The Last Sentinel

"Notification: The Azure Phoenix spaceship has entered the main base of the Human Alliance (Human Supremacist Alliance) in the Eastern Continent [Divine Capital] of the Southern Heavenly Gate Project."

"The main base of [Shen Du] has a long history. As the original base for mankind to explore the deep underground world, it first appeared in the Tang Dynasty. The first founder was Yuan Tiangang, a great feng shui master and geomancer in the Tang Dynasty. It was fully developed during the reign of Wu Zetian. Today, it is one of the two oldest main bases in the Eastern Continent and the root of Luoyang, the deep underground world city of mankind on the far side of the moon."

"The Azure Phoenix is ​​undergoing a security check. Please wait."

Looking out through the ship's side, Ye Feng saw a vast, dark underground space with floating streetlights flashing. Under the red and blue lights, rows of spaceships were lined up to be inspected by security robots.

The Mystic Maiden was right. The prevalence of spaceships in the underground world was terrifying. At a glance, there were all sorts of transport ships, including personal single-unit ships similar to the Azure Phoenix, as well as rail-hauled freight ships that sped along the edges of caves. There were even some classic medieval steampunk-style wooden sailboats. Of course, despite being called medieval steampunk, they emitted a white, hazy mist after traveling a short distance...

Looking at the bizarre and wonderful new world outside, the advisor murmured, "This life hasn't been in vain! I've finally seen what the future world looks like!"

The Mystic Woman said, "Due to the protection of the Earth's crust, the underground world has great limitations in terms of spatial layout and vehicle passage. One day when you go to the moon, go to Chang'an and Luoyang and see for yourselves. Those are the real cities that never sleep, the ultimate expression of Eastern civilization."

The advisor asked curiously, "Team Leader Xuan Nu, are these people all members of the underworld's genius club?"

Xuan Nu shook her head. "No, these are all AI robot fleets. The underworld implements very strict household registration regulations, with a joint liability mechanism for individuals and organizations. If an unfamiliar person appears, their entry will be investigated and they will be expelled as well!"

Ye Feng asked, "How many people are there in the underworld now?"

The Mystic Maiden said, "Around 100,000. This includes the number of people at the lunar base. As for Earth, the uninhabited areas at the North and South Poles account for 10,000, the Eastern Region has about 30,000 permanent residents, and the Western Region has more than 20,000. The more than 30,000 in the Eastern Region are divided among 35 bases, with each base having no more than 1,800 people!"

Just then, a flurry of flashing lights came from outside the door, and a voice echoed around, "All ships halt. Welcome back to base, Team Leader of the Southern Heavenly Gate Project, [Mysterious Maiden]! Welcome to the Underground World, new member of the Southern Heavenly Gate Project, [Anonymous]!"

Outside the window, drones emitted colorful beams of light in welcome.

The Mystic Maiden seemed accustomed to the flattery from these AIs, and the Azure Phoenix whistled past, passing through the portal of salvation.

Outside the porthole, a huge, downward-facing underground harbor appeared. The platform had a multi-dimensional honeycomb structure. At first glance, the entire harbor had an inward-looking layout. The further in you went, the larger the area became. In the center was a huge jade-green sci-fi plaza, and around the edge of the plaza were hundreds of spaceship docking berths.

The spaceship's engines emitted a blue-white glow as it slowly docked at the pier.

The cabin door opened, revealing a quiet dock and a cool breeze.

The temperature was around ten degrees Celsius. What came into view was the cold metal dock and the Great Xia Xuan Shui Black Dragon Banner, which fluttered in the wind.

"Oh—" came the aged voice, "He must be the new researcher who was exceptionally admitted! A very young lad."

Ye Feng looked in the direction of the sound and saw an old man wearing a faded interstellar officer's uniform. He had a weathered mustache and white hair, which gave him a somewhat carefree air despite his age.

The Mystic Maiden said, "Yes, his name is Ye Feng!"

The old man raised his hand towards Ye Feng and said, "The garrison commander of the Luoyang base, they all call me Old Camel."

Ye Feng nodded. "Greetings, Camel Garrison Commander."

Camel raised his hand and said, "Go and report for duty. I'm sure that girl Chang'e is getting impatient."

The Mystic Maiden said, "Alright."

As Ye Feng walked past the old camel, he keenly noticed a meaningful glint in the old camel's eyes, as if the old camel had seen through him and knew all his trump cards.

Xuan Nu walked ahead and said, "When Old Camel was young, he was a garrison officer and the most outstanding captain of the Containment Foundation. His future was originally very bright. Unfortunately, during a containment process, he encountered an S-class mutation. The original A-class containment object became S-class. Although Old Camel survived, all the other members of the team were killed. After that, he left the lunar battlefield and returned to his home planet to become a dock patrolman."

The advisor said from behind, "It's clear he's a true warrior who has survived countless hardships; he deserves respect."

The Goddess of Mystery led the way, saying, "These walls are sculpted statues of great human beings. You can come and take a look when you have nothing to do, but not now. We're very busy and need to go and report to Chang'e."

The group strolled past a series of human statues, most of which were high-relief sculptures carved directly onto natural rock walls. The human heroes depicted varied in size and attire, some as tall as three or five stories. Among them were Yuan Tiangang, the first-generation founder of the [Divine Capital] base, dressed in ancient costume and a feng shui master in Tang Dynasty attire, and Li Chunfeng, who sat alongside Yuan Tiangang. Further on were Zu Chongzhi, Zhang Heng, Zheng Fuguang, Shen Kuo, and various well-known modern scientists, followed by famous quotes from scientific philosophy.

The world under the microscope, the universe outside the telescope—science makes everything possible.

Science is both the highest achievement of human wisdom and the most promising source of material well-being.

Theory is gray, but the tree of practice is evergreen.

Man is the measure of all things.

As the advisor hurried along, he muttered under his breath, "See that? This is the hall of science, the gathering place of human genius."

"Compared to this place, the so-called academies of sciences and scientific associations on the ground are nothing more than marketplaces for power and desire!"

"Look at these famous quotes, wow!"

Just then, Ye Feng saw a huge black stone tablet. An ancient circle was carved on the tablet, and around the circle were inscribed ancient Chinese mathematical concepts and values: [Method of Exhaustion], [Meaning Ratio], [Reversal Formula], [355/113], [3.1415926]

Ye Feng stopped and looked at the circular black stone tablet above his head, lost in thought.

The advisor blinked. "Isn't this pi? The method of exhaustion and the ratio of pi to pi are units of ancient mathematics."

The Mysterious Woman said, "This is the first formula for pi left by Zu Chongzhi. Zu Chongzhi was the first to propose pi and calculate it to seven digits, which is a thousand years earlier than the West."

Ye Feng pointed to the writing above and asked, "What does 'reversal formula' mean?"

The Mysterious Woman said, "The value of pi, abbreviated as π, is believed by Zu Chongzhi to mean that if pi can be calculated to its full extent, it means that there exists a formula called the inverse formula. The moment the inverse formula is established, the Great Dao is fifty, and one is lost. The appearance of the inverse formula means that the lost one has been found."

The advisor said, "So what if we find it?"

After a pause, Xuan Nu said, "That means time can be reversed, and the fourth wall has been broken."