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“A lot of people died?”

“Yes, around three thousand. It happened very fast. Some people were in buildings with shelters they got to in time, and others were near spacesuits, or air locks. Other than them, the whole city-state died. The survivors decided to leave it empty as a memorial.”

“So this is like a cemetery now.”

“Yes. There’s a memorial in here somewhere, I think on the other side. I want to take a look at the inner surface of the break.”

The inspector consulted with Passepartout, then led Swan through the interior space to a boulevard on the other side of the cylinder. The neighborhood here had a Parisian scale, with wide
streets running between trapezoidal housing blocks four and five stories tall.

They hovered over an area of crumpled pavements and tilted buildings, which resembled old photos of earthquake-damaged areas on Earth. It was strange how still it was.

“Aren’t there enough nickel-iron asteroids around that no one needs to hollow a conglomerate?” Swan asked.

“You would think so. But they hollowed out a few of these and found they worked fine. Keep the walls thick enough and the rotation and interior air pressure are nowhere near enough to test them. They should work and they do. But this one broke. A little meteor hit just the wrong spot.”

They floated over an area where the intense buckling had left plates of white concrete thrown up and out, leaving a long gash between them. The gash was open to space; Swan could see stars through it.

T
hey left the devastated street and floated back out of the asteroid. Outside they toed and jetted over the surface of the rock, negotiating the typical asteroid mini-g. Swan had spent some time in this g during her terrarium-building days, and she saw that the inspector was expert in it, which of course made sense for someone based in the asteroid belt.

When they got to the outside location of the open seam, they found several of the Interplan team already at work around it. Genette made a few balletic leaps, twisting in descent to float down headfirst, taking photos of the inside of the rupture. Close inspection of a few small pits to each side was accomplished by way of one-handed handstands, faceplate centimeters from the rock.

After a while: “I think I’ve got what I need.”

They floated there, watching the others continue to work. Genette said, “You have a qube there in your skull, isn’t that right?”

“Yes. Pauline, say hello to Inspector Genette.”

“Hello to Inspector Genette.”

“Can you turn it off?” the inspector asked.

“Yes, of course. Will you be turning off yours?”

“Yes. If that is indeed what really happens when we turn them off.” Through the faceplates Swan could see the inspector’s ironic smile. “All right, Passepartout has been put to sleep. Has Pauline?”

Swan had indeed pressed the pad under the skin on the right side of her neck. “Yes.”

“Very good. All right, now we can talk a little more openly. Tell me, when your qube is on, is it recording what you hear and see?”

“Normally, yes. Of course.”

“And does it have direct contact with any other qubes?”

“Direct contact? Do you mean quantum entanglement?”

“No, no. Decoherence makes that impossible, we are told. I only mean radio contact.”

“Well, Pauline has a radio receiver and transmitter, but I select what goes in and out.”

“Can you be sure of that?”

“Yes, I think so. I set the tasks and she does them. I can check everything she’s done in her records.”

The little silver figure was shaking its head dubiously.

“Isn’t it the same for you?” Swan asked.

“I think so,” Genette said. “I’m just not so sure about all the qubes that are not Passepartout.”

“Why? Do you think qubes may be involved with what happened here? Or on Mercury?”

“Yes.”

Swan stared in surprise at what seemed to be a big spacesuited doll floating beside her, feeling a little afraid of it. Its voice was in her ear because of her helmet mike, speaking from almost within her, much as Pauline did. A clear high countertenor, pleasant and amused.

“There are quite a few little crater pits to each side of the break here. Like that one…” Genette pointed with a forefinger, and a green laser dot appeared on the rim of a small pit, quickly circled the rim, then fixed at its center. “See that? And then that?” Circling another one. They were very small. “These are fresh enough that they may have happened during or after the break.”

“So, ejecta?”

“No. Gravity here is so slight, the ejecta seldom come back. If anything did, it would almost dock. These pits are deeper.”

