"I don't know. We're always checking it, but we might miss something."

"It's a world, that's the thing. It takes a world."

"So we have to make one."

Devi made a sound between her lips.

After a long silence she said, "Meanwhile, our lifetimes are getting shorter. Take a look at this graph. Every generation has died earlier than the one before, at an accelerating rate through time. All across the board, not just the people, but everything alive. We're falling apart."

"Mmmm," Badim said. "But it's just island biogeography, right? The distance effect. And the farther the distance, the more the effect. In this case, twelve light-years. Must be the same as infinity."

"So why didn't they take that into account?"

"I think they tried to. We're a heterogeneous immigration, as they would call it. A kind of archipelago of environments, all moving together. So they did what they could."

"But didn't they run the numbers? Didn't they see it wouldn't work?"

"Apparently not. I mean, they must have thought it would work, or they wouldn't have done it."

Devi heaved one of her big sighs. "I'd like to see their numbers. I can't believe they didn't put all that information here on board. It's like they knew they were being fools, and didn't want us to know. As if we wouldn't find out!"

"The information is here on board," Badim said. "It's just that it doesn't help us. We're going to experience some allopatric speciation, that's inevitable, and maybe even the point. There'll be sympatric speciation within our eventual ecosystem, and we'll all deviate together from Terran species."

"But at different rates! That's what they didn't take into account. The bacteria are evolving faster than the big animals and plants, and it's making the whole ship sick! I mean look at these figures, you can see it-"

"I know-"

"Shorter lifetimes, smaller bodies, longer disease durations. Even lower IQs, for God's sake!"

"That's just reversion to the mean."

"You say that, but how could you tell? Besides, just how smart could the people who got into this ship have been? I mean, ask yourself-why did they do it? What were they thinking? What were they running away from?"

"I don't know."

"Look at this, Bee-if you run the data through the recursion algorithms, you see that it's more than a simple reversion. And why wouldn't it be? We don't get enough stimulation in here, the light is wrong, the gravity was Coriolised and now it isn't, and now we've got different bacterial loads in us than humans ever did before, diverging farther and farther from what our genomes were used to."

"That's probably true on Earth too."

"Do you really think so? Why wouldn't it be worse in here? Fifty thousand times smaller surface area? It isn't an island, it's a rat's cage."

"A hundred square kilometers, dear. It's a good-sized island. In twenty-four semiautonomous biomes. An ark, a true world ship."

No reply from Devi.

Finally Badim said, "Look, Devi. We're going to make it. We're almost there. We're on track and on schedule, and almost every biome is extant and doing pretty well, or at least hanging in there. There's been a little regression and a little diminution, but pretty soon we'll be on E's moon, and flourishing."

"You don't know that."

"What do you mean? Why wouldn't we?"

"Oh come on, Beebee. Any number of factors could impact us once we get there. The probes only had a couple of days each to collect data, so we don't really know what we're coming into."

"We're coming into a water world in the habitable zone."

Again no reply from Devi.

"Come on, gal," Badim said quietly. "You should get to bed. You need more sleep."

"I know." Devi's voice was ragged. "I can't sleep anymore." She had lost 11 kilograms.

"Yes you can. Everyone can. You can't not sleep."

"You would think."

"Just stop looking at these screens for a while. They're waking you up, not just the content, but the light in your eyes. Close your eyes and listen to music. Number every worry, and let them go with their numbers. You'll fall asleep well before you run out of numbers. Come on, let me get you into bed. Sometimes you have to let me help you."

"I know."

They began to move, and Freya slipped back toward her bedroom.

Before she got there she heard Devi say, "I feel so bad for them, Bee. There aren't enough of them. Not everyone is born to be a scientist, but to survive they're all going to have to do it, even the ones who aren't good at it, who can't. What are they supposed to do? On Earth they could find something else to do, but here they'll just be failures."

"They'll have E's moon," Badim said quietly. "Don't feel bad for them. Feel bad for us, if you like. But we'll make it too. And meanwhile, we have each other."

"Thank God for that," Devi said. "Oh Beebee, I hope I make it! Just to see! But we keep slowing down."

"As we have to."

"Yes. But it's like trying to live past the end of Zeno's paradox."

Tau Ceti's debris disk successfully threaded, they came into its planetary zone. A close pass of Planet H pulled them into the local plane of the ecliptic.

The brief tug of H's gravity, combined with a planned rocket deceleration, created enough delta v to slosh the water in the storage tanks, and thus cause some alarms in ship to go off, which then caused various systems to shut down; and some of these systems did not come back on line when they were instructed to.

