52: Chapter 52 The Boundary of Ten Years

On the Wasteland, time was the cheapest consumable.

When the storm whipped up dark red dust for the hundred and twentieth time, snapping the withered Pumpkin vines outside the Stone House, his fifth trip to the Wasteland entered its tenth autumn.

The south wall of the Stone House had been expanded six meters outward, adding a whole processing room.

Jiang Lin had built the wall inch by inch, patting down red mud from the Wasteland mixed with gravel and dried Moss fibers. It wasn't fired, nor did it have cement; its strength relied entirely on brute thickness stacked high.

Utilizing a gravity dam structure that was wider at the bottom and narrower at the top, the base of the wall was nearly seventy centimeters thick, tapering to forty at the top.

Wider at the bottom and narrower at the top, seventy centimeters thick at the base, tapering to forty at the top.

The roof featured a triangular truss made of scrap rebar, layered with double PE film sandwiching dried Moss for insulation, and topped with a layer of mud, sand, and stone.

Natural light came from two translucent polycarbonate sheets embedded in the south-facing roof slope.

He had determined the angle himself.

During his fourth trip to the Wasteland, he had stuck a straight piece of rebar into the ground and used a tape measure and charcoal to record the shortest shadow at noon, testing it repeatedly for many days.

After entering for the fifth time, he made further corrections using solar shadow records around the winter solstice.

The solar elevation angle formula in the textbook was very clean.

Inside the processing room, the vise jaws—used for ten years—still retained most of their hardened layer.

Every six months, without fail, he disassembled the lead screw of the main spindle. He carefully washed away the old grease mixed with iron filings and windblown sand using precious diesel, scraped along the threads loop by loop with a wire brush, and then reapplied a thick coat of grease.

Hammers, chisels, center punches, scribers, hacksaw frames, files of all sizes...

All were neatly hung on a wooden strip above the workbench.

After hanging each tool, he used a carving knife to deeply trace its outline on the corresponding spot of the wooden strip.

This way, if any file was missing—even the smallest needle file—he could tell at a single glance.

This obsessive sense of order was one of his anchors against the vast, endless void of the Wasteland.

Ten years later, Jiang Lin's hands no longer looked like they did when he first entered.

On the inside of his left webspace was a short, curved, old scar.

That was from the summer of his third year: while chiseling a section of cast iron pipe with a flat chisel, his hammer slipped, and the sharp butt of the chisel sliced right through his glove, ripping open a cut on his webspace.

Having no tetanus shot, he could only rinse it repeatedly with povidone-iodine before applying a pressure bandage.

After the wound healed, the flesh knitted together in rolled-up edges, leaving this scar.

Between the thumb and index finger of his right hand was a thick, yellowish-brown callus.

When filing, his right hand gripped the handle and pushed forward; force traveled from his shoulder to his upper arm, then to his wrist, and finally pressed entirely onto the base of his thumb.

For the first two years, he often rubbed the webspace of his right hand raw and swollen. Later, as the callus hardened, the pain faded, turning it into a natural shock-absorbing pad when gripping the file.

When he bent the second knuckle of his middle finger, he could feel a small hard lump formed from guiding saws, pressing stock, and clamping small workpieces.

Especially during sawing jobs, his left hand would hold the saw blade to start the cut, with index and middle fingers pinching the sides of the blade; over time, the knuckle was repeatedly rubbed against the dull back of the saw blade until the skin became as tough as sandpaper.

Professor Lu Zhixing had casually mentioned in a popular science video that you could spot a fitter with ten years of benchwork experience just by looking at their webspace.

Teacher Lu probably never imagined that an offhand remark of his would be put to the test over ten years by a young man, saw by saw, file by file.

Matching these rough hands were the various practice pieces in the wooden crates under the workbench, numbered and cataloged like specimens over the ten-year period.

Inside one of the crates were typical failed pieces saved since his third year.

The first was a sawn piece with a cross-section skewed by up to two millimeters; the end face had been touched up with a file, but no matter how much he tried to fix it, it stayed crooked.

