Yang Dong wanted to save herself, but she knew there was little hope.

What sentence does it end? Hopefully only the end of physics.

Too frightening.

She stood on the balcony of the control center's top floor, surveying the stopped particle accelerator. From her perch, she could take in the entire twenty-kilometer circumference of the collider. Contrary to usual practice, the ring for the collider wasn't an underground tunnel, but enclosed within an aboveground concrete tube. The facility looked like a giant full stop mark in the setting sun.1

Once, Yang Dong had held a basic belief: Life and the world were perhaps ugly, but at the limits of the micro and macro scales, everything was harmonious and beautiful. The world of our everyday life was only froth floating on the perfect ocean of deep reality. But now, it appeared that the everyday world was a beautiful shell: The micro realities it enclosed and the macro realities that enclosed it were far more ugly and chaotic than the shell itself.

It would have been better if she could just stop thinking about such things. She could choose a career that had nothing to do with physics, get married, have children, and live a peaceful, contented life like countless others. Of course, for her, such a life would be only half a life.

Something else also bothered Yang Dong: her mother, Ye Wenjie. By accident, she'd discovered on her mother's computer some heavily encrypted messages that she had received. This aroused an intense curiosity in Yang.

For the first time in her life, Yang Dong kept a secret from her mother, and recovered the information in the deleted documents. It took her several days to read through the recovered information, during which she learned a shocking amount about the world of Trisolaris and the secret shared by the extraterrestrials and her mother.

Like many elderly people, Yang's mother wasn't familiar with the details of the web and her own computer, so she had only deleted the decrypted documents instead of digitally shredding them. She didn't realize that even if she had reformatted the hard drive, the data would still have been easily recoverable.

Yang Dong was utterly stunned. The mother she had depended on for most of her life turned out to be someone she didn't know at all, someone she couldn't even have believed existed in this world. She didn't dare to confront her mother, never would, because the moment she asked about it, her mother's transformation in her mind would be complete, irrevocable. It was better to pretend that her mother was still the person she had always known and continue life as before. Of course, for Yang, such a life would be only half a life.

Yang Dong leaned against the banister and stared at the abyss beneath her, terrified as well as enticed. She felt the banister shake as it bore more of her weight, and she stepped back as though shocked by electricity. She dared not stay here any longer. She turned to walk back into the terminal room.

Was it really so bad to live only half a life? As far as she could see, a considerable number of the people around her lived only half lives. As long as one was good at forgetting and adjusting, half a life could be lived in contentment, even happiness.

But between the end of physics and her mother's secret, Yang had lost two such half lives, which added up to a whole life. What did she have left?

This was where the center kept the terminals for the supercomputer used to analyze the data generated by the collider. A few days ago, all of the terminals had been shut down, but now a few were lit. This gave Yang Dong a bit of comfort, but she knew that they no longer had anything to do with the particle accelerator -- other projects had taken over the supercomputer.

Yang Dong felt the breath of nature seeping into this place that had once been dominated by abstract numbers and theories. She felt as if she were being released from confinement.

It was a mathematical model of the Earth. Unlike similar projects in the past, this model combined factors from biology, geology, astronomy, atmospheric and oceanic sciences, and other fields of study to simulate the evolution of the Earth's surface from past to future.

Green Glasses directed her attention to a few large-screen displays. These did not show scrolling columns of numbers or crawling curves on a chart; instead, they showed bright, colorful pictures, as though one were viewing the continents and oceans from high above. Green Glasses manipulated the mouse and zoomed in on a few places to show close-up views of a river or a copse of trees.

There was only one young man in the room, who stood up as Yang Dong came in. He wore glasses with thick, bright green frames, a distinct look. Yang explained that she was here only to retrieve a few personal items, but after Green Glasses heard her name, he became enthusiastic and explained the program running on the terminals to her.

After the explanation from Green Glasses, Yang Dong retrieved her things, politely said good-bye, and turned to leave. She could feel Green Glasses staring at her back, but she was used to men behaving this way, so instead of being annoyed, she felt comforted, as if by sunlight in winter. She was seized by a sudden desire to communicate with others. She turned to face Green Glasses. "Do you believe in God?"

Green Glasses was similarly stunned. After a while, he managed to close his mouth and ask, carefully, "What kind of 'God' do you mean?"

"Just God." That overwhelming sensation of exhaustion had returned. She had no patience to explain more. "I don't."

Yang Dong was shocked by her own question. But considering the model displayed on the terminals, the question wasn't entirely out of place.

