Julian date 2459504, Monday, morning.
Lu Weiming's line—they eat from the same pot—Zhou Yan had turned over for two days.
On the third day she copied the whiteboard list whole into the paper notebook, marking each item's inputs. Halfway through she couldn't keep going, because she had begun writing the same few words in the same column, over and over.
International Atomic Time. Every station's time stamps trace back to it in the end—Kashgar's hydrogen maser, Miyun's cesium, Tianma's hydrogen maser, each compared daily, the comparisons weighted together into one paper timescale. Planetary ephemerides. She used DE436, Lu Weiming DE440; different versions, same house, and the batch of radar and optical observations that fix the ephemeris is the same batch, errors strongly correlated. The dust archive. All-sky hydrogen column density and dust emission maps—there are only two or three, and the whole world uses them. The solar-wind density model, the same one. Pulsar positions, proper motions, parallaxes—the same set of measurements, out of the same few papers. Dispersion-correction algorithms, one suite. Analysis software—only two and a half packages left in the world, authors overlapping, down to a constant inside them copied from the same book. Even the leap-second table is the same one, the same bulletin.
She counted nine shared inputs. If any one of the nine carried a slowly varying systematic bias, every station's residuals would lift at the same moment, lift the same height, and settle back together. The more stations, the more in step the lift.
Those twenty-three items looked like twenty-three legs; they grew on one skeleton. Break the legs one by one, the skeleton still stands.
She wrote a twenty-fourth item on the whiteboard, then wiped it off. It wasn't a twenty-fourth item; it was a footnote to the first twenty-three. In the end she wrote it in the lower right corner of the whiteboard, outside the list, like a marginal note: common ancestor.
Hu Yisu came in with printouts and saw the two words.
What does it mean.
It means, she said, that we killed twenty-three items, and what we killed may be twenty-three shadows.
Then this half year was for nothing.
Not for nothing. We broke twenty-three legs.
Legs broken, skeleton standing—that's for nothing. He said it fast; the sentence had been waiting in his mouth for her to finish.
Knowing it's a skeleton is not nothing.
He put the printouts on the desk and didn't leave. Shijie, to kill a skeleton, what does it take.
An observation that doesn't eat from that pot.
Where is there one.
She didn't answer. He didn't press. He never pressed a deflected question—but he would remember, and come back at it from another direction a few days later.
To kill the common ancestor there was only one way. Find an observation that ate none of these inputs.
She worked out how old it would have to be. International Atomic Time took shape in the seventies; planetary ephemerides existed by the late sixties and were in wide use by the eighties; digital sampling came later still. To eat nothing from this pot, the observation had to predate 1972.
The oldest data she had was from 2004.
The archive room was under the main machine room; the smell of cardboard boxes met you at the door. The archive keeper's name was Qiao, sixty, reading glasses on; he pushed a bound register at her. In the winter of 2000 a storeroom heating pipe burst and soaked a batch; what didn't get soaked was later destroyed under the decommissioning procedure—the list is here.
She flipped through. Thirty-seven reels, the earliest from 1981. Against the soaked batch it said only "dates unknown, twenty-four reels."
Is there a catalog of anything earlier.
Master Qiao shook his head. Anything before 1980 doesn't go in this register. Tapes back then traveled with the station—whoever was on duty took them home, and when people retired, some came back and some didn't.
And the ones that came back.
The ones that came back were recataloged once, in the 2001 batch. I did the recataloging. He turned the register back two pages and pointed to a line in pencil, written very small: at recataloging, three crates missing, original numbers consecutive, presumed never returned to storage.
Is there a list of what was in the three crates.
Crate numbers. No contents.
She copied down the three crate numbers. Done, she asked: where are the three crates now.
Master Qiao took off the glasses and wiped them with his sleeve. Girl, he said, the older a thing is, the longer it lives only in someone's memory. The person goes, it's gone.
She phoned Old Tang.
What do you want this for.
I'm looking for an observation that doesn't depend on a modern clock.
Three seconds of silence on the line.
Go ask Old He.
Old He has some?
In the nineties the station cleared its stores, and he carted home the part that was his own. A three-wheeled cart, two trips. I helped him move it—one cardboard box, all tapes. He wouldn't let me look inside.
Where is he now.
Beijing. I'll give you the address. Zhou Yan—
Mm.
If you're going to him, I won't stand in your way. But once you've been to him, this stops being the station's business.
I know.
You don't.
The day before she left she went to Eli's workshop. Eli was grinding a part at the bench vise, the wheel whining; she stood and shouted twice before he shut the machine off.
