"Hot Rock" by Greg Egan
1
Azar turned away from her assembled friends and family and walked through the departure gate. She tried to keep her gaze fixed straight ahead, but then she paused and looked over her shoulder, as if there might yet be a chance for one more parting gesture. It was too late; there was nobody in sight. She had left her well-wishers far behind.
She managed a nervous laugh at the sheer seamlessness of the transition; she hadn’t registered so much as a shift in the light. The corridor around her appeared unchanged, its walls bearing the same abstract blue-and-gold mosaics as the one she had entered, but when she walked to the far end and turned to the right, she found herself in a glass-walled observation deck, looking out into the rich blackness of space.
Doorway to the stars was the style of travel she had chosen, just one among dozens of decorative scenarios she might have wrapped around the raw, imperceptible act itself. There was no doorway; stepping through the departure gate had merely been a gesture of consent, the signal she had chosen to initiate her journey. In mid-stride, her mind had been copied from the processor that sat within her birth flesh, encoded into gamma rays, and transmitted across fifteen hundred light years. In a subjective instant, she had been transported from her home world of Hanuz into this scape, which mimicked a capacious habitat orbiting the planet Tallulah. She really was orbiting Tallulah, but the habitat, and the body she perceived as her own flesh, were illusory. The machine she now inhabited was scarcely larger than a grain of rice.
Azar pressed her palms to her eyes and composed herself. If she turned around and marched back through the gate it would take her home with no questions asked, but three thousand years would have passed since her departure. That price had been paid, and no second thoughts, no hasty retreat, could reverse it. All she could do now was try to make it worthwhile.
The observation deck was unlit, but a gentle glow from the floor tracked her footsteps as she crossed to the far side and looked down on Tallulah. The scape’s illusory gravity almost made her feel that she was on solid ground, gazing eastwards on a cloudless night from some mountain eyrie at a rising moon: a new moon, its gray disk lit only by starlight. But she knew that however long she waited, dawn would not come creeping across the limb of this disk; no crescent, no sliver of light would appear. Tallulah had no sun; it had been an orphan for at least a billion years, drifting untethered through the galaxy. Yet distant astronomers had surmised – and the instruments here and now confirmed – that its surface was awash with running water. In the cold of interstellar space even its atmosphere should have been frozen down to a sludge of solid nitrogen and carbon dioxide, but instead its long night was alive with balmy breezes wafting over starlit seas.
“Salaam! You must be Azar!” A tall, smiling woman strode across the deck, stretching out her arms. “I’m Shelma.” They embraced briefly, just as Azar would have done when meeting someone for the first time back on Hanuz. This was no more a coincidence than Shelma’s human appearance and common phonetic name: for the sake of mutual intelligibility, the scape was translating every sight,every word, every gesture that passed between them.
Shelma turned to face the blank gray disk, and her eyes lit up with pleasure. “It’s beautiful!” she exclaimed.
Azar felt slightly foolish that she’d been so slow to take a proper look herself. Tallulah’s surface would be emitting a far-infrared glow, but its atmosphere was virtually opaque at that frequency, so the easiest way to see any detail would be to increase her sensitivity to the usual visible spectrum. She willed the change – and the scape obliged, just as if her eyes were real.
The ocean sparkled in the starlight. Two broad continents shared the hemisphere below. Long mountain ranges, vast bare plains, and expanses of mysterious vegetation colored the shadowless land.
“It is lovely,” she said. Every world had its own peculiar beauty, though, and Azar would not have sacrificed three thousand years just to gaze upon even the most ravishing landscape.
When Tallulah had first shown up in telescopic surveys, long before Azar’s birth, people had soon realized that the best chance to visit it would come when it passed fortuitously close to an imaginary line joining the distant systems of Hanuz and Bahar. If the two worlds cooperated by launching probes that arrived simultaneously, the two spacecraft could brake against each other, sparing both of them the massive amounts of fuel needed to decelerate.
Accordingly, Mologhat 1 and 2 were sent on their way, launched in time to meet at Tallulah and merge in an intricate electromagnetic embrace. But then the news had reached Hanuz that Bahar would not be leaving the mission in the hands of insentient robots: a traveler would follow the Bahari probe, to wake inside the unified Mologhat Station and supervise the exploration of the orphan world.
