Those who face the wall, but are in the Nascent Soul stage.

Chapter 434 Physics Lesson (3k)

In late spring, orioles fly and grasses grow tall.

Compared to the branch campus located in the underground city, Tsinghua's old campus has indeed not changed much since two hundred years ago... The biggest change is probably the ancient trees on campus that survived the great trough and are all two hundred years old.

The green environment has indeed become much better.

The late spring wind carries willow catkins, swirling and drifting onto the road. The catkins habitually seek out chronic rhinitis sufferers, a condition that no longer exists in this era. But before they can find a suitable target, they are precisely captured by a fast-moving robot vacuum cleaner.

"Hmph, nothing but ants," the robot vacuum scoffed.

It stuffed the willow catkins into its own garbage bin, and a high-temperature plasma cluster was generated in the inner chamber, instantly refining all the willow catkins.

This robot vacuum cleaner, which looks just like WALL-E, has a cold and ruthless glint in its eyes. With it around, no amount of poplar catkins, willow catkins, or dust larger than 0.5 pm can drift into the stairwell.

It is the best robot vacuum cleaner.

Below the garbage, I am invincible; above the garbage, I am one for one.

I've heard of a legendary silicon-based empire in the Milky Way; I wonder how it compares to mine?
The robot vacuum cleaner stands with its hands behind its back, exuding a high-tech and sophisticated air.

After the inexplicable close-up ended, several students, carrying their textbooks, quickly walked over, kicked away the robot vacuum cleaner blocking their way, and hurriedly headed straight for the classroom.

"I'm really fed up. I used to have to go to university at 8 am, and after finally graduating with my doctorate, I worked in a research institute for two years. Now I wake up and have to go back to work at 8 am. I'm already in my thirties and I still have to go to university."

“Brother Li, it’s because knowledge has become devalued. Our doctoral dissertations are now at best on par with undergraduate theses. We’ll just have to learn it all over again.” Another student smiled helplessly.

These young college students, with an average age of around thirty, ran briskly through the park, creating gusts of wind.

"Wait, excuse me... are you Professor Ding's students?"

A clear voice came from over.

The young man who had just complained about having to go back to university at his age turned around and saw the tall and slender figure. She was very tall, about 1.9 meters, and this unusual height made the student guess who she was.

"You...you're...from the Space Force?"

He habitually refers to the people in the sky as the Space Force.

"Yes, I'm from the former Asian Fleet. I'm here for exchange and learning. My name is Xizi, and I'm here specifically to listen to Professor Ding's lectures." Xizi introduced herself with a poised and confident demeanor.

This was her second time on Earth. The first time was at the end of the Doomsday War. Since they had never lived on Earth for an extended period, the people from Fleet International were often not used to such a vast land and sky. Xizi was no exception; on Earth, she could hardly distinguish between east, west, south, and north.

After all, the cardinal directions are never used as directions in space.

In other places, there are screens everywhere that can serve as directions and navigation, but at Tsinghua University... or rather, in the entire city of Beijing, the number of screens is pitifully small. This old campus of Tsinghua University is even more like an ancient tourist attraction, with not a single screen available for information.

Xi Zi had knocked on the wall countless times out of habit, but the old brick walls only silently mocked her.

Left with no other choice, she could only ask a few students.

"Just call me Li Ran. We are indeed going to Professor Ding's class. You can come with us," Li Ran said to Xizi.

"it is good."

Xi Zi followed behind Li Ran. She noticed the worn canvas bag behind him and the half-eaten red bean bun in his hand, thus guessing his identity as a person from the Common Era... It was really easy to distinguish between people from the Common Era and modern people. Xi Zi mingled in the crowd, silently calculating the ratio of people from the Common Era to modern people in Tsinghua University.

People in the Common Era made up almost half of the population.

It truly deserves to be the city with the highest population density in the Common Era.

As Xizi walked through a green park, she stopped and looked up at the ancient locust tree overhead. It would take three people to encircle the tree, its branches leaning diagonally towards the red brick wall beside it. The newly sprouted locust leaves were a tender green, contrasting beautifully with the three gilded characters "Department of Physics" on the wall.

The characters are old, with some wear on the edges. When the sunlight shines on them, it's as if the characters are coated with a warm light.

"What a huge tree! I've never seen one like it before," Xizi exclaimed.

“It was planted during the May Fourth Movement, almost three hundred years ago, of course it’s big.” Li Ran swallowed the steamed bun whole. “There are three-hundred-year-old things everywhere here. Look at that building behind the library? The sign says ‘1911’, it’s also over three hundred years old, and it’s still used to store experimental equipment.”

"It feels so strange... like I've stepped into ancient times." Xi Zi looked around.

"Your ancient times, our modern times," Li Ran said with some emotion.

The group soon arrived at the entrance of the lecture hall. The door was made of wood and covered with a copper door knocker. The green rust on the door felt slightly rough on their hands.

"Just go in and find a place to sit... It might be a little hard to find, Professor Ding Yi's classes are quite popular, but since you're here on exchange, there should be seats available for exchange students. I'll go sit next to my friend."

"Thank you, thank you. I can find a seat myself," Xizi said repeatedly.

When she pushed open the door, the room was already packed with people, with even more standing at the back. A six-dimensional sophon floated in the room, ready to broadcast Ding Yi's lesson live. Xizi, being quite tall, simply stood at the very back and pulled out her specially purchased paper notebook.

