8:00 AM.
Shida Affiliated Middle School. The lecture hall on the third floor of the administration building.
The early summer sun was already bright.
It passed over the tops of the tall sycamore trees outside, slanting through the glass windows of the hallway.
It cast a bright, trapezoidal patch of light on the dark green blackboard.
The classroom door was pushed open.
Professor Wang walked in.
He wore an old, dark gray jacket, unzipped to reveal a plaid shirt that had been washed soft.
On his feet were the same old Beijing cloth shoes.
And in his hand, he still carried that chipped enamel mug printed with the words "Labor is most glorious."
He walked to the lectern.
He placed the mug on the edge of the wooden desk.
He wasn’t scowling; instead, he was beaming.
The wrinkles on his face crinkled together, making him look like an old man in a great mood after a morning stroll with his bird in the park.
The six top third-year middle school students below sat upright and attentive.
All except for Lin Yi, who rested his chin on one hand.
The other five boys sat with their backs ramrod straight.
The aftershocks of yesterday afternoon’s show of force—a lesson in "real physics"—still lingered.
"Why the long faces?"
Professor Wang unscrewed the lid of his mug, blew on the floating tea leaves, and took a big gulp.
"Yesterday afternoon must have scared you, huh?"
He set down his mug, his gaze sweeping over the heads of the province’s brightest middle schoolers in the first two rows.
"I’m Wang Yourong. For the next two weeks or so, you’re all under my charge."
"Yesterday was just tilling the soil, pulling out those delicate weeds of ’genius’ you’ve all got."
"Today,"
Professor Wang turned and took a full-length piece of white chalk from the chalk box.
"we’re officially starting the strong medicine."
He jabbed the blackboard with it, making a sharp TAP.
"This provincial team training camp is, at most, fourteen days long."
"Time is short, and the task is heavy."
"I don’t care if you can digest it on the spot."
"My only job is to cram as much as I can into your heads."
"Even if you can’t swallow, you’re going to force it down."
"Once you’re back in your dorms, you can ruminate on it yourselves."
As soon as his voice fell, Professor Wang turned to face the massive blackboard.
SHHH SHHH SHHH—
The chalk flew across the blackboard.
He didn’t use a ruler.
Relying purely on the stability of his wrist, he drew a square on the left side of the board.
Then, he drew a second square diagonally behind the first.
Four diagonal lines precisely connected the eight vertices.
A standard, three-dimensional wireframe of a cube, complete with perspective, appeared on the blackboard.
With a flick of his wrist, Professor Wang quickly drew sawtooth resistor symbols along the twelve edges.
"Twelve identical resistive wires."
Professor Wang’s voice suddenly rose in pitch, his words coming out in a rapid-fire burst, like a roaring engine.
"The resistance of each is R."
"Soldered together to form this cube."
He switched to a piece of red chalk.
On the outermost, bottom-left vertex of the cube, he heavily marked a red dot and labeled it with the letter A.
On the innermost, top-right diagonal vertex, he marked another red dot and labeled it with the letter B.
He drew two wires connecting them to a DC power source labeled U.
"Don’t give me any nonsense about Kirchhoff’s laws, and don’t even think about using calculus to build an electromagnetic field model."
Professor Wang tossed the red chalk into the box.
He turned around, planting his hands on the lectern.
"Just use Ohm’s law from your middle school textbook."
"And the most basic knowledge of series and parallel circuits."
"Who can tell me,"
"if the current enters at point A and exits at point B,"
"what is the total equivalent resistance of this cube?"
The classroom fell instantly silent.
Wang Huashao sat in the second row.
The ballpoint pen he was twirling in his hand fell onto the desk with a CLATTER.
His eyes widened.
He stared intently at the intricate, three-dimensional spiderweb on the blackboard.
His gaze followed the wire in from point A.
At the first vertex, the current split into three paths.
Then it reached the next set of vertices and split again.
Some paths converged, while others diverged.
In less than ten seconds, Wang Huashao felt his eyes begin to sting.
His mind felt like a tangled mess of countless woolen threads.
’I can’t tell which ones are in series and which are in parallel at all.’
The current scrambled through the inside, with no clear, unidirectional path.
He picked up his pen.
He tried to flatten the three-dimensional figure on his white scratch paper.
He wanted to draw it as a two-dimensional schematic to find a familiar series-parallel structure.
After drawing a few boxes and intersecting lines,
his brain completely froze.
The lines had become a hopeless knot.
In the first row, on the right,
Zhou Kai’s brows were knitted tightly together.
He didn’t pick up his pen.
His hands were clasped together.
He was frantically building a 3D model in his mind, trying to find an entry point.
But the twelve resistors were all interconnected. Moving one would affect them all; a slight change at one node would alter the voltage distribution of the entire network.
Miao Shian pushed up the gold-rimmed glasses on his nose.
On his scratch paper, he had quickly jotted down several nodal current equations.
But there were too many variables.
Six intermediate nodes, twelve branches.
Using middle school algebra to solve this system of multivariate linear equations would require a hopelessly large amount of calculation.
"Can’t figure out the series and parallel connections, right?"
Professor Wang laughed heartily, looking at their frustrated expressions.
His laughter was loud and resonant.
"That’s right."
"Because your minds are stuck in linear, two-dimensional, test-oriented thinking."
Professor Wang walked down from the platform and stood in the middle of the aisle.
"Physics isn’t about brute-force calculation. In physics, you have to find its beauty."
"The world is three-dimensional."
He walked back to the blackboard.
