by Cixin Liu
At the time of the catastrophe, Trisolaris was in a stable era, orbiting around one of the three stars in the system at a distance of about 0.6 AU. The photoid struck the star and tore a hole through the photosphere and the convection zone. The hole was about fifty thousand kilometers in diameter, wide enough for four Earths laid side by side. Whether as a result of a deliberate choice by the attacker or coincidence, the photoid struck the star at a point along the line where the star intersected Trisolaris’s ecliptic plane. Viewed from the surface of Trisolaris, an extremely bright spot appeared on the surface of the sun. Like a furnace with its door open, the powerful radiation generated by the core of the sun shot through the hole; passed through the convection zone, the photosphere, and the chromosphere; and struck the planet directly. All life outdoors on the hemisphere exposed to the radiation was burnt to a crisp within a few seconds.
Next, material from the core of the sun erupted from the hole, forming a fifty-thousand-kilometer-thick fiery plume. The spewed material was tens of millions of degrees in temperature, and while some of the material fell back onto the surface of the sun under the influence of gravity, the remainder reached escape velocity and shot into space. Viewed from Trisolaris, a brilliant tree of fire grew from the surface of the sun. About four hours later, the ejected solar material reached 0.6 AU from the surface of the sun, and the tip of the flaming tree intersected the orbit of Trisolaris. After another two hours, the orbiting planet reached the tip of the fire tree and continued to pass through the ejected solar material for about thirty minutes. During this time, the planet might as well be moving through the interior of the sun—even after the journey through space, the spewed material was still at a blazing temperature of tens of thousands of degrees. By the time Trisolaris emerged from the fire tree, it glowed with a dim red light. The entire surface had liquefied, and an ocean of lava covered the planet. Behind the planet was a long white trail through space—steam from the boiled-off ocean. The solar wind stretched the trail out, making the planet appear as a long-tailed comet.
All signs of life on Trisolaris had been cleansed away, but only the fuse of the catastrophe had been lit.
The ejected solar material caused drag against the planet. After passing through the material, Trisolaris slowed down, and its orbit fell lower toward the star. The fire tree acted like a claw extended from the sun, pulling Trisolaris down with each revolution. After about ten more revolutions, Trisolaris would fall into the sun itself, and the cosmic football game played between three suns would come to its end. But this sun wouldn’t survive long enough to see itself emerge as the victor.
The solar eruption also lowered the pressure inside the sun, temporarily slowing down the fusion within the core. The sun dimmed rapidly until it was but a hazy outline. The giant fiery tree growing from the surface, in contrast, appeared even more striking, more brilliant, like a sharp scratch made against the inky black film of the universe. The diminished fusion meant that the core radiation no longer exerted sufficient pressure against the weight of the solar shell, and the sun began to collapse. The dim shell fell into the core, triggering a final explosion.
This was the sight witnessed by humankind three days ago on Earth.
The solar explosion destroyed everything within the planetary system: The vast majority of spaceships and space habitats trying to escape were vaporized. Only a few extremely fortunate ships that happened to be behind the two other suns, which acted as shields, were safe.
Thereafter, the remaining two suns formed a stable double-star system, but no life would witness the regular sunrises and sunsets. The cinders of the exploded star and the incinerated Trisolaris formed two vast accretion discs around the two suns, like two gray graveyards.
“How many escaped?” Cheng Xin asked softly.
“Counting the Trisolaran Fleets far from home, no more than one-thousandth of the entire population.” Sophon’s reply was even softer than Cheng Xin’s query. She was focused on the Way of Tea, and did not raise her head.
Cheng Xin had much more to say, words from one woman to another, but she was a member of the human race, and the chasm that now divided her from Sophon could not be crossed. She resorted to the questions the leaders had wanted her to ask. The conversation that followed would come to be known as the Conversation of the Way of Tea, which would profoundly change the subsequent progress of history.
“How much longer do we have?” Cheng Xin asked.
“We can’t tell. The attack could come at any moment. But probabilistically, you should have a bit more time: maybe as long as one to two centuries, like your last experiment.” Sophon glanced at Luo Ji and then sat up straight, her face expressionless.
“But—”
“Trisolaris was in a different situation from the Solar System. First, the broadcast only included the coordinates of Trisolaris. To discover the existence of Earth based on this requires examining the record of communications between the two worlds from three centuries ago. That will definitely happen, but it will take time. More important, from a distance, the Trisolaran system appears far more dangerous than the Solar System.”
Cheng Xin looked at Luo Ji in shock, but the latter showed no reaction. She asked, “Why?”
Sophon shook her head determinedly. “We can never explain this to you.”
Cheng Xin returned to the planned questions. “The two attacks we’ve seen both used photoids striking the stars. Is this a common attack method? Will the future attack on the Solar System be similar?”
“Dark forest attacks all share two qualities: one, they’re casual; two, they’re economical.”
“Elaborate, please.”
