Bai Yang turned his head to look at the three people standing behind him.

Wang Ning stood in the middle. Bai Yang watched as his face changed colors like a traffic light—first red, then green, and finally white. He raised his right hand to clutch his chest, his expression pained.

Then he remembered the heart was on the left side.

So he switched to his left hand, tightly gripping the shirt over his chest, continuing his pained expression as he staggered back two steps.

Zhao Bowen and Bai Zhen quickly moved to support him.

“Old Wang, what’s wrong with you?”

“I… I’m having a heart attack…” Wang Ning gasped for breath.

“Since when did you have heart problems?”

“Starting from now.”

The three left the room. Bai Yang sat at his desk and through the wall, faintly heard the others arguing. It started as a discussion but turned into an outright quarrel, their voices penetrating both wall and headphones. Bai Yang could vaguely make out “Even electromagnetic signals travel at the speed of light”—that was Zhao Bowen; “Who would believe that!”—that was Wang Ning; and “We’re completely screwed”—that was Dad.

Dad, Wang Ning, and Zhao Bowen argued in the living room for half an hour, then suddenly fell silent. They sat quietly for a long while, all wanting to speak but not speaking, until finally, all three stood up simultaneously.

“I’m going to the bathroom.”

“I’m going for a smoke.”

“I’m… I’m going!”

Bai Yang went downstairs to throw out the trash and saw Zhao Bowen sitting on the stairs of the first floor, smoking.

The corridor was very dark, with no lights on. Old Zhao sat silently in the darkness, only the red cigarette tip slowly blinking on and off.

“Uncle Zhao.”

Zhao Bowen moved aside a bit, and Bai Yang sat down next to him. The two sat side by side on the steps, looking out at the dark greenery beyond the building entrance and the lights in the residential buildings opposite.

“Yangyang.”

“Hmm?”

“You’ve done something momentous.” Zhao Bowen smiled. “You might have changed the destiny of all humanity.”

“Don’t joke about that.”

“I’m not joking.” Zhao Bowen blew out a smoke ring, the half-burnt cigarette crumpled between his fingers. “You’ve made an unprecedented discovery that may never be repeated. If we were to make a list of the hundred most important people since the dawn of humanity, Yangyang, you would be among them. All those emperors and rulers of various dynasties would at most be listed alongside you, Bai Yang.”

“Don’t mock me, Uncle Zhao.” Bai Yang rested his chin in his hand, staring blankly at the residential building opposite, where lights shone from every window, each containing a peaceful, happy family.

Human civilization would be destroyed in just five years—what was the point of listing the hundred most important people in human history now?

Was it like writing an obituary before burying the dead?

“Want to give an acceptance speech?” Zhao Bowen asked.

“Thanks to CCTV, thanks to BTV, thanks to Bilibili, thanks to NGA, thanks to Zhihu, Weibo, and Baidu Forums,” Bai Yang said.

“Bravo!”

Zhao Bowen clapped enthusiastically.

As the applause died down, silence returned.

Old Zhao bit the cigarette between his lips and took a long drag, the red-hot tip suddenly brightening in the darkness.

“Without exaggeration, today might be the most important day since humans left Africa, in millions of years. We’re witnessing history.”

“But it’s just an ordinary day.” Bai Yang looked up at the sky.

“Any day in history is just an ordinary day.” Zhao Bowen smiled. “What later generations see as earth-shattering changes are just another day of eating and sleeping for those who lived through it.”

“Has it always been like this?”

“Always has been.”

Old Zhao smoked silently until only a cigarette butt remained.

“What are we going to do about this?” Bai Yang asked.

“We can’t just sit and wait for death. We need to find a way to change that future,” Zhao Bowen answered.

“How?”

“No clear ideas yet.” Zhao Bowen shook his head. “This problem might be too difficult for us to solve alone, but many hands make light work. Once I report this up, and the state machinery starts moving, those top think tanks from Tsinghua, Peking University, Chinese Academy of Sciences, and all those places should be able to figure something out.”

“Uncle Zhao, you’re also a professor at Nanjing University.”

“Associate.”

Zhao Bowen dropped the cigarette butt and ground it firmly under his foot.

“I’m still very confused about all this,” Bai Yang suddenly said.

“Confused about what?”

