A week before the debate,
The shoot was simpler than expected.
The Science Team had already filmed a trailer with Chris’s side.
“There will be no staging, of course.”
The director said.
“But we do want a composition where the two of you are clearly contrasted.”
Seha nodded.
After doing it a few times, standing in front of a camera was becoming more and more familiar.
“This is the footage from Chris’s side.”
The monitor turned on.
A rocket launch appeared.
The countdown,
ignition,
and ascent.
For the first few seconds, it looked perfect.
The thrust and the angle were both as calculated.
But then,
the screen shifted into slow motion.
As the rocket climbed in altitude, its attitude twisted ever so slightly.
An error so small it was almost impossible to distinguish with the eye. But Seha’s eyes, sensitive to angles, could see it.
The next moment, the correction thrust activated.
And that correction created an error in another direction.
Everything was chained together.
When a small correction was made, a deviation occurred elsewhere, and now an even larger correction was required. This chain reaction led to vibrations large enough to shake the entire body, and the trajectory grew more and more unstable.
At last, the rocket completely deviated from its designed path.
Kwa-gwang!
An explosion.
The launch vehicle shattered into pieces in midair and disappeared.
The screen stopped.
“We’re not trying to emphasize the failure itself. We want to give viewers the impression that it was a dangerous but worthwhile challenge...”
His words did not reach Seha.
Seha’s gaze was fixed only on the screen.
“Just one more time...”
“Yes?”
“Could I see the launch scene just one more time?”
The same footage played again.
Seha stared piercingly at the screen. Not at the explosion, but at the attempt the rocket had made to control its attitude before then.
The control system was following the existing energy minimization formula.
Whenever an error occurred, it tried to correct the instantaneous deviation while consuming the least fuel.
“It flew like this, right?”
Seha traced the rocket’s trajectory with his hand.
A point.
The next point.
Another point.
His gaze returned to the screen.
The rocket was controlling its body by continuously plotting points on a graph. But every one of those attempts ended in vain.
Kwa-gwang!
“It wasn’t a collection of points.”
“What?”
Perhaps sensing something unusual, Theo approached Seha.
“This rocket...”
Seha said in a low voice.
“Never once got onto the minimum energy surface.”
Each individual choice had been optimal at that moment.
But the whole they formed failed to converge to a minimum.
Before Seha’s eyes, a vast energy terrain unfolded.
Local minima,
shallow basins.
And the path to the minimum energy surface that no one had been able to define until now.
‘I understand. Why dead solutions had no choice but to keep appearing.’
It was because the minimum at each moment killed the gradient—the direction in which energy changed most steeply—but could not control the variation that followed.
“Um, would it be all right if we continued filming?”
“Yes? Yes.”
Seha nodded blankly.
He could not prove it yet. But he had clearly grasped the direction leading there.
After the shoot ended, Seha stood there for a long while.
Local minimum.
Variation.
Existence of solutions.
Seha closed his eyes and slowly drew in a breath.
Like a diver just before plunging into the deep sea.
When he opened his eyes, it was a dense forest of thorns.
Blocked on all sides.
No matter where he went, he could not find a path.
When he pushed aside one thorn, an even thicker branch sprang out from behind it.
‘Was it like this?’
If he reduced one error, a larger deviation arose in another direction.
Seha stopped walking.
“What is he doing?”
Sujeong asked with a worried expression.
In the classroom after the shoot had ended, Seha stood there like a man whose soul had left him.
Theo shook his head.
“For now, let’s not disturb him and leave him be.”
Even after several days passed, Seha’s condition remained the same.
Even while eating, his hand would stop with the fork still held in it. He did not notice his food growing cold, and at times he did not even recognize who was sitting beside him.
“Seha.”
When his name was called, he reacted a beat late.
“...Yes?”
Theo sighed.
“Will you be all right for the debate? You don’t look well. Should I say we’ll do it later?”
Seha shook his head fiercely.
“I don’t want that. Chris will think I ran away.”
