Tomb of Seven Billion Humans

This is the final departure from the sun, one from which there will be no return.

As the distance increased, the sun dimmed, and Xiao Yu's heart grew inexplicably heavy.

The road ahead is long and arduous, stretching over 10.5 light-years, and spanning 6,300 years.

What strange occurrences might he encounter on this journey? What dangers lie ahead? Xiao Yu does not know. But still, he has decided to set out. What drives a scientist is the mad desire for exploration, a desire so intense that even life itself can be sacrificed.

Thus, Xiao Yu chose not to continue developing within the solar system, but rather, after acquiring the ability for interstellar travel, he immediately chose to depart.

To be precise, Xiao Yu's current technology can only be said to have achieved interplanetary travel. For at the speed of nuclear fusion propulsion, interstellar travel takes millennia, long enough to exclude any life form with a lifespan under ten thousand years. However, after merging with the computer and abandoning his physical body, leaving only his spirit, Xiao Yu's lifespan has become nearly infinite. It is through this almost cheating method that he has gained the ability to embark on interstellar travel using interplanetary technology.

Humans once calculated that the minimum threshold for interstellar travel is to reach five percent of the speed of light, which is about fifteen thousand kilometers per second. At such a speed, it would take about two hundred years to travel from the solar system to the Tianyuan Four-Star System, a time frame that was already within the acceptable range for human lifespans of that era.

However, before the development of a new generation of engines, a speed of fifteen thousand kilometers per second remains a distant dream for Xiao Yu.

Returning once again from Jupiter to Titan, Xiao Yu did not descend. On Titan, two large-scale photon computers had already been transplanted by Xiao Yu onto the Solar and the Voyager. Now, the base is entirely controlled by the computer from that initial small spacecraft.

Although, in Xiao Yu's current view, this computer is far too outdated, with its computing speed being too slow, it is sufficient for now as the ninety-nine bases on Titan have ceased operation, and all machinery has been sealed. Only some simple maintenance tasks remain, which the computer can handle.

Titan's atmosphere contains very little oxygen, and the temperature is low, so there is no need to worry about rust or mechanical damage. Xiao Yu hopes that these machines and devices can last for a long time, remaining intact for thousands or even tens of thousands of years.

Due to the stripping of a large portion of Venus' atmosphere, leading to a decrease in surface temperature, it is possible that in the infinite future, intelligent life might evolve on Venus. Therefore, Xiao Yu hopes that what he has left behind can guide these future Venusian beings in their evolution, and perhaps serve as evidence that humanity once existed within the solar system.

As he gazed at Titan, shrouded in mist from space, Xiao Yu's heart was filled with emotion.

"Twenty years have passed just like that," Xiao Yu silently calculated in his heart.

In the blink of an eye, twenty years have passed since he left Earth.

During these twenty years, many things have happened. The carefree days on Earth still seem like they were just yesterday.

Memories flowed through Xiao Yu's mind, one after another.

The first time he left Earth, the fear when facing the collision of Jupiter and its moons, the joy of his first feast, the struggles on Titan, the excitement of mastering controlled nuclear fusion technology, and so on, one by one, event after event.

"Let's go, let's go. Though it is safe and comfortable within the solar system, without experiencing storms, how can there be great achievements? Let's go, let's go. The boundless universe is my ultimate goal of exploration."

Xiao Yu cast aside his countless thoughts, controlling the massive fleet as it headed toward Saturn.

Within Saturn's system, Xiao Yu would perform the final refueling before leaving the solar system to embark on a long journey toward Tianyuan Four.

Xiao Yu frantically refueled, staying in Saturn's atmosphere for half a month until the ships were completely filled before leaving Saturn.

After one last lingering look at Titan, Xiao Yu resolutely pressed forward, racing out of the solar system.

At this moment, Xiao Yu had already loaded half of the fleet's ships, including three county-class ships—Voyager, Solar, and Tianyuan—and nearly five hundred village-class and township-class ships, with various supplies. If not for the need to keep some ships mobile in case of unforeseen circumstances, Xiao Yu might have loaded all the ships with supplies.

