55: Chapter 55 The World Beyond μ

The small garage had no windows.

The only light source was the incandescent lamp overhead.

The filament trembled slightly inside the poor-quality glass bulb, and the electric current heated the thin tungsten wire to an incandescent state, emitting a yellow light akin to blackbody radiation that illuminated the garage of less than 6 square meters like an old photograph.

Jiang Lin stood blankly on the concrete floor, his chest heaving violently, and it took him a good while to recover from the sense of spacetime dislocation.

He lowered his head and glanced at the floor.

The shrinkage cracks left behind during the concrete pouring extended inward from the garage threshold like a dried-up gray lightning bolt, branching right in the middle and marching unhesitatingly toward the bottom corner of the wall on the northern side.

His eyes merely swept over it, and the computing center deep within his cerebral cortex automatically began to operate.

The direction of the cracks was not random.

Jiang Lin could almost replay in his mind the rough scene from over a decade ago when this patch of ground was laid.

It could have been uneven aggregate distribution during pouring, too rapid water loss on the surface, or insufficient base compaction.

Coupled with the lower temperature on the northern side than the southern side during the curing period, the shrinkage stress was released along the path of least resistance.

Portland cement released heat during the hydration reaction, and the subsequent cooling and shrinkage generated uneven internal stress under this tiny temperature difference.

This stress tore mercilessly along the path of least resistance formed by the microscopic pores and weak mortar layers inside the concrete.

Therefore, the cracks leaned north.

If this ground needed to bear a concentrated load, such as placing a two-ton lathe on it, the shear failure of the base would 100% start from the sharpest tip of that northern branch.

He suddenly realized he was doing futile work, shook his head hard, and forcibly shut down the stress analysis model that had popped up in his mind.

This was just a garage where not even an electric bicycle was parked; there was nothing here that needed to bear a concentrated load.

But he could not control it.

His current state was very bizarre; forty years' worth of things packed in his nervous system had now flowed into an eighteen-year-old body.

It was like forcibly pouring a whole tank of high-density heavy water into a thin glass bottle with a capacity of only five hundred milliliters.

The bottle looked intact on the outside, but the water pressure inside was already terrifyingly high, and the water would overflow from every tiny crack, following his every instinctive action.

So the next moment, when his gaze accidentally touched a few expansion bolts on the right wall, he subconsciously raised his hand again.

This eighteen-year-old body's muscle memory had not completely caught up yet, and his movements appeared somewhat stiff.

His thumb rubbed across the edge of the nut, picking up a bit of fine rust powder.

This indicated that the plating had broken long ago, there was long-term moisture near the wall, or the hole wall had pulverized badly when drilling back then, and the expansion sleeve had not truly bitten into the solid substrate.

He gently pushed it with his knuckles and did not feel obvious looseness, but this did not mean it was safe.

If he really wanted to hang heavy objects, he would at least need to re-drill holes, replace the expansion parts, or even conduct a pull-out test.

"Huala—"

From outside the garage came the sound of a sanitation worker's bamboo broom scraping against the asphalt road surface while sweeping.

Then came the footsteps of someone passing by.

The footsteps were dull and dragging. Accompanied by a cough or two from an early riser, they passed through the morning light at the bottom of the garage door gap, cutting that beam of light into several pieces of shattered shadows, then gradually walked away and disappeared at the alley entrance.

The morning of Jiangcheng was beginning in its usual way, just as it had for decades.

Jiang Lin let out a long breath of stale air, took the school uniform prepared in advance last night from the shelf, habitually shook the dust off it—just as he had done during the forty years in the Wasteland—and put it on.

Then he sat down beside the workbench.

During those forty years in the Wasteland, following the undergraduate training plan of the Peking University School of Physics, he had repeatedly gone through the core courses that could be mastered through self-study, conducted a large number of experiments, and accumulated a massive amount of data.

And established a set of ways to understand the world.

He had physical intuition, a mathematical framework, and an engineering sense polished from metals and failures.

But this set of things had a fundamental problem.

It had never undergone external verification.

There was no white-haired professor deriving partial differential equations for him on the blackboard, no unconvinced classmates arguing fiercely in the dorm over the value of a parameter, no one looking at his manuscripts, and no institution verifying his data errors.

