"Mr. Watson, please come! I need you!"

Just as when humans first made a telephone call, the first meaningful sound humanity sent into space turned out to be an unremarkable yet dramatically charged five words: "Tending toward the infinite."

Somewhere in the universe, that sound echoed. There was a computational array there, with an intelligent entity located roughly every 300,000 kilometers; according to that alien civilization's histories, that spacing was chosen to honor a certain tradition. The machine, long silent, suddenly activated when it heard those words.

"Sentient beings! What a profound sentence!"

"Only these five words? We must visit that civilization."

"But before that, how should we interpret this sentence?"

The central node that asked the question was immediately answered by the twelve surrounding nodes, which returned their viewpoints all at once and chattered them to the central node.

"Okay, information processed. We will depart for the signal source now. We will be saved."

Yu Yang was astonished to see that five seconds after he uttered that sentence, the surrounding space underwent a drastic change. Everything in the nearby laboratory warped and reshaped, and suddenly it became the scene from his own home. Sitting on the sofa was a person who was exactly his double, looking at him with an expression that was hard to classify as fear, curiosity, or anxiety, but suffused with an unforgettable sense of world-weariness.

"Are you me?"

"Th‑this can't be."

"Five light-seconds away, the same order of magnitude as Earth–Moon distance — that's too close, how is that possible? No, no, no, how could this be light-speed travel? Is it nonlocal action? But I didn't transmit a Rosetta Stone system, only those five words, and you parsed them within five seconds? What kind of miracle is this?"

Yu Yang fired off questions like a machine gun, but the other side seemed not to hear.

"Are you Yu Yang?" the other asked, somewhat surprised.

"Yes, I am." Yu Yang felt a surge of fear of the unknown but spoke cautiously. In truth, he wasn't very surprised that the other knew his name — after all, today had already been overflowing with astonishing things.

"Tending toward the infinite — can you help us interpret that sentence? The empire's twelve chief scientists have done a lot of analysis."

"Our philosophers say there are two kinds of beings in this universe: those who build up from a finite world toward the infinite, and those who, by comprehending the infinite, look down upon the finite world. They insist on telling you: 'Tao begets One; One begets Two; Two begets Three; Three begets the ten thousand things.'"

Yu Yang's heart skipped a beat. Of course he knew that saying, but he was startled that the alien Yu Yang knew it too — how much of human civilization did they understand?

"Our cosmologists say our universe is finitely infinite; this must be an alien cosmologist interpreting the ultimate mystery of the cosmos. The observable universe is accelerating in its expansion, which means distant regions recede faster than light. As an agent's observational horizon expands, its observable universe actually shrinks, and inevitably a singularity must arise. After the singularity, the observable universe will contract."

Indeed, Yu Yang had heard this theory back in college — then it was only a hypothesis, but now it had become a cold fact.

"Mathematicians believe that when mathematics evolves into higher-level mathematics, it too will encounter singularities, and after those singularities, the sad truth for intelligences is that they must accept the comprehensive stagnation of their science." The alien Yu Yang shook his head. "It's like how you can't actually travel at the speed of light or even near light speed; theoretically possible, but the energy cost is too great."

Yu Yang thought to himself that human mathematics had been drifting toward unavoidable stagnation over the past decades; perhaps soon, within a single lifetime, it would be impossible to master the entirety of mathematical theory, much less build new theories.

"And physicists say the universe will unavoidably head toward heat death — by then the universe will be a completely random machine, forever and ever."

"But I didn't think that far. I was just at college when my son messaged me on WeChat about a calculus problem, and I accidentally sent it out." Yu Yang shrugged.

A look of clear dejection and disappointment flashed across the alien Yu Yang's face — he knew Yu Yang was right. But he was, of course, furious at being triggered by such a prank.

"Still, I think the things you said seem to be correct," Yu Yang smiled confidently. In that moment, facing this unknown being identical to himself, he felt less afraid. "Yes. By intuition, it seems all these accounts describe the same phenomenon."

The alien Yu Yang's face changed abruptly; he seemed to be pondering the logic of that sentence and was delighted. After a long while he laughed awkwardly, "Yes, why did we never think of that? It's so straightforward."

Yu Yang looked sorrowful. "And I want to say that my life will also slowly head toward that singularity. My life has been scripted since youth: kindergarten, elementary school, middle and high school, university, find a decent job, marry and have children. The fire in one's heart slowly dims, and the path of life becomes harder. I slowly move toward death; my body ages and my energy wanes. I constantly feel the singularity approaching. On cosmic scales such things are so distant, but on the scale of an individual, it's an unavoidable reality."

"You won't," the alien Yu Yang said. "I, I, never mind, I promise you won't. After all, you saved our entire civilization." He continued, "Although that tragic future will not change, we already know how to change the future, because the ancient philosophers gave us wisdom," he paused, "and courage."

Yu Yang looked into his eyes. At that moment he seemed to receive an endless flood of information from them, needing nothing more than a glance. His reason told him not to overthink. He smiled and nodded, understanding.

"There isn't much time left," the alien Yu Yang said with a smile to the identical man. "Yu Yang is a good name. A fish enters the sea — in the Northern Darkness there is a fish, its name is Kun; the Kun is so large one does not know how many thousands of li it spans. A fine name. Farewell, Yu Yang." The alien Yu Yang slowly withdrew from Yu Yang's conscious world and returned to his home star.

This universe once had an ironclad law: causality. An effect cannot precede its cause nor happen without a cause. Yet behind that rule was the implication that as long as you do not violate it, anything could happen.

That made temporal editing possible. If a segment of time's events is deleted without violating causality, then it is legal.

Only now did the alien Yu Yang understand why he had edited almost all of his empire's time — from the naïveté on their homeworld through the rise to prosperity, reaching a peak, and then the inevitable slow decline in the epic of years. He had been decisive. The empire returned to a naive era. His future self would start over again from the beginning, fearless and no longer confused.

And he understood that he could never bear to cut out their brief meeting of a dozen or so minutes, because that should be the most beautiful exception across the universe's entire timeline.