During this time, Xiao Yu deeply understood one truth. In the vastness of space, the most dangerous places are not where meteors fly wildly, but where there is emptiness. For in such places, every celestial body is at least a thousand years of travel away. There is nothing there, and should an unexpected situation arise, there will be no way to replenish supplies. You can only wait for your energy to run out, and then die, becoming a cold, drifting stone in the endless expanse of time.

This is just interstellar travel. If it were galactic travel, it would be even more terrifying. There, to obtain a piece of scrap metal, you might need to travel at the speed of light for millions of years.

Endless time is the greatest enemy of interstellar travel.

Xiao Yu's mind wandered as he haphazardly thought about various things while controlling the fleet to slowly accelerate. Back when he first left Earth, Xiao Yu had been eager to leave the solar system. But now that he was truly about to leave, he found himself reluctant.

Xiao Yu thought of someone—a girl, young, beautiful, full of vitality, pure, and lovely. It was back on Earth; she was a researcher in Xiao Yu's laboratory.

The girl liked Xiao Yu, but Xiao Yu, who was entirely focused on science, had no interest in matters of love. He even harshly criticized her for it, causing the girl to leave the laboratory in dismay.

Xiao Yu never thought he was wrong, but now, at this moment, he felt a pang of regret.

"She must be dead by now, right? She died with the seventy billion humans. But it seems that ever since she left the lab and up until Earth's destruction, during those seven years, I never received any news about her. I don't know what happened to her."

As he thought, Xiao Yu activated the Solar's three-dimensional color projector and began to create a human figure.

In the Solar's cabin, as the three-dimensional color projector moved, a girl's figure gradually appeared.

"Hmm, no, her eyes should be bigger. Uh, okay, her waist should be slimmer, her nose more prominent, her chest larger..."

Xiao Yu adjusted various parameters, and gradually, a smiling girl's figure was projected in the air.

She stood there, gazing forward with eyes full of warmth, as if there were many things she wanted to say.

Xiao Yu generated a piece of code, and after executing it, the girl began to speak.

"Director Xiao, how have you been?"

Her voice was soft, shy, and exactly as it was when she spoke on Earth.

Xiao Yu stared at her figure, murmuring, "Chen Mo, I'm fine, I'm still alive. What about you?"

"I've been dead for twenty years now," the girl said with a gentle smile.

"Yes, you're dead, you died twenty years ago. And I, I have gained infinite life. But I no longer have a body," Xiao Yu said sadly.

Separating the body from the spirit is a very risky endeavor. Back on Earth, Xiao Yu had happened upon a mysterious substance from outer space. After years of research, he took the enormous risk of separating his spirit from his body. Until he fully understood all the properties of this substance, Xiao Yu dared not take such a risk again.

In other words, even if he had another body, Xiao Yu would not choose to merge with it. For once merged, he would be unable to separate again, and Xiao Yu would once more be subject to the limitations of a physical form, to aging, sickness, and death.

"Chen Mo, wait for me. When I fully understand the human genetic code, I will bring you back to life," Xiao Yu murmured.

When Xiao Yu left Earth, he had stored a human gene bank and a sperm bank. However, during the escape from the Jupiter-Moon collision, these were lost due to a meteor strike.

"I'll wait for you," Chen Mo said with a slight smile. After saying this, her figure dissolved into light and disappeared.

"When you're resurrected, I will accept your confession," Xiao Yu whispered, staring blankly at the light into which Chen Mo's figure had dissolved.

"Ah..." Xiao Yu sighed, pulling his mind away from the endless thoughts, and continued to steer the vast fleet away from the solar system.

Gradually, several months passed in a blur.

Xiao Yu's fleet had reached the orbit of Uranus.

"We're nearing the orbit of Uranus. Here, I'll leave a tombstone for human civilization," Xiao Yu thought.

The orbit of Uranus is about 2.7 billion kilometers from Earth's orbit. From here, the sun appears only as a bright spot in the sky, indistinguishable from the other stars.

With a sigh, Xiao Yu used his stored metal materials to craft a tombstone, and with nuclear fusion technology, he created a battery—a battery that could last for millions of years to power an eternal light.

This tombstone will orbit the sun every 130 years, and for a million years, this eternal light will shine, illuminating the words engraved upon the tombstone:

"Tomb of Seven Billion Humans!"

"Erected by Xiao Yu, one of humankind!"