—In the past five years, humanity has been digesting the technology transmitted back from the Trisolaran world. The technology has been exploding rapidly. In order to prevent the grassroots officers and soldiers from being eliminated, the Solar System Fleet Joint Council launched the call for 're-learning of space soldiers', encouraging young and promising outstanding space soldiers to go to Earth for further study.

As the location of the nation's top universities, Earth boasts educational resources far surpassing those of other planetary governments, thus attracting a large influx of young space force soldiers. These young space force soldiers travel to universities around the world as exchange students.

Xi Zi was one of them; she voluntarily gave up those top Latin-language universities and came to Tsinghua University.

Basic physics is one of the key subjects these exchange students are required to study.

Ding Yi was sitting on an old chair next to the podium, holding a stainless steel thermos in his hand. He also spotted Xizi out of the corner of his eye. Seeing his "savior" appear at the back of the classroom, the old man was slightly surprised.

However, the surprise was only momentary; getting to class was the priority.

Ding Yi, holding a thermos, smiled at the few hundred students in the lecture hall and said:

"I never imagined that my old bones would be able to teach physics at a university after two hundred years."

This lame joke made the students in the audience burst into laughter.

"Teacher Ding, if you can't even teach us physics, then we might as well switch careers and become immortals," a student in the front row said.

"It's a pity that Professor Luo Qing, Dr. Luo Ji, and Mr. Sensor don't teach classes. If any of the three of them were to teach, we would really have to neglect you."

"That's right, if you can't teach us, we'll have to go find Little Moss to take online classes."

The students' comments made the atmosphere in the class even more lively. Ding Yi also smiled. He gestured for the class to quiet down and began today's lesson.

"Over the past semester, we've covered most of the unified cosmological theory given by the risk eliminaters. Today, let's talk about the two dark clouds hanging over the edifice of physics."

"Two dark clouds? The contradiction between the 'ether' hypothesis and the Michelson-Morley experiment results is one, and the conflict between Boltzmann's equipartition theorem and experimental data on the specific heat capacity of gases is another... These two dark clouds of classical mechanics are still floating around?"

Some students were shocked.

A modern student said, "That's not right. Didn't these two dark clouds respectively give rise to Einstein's theory of relativity and Planck's theory of energy quantization? These are landmark events in the transition from ancient physics to modern physics. And both of these theories have been encompassed in the 'unified universe' theory. Where are the dark clouds in the edifice of physics today?"

“Yes,” Ding Yi interrupted the discussion below.

Faced with the students' questions, Ding Yi calmly replied.

"Although Mr. Sensor, the risk avoider, firmly believes that the unified theory encompasses all the laws and phenomena in the universe, it still cannot include the two derived theories. This is also a recent result that I have discussed with Professor Yang, whom you are familiar with."

"Which Professor Yang? Does our physics department have a professor surnamed Yang?"

Ding Yi took a sip of tea, glanced at Zhi Zi who was live-streaming, and said calmly.

"Turn to page 62 of 'Fundamental Physics,' and you'll find the book with the title 'Professor Yang.'"

Two or three hundred students, along with at least one hundred thousand online viewers, simultaneously pulled out their textbooks/e-books and found the so-called "Teacher Yang".

The expressions on the faces of all the students in the classroom instantly became a variety of colors.

“Our old man Yang is really living a long life,” a student said in a hoarse voice.

"Old Yang used to practice boxing with Luo Qing in his early years, and he is very healthy. He is also a neighbor of Dr. Luo Ji in Tsinghua University. Because of this, I often explored the cutting-edge physics with him and came to the conclusion of these two dark clouds, but you should not disturb him."

The students nodded like chicks pecking at rice.

The chalk was white, and the sound of it scratching across the blackboard was a little rough. Ding Yi turned around and wrote the words "parity non-conservation" and "quantum uncertainty". The strokes were not very neat, and at the end, he drew a horizontal line under the words "non-conservation" and "uncertainty".

"These are the two dark clouds."

He turned around and put the chalk in the blackboard tray. "These two things may not be considered cutting-edge now, and undergraduates are very familiar with them, but they are indeed two confirmed dark clouds."

The classroom fell silent for a moment. A boy in the back row raised his hand: "Professor Ding, I remember that quantum mechanics was the cloud over classical mechanics. After the Altar of Truth incident, wasn't this cloud already proven to be included in the 'Grand Unified Theory of the Universe'? Why has it resurfaced?"

Ding Yi nodded: "Quantum mechanics and relativity, two conflicting modern physics theories, are indeed encompassed in string theory, and string theory is indeed one of the surface phenomena of the Grand Unified Formula."

"But," Ding Yi emphasized slightly.

"Quantum mechanics is quantum mechanics, and quantum uncertainty is quantum uncertainty. It may seem that theory contains phenomena, but in practice they are two different things."

Ding Yi said quietly, "I noticed this back in 2005... oh, I don't mean 205, I mean 05 AD when I was messing around with macro fusion and ball lightning, but now I've only grasped a vague feeling and realized where the problem lies."

Before starting the lecture, like countless middle school teachers who love to talk about their lectures to the point of doing the splits, Ding Yi recounted a story from the past.

(End of this chapter)