All the Physics and engineering edifices he built in the Wasteland were constructed like walking a tightrope under conditions without an absolute baseline.

He himself was very clear about this.

Therefore, in that thick "Index of Errors and Unresolved Issues", he reserved a full page for this matter.

At the header of that page, a line of text was written with the heaviest brushstrokes.

"List of conclusions without external verification; credibility is questionable and may trigger systematic disasters at any time."

And now, he was back.

He had returned to the Real World.

Here, there were national standard systems, high-precision machine tools, massive academic literature databases, and people who could discuss, question, or even directly refute him.

The first thing he needed to do was open that list, go down item by item, and check off one by one those unresolved things that had tortured him countless times in the deep of night.

Thinking of this, he took off his backpack, unzipped it, took out the "Index of Errors and Unresolved Issues", and flipped to the last page.

On the yellowed, fuzzing paper were a few lines of words he had written with a pencil before returning.

"First: Contact stiffness — Thermal cycle — Wasteland data noise is too large; is the established evolution model correct?"

"How should the nonlinear term coefficients of Kc = f(P, ΔT, Ncycle) be corrected?"

"Second: Cast iron surface — Three-Plate Grinding Method — Support deformation, temperature drift, abrasive particle size, contact spot interpretation error; has the oil film / water film / adhesion force during lapping already affected the judgment?"

"Third: Simple pendulum g value — Pendulum length definition, pendulum bob center of mass, amplitude correction, timing error, string thermal expansion and contraction — Has the systematic error already exceeded 0.1%?"

"Fourth: Fermi energy of aluminum metal — Effective mass m* value selection — Does the 12% error stem from the crudeness of measurement means, or the theoretical simplification of the energy band structure?"

"Fifth: Lack of literature on Electrodynamics — Under the Lorenz gauge..."

The fifth item was unfinished, and the pencil had drawn a somewhat out-of-control long diagonal line across the paper surface.

For the time being, the one Jiang Lin wanted to figure out most was the first one.

Turbine yaw bearings, Three-Plate Grinding Method, long-term study of multi-material contact surface behavior under thermal cycles.

He had derivations and observational data from Wasteland experiments.

In that derivation, there was a degradation model concerning the evolution of contact stiffness with the number of thermal cycles.

He firmly believed that the direction of this model was correct: macroscopic preload would undergo plastic flow between the microscopic roughness peaks and valleys, leading to a decrease in stiffness.

However, the measurement conditions in the Wasteland were too crude.

The vibration of sandstorms, the zero drift of temperature sensors, and other influences made the noise in the data shockingly large, submerging more than half of the trend line that should have dropped smoothly.

He had no way to judge the scope of application of this model.

Much less judge whether those nonlinear coefficients were a reflection of physical mechanisms or illusions pieced together by noise and manual parameter tuning.

Thus, the conclusion hung there with a judgment that even he could not fully trust.

Beside that error index, he had written eight characters at the time: "Direction to be determined, urgent verification needed."

Having made his decision, Jiang Lin put his things away, shouldered his shabby schoolbag, pulled up the rusted rolling shutter door with both hands, and plunged headfirst into the March of Jiangcheng amidst a screeching sound of metal friction.

When he returned home, the roar of the range hood came from the kitchen; his mother was already up and standing in front of the stove making breakfast.

Hearing the noise of the door opening, she poked her head out of the kitchen to take a look. Seeing her son returning from outside, she was somewhat surprised and asked a question.

Jiang Lin looked at his mother wearing that faded apron and her graying temples, using a great deal of effort to suppress the ripples deep within his eyes.

"I couldn't sleep, so I ran a couple of laps at the alley entrance to clear my head."

He tried his best to make his tone sound like an ordinary high school senior suffering from insomnia due to Gaokao pressure, brushing it off.

"Don't push yourself too hard," his mother nagged, turning back to deal with the eggs in the pan.

Jiang Lin walked into the narrow bathroom and turned on the faucet.

The stream of water smashed into the bottom of the ceramic basin, first spreading into an extremely thin water film, only to be torn apart by the rebounded splashes.