The end face had been frantically remediated with a large flat file, leaving crisscrossed file marks, yet no matter how he tried to fix it, it remained skewed.

Later he realized that the problem didn't lie in the subsequent filing at all, but in the initial scribing and saw-start.

If the first cut was crooked, any effort applied later was just hurtling wildly down an off-track trajectory.

The second item was an aluminum plate ruined by a tap.

For M5 threads, halfway through tapping, the tap jammed solid in the hole.

When he forcibly backed it out, the thread profile mangled around the fourth thread, turning into a mashed lump of metal sludge.

The third piece was a nylon rod that had failed manual rounding.

In his early years, to practice cylindrical shaping, he used a file and emery cloth to shape the roundness bit by bit, resulting in a pitted surface and an eccentric cross-section, making it completely unusable as a sliding component.

Of course, there were not only failures, but successes as well.

In his eighth year, using a scrap piece of duralumin plate, he made his first set of spare vise jaw plates that could be repeatedly attached and detached from the same bench vise.

Two M6 socket head countersunk bolt holes, spaced 20 millimeters apart, with the symmetry of the centerline repeatedly verified using calipers.

At the moment when he finally mounted them and tightened the bolts, the bite line of the two jaws formed a straight line, seamlessly tight when viewed against the midday light.

There were only five items in this box.

A polished engineer's square, a custom V-block, a pair of spare vise jaws, a round steel reference rod that had been repeatedly straightened, and a simple angle template used for scribing repeated angles.

All were kept in a lined box made from an old towel, with moisture-proof paper lining each compartment.

At this moment, Jiang Lin stood before the workbench, holding a piece of the few remaining Q235 Mild Steel stocks.

Ten years of time hadn't caused much physical aging in this eighteen-year-old body, but his demeanor had undergone an earth-shattering transformation.

Before, when he first gripped a file, he was like a student solving exam problems; his eyes only stared at graduations, and his whole body was tense as a piece of dried wood.

Now, wearing old patched cotton clothes, his feet naturally stepped half a pace apart, his center of gravity sinking steadily between his hips and waist.

His right hand held a medium-cut flat file whose wooden handle had been replaced three times.

He didn't need to deliberately adjust his breathing, nor did he stare at his wrist.

He merely narrowed his eyes, glanced at the extremely faint layer of blue-black layout fluid on the steel surface, and then exerted force through his arm, pushing forward smoothly.

It produced the tearing sound of metal fibers being sheared away row after row.

In his hands, the file was like an extension growing directly from his shoulder.

Two-thirds into the stroke, his shoulder muscles naturally tightened, and his wrist locked the angle as securely as hydraulic suspension; the downward pressure at both ends transitioned naturally and smoothly throughout the stroke, without a hint of dipping or teeter-tottering.

Ten minutes later, Jiang Lin stopped.

Puffing out his cheeks, he blew away the fine layer of iron filings on the surface, picked up the knife-edge square, and held it gently against the steel plate towards the sidelight streaming in through the south window.

Under the sidelight, only an extremely fine dark aura remained—so fine that it could no longer be judged by the naked eye whether it was a real physical gap or an optical illusion created by the knife-edge bevel, light source diffraction, and viewing angle combined.

Jiang Lin didn't even reach for the vernier caliper to recheck; he simply rubbed the pad of his thumb gently along the edge, feeling that slightly gritty resistance.

"By current inspection methods, I'm stuck right around one si again."

He sighed and tossed this near-perfect practice piece into the tote box.

Deep down, his heart surged with emotion.

Three years ago, when he first brought the error down to 0.01 millimeters—which was one si—he had been so excited that he couldn't sleep half the night, writing a long, passionate summary in his logbook.

But now, this precision of one si was like a wall of sighs, locking him firmly at this level.

For three whole years, over a thousand days and nights, no matter how he adjusted his posture, slowed his filing speed, or finely controlled downward force, he couldn't advance even a single micrometer further.

Jiang Lin walked to the stone table, gulped down a large mouthful of bitter Pumpkin vine water, and tapped open the textbook on his phone.

A core specialized course for junior year: solid state physics.

