Chapter 84
I continued smoothly spinning out stories about the mathematics woven into every corner of everyday life.
Click-. Click-.
Mathematics used in the natural sciences.
Financial mathematics for reading the flow of money.
The mathematics inside algorithms and programming, the backbone of the IT age.
And even the mathematics behind future technologies like artificial intelligence, blockchain, and quantum computing.
I tailored the content to be interesting while keeping it exactly at a high-school level.
The unnis and oppas listened to my talk with rapt interest.
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About an hour later.
After explaining everything so enthusiastically, my mouth had gone bone-dry.
I popped open a plastic bottle and gulped down the water.
“Phew… Tasty.”
I paused to catch my breath.
Before I knew it, it was time to wrap up the lecture.
“Unnis and oppas. So far, I’ve only talked about mathematics you can actually use in real life, right? But actually… there are lots of even more fun things you can enjoy only in pure mathematics!”
I raised my voice excitedly.
After all, this was my field of study, so I couldn’t help getting excited.
“For example… Oh, right! Let me tell you about the Riemann zeta function, which you could call my specialty… If you plug in negative one or zero, you get this!”
Click-.
I moved to the next screen.
A strange formula appeared on the screen.
[ ζ(-1) : 1 + 2 + 3 + 4 + … = -1/12 ]
[ ζ(0) : 1 + 1 + 1 + 1 + … = -1/2 ]
The formulas were truly bizarre.
If you kept adding the natural numbers in order, the result became negative one-twelfth?
Not only that, but even if you kept adding 1 forever, it somehow became negative one-half?
They were equations that implied results completely opposite to our intuition.
— …?
The moment.
The expressions on the faces of the unnis and oppas who saw those strange formulas all froze into blank stares.
Uh-oh!
Only then did I realize I had made a mistake.
I had gotten so excited that I’d blurted out the conclusion without any proper buildup.
“Oh, no! I’m not messing with you!”
I hurriedly waved both hands and continued, as if making excuses.
“Normally, that series really does diverge to infinity! But if you look at it from the perspective of a function’s analytic continuation, these are the exact values you get. So just think of it as, ‘Aha, if we assume a particular situation, we get negative one-twelfth!’”
— …?
“Of course, if I only put it that way, it might make us mathematicians look like people who scribble ridiculous nonsense on paper for fun.”
Heads nodded here and there.
So what the heck is this supposed to mean…?
Even if it’s true in some special situation, what the hell is the point of such a bizarre result…?
That was the expression on every face.
“Please, hear me out. I didn’t write this down arbitrarily—it’s a value derived with rigorous logic! In fact, in the field of physics called quantum field theory, this [1 + 2 + 3 + 4 + … = -1/12] value actually pops up and gets used for real…!”
— Holy crap…
— Really?
A few of the unnis and oppas murmured with skeptical expressions.
If I’d had my way, I would have derived the analytic continuation of the Riemann zeta function right here and proved the formula’s validity, but…
If I did that to high school students, I’d inflict brain damage on them like I’d hit them with Unlimited Void.
Hold it, hold it. Yoo A-yeon.
This isn’t a gathering of mathematicians!
“Anyway! I absolutely didn’t bring this up to give you unnis and oppas a headache!”
I clasped both hands in front of my chest and said emphatically.
“Even if you can’t use it in an actual industry… pure mathematics is packed with things this fascinating and fun all on its own! That’s what I wanted to tell you…!”
I slowly looked around the auditorium.
Then I cleared my throat once or twice.
“Ahem, so. If you think practical mathematics that can be used in industry is fun, then you can go to engineering school or choose a major like statistics or economics.”
I smiled brightly.
“But if you think mathematics developed purely through logic is fun, then you can come to the mathematics department…!”
Then I puffed out my chest and shouted confidently.
“Because, you see, I’m going to become a professor in Seoul National University’s Department of Mathematical Sciences next year…! I’d be so happy to meet you then. So I thought I’d take a moment to advertise…!”
Bow-.
I said that and lowered my head deeply.
…Ah.
Only after lowering my head did my face belatedly flare hot.
Once my favorite subject came up, I’d gotten excited without realizing it; my speech sped up and my voice grew louder.
A six-year-old had suddenly lit up her eyes and passionately rambled on about zeta functions and analytic continuation.
What if… the unnis and oppas thought I was kind of weird?
I subtly raised my eyes to check the audience’s reaction.
And then.
Clap-clap-clap-clap-clap-clap-clap—!!!
