by Cixin Liu
Next, Cheng Xin and Guan Yifan had to turn to a task that terrified them but was absolutely necessary: determining how much time had elapsed in this frame of reference. There was a special technique for radiometric dating under reduced-lightspeed conditions: Some elements that did not decay under normal lightspeed decayed at different rates under reduced lightspeed, which could be used to precisely tell the passage of time. Given its scientific mission, the shuttle was equipped with a device for measuring atomic decay, but the instrument required a computer for processing. Yifan had to go to some trouble to connect the instrument to the neural computer on the shuttle. They directed the instrument to test the ten rock samples taken from different parts of the planet one after another so that the results could be compared. The assay required half an hour.
While waiting for the test results, Cheng Xin and Guan Yifan left the shuttle and waited in the clearing. Sunlight illuminated the clearing through gaps in the canopy. Many strange, small creatures flitted through: Some were insects with spinning rotors on top like helicopters; others were like tiny, transparent balloons that drifted through the air, giving off a rainbow sheen as they passed through shafts of sunlight; but none of them had wings.
“Maybe several tens of thousands of years have passed,” Cheng Xin muttered.
“Or even longer,” said Guan Yifan, looking deep into the woods. “In our current state, tens of thousands of years aren’t very different from hundreds of thousands of years.”
Then they said no more, but sat on the stairs outside the shuttle, leaning against each other and taking comfort in their heartbeats.
Half an hour later, they climbed back into the shuttle to face facts. The screen on the control panel showed the test results from the ten samples. Many elements had been tested and the charts were complicated. All the samples yielded similar results. Underneath, the average of the results was listed simply:
Average atomic decay dating results (error range: 0.4%): Stellar time periods lapsed: 6,177,906; Earth years lapsed: 18,903,729.
Cheng Xin counted the digits in the last number three times, turned around, and quietly exited the shuttle. She descended the stairs and returned to this purple world. Tall purple trees surrounded her, a beam of sunlight cast a tiny circle of brightness next to her feet, moist wind lifted her hair, living balloons drifted overhead, and almost nineteen million years followed her.
Yifan came to her. They locked gazes, and their souls embraced.
“Cheng Xin, we missed them.”
More than eighteen million years after the DX3906 system turned into a reduced-lightspeed black hole, seventeen billion years after the birth of the universe, a man and a woman held each other tightly.
Cheng Xin sobbed her heart out over Yifan’s shoulder. In her memories, she had cried like this only once before, when Tianming’s brain had been taken out of his body. That was... 18,903,729 years plus six centuries ago, and those six centuries were but a rounding error at such geologic timescales. This time, she cried not only for Tianming. She cried out of a sense of surrender. She finally understood how she was but a mote of dust in a grand wind, a small leaf drifting over a broad river. She surrendered completely and allowed the wind to pass through her, allowed the sunlight to pierce her soul.
Letting the past go, she allowed her growing esteem for Guan Yifan to take over her heart.
They sat on the yielding humus and continued to hold each other, letting time flow by. The dappled sunlight gently shifted around them as the planet continued to rotate. Sometimes Cheng Xin asked herself, Has another ten million years passed by? A small, rational part of her mind strangely whispered to her that such a thing was possible: There really were worlds where one could step through a thousand years at will. Consider the death lines: If they ruptured and expanded just a bit, the speed of light within would rise from zero to an extremely small number, like the rate at which continents drifted over the ocean: a centimeter for every ten thousand years. In such a world, if you got up from your lover and walked a few steps away, you would be separated from him by ten million years.
They’d missed each other.
After they knew not how long, Yifan asked her softly, “What should we do?”
“I want to look more. There must be some sign.”
“There really won’t be anything. Eighteen million years will erase everything: Time is the cruelest force of all.”
“Carving words into stone.”
Yifan looked at Cheng Xin, confused.
“艾 AA would know to carve words into stone,” Cheng Xin muttered.
“I don’t understand....”
Cheng Xin didn’t explain; instead, she grabbed Yifan by the shoulders: “Can you have Hunter do a deep scan of this area and see if there’s anything under the surface?”
“What are you looking for?”
“Words. I want to see if there are words.”
Yifan shook his head. “I understand your desire, but—”
“To better last through the eons, the words ought to be large.”
Yifan nodded, but obviously only to appease her. They returned to the shuttle. Although this was a walk of only a few steps, they leaned against each other as if afraid time would divide them if they were physically separated. Yifan contacted Hunter and directed it to do a deep scan of the area within a circle centered on this coordinate with a radius of three kilometers. The depth of the scan was set to be between five and ten meters, focusing on human writing or other significant markings.
Hunter passed overhead fifteen minutes later and sent back the results about ten minutes after that: nothing.
Guan Yifan ordered the ship to do another scan at a depth range between ten and twenty meters. This took another hour, the bulk of which was spent waiting for the ship to pass overhead. Still nothing. At that depth there was no more soil, only bedrock.