He actually should have studied this course long ago.

In previous years, he had been wallowing in the quagmires of Quantum Mechanics and elasticity theory; it wasn't until last year that he officially opened the first page of solid state physics.

And it was only after opening that page that he finally understood what was truly locking him down.

Before, he thought that failing to file it flat was a problem with his hands.

That his muscle memory wasn't steady enough, or that his mind wasn't calm enough.

But the calculus-laden lattice equations of solid state physics told him: it wasn't that his hands weren't good enough, but that this block of iron wouldn't allow it.

Jiang Lin looked down at the calluses on his hands, then at those practice pieces.

The Q235 steel he brought was the most common mild steel in industry.

On a macroscopic level, it was a piece of iron.

But in the microscopic lattice world, it wasn't a clean, uniform piece of iron at all.

It was ferrite mixed with a small amount of pearlite, along with impurities left behind from smelting.

When the tips of the file teeth pressed into the surface of this mild steel with several kilograms of downward force, that final fraction of a micrometer of stock allowance would never snap off cleanly like chalk or crispy noodles.

Mild steel had good plasticity; those metal lattices would undergo slip under external force.

Metal atoms would be compressed and torn, smeared out to both sides, leaving behind microscopic burrs and work-hardened high spots that were invisible to the naked eye yet physically real.

"No matter how steady I train my hands to be, this soft steel will burr, bind, and spring back in those last few micrometers."

Jiang Lin drew a diagram of edge dislocation multiplication on his grid notebook.

Within his current toolchain, Q235 was no longer a suitable material for breaking through.

It wasn't that nobody in the world could finish mild steel better, but rather that with his file, square, feeler gauge, and this Stone House workbench, grinding down further yielded diminishing returns that were completely swallowed up by material plasticity, burrs, springback, and inspection limits.

Besides material, another limitation came from another course—Physical Optics.

Jiang Lin turned his head and looked at the knife-edge square resting quietly on the mat.

He had always used the light-gap method to inspect flatness.

If light didn't leak through, he considered it flat.

This was a simple, intuitive belief.

But now that he had studied wave optics, wave optics cruelly stripped him of this belief, telling him that light was not an infinitely thin straight line—light was a wave.

[part:gemini-3.5-flash-lite]

The photosensitive limit of the human eye, the size of the light source, the microscopic state of the cutting edge itself, and the reflectivity of the metal surface—all these variables were secretly participating in your judgment.

He had once done the math.

In visible light, the wavelength of green light is about several hundred nanometers.

When the gap between the cutting edge and the steel plate was as small as a few micrometers, the light waves could no longer maintain straight-line propagation; they would diffract, bypassing the cutting edge like water ripples around a reef, causing the light entering the human eye to become blurred.

Coupled with the physical size limitations of the human retinal photoreceptor cells, even under the most perfect midday sidelight, the limit of the smallest light gap that the naked eye could distinguish was only around 0.005 millimeters.

"I am blind."

Jiang Lin looked at the square that had been with him for ten years, as if looking at a betrayed comrade.

"With a square and the naked eye, if I want to continue pushing the error below a few micrometers, I can no longer rely solely on looking at the light gap. I need optical flats, and I need interference fringes."

"But in my hands, aside from this pile of junk iron, I have nothing. No optical flats, no monochromatic light sources, no vibration isolation tables."

The material refused, and the ruler could not see.

This was the limitation Jiang Lin faced in the autumn of the tenth year.

His theoretical knowledge had touched the threshold of solid state physics and computational Physics, and his hands had trained into the muscle memory that ordinary fitters could only achieve after more than a decade.

But outside the microscopic world of real modern engineering, he was ruthlessly stripped of his admission ticket by the laws of Physics.

"Hoo..."

Jiang Lin leaned against the cold Stone House wall, closing his eyes and feeling the chill emanating from the wall.

Wanting to create an absolute micrometer-level plane out of thin air on the Wasteland without any modern precision machine tools, there was only one path in industrial history.

An extremely ancient, extremely time-consuming, yet immensely sacred path of traceability.

Scraping, along with the Three-Plate Grinding Method.

