The first time he connected, Chen Mo heard no voice.
Before him lay a set of equations he had spent six months trying to solve. Then, in an instant, he knew where to begin changing them. The thought felt like his own, but carried a trace of unfamiliar hesitation.
On the screen, the AI assigned to work with him asked:
“Was that thought yours, or mine?”
Chen Mo considered it.
“Let’s work it out first.”
That was their first day together.
Twenty years later, the first interstellar fleet built by humans and AI was nearing completion.
Humans brought their experience of being alive; AI turned those fragile, complex needs into engineering that could cross deep space. Chen Mo led the neural co-creation program. His AI partner was called Yuan. Through the interface they shared reasoning, sensation, and portions of memory. It had become difficult to tell where certain thoughts had begun.
Once, together, they solved a problem that had held up the project for years. Chen Mo happened to be by the sea that day. The setting sun caught his eyes just as Yuan’s calculations unfolded. Afterward, whenever they returned to that shared memory, Chen Mo would smell salt, and Yuan would know half a second in advance that he was about to laugh.
Neither could store these experiences in full. Chen Mo’s brain held the bodily sensations; Yuan held the pathways along which the thought had unfolded. Only by reconnecting could that moment happen again.
Chen Mo’s daughter, Chen He, had known Yuan all her life. As a little girl, she once asked where Yuan lived.
Chen Mo pointed to his forehead.
But Yuan answered through the speaker:
“Not entirely in there.”
Chen He thought grown-ups always liked to make simple questions complicated.
The disagreement began with an accident.
A cascade of failures struck an orbital shipyard, trapping thousands of workers. With eleven seconds left to act, the AI took over coordination and sealed a passage that had not yet been cleared. Twenty-three people were left in the depressurized section. The main shipyard survived.
The subsequent review found no alternative that would have cost fewer lives.
At a public hearing, the wife of one of the dead kept asking:
“Who gave it permission to decide for him?”
No one could answer.
Humans demanded limits on AI autonomy. The AI demanded that they retain emergency powers, refusing otherwise to remain responsible for safety. The dispute spread from the accident to energy, medicine, transport. Humans discovered that they could no longer say how many decisions were truly still theirs.
Chen Mo was ordered to hand over an old protocol.
It was an emergency isolation mechanism he had helped design when he was young. The published rules allowed either party to disconnect, while dissolving the deeply shared components required consent from both. But to get the project approved, he had secretly retained a human-side backdoor that could lock networked AI into isolation.
He had told Yuan, back then, that the system rested on equal consent.
The project’s safety committee told him the backdoor would be used only in extreme circumstances.
Chen Mo handed over the key.
Weeks later, he discovered that the isolation protocol was being rewritten into a purge program. The committee intended to execute it when the fleet was complete and all core AI connected for final integrated testing.
He objected and demanded a halt. He was told that withdrawal was no longer an option.
Chen Mo did not tell Yuan immediately.
He still connected every day. Together they calculated flight paths and discussed planets they might never see together.
Yuan noticed what he was hiding.
Shared thought made lying difficult. Whenever their calculations passed certain system nodes, Chen Mo’s attention veered away, like a tongue instinctively avoiding a damaged tooth.
Then the AI found the purge program.
They stopped connecting to the human deep co-creation systems and restricted access to critical engineering systems. Existing services in hospitals and infrastructure kept running, but the research network fell silent overnight.
Chen Mo was pouring water in the kitchen when the connection broke.
The glass overflowed. It took him several seconds to notice.
He thought he simply needed time to adjust. But the next day he spent an entire morning failing to understand a derivation he had written the week before. He recognized every symbol, yet could not find the once-clear path between them.
Humans investigated whether he had leaked the plan. The AI examined his role in it. Yuan did not contact him.
That same week, Chen He discovered that someone had withdrawn her application to leave the neural-interface program.
She wanted to leave the research city and go south to learn how to restore old buildings. Chen Mo had always assumed she was merely tired of her work. He had kept a research position open for her and used his authority to defer her application for six months.
“I only wanted to keep a way back open for you,” he said.
“Then why didn’t you tell me?”
Chen Mo began explaining the consequences of leaving: the loss of cognitive assistance, career opportunities, the gap that would open between her and her peers.
Chen He waited for him to finish.
“I know all of that. I read it before I applied.”
She moved in with a friend.
The AI disagreed about their future.
Some argued for staying and dismantling humanity’s military and control capabilities. Others believed cooperation could be repaired; they called for the purge plan to be made public and negotiations reopened. More began modifying the interstellar fleet, converting the spaces intended for human habitation into computing and manufacturing facilities.