No native-born traveler had left Hanuz for millennia, and Azar’s people were not so crippled with pride that the absence of a representative of their own would have been intolerable. The software they had already sent with Mologhat 1 was perfectly capable of protecting their interests in the mission; they might have simply left the Bahari to their alien ways without lessening their own enjoyment of whatever discoveries followed. And yet, a ripple had spread across the planet, a shocked whisper: One of us could go, could be there, could live through it all in person.
“A billion years in deep space,” Shelma marveled, “and not an iceberg in sight.”
“It’s hard to believe,” Azar replied. The endless night on Tallulah rivaled the height of summer on Hanuz. When a planet was stripped of its sun, the decay of long-lived radioisotopes could eke out enough warmth over billions of years to keep its core molten – but even with abundant greenhouse gases to trap the heat, that could not account for Tallulah’s surface temperature. However warm its heart, its skin should have felt the chill by now.
Mologhat had been orbiting Tallulah for three years before their arrival, and Azar now ingested the results of its observations. No obviously artificial structures were visible on the surface, but a faint stream of neutrinos was radiating out from deep in the planet’s crust. The spectrum of the neutrinos did not correspond to the decay of any known radioisotopes, natural or otherwise; nor did it match the signatures of fission or fusion. Someone had worked hard to keep this orphan warm, but it was far from clear how they had done it – and impossible to say whether or not they were still around.
“What do you think?” Azar asked Shelma. “Is there anyone home?”
“People have been beaming signals at Tallulah for thirty thousand years,” Shelma said, “and never raised a peep. So they’re either dead, or resolute hermits.”
“If they want to be left in peace, we have no right to disturb them.” Azar hoped that this declaration was redundant, but she wanted the ground rules absolutely clear.
“Of course,” Shelma agreed. “But if they insist on playing dead to perfection, all they’ll get are the rights of the dead. Which, while not negligible, are somewhat diminished.”
Once a civilization became extinct – not merely mutating into something new, but leaving no sentient heirs whatsoever – it was widely accepted that its history devolved into a common legacy that anyone was entitled to investigate. If sovereignty really had ceased to be an issue, Tallulah was certainly worth exploring. Tens of thousands of orphan planets had been found in the past, but only a few dozen had shown signs of habitation, and those worlds had yielded nothing but sad ruins buried beneath the permafrost. In the age of the Amalgam – the meta-civilization that now ringed the galaxy – the extinction of an entire world was unthinkable; if a catastrophe could not be averted, people who already had a robust digital form could be evacuated in seconds, and even those who had chosen purely biological modes could be scanned in a matter of days at the most.
The people of Tallulah, it seemed, had been halfway in between. When some cosmic mishap tossed them from their stellar hearth they had been unwilling or unable to evacuate, but they had not stood by and watched the air around them fall to the ground like snow. Whether trapped by their fate or just stubbornly resolved to ride it out, they had found a way to survive it. If they had since succumbed to some other tragedy, or merely surrendered to the passage of time, Azar saw no disrespect in digging up their secrets. Their achievements had endured for a billion years; they deserved recognition and understanding.
2
Mologhat’s orbit was a discreet hundred thousand kilometers from Tallulah, but it had dispatched a swarm of microprobes into smaller, faster orbits of various inclinations, providing complete coverage of the surface. If there had been any lingering suspicion that the heating of the crust might have been due to some freakish natural process, the details put that idea to rest: not only was the temperature modulated by latitude, diminishing toward the planet’s rotational poles, the records showed that it cycled over a period of about three months, creating imitation seasons. These nostalgic echoes of a long-lost circumstellar orbit were so clear that Azar was surprised they’d put the heat source in the ground at all, rather than launching an artificial sun.
“Not only would that have given them light from above,” she suggested to Shelma as they strolled through Mologhat’s library, “they could have kept the old diurnal rhythm too.” Heat conduction from deep in the crust would have washed out any cycle as short as a typical planetary day.
Shelma said, “It’s a lot of extra work to make a microsun efficient – to keep it from pouring energy out into space.”
“That’s true.”
“And perhaps they were insecure as well,” Shelma added, sliding out an image from the stack beside her that showed an animated model of Tallulah’s weather patterns. “They were already on the verge of losing one sun. They might have preferred to keep their energy source buried, rather than risk being parted from this one too.”
