Eight-year-and-three-month-old Nangong Wentian sat on the stone steps in the courtyard, surrounded by a circle of children.
The oldest was thirteen, the youngest just four. Some sat, some squatted, and some simply lay on the ground, all staring at him with eyes full of curiosity.
"Brother Wentian," four-year-old Xiao Wu raised his hand, "what are we learning about today?"
Nangong Wentian looked up at the sky. The autumn sun was warm, a few white clouds drifting lazily by. In the distance, farmers were harvesting rice, the roar of tractors carrying over.
"Today, we'll talk about water," he said.
"Water?" Xiao Wu tilted his head. "What's there to talk about with water?"
Nangong Wentian stood up, walked to the water vat in the corner of the courtyard, scooped out a ladle of water, and poured it into a chipped bowl. Then he carried the bowl back and placed it in the middle of the children.
"Look, what is this?"
"Water!" the children chorused.
"What is water?"
The children were stumped. Water was just water, what else could it be?
Nangong Wentian crouched down, pointing at the water in the bowl. "Does water move?"
"Yes!" Xiao Wu answered eagerly. "It flows when you pour it!"
"And what else?"
"It falls down when it rains!"
"Anything more?"
"Water in rivers flows to the sea!"
Nangong Wentian nodded, then pulled a small stone from his pocket and tossed it into the bowl. Water splashed up, landing on a few children's faces, making them giggle.
"When the stone is thrown in, what happens to the water?"
"It splashes!" Xiao Wu wiped the droplets from his face. "And it wobbles!"
"Why?"
Xiao Wu was stumped again. Why? Because the stone fell in, of course.
Nangong Wentian didn't answer directly. Instead, he pointed at the water in the bowl. "Look, the water is wobbling. As it wobbles, it slowly stops. Where did the energy of that wobbling go?"
The children looked at each other. Energy? What was energy?
Nangong Wentian changed his phrasing. "When you run until you're tired, don't you need to rest?"
The children nodded.
"When you run, you have strength. When you're tired from running, you've used up that strength. It's the same with water. When the stone is thrown in, it gives the water some 'strength,' so the water wobbles. As it wobbles and wobbles, that 'strength' gets used up, and the water stops wobbling."
Xiao Guang, listening nearby, seemed thoughtful. He was thirteen this year, older than the other children, and could understand a bit more. But he had never thought before about what relationship water and strength could have.
"Then..." a girl named Sayuri raised her hand, "where does the water's strength go after it finishes wobbling?"
Nangong Wentian pointed at the ground. "It goes into the earth. When the water wobbles, it touches the bowl, the bowl touches the ground, and the strength is transmitted into the earth."
Sayuri nodded, not fully understanding but getting the gist.
Nangong Wentian scooped another ladle of water and poured it into the bowl. This time, instead of throwing a stone, he gently traced his finger across the water's surface.
"Look, I'm giving the water a very small amount of strength, so it moves gently. The stone gave it a large amount of strength, so it moved vigorously."
He stopped his hand, and the water's surface slowly grew calm again.
"Strength can be great or small. Great strength moves powerfully; small strength moves lightly. This is... the amount of energy."
He had originally wanted to say "conservation of energy," but immediately realized that term was too complex for these children. Change the phrasing, use something they could understand.
Xiao Wu suddenly pointed at the sky: "What about the clouds up there? Are clouds water too?"
Nangong Wentian looked up at those few white clouds and smiled: "Yes, clouds are water too."
"How can clouds be water? Water is wet, clouds are dry!"
"Water can change." Nangong Wentian stood up, walked to the water vat, and scooped another ladle of water. "Look."
He poured the water on the ground. It seeped into the soil and quickly disappeared.
"Where did the water go?"
"Into the ground!" the children chorused.
"Right. And if I boil the water?"
The children had never boiled water and didn't quite understand.
Xiao Guang chimed in from the side: "When water boils, it makes steam. That steam is water that changed."
Nangong Wentian nodded: "Yes. Water can turn into vapor and float up to the sky. It's cold up there, so the vapor turns back into tiny water droplets. Lots of tiny droplets gathered together become clouds."
Xiao Wu stared wide-eyed at the clouds in the sky, his mouth hanging open. So clouds were made from water!
"Then..." he thought for a moment and asked again, "why do clouds fall down?"
"Because they get too heavy." Nangong Wentian pointed at the sky. "When too many tiny droplets gather, they become too heavy and fall down. When they fall, that's rain."
Xiao Wu seemed lost in thought. He looked down at the puddle of water that had already seeped into the ground, then looked up at the clouds in the sky, his eyes shining.