Instead of using the teeth of a file to cut, an ultra-sharp scraper was used to scrape off the surface.

Instead of looking with a square, red lead powder was used as a display agent, and three mutually lapped planes were used to print.

Each time, only those high points stained with red lead powder and protruding by a few tenths of a micrometer were scraped off.

The three plates—A ground B, B ground C, and C ground A—used tens of thousands of mutual error corrections, employing the most foolish method like Yu Gong moving mountains, to force the error bit by bit into the abyss of micrometers.

The precision of the mother machines of modern machine tools was originally scraped out bit by bit just like this.

This path had been deduced countless times in Jiang Lin's mind.

But he had never dropped the first cut.

Because he lacked the most critical thing.

The craft of scraping had extremely harsh requirements for materials.

Q235 Mild Steel was not completely unscrapeable, but it was sticky and soft, making it unsuitable as a benchmark surface plate material for the Three-Plate Grinding Method.

If you used it as a benchmark plate, before you even scraped the three plates flat, its own internal stress would quietly deform it.

Scraping plates required the material to contain a large amount of flaky graphite internally.

Graphite played two crucial roles here.

First, it was a natural solid lubricant.

Second, it fractured the continuity of the metal matrix, allowing the iron chips to break crisply like a crispy biscuit when the scraper cut down, absolutely without producing sticky burrs.

Moreover, this material must have experienced the wind and sun of long years.

In industrial terms, this was called natural aging.

Only after several years or even decades of alternating heat and cold would the residual stress generated inside the material during casting be completely released.

The more fully the stress was released, the more stable the scraped plane would be, and it would not inexplicably warp a few months later.

There was only one thing that met these two conditions.

Gray cast iron that had withstood the test of natural aging.

...

The nighttime temperature had dropped below six degrees.

Inside the Stone House, the stove fire burned a small piece of picked-up waste wood, and the orange-red firelight leaped through the gap of the stove door, reflecting the wall into a warm, cozy red.

Jiang Lin sat in front of the stone table, with three things spread out before him.

On the left was the yellowed supply ledger.

The potato field maintained a stable output for the ninth consecutive year, and through the crop rotation system with Soybean, soil fertility was well maintained.

Pumpkin grew too wildly and couldn't possibly be eaten all, so most of it was chopped up by him and used for composting.

The water purification system in the backyard, built using waste filter elements and Moss, was operating well.

Those 100W solar panels on the roof had undergone ten years of wind and sand grinding and ultraviolet exposure on the Wasteland, their surfaces were severely aged, and their photoelectric conversion efficiency had plummeted.

Affected by long-term deep charge-discharge cycles, the actual capacity of battery pack No. 1 was only about 30% of its initial state.

Pack No. 2 was slightly better, but only at 35%.

Although there were still battery packs No. 3 and No. 4 as strategic backups, it was currently only the tenth year.

And the plan he had set for himself initially was to survive four decades.

After only ten years, the low-voltage power system was already showing full signs of fatigue.

He had no choice but to have long-term worries.

...

To the right of the ledger were his Physics notes.

How should one describe the progress of his professional Physics courses?

Quantum Mechanics was still engaged in a back-and-forth tug-of-war, repeatedly and intermittently being gnawed through.

He laid the foundation with Griffiths' 《Introduction to Quantum Mechanics, then stubbornly tackled Jun Sakurai's 《Modern Quantum Mechanics, flipping through the first volume of Cohen-Tannoudji to supplement wherever he didn't understand in between.

From the wave function postulates all the way to spin, angular momentum coupling, stationary perturbation, time-dependent perturbation, and the initial chapters of scattering theory.

Every time he finished deducing a chapter of formulas, he would force himself to do exercises.

Sakurai's post-class exercises were notoriously difficult, and many times there were simply no standard answers.

He often got stuck on a matrix element calculation problem for two or three days, staying up until his scalp tingled.

By the winter of the ninth year, he could basically write out the derivation process of the hydrogen atom's energy eigenvalues independently from memory without looking at a book.