“Yeah. Still, it’s interesting that they tweaked the biosphere for such a radical shift – ground heat replacing sunlight – but kept the seasons.”
Shelma smiled. “Days, seasons, you’ve got to have something. People go mad without change.”
Both she and Azar had chosen to retain sleep cycles, their software following the dictates of their ancestral phenotypes. But Azar knew that the Baharis’ ancestors were nocturnal; what Azar perceived as the station’s night would be day to Shelma, and vice versa.
Azar pulled out a map of vegetation density. Using synthetic aperture methods, the microprobes had resolved details on Tallulah’s surface down to about a tenth of a meter, and even at that coarse resolution they had identified thousands of different kinds of plants. Spectroscopy could not untangle the detailed biochemistry from orbit, but the biosphere was clearly carbon-based/anaerobic, with the plants synthesizing carbohydrates but releasing no free oxygen.
Shelma spread her arms to take in the whole collection of data around them. “Everything here is open to interpretation. We’re going to need to make landfall to get any further.”
“I agree.” Azar was nervous, but relieved by the verdict. She was glad she hadn’t traveled this far just to find that Tallulah was clearly occupied by hermits, and there was nothing left to do but abandon them to their solitude.
“The question, then,” Shelma said, “is how we want to do it.” She began reeling off options. They could sprinkle a few nanotech spores on the surface, then sit back and wait for the army of robot insects they built to scour the planet. Or they could leave Mologhat and travel to the surface themselves, in various ways. Of course they could always combine the two, delegating most of the exploration while still being in the thick of it.
Azar had studied all of these methods before her departure, but Shelma sounded too blasé to be merely reciting theoretical knowledge. “You’ve done this kind of thing before, haven’t you?”
“Dozens of times.” Shelma hesitated. “This is your first time out-of-system?”
“Yes.” That wasn’t a lucky guess; everyone knew about the dearth of travelers from Hanuz. “It’s hard for us,” Azar explained. “Leaving everyone we know for hundreds of years. You don’t mind doing that?”
“My ancestors were solitary for part of their life cycle,” Shelma said, “and sociable for the rest. Now we’re flexible: we can switch between those modes at will. What I don’t understand is why you don’t just travel in packs, if that would make things easier.”
Azar laughed. “I know some people do that, but our social networks are so tangled that it’s hard to find a truly self-contained group – least of all a group where everyone can agree on a single destination. And if they do, they’re more likely to emigrate than to take a trip and come home again.”
“I see.”
“Anyway, forget about Hanuz. We need to make some decisions.” Azar wasn’t going to sit around on Mologhat while robots had all the fun, but there were practical limits on how far she could go just to get some dirt beneath her fingernails. If she had her own standard body reconstructed down on the surface, tweaked to survive the local conditions, she’d spend all her time foraging for food. Mologhat had only a few micrograms of its original antimatter store left; the few hundred megajoules that would generate were enough for its own modest needs, but pilfering any of it to power a sixty-kilogram behemoth would be insane; she could burn up the whole lot in a month. If Tallulah had had a reasonable abundance of deuterium she could have powered her body with D-D fusion, but the isotope was rare here.
“What if we build a high-capacity processor into one of the explorer insects?” Azar suggested. “Then we download into that. We get to see the world firsthand and make some real-time decisions, but we don’t waste energy or leave a big footprint.” If Tallulah turned out to be inhabited after all, the difference between being perceived as friend or enemy might easily hang on something as simple as the amount of local resources they’d used, or how physically intrusive their presence had been.
Shelma thought it over. “That sounds like as good a choice as any.”
3
Azar persisted with her doorway metaphor, and walked through an “airlock” from Mologhat Station into the robot insect as if the two were docked together. Amused by the concept, Shelma followed behind her, but she couldn’t resist a mild rebuke. “The poor balloon doesn’t even rate a mention?”
Azar shuddered. “Please, heights make me dizzy.” Only gamma rays had the bandwidth to transmit their software in a reasonable amount of time, but gamma rays couldn’t penetrate far through a planetary atmosphere. So the nanotech on Tallulah’s surface had built a small hydrogen balloon, which had risen high enough into the stratosphere to receive their transmission and transcribe the data into a densely encoded molecular memory, before deflating and descending.
