Breakthrough

"..."

Faced with Zhang Yang's question, the three fell silent for a moment.

They looked at one another, unsure how to answer.

They couldn't exactly say "Positron Cannon" and "Spacetime Bulletin," could they?

That would be ridiculous.

They'd be giving away their secret.

"Time travel."

Jiang Ran answered first:

"Aren't there lots of movies and science fiction novels these days that invent time machines, letting people go back to the past?"

"Once you return to the past and change history, the course of subsequent events changes along with it, leading to a worldline that develops differently."

"To use your example, Professor Zhang, suppose you're unhappy with your life as a teacher today, so you take a time machine back to the past—to the moment you failed your college entrance exams at eighteen."

"Then you tell your eighteen-year-old self that retaking the exams and going to college is a dead end, and that the internet boom is just around the corner, so you should head south and go into business."

"Your eighteen-year-old self takes your advice, doesn't retake the exams, and heads straight to Guangzhou. At that moment, the worldline jumps from A worldline to B worldline... The entire course of history, from when you were eighteen up to the present, changes."

"You wouldn't be teaching at Donghai University anymore, and we wouldn't be your students. But maybe you'd have become a household-name internet tycoon—or even the richest man in Longguo."

Jiang Ran's reasonable hypothetical earned an approving look from Zhang Yang.

He patted Jiang Ran on the shoulder.

"Young man, which college are you from? What's your name?"

"Professor Zhang, I'm Jiang Ran, from the College of Computer Science."

"Very good."

Zhang Yang's voice brimmed with approval.

"I'll have to give you a high score in my general education class. You've been paying close attention."

"Thank you, Professor." Jiang Ran smiled.

Zhang Yang picked up the chalk again and looked at Cheng Mengxue and Qin Feng.

"Jiang Ran's absolutely right. As long as you change a choice at some point in the past, you can change established history and the worldline, making it jump."

"In fact, you don't even need to change the [past]. Different choices made at [the present] can also lead the [future] down different worldlines."

"For example, when you graduate with your bachelor's degree, will you go on to graduate school and earn a doctorate? Get a job at a big company? Or take the civil service exam?"

"Each different choice will lead your life down a different worldline."

With the chalk, he drew four or five more parallel lines branching off the line representing A worldline, each one standing for an infinite possibility for the future.

"But... no matter what you choose or what kind of future you head toward, don't romanticize the paths you didn't take."

Professor Zhang gazed at the branching lines and smiled wistfully.

"Every choice, every life, comes with both success and regret. What matters most is cherishing the present and walking the road beneath your feet."

Seeing that the time was right, Cheng Mengxue gave Jiang Ran a look. He nodded.

It was time to bring up the biggest question of the day—the one they cared about most.

"Um, Professor Zhang."

Cheng Mengxue raised her hand again.

"There's something I've been wondering about..."

"[Once a worldline jumps, is it possible for us to retain our memories of the original history, the original worldline?]"

"Like in your example just now: if you changed your choice the year you failed the exams at eighteen and went south to do business, would the future version of you, sitting in the CEO's office of a listed company, still remember teaching at Donghai University?"

Jiang Ran and Qin Feng exchanged a discreet glance.

That was right.

This was the point of today's visit.

This was what they most wanted to know.

They said nothing, waiting for Professor Zhang's answer.

"[Impossible]."

Professor Zhang answered without hesitation.

Cheng Mengxue froze.

"Impossible?"

Professor Zhang nodded.

"Impossible."

His tone was firm, leaving no room for doubt.

"[After a worldline changes and jumps, even if a person's life is completely transformed and the world itself has changed beyond recognition, it's absolutely impossible for anyone to retain memories of the original worldline.]"

"Why?" Jiang Ran asked.

"It's not hard to understand."

Zhang Yang set down the chalk and picked up the eraser, pointing at the branching lines on the blackboard.

"As I said, A worldline and B worldline can't exist at the same time. So no matter what method you use to make a worldline jump, our history and past can only unfold along one of them."

"So... suppose we jump from A worldline to B worldline. Do you think A worldline disappears?"

Zhang Yang looked at the three of them.

They thought about it briefly, then nodded.

"Wrong!"

Zhang Yang emphatically corrected them.

"A worldline doesn't disappear. It never existed in the first place! It never existed from the very beginning!"