I'm away three days. Feed Lao Wu once for me, Wednesday. The feed's on the fridge door, one pinch, no more.
I don't do the molting. Eli said.
Just feed.
And the water.
Twenty.
Eli wiped his hands on cotton waste and looked at her a while. That crayfish of yours—its shell has gone as dark as the heart of the dish.
She didn't take it up.
Where are you going.
Beijing.
What's in Beijing.
A reel of tape.
Eli draped the cotton waste over the vise and didn't smile. He only said: the day you climbed the tower, I was down below, and I saw you stop once on the ladder.
She said nothing.
Where you stopped was rung three hundred. Eli said. I counted.
She still said nothing. Eli said nothing either; he bent down, picked a nut off the floor, set it on the bench, squared it. He said: All right. The crayfish, I'll feed. Go.
Julian date 2459504, afternoon, Kashgar to Ürümqi.
She started chewing gum ten minutes before boarding. On the climb the hiss in her right ear rose half a tone and stayed at that new height. She swallowed twice; no use; she let it be. When the cruise flattened out, the hiss did not come all the way back down to where it sat on the ground—a little sharper than on the ground. She noted that altitude the way she'd note a scale marking.
The seat next to hers held a woman with a small child; the child spent the whole flight tearing one sheet of paper into very thin strips and stuffing them, one at a time, into the crack of the seat. She spread Lu Weiming's CSV printout on the tray table; the child reached for it; she moved the paper half a foot in.
The phone buzzed. Zhou Yao: Mailed the drawing. SF Express. Tracking number, SF plus fourteen digits.
She sent back: Good.
Zhou Yao: Don't lose it.
She copied the number onto the last page of the paper notebook, miscopied one digit, crossed it out, copied it again.
They landed at dusk, a four-hour layover. In the terminal she went through the printout once more and stopped on the self-check quantity in the third column: what Lu Weiming was recording wasn't the data, it was the pipeline itself. In the margin she wrote a line: he doesn't trust himself either.
The terminal announcements ran two delays; her flight wasn't one of them. She messaged Old Tang: Old He's address received. Going tomorrow morning. Old Tang sent back one word: Mm.
Eleven forty at night, Beijing. She took a room in a guesthouse by the Third Ring Road; the window faced a wall.
Before sleep she ran through the order of what she would say tomorrow. Residuals first, starting from the rise on the histogram's right shoulder, how the three lines had gone one funeral at a time; then the nine-star stack, the joint significance; then the two curves lifting once on one and the same time axis; the number last. She saved the number for last, because once it was said there was nothing left to explain—the rest belonged to whoever asked.
She ran it through twice; both times the same. Done, she turned off the light. The hiss in her right ear was still at its new height. She thought about what to wear tomorrow, thought for thirty seconds, and slept.
Julian date 2459505, morning. An old three-story walk-up, no elevator. The stairwell was stacked with cabbage and old cardboard boxes; a row of milk boxes was screwed to the wall.
She stood downstairs ten minutes before going up. Not hesitating whether to go—she understood that once this door opened, the thing left Kashgar, and once out it could never be called back into the station. Old Tang's line on the phone—once you've been to him, this stops being the station's business—she ran it through again in the stairwell, along the budget line: out of the station, next year's budget report gains one more pair of eyes; one more pair of eyes means one more place for a signature; one more place for a signature means one more person with the right to say "let's wait a bit." She wound the bag strap twice around her hand, let go, and went up.
The door opened a crack, security chain on. The chain came down; behind the door stood an old man in a wool vest, a shirt underneath, the collar buttoned to the second button.
He Zhaoting was seventy-four. He reached to take her bag; his hand shook; the strap took two tries to come off the hook. He spoke on the loud side—the loudness of a man who cannot hear his own voice.
The study faced north. One wall of books, one wall of tapes. The tapes stood in plastic cases, handwritten labels on the backs in blue ink, not all in the same hand, some of the ink feathered. She stood in front of the rack and read the labels: 69.11 calibration, 70.3 flux, 71.8 solar radio, 73.5 lunar-reflection test reception. Dust lay on the top row, and in the dust one streak where fingers had wiped—someone had handled it recently.
He poured her tea. The cup came on its saucer; as he set it down, the saucer clicked once on the glass sheet.
She talked for twenty minutes. From the rise on the right shoulder of the residual histogram, to the funerals one at a time, to the nine-star stack, to four hundred light-years and 8,200 years lifting once on one and the same time axis, to Tianma's 4.6 times. She spoke neither fast nor slow, and in the middle of it there was not one adjective. It was the only way she knew to present anything.
