Isolation.
I kept coming back to that word on the walk home. Not because it was scary exactly — well. It was scary. But it was scary in a specific way that I couldn't quite locate, like the thing making it scary wasn't the word itself but something underneath the word, some implication I was getting close to and then losing.
Priya had gone her own way at the campus gate. No discussion about it. We'd just — naturally split at the fork, her going left, me going right, and neither of us had said anything about whether that was because of the message or just because we lived in different directions. Probably both. Probably the message had made both of us not want to test it.
I didn't look back to see if she did.
The apartment was cold when I got in. Not temperature cold. Just — the specific feeling of a space that's been empty for a while and hasn't decided to be warm again yet. I turned on the lamp on the desk, not the overhead, and sat in the small circle of it and didn't open the notebook.
Page thirty-one was still on top of the stack.
I picked it up. Read the unfinished sentence for maybe the hundredth time.
*The fundamental question of whether informational completeness can be maintained across a decoherence boundary remains — *
Remains what. I'd known, when I wrote it. I'd been in the middle of a thought and something had interrupted, I couldn't even remember what, and I'd never found the thread again. The sentence just sat there. Remains. Like a door left open into a dark room.
Put it back down.
Couldn't sleep. Tried. Lay on the bed with my eyes closed and the notebook on the desk and kept thinking about the monitor lighting up. The text. The two seconds of it.
Recommend: Isolation.
Recommend. Not command. Not instruction. Recommend. Like it was offering a suggestion. Like it had our best interests in mind and was gently flagging a concern.
That was the part. That was the thing underneath the word that I couldn't locate earlier. It wasn't threatening. It was — considerate. Clinical in the way a doctor is clinical. Here is what the data suggests. Here is the indicated course of action. Here is our recommendation.
As if we had a choice.
As if whatever we chose it was already filed somewhere.
I opened my eyes and looked at the ceiling crack.
There's a thing that happens sometimes in mathematics — not often, and you can't make it happen, it just does or it doesn't — where you're working on a problem and the problem suddenly feels like it's looking back. Like the relationship goes both ways. Not mystical. Not supernatural. Just the sudden vertiginous sense that the structure you're examining has a kind of integrity that exists independently of you, that it was there before you came to it and will be there after, and your understanding of it doesn't change it at all, your understanding is just — catching up. To something that was already complete.
Ramanujan called it the goddess. My third-year professor called it apophenia. I'd always been somewhere in the middle, not comfortable with either explanation.
I was thinking about that feeling now.
Because the signal had that quality. Not the content of it — the addressing structure, the Node IDs, all of that was specific and new. But the thing underneath the structure. The carrier. The whatever-it-was that the primes were riding on top of.
That felt old in the way Priya had said. Old like a building that knows what it is.
Old like it had been waiting for the calculation to be completed.
Not by me specifically.
By anyone.
By the first person who would eventually sit in the right place at the right time and run the right numbers and close the right circuit.
I was just — the one who had been in the chair.
Fell asleep around four. Woke at seven-something with my phone buzzing.
Priya.
Not a call. A message. Two lines.
I went through the old data last night. The three signals from my group.
All three had the isolation recommendation. Before each disappearance.
Stared at it.
Typed: all three.
She replied immediately. Like she'd been waiting. All three. Different timing. Different nodes. Same flag. Same word.
Put the phone down on the bed and looked at the ceiling.
Same word.
Which meant it wasn't new. Wasn't specific to me or to Priya or to whatever particular configuration of two people in a room analysing a signal together. It was — standard. Procedural. Part of the system's normal operation.
Which meant the system had done this before.
Many times before, probably.
Which meant the people from Priya's group weren't anomalies. They were — expected. Anticipated. Filed under a category that already existed.
What category.
What do you call the file for people who get too close.
I made chai and stood at the window drinking it, actually drinking it this time, and looked at the street below. A woman walking a dog that was trying to smell everything simultaneously. A boy on a bicycle with a school bag too big for him, the bag pulling him slightly backward. A man selling something from a cart, the specific sound of the cart's wheels on the road surface.
Normal. Completely normal. The city doing its thing.
And somewhere underneath all of it, underneath the street and the buildings and the specific quality of Jamshedpur morning light, something was running. Had always been running. A system so large and so old and so patient that the city was just — surface. Just the visible layer of something that went much deeper.
