I Promise to Walk With You for Half of my Life’s Journey - Chapter 9

The early summer breeze began to grow thick, and the evening self-study classroom was filled with nothing but the rustling sound of pen nibs gliding across paper.

Cheng Sutong’s gaze was frozen on the final problem of her physics paper. The complex model of the electromagnetic field was sketched on her scratch paper like a spiderweb, but a key transition point remained stubbornly blocked.

“Here.”

A cool voice fell from above. An Chuxin had appeared by her side at some unknown moment. Her fingertip pointed to a spot on the scratch paper as the scent of chalk dust mingled with her cold white tea fragrance.

“You judged the direction of the Lorentz force incorrectly. The particle is negatively charged, but you used the left-hand rule for a positive charge.”

Cheng Sutong froze, looking at the force analysis she had drawn countless times. Such a basic mistake was unlike her. She looked up and met An Chuxin’s eyes.

“Teacher, I am doing competition problems,” she said softly. This paper was not part of the standard curriculum.

An Chuxin remained silent for a few seconds. She suddenly leaned over, took the scratch paper from Cheng Sutong, and drew a new trajectory line next to the incorrect force diagram. Her strokes were decisive and the lines were clean.

“The experimental portion of the provincial competition accounts for 40% of the score,” An Chuxin’s voice was low, audible only to the two of them. “Given your current physical condition, can you stand in a laboratory for three hours of continuous operation?”

“I can.”

“I want the truth. Do not try to be brave. I need an objective assessment.”

Cheng Sutong looked at the corrected trajectory lines on the paper and slowly exhaled two words: “I cannot.” She paused and added, “But I want to try.”

An Chuxin straightened up and sighed. “Starting today, stay for one hour after school every day. I will practice with you.”

The physics laboratory was on the top floor of the old teaching building. An Chuxin had her sleeves rolled up as she adjusted the oscilloscope. Her fingers were long and slender, and her movements were powerful. Turning knobs, wiring, and calibrating—every step was concise and precise.

Cheng Sutong leaned against the laboratory bench and watched her.

“The first experiment is measuring gravitational acceleration. Use the simple pendulum method. The equipment is over there; assemble it yourself.”

This was the third day of their special training. There was no idle chatter. Every session went directly into the experiments. An Chuxin’s method was somewhat brutal. She would demonstrate the correct operation only once and then retreat to the window to watch Cheng Sutong repeat it. She would not remind her of mistakes during the process. Instead, she critiqued them point by point only after everything was completed.

An Chuxin checked her watch. “You were seven minutes slower than yesterday, and your hand shook three times while taking readings. Why?”

“The light was too strong. The glare reflected off the scales.”

“The lighting conditions at the competition site might be even worse.”

An Chuxin walked over and stood very close behind her. She was so close that Cheng Sutong could feel her breath. “Close your eyes.”

“What?”

“Close your eyes.”

Cheng Sutong closed her eyes. The moment her vision was stripped away, her other senses were suddenly magnified.

“Now, tell me the formula for the period of a simple pendulum.”

$$T = 2pisqrt{frac{L}{g}}$$

“What is the key to measuring $L$?”

“It is the distance from the suspension point to the center of the sphere. You must subtract the radius.”

Through the back and forth questioning, Cheng Sutong discovered that the details interfered with by the strong light became clear in the darkness. She suddenly realized that An Chuxin was training her to use muscle memory as a substitute for visual reliance.

“You can open your eyes now.”

Cheng Sutong opened her eyes to find that An Chuxin had brought sunglasses and a shaded hat at some point.

“Put them on,” An Chuxin said while handing them to her. “Adapt to different light conditions. Also, from tomorrow onward, I will ask questions randomly during the experiments to simulate on-site pressure.”

Cheng Sutong took the sunglasses and held them in her hand.

A week before the provincial competition, a sudden rainstorm arrived.

Training ended at 9:00 PM. The curtain of rain was so heavy that the streetlights three meters away were invisible. Cheng Sutong stood at the entrance of the laboratory building and frowned as she watched the campus paths rapidly flood. She had not brought an umbrella.

“Get on my back.”

An Chuxin opened a large black umbrella and simultaneously crouched down in front of her.

Cheng Sutong was stunned. “Teacher?”

An Chuxin turned her head. “The water is too deep. You will catch a cold if you wade through it. Hurry up.”

After hesitating for a few seconds, she finally leaned onto An Chuxin’s back. The tilt of the umbrella shielded them both completely. The moment An Chuxin stood up, Cheng Sutong instinctively wrapped her arms around her neck. She felt the tensed shoulder blades beneath the fabric and the warmth of her body heat.