He Zhaoting did not interrupt. Halfway through he got up and refilled the water, set the cup back at her hand; the saucer clicked again.
When she finished, she waited.
What he asked first was not the data. Whose student are you.
She said the name.
Gone six years now. He said.
Gone six years.
Mm. He moved his hands off his knees, then put them back.
Then he asked: this residual you speak of—is it what's left after everything has been subtracted?
Yes.
What's left after everything has been subtracted—everyone wants to stuff something into it. He said.
She didn't take it up. He hadn't asked her to.
He asked: do you have children.
One. Twelve.
Mm.
He asked nothing more, and did not come back to the data.
She added what she had come to say: I need an observation that eats none of the modern inputs. Quartz-clock era, hand-computed ephemeris, the older the better.
There were no atomic clocks then. She said.
Quartz. He said. Compared once a day against short-wave time signals. Millisecond level.
Then that zero lag within zero point three seconds—
He didn't take it up. She finished it herself: a bad clock can wipe out synchrony; it cannot manufacture synchrony. Even if the time axis of 1968 is rotten, so long as the thing is still there, it is an observation that eats nothing from this pot.
She sat and waited for him to speak. He sat, hands on his knees, looking at the windowsill.
Then he said something. He sat to her right; her right ear was turned toward him. She didn't catch it.
What did you say.
He raised his voice—the raise of the old, not the raise you use on the hard of hearing: I asked, how much is the lag.
Zero.
Zero how much.
Zero. Within the error, zero point three seconds.
He Zhaoting said "Mm." Bracing one hand on the table edge he stood, walked to the shelves, and searched upward. The search went on long enough that she wanted to go and help, and didn't dare.
He pulled down a cardboard box; a little dust drifted off the lid. Inside were three reels, plastic cases, blue-ink labels.
He set the box on the table, one hand resting on the lid, and did not lift it at once.
April of '68, he said. I was twenty-two that year.
She waited.
A radar station in the northwest, military equipment turned civilian, the unit number struck off long ago; the place is a goji field now. We ran one calibration a day, recording system noise temperature and gain. Up at four in the morning; first thing was the cold sky, then the hot load on, then record again. Four times a day, three hundred sixty days a year. Two years and three months.
She asked: what can calibration records show.
Nothing. He said. Calibration exists for other people's data. It produces no conclusions of its own. It only tells you whether the machine today is still the machine it was yesterday.
One copy of the record went onto paper, one onto tape. The paper copy went up the chain, and once it went up, no one ever asked after it. The three reels I kept myself. No one asked after those either.
He took his hand off the lid.
He pushed the box a little toward her, into the circle of the desk lamp.
The label read: 68.4.7 calibration / for calibration use. The second dot had feathered into one fat blur.
She opened the paper notebook to a blank page and, in the corner, converted that date into a Julian date and wrote it down:
2439954.
She closed the notebook and clicked the cap onto the pen. He Zhaoting was already up fetching the thermos, walking slower than when he had come in.
She took one reel; the other two he kept. The reel wouldn't lie flat in the laptop bag; she wedged it with the sweater rolled inside. She asked why he was giving it to her.
He said: You will bring it back.
Downstairs she messaged Old Tang: Got one reel. April '68.
Old Tang came back fast: He gave it to you?
Gave it.
A long while later, Old Tang sent one line: Then what you owe him now is no longer one reel.
She didn't reply.
That afternoon, in the guesthouse, she phoned Hu Yisu and had him look up the radar station.
Hu Yisu called back after forty minutes: one line only. A certain unit, a certain station, dissolved in 1979; no record of where the personnel went.
Anything else.
A handover inventory. What was handed over was the barracks and three trucks. The equipment column is blank.
And the equipment.
Written off. Or carted away. Or still under the goji field. He said, Shijie, should I keep digging.
Dig. Find out whether that station kept any other records from those two years. Paper counts too.
He agreed.
At night she took the reel out of the laptop bag and looked at it a long time on the desk. The plastic case had yellowed; one corner was cracked, the crack mended with clear tape. She pried the case open; the reel sat inside, the tape wound even, a thin sheen on its surface. She pressed a fingertip against the teeth of the spool and turned it half a circle: it turned, with a slight drag.
Near the outer edge, a stretch of the magnetic coating had wrinkled, about two fingers wide. She didn't know what that meant, and she knew better than to take the risk.
She put the reel back in its case, back into the bag, padded with the sweater. Before lying down she wrote in the paper notebook: 68.4.7, three reels, took one. Owe two.