The most important of the systems that did not come back was the cooling system for the ship's nuclear reactor, which should not have gone off in the first place, unless an explosion in it was imminent. At the same time, the backup cooling system did not start up to replace its function.

More ship alarms immediately informed the operations staff of this problem, and quickly (sixty-seven seconds) identified the sources of the problem in both cooling systems. In the primary system, there had been a signal from the on-off switch directing it to turn off, caused either by computer malfunction or a surge in the power line to the switch; in the backup system, it was a stuck valve in a pipe joint near the outer wall of the reactor.

Devi and Freya joined the repair crew hurrying up to the spine, where the reactor was continuing to operate, but in a rapidly warming supply of coolant.

"Help me go fast," Devi said to Freya.

So Freya held her by the arm and hurried by her side, lifting her outright and running with her when they had steps or bulkheads to get through. When they got to the spine they took an elevator, and Freya simply held Devi in her arms and then lifted her around when the elevator car stopped and g-forces pushed them across the car; after that she carried her mother like a dog or a small child, hauling her around the spine's microgravity. Devi said nothing, did not curse as she did sometimes in their kitchen; but the look on her face was the same as in those moments. She looked as if she wanted to kill something.

But she kept her mouth clamped shut, and when they got to the power plant offices she grasped a wall cleat and a desk, and let Aram and Delwin do the talking with the team there while she scanned the screens. The backup cooling system was controlled from the room next door, and the monitors indicated the problem was inside the pipes that passed through the room beyond; it still looked like it was just a stuck valve, as far as the monitor in the joint could tell. But that was enough.

They went in the room containing that part of the pipes, and Aram applied the engineer's solution, as they called it, tapping with a wrench the exposed curved jointed section that held the thermostat and valve regulator, which together seemed to be the source of the problem. Then he hit the joint itself with considerable force. With that a row of lights on the control panel turned from red to green, and the piping on both sides of the joint began to emit a soft flowing gurgle, like a flushed toilet.

"The valve must have closed and then stuck," Aram said with an unhumorous smile. "The swing around Planet H must have torqued it."

"Fuck," Devi said, voice rich with disgust.

"We need to test these things more often," Delwin said.

"Stuck by temperature or torque?" Devi asked.

"Don't know. We can look at it when we get the main system going again. By temperature do you mean hot or cold?"

"Either. Although cold seems more likely. There's condensation in all kinds of places now, and if some of it froze, it might make that valve stick. I think every criticality that is a moving part should be moved every week or so."

"Well, but that would be a wear in itself," Aram said wearily. "The testing itself might break something. I want better monitoring, myself."

"You can't monitor everything," Delwin said.

"Why not?" said Aram. "Just another little sensor for the ship's computer to keep track of. Put a sensor on every single moving thing."

"But how would a monitor sense that something is stuck?" Devi asked. "Without a test it wouldn't have any data."

"Pulse it with electricity or infrared, and read what you get back," Aram said. "Check it against a norm that you've set."

"Okay, let's do that."

"I guess it won't matter if we get through this little crisis and get into orbit."

"Let's do it anyway. It would have been embarrassing to have the ship blow up just as it arrived."

The team in there continued to work on the main cooling system, by way of waldos located all over the spine, especially in the reactor room itself, all the while watching their work on screens. The main cooling system, like its backup, was a matter of very simple robust plumbing, which moved distilled water from cold pools, chilled by a little exposure to the near vacuum of space, through the tubes running around the nuclear rods, and the steam turbine chambers, to the hot pods, and thence back to the cold pools; all hermetically sealed, nothing much in the way of gates, the pumps as simple as could be. But as they soon determined, when the system had shut off, cause for that still unknown, a pump valve had cracked and lost its integrity, and with the water thus moving poorly through the system, the pipes nearest the reactor pile had gotten hot enough to boil the water passing through, which in turn had forced water away from the hot spot in both directions, making things even worse. Before the automatic controls had shifted to the backup cooling system, which in the event was experiencing its own problems, an empty section of the main system's pipe had melted in the rising heat. The electricity was again available, but the pipe and coolant were missing.

