Cixin Liu - Death's End

Yifan said, “Lightspeed spaceflight was a tremendous milestone for humankind. It was like another Enlightenment, another Renaissance. Lightspeed flight fundamentally transformed human thinking and changed civilization and culture.”

“I can see that. The moment I entered lightspeed, I felt myself change. I realized that I could, in my lifetime, leap across space-time and reach the edge of the cosmos and the end of the universe. Things that used to seem only philosophical suddenly became concrete and practical.”

“Yes. Things like the fate and goal of the universe used to be only ethereal concerns of philosophers, but now every ordinary person must consider them.”

“Has anyone in the new world thought of going to the end of the universe?”

“Of course. Five ultimate spaceships have already been launched.”

“Ultimate spaceships?”

“Some call them doomsday ships. These lightspeed ships have no destination at all. They turn their curvature engines to maximum and accelerate like crazy, infinitely approaching the speed of light. Their goal is to leap across time using relativity until they reach the heat death of the universe. By their calculations, ten years within their frame of reference would equal fifty billion years in ours. As a matter of fact, you don’t even need to plan for it. If some malfunction occurs after a ship has accelerated to lightspeed, preventing the ship from decelerating, then you’d also reach the end of the universe within your lifetime.”

“I pity Solar System humans,” said Cheng Xin. “Even at the very end, most of them lived lives confined to a tiny portion of space-time, like those old men and women who never left their home villages during the Common Era. The universe remained a mystery to them until the end.”

Yifan lifted his head to gaze at Cheng Xin. Under 3G, this was a very strenuous exercise. But he persisted for some time.

“You don’t need to pity them. Really, let me tell you: don’t. The reality of the universe is not something to envy.”

“Why?”

Yifan lifted a hand and pointed at the stars of the galaxy. Then he let the 3G force pull his arm back to this chest.

“Darkness. Only darkness.”

“You mean the dark forest state?”

Guan Yifan shook his head, a gesture that appeared to be a struggle in hypergravity. “For us, the dark forest state is all-important, but it’s just a detail of the cosmos. If you think of the cosmos as a great battlefield, dark forest strikes are nothing more than snipers shooting at the careless—messengers, mess men, etc. In the grand scheme of the battle, they are nothing. You have not seen what a true interstellar war is like.”

“Have you?”

“We’ve caught a few glimpses. But most things we know are just guesses…. Do you really want to know? The more you possess of this kind of knowledge, the less light remains in your heart.”

“My heart is already completely dark. I want to know.”

And so, more than six centuries after Luo Ji had fallen through ice into that lake, another dark veil hiding the truth about the universe was lifted before the gaze of one of the only survivors of Earth civilization.

Yifan asked, “Why don’t you tell me what the most powerful weapon for a civilization possessing almost infinite technological prowess is? Don’t think of this as a technical question. Think philosophy.”

Cheng Xin pondered for a while and then struggled to shake her head. “I don’t know.”

“Your experiences should give you a hint.”

What had she experienced? She had seen how a cruel attacker could lower the dimensions of space by one and destroy a solar system. What are dimensions?

“The universal laws of physics,” Cheng Xin said.

“That’s right. The universal laws of physics are the most terrifying weapons, and also the most effective defenses. Whether it’s by the Milky Way or the Andromeda Galaxy, at the scale of the local galactic group or the Virgo Supercluster, those warring civilizations possessing godlike technology will not hesitate to use the universal laws of physics as weapons. There are many laws that can be manipulated into weapons, but most commonly, the focus is on spatial dimensions and the speed of light. Typically, lowering spatial dimensions is a technique for attack, and lowering the speed of light is a technique for defense. Thus, the dimensional strike on the Solar System was an advanced attack method. A dimensional strike is a sign of respect. In this universe, respect is not easy to earn. I guess you could consider it an honor for Earth civilization.”

“I thought of something I wanted to ask you. When will the collapse of space in the vicinity of the Solar System into two dimensions cease?”

“It will never cease.”

Cheng Xin shuddered.

“You are scared? Do you think that in this galaxy, in this universe, only the Solar System is collapsing into two dimensions? Haha…”

Guan Yifan’s bitter laughter caused Cheng Xin’s heart to seize up. She said, “What you’re saying makes no sense. At least, it doesn’t make sense to lower spatial dimensions as a weapon. In the long run, that’s the sort of attack that would kill the attacker as well as the target. Eventually, the side that initiated attack would also see their own space fall into the two-dimensional abyss they created.”

Nothing but silence. After a long while, Cheng Xin called out, “Dr. Guan?”

“You’re too… kind-hearted,” Guan Yifan said softly.

“I don’t understand—”

“There’s a way for the attacker to avoid death. Think about it.”

Cheng Xin pondered and then said, “I can’t figure it out.”

“I know you can’t. Because you’re too kind. It’s very simple. The attacker must first transform themselves into life forms that can survive in a low-dimensional universe. For instance, a four-dimensional species can transform itself into three-dimensional creatures, or a three-dimensional species can transform itself into two-dimensional life. After the entire civilization has entered a lower dimension, they can initiate a dimensional strike against the enemy without concern for the consequences.”

Cheng Xin was silent again.

“Are you reminded of anything?” Yifan asked.

Cheng Xin was thinking of more than four hundred years ago, when Blue Space and Gravity had stumbled into the four-dimensional fragment. Yifan had been a member of the small expedition that conversed with the Ring.

Did you build this four-dimensional fragment?

You told me that you came from the sea. Did you build the sea?

Are you saying that for you, or at least for your creators, this four-dimensional space is like the sea for us?

More like a puddle. The sea has gone dry.

Why are so many ships, or tombs, gathered in such a small space?

When the sea is drying, the fish have to gather into a puddle. The puddle is also drying, and all the fish are going to disappear.

Are all the fish here?

The fish responsible for drying the sea are not here.

We’re sorry. What you said is really hard to understand.

The fish that dried out the sea went onto land before they did this. They moved from one dark forest to another dark forest.

“Is it worth it to pay such a price for victory in war?” Cheng Xin asked. She could not imagine how it was possible to live in a world of one fewer dimension. In two-dimensional space, the visible world consisted of a few line segments of different lengths. Could anyone who was born in three-dimensional space willingly live in a thin sheet of paper with no thickness? Living in three dimensions must be equally confining and unimaginable for those born to a four-dimensional world.