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 that 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.
Jake said, “I thought that was no coincidence. The Old Passengers’ machines have blasted specks of dust before, but when you appeared so soon afterward I knew it wasn’t down to chance.”
The N3ers?
“The Old Passengers lived here after the Builders?” Azar said.
“Yes,” Juhi replied. “A few of their animals are still around. They built thousands of machines that aim to protect Tallulah, but some of them are a bit trigger happy.”
“So your ancestors met the Old Passengers?” Shelma asked.
“Hardly!” Rahul sounded as amused as Azar would have been by the same query in relation to trilobites or dinosaurs. “At least, not above ground. For all we know, some of the Old Passengers might still be alive, deep in the rock. But if they are, they’re not very communicative.”
Azar said, “What exactly is going on in the crust, besides the heating process? How do the hoops connect to the Spiral In philosophy?”
Juhi said, “Once you give up your flesh and become information, don’t you look for the fastest way to process that information?”
“Not always,” Azar replied. “In our culture most of us compromise – to stay connected to each other, and to the physical world.”
“In our culture,” Rahul said, “there is no one coming and going over thousands of light years. There are only your biological cousins – and to Spiral In, if your cousins don’t follow you down, that’s their loss.”
Shelma said, “So the hoops can be used for information processing?”
“Some of them,” Jake replied. “The ones you’ve seen up in the water, probably not. But in the ground there are a billion different varieties.”
“
A billion?
” Shelma turned to Azar so they could exchange stunned expressions – or at least so Shelma could hallucinate a version of Azar curling her five tails in the appropriate manner.
“Maybe more,” Jake said. “The truth is, nobody above ground really knows. But we do know that some of them can be used as computing elements. Every time Spiral In becomes serious, they study the hoops, learn how to use them ... then disappear into the ground.”
Azar was beginning to realize that she hadn’t really thought through the implications of the Ground Heaters’ process; even the ash it left behind opened up avenues that the Amalgam had only dreamed of. Amalgam femtocomputers were blazingly fast while they lasted, but they decayed as rapidly as the most unstable nuclei. You then had to rebuild them from scratch, making the whole process a waste of time for all but a handful of specialized applications. If you could build complex structures on a nuclear scale that were permanently stabilized – by virtue of possessing far less energy than their individual parts – then that changed the rules of the game completely. A femtocomputer that didn’t blow itself apart, that kept on computing non-stop, would run at least six orders of magnitude faster than its atomic counterparts.
She said, “So Spiral In use the hoops to retreat into virtual reality. But why don’t you use the heating process yourself, just for the energy? If you want to escape from Tallulah, why not take this process and run?”
Rahul gestured at one of the machines in the corner of the chamber, a clunky, unprepossessing structure with a dozen cables snaking out of it. “There’s a sample of deep rock in there. Do you know how much power it’s generating? Less than a microwatt.”
Azar stared at the machine. Her intuition balked at Rahul’s claim, but on reflection it was entirely plausible. In bulk, buried beneath an insulating blanket of rock several kilometers thick, the miraculous fuel would be white hot, but up here in the water a small piece would barely be warmer than its surroundings. Its power to keep the whole planet from freezing came from its sheer quantity, and its spectacular efficiency was tuned for endurance, not a fast burn.
She said, “So in its normal state the process runs slowly. But this isn’t like some radioisotope with a half-life that can’t be changed.”
“No,” Rahul said, “it’s worse than that. If you take a sample of ore containing a radioisotope, you can concentrate the active ingredient. If we purify deep rock – if we remove some of the ordinary minerals it contains in the hope of producing a denser power source – the process down-regulates automatically, maintaining the same output for a given total mass. It knows what you’re doing, and it cheats you out of any gain.”
“Ah.” Azar was torn between empathy for the lizards’ frustration and admiration for the Ground Heaters’ ingenuity. It seemed the femtotech had been designed with very strong measures to protect against accidents and weaponization.
Shelma said, “But in all the time you’ve been studying it, surely you’ve made some progress? You say Spiral In have learned to use the hoops as computing devices; that must give you some insight into the whole process.”
“Using the hoops isn’t the same as controlling their creation,” Juhi said. “It’s like ... building a computer out of fish bones, compared to engineering the biology of a fish. Spiral In learn enough to embed their minds in the rock in the simplest possible way. From that starting point, perhaps they migrate to more refined modes. Who knows? They’ve never come back to tell us.”
“If Spiral In can migrate into the rock,” Azar said, “why are so many of them still here, above ground?”
“After each migration the philosophy dies out,” Juhi replied, “but every few generations it becomes popular again. It starts out as an abstract stance – an idea about what we ought to do, eventually, sometime before we find ourselves confronting the Next Passengers – but then it reaches a critical mass, with enough people taking it seriously for the practicalities to be rediscovered. Then everyone who was serious goes underground ... and everyone who was just spouting empty rhetoric defects to a different philosophy. We’re at a point in the cycle right now where there’s a lot of rhetoric, but not much else.”
Azar was too polite to suggest that Spiral Out seemed to be in much the same state themselves, but in their case there was nothing cyclic about it.
Shelma turned her robot’s gaze from lizard to lizard, as if searching for a crack in their pessimistic consensus. “It must be possible to harness this process,” she said. “To adjust it, to manipulate it. A single nuclear reaction has its rate fixed by physical laws, but this is a
system
– a flexible, programmable network of nuclear machines. If someone built this system for their own purpose – with details that they chose for themselves, that weren’t forced upon them by the underlying physics – then it can be
rebuilt
. You should be able to reverse-engineer the whole thing, and put it together again any way you like.”
Jake said, “Someone built the deep rock, that’s true. And if we were willing to choose the same path as the Builders, perhaps we could match their feat. But though the Builders set Tallulah in motion, in the end their philosophy was Spiral In. To make deep rock, the Builders
became
deep rock.
“I don’t believe it can be done any other way. To understand it well enough to change it, we would have to become it. And then we would have changed ourselves so much that we would no longer want the very thing that we set out to achieve.”
8
As the discussion wound its way back and forth between Tallulah’s uncertain history and the competing visions of its future, Azar seized upon one piece of good news that Rahul let slip almost in passing. The lizards couldn’t re-create the femtotech from scratch, or even ramp it up into a useful form of propulsion, but they did believe that there was a very good chance that they’d be able to
graft it
. Given an empty world on which to experiment, they hoped that introducing samples of the deep rock into the crust would cause the femtotech to replicate, spreading through the native rock and ultimately creating a second Tallulah.
That was a wonderful prospect, but they’d already missed at least one opportunity. Some two hundred thousand years before, Tallulah had passed through an uninhabited system, but Spiral Out had been at a low ebb and hadn’t even managed to launch exploratory probes. Since then they’d simply been hanging around waiting for their next chance. The Ground Heaters had given them an extraordinary gift, rescuing them from their dying planet, but between the culture of dependency that gift had created, the constant temptations of Spiraling In, and the stress of not knowing whether the next world they encountered would turn out to be the home of the Next Passengers, they had ended up paralyzed.