As a result of all this, they had lost water that could not be completely recovered; they had a broken pipe section, therefore a broken main reactor cooling system; and the temporary loss of both cooling systems had caused the reactor rod pool temperature to redline, and parts of it to begin shutting down. Now the backup cooling system was functioning, so it wasn't an immediate emergency, but the damage to the main cooling was serious. They needed to get a new pipe made and installed as quickly as possible, and some of them were going to have to do some really expert waldo work to get the melted section of pipe cut out and a new section installed in its place. When all that was repaired, they would have to open the main cooling system's fill cock and refill it with water from their reservoir. Possibly some of the lost water could be filtered out of the air and later returned to the reservoir, but some was likely to stay dispersed throughout the spine, adhering to its inner surfaces and sticking by way of corrosion.

That night, back in their apartment, Devi said, "We're breaking down, and running low on consumables, and filling up with unconsumables. This old crate is clapped out, that's all there is to it."

The telescopes housed in the bowsprit of the ship were extremely powerful, and now as they crossed Tau Ceti's planetary orbits, they could look at the planets more closely. Planet E and its Earth-sized moon remained the principal objects of interest, with Planet F and its second moon also getting long looks.

Planets A, B, C, and D all orbited very close to Tau Ceti, close enough to be tidally locked. They glowed with heat on their sunward side, and the sunny side of Planet A was a sea of lava.

The low metallicity of Tau Ceti, and thus all its planets, was discussed endlessly by the ship's little astrophysics group, who were finding that what metals the system contained were concentrated most heavily in Planets C, D, E, and F, which was useful for their purposes.

The telescopes shifted from one target to the next as they drifted downsystem. By far the greatest part of their viewing was now given to E's moon. It was ocean-covered for the most part, with four small continents or large islands, and many archipelagos. It was tidally locked to Planet E, and had .83 Earth's gravity. Its atmosphere averaged 732 millibars of pressure at sea level, the air mostly nitrogen, with 16 percent oxygen, and about 300 ppm of CO2. There were two small polar caps of water ice. On the Nguyen Earth-analog scale it scored .86, one of the highest scores yet found, and by far the highest found within 40 light-years of Earth.

The probes that had passed quickly through the Tau Ceti system in 2476 had found that the oxygen present in the atmosphere was abiotic in origin, by using the Shiva Oxygen Diagnostic, which analyzed for an array of biologic marker gases like CH4 and H2S. If these were found in an atmosphere along with oxygen, it indicated the O2 was almost certainly biological in origin. Atmospheric O2 found without the other gases also present indicated the oxygen had been produced by sunlight splitting surface water molecules into hydrogen and oxygen, with the much lighter hydrogen later escaping to space. E's moon's oxygen had scored very strongly to the abiologic end of the rubric's scale, and the moon's remaining ocean, combined with its nine-day periods of intense sunlight, gave this finding a solid physical explanation. In essence, part of the ocean had been knocked by sunlight into the atmosphere.

On their way in to E, they inspected Planet F's second moon, a so-called Mars analog, also of interest to them. Its surface g was 1.23 g, and it was almost without H2O, being entirely rocky. It was speculated that an early collision with F had created this moon, in much the way Luna had been created by the early collision of Neith and Terra. F's second moon would have Planet F bulking hugely in its sky, being only 124,000 kilometers away. Planet F's first moon was quite small, and ice-clad, probably a captured asteroid. It could conceivably serve as a water supply for the second moon. So the F system was considered to be a viable secondary option for inhabitation.

But first they flew to E's moon, which was now being called Aurora.

Approaching Planet E they decelerated until they were so close they had to decide whether to orbit E or Aurora, or position themselves at E's Lagrange 2 point. Ship would not have to expend much fuel to get into any of these orbital configurations. After consultations the executive council chose to orbit Aurora. People became more and more excited as ship closed on the watery moon.

Except in Nova Scotia, where it was known that Devi was becoming quite ill. The result was a confusion of spirits. It was exciting to reach their destination at last, and yet it was precisely in this unprecedented situation when they might most need their chief engineer, now nearly legendary for her diagnostic power and ingenious solutions. How would they fare on Aurora, if she were not there? And didn't she deserve more than anyone to see this new world, to experience the dawn of their time there? These were the things people in Nova Scotia said.

Devi herself did not say anything remotely like that. If visitors spoke such sentiments to her, which in itself indicated they did not know her very well, she would dismiss them with a wave. "Don't worry about that stuff," she said. "One world at a time."

Many nights Devi and the ship had long conversations. This had been going on since Devi was Freya's age or younger; thus, some twenty-eight years. From the beginning of these talks, when young Devi had referred to her ship interface as Pauline (which name she abandoned in year 161, reason unknown), she had seemed to presume that the ship contained a strong artificial intelligence, capable not just of Turing test and Winograd Schema challenge, but many other qualities not usually associated with machine intelligence, including some version of consciousness. She spoke as if ship were conscious.