This was not the time for this.
He had to prepare for the debate.
He tried to steady his mind, but it was no easy task.
“I’m sorry.”
He did not want to worry them.
Looking ashamed, Seha lowered his head.
After that day, Seha deliberately avoided spending time alone.
Because if he was alone, he felt his thoughts would sink too deeply.
But the result did not change much. Even when he was with people, conversations did not really enter his ears, and there were plenty of times when he closed and opened his eyes to find that hours had passed.
Time flowed, and the debate date drew closer by the day.
“Will he really be all right?”
Clink.
Sujeong slowly stirred her coffee with a straw.
The ice knocked against itself inside the glass, making a clear sound.
“His own wishes matter most. Seha wants to do it.”
The trailer had already aired, making it difficult to back out, and Seha felt a sense of responsibility.
Theo thought that if a situation too difficult to handle arose, he would have to step in himself.
The day of the debate arrived.
Seha sat in the studio waiting room. On the screen attached to the wall, the preview video was playing on repeat.
Seha slowly lifted his head and looked into the mirror.
He saw a man wearing a mask. The man had his arms crossed as if displeased.
“You feel frustrated too, don’t you? But it’s all right. I think it will be resolved soon.”
Seha tried drawing formulas in the air. The path that had been tangled like a skein of thread looked different now. It felt as though, if he had just one trigger, he could unravel everything.
“Mr. Yu, you’ll have to go out soon.”
A staff member’s voice came from beyond the door.
“Yes, understood.”
The debate began.
‘Focus.’
Seha opened his eyes wide and tried to listen intently to what his opponent was saying.
With the help of his teammates, he had thoroughly prepared his rebuttals as well. But Seha’s thoughts stubbornly dragged him back into the forest.
Wung, wung—
The sounds around him grew distant, as if a well-soundproofed door had been closed.
Chris’s passionate speech, the host’s questions, the staff’s murmuring—all of it failed to reach Seha’s thoughts and scattered away.
Once again, the thorn forest unfolded before his eyes.
Seha’s gaze swept over each thorn in the forest as though feeling them out.
“Mm?”
Now that he looked, the thorns before him were not vague chaos.
Seha’s viewpoint rose high into the sky.
An endlessly spreading, vast forest. His eyes turned cold. Ducky began calculating the forest’s pattern.
“Here.”
He stopped walking.
The place where the thorns were densest. A place where the slightest movement seemed certain to inflict a wound.
A local minimum.
Seha realized.
The thorns of this forest did not exist to stab people.
‘To tell me to stop?’
The most stable spot, a point where, as long as one remained there, there was no need to worry about getting hurt.
But this was not the destination.
It was only a temporary stop, extremely vulnerable to external factors such as sensor noise, modeling error, time delay, wind, or vibration.
Unable to endure it any longer, Seha picked up the pen in front of him.
As he walked toward the whiteboard as if possessed, Peter and Chris were startled.
Sseu-sseuk.
Equations began to be written on the board.
“Seha?”
Peter half rose from his seat and called out to him.
It was movement not included in the plan.
The camera director instinctively reframed. Centered on Seha.
The formula began in a familiar form.
An energy function, state variables, and equations defining them.
The chat window instantly went wild.
└What? This isn’t scripted right now, is it?
└What is it, what is it?
└Looks like a broadcast accident. Yu Seha’s eyes have gone a little crazy.
└The production crew seems flustered too, don’t they? Look at Peter’s face.
└No, why is the camera only following him around and filming him lolololol
└I’m a dynamics professor. Seha is currently writing down the local minimum conditions. It seems he’s trying to point out the blind spot in the existing control logic that evaluates that point as stable. Until now, there has been no alternative except correcting errors through experiments, but.........
└It’s also a problem we field engineers always encounter in practice. But can this be broken through with theory?
└I’m just an ordinary viewer and I don’t understand any of it. But why am I getting chills? Damn.
