by Cixin Liu
“I suppose this is also a lost art?” asked Cheng Xin as she took the paper.
“Obviously. We hardly see paper now.”
Cheng Xin sat down and began to fold. Her thoughts returned to that drizzly afternoon in college. She and Tianming sat by the reservoir and watched as the tiny paper boat she made drifted away on the water covered by mist and rain. Then she thought about the white sail at the end of Tianming’s stories.…
AA picked up the canopied paper boat and admired it. Then she indicated that Cheng Xin should follow her into the bathroom. With a pocketknife, she cut off a tiny corner from the bar of soap, poked a hole in the stern of the boat, and stuck the soap fragment into the hole. After giving Cheng Xin a mysterious smile, she deposited the boat into the calm water in the bathtub.
The boat began to move by itself, sailing from one edge of the tub to the other.
Cheng Xin understood right away. As the soap dissolved in the water, it lowered the surface tension of the water behind the boat. But as the tension in the water in front of the boat remained unchanged, it pulled the boat forward.
A bolt of lightning seemed to illuminate Cheng Xin’s thoughts. In her eyes, the serene surface of the water in the tub turned into the darkness of space, and the white paper boat sailed across this endless sea at the speed of light.…
Then Cheng Xin remembered something else: Tianming’s safety.
The string of her thought stopped vibrating immediately, as though a hand had been placed against it. Cheng Xin forced herself to look away from the boat, maintaining, as much as possible, a look of boredom and disinterest. The boat had now reached the other edge of the tub and stopped. She picked it out of the tub, shook off the water, and dropped it on the washstand. She almost tossed the boat into the toilet to flush it away, but thought that might appear excessive. She made up her mind, however, to not put the boat in water again.
Danger.
Though Cheng Xin also leaned to the view that no sophons were present in the Solar System, it was better to be cautious.
Cheng Xin and AA locked gazes. They each saw in the eyes of the other the same thing: the excitement of enlightenment dancing within. Cheng Xin looked away. “I don’t have time to waste on silly games. If you want a bubble bath, go for it.” She left the bathroom.
AA followed. They poured themselves two glasses of wine and began to chat about random topics. First, they discussed the future of the Halo Group in the Bunker Project. Then they recalled their college lives in different centuries. Then they talked about life in the present. AA asked Cheng Xin why she had not found a man she liked after living in the new age for so long, and Cheng Xin replied that she couldn’t live a regular life, not yet. Then she pointed out that AA’s problem was that she dated too many men—of course she was welcome to bring her boyfriends to visit Cheng Xin, but it was best to bring only one at a time. They also discussed the fashions and tastes of the women of their respective eras, their similarities and differences.…
Language was merely the vehicle through which they expressed their excitement. They dared not stop, lest the silence rob them of their hidden joy. Finally, in a break in the meandering conversation that would not be noticed by a listener, Cheng Xin said, “Curvature—”
She finished her sentence with her eyes: propulsion?
AA nodded. Her eyes said, Yes, curvature propulsion!
Excerpt from A Past Outside of Time
Motion Through Bending Space
Space wasn’t flat, but curved. If one imagined the universe as a large, thin membrane, the surface would be shaped like a bowl. The entire membrane might even be an enclosed bubble. Though at the local scale, the membrane seemed flat, the curvature of space was omnipresent.
During the Common Era, many ambitious ideas for spaceflight were proposed. One of them involved folding space. The idea was to imagine an increase in the curvature of space and fold it like a sheet of paper so that two spots tens of millions of light-years apart could touch each other. Strictly speaking, this wasn’t a plan for spaceflight, but “space-dragging.” It didn’t involve navigating to the destination, but pulling the destination over to you by bending space.
Only God could have carried out such a plan—and once the limitations of basic theory were taken into account, perhaps not even God.
Later, there was a more moderate and localized proposal for taking advantage of curved space for navigation. Supposing a spaceship could somehow iron flat the space behind it and decrease its curvature, the more curved space in front of it would pull it forward. This was the idea of curvature propulsion.