Swan nodded. The asteroid’s lumpy surface had many rocks lying loosely on it. “So what did the accident report call these craters?”

“Anomalies. They speculated they might be pit ruptures, where ice deposits melted at the heat of impact. Could be. But I take it you have looked at the accident report for Terminator?”

“Yes.”

“Do you remember there were anomalies there too? Whatever struck the tracks didn’t hit cleanly. There are outlier craters, very small, that were not there before the event. Now, on Mercury they could be ejecta coming back down, I grant you that—”

“Couldn’t the impactor have broken up coming in?”

“But that usually happens where there’s an atmosphere heating and slowing it.”

“Couldn’t Mercury’s gravity do it?”

“That effect would be negligible.”

“I don’t know, so maybe it didn’t break up.”

The little figure nodded. “Yes, that’s right.”

“What do you mean?”

“It didn’t break up. In fact, it came together.”

“What do you mean?”

“I mean it was never comglomerated, until the very last moment. That’s why none of the detection systems on Mercury saw it coming. They should have seen it, it had to come from somewhere,
and yet it was not detected by the surveillance systems. So to me this indicates an MDL problem. Minimum detection limit. Because there is always a minimum limit of detection, either inherent to the detection method, or else artificially set higher than the actual minimum.”

“Why do that?”

“Usually to keep warnings from going off all the time when there isn’t really any danger.”

“Ah.”

“So, each system is different, but in the Mercurial defense apparatus, what they call the method reporting level is almost equivalent to the system’s method detection limit. In other words they set their reporting level at twice the detection level, which is six or seven times the standard deviation in their measurement variability. It’s a typical setting to make people comfortable they’ll generate both the fewest false negatives and the fewest false positives.

“So, but consider what then lies below that reporting level. Basically, only very little rocks—pebbles, well less than a kilogram each. But if there were a lot of them, and they converged only at the last second, with each one coming in from a different quadrant of the sky, and at a different speed, but timed such that they all arrived at the same spot, at the same time… Then they would just be little pebbles, until the last second. They could have been tossed from the far side of the solar system, maybe, and over a number of years, maybe. And yet even so, if thrown correctly, eventually they make their rendezvous. Many thousands of them, let us say.”

“So, a kind of smart mob.”

“But not even smart. Just rocks.”

“Could that work? I mean, could anything calculate how hard to throw them, and on what trajectory?”

“A qube could. With enough of the solar system’s masses identified as to locations and trajectory, and enough calculating
power, it can be done. I asked Passepartout to do it—to calculate an orbit for something like a ball bearing or a boccino, thrown from the asteroid belt to hit a particular target on Mercury. It didn’t take long.”

“But could the throws be made? I mean, would it be possible to build a launcher that would launch them with the necessary precision?”

“Passepartout said there are machines in existence with tolerances two or three magnitudes more precise than would be necessary. One would only need a steady launch platform. The stabler the better, in creating consistency.”

“That’s quite a shot,” Swan said. “How many masses get included in the trajectory calculation?”

“I think Passepartout included the heaviest ten million objects in the solar system.”

“And we know where all those are?”

“Yes. Which is to say the AIs know where they are. And all the biggest terraria and spaceships conform to itineraries set years in advance. As for the calculations, it takes a qube to be able to do it in a reasonable amount of time, meaning fast enough to use it for real-time launch instructions.”

“How long does it take?”

“For a qube similar to Passepartout, three seconds. For conventional AIs, about a year per pebble, which of course would render the method inoperable. You have to have quantum computing to be able to do it.”

Swan was feeling sick to her stomach, as if she were back in the utilidor. “So ten thousand little rocks thrown downsystem, over a matter of months or years, with such directions and velocities that they all arrive at one spot at the same time.”

“Yes. And a few stochastic gravitational fluctuations no doubt cause a little bit of scatter at the end. Indeed when that happens, those pebbles must usually miss entirely.”

“But some just barely miss.”