└The professors are rushing the chat lololol
“Uh? We’re live right now, aren’t we?”
One of the staff members whispered.
[140,649]
The producer glanced at the number of concurrent viewers and radioed the production team.
“We’re not cutting. Keep going.”
Seha’s hand sped up.
All the information he had accumulated until now had not been meaningless. Pieces that had seemed unrelated connected into a single flow, as if swept downstream by a river.
“I got it!”
The whiteboard filled with local minimum coordinates, and Seha covered them with a geometric curved surface.
This problem was not about finding a minimum value.
It was about proving a stable structure that made all values flow into the minimum.
Tuk.
There was no more space left on the board.
The pen stopped.
Only then did Seha come to his senses and look around.
“Ah...”
He let out a small cry.
‘When on earth did I come out here?’
The equations packed densely across the board, dozens of pairs of eyes staring at him, and Peter and Chris’s flustered expressions.
His sense of reality returned.
Seha’s face turned red.
This was a debate. It was not a place where he could occupy the board alone.
Seha hurriedly put down the marker.
“I’m sorry.”
At a loss, Seha bowed his head to the people in the studio.
When the producer gave a signal, the camera alternated between Seha and the whiteboard.
Complexly intertwined equations and coordinates, and a single curved surface covering them.
“This is...”
Chris was looking at the board as well.
At first, he too had been flustered. Afterward, he tried to understand what Seha was writing.
‘I definitely saw this when he was tutoring me at the company...’
Seha apologized repeatedly and lifted the eraser to wipe the board.
“Wait!”
Chris rose from his seat.
“That’s the energy stabilization equation you wrote just now, right? And you’re saying it ultimately doesn’t work.”
Seha nodded.
“Because local minima are extremely vulnerable to external variables.”
Step, step.
He stood in front of the board and stared at the equations for a long while.
Then, after choosing his words for a moment, he slowly opened his mouth.
“During modeling, I blew it up hundreds of times.
I adjusted the fuselage and the parameters, replaced sensors, and tuned the algorithm. Even so, it blew up during actual launches. By accumulating that countless amount of failure data, I raised the success rate to 95%.
And you’re still going to say this doesn’t work?”
A low exclamation flowed through the studio.
Human tenacity, effort, and achievement.
They were virtues that deserved respect.
Seha did not want to disparage their efforts.
But as a mathematician, he had no other method than to state the facts.
“It’s like primitive tribes chewing on the grass and trees around them when they were sick.”
Chris’s eyebrows twitched at the blunt analogy.
“As it happened, you picked a poppy and chewed on it. By luck, the pain subsided.”
Seha pointed at the board.
The countless minimum points scattered beneath the curved surface.
“But you don’t know why the pain subsided.
You don’t know what component acted, through what pathway, under what conditions.”
Seha raised his head and looked straight at Chris.
“May I ask you one question?”
Chris nodded.
“You said 95 percent earlier, but if we look only at launch vehicles designed and flown for the first time, what is the success rate?”
Chris’s mouth opened, then closed.
“...40 percent, or lower.”
“If we complete the theory, we can extract morphine from the poppy. A perfect prescription suited to the symptoms becomes possible.
The method you are using now is like people waiting for lightning to strike from the sky in order to obtain fire.
Of course, that too is meaningful. It was how humanity first obtained fire.
But mathematics makes it possible to kindle fire through friction.”
Chris stared intently at Seha.
“You’re saying you can do that?”
Seha nodded.
“Yes. Now I know for certain. I can prove this. It is a theory that will dramatically raise the success rate of the rockets you make from now on.”
[150,827]
[160,272]
[170,861]
The number of viewers jumped every few seconds.
“Uh, this...”
The producer and the writer beside him swallowed in unison.
The speed at which the chat window scrolled visibly increased as well.
“When exactly would that become possible?”
The camera captured the tense conversation between the two in close-up.
At Chris’s words, Seha smiled.
“If you want, right here and now.”
[201,007]
The chat window exploded.