Unlike folding space, curvature propulsion couldn’t get a spaceship to its destination instantaneously, but it would be possible to drive it asymptotically to the speed of light.
Until Yun Tianming’s message had been correctly interpreted, curvature propulsion remained a dream, like hundreds of other proposals for lightspeed spaceflight. No one knew whether it was possible at either a theory or practice level.
Broadcast Era, Year 7
Yun Tianming’s Fairy Tales
A jubilant AA said to Cheng Xin, “Before the Deterrence Era, clothes with animated images were popular. Back then, everyone looked like blinking Christmas trees, but now, only children dress like that. Classical looks are in vogue again.”
But AA’s eyes were saying something else entirely. Her eyes dimmed. This interpretation looks very good, but it’s still impossible to be certain. We can never get confirmation.
Cheng Xin said, “I’m most surprised that precious metals and gems no longer exist! Gold is now a common metal, and both of our drinking glasses are made of diamonds.… Did you know that where—er, when—I come from, owning a tiny diamond—like this big—would have been an unattainable dream for most girls.”
Her eyes were saying, No, AA, this time it’s different. We can be sure.
“Well, at least you had cheap aluminum. Before the invention of electrolysis, aluminum was a precious metal as well. I’ve heard that some kings even had crowns made of aluminum.”
How can we be sure?
Cheng Xin couldn’t express what she wanted with only her eyes. IDC had once offered to build her a sophon-free room in her apartment. That would have involved a large amount of noisy equipment, so she had turned them down. Now she regretted that decision.
“Snow-wave paper,” she whispered.
AA’s eyes lit up again. The flame of excitement burned even brighter than before.
“There’s really nothing else that will flatten this?”
“No. Only the obsidian from He’ershingenmosiken will do the job. I was hoping to get the obsidian slab back from Needle-Eye.”
The clock in the corner of the room sounded. Ethereal looked up and saw it was almost sunrise. He looked down and saw that only about a palm’s width of the snow-wave paper lay flat on the floor, not enough for a painting. He dropped the iron and sighed.
* * *
A scroll was a rolled-up sheet of paper with curvature; a section was pulled out and ironed flat, decreasing the curvature.
This was clearly a hint for the difference in space in front of and behind a ship driven by curvature propulsion. It couldn’t mean anything else.
“Let’s go,” said Cheng Xin as she got up.
“Yes,” AA said. They needed to get to the nearest sophon-free room.
* * *
Two days later, the IDC chair announced at a committee meeting that the heads of all the working groups had unanimously endorsed the curvature propulsion interpretation.
Yun Tianming was telling the Earth that the Trisolaran ships used space curvature drives.
This was an extremely important piece of strategic intelligence. Out of all the possible paths for researching lightspeed spaceflight, curvature propulsion was confirmed to be feasible. Like a beacon in dark night, this indicated the right direction for further development of human spaceflight technology.
Equally important was the fact that th
e interpretation provided the model for how Tianming had hidden his message in the three stories. He employed two basic methods: dual-layer metaphors and two-dimensional metaphors.
The dual-layer metaphors in the stories did not directly point to the real meaning, but to something far simpler. The tenor of this first metaphor became the vehicle for a second metaphor, which pointed to the real intelligence. In the current example, the princess’s boat, the He’ershingenmosiken soap, and the Glutton’s Sea formed a metaphor for a paper boat driven by soap. The paper boat, in turn, pointed to curvature propulsion. Previous attempts at decipherment had failed largely due to people’s habitual belief that the stories only involved a single layer of metaphors to hide the real message.
