take the exam again. I passed the following year and got into Donghai University. Then I went to the Dragon Country Academy of Sciences to earn my doctorate, returned to my alma mater to teach, and became your teacher."

As he spoke, he traced his finger along the branch in the line, then followed the upper branch.

"That was the path I chose back then. It's the life I have now. So we can call this worldline the A worldline."

Jiang Ran and the others nodded.

The concept wasn't hard to understand, especially since they'd discussed it countless times among themselves.

"But when I failed the entrance exam at eighteen, I had another choice."

Teacher Zhang Yang moved his finger back to the branch point.

"I could have decided not to repeat the year and gone straight into the workforce, or headed south to find a job."

"I might even have seized the internet boom in those years and become the head of a publicly traded company, an internet mogul, or a financial tycoon or something."

Cheng Mengxue laughed at Zhang Yang's joke.

But anything was possible. Who could predict what would have happened if he'd taken the path he hadn't chosen? What kind of life would it have led to?

This time, Teacher Zhang Yang didn't trace his finger up the branch. Instead, he followed the lower parallel line.

"So the worldline I didn't choose—the one where I didn't become your teacher but instead became the head of a publicly traded company—would be called the B worldline... You understand that, right?"

The three nodded again.

Having experienced several worldline changes, they could naturally understand that different choices would lead to different branching worldlines.

"But..."

Teacher Zhang Yang changed his tone.

"[These two worldlines cannot exist at the same time.]"

"[Or rather, no two worldlines can exist at the same time. Our world can only run along a single worldline.]"

His tone grew more emphatic.

"It's like the thought experiment Schrödinger's Cat. The cat in the box is either dead or alive. It absolutely cannot be 'both dead and alive,' or in some ridiculous 'superposition of being dead and alive.'"

Schrödinger's Cat.

It was a widely known thought experiment.

In the 1930s, the Copenhagen school, led by Niels Bohr, proposed the idea of "quantum superposition." In other words, a quantum could be in multiple places or states [at the same time].

Einstein and Schrödinger considered this view absurd.

Einstein once wrote to Schrödinger, pointing out that the state of an unstable barrel of gunpowder being both exploded and unexploded at once was ridiculous.

Schrödinger agreed.

To further illustrate how absurd it was, he proposed the famous thought experiment, Schrödinger's Cat—

A cat, a bottle of poison, and a radioactive source were sealed inside a box.

Whether the poison was released—and thus whether the cat lived or died—depended on the state of the radioactive atom.

So, according to the Copenhagen interpretation of quantum mechanics, before someone opened the box to observe the cat, it was in a superposition of being alive and dead.

That was obviously ridiculous.

Even if the box wasn't opened, the cat inside could only be dead or alive. It couldn't be both dead and alive.

Just as Teacher Zhang Yang had explained, he couldn't choose both to repeat his final year and not to repeat it, nor could he be on two worldlines at once.

But...

The truly ridiculous part was still to come.

Schrödinger's Schrödinger's Cat experiment had originally been intended as a criticism, even a mockery, of the Copenhagen school.

But as it turned out...

Because the experiment was easy to understand and spread widely, this seemingly self-contradictory experiment had become part of the basic framework of modern quantum mechanics.

Schrödinger himself might have been speechless and helpless if he'd seen how things had turned out.

"Now, here's the important part."

Teacher Zhang Yang tapped the blackboard.

"Since different worldlines can't exist at the same time, for us, currently on the A worldline, to jump to the B worldline, we'd have to use some unconventional method."

He smiled slightly and looked from one of them to the next.

"Now, the three of you, think about this—"

"What kind of action could cause a worldline to change?"

"What would make our world jump from the A worldline... to the B worldline?"