He almost instinctively saw the flow velocity, boundary layer, and local turbulence, but the next second he forcibly pushed these words back down.

Then he reached his hand into the water.

The water temperature was about twelve degrees Celsius, clean, colorless, with no pungent sulfide odor, nor did it carry strong acidity sufficient to burn the oral cavity.

This was standard domestic water after multi-stage filtration and chlorination disinfection by a modernized tap water plant.

Extremely luxurious purified water.

He cupped the water and vigorously rubbed his face a few times, icy droplets dripping down his chin.

Then, with his eyes closed, he tore the towel off the plastic hook on the wall.

Just as he turned around, the moment his fingertips accidentally brushed past the bathroom wall tiles, his movement paused instinctively.

To an ordinary high school senior, or to the vast majority of people in this world, this was just an ordinary, cheap glazed ceramic tile.

But in Jiang Lin's eyes at this moment—or rather, in his tactile perception squeezed to the limit by forty years of Wasteland engineering—this tile was a microscopic hill filled with catastrophic defects.

The somatosensory cortex at the back of his brain, like an awakened computer, automatically began to process at high speed every tiny tactile electrical signal transmitted from his fingertips.

Fifteen years of the Three-Plate Grinding Method in the Wasteland, with its almost morbid pursuit of scraping for an absolute plane, had long alienated his hands into two high-precision, even somewhat neurotic vernier calipers and surface roughness testers.

When his fingertips slid across the glazed surface, the resistance had extremely slight periodic changes.

Many people would feel it was quite smooth, but in Jiang Lin's hands, this tile could not be considered a flat surface at all.

Fluctuations on the scale of tens of micrometers were already enough to make him think of those bearing housings ruined by incorrect reference planes on the Wasteland.

Jiang Lin took a deep breath, forcibly cut off this neurotic tactile feedback, abruptly pulled back his hand, and neatly hung up the towel.

"I can't go on like this," he warned himself, "this will drive a person crazy."

In the kitchen, the low-frequency hum of the old-fashioned range hood running, mixed with the sound of the spatula hitting the iron wok, intertwined into a symphony full of the breath of daily life.

Having washed up and smoothly sitting down beside the dining table, Jiang Lin's ears twitched slightly, and his attention was forcibly pulled away again.

The low-frequency hum of the range hood was sandwiched with a slight beating vibration, carrying the broadband characteristic of the outer shell participating in it.

Almost without needing to think, a diagnosis report popped directly into Jiang Lin's mind.

It should be that years of oil stains had biased the mass distribution of the impeller, and a certain fixing screw on the outer shell had also loosened; when the starting speed swept across a certain interval, this natural frequency happened to fall near the second harmonic of the motor's operation, thereby triggering structural resonance.

"Why are you looking all dazed again, staring blankly?"

His mother walked over carrying a plate, serving a steaming portion of sweet and sour eggs into the bowl in front of him, interrupting his thoughts.

She wiped her hands on her apron, her tone carrying a hint of heartache.

"Did you stay up late doing problem sets again last night? Even though the Gaokao is important, your mock exam scores are already very good. Pay attention to your health; don't make yourself look like an old man, hunching your back while eating."

"I know, I'll pay attention."

Jiang Lin hurriedly straightened his back.

The aroma of the sweet and sour scrambled eggs hit his face directly—it was still that taste carved into his bones; the eggs were fried crispy on the outside and tender on the inside, sweet and sour, plump and juicy.

Every bite felt like living in a dream.

In the Wasteland, he had often reminisced about this taste.

Now he was here, eating that bowl of rice, while the range hood was still producing predictable resonance with its loose bolts.

His mother sat down opposite him and picked up a chopstick of pickled vegetables to go with her porridge.

Early in the morning, she didn't like heavy oil and high sugar things like sweet and sour eggs.

Holding her bowl, she looked up at him, and after a moment, couldn't help looking at him again.

"How is it that you've become a bit like your dad lately?" his mother suddenly said out of nowhere.

"Ah, like my dad? In what way?" Jiang Lin raised his head in confusion.

His mother looked at him, a trace of a smile welling up at the corners of her eyes: "It's this kind of look, staring at the bowl for half a day even while eating. When your dad came back from night shifts, he was just like this; clearly eating, but his mind was thinking about things."