Thunderous applause burst out, including from the high school unnis and oppas and even the teachers seated in the back rows.
Applause raining down from every direction gently enveloped my body.
‘Fwoooah… feels goood…’
I felt as if five thousand helium balloons had been tied to my body and I might float away.
Getting showered with applause is always the best!
I enjoyed the brief round of applause, drooling with a goofy grin.
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In the middle seats of the auditorium.
Seo Eun-chae was staring intently at the tiny lecturer onstage.
At first, she had simply been happy to see her.
What? A-yeon is coming to give a lecture at our school?
I’ve gotta brag to my friends that I’m close with A-yeon!
She had taken her seat with that carefree attitude.
But.
…
At some point.
Without realizing it, Eun-chae had become completely absorbed in Yoo A-yeon’s lecture.
The odds in gacha games.
The normal distribution hidden in game rankings.
Mathematical formulas used throughout industry.
And even the nonsensical formula claiming that the sum of all natural numbers was negative.
‘Was mathematics… really this much fun?’
It was hard to believe this was the same math that gave her headaches in her collections of past exam problems.
Onstage, A-yeon seemed to sparkle when talking about the things she loved.
Somehow, that sparkle seemed to spread to Eun-chae, too.
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Come to think of it, Eun-chae had never had a firm career path until now.
She was smart, so she did fairly well in school.
Her grades were always near the top, and her teachers often praised her.
But she didn’t have any particular university or department she actually wanted to attend.
It was just that everyone in South Korea studied together…
She had merely followed along out of inertia, doing what everyone else did.
She had no opinions of her own.
‘Well… maybe I’ll go to medical school since doctors make good money.’
Whenever she pictured the future, that was the only vague, blurry image she could see.
The only thing she could confidently say she liked was chess, which she had held onto for over ten years.
But in South Korea, where chess was still woefully underdeveloped.
It was impossible for her to imagine making a living from chess alone.
That was why the career-preference section on Eun-chae’s forms had remained blank.
But then.
— If you think mathematics developed purely through logic is fun! then you can come to the mathematics department…! Because, you see, I’m going to become a professor in Seoul National University’s Department of Mathematical Sciences next year…! I’d be so happy to meet you then. So I thought I’d take a moment to advertise…!
Those words from A-yeon onstage struck Eun-chae right in the middle of her heart.
“The mathematics department…”
Eun-chae repeated the words under her breath.
Strangely, her heart began pounding.
It was the first time in her life mathematics had ever felt this fun.
And then.
She found herself wanting to listen just a little longer to the adorable little professor’s lessons, which sparkled every time she explained something she loved.
No. She wanted to listen to lots of them. Every single day.
Whenever she didn’t understand something, she wanted to visit A-yeon’s lab, ask her tons of questions, and bother her by petting her.
‘I want to take a university course taught by A-yeon.’
The blurry picture in Eun-chae’s mind slowly began to come into focus.
Seoul National University’s Department of Mathematical Sciences.
A scene of her enrolling there and attending Professor Yoo A-yeon’s class.
No matter what future she had imagined until now, it had always left her indifferent.
But this picture, at least, made her heart flutter for some reason.
‘That’s it. I’ll apply here.’
That was how Eun-chae made up her mind.
‘Huh… but is it okay to decide something this impulsively?’
Then Eun-chae carefully retraced her thoughts.
To decide on such an important career path in life immediately after hearing a single lecture…
She wondered if this was really okay.
But.
‘Who cares?’
Eun-chae gave a little snort of laughter.
If she hadn’t heard this lecture, she would have just applied anywhere her grades allowed, without giving it a thought.
Without any opinion of her own.
Following everyone else.
Compared to that, she thought this choice—made because “math is fun” and because “A-yeon is cute”—was
far healthier and more true to herself.
For the first time in her life, Eun-chae had chosen a career according to her own heart, not because someone else told her to.
Onstage.
A-yeon was wrapping up the lecture with a deep bow.
The person who had just delivered such an impressive lecture was blushing hotly, fanning her face with her hands in embarrassment.
Clap-clap-clap-clap-clap-clap-clap-clap-clap-clap-!!!
The applause bursting from the auditorium.
Clap-clap-clap-.
Eun-chae added the sound of her own clapping to the ovation.
Yoo A-yeon stood onstage with a blissful expression, drooling with a goofy grin.
Looking fondly at A-yeon, Eun-chae murmured softly.
“…Our adorable Professor Yoo A-yeon, I hope I can see you at university next year.”