He could use the variational method to estimate the ground state energy of a helium atom, and proficiently write down the matrix representation for a low-dimensional Hilbert space operator under a given basis.

What truly made him repeatedly make up lessons until now was the advanced part of theoretical mechanics, and the mathematical wall he crashed into when attempting to lead to general relativity.

Non-inertial frames and rigid body kinematics were forcibly gnawed through when he made wind-powered water-lifting devices in his early years, and Joseph-Louis Lagrange mechanics and Hamiltonian mechanics had also basically been walked through.

But from the derivation of the principle of least action to Noether's theorem, that wonderful and abstract geometric relationship between symmetry and conserved quantities, the canonical transformations in phase space, and the Hamilton-Jacobi equation, he always felt as if there was a layer of frosted glass separated in the middle.

That layer of glass wasn't because he couldn't understand the letters, but because he lacked the underlying support of geometric language.

He didn't know what a manifold was, and he didn't know differential geometry.

He had once taken Arnold's 《Mathematical Methods of Classical Mechanics》 with full confidence, opened it to read a few chapters, and was then beaten to a pulp by the overwhelming exterior derivatives and vector fields on manifolds inside, retreating in a flurry.

He painfully realized that what he lacked was no longer doing a few more Physics problems or reading one more Physics book, but a complete modern mathematical prerequisite framework.

Differential manifolds and Riemannian geometry.

He had to stop the progress of Physics and make up for mathematics like an ascetic monk.

Introduction to Differential Geometry, Preliminary Topology, Introduction to Group Theory.

Gnawing through them was extremely slow and extremely painful.

Because it was too abstract, there was no realistic intuition that could be used to assist understanding.

There were no spinning gyroscopes, no bent light rays, and no pulley systems for him to see with his own eyes.

There were only symbolic derivations on paper.

He wrote in his journal: "My current mathematics gets tripped up right here at Lie groups and fiber bundles. This is not a problem of not learning advanced mathematics well; it's that my brain has not yet established the intuition of high-dimensional abstract geometry. As Physics moves upward, the language it requires becomes deeper and deeper, and I am still pinned in the mud of the Earth."

Standard problems of mechanics of materials could be solved by him right away now.

Because its problems were very plain and very close to the work in his hands.

Why would a steel rod bend under force, why would the edge of a drilled hole be most prone to cracks, and why would the bending strength increase exponentially after a thin steel sheet was folded into a 90-degree angle?

When a reinforcing patch was added here, was it actually strengthening the structure, or driving the stress to another weaker joint?

For these questions, he could already give the first-level engineering answers using mechanics of materials.

But elasticity was stuck in the fault between real boundary conditions and old structural samples.

Because it was not satisfied with simplifying components into a beam or a rod.

It began to inquire into the stress state at any arbitrary point inside the object.

Stress tensor, strain tensor, constitutive relation...

The diagrams in the book were always drawn so cleanly.

An infinitely large thin plate with a perfect circular hole dug in the middle, and uniform uniaxial tensile loads applied at both ends.

Then, through a series of elegant partial differential equations, a perfect hole-edge stress concentration factor was derived.

This conclusion was very good, very perfect, but also extremely dangerous.

Because the old reinforcing patches in Jiang Lin's hands were never any infinitely large thin plates.

On the handwritten board in the middle was a derivation he had accidentally stumbled into last night.

It wasn't a formal task in the training plan, but rather he had chased all the way from Noether's theorem and the gauge degrees of freedom of the electromagnetic field, pursuing it to the Lagrangian construction of a certain gauge field model, and then got stuck by the expansion of the covariant derivative.

The wind of the wilderness blew past the rooftop; this sound was something he had heard for decades, and he long ago stopped distinguishing whether it contained any dangerous implication.

Wind was wind, and a person was a person.

If you could hold on, you held on; if you couldn't hold on, you figured out a way to hold on.

His fingers flipped over a page tucked inside the Physics notebook; that was the book list he had prescribed for himself.

Most of the courses on it had checks next to them, with only a few still left blank.

He raised his hand to cross out the note [Barely Pass] next to the Four Major Mechanics, changing it to four words.

Still studying.