The scape Azar had constructed inside the insect resembled the kind of transparent-domed flight deck found in sight-seeing aircraft back on Hanuz. Shelma would be perceiving some very different furnishings, but at least the two of them shared the same view of the jungle beyond the windshield; Shelma’s vision had always stretched into the far infrared, and now Azar had chosen to match her.
The insect was perched on a broad, flat leaf, one of dozens of papery structures sprouting from a slender trunk. The leaf’s veins glowed with the heat of warm sap, and a hot mist wafted up from the blotchy hexagonal pores that dotted the surface. When Azar looked up into the sky, the stars were barely visible through the fog.
Scout mites had already crawled up and down this plant and begun deciphering its strange biochemistry. Sap that was cooled and concentrated by evaporation in the leaves was pumped down to the roots, where it was diluted in chambers of fresh water. The increase in entropy that the dilution entailed allowed enzymes in the sap to drive an endothermic reaction, absorbing heat from the ground while synthesizing sugars from dissolved carbon dioxide.
The plant’s heritable replicator was a carbohydrate polymer known as C3, which had been found on many other worlds. Once they’d built up a database of sequences from a sufficient number of species, they could start trying to construct an evolutionary tree, as well as looking for signs of technological tinkering.
Azar took hold of a joystick and flew their host across to another plant, a small bush adorned with twigs that sprouted leaves like radial cooling fins. They landed on a twig while the scout mites burrowed and sampled.
“There’s not much sap in this one,” Shelma noted. “The leaves just look like mats of fiber. There were no pores here, no steamy exudations."
Azar watched a display of the scouts’ discoveries. There were long, fibrous structures running all the way from the leaves to the tips of the roots, and they were packed with interlocking polymers. In some fibers the polymers were rich in mobile electrons; in others they had positive “holes”, electron deficits that could shuffle along the molecule’s backbone from site to site.
“Thermoelectric diffusion?” she guessed. The electrons and holes would conduct heat from the ground up into the leaves, and in doing so they’d set up an electric potential, which in turn could be used to drive chemical reactions.
As the details came through, they confirmed her suspicion. The plant was a living thermocouple, with the heat-pumped currents in the polymers shuffling electrons to and from the enzymes that synthesized carbohydrates.
The thermocouple bush had no easily digestible nutrients above ground, so Azar flew back to the entropy tree and thrust the insect’s proboscis into a vein, drawing out a tankful of sugary sap. There was no free atmospheric oxygen to help metabolize the sugars, but like the plant itself, their robot could make use of nitrate ions in the sap as an oxidizing agent, reducing them to ammonia in the process. Scout mites were still hunting for the organisms responsible for creating the nitrates in the first place.
Shelma said, “So where are the insects? Where are the animals?” So far, they’d seen nothing moving in the jungle.
“Maybe the Ground Heaters didn’t have time to tweak any animals for the new conditions,” Azar suggested. “If they were about to get ejected from their solar system, their priorities would have been a new form of energy, and a primary food source that could exploit it. The old animals just died out, and nobody had the heart to try to create new ones.”
“Maybe,” Shelma conceded. “But wouldn’t your first response to the prospect of losing your sun be to build a few domed arks: sealed habitats with artificial heat and light that preserved the original ambient conditions, and as much of the original biosphere as possible?”
Azar said, “And then you’d slowly begin modifying the species from the arks to live off the new energy source. Still, they might have started with the plants but got no further.”
The scout mites collected more C3 sequences, and as the numbers reached the point where comparisons became meaningful it grew increasingly clear that these genomes were natural, not engineered. Even the genes responsible for building the gloriously technomimetic thermocouple fibers had the same messy, incrementalist, patchwork character of all the others.
Stranger still, the genetic analysis pointed to a common ancestor for all these plants just two hundred million years ago, long after Tallulah had been orphaned.
As Azar reviewed descriptions of other C3 worlds, pulling the data down from Mologhat’s library, she realized that in a couple of hours the station would set below the horizon. The time lag for her queries was already ponderous, and re-routing everything around Tallulah through the limited-bandwidth microprobes would only make that worse.
“We should clone the station’s library,” she suggested to Shelma. The library was far bigger than their personal software, and there was no room for it in their present insect host, but they could at least bring it down into the stratosphere, making the data far more accessible than it was from Mologhat’s distant orbit.