“Everything.” Bai Yang patted his cheeks. “Why did all this happen, why is there communication across time? And why did the time capsule transmission fail? Was it really because someone dug it up?”

“I can’t answer your first question either.” Zhao Bowen said. “Nobody knows why this is happening. I suspect the problem isn’t on our end but on BG4MSR’s end.”

“Black Moon?”

“It could be caused by Black Moon.” Zhao Bowen nodded. “We just don’t have direct evidence yet to prove it’s the culprit behind the trans-temporal communication.”

“Isn’t it obvious though?” Bai Yang asked. “It’s the only object beyond our understanding.”

“It seems obvious, but until we find concrete evidence, it can only be considered highly suspicious,” Zhao Bowen said. “As for your other questions, I’ve been thinking about them lately and came up with some unreliable speculations. They’re just my thoughts, but I can share them with you—after all, I won’t be legally responsible for what I tell you.”

“Tell me, Uncle Zhao!” Bai Yang perked up. “Telling me doesn’t count as spreading rumors!”

“First, Yangyang… do you think it’s difficult to send a time capsule, a time mail, twenty years into the future?” Zhao Bowen pulled out another cigarette from his pocket.

Today he had smoked more than he usually did in a week.

Bai Yang was taken aback by the question.

“Difficult?”

“No, it’s not difficult, actually not difficult at all.” Zhao Bowen flicked his lighter with a “snap” and lit the cigarette, cupping it in his hands. “Old Wang’s thinking was right—burying a time capsule isn’t hard, and getting it to twenty years later isn’t hard either. But why have we failed so many times?”

After asking this question, Old Zhao took a deep drag.

“Because of world destruction and social upheaval,” Bai Yang answered. “The capsules would be dug up.”

“Yes, that’s the reason, or at least very likely the reason, which is why we need double-blind procedures to prevent anyone from knowing both what the capsule is and where it is.” Zhao Bowen nodded. “But we need to learn to see the essence through the phenomenon, Yangyang. We need to learn how to extend and generalize a single example to the universal domain—”

Zhao Bowen picked up a small stone from the ground.

“Yangyang, if I throw this stone into the greenery by the entrance now, do you think it could survive until twenty years later?”

Bai Yang paused.

Before he could answer, Zhao Bowen revealed the answer himself: “It definitely can. If we just throw this stone randomly into the greenery, as long as nothing unexpected happens, like being unlucky enough to get crushed by a car, it will remain intact for twenty years, because no one would bother with an unremarkable stone.”

Bai Yang nodded.

“But—” Zhao Bowen changed his tone, “if we want to send this stone to BG4MSR twenty years later, still just tossing it into the greenery, can we do it?”

“No.”

“Right, we can’t. To send the stone to BG4MSR, we must put it in a time capsule and follow double-blind rules, or it will fail. If we just toss it into the greenery, it’s guaranteed not to reach the other party.” Zhao Bowen asked, “Why do we get such different results with the same stone?”

“Because in the first case, we don’t need to deliver it to a specific person. No matter where the stone ends up in twenty years, as long as it still exists, that’s fine,” Bai Yang said. “But in the second case, we need to deliver it to someone specific, which makes it much more complicated.”

Zhao Bowen nodded. “What’s the essential difference?”

Bai Yang pondered for a few seconds. “The essential difference…”

“Don’t rush to answer. Let’s look at a second example.” Zhao Bowen continued using stones as examples. “Now let’s pick up two more stones, making three in total. If we throw these three stones into the greenery, can they survive for twenty years?”

“Yes.”

“Right, they can,” Zhao Bowen said. “Now, if we arrange these three stones in a line in the greenery, Yangyang, can this stone formation successfully remain intact for twenty years?”

“No,” Bai Yang said. “It would get disrupted.”

“Why do we get such different results with the same three stones?”

“Because… in the first case, we don’t need to maintain the formation. The formation is too easily disturbed, too easily disrupted by people.”

“Yes, but that’s just the surface appearance. We need to see the essence. Only by seeing the essence can we apply the principle broadly and find other methods for sending time mail.” Zhao Bowen nodded and turned his head, holding up two fingers. “Yangyang, now I want to introduce two very important concepts: one is called purpose, and the other is carried information.”