Yang pointed to the large screens. "But the physical parameters governing the existence of life are utterly unforgiving. Take liquid water as an example: It can exist only within a narrow range of temperatures. Viewing the universe as a whole, this becomes even more apparent: If the parameters of the big bang had been different by even one million billionth, we would have no heavy elements and thus no life. Isn't this clear evidence for intelligent design?"

Yang Dong glanced over at another terminal and saw that the supercomputer was operating at full capacity. A machine like that consumed as much electricity as a small city, but she didn't tell Green Glasses to stop.

Green Glasses shook his head. "I don't know enough about the big bang to comment, but you're wrong about the environment on Earth. The Earth gave birth to life, but life also changed the Earth. The current environment on our planet is the result of interactions between the two." He grabbed the mouse and started clicking. "Let's do a simulation."

He brought up a configuration panel on one of the large screens, a window filled with dense fields of numbers. He unchecked a checkbox near the top, and all the fields became grayed out. "Let's uncheck the option for 'life' and observe how the Earth would have evolved without it. I'll adjust the simulation to be coarse-grained so as not to waste too much time in computation."

A newly formed planet appeared on the large screen. Its surface was still red-hot, like a piece of charcoal fresh out of the furnace. Time passed at the rate of geological eras, and the planet gradually cooled. The color and patterns on the surface slowly shifted in a hypnotic manner. A few minutes later, an orange planet appeared on the screen, indicating the end of the simulation run.

"But… where are the oceans?"

"You're saying that without life, liquid water would not exist on Earth?"

"Do you think life is nothing but a fragile, thin, soft shell clinging to the surface of this planet?"

"There are no oceans. No rivers either. The entire surface is dry."

"The computations were done at the coarsest level; to do it with more precision would require over a month." Green Glasses moved the mouse and zoomed in on the surface of the planet. The view swept over a broad desert, over a cluster of strangely shaped, towering mountain peaks, over a circular depression like an impact crater.

"But --"

"Isn't it?"

"Earth. Without life, this is what the surface of the planet would look like now."

"The reality would probably be even more shocking. Remember, this is only a coarse simulation, but at least you can see how much of an impact life had in the present state of the Earth."

"What are we looking at?" Yang Dong asked.

"Only if you neglect the power of time. If a colony of ants continue to move clods the size of grains of rice, they could remove all of Mount Tai in a billion years. As long as you give it enough time, life is stronger than metal and stone, more powerful than typhoons and volcanoes."

"Then how did the oceans disappear?"

"But the formation of mountains depends on geologic forces!"

"Not necessarily. Life may not be able to uplift mountains, but it can change the distribution of mountain ranges. Let's say there are three mountains, two of which are covered by vegetation. The one that is nude would soon be flattened by erosion. 'Soon' here means on the order of millions of years, a blink of an eye in geological terms."

"We'd have to examine the records of the simulation, which would be a lot of work. However, I can give you an educated guess: plants, animals, and bacteria all have had important roles in the present composition of our atmosphere. Without life, the atmosphere would be very different. It's possible that such an atmosphere would not be able to shield the surface of the Earth against solar winds and ultraviolet rays, and the oceans would evaporate. Soon, greenhouse effects would turn the Earth's atmosphere into a copy of Venus's, and then water vapor would be lost to space over time. After several billion years, the Earth would be dry."

Yang Dong said no more as she stared at that yellow husk of a planet.

"Thus, the Earth that we live on now is a home constructed by life for itself. It has nothing to do with God." Green Glasses held out his arms in mock embrace of the large screen, clearly pleased with his own oration.

Yang Dong was not really in the mood to discuss such matters, but the moment Green Glasses unchecked the option for life in the configuration panel, a thought had flashed into her mind. She asked the next terrifying question: "What about the universe?"

"The universe? If we use a similar mathematical model to simulate the entire universe, and uncheck the option for life at the beginning, what would the resulting universe look like?"

Yang Dong held her tongue. She said good-bye again and struggled to put on an appreciative smile. She left the building and stared up at the star-studded night sky.

Green Glasses thought for a moment. "It would look the same. When I talked about the effects of life on the environment, it was limited to the Earth. But if we're talking about the universe, life is exceedingly rare, and its impact on the evolution of the universe can be ignored."

She knew that she could no longer save herself. She tried to stop thinking, to turn her mind into empty darkness, but a new question stubbornly refused to leave her alone: Is Nature really natural?

From her mother's secret documents, she knew that life was not so rare in the universe. In fact, the universe was downright crowded. How much has the universe been changed by life?

A wave of terror threatened to overwhelm her.