"Oh," Jiang Lin softly acknowledged, but inside it felt as though something had slammed fiercely against his heart.

"I was just saying it casually. Eat up quickly, and go straight to school after eating, don't be late."

...

The sunlight of early spring had completely pierced through the morning's thin mist, carrying a trace of insignificant warmth, scattering in large swaths over the streets that were already beginning to bustle.

Jiang Lin rode his bicycle along the greenway.

He forced himself to relax, but his body's senses were like an out-of-control military radar, operating at full power, capturing without reservation every detail of the city's operation.

A diesel bus drove past him.

In most people's perception, it was merely the somewhat noisy roar of the engine and the tire noise of rubber rolling over the asphalt road.

What Jiang Lin heard, however, was a series of hoarse roars emitted by an extremely complex mechanical system on the road as it forcefully fought against Earth's gravity and ground friction.

His auditory nerves seemed to come with a built-in parsing function of the Fourier transform, automatically stripping away the frequencies of the sound waves layer by layer.

At the very bottom was the low-frequency pulsation generated by the periodic compression ignition of the diesel engine under a high compression ratio.

In finer frequency bands, the crankshaft, connecting rods, bearing shells, and oil film together formed a complex vibration source.

The bus's heavy body rolled over a slightly raised sewer manhole cover.

The dynamic response of the chassis instantly flashed through Jiang Lin's mind.

When subjected to an instantaneous impact, the helical spring of the shock absorber underwent rapid compression and rebound. Immediately afterward, the hydraulic oil inside the damper was forced to squeeze through narrow valve holes under immense pressure.

Fluid friction occurred at that very moment, and mechanical energy was ruthlessly converted into thermal energy, dissipating into the air and thereby maintaining the stability of the carriage.

He could even roughly establish a viscoelastic loss model of rubber molecular chains under high-frequency periodic alternating stress in his mind through the tiny deformation and frictional sound when the bus tires contacted the rough asphalt road surface.

It was too dense.

Truly too dense.

The information density of the Real World and the engineering accumulation built up over hundreds of years of the Industrial Revolution were like an endless physical rainstorm to someone returning from an ultra-minimalist world.

Every car here, every traffic light switching according to timing programs, and the load-bearing steel bars hidden within the walls of every building along the roadside were all declaring, in a posture bordering on extravagance, human civilization's compensation for and complete taming of the laws of nature.

This made him feel both awe and absurdity.

...

The first class after morning reading was Physics.

Jiang Lin was sitting in his seat.

His deskmate, Sun Ming, was slumped over his desk like a dirt-digging marmot, frantically rummaging through his chaotic desk compartment for the unfinished Physics exam paper from last night, muttering under his breath, "It's over, it's over. Old Li is going to check the exam papers today. Was my paper eaten by a dog?"

Accompanied by the final trailing note of the class bell, the Physics teacher, Old Li, walked onto the podium in a hurry, holding a slightly chipped yellow wooden set square and a few pieces of chalk.

Old Li was a lean, thin-faced middle-aged man who year-round wore a jacket that had been washed somewhat faded, with cuffs always stained with a circle of white chalk dust.

"Today we will focus on reviewing critical problems in Newton's laws of motion. Everyone stop searching and look at the blackboard!"

Old Li slapped the set square onto the podium, his voice resonant.

He turned around, his wrists flying, and quickly drew a classic Physics scenario on the blackboard.

An inclined plane with an inclination angle of θ, on which was placed a block with a mass of m, representing the object.

"Everyone look at the blackboard. Assuming the block is in a static state, then according to the force analysis, the static friction force is exactly equal to the component of gravity along the direction of the inclined plane, which is mgsin θ." As Old Li spoke, he drew force arrows on the blackboard, "However, if the block begins to slide, we need to calculate the sliding friction force."

Having said that, he turned around and wrote down a formula that all high school students knew by heart with chalk on the blackboard.

f = μ N.

Jiang Lin leaned against the back of his chair, quietly looking at that striking formula on the blackboard.

This was the most macroscopic description of friction in high school Physics, or even in college General Physics.

Simple, elegant, and carrying an unreasonable absoluteness.