He picked up a piece of yellow chalk.
Following the direction of the current flowing from point A, he drew three identical yellow arrows on the three branching paths.
"Look here."
"Symmetry."
Professor Wang’s voice reverberated through the classroom.
"Current is like a flow of water."
"Entering at point A, it faces three identical paths. The length is the same, the resistance is the same, and their spatial positions are topologically equivalent."
"No single path is more special than any other."
"Therefore, the total current splits here into three absolutely equal parts."
The yellow chalk jabbed three heavy dots on the blackboard.
It made a dull thudding sound.
Chalk dust drifted down through the morning light.
"Since the currents are equal and the resistances are equal,"
"then the potential drop at these three vertices must be exactly the same."
"These are called equipotential points."
Professor Wang’s speaking pace grew faster and faster.
His eyes shone with an almost fanatical light—the pure love for physics that belonged to an older generation of scholars.
"Between equipotential points, there is no potential difference."
"It’s like two bodies of water at the same height. If you connect them with a pipe, the water won’t flow."
"With no potential difference, no current will pass through."
"So, you can treat these three points as a single node."
"You can short-circuit them, pinch them together!"
"You can also strip them from the original circuit and fold them!"
The six students below found their breathing growing ragged.
Not a single one of them spoke.
The only sounds in the classroom were the frantic scratching of pen tips on paper and heavy breathing.
Chen Zhuo was completely absorbed.
He stared at the cube on the blackboard, now being deconstructed by the yellow chalk.
He was filled with the unconcealable excitement that comes from grasping a new, intricate, and complex piece of knowledge.
The gel pen in his hand flew across his notebook.
The smooth rollerball skated across the paper, making a fine, rustling sound.
Because he was writing so fast and with so much force,
the black ink bled through the thin paper, leaving deep indentations on the other side.
Chen Zhuo didn’t copy Professor Wang’s original diagram from the blackboard.
He didn’t need to.
Following Professor Wang’s line of thought about equipotential points,
he quickly constructed a collapsed model in his mind.
Then, on the paper, he rapidly reduced the dimensions of the complex three-dimensional cube, layer by layer.
First layer: three resistors in parallel.
He drew the symbol and wrote 1⁄3R.
Second layer: six resistors in parallel.
He drew the symbol and wrote 1⁄6R.
Third layer: another three resistors in parallel.
He drew the symbol and wrote 1⁄3R.
The three-layer structure, connected in series.
The tip of his gel pen drew one last horizontal line on the paper.
He smoothly wrote down the final result: 5⁄6R.
The moment he finished writing, Chen Zhuo let out a long, natural breath.
His chest rose and fell slightly.
The physical thrill of instantly untangling such a chaotic mess left him feeling utterly clear-headed.
Because he was gripping his pen too tightly,
the side of his thumb accidentally smudged the black ink he had just written, which hadn’t yet dried.
It left a faint black smear.
But he couldn’t be bothered to wipe it off.
After Professor Wang finished with the resistor cube,
he didn’t even take a sip of water.
With a sharp swipe of the eraser, he wiped away half the diagram.
Right next to it,
he drew a triangle with an arrow, preceded by a vertical line.
"Do you recognize this symbol?"
Professor Wang tapped the blackboard.
"A diode."
"Current can only flow in the direction of the arrow. It’s like a one-way valve."
"Reverse direction? Sorry, infinite resistance. This road is closed."
He turned to look at the group of middle schoolers, who were furiously taking notes.
"The core of this morning’s theory lesson is these two things:"
"symmetrical equivalent circuits and non-ohmic unidirectional components."
The next two and a half hours were a high-intensity, ferocious, cram-style indoctrination.
How to find the balance point in complex bridge circuits.
The recursive thinking for finding the limit of an infinite resistor network.
The different topological states of non-linear circuits containing diodes under forward and reverse bias.
A massive number of diagrams, logical deductions, and extreme physical models.
It was like a torrential downpour
crashing down on this group of top third-year students.
Professor Wang lectured with exhilarating gusto.
The students below took notes until their wrists cramped.
Wang Huashao felt like his right hand wasn’t his own anymore.
He shook his aching wrist while gritting his teeth, his eyes glued to the board as he copied frantically.
It felt like the tip of his gel pen was striking sparks on the paper.
Zhou Kai didn’t even dare to take a sip of water.
The cup on his desk remained capped.
His eyes were fixed on the diagram on the board, afraid that if he looked down for even a second, the lines would change and the train of thought he’d worked so hard to establish would be completely broken.
11:30 AM.
Class was dismissed.
Professor Wang walked out with his mug, looking thoroughly satisfied.
He left behind a blackboard densely packed with white chalk writing.
In the lecture hall, the lecture hall looked like a battlefield ravaged by a storm.
Wang Huashao was slumped in his chair.
He looked at the full eleven pages of notes he’d taken.
His mind was a jumble of nodes, arrows, and equipotential points.
They spun wildly in his brain, fighting with each other.
He Gui was sprawled on his desk, his face pressed against the cool surface, as if every last ounce of his strength had been drained.
Miao Shian took off his gold-rimmed glasses and rubbed the bridge of his nose.
"I feel like... my brain capacity has just been forcibly expanded by two sizes,"
he said with a wry smile.
Chen Zhuo closed his notebook.
He stuck the gel pen, its ink now visibly a fifth lower, into the pocket of his shorts.
He glanced at the black ink stain on the side of his right thumb.
He shook his slightly sore wrist.
He didn’t say anything.
He just stood up and headed for the cafeteria.

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