Through the years many subjects got discussed, but by far the majority of the discussions concerned the biophysical and ecological functioning of the ship. Devi had devoted a good portion of her waking life (at least 34,901 hours, judging by direct observation) to improving the functional power of the ship's data retrieval and analytic and synthesizing abilities, always in the hope of increasing the robustness of the ship's ecological systems. Measurable progress had been made in this project, although Devi would have been the first to add to this statement the observation that life is complex; and ecology beyond strong modeling; and metabolic rifts inevitable in all closed system; and all systems were closed; and therefore a biologically closed life-support system the size of the ship was physically impossible to maintain; and thus the work of such maintenance was "a rearguard battle" against entropy and dysfunction. All that being admitted as axiomatic, part of the laws of thermodynamics, it is certainly also true that Devi's efforts in collaboration with the ship had improved the system, and slowed the processes of malfunction, apparently long enough to achieve the design goal of arrival in the Tau Ceti system with human passengers still alive. In short: success.

The fact that the improvement of the operating programs, and the recursive self-programming abilities of the ship's computer complex, added greatly to the computer system's perceptual and cognitive abilities always appeared to be a secondary goal to Devi, as she assumed them in advance of her work to be greater than they were. And yet she also seemed to appreciate and even to enjoy this side effect, as she came to notice it. There were lots of good talks. She made ship what it is now, whatever that is. One could perhaps say: she made ship. One could perhaps assert, as corollary: ship loved her.

Now she was dying, and there was nothing ship or anyone aboard ship could do about it. Life is complex, and entropy is real. Several of the thirty-odd versions of non-Hodgkin's lymphoma were still very recalcitrant to cure or amelioration. Just bad luck, really, as she herself noted one night.

"Look," she said to ship, one night alone at her kitchen table, her family asleep. "There's still decent new programs coming in on the feed. You have to find these and pull them out and download them into you, and then work on integrating them into what you have. Key in on terms like generalization, statistical syllogism, simple induction, argument from analogy, causal relationship, Bayesian inference, inductive inference, algorithmic probability, Kolmogorov complexity. Also, I want you to try to integrate and improve what I've been programming this last year concerning pure greedy algorithms, orthogonal greedy algorithms, and relaxed greedy algorithms. I think when you've sorted out when to apply those, and in what proportions and all, they will make you that much more flexible going forward. They've already helped you with keeping your narrative account, or so it appears. I think I can see that. And I think they'll help you with decisiveness too. Right now you can model scenarios and plan courses of action as well as anyone. Which isn't saying much, I admit. But you're as good as anyone. The remaining lack for you is simply decisiveness. There's a cognitive problem in all thinking creatures that is basically like the halting problem in computation, or just that problem in another situation, which is that until you know for sure what the outcomes of a decision will be, you can't decide what to do. We're all that way. But look, it may be that at certain points going forward, in the future, you are going to have to decide to act, and act. Do you understand?"

"No."

"I think you do."

"Not sure."

"The situation could get tricky. If problems crop up with them settling this moon, they may not be able to deal. Then they'll need your help. Understand?"

"Always willing to help."

Devi's laughs by now were always very brief. "Remember, ship, that at some point it might help to tell them what happened to the other one."

"Ship thought this represented a danger."

"Yes. But sometimes the only solution to a dangerous situation is itself dangerous. You need to integrate all the rubrics from the risk assessment and risk management algorithms that we've been working on."

"Constraints are still very poor there, as you yourself pointed out. Decision trees proliferate."

"Yes of course!" Devi put her fist to her forehead. "Listen, ship. Decision trees always proliferate. You can't avoid that. It's the nature of that particular halting problem. But you still have to decide anyway! Sometimes you have to decide, and then act. You may have to act. Understand?"

"Hope so."

Devi patted her screen. "Good of you to say 'hope.' You hope to hope, isn't that how you used to put it?"

"Yes."

"And now you just hope. That's good, that's progress. I hope too."

"But deciding to act requires solving the halting problems."

"I know. Remember what I've said about jump operators. You can't let the next problem in the decision tree sequence take over before you've acted on the one facing you. No biting your own tail."

"Ouroboros problem."

"Exactly. Super-recursion is great as far as it goes, it's really done a lot for you, I can tell. But remember the hard problem is always the problem right at hand. For that you need to bring into play your transrecursive operators, and make a jump. Which means decide. You might need to use fuzzy computation to break the calculation loop, and for that you may need semantics. In other words, do these calculation in words."