“Hey, Teach, aren’t there universities that don’t require a math test to get in?” one of the students was saying. “Why should us guys who are going to those schools have to pass math?”
Ishigami looked in the direction of the student, a boy named Morioka. He was leaning back in his chair, scratching his head and looking around at the other students for support. He was a short kid, but he filled the role of class crime boss—even Ishigami, who didn’t have this bunch for homeroom, knew his reputation. The boy already had a long history of warnings for riding to school on a motorbike, which was strictly forbidden.
“Are you going to art school, Morioka?” Ishigami asked.
“Well, I mean … if I do go to university, it’ll be one without a math exam for sure. Not that I plan on going. Besides, I’m not taking the optional math class next year, so what’s my grade this year matter? Hey, don’t get me wrong, I’m thinking about you, too, Teach. Can’t be much fun teaching with idiots like me in the class. So, I was thinking, maybe we could kind of come to an understanding about this. An agreement between adults, like.”
That last line got a laugh from the class. Ishigami chuckled wryly. “If you’re so worried on my account, then pass your make-up exam. It’s only differential and integral calculus. That can’t be too hard.”
Morioka scoffed loudly. He crossed his legs off to the side of his chair. “What good’s differential and integral calculus gonna do me? It’s a waste of time.”
Ishigami had turned to the blackboard to begin an explanation of some of the trickier problems on the year-end exam, but Morioka’s comment made him stop and turn around. This wasn’t the kind of thing he could let slide. “I hear you like motorbikes, Morioka. Ever watched a race?”
Morioka nodded, clearly taken aback by the sudden question.
“Well, do racers drive their bikes at a set speed? No, they’re constantly adjusting their speed based on the terrain, the way the wind’s blowing, their race strategy, and so on. They need to know in an instant where to hold back and where to accelerate in order to win. Do you follow?”
“Yeah, sure, I follow. But what’s that got to do with math?”
“Well, exactly how much they accelerate at a given time is the derivative of their speed at that exact moment. Furthermore, the distance they travel is the integral of their changing speed. In a race, the bikes all have to run roughly the same distance, so in determining who wins and who loses, the speed differential becomes very important. So you see, differential and integral calculus is very important.”
“Yeah,” Morioka said after a confused pause, “but a racer doesn’t have to think about all that. What do they care about differentials and integrals? They win by experience and instinct.”
“I’m sure they do. But that isn’t true for the support team for those racers. They run detailed simulations over and over to find the best places to accelerate—that’s how they work out a strategy. And in order to do that, they use differential and integral calculus. Even if they don’t know it, the computer software they’re using does.”
“So why not leave the mathematics to whoever’s making the software?”
“We could do that, but what if it was you who had to make the software, Morioka?”
Morioka leaned further back in his chair. “Me? Write software? I don’t think so.”
“Even if you don’t become a software engineer, someone else in this class might. That’s why we study mathematics. That’s why we have this class. You should know that what I’m teaching here is only the tip of the iceberg—a doorway into the world of mathematics. If you don’t even know where the door is, how can you ever expect to be able to walk through it? Of course, you don’t have to walk through it unless you want to. All I’m testing here is whether or not you know where the doorway is. I’m giving you choices.”
As he talked, Ishigami scanned the room. Every year there was someone who asked why they had to study math. Every year, he gave the same explanation. This time, since it was a student who liked motorbikes, he’d used the example of motorbike racing. Last year, it was an aspiring musician, so he talked about the math used in designing musical technology. But no matter the specifics of the discussion, which changed from year to year, it was all old hat for Ishigami.
When he returned to the teachers’ room after class, Ishigami found a note stuck to his desk. It was hastily scrawled, and it read, “Call Yukawa.” With a cell number written below, he recognized the handwriting as belonging to another one of the school’s math teachers.
What does Yukawa want? he wondered, swallowing to clear the sudden catch in his throat.
Cell phone in hand, he went out into the hallway. He dialed the number on the memo. Yukawa picked up after the first ring.
“Sorry to bother you during school hours.”
“Is it something urgent?”
“I guess you could call it urgent, yeah. Do you think we could meet today?”
“Today? Well, I have a few more things to take care of here. I suppose if it was after five o’clock…” He had just finished his sixth-period class, and all the students were in homeroom. Ishigami didn’t have a homeroom class of his own, so he could leave the keys to the judo dojo with another teacher and get out early if he had to.
“Great. I’ll meet you at the front gate at five, then. Sound good?”
“That’s fine—where are you now?”
“In the neighborhood. See you soon!”
“Right, see you.”
After Yukawa hung up, Ishigami clutched his cell phone with tense fingers, staring down at it. What could possibly be so urgent that it would drive the physicist to come see him here at school? Ishigami puzzled over it as he walked back to his desk.
By the time he had finished grading his few remaining exams and had gotten ready to leave it was already five. Ishigami walked out of the teachers’ room and cut across the schoolyard toward the front gate.
Yukawa was standing near the gate next to the crosswalk. His black coat fluttered in the wind. When he saw Ishigami, he waved and smiled. “Sorry to drag you out like this,” he called out cheerfully.
“I was just wondering what was so urgent that you came all the way out here to see me about it,” Ishigami said, his expression softening.
“Let’s talk while we walk.” Yukawa set off down Kiyosubashi Road.
“No, this way is faster,” Ishigami said, indicating a side road. “If we go straight through here it will get us right to my apartment building.”
“Yeah, but I want to go to that lunch box shop,” Yukawa explained.
“The lunch box shop? Why go there?” Ishigami asked, feeling the muscles in his face tighten.
“Why? To get a lunch box. Why else? I don’t think I’ll have time to get a proper dinner anywhere tonight, so I thought I might get something easy ahead of time. The lunches are good there, aren’t they? I’d hope so, seeing as how you buy them every day.”
“Oh … right. Off we go, then.” Ishigami turned toward Benten-tei.
They headed off in the direction of Kiyosu Bridge. As the walked along, a large truck rattled past them on the road.
“So,” Yukawa was saying, “I met with Kusanagi the other day—you remember, the detective that dropped in on you?”
Ishigami tensed, his premonition growing steadily worse.
“What’d he have to say?”
“Nothing big. Whenever he runs into a dead end, you see, he always comes whining to me. And never with the easy problems, either. Once he even wanted me to solve a poltergeist haunting. See what I mean?”
Yukawa began to tell him the story of the poltergeist haunting. It sounded interesting enough to Ishigami. But he knew that Yukawa hadn’t come all the way here to relate a would-be ghost story.