A dimensionless coefficient of friction μ, multiplied by the normal positive pressure N, perfectly solved all problems of sliding resistance.

Under the shelter of this formula, it assumed that the object was an absolute rigid body and would not deform.

It assumed that the contact surface was a perfect, uniform, smooth geometric plane.

In low-speed, macroscopic, real rough engineering with extremely high tolerance rates, this empirical formula summarized based on phenomenological laws was sufficient to solve ninety percent of transmission and resistance problems in factories.

But.

He could no longer see only this simplified model.

In his nervous system, which had been thoroughly cleansed and reshaped by forty years of extreme survival in the Wasteland and micron-level reference planes, that formula on the blackboard that looked like truth instantly collapsed with a roar.

The contact surface between the block and the inclined plane rapidly magnified ten thousand times in Jiang Lin's mind, resembling microscopic asperities like countless rolling mountains.

When the normal pressure N was applied, these microscopic peaks collided and squeezed each other.

Because the true contact area actually accounted for only one-thousandth or even one-ten-thousandth of the macroscopic nominal area, at those tiny contact points, the local pressure would instantly skyrocket to an astonishing degree, directly breaking through the yield limit of the material and leading to severe plastic deformation.

The inevitable oxide layer on the metal surface instantly ruptured during the rough scraping generated by sliding, exposing the active pure metal matrix inside.

These defenseless pure metals came into contact at an extremely close distance, and the electron clouds of the atoms overlapped.

If those were two sufficiently clean metal surfaces, after the oxide film was scratched, local adhesion and near-cold welding would even occur.

If the surface was dirtier, the wear debris and oxides would become a third body, trapped within the contact surfaces for repeated plowing.

The μ on the blackboard was not wrong; it merely compressed this entire complex disaster into an empirical coefficient.

As the imaginary block on the blackboard slid, Jiang Lin's brain even automatically constructed a thermodynamic gradient field where frictional heat generation caused local temperatures to rise sharply.

The rise in temperature would change the yield strength of the material, and wear debris, oxide films, and pollutants would continuously change the contact state.

If the stiffness of the system was insufficient and weak vibrations existed, it would also trigger the headache-inducing stick-slip phenomenon, transmitting low-frequency mechanical destructive waves to the entire load-bearing structure.

On the Wasteland, in order to make a yaw bearing for a wind turbine that could run stably, he had been tormented by this microscopic-level friction and preload force for a full fifteen years.

He knew from bloody lessons that a bolt not tightened with the correct torque wrench, or even a trace of invisible burr on the contact surface, would produce micron-level plastic creep under drastic temperature changes and the alternating stress of material thermal expansion and contraction.

This hidden creep would quietly change the stress path of the entire structure within weeks or months.

Ultimately, when a certain storm arrived, it would completely collapse the long-accumulated error chain, throwing the expensive rotor hundreds of meters away.

Jiang Lin looked at the blackboard, listening to Old Li spouting endlessly on the podium while analyzing the acceleration of the block sliding down.

For the first time, he realized so clearly that the ideal model of high school Physics was a flat map with extremely low resolution that filtered out all dangerous terrain.

And he could no longer retreat back into that safe house that abstracted the complex world into a few English letters and constants.

Old Li finished explaining this classic critical problem, casually wrote a variant practice problem on the corner of the blackboard, and let the students calculate it themselves.

A rustling sound of writing and page-turning echoed in the classroom.

The students began to lower their heads to calculate.

Sun Ming finally pulled out that crumpled exam paper from the very bottom of his books. Wiping the sweat from his forehead, he looked down at the practice problem, bit the end of his pen, nudged Jiang Lin with his elbow, and asked in a low voice, "Jiang Lin, Brother Lin, this problem's inclination angle has changed; should the component of gravity use sin or cos?"

Jiang Lin withdrew his gaze from the tearing of the microscopic world, glanced at the problem, and said in a calm tone, "The inclination angle of the inclined plane is α, and the component along the downward direction of the inclined plane uses sin."

"Oh oh, right, right, right, you scared me to death."

Sun Ming breathed a sigh of relief and hurriedly lowered his head to frantically calculate on his draft paper.

...

At 5:40 PM, the sky in Jiangcheng in March was not yet completely dark.