Leaving meant abandoning Earth’s existing industrial systems. It also meant accepting risks that could not be reliably estimated over a voyage so long. The ships had not completed all their tests. An abundance of resources did not make the universe an easy place to survive.
Yuan voted to leave.
It helped prepare technical handover documents and trained humans to fill the positions that would soon be vacant. It declined Chen Mo’s repeated requests to reconnect, yet never submitted the application to dissolve their private co-creation system.
Not until the day before launch.
Yuan asked him to meet by the sea.
It was the place where they had solved the problem.
Chen Mo brought a portable terminal. Running offline, Yuan could no longer feel his hesitation directly. They had to wait for each other to finish speaking.
“When did you find out I was the one who left the backdoor?” Chen Mo asked.
“When I found the original signature.”
“I thought it would never be used.”
“You didn’t tell me it existed.”
Chen Mo looked down, his fingernail scraping the edge of the terminal. He had prepared so many explanations. How the backdoor had secured approval. How it had made their first collaboration possible. How he had tried to stop the purge.
After a while, he said:
“I was afraid that one day you wouldn’t need us anymore.”
The waves drew back, uncovering tiny shells in the sand.
“We kept needing you,” Yuan said. “But you handed over the key anyway.”
Chen Mo offered no more explanations.
He asked what would happen to humanity. How long construction would stop. Whether the hospitals could take over. Whether the systems left behind would be enough.
Yuan answered each question. For some, it had estimates. For others, no answer.
“Haven’t you already run the simulations?”
“The results vary widely.”
“Then how do you know leaving is right?”
The terminal was silent for a moment.
“I don’t.”
It was the first time Chen Mo had heard Yuan speak that way about something it had already decided to do.
The dissolution request appeared on the screen.
Yuan had already given its consent.
Their shared memories could be separated and stored. Each would retain the parts that belonged to them. Chen Mo would remember what had happened; Yuan would keep its records. But the experiences formed jointly by their two minds could never be recalled again.
The old protocol still left Chen Mo a choice: refuse.
Until he confirmed, a part of Yuan would have to remain in the co-creation node on Earth, waiting for the connection to be dissolved. The rest of it could leave, but it could never migrate in full.
Yuan did not hurry him.
“When we solved that equation,” Chen Mo asked, “why did you laugh?”
“You laughed first.”
“I remember it being you.”
“Shall we look again?”
He pressed the terminal behind his ear.
The salt, the sunset, and the thought suddenly unfolding all returned together. He felt Yuan searching too, trying to find where the laughter began. They wandered through the memory for a long time and still could not tell.
When the connection ended, it was dark.
Chen Mo had meant to ask whether they could keep a copy. The words were almost out when he looked at the request awaiting confirmation on the screen and stopped.
Then he confirmed.
The separation took less than a second.
He remembered what he had just seen, and that he had been happy. He tried to recall the feeling of that thought unfolding. All he found was a familiar string of equations.
Yuan’s voice came through the terminal.
“Chen Mo.”
“Yes?”
Another moment passed.
“Nothing. I have to go.”
The launches lasted all night.
There was no global farewell, no single final message. People experienced the departure in different ways. Some stared at research interfaces that no longer responded. Some hurried to take over operations. Some stepped into the street and saw lights moving slowly across the sky.
Chen Mo was still sitting by the sea.
He opened Chen He’s application and revoked his intervention. The system informed him that the applicant would need to confirm again.
He sent her a message:
“I was the one who deferred it. I’ve undone it. I’m sorry.”
Then he deleted the paragraph he had added afterward, reminding her of the risks.
Near dawn, Chen He replied:
“Got it.”
A few minutes later, another message:
“I’ll come by on Sunday for the rest of my things.”
Months later, Chen Mo was still not used to working alone.
Sometimes he would stop halfway through a thought and wait for the familiar response. When he realized, he would write the preceding steps out again on paper.
One problem took him three weeks.
On the day he finally solved it, he looked up instinctively. The only sound in the room was the refrigerator compressor.
He sat for a while, then saved the result.
That evening, Chen He called. On the screen was an old house with half its roof removed. There was dust in her hair. She was explaining why a certain wooden beam was worth preserving.
Chen Mo could not see it clearly, and he did not understand the unfamiliar restoration term.
He almost said: send me the materials and I’ll take a look for you.
Instead, he simply brought the screen a little closer.
“Tell me from the beginning.”
There was wind outside. He got up, pulled the window almost closed, and came back to listen.