“Exactly. Like these little pits we see. Caused perhaps by a spaceship that changed flight plans, or the like. So maybe one or two percent of the pebbles experience a clinamen of this sort, or so Passepartout guesses.”

Now the wrench in her gut was getting severe. “So someone is doing this on purpose.” She waved at the abandoned terrarium.

“That’s right. And also, a qube has to be involved.”

“Shit.” She put an arm across her stomach. “But how… how could someone…”

The inspector put a little hand to her arm.
Ygassdril
floated under them, cold and dead. A gray potato. “Let’s get back to the
Justice
.”

B
ack inside the Interplan hopper, after they had eaten a meal, Swan stayed up late in the galley, and again the inspector did too.

Swan, who had not been able to stop thinking about the day’s revelations, said, “So, all this means that whoever—”

Genette raised both hands and stopped her. “Qubes off again, please.”

After they had both turned off the devices, she continued: “That means whoever did this could have done it years ago.”

“Or at least quite some time ago, yes. Some stretch of time.”

“And there wasn’t a single launch site.”

“No. But maybe there is still the launch mechanism. Their gun, or catapult, or whatever it was, would have to be a very precise instrument. A particularly fine bit of manufacturing. The tolerances Passepartout suggested were really quite fine, requiring molecular printers and so forth. We might be able to find the factory that made something so particular—we’re looking into that. And then, who might have ordered it.”

“What else?” Swan asked.

“We are looking for the program for the factory, and the design of the instrument. Its printing instructions. Also the orbital
program needed to make the calculations. Qubes don’t make that kind of thing up without being asked to do it—or so we have been assuming until now. The qube that did it would have that action recorded in it, as I understand it. And so the program is likely to still exist somewhere. And there are still only a finite number of factories making qubes.”

“Couldn’t they have destroyed their qube when they were done using it?”

“Yes. But there’s no reason to assume they’re done.”

This was a chilling thought.

“We must look for the qube, the orbit program, the factory program, also the factory, and the launcher itself, and whatever the launch platform was.”

Swan frowned. “All those could be destroyed, or cleaned pretty clean.”

“It’s true. You see the nature of the problem very quickly. Even so, this investigation has to turn into a check of the records, a kind of bookkeepers’ search. As our work so often becomes.” Another ironic smile: “It is not often as dramatic as is sometimes portrayed.”

“That’s fine. But while you’re doing that, what else can we do? What can I do?”

“You can look at the other end of the problem. And I will join you in that.”

“The other end?”

“The motive.”

“But how would you determine that? And having done so, how would you locate it? Doing something like this is so sick that it makes me sick to think about it. It’s evil.”

“Evil!”

“Yes, evil!”

Genette shrugged. “Putting that aside, let us presume anyway that it is rare impulse. And so it may leave signs.”

“That someone hates Terminator? That someone is capable of killing worlds?”

“Yes. It’s not a common impulse. It may therefore stick out. And besides, it may be a political act, a kind of terrorism or war. It may be meant to convey some message, or force some action. So we can follow it that way.”

Swan felt her stomach clenching. “Damn. I mean—there’s never been a, a war in space. We’ve managed without them.”

“Until now.”

That gave her pause. For a generation at least there had been warnings from people all over the system that the conflicts between Earth and Mars could lead to war, or that Earth’s writhing problems were going to drag everyone down with them. Little wars and terrorist attacks and sabotages had never entirely disappeared on poor Earth, and Swan had sometimes thought that diplomats played on the notion that Earth’s discord might spread, in order to boost their own prestige, their own budgets. Diplomacy as necessary peacemaking in a system on the brink—it had been very convenient for them. But what if it turned out to be true?

She said, “I guess I thought spacers knew enough to avoid all that. That once we got out here we would do better. Be better.”

“Don’t be a fool,” the inspector said crisply.

Swan gritted her teeth. After an intense struggle for self-control she said, “But it could be some psychopath. Someone who has lost their mind and is killing just because they can.”