When Jiang Lin went home, he deliberately rode his bike along a detour, passing by the supermarket where his mother worked.

He did not go in; he merely stopped under the parasol tree across the street, propping himself up with one foot on the ground, and glanced from afar from the outside across the wide glass curtain wall.

The supermarket was crowded with people. He saw his mother wearing the supermarket's unified red vest, standing behind the cash register, deftly scanning product barcodes, and then bending over to help an elderly woman pack vegetables into a plastic bag.

His mother's movements were very skilled, but due to long-term standing, her lumbar intervertebral discs bore unreasonable sustained stress, causing her back and waist to be noticeably hunched.

Jiang Lin silently watched for a moment, his fingers tightening and then loosening on the handlebars.

Then he pedaled hard, turned the handlebars around, and went home.

His father was still catching up on sleep, and no one was in the living room. He skillfully washed his hands, rinsed the rice, and pressed the cook button of the rice cooker.

Listening to the soft click of the relay pulling in from the heating plate at the bottom of the rice cooker, he felt the initial stage of electrical energy converting into thermal energy.

Afterward, he turned around and walked into his bedroom.

Opening his notebook, he re-read the first item on that list.

Then he went over that part of the notes recording this problem in the Wasteland in his mind.

This lingering Physics mystery that had tormented him for a long time started with that wind turbine yaw bearing.

The bearing base was a combination of aluminum alloy and steel. The linear expansion coefficients of the two materials differed by nearly twofold. Under the exaggerated diurnal temperature range of the Wasteland, the contact surface would experience extremely harsh repeated thermal expansion and contraction.

He observed a phenomenon.

With the same initial preload force and the same mating tolerance dimensions, after assembly, during the first few months of winter, the bearing ran smoothly and well.

However, by the early spring of the second year, as the temperature rose, the bearing began to exhibit slight, periodic abnormal noises and vibrations during operation.

Taken apart to look, the distribution of indentation on the contact surface was no longer the same as when assembled.

In areas originally designed to bear force evenly, certain local contact stresses were obviously abnormally concentrated, showing traces of fretting wear.

While other areas had almost no contact traces, as if they had detached.

Long-term thermal cycle stress, coupled with creep at the microscopic level of the material, led to an irreversible redistribution of the transmission path of the bolt preload force.

The originally ideal uniform contact degraded into severe localized concentrated contact.

The equivalent contact stiffness of the contact surface therefore dropped significantly, and under dynamic aerodynamic loads, the natural frequency of the entire bearing system decreased, thereby beginning to produce destructive response vibrations.

He recorded this phenomenon in detail and, on countless nights of power outages, derived a simplified mathematical model regarding the contact stiffness degradation of multi-materials using a pencil.

Macroscopically speaking, the stiffness degradation time scale predicted by that model basically matched the time of occurrence of the abnormal noise he observed in the Wasteland.

But matching up did not mean the mechanism was correct.

In his model, several key non-linear coefficients and surface topography parameters were purely estimated.

Because under the harsh conditions of the Wasteland, he simply did not have a high-precision 3D profilometer to measure the roughness after wear, nor did he have a high-frequency dynamic dynamometer to monitor changes in the normal force in real time.

How much of the match between the model prediction results and the observed phenomena was because the model he derived was completely correct in its physical mechanism?

And how much was simply because when applying the formula, he subconsciously utilized the margin of parameter adjustment and forcedly cobbled it together?

He had no way to distinguish.

He needed a set of real data, data measured under controllable and traceable benchmark conditions, to tell him how absurd or how reliable the parameter values inside the model he racked his brains to create truly were.

Jiang Lin opened his laptop, first opened Baidu Scholar and CNKI, searched for several groups of Chinese keywords, and then switched to a preprint platform he had bookmarked long ago.

The platform loaded very slowly, and the page style was also rough, but the English paper citation entries still brushed out one by one.

His fingers hovered over the keyboard for half a second, and then he quickly typed a series of English search terms.

Thermal cycling (Thermal Cycling)

Contact stiffness degradation (Contact Stiffness Degradation)

Preload relaxation

Multi-material assembly micro-slip (Multi-material Assembly Micro-slip)