“Good point,” Azar conceded. “But why does anyone steer a whole planet from system to system? If it was the Ground Heaters, surely they could have made smaller, faster spacecraft using the femtotech.”
Shelma threw up her hands. “Let’s go back to the beginning. The Ground Heaters grew up with tidal heating. When that started running down, they got lucky; they managed to devise a spectacularly good replacement. So what would they do next?”
“Some cultures would have sent out nanotech spores,” Azar said, “followed by a wave of digitized travelers. But we know they didn’t do that, or the femtotech would still be around somewhere else.”
“They didn’t found colonies, but they still ended up traveling.” Shelma laughed. “I was going to say that it must have been a deliberate choice—that they could have resisted any natural ejection from their system if they’d really wanted to—but maybe they only had fusion power then. That would explain why’s there’s no deuterium around: they used it all up while they were developing the femtotech.”
“But either way,” Azar said, “once they were free of their star and able to steer themselves, they decided to make the best of it. To see a few sights along the way. And where do you go, if you grew up around a dwarf star? You take a tour of other dwarf stars—”
“Until you find one with an inhabited planet,” Shelma said, “where they’re facing the same problems you faced.”
“And then what?” Azar frowned. “I can’t believe the N3ers conquered the Ground Heaters!”
“No,” Shelma agreed. “And why would they need to? Why wouldn’t the Ground Heaters simply share the femtotech, to help out their fellow thermophiles? If they weren’t feeling generous and sociable, why visit an inhabited world at all? If they’d simply been looking for territory there would have been plenty of sterile worlds for them to choose from.”
Azar said, “Maybe the Ground Heaters died out before they reached the N3 world. They’d programmed some billion-year spree for Tallulah into the femtotech, but they lost heart along the way. The ghost ship came into the N3 system, and the locals couldn’t believe their luck: an empty planet, habitable for ten-to-the-eighteenth years, right on their doorstep! But they couldn’t park it, they couldn’t steer it, they had to go along for the ride. And a quarter of a billion years later, the same thing happened to the lizards.”
Shelma thought for a while. “That almost makes sense, but I can’t quite believe that neither of these free-riders had any interest in turning the femtotech into a propulsion system and founding a few colonies elsewhere.”
“Maybe they did. Maybe we’ve missed them. Tallulah went unnoticed for a very long time.”
“We’re missing something,” Shelma said. “But perhaps our hosts will be able to enlighten us.”
Hours passed with no more contact from the lizards. The sentries were changed, but the replacements were equally determined not to engage with them.
Azar paced the flight deck. “They must be trying to work out if we’re telling the truth or not. Checking to see if Tallulah’s brought them close to a very faint brown dwarf—a port of call that they failed to anticipate.”
“You’d think they’d have good enough telescopes to be sure,” Shelma said irritably. “Given what’s at stake.”
“Maybe they got complacent. I mean, if you do a thorough sweep of the sky and get a very clear verdict that there’s nothing to worry about for the next 100,000 years, how motivated are you to keep repeating the search?”
“Ideally, it would all be automated,” Shelma replied. “Motivation wouldn’t come into it.”
“Well, we might not have landed on the best of all possible worlds after all.”
The lights on the flight deck were starting to soften. Ever since she’d arrived on Mologhat, Azar had been sticking scrupulously to her usual diurnal rhythm; to sleep was part of her identity. But she was too anxious now, and she willed the urge away. Her sense of self would just have to stretch to encompass an exception when she was captive to confused, paranoid lizards.
The sentries were changed again. Azar recognized them as two of the crowd who’d first appeared in the forest; her software had dubbed them Jake and Tilly, but they hadn’t said much then, and she didn’t bother trying to speak to them now. Let the telescopes confirm her and Shelma’s honesty, and then they could all finally engage in a civilized discussion.
Jake said, “Come with us. Quickly. We don’t have much time.” He swam a short way toward his prisoners, then darted back toward the chamber’s entrance.
Azar was dumbfounded.
“Come with you where?” Shelma asked.
“Out of here,” Tilly said. “We think the Circlers are planning to kill you.”
Azar glanced at Shelma. The insect could probably defend itself against most of the lizards’ technology, but it was not indestructible. They’d left backups in the jungle before setting out for the coast, but those snapshots of their minds were missing all the crucial discoveries they’d made since. In any case, even if they survived here, what kind of dialogue could they have with people who wanted them dead?
Shelma addressed her privately. “So do we leave the bodies as decoys?”
Azar was unsure. The insect on its own would face technical problems communicating with the lizards-it was too small to stock the raw materials for more than a few minutes’ speech—and she also found something comforting about the way it was now hidden inside a larger target.
“What if we split the difference?” she suggested. Her lizard body had enough redundancy in its engineering to allow its nanotech to make two bodies from the same materials; she instructed it to divide into a mimic of Shelma’s, along with a somewhat less sturdy copy of its original form. Then she loaded both with non-sentient software that could easily pass a half-baked Turing test from their would-be executioners.