The two-dimensional metaphors were a technique used to resolve the ambiguities introduced by literary devices employed in conveying strategic intelligence. After a dual-layer metaphor, a single-layer supporting metaphor was added to confirm the meaning of the dual-layer metaphor. In the current example, the curved snow-wave paper and the ironing required to flatten it served as a metaphor for curved space, confirming the interpretation of the soap-driven boat. If one viewed the stories as a two-dimensional plane, the dual-layer metaphor only provided one coordinate; the supporting single-layer metaphor provided a second coordinate that fixed the interpretation on the plane. Thus, this single-layer metaphor was also called the bearing coordinate. Viewed by itself, the bearing coordinate seemed meaningless, but once combined with the dual-layer metaphor, it resolved the inherent ambiguities in literary language.
“A subtle and sophisticated system,” a PIA specialist said admiringly.
All the committee members congratulated Cheng Xin and AA. AA, who had always been looked down on, saw her status greatly elevated among the committee members.
Cheng Xin’s eyes moistened. She was thinking of Tianming, of the man who struggled alone in the long night of outer space and an eerie, sinister alien society. To convey his important message to the human race, he must have racked his brain until he had devised such a metaphorical system, and then spent ages in his lonely existence to create over a hundred fairy tales and carefully disguise the intelligence report in three of those stories. Three centuries ago, he had given Cheng Xin a star; now, he brought hope to the human race.
Thereafter, steady progress was made in deciphering the message. Other than the discovery of the metaphorical system, the effort was also aided by another guess that was commonly accepted, though unconfirmed: While the first part of the message to be successfully deciphered involved escape from the Solar System, the rest of the message likely had to do with the safety notice.
The interpreters soon realized that compared to the first bit of intelligence, the rest of the information hidden in the three stories was far more complex.
At the next IDC meeting, the chair produced a custom-made umbrella that looked just like the one in the fairy tales. The black umbrella had eight ribs, and at the end of each was a small stone sphere. In this era, umbrellas were no longer in common use. To avoid the rain, modern people used something called a rainshield, a device about the size of a flashlight that protected the user by blowing air up to form an invisible canopy. People certainly knew about umbrellas and saw them in movies, but few had experience with the real thing. Curious, they played with the chair’s umbrella, and noticed that, just like in the stories, the canopy could be kept open by spinning. Spinning faster or slower resulted in corresponding alarm sounds.
“This is really tiring,” someone complained as he spun the umbrella.
Everyone gained new respect for the princess’s wet nurse, who’d managed to spin the umbrella nonstop for a whole day.
AA took over the umbrella. Her hands weren’t as strong, and the canopy began to fall. They all heard the warning birdsong.
Cheng Xin had kept her eyes on the umbrella since the chair had opened it. Now she cried out to AA, “Don’t stop!”
AA spun faster, and the birdsong stopped.
“Faster,” said Cheng Xin.
AA put all her strength into spinning, and the wind chime began to play. Then Cheng Xin asked her to slow down, until the birdsong appeared. This went back and forth a few times.
“This is not an umbrella at all!” said Cheng Xin. “But I know what it is now.”
Bi Yunfeng, who stood to the side, nodded. “Me too.” Then he turned to Cao Bin. “Probably only the three of us can recognize this object.”
“Yes,” said an excited Cao. “But even in our time, this was rarely seen.”
Some of the attendees looked at these three individuals from the past; others looked at the umbrella. All were puzzled, but also expectant.
“It’s a centrifugal governor,” said Cheng Xin. “For steam engines.”
“What’s that? Some kind of control circuit?”
Bi Yunfeng shook his head. “The world wasn’t electrified back when this was invented.”
Cao Bin explained. “This was a device from the eighteenth century for regulating the speed of a steam engine. It’s made of two or four lever arms equipped with spherical masses at the ends and a central spindle with a sleeve—it looks just like this umbrella, except with fewer ribs. The steam engine’s operation rotates the spindle. When it spins too fast, the metal balls lift the lever arms due to centrifugal force, which pulls up on the sleeve and reduces the aperture of the throttle valve connected to the sleeve, thereby reducing the fluid entering the cylinder and the engine’s speed. Conversely, when it spins too slowly, the lever arms fall due to the weight of the metal balls—like an umbrella closing—and the sleeve is pushed down, increasing the aperture of the throttle valve and the speed of the engine.… This was one of the earliest industrial automatic control systems.”
