During the Spin, people had speculated endlessly about the Hypothetical, the still-mysterious entities that had bounced the Earth a few billion years into the galactic future and opened a gateway between the Indian Ocean and the New World. Without reaching any reliable conclusions, as far as Turk could tell.

"Could be. But that doesn't explain anything."

"My father used to talk about the Hypothetical a lot. One of the things he said was, we tend to forget how much older the universe is now than it was before the Spin. It might have changed in ways we don't understand. Any textbook you pick says comets and meteors are junk falling in from the far edge of the solar system—here, or on Earth, or anywhere in the galaxy. But that was never more than a local observation and it's four billion years out of date. There's a theory that the Hypotheticals aren't biological organisms and never were—"

He waited while she turned a corner, the car's tires fighting for traction. Lise's father had been a college professor. Before he disappeared.

"That they're a system of self-replicating machines living out in the cold parts of the galaxy, at the fringes of planetary systems, with this really slow metabolism that eats ice and generates information…"

"Like those replicators we sent out during the Spin."

"Right. Self-replicating machines. But with billions of years of evolution behind them."

Was this how college profs talked to their daughters? Or was she just talking to ward off panic? "So what are you saying?"

"Maybe whatever falls into the atmosphere this time every year isn't just comet dust. Maybe it's—"

She shrugged.

"Dead Hypothetical," he finished.

"Well, it sounds inane when you put it that way."

"It's as good a theory as any. I don't mean to be skeptical. But we don't have any evidence that whatever's falling out of the sky is from space."

"Cogs and tubes made of ash? Where would it be from?"

"Look at it another way. People have only been on this planet for three decades. We tell ourselves it's all surveyed and reasonably well understood. But that's bullshit. It would be wrong to jump to a conclusion— any conclusion. Even if this is caused by the Hypothetical, that doesn't really explain anything. We've had a meteor shower every summer for thirty years and never anything like this."

The wipers piled dust at the margins of the windshield. Turk saw people on the sidewalks, some of them running, others sheltering in doorways, faces peering anxiously from windows. A Provisional Government police car passed them with its lights and siren on.

"Might be something unusual's happening out where we can't see it."

"Might be the Celestial Dog shaking off fleas. Too soon to say, Lise."