Guan Yifan adjusted the scanning range to between twenty and thirty meters. “This is the last time,” he said to Cheng Xin. “The sensors can’t go deeper than that.”
They waited for the ship to orbit Planet Blue another time. The sun was setting and the sky was full of lovely, fiery clouds, while the purple woods were limned with a golden glow.
This time, the shuttle’s screen showed the images transmitted back by the ship. After processing by enhancement software, they could see a few fragments of white words embedded in the dark rock: “e,” “liv,” “a,” “life,” “you,” “little,” “side,” “Go.” The white color was to indicate that the words were carved into the bedrock; each character was about a meter square, and they were arranged into four rows. The words were twenty-three to twenty-eight meters below them, carved into a forty-degree incline.
WE LIVED A HAPPY LIFE TOGETHER
WE GIVE YOU A LITTLE
SURVIVE THE COLLAPSE INSIDE
GO TO THE NEW
Hunter’s AI invoked the geological expert system to interpret the results. They found out that the giant characters had initially been carved into the surface of a large sedimentary rock formation on the side of a mountain. The original surface was about 130 square meters. Over the eons, the mountain on which the rock had been located sank, and that was how the carved rock ended up below them. More than four lines of text had been carved into it, but the lower portion of the rock had been broken up during the geological transformations and all the text there lost. The surviving text was incomplete as well—the last three lines all had missing characters at the end.
Cheng Xin and Guan Yifan embraced again. They cried tears of joy at the news concerning 艾 AA and Yun Tianming, and shared the happiness that they had enjoyed more than one hundred eighty thousand centuries ago. Their despairing hearts grew peaceful.
“I wonder what their life here was like?” Cheng Xin asked, tears glistening in her eyes.
“Anything was possible,” said Yifan.
“Did they have children?”
“Anything was possible. They could have even founded a civilization her
e.”
Cheng Xin knew that was indeed possible. But even if that civilization had lasted ten million years, the eight million-plus years that had come after would have erased all traces of it.
Time really was the cruelest force of all.
Something strange interrupted their meditation: a rectangle limned by faint lines of light, about a man’s height, hovered over the clearing like the dashed selection lines marked out by dragging a mouse. It moved through the air, but did not go far before returning to its original position. It was possible that it had been there all along, but the outline was so faint and thin that it was invisible during daytime. Whether it was made by a force field or actual substance, there was no doubt it was the creation of intelligence. The lines making up the rectangle seemed to evoke the line-shaped stars in the sky.
“Do you think this is the... gift they left for us?” Cheng Xin asked.
“Seems hard to believe. How could it have survived more than eighteen million years?”
But he was wrong. The object had indeed survived eighteen million years. And, if necessary, it could survive until the end of the universe, because it existed outside of time.
The door remembered that, initially, it had been placed next to the rock carved with text, and it had a real metal frame. But the metal had eroded away after only five hundred thousand years, though the object had always remained brand new. It had no fear of time because its own time had not yet started. It had been thirty meters underground, next to the carved rock, but it had detected the presence of humans and risen to the surface. During the process, it did not interact with the crust, moving like a ghost. It now confirmed that these two were indeed the ones it had been expecting.
“I think it looks like a door,” Cheng Xin said.
Yifan picked up a small branch and tossed it at the rectangle. The branch passed through it and landed on the other side. They saw a luminescent flock of little balloon creatures drift over. A few passed through the rectangle and one even crossed the glowing outline.
Yifan reached out and touched the frame. The light and his finger passed through each other, and he felt nothing. Without even thinking, he extended his hand into the space outlined by the rectangle. Cheng Xin screamed. Yifan pulled his hand back, and everything looked unharmed.
“Your hand.... It didn’t go through.” Cheng Xin pointed to the other side of the rectangle.
Yifan tried again. His hand and forearm disappeared as they entered the plane of the rectangle and did not go through. From the other side, Cheng Xin saw the cross section of his forearm, like the surface of a window. All his bones, muscles, and blood vessels were clearly visible. He pulled his hand back and tried again with a branch. It went through the frame without problems. Right after, two insects with spinning rotors passed through the rectangle as well.
“It really is a door—a smart door that recognizes what’s going through it,” Yifan said.
“It allowed you in.”
“Probably you, as well.”
Cheng Xin gingerly tried, and her arm also disappeared in the “door.” Yifan observed the cross section of her arm from the other side, and had a moment of déjà vu.
“Wait for me here,” Yifan said. “I’ll go investigate.”
“We should go together,” Cheng Xin said resolutely.
“No, you wait here.”
Cheng Xin grabbed him by both shoulders and turned him to face her. She looked into his eyes. “Do you really want us to also be separated by eighteen million years?”
Yifan stared back into her eyes for a long moment, and finally nodded. “Perhaps we should bring some things with us.”
Ten minutes later, they passed through the door, hand in hand.