Thus was the first level of the dual-layer metaphor in the umbrella decoded. But unlike the soap-propelled boat, the centrifugal governor didn’t seem to clearly point to anything. This second-layer metaphor could be interpreted in multiple ways, with two possibilities deemed most likely: negative-feedback automatic control and constant speed.
The interpreters began to look for the corresponding bearing coordinate for this dual-layer metaphor. Soon, they fixed on Prince Deep Water. The prince’s height didn’t change in the observers’ eyes regardless of distance. This could also be interpreted in multiple ways, with two possibilities being most obvious: a method of information transmission where the signal strength did not decay due to distance, or a physical quantity that remained constant regardless of the frame of reference used.
Taken together with the metaphorical meanings of the umbrella, the true meaning instantly emerged: a constant speed that did not change with the frame of reference.
Clearly, it referred to the speed of light.
Unexpectedly, the interpreters found yet another bearing coordinate for the metaphor of the umbrella.
The He’ershingenmosiken bath soap is made from those bubbles, but collecting the bubbles is no easy matter. The bubbles drift very fast in the wind.… Only if someone were running as fast as the bubbles, such that they’re at rest relative to the bubbles, would they be able to see them. This is possible only by riding the fastest horses.… The soap-makers ride these horses to chase after the wind and try to collect the bubbles with a thin gauze net.… The bubbles have no weight, which is why pure, authentic He’ershingenmosiken soap also has no weight. It’s the lightest substance in the world.…
The fastest; with no weight, or massless—this was a clear, single-layer metaphor for light.
Everything indicated that the umbrella stood in for light, but capturing the bubbles from the bubble tree had two possible interpretations: collecting the power of light or lowering the speed of light.
Most interpreters didn’t think the first interpretation had much to do with humanity’s strategic goals, so most of the focus was on the second interpretation.
Although they still couldn’t tell the exact meaning of the message, the interpreters debated
the second interpretation, concentrating on the connection between lowering the speed of light and the cosmic safety notice.
“Suppose that we could lower the speed of light in the Solar System. That is, within the Kuiper Belt or Neptune’s orbit, we could produce an effect observable from a distance—at cosmic scales.”
This thought excited everyone.
“Suppose we reduced the speed of light by ten percent within the Solar System—would that make a cosmic observer think we’re safer?”
“Undoubtedly. If humans possessed lightspeed spaceships, it would take them longer to emerge from the Solar System. But it wouldn’t mean that much.”
“To really indicate to the universe that we’re safe, a reduction by ten percent is insufficient. We may have to reduce the speed of light to ten percent of its original value, or maybe even one percent. Observers would see that we’ve surrounded ourselves in a buffer zone that made certain that our ships would take a long time to emerge from the Solar System. This should increase their feelings of safety.”
“But by that reasoning, lowering the speed of light to one-tenth of one percent would be insufficient. Think about it: Even at three hundred kilometers per second, it still wouldn’t take that long to get out of the Solar System. Also, if humans were capable of modifying a physical constant within a region of space with a radius of fifty astronomical units, then this would be tantamount to a declaration that humans possessed very advanced technology. Instead of a cosmic safety notice, it would be a cosmic danger warning!”
From the dual-layer metaphor of the umbrella and the bearing coordinates provided by Prince Deep Water and the bubble tree, the interpreters were able to ascertain the general tenor of their import, but not the specific strategic intelligence. The metaphor was no longer two-dimensional but three-dimensional. Some started to guess at the existence of yet another bearing coordinate, and the interpreters searched exhaustively through the stories, but they turned up nothing.
Just then, the mysterious name He’ershingenmosiken was finally deciphered.
