"Just how big is that boulder you're trying to move?" White Gongzi asked with an easy smile.
Crew Boss Teng Yifeng rubbed the back of his neck. "Roughly two zhang long and one zhang wide—a whole solid slab of stone. The workers can't budge it an inch. It's really giving us trouble. We didn't dare bother the Saintess or trouble Dao Xuan Tianzun again, but the crew from Gao Village said you might have a way to move heavy stuff."
White Gongzi laughed. "Haha! That little rock? Easy. Just use some physics and it'll slide right out of your way."
He said it casually—but someone was listening closely.
Song Yingxing's brow furrowed. Move a boulder that size? He actually knew a way—by using massive wooden gears: one standing upright, one lying flat. The two gears mesh; oxen turn the upright one, which spins the horizontal gear and drags the stone along.
(Ming Context: Gears were known from waterwheels and armillary spheres, but not widely used in manual engineering—Song Yingxing described them later in his book Tiangong Kaiwu.)
But this little boy—barely grown—already knew the same trick? And what was this "physics" he mentioned? Should he… ask?
Before he could decide, Daoist Ma Tianzheng spotted the White family and waved. "Ah, Lady Bai! Young Master Bai! Long time no see. A poor Daoist greets you both."
Lady Bai smiled warmly. "Daoist Ma, it's been ages. We heard you were traveling under Tianzun's orders—have you returned?"
Ma Tianzheng nodded. "Thankfully, yes. I've completed what Tianzun asked. I was planning to return to Gao Village tomorrow to report back."
Lady Bai pointed skyward with a grin. "No need to go far—Tianzun has come to the county. Look up, and you'll see him."
Ma Tianzheng's eyes widened. He looked up and saw a small floating cloud drifting low over the town. Startled, he brushed dust off his robe and dropped to his knees. "Disciple Ma Tianzheng pays respects to Dao Xuan Tianzun!"
The cloud shimmered slightly in response.
Ma Tianzheng beamed. He answered me!
Before he could say more, Song Yingxing tugged his sleeve. "Daoist Ma—you know that young man? Could you introduce me? I have many questions I'd like to discuss with him."
Realizing he'd nearly forgotten, Ma Tianzheng quickly led Song Yingxing forward. "Tianzun, this is Song Yingxing, a gentleman from Fengxin County in Jiangxi." He then turned to Song. "This is Young Master Bai of the White Fort."
The moment Li Daoxuan (Dao Xuan Tianzun) heard the name Song Yingxing, his eyes lit up. Finally! The great Ming scientist himself—caught in my timeline at last!
If he was within Tianzun's sphere of influence, there was no escaping. Li Daoxuan already had ten thousand ways to "convince" him to stay.
Excellent. Let White Gongzi and Song Yingxing chat a bit first. The boy might only know middle-school physics, but that alone was enough to blow Song Yingxing's worldview apart.
Song Yingxing clasped his hands respectfully. The youth before him was nearly thirty years younger, yet he didn't dare underestimate him. "Young Master Bai, I overheard you mention moving that massive stone through physics. May I ask what method you intend to use?"
White Gongzi looked the scholar up and down, noting that hungry curiosity in his eyes, and couldn't help smiling. Finally—someone who actually wanted to talk science! Back in Gao Village, no one could keep up with his learning anymore. Time to show off a bit.
He grinned. "Gears!"
Song Yingxing's eyes went wide. "Gears? That's my idea as well!"
White Gongzi blinked. "Wait, you know about gears too? Have you studied the Heavenly Book's Physics Chapter?"
"The what?" Song Yingxing frowned. "What's that?"
"Oh, never mind," White Gongzi chuckled in relief. "For a second I thought there were others outside Gao Village who'd read it. Scared me."
Song Yingxing grew curious. "May I ask—what exactly is this Heavenly Book's Physics Chapter?"
White Gongzi waved it off. "That's hard to explain in a few words. Let's check out the stone first."
Soon, the group arrived at the construction site outside the city. A massive boulder sat right in the middle of the road. The villagers had two choices: move it, or rebuild the road around it. For the smooth running of the future solar bus project, moving it was the only proper solution.
"Have you figured out roughly how heavy it is?" White Gongzi asked.
Teng Yifeng bowed. "We have no way to weigh such a thing, sir. We don't know its mass."
Song Yingxing smiled inwardly. We'd need to use Cao Chong's elephant-weighing trick, he thought. But an elephant can move onto a boat—this stone can't, so there's no way to measure it.
Before he could speak, White Gongzi pulled out a soft measuring tape—the kind used for tailoring—and measured the stone's diameter. Then he scribbled rapidly on a piece of paper. "About sixty thousand jin," he announced casually.
Song Yingxing froze. "What?!"
The young man kept calculating, eyes darting across the page. "To move a sixty-thousand-jin boulder, we'll need a main gear of about X diameter, paired with a smaller gear of X diameter… Let's see… okay, that ratio works. Send for the blacksmith—have him forge the gears according to my numbers. Bigger is fine, smaller is not. Otherwise, even two oxen won't have enough torque."
"Mount the gears here, attach oxen to pull this side, and have workers pry from the other side with iron rods—the stone will roll right off."
Song Yingxing stood there, utterly stunned. I knew gears could lift heavy things—but I could never calculate precise ratios, or predict how much force was needed. I just made them as large as possible and hoped for the best. How can a child compute this exactly?
He had to ask. "Young Master Bai, how did you calculate it so precisely? How can you know how large the gears must be for the strength of two oxen to move that weight?"
White Gongzi chuckled. "It's simple—gear diameter determines mechanical advantage. The bigger the difference between the large and small gear, the greater the force multiplier. You take the average pulling power of two oxen, divide by the ratio of the diameters… ah, too hard to explain verbally. Here—look at the formula."
He quickly scribbled out an equation.
Song Yingxing stared at the strange symbols, completely lost.
Heaven above… I thought I understood the workings of nature. Turns out I've barely scratched the surface.
He bowed deeply. "Forgive my boldness—but might I have the honor of reading this Heavenly Book's Physics Chapter you spoke of? I would gladly pay a great price."
White Gongzi just laughed. "Who cares about payment? Tianzun said knowledge is meant to be shared. If you want to learn—it's yours."
(Ming Trivia: Song Yingxing's encounter here foreshadows his future authorship of the scientific masterpiece Tiangong Kaiwu, which in this retelling draws direct inspiration from Dao Xuan Tianzun's "Heavenly Book.")