"Brother Wentian," he suddenly asked, "is there water on the stars too?"
Nangong Wentian was taken aback.
Stars.
He looked at Xiao Wu, this four-year-old child whose eyes were full of curiosity and longing. He remembered when he was little, he too had looked up at the starry sky and asked the same question.
"I don't know," he said honestly. "Maybe there is, maybe there isn't. No one has gone to look yet."
Xiao Wu was silent for a moment, then said seriously: "I'll go look in the future."
Nangong Wentian looked at him, a complex emotion welling up in his heart. This child would become a member of the Mars exploration team in the future, leaving human footprints on the red planet.
"Alright," he said softly. "We'll go look together in the future."
Xiao Wu nodded vigorously, as if making some kind of promise.
The afternoon sun was warm. The children sat gathered in the courtyard, listening to this "little teacher" who wasn't much older than them talk about those strange but interesting things.
Water can change, strength can move, clouds are made of water, stars are far away...
For every question, Nangong Wentian could explain it in words they could understand. Without using complicated terms, without those hard-to-understand formulas, just using things around them, things they had seen.
Xiao Guang, listening nearby, suddenly asked: "Wentian, where did you learn all this?"
Nangong Wentian glanced at him and said calmly: "I read it in books."
Xiao Guang didn't believe it. He had read things in books too, but they were never explained like this. Those books were full of words he couldn't understand, things he couldn't make sense of—nothing this interesting.
But he didn't press further.
He knew Wentian had many secrets. He didn't know what those secrets were, but he knew that everything Wentian did was right.
In the evening, the children dispersed, each going to eat. Nangong Wentian sat on the stone steps, gazing at the sunset on the horizon.
Xiao Guang walked over and sat down beside him.
"Wentian," he suddenly said, "you spoke really well today."
Nangong Wentian did not reply.
"Those kids," Xiao Guang pointed toward the cafeteria, "they all really like you. That kid Xiao Wu, who usually ignores everyone, loves listening to you talk."
Nangong Wentian remembered Xiao Wu's final question—"Is there water on the stars too?"
He remembered the child's earnest gaze, remembered the determination in his voice when he said, "I'll go see for myself someday."
"Xiao Guang," he suddenly said, "do you know, some people will do amazing things in the future."
Xiao Guang was taken aback. "Who?"
"Xiao Wu." Nangong Wentian looked at the last trace of red on the horizon. "He'll go to Mars someday."
Xiao Guang blinked. "Mars? That red star?"
"Mhm."
"How do you know?"
Nangong Wentian fell silent for a moment, then said, "Just a guess."
Xiao Guang didn't believe him, but didn't press further. Leaning back on the steps, he also looked toward the horizon and softly asked, "What about me? What will I do in the future?"
Nangong Wentian turned to look at him. Thirteen-year-old Xiao Guang, thin, with bright eyes, always following behind him, helping him pass things, keeping watch, helping him with things others didn't understand.
"You," Nangong Wentian said seriously, "will create many incredible things in the future."
Xiao Guang grinned. "Really?"
"Really."
"What will I make?"
Nangong Wentian thought for a moment, then pointed toward the distant kitchen. "That washing machine, remember?"
Xiao Guang nodded.
"That gear, you helped me find the metal sheet for it. That screw, you helped me tighten it. That..."
"But you made all those things," Xiao Guang scratched his head. "I just helped."
"Helping is enough." Nangong Wentian looked at him. "You'll do even better than me in the future."
Xiao Guang was stunned. He opened his mouth, wanting to say something, but no words came out.
The sunset on the horizon gradually faded, and stars began to twinkle. Xiao Wu ran out, pointing at the sky and shouting, "Brother Wentian, look, stars!"
Nangong Wentian looked up. The autumn night sky was exceptionally clear, filled with shimmering stars, the Milky Way stretching across the heavens.
"So beautiful," he whispered.
Xiao Wu ran over, tugging at his sleeve. "Brother Wentian, are there really no people on those stars?"
"Maybe there are," Nangong Wentian patted his head, "maybe not. When you go there someday, you'll know."
Xiao Wu nodded vigorously, his eyes shining as if holding the entire starry sky.
After dinner, all the children went to sleep. Nangong Wentian lay flat on his bed, gazing at the starry sky outside the window.
The Star Core lay quietly in the wooden box in the kitchen. Those parts salvaged from the junkyard, those circuits he had soldered himself, waited in the darkness to be awakened once more.
And he knew that someday, this knowledge would be passed on.
Passed on to Xiao Guang, to Xiao Wu, to those children willing to listen to his "story of water."
Passed on to them, a different future.