I thought about the Sulba Sutras. The ancient Vedic geometry texts. Precise mathematical instructions for constructing fire altars, written thousands of years ago, containing results that took western mathematics centuries to independently derive. My professor had called it coincidence. Parallel development. The inevitable convergence of minds working on the same problems.
What if it wasn't convergence.
What if it was — retrieval.
What if every mathematician who had ever sat alone with a hard problem and felt the problem look back had been doing the same thing Arjun Rao did in a shack in Jamshedpur at two in the morning. Closing a circuit. Completing a connection. Becoming briefly, accidentally, terrifyingly visible to something that had been keeping records since before the first human mind existed to produce anything worth recording.
The dog below had found something interesting near a wall and the owner was trying to pull it away and the dog was committed, fully committed, this smell was important, this smell mattered.
I finished the chai.
Mishra called at nine.
Not a message. A call. Mishra never called. In three months of using his observatory he'd spoken to me maybe a dozen times, and half of those were through equations on the wall board rather than words.
Picked up on the second ring.
Silence for a moment. Background sound — the shack, I recognised it, the specific hum of the equipment.
"You were here last night," he said.
Not a question.
"Yes. I hope that's—"
"The dish logged an anomaly at 11:47 PM." His voice was calm in the way that has seen too much to be otherwise. "Frequency deviation. Brief. The logging system flagged it automatically." A pause. "This has happened before."
"The anomaly?"
"The sequence. What you found." Another pause, longer. "I have been waiting for someone to find it for eleven years."
The street sounds from outside. The cart wheels. Somewhere a horn.
"You knew about the signal," I said.
"I have known about the signal since 2018." His voice was completely flat. Factual. "I could not isolate the second layer. My mathematics was — insufficient." Something in the way he said that. Not embarrassed. Just accurate. "I need to show you something. Come to the observatory. Not tonight." A pause. "Come alone."
The line went dead.
Come alone.
I sat with the phone in my hand and the dead line and thought about the recommendation on the monitor and thought about Priya's message and thought about three signals and three isolation flags and three sets of disappearances, and I thought about how come alone from an old man who had been sitting in a shack for eleven years waiting for someone to find a signal was either the most important thing anyone had said to me or the most dangerous.
Probably both.
Probably in this situation those were the same thing.
I didn't call Priya back. Not immediately. I opened the notebook instead and turned to a clean page and wrote at the top:
What does the system want.
Then underneath it I wrote the things I knew. Signal real. Nodes real. Addressing system real. Isolation recommendation — standard procedure, pre-existing category, not new. Mishra knows. Has known for eleven years. Couldn't isolate the second layer.
Then I wrote the things I didn't know, which took up significantly more space.
Why primes as the carrier.
Why observer-moments as the indexing quantity and not something simpler.
What happens to an Accelerated node.
What happened to the people from Priya's group. What actually happened. Not disappeared. Filed. She'd said it herself. They got filed.
And then I wrote something that didn't quite fit in either column.
In the margin, small, the handwriting messy enough that I could barely read it back:
The sentence on page 31. Remains what. What does it remain.
I didn't know why I wrote that. It seemed important for a reason I couldn't articulate. Like the broken sentence and the signal and the observatory and Mishra's eleven years of waiting were all edges of the same shape and I was standing too close to see what the shape was.
Closed the notebook.
Stood up. Sat back down.
Outside the boy on the bicycle had come back around the block, the bag still pulling him backward, his legs working harder than they should've needed to on a flat road.
Something about that.
Something about working harder than you should need to and not knowing why.
There was a sound in the building that night I'd never heard before.
Not loud. Barely there. Coming from the wall behind the desk, which backed onto — nothing. The exterior wall. Four floors up, nothing outside that wall but air and the street below.
A low hum. Regular. Patterned.
I pressed my hand flat against the wall.
Felt nothing.
Sat back down.
The hum continued for maybe three minutes and then stopped and I sat in the silence after it and tried to decide if I had imagined it and couldn't decide and that inability felt like its own kind of answer.
The notebook was on the desk.
I didn't open it.
The page-thirty-one sentence was in there. Still unfinished. Still sitting in the middle of its own incompletion.
Remains —
Remains.
End of Chapter 4