“These attacks are not part of some interstellar war, but a matter of conveniently eliminating possible threats. By ‘casual,’ what I mean is that the only basis for the attack is the exposure of the target’s location. There will be no reconnaissance or exploration conducted against the target beforehand. For a supercivilization, such exploration is more expensive than a blind strike. By ‘economical,’ what I mean is that the attack will employ the least expensive method: using a small, worthless projectile to trigger the destructive potential already present in the target star system.”
“The energy within the stars.”
Sophon nodded. “That is what we’ve seen so far.”
“Any possible defenses?”
Sophon smiled and shook her head. She spoke patiently, as though to a naïve child. “The whole universe is in darkness, but we remain lit. We’re a tiny bird tied to a branch in the dark forest, with a spotlight trained on us. The attack could come from any direction, at any time.”
“But based on the two attacks we’ve seen, there may be a way to engage in passive defenses. Even some Trisolaran ships survived in the home star system behind the other suns.”
“Please believe me. Humankind has no chance of surviving a strike. Your only choice is to try to escape.”
“Become refugees among the stars? But we cannot manage to get even one-thousandth of our population away.”
“That’s still better than complete annihilation.”
Not by our values, Cheng Xin thought, though she said nothing.
“Let’s talk no more of this. Please don’t ask more questions. I’ve told you everything I can. I asked my friends here for tea.” Sophon bowed to the two, and then presented two bowls of green tea.
Cheng Xin had many more questions on her list. She was anxious as she accepted the tea, but she knew that asking more questions would be useless.
Luo Ji, who had said nothing so far, seemed relaxed. He appeared familiar with the Way of Tea, and holding up his bowl in the palm of his left hand, he rotated it three times with his right hand before taking a drink. He drank slowly, letting time pass in silence, not finishing until the clouds outside the window were colored a golden yellow by the setting sun. He set down the bowl slowly, and said his first words. “May I ask some questions, then?”
Luo Ji’s respect among
the Trisolarans had been shown through Sophon’s attitude. Cheng Xin noticed right away that while Sophon was gentle and friendly with her, she was awed by Luo Ji. Whenever she faced Luo Ji, her eyes revealed her feelings, and she always sat farther away from Luo Ji than Cheng Xin, and bowed to him slower and deeper.
In response to Luo Ji’s question, Sophon bowed again. “Please wait.” She lowered her eyes and sat still, as though deep in thought. Cheng Xin knew that several light-years away, on the ships of the Trisolaran Fleet, Sophon’s controllers were engaged in an urgent debate. About two minutes later, she opened her eyes.
“Honored Luo Ji, you may ask one question. I can only affirm, deny, or tell you I don’t know.”
Luo Ji set down the tea bowl again. But Sophon raised her hand, asking him to wait. “This is a gesture of respect from our world to you. My answer will be true, even if the answer could cause harm to Trisolarans. But you have only one question, and my answer must be from those three choices. Please consider it carefully before you speak.”
Cheng Xin gazed at Luo Ji anxiously, but the latter didn’t pause at all. In a decisive tone, he said, “I’ve considered it. Here’s my question: If Trisolaris showed certain signs of being dangerous when observed from a distance, does there exist some sign that can be shown to the universe to indicate that a civilization is harmless and will not threaten anyone else, thus avoiding a dark forest strike? Can Earth civilization broadcast such a ‘safety notice,’ if you will, to the universe?”
Sophon did not answer for a long time. Again, she sat still, pondering with her eyes lowered. Cheng Xin felt time flow more slowly than ever. With every passing second, her hope diminished, and she was certain that Sophon’s answer was going to be no or I don’t know. But abruptly, Sophon looked up at Luo Ji with clear eyes—before then, she had never even dared to meet his gaze directly—and answered without any doubt:
“Yes.”
“How?” Cheng Xin couldn’t help herself.
Sophon looked away from Luo Ji, shook her head, and refilled their tea bowls. “I can tell you nothing more. Really. I can never tell you anything again.”
* * *
The Conversation of the Way of Tea gave the tiniest bit of hope for the expectant mass of humanity: It was possible to broadcast a safety notice to the cosmos to avoid dark forest strikes.
Excerpt from A Past Outside of Time
The Cosmic Safety Notice: A Lonely Performance Art
After the conversation between Sophon, Cheng Xin, and Luo Ji was publicized, everyone began to ponder the problem of how to broadcast a safety notice. Countless proposals flooded in, sent by sources as august as the World Academy of Sciences and as humble as elementary schools. It was perhaps the first time in the history of humanity that the entire species focused their mental energy on the same practical problem.
The more they thought about it, the more the safety notice turned into a riddle.
All the proposals could be divided into two broad categories: the declaratory camp and the self-mutilation camp.
The declaratory camp’s basic conception, as can be intuited from the name, was a broadcast to the universe proclaiming the harmlessness of Earth civilization. Their main efforts were directed at how to express such a message. But in the eyes of most, their premise seemed foolish. No matter how well crafted the message, who in this heartless universe would believe it? The fundamental requirement for a safety notice was that the countless civilizations in the universe would trust it.
The self-mutilation camp represented the majority view. They theorized that the safety notice had to represent the truth, which implied that the notice required both “talking” and “doing.” And of the two, “doing” was the key. Humanity had to pay a price for living in the dark forest and transform Earth civilization into a truly safe civilization—in other words, Earth civilization had to mutilate itself to eliminate its potential to threaten others.