Outside of Time Our Universe
Primordial darkness.
Cheng Xin and Guan Yifan were once again immersed in a time vacuum. The sensation was similar to when they had entered reduced lightspeed back in the shuttle. Time did not flow here, or maybe it was more accurate to say that time did not exist. They lost all sense of time, and experienced again that feeling of stepping across time, but existing outside of it.
Darkness disappeared; time began.
There is no appropriate expression in human language to express the moment at the start of time. To say that time began after they entered the door would be wrong because “after” required time. There was no time here, and thus no before or after. The time “after” they entered could have been shorter than a billion-billionth of a second, or longer than a billion billion years.
The sun brightened. It did so very gradually: At first it was just a disk, and then the light began to unveil the world. It was like a song that began as barely audible notes, then grew and grew into a mighty chorus. A circle of blue appeared around the sun, expanded, and turned into a blue sky. Under the blue sky, a pastoral scene slowly took shape. There was an unplanted field with black soil; next to it was an exquisite white house. There were also a few trees that brought a hint of the exotic with their broad, strangely shaped leaves. As the sun continued to brighten, the peaceful scene appeared like a welcoming embrace.
“There are people here!” Guan Yifan pointed at the distance.
They could see the backs of two figures standing on the horizon: a man and a woman. The man had just put down his uplifted arm.
“That’s us,” said Cheng Xin.
In front of those two figures, they could see a distant white house and trees, exact duplicates of the ones nearby. They couldn’t see what was at the feet of those figures due to the distance, but they could guess that it was another black field. At the end of the world was a duplicate of it, or maybe a projection.
Duplicates or projections of the world existed all around them. They looked to their sides and saw the same scene repeated. The two of them also existed in those worlds, but all they could see were the backs of those figures, who turned their heads away as Cheng Xin and Yifan turned to look at them. They looked behind them and saw the same thing—except now they were looking at the world from the other direction.
The entrance to the world had disappeared.
They followed a path of stepping-stones, and around them, the copies of themselves in the copies of their world walked along with them. The path was broken by a brook with no bridge over it, but the brook was so small that they could step over it. Only now did they realize that gravity was a standard 1G. They passed the copse of trees and came to the white house. The door was shut and the windows covered by blue curtains. Everything looked brand new, dustless—as a matter of fact, they were brand new, also, as time had just begun to flow.
In front of the house was a pile of simple, primitive farming tools: shovels, rakes, baskets, water pails, and so on. Although some of them were shaped a bit oddly, it was easy to tell their function by appearance. What most drew their attention, though, was a row of metal columns erected next to the farming tools. They were about the height of a person, and the smooth surfaces glinted in the sunlight. Each column had four metal attachments that seemed to be folded limbs. The columns were probably robots in a resting state.
They decided to familiarize themselves with the environment before entering the house, and so they continued to walk past it. After a bit less than a kilometer, they reached the edge of the small world and faced the duplicate world before them. At first, they thought it was just a reflected image of their own world, though it was not mirrored. But after they were halfway there they decided that it couldn’t be a reflection: Everything looked so real. They took a step forward and entered the duplicate world without any resistance. Looking around, Cheng Xin was struck with a hint of terror.
Everything looked the same as when they had first entered the world. They were in the same pastoral scene, with duplicates of the scene before them and to the sides, and in those copies, copies of them also existed. They turned around to look back, and they saw copies of themselves at the far end of the world they had just left, looking behind them.
> Yifan let out a long sigh. “I don’t think we need to go any farther. We’ll never reach the end.” He pointed up and then down. “I bet that without these barriers, we’d see the same scene above and below us as well.”
“Do you know what this is?”
“Are you familiar with the work of Charles Misner?”
“Who was he?”
“A physicist of the Common Era. He was the one who first came up with this concept. The world we’re in is actually very simple. It’s a regular cube about a kilometer on each side. You can imagine it as a room with four walls and a ceiling as well as a floor. But the room is constructed such that the ceiling is also the floor, and each wall is the same as the opposite wall. In reality, it has only two walls. If you walk through one of the walls, you’ll immediately reappear at the opposite wall, and the same is true of the floor and ceiling. Thus, this is a completely enclosed world in which the end is also the beginning. The images we see all around us are the result of light returning to the starting point after crossing the world. We’re still in the same world we started from, because this is the only world that exists. Every copy we see around us is just an image of this world.”
“So this is...”
“Yes!” Yifan swept his arm around to indicate everything. “Yun Tianming once gave you a star, and now he’s given you a universe. Cheng Xin, this is an entire universe. It might be small, but it’s a complete universe.”
Cheng Xin looked around, at a loss for words. Yifan sat down quietly on a ridge in the field and picked up a fistful of black earth, letting the soil slip from between his fingers. He sounded depressed. “He’s quite a man to be able to give the woman he loved a star and a universe. But I can’t give you anything.”