He wiped away A worldline with the eraser and explained:

"If I'd chosen to go south and do business after failing my exams at eighteen, I would've followed B worldline. The events that should have happened on A worldline would never have happened. They wouldn't have existed from the start."

"[So how could history that never existed, a worldline that never existed, or events that never happened... possibly exist in someone's memories?]"

Jiang Ran and the others fell silent.

They had no answer.

How could they argue with that?

Professor Zhang's explanation was logical and well-reasoned. It was airtight.

But...

Jiang Ran was an "exception," a "bug." What could anyone possibly say about that?

Still.

Since Professor Zhang was so certain, the three of them felt somewhat relieved.

If everyone in the world was normal, if nobody had a special constitution like Jiang Ran's or memories from before a worldline changed... then their current situation was safe after all.

Ding-dong, ding-dong.

Two WeChat notification chimes rang from the phone on the lectern.

Zhang Yang glanced at the screen and saw a WeChat message from a teacher in the faculty office.

He set down the eraser and dusted off his hands.

"Think about it for a moment. I'll reply to a message."

With that, he picked up his phone. Without hiding it, he replied right in front of the three of them.

It was a WeChat message from Professor Meng in the faculty office:

[Professor Zhang, do you still need the new lesson-plan books? I can ask a student to bring a few over to you.]

He opened the chat and started typing.

Professor Zhang's keyboard was different from Jiang Ran and the others'. He used a nine-key keypad.

People born in the 2000s like Jiang Ran, Cheng Mengxue, and Qin Feng all used full keyboards to type on their phones.

They'd grown up using large-screen smartphones and had never used button phones, so they'd never even encountered a nine-key keypad.

Early button phones, led by Nokia, used the number pad to type because of technological limitations.

Each number key from one to nine corresponded to three or four English letters. To type, you had to press a combination of number keys in sequence.

Since each number key corresponded to multiple letters, typing wasn't very accurate. You often had to select each character individually, which was inconvenient.

But input methods had since grown much smarter, and the accuracy of nine-key typing had gradually improved. These days, people rarely needed to select characters; the input method automatically arranged suggestions based on context.

Going by the people around them, most people who still stuck with nine-key input were born in the '80s or '90s, while young people born in the 2000s or 2010s almost all used full keyboards.

As someone who'd grown up with button phones, Professor Zhang's thumb flew across the nine-key pad, typing by muscle memory as if he were touch-typing. He pressed several number keys—

28...926...

!

The numbers etched in his mind triggered something. Jiang Ran held his breath.

28926...

What a familiar string of numbers!

Those were the first few digits of that mysterious message!

Professor Zhang's thumb kept moving, pressing two more keys, 53. Three Chinese characters, "no longer needed", immediately appeared in the suggestion bar.

Then he quickly pressed 943943, and two more characters, "thank you", appeared in the suggestion bar.

He pressed send.

The five characters, "no longer needed thank you", were sent at once.

Jiang Ran's heart raced.

He looked up at Qin Feng and Cheng Mengxue.

The other two had the same look of shock and delight in their eyes.

A nine-key keypad...

Who would've thought?

The mysterious string of numbers was encoded using nine-key input!

Since the first five digits, 28926, stood for the two characters "no longer"... What on earth did the remaining 9426494642 mean?

They just had to try it and see!

"Professor Zhang, we have to go!"

Jiang Ran turned and ran.

"Eh? What?"

Zhang Yang looked bewildered.

"Have you figured it all out? I can explain a bit more."

"Thank you, Professor Zhang!"

Jiang Ran nodded gratefully.

"We have another class coming up, but we'll come ask you more questions later!"

Trying to contain their excitement, the three rushed out of the classroom and headed to the flower bed outside.

"How did we not think of the nine-key keypad?"

"Can't see the forest for the trees!"

"I've never used nine-key input!"

They were full of regret.

But it really wasn't their fault.

For people their age, nine-key input was a genuine blind spot.

"Quick, try it!"

Cheng Mengxue urged.

Jiang Ran nodded and pulled out his phone.

289269426494642.

At last, they'd found the answer to the string of garbled numbers that had tormented him and lingered in his mind for so long.

He switched his phone's keyboard to nine-key input, then pressed the numbers in order:

Don't... believe... it...

As he pressed each number, the corresponding Chinese characters assembled from the pinyin and appeared in turn.

When he pressed the final number on the nine-key pad,

The three stared wide-eyed

At the sentence assembled in the input field—

[Don't believe it]