Most of the self-mutilation plans focused on technology and advocated humanity to retreat from the space age and the information age and found a low-technology society—perhaps a society reliant on electricity and the internal combustion engine, such as at the end of the nineteenth century, or even an agrarian society. Considering the rapid decline in global population, these plans were feasible. In that case, the safety notice would be nothing more than an announcement that the Earth possessed a low level of technology.
More extreme ideas emerging from the self-mutilation camp proposed intellectual disablement. Using drugs or other neuromanipulation techniques, humans could lower their own intelligence. Moreover, such lowered intelligence could be fixed via genetic manipulation in future generations. As a result, a low-technology society would result naturally. Most people were revolted by the notion, but it remained in wide circulation. According to the proponents, the safety notice was equivalent to public disclosure of humanity’s low intelligence.
There were other ideas as well. For instance, the self-deterrence camp advocated building a system that, once activated, would be beyond human control. The system would monitor humanity for any behavior incongruent with its self-proclaimed safe nature and initiate the destruction of the world upon detection.
This was a feast for the imagination. Countless plans competed for attention: some subtle, some strange, yet others as sinister and terrifying as cults.
But none of these plans captured the essence of the safety notice.
As Sophon pointed out, a key characteristic of dark forest strikes was their casual nature. The attacker did not bother to conduct close-range surveillance of the target. All these plans engaged in performance art with no audience. No matter how faithful the act, no one would see it except the performer. Even under the most optimistic conditions—suppose some civilizations, like doting parents, cared to observe Earth civilization up close, perhaps even devoting long-term monitoring equipment to the Solar System similar to the sophons, they would still make up only a minuscule portion of the large number of civilizations in the universe. In the eyes of the vast majority of civilizations, the sun was but a dim dot many, many light-years away, showing no distinguishing details at all. This was the fundamental mathematical reality of the cosmic dark forest.
Once, when humankind had been far more naïve, some scientists had believed that it was possible to detect the presence of distant civilizations by astronomical observation: for instance, the absorption spectral signatures of oxygen, carbon dioxide, and water vapor in exoplanetary atmospheres, or electromagnetic emissions. They even came up with whimsical notions like searching for signs of Dyson spheres. But we found ourselves in a universe in which every civilization endeavored to hide itself. If no signs of intelligence could be detected in a solar system from far away, it was possible that it really was desolate, but it was also possible that the civilization there had truly matured.
A safety notice was in reality a universal broadcast as well, and it had to ensure that all listeners would trust its message.
Take a distant star, a barely visible dot. Anyone casually glancing at it would say: Oh, that star is safe; that star will not threaten us. That was what a cosmic safety notice had to accomplish.
Utterly impossible.
Another mystery that no one seemed able to solve: Why wouldn’t Sophon tell humanity how to broadcast such a safety notice?
It was understandable that the survivors of Trisolaran civilization would no longer transfer technology to humanity. After the gravitational wave broadcast, both worlds faced enmity from the entire galaxy, even the entire universe. They were no longer each other’s greatest threats, and the Trisolarans had no time to spare for the Earth. As the Trisolaran Fleet sailed farther away, the connection between the two civilizations grew ever more tenuous. But there was one fact that neither Trisolarans nor humankind could forget: Everything that had happened started with Trisolaris. They were the ones who had initiated the invasion of the Solar System; who had attempted, but failed, to commit genocide. If the Earth mana
ged to make great leaps in technology, revenge was inevitable. Humans were likely to come after whatever new home the surviving Trisolarans found among the stars, and they might complete their revenge before the Earth was destroyed in a dark forest strike.
But a safety notice was different: If such a notice could make the whole universe believe the Earth was harmless, then, by definition, the Earth would be harmless toward the Trisolarans. Wasn’t this just what they wanted?
Broadcast Era, Year 7
Sophon
Although there were no clues for how to send out a true safety notice, and any serious research only confirmed the impossibility of such an endeavor, the public’s yearning for the notice could not be stopped. Although most people understood that none of the existing proposals would work, attempts to implement them never ceased.
A European NGO tried to build an extremely powerful antenna that would take advantage of the Sun’s amplification ability to broadcast their draft version of such a notice. The police stopped them in time. The six droplets in the Solar System had left six years ago, and there were no more blocks on the Sun’s amplification function, but such a transmission would have been extremely dangerous and exposed the Earth’s location even sooner.
Another organization named Green Saviors had several million members. They advocated humanity’s return to an agrarian existence, thereby proclaiming their safety to the universe. About twenty thousand of their members moved to Australia. On this sparsely populated continent where the Great Resettlement was but a memory, they planned to create a model society. The agrarian lives of these Green Saviors were continuously broadcast to the rest of the world. In this age, it was no longer possible to find traditional farming implements, and so the tools they used had to be custom-made with funds from their sponsors. There wasn’t much arable land in Australia, and all of it was devoted to high-end, expensive foods, and so the settlers had to open up new land in desolate areas designated by the government.