Tilly remained guarding the fake prisoners, and they followed Jake through the tunnels, leaving by a different route than they’d come. They did not travel unobserved, but the few lizards Azar glimpsed at intersections merely watched them pass in silence; presumably they belonged to Jake’s faction, and were standing lookout in aid of their escape.
On the surface the ribbon-weeds carved the forest floor into a kind of maze, and while it was possible to cheat and squeeze your way between the edges of the fronds that didn’t quite touch, it certainly was faster if you knew the maze so well that you didn’t have to.
After a while, Jake halted and gestured urgently at a stubby, bulbous plant in the undergrowth. Since leaving the chamber he hadn’t spoken at all; words decayed quickly in the water, to the point of losing their meaning, but the residue would still be easy to track. When Shelma did nothing he ducked down, tore a bulb from the plant, and stuffed it into his mouth. Shelma took the hint and did the same. The scouts hadn’t come across this plant before, but the robot’s nanotech quickly analyzed the bulb’s contents. There were few conventional nutrients in it, but it was packed with organic azides, nitrogen-rich compounds with an extremely high energy density The plant was C3, but its genome suggested that the lizards had modified it to produce this edible rocket fuel, and despite its modest appearance its roots probably ran deeper into the ground than the ribbon-weeds rose up into the ocean. The nanotech didn’t take long to devise a pathway to metabolize the azides safely—which was lucky, because Jake was already powering ahead at five times his previous swimming speed.
As their robot body struggled to catch up with him, Shelma said, “Now I know why they don’t bother with vehicles.” Azar had once tweaked her own flesh to enable her to run non-stop across a continent—purely for the physical joy of it—but it seemed that with the right dietary supplement, anyone on Tallulah could moonlight as a high-performance submarine.
As they sped through the forest, the thermal/sonar images of the ribbon-weeds on either side of them blurred together like the walls of some long, twisted canyon. “If ‘the Circlers’ really want to kill us,” Azar said
, “I hope that doesn’t mean all of them.” References to that cryptic self-description had been present even in distant traffic coming through the fibers; the group was certainly not confined to one colony.
Shelma said, “I’m sure this is all just a misunderstanding. They think this is the end of the line for them—that Tallulah’s come within reach of another dying world, and we’re its inhabitants, intent on taking over.”
“You think they have a guilty precedent in mind?” Azar suggested. “Maybe that’s what happened with them and the N3ers.”
“Maybe. But I think it’s more likely that the N3ers were long gone, and that’s part of the shock. The lizards weren’t expecting to be around to meet their own replacements, either.”
Azar said, “So how do we convince them that there is no threat, if they refuse to believe the evidence of their own telescopes?”
“Good question. How faint is the faintest dwarf star, and how far would they be willing to believe we’ve come?”
The forest gave way to a dense carpet of smaller plants, but Jake still knew how to find the fuel bulbs among them. This time when they stopped, he risked talking. “I think you’re safe for now,” he declared. “But we should keep moving. I have friends who’ll shelter us, but they’re still a few hundred kilometers away.”
“We don’t want to put anyone’s life in danger,” Azar said, borrowing Shelma’s lizard body but inflecting the words with the identity tag she’d used when she’d had her own.
“You won’t,” Jake assured her. “The three philosophies have been at peace for millennia; we’re not going to start killing each other now.”
“The three philosophies?” Shelma asked.
“Circlers, Spiral In, Spiral Out.”
“We’ve heard those phrases, but we don’t know what they mean.”
Jake flexed his body like an athlete limbering up for a sprint. “If you want to keep talking, swim close beside me and synch your tail with mine.” As he started moving, Shelma followed his advice. The layer of water trapped between them let them communicate without their words being lost in the flow.
“The Circlers,” Jake said, “are resolved to stay. To stay on Tallulah, and to stay as they are. They accept that we didn’t build this world ourselves, that it came to us as a gift, but to the Circlers that’s not the point. The Builders are gone, and now Tallulah belongs to us.”
Azar said, “So they’re ready to fight off any intruders?”
“They’re willing,” Jake replied, “but I wouldn’t call them ready. They weren’t expecting you. Nobody was.”
“We really don’t want this place as our home,” Shelma said. “We have worlds of our own, powered by sunlight. You believe that, don’t you?”
Jake considered the question. “I suppose it’s possible for life to evolve that way, around the right kind of star. Some experts claim the radiation would be fatal, but I believe there could be a narrow habitable zone. To travel more than a thousand light years, though ...”
Shelma explained about Mologhat 1 and 2, meeting and canceling their momentum against each other. About the digital forms she and Azar had taken, crossing the light years as gamma rays in a subjective instant.
Jake said, “Now you’re trying to tell me that Spiral In is really the same as Spiral Out.”
“Spiral Out is about travel?” Azar said. “The idea that you should leave Tallulah and look for a new home?”
“Yes. Spiral Out is my own philosophy.”
Azar tried to frame her next question as politely as possible, and hoped the translator would be able to honor her intent. “Then if you don’t mind me asking, why are you still here?”
“Travel isn’t easy,” Jake declared. “We’ve been waiting for Tallulah to bring us close to an empty world that we could claim as our own. But the last time that happened—before I was born—our numbers were small and our technology was untested. The opportunity was lost.”