The world was shrunk down into this small space.

“Teacher,” Cheng Sutong rested her chin lightly on An Chuxin’s shoulder. “Can I ask a theoretical question?”

“Ask.”

“If there is a closed system with a very high initial entropy, it means it is chaotic and on the verge of collapse. But if a self-organizing force emerges within the system and manages to lower the entropy, is that impossible according to the Second Law of Thermodynamics?”

“In an absolutely closed system, yes, it is impossible.” She stepped steadily into the accumulated water while carrying Cheng Sutong. “But the real world is never absolutely closed. There is always energy input, or something else.”

She turned her face slightly, and Cheng Sutong saw the lines of her profile moistened by the rainy mist.

“Or a strong directional interaction force is generated within the system. That force itself can temporarily counteract the increase in entropy.”

Cheng Sutong tightened her arms and pressed her face closer to the back of An Chuxin’s neck. There was a warm pulse beating there. It beat once, then twice, gradually syncing with her own heartbeat.

She asked softly, “How long can that force last?”

An Chuxin did not answer immediately. They had already reached the corridor of the teaching building. She carefully set Cheng Sutong down, closed the umbrella, and shook off the rainwater. Then she turned to look at Cheng Sutong under the dim corridor light.

“In physics formulas, the duration of a force depends on the impulse.” She reached out and brushed away the rain-dampened strands of hair from Cheng Sutong’s forehead. “But in a human system, it can be for a lifetime.”

The moment Cheng Sutong stood at the laboratory bench on the day of the provincial competition, she suddenly understood the meaning behind all of An Chuxin’s brutal training.

The surrounding area was filled with the breathing of other candidates and the clatter of equipment. The sound of the proctors pacing back and forth felt like a countdown. The moment she put on her sunglasses, the world grew quiet. All distractions faded, leaving only the instruments before her and the steps in her mind.

She knew how many turns to twist a knob, how deep to plug in a wire, and what angle to maintain her line of sight when reading. She no longer needed to think because her muscles remembered.

An hour into the experiment, the familiar dull pain in her chest arrived. It felt as if a hand were slowly tightening around her heart. Cheng Sutong’s movements paused for a second before she continued. She operated the equipment with her left hand while her right hand reached into her pocket to grip a small medicine bottle.

It was the fast-acting heart relief pills An Chuxin had given her before the competition. An Chuxin had told her, “If you really feel unwell, take one. It is not shameful. Your grades are not more important than your life.”

But Cheng Sutong did not open the cap. She took a deep breath and continued connecting the next circuit.

The final experiment was an optical measurement requiring extremely fine eyepiece adjustment. Sweat slid into her eye and caused a sting. Cheng Sutong blinked away the sweat and suddenly remembered An Chuxin’s voice saying, “Close your eyes. Tell me the grating equation.”

She actually closed her eyes. In the darkness, the formula emerged automatically: $d sintheta = klambda$. Every letter was clear.

When she opened her eyes again, her hand was steady.

The moment the bell rang to end the exam, Cheng Sutong nearly collapsed. She leaned against the laboratory bench and watched the proctors collect the papers. She had done it. She had stood for the full three hours and completed all the experiments.

When she walked out of the exam hall, the crowd was bustling. Parents eagerly crowded around to ask how the exam went. Cheng Sutong walked through the crowd alone.

Then she saw An Chuxin.

She was standing quietly under a plane tree outside the school gate. She stood there as if she had known all along that Cheng Sutong would come out from this direction.

Cheng Sutong quickened her pace. With every step, the dull pain in her chest became clearer, but something more overwhelming surpassed the pain. She came to a halt in front of An Chuxin.

“For the last optical experiment, I used the method you taught me. I closed my eyes and recalled the formula.”

The corner of An Chuxin’s mouth curled slightly. She took a thermos from her bag, unscrewed it, and handed it over. “This is warm water. Drink it slowly.”

Cheng Sutong took the cup. The water temperature was perfect. She took small sips, and her eyes never left An Chuxin.

“Teacher, I am not a closed system.”

An Chuxin raised an eyebrow, waiting for her to continue.

Cheng Sutong gripped the cup tightly. “I have energy input. You are my energy input, so my entropy has decreased. I can feel it.”

The noise of the crowd faded into background noise at that moment. The plane tree leaves rustled. An Chuxin raised her hand as if she wanted to touch the girl’s face, but she stopped mid-air and instead took back the thermos.

“Since the exam is over, get some good rest,” she said. She turned around and added, “Let’s go. I will take you back.”

But Cheng Sutong saw her reddened ears. In the blazing midsummer sun, that touch of red moved her heart more than any certificate ever could.

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