Shelma said, “So what’s Spiral In?”
“They aim to take the form you claim to have taken. To become pure information. But not for travel: to stay on this world. To join with this world.”
It was an odd way of putting it, but Azar thought she caught his meaning. In almost every culture with the means to go digital, there was a subculture who advocated a kind of implosion: a retreat into a universe of scapes divorced from physical reality.
“To join with this world?” Shelma pressed him.
“With the heat. With the hoops. With the Builders themselves.” Jake emitted a token of mirth that Azar heard as curt laughter. “Some Spiral In people believe that there are ten thousand cultures under the ground.”
The ocean floor passed beneath them in a blur.
“Hoops?” Azar said.
“You haven’t seen the hoops yet?” Jake replied. “When the rock turns to heat, what’s left are the hoops.”
“The ash,” Shelma said privately. “He’s talking about the ash!”
“We’ve seen them,” Azar said. “But we’re not quite sure what they are.”
Jake fell silent for a while, then he said, “How much do you know about relativity?” The translator marked the final word with a cautionary footnote: the scouts hadn’t heard it in use before, so the meaning was being inferred purely from its etymology.
“I understand the basics.” Azar had studied relativity as a child, but without the full library to call on she would be unwise to claim to be an expert.
“Imagine,” Jake said, “a hoop made of something extraordinarily strong, spinning at close to the speed of light. From the hoop’s point of view, it’s under enormous tension. But from the point of view of a bystander watching it spin, it’s moving so rapidly that some of that tension manifests itself as a decrease in its energy.”
Azar was familiar with the principle, though she was more used to thinking of the opposite effect. When you considered a gas under pressure, that pressure was due to the momentum of molecules moving from place to place. But if you were moving rapidly relative to the gas—or vice versa—then some fraction of that momentum in motion looked to you instead like energy standing still. The shift in perspective transformed pressure into energy.
Tension was simply negative pressure, so for a moving object under tension the effect changed sign: the total energy would be decreased. The quantities involved would normally be immeasurably small, though. Azar said, “Are you telling us that these hoops are under so much tension that their energy drops to ten percent of their rest mass?”
“Yes.”
“Despite the kinetic energy of rotation? Despite the energy that goes into stretching the hoop?”
“Yes,” Jake replied. “The effect of the tension outweighs both of those increases.”
Shelma passed some calculations privately to Azar, then addressed Jake. “I think there’s a problem with your theory. If you take a hoop and spin it ever faster, the only way its energy will begin to decrease is if the speed of sound in the hoop exceeds the speed of light.”
Azar checked the calculations; Shelma was right. The total energy of the hoop depended on the precise relationship between the elasticity of the hoop material and the tension it was under. But so, too, did the speed of sound in the material. Linking the two equations showed that the total energy couldn’t fall in response to an increase in tension without the speed of sound becoming greater than lightspeed—which was relativity’s way of telling you that no material with the necessary properties could exist.
Jake was unfazed. “We’ve known that result for a long time. It doesn’t change the facts.”
“What are you claiming?” Shelma asked incredulously. “That the speed of sound does exceed the speed of light?”
“Of course not,” Jake said. “I agree that you can’t construct a motionless hoop and then simply spin it up to a velocity so great that its energy begins to fall. But hoops that are already rotating can change their composition-spitting out particles and transforming into a new material th
at can only exist under tension. So you have to approach the final state through an intermediate structure: a high-energy, low-tension hoop that decays into a high-tension, low-energy hoop, with the energy difference going into the particles that are emitted in the decay process.”
Shelma considered this. “All right, I think I see what you’re getting at. But can you explain the details of this intermediate structure, and exactly how it can be synthesized?”
“The details?” Jake said. “We’ve been on Tallulah for a million years. What makes you think that we’ve untangled all the details?”
7
They reached an isolated burrow, far from any colony. Jake went in first, then emerged with two friends, whom Azar’s software named Juhi and Rahul.
Juhi said, “Jake tells us you came from the world of a bright star. Is that true?”
Shelma replied, “Absolutely.”
“So your real body is not like this at all?”
Shelma sketched her ancestral, five-fold symmetric shape in the sand. Juhi said something that the translator couldn’t parse.
They entered the burrow and swam together to the deepest chamber, a much larger space than the prison they’d escaped from. It contained a transceiver and some other equipment that Azar didn’t recognize—and in the circumstances it seemed both discourteous and unwise to send the scouts to sniff it out.
Rahul said, “Our friends in Jute”-the colony they’d left—”tell us that the Circlers still think they’re holding you. They’re hoping to find out more about the invasion plans.”
Invasion plans was a phrase Azar associated with ancient history and broad comedy. The zombie software she’d left in the bodies would keep reciting the truth to the bitter end, but now she almost wished she’d programmed some kind of parody of a confession.
Shelma said, “We’re grateful for your help. We didn’t come here to cause trouble, but before we even knew that Tallulah was inhabited we lost the means to depart.” She explained Mologhat’s fate.
Godlike Machines Page 45