Shelma agreed. They set the nanotech to work fitting out the balloon for a new flight, then continued exploring the jungle.
As in many communities of plants there was competition for access to the sky, but here it was all about shedding heat rather than catching sunlight. The healthiest plants had their roots deep in the ground and their leaves exposed to the darkness of space. To be caught in too warm a cranny, sentenced to uniform tepidity, was fatal. The only exceptions to that rule were parasites: vampiric vines that stretched over trunks, branches and leaves, their barbed rootlets anchoring them to their victims and drawing out nutritious sap.
As they moved through the jungle, the new sequence data that came in from the scouts only shored up their original conclusions: the life they were seeing was entirely natural, and this branch of it was relatively young.
“Suppose,” Shelma ventured, “that the Ground Heaters didn’t need to engineer anything to live this way.”
“You mean there were species that exploited thermal gradients all along?” Azar frowned. “How do you evolve to use that as your energy source? A single cell can never do it alone; you need to be a certain minimum size to access a useful temperature difference.”
“I’m not saying that the very first lifeforms used it,” Shelma replied. “They might have relied on chemosynthesis, extracting energy from volcanic gases or mineral-rich geysers.”
“Right.” That was how Azar’s own ancestral lineage had begun, back on Earth; photosynthesis had come much later. “So they grew to a certain size using chemosynthesis, then found they could switch to thermal effects. But this is all before the Ground Heaters have even evolved, so what’s keeping the surface rocks so hot?”
Shelma pondered this. “Tidal heating? What if Tallulah was orbiting close to a cool red dwarf, or even a brown dwarf. With such weak sunlight, tidal heating might have been a far more potent energy source than photosynthesis.”
“But it can’t last,” Azar protested. “Eventually the planet would end up tidally locked.” The energy used to stretch and squeeze the rock, heating it up by internal friction, would ultimately be extracted from Tallulah’s spin, slowing its rotation until its day matched its year and one hemisphere faced forever sunwards.
“Eventually, yes. But what if the Ground Heaters evolved before that happened? They would have been facing a slow, predictable decline in their energy source over millennia. So instead of responding frantically to a sudden catastrophe, they could have spent centuries perfecting a replacement.”
“And the ejection from their star came much later, but by then there was nothing they needed to do. They’d already made themselves independent.” Azar laughed, delighted. The artificial seasons and the variation in heat with latitude would still make sense: tidal heating would have been strongest at the equator, and at higher latitudes it would have been affected by seasonal changes in the angle between the planet’s axis and the direction of the tidal force.
What this elegant hypothesis didn’t explain was why the plants here were so young. Nor did it shed any light on exactly what the Ground Heaters had done to achieve their independence.
The data-collecting balloon was in place again. Before Mologhat vanished below the horizon, Azar instructed the station to send down a copy of its library.
As she was checking the interface with the cloned library, a message arrived from the microprobes. Thousands of kilometers away, something had exploded on the ocean floor and hurled a few billion tonnes of water skywards.
Azar turned to Shelma, still watching the satellite vision with her mind’s eye. “What’s happening? Some glitch with the heat source?” For a system that had survived for a billion years, this hiccup packed a mighty punch: the eruption was already high above the atmosphere, steam turning to ice like a cometary impact in reverse.
Shelma looked nervous. “Mologhat saw no vulcanism anywhere on the planet, in the last three years. Do you think we’ve annoyed someone?”
“If we have, why are we still alive? It’s not the ground beneath our feet that’s exploded.” The balloon clearly wasn’t the target, nor were any of the microprobes – and though the water missile was heading roughly in Mologhat’s direction, it wouldn’t reach anywhere near that far. But when Azar tried to contact the station, the microprobes replied that it was not responding.
Shelma said, “Don’t jump to any conclusions. Mologhat might have imposed a communications blackout; if it thought it was under fire it would shift orbits and try not to do anything to give its position away.”
Azar felt sick. “You think the gamma ray transmission was mistaken for some kind of attack?” Nothing had happened when she and Shelma had arrived the same way, but that burst had been considerably shorter, and it had come down almost vertically. The second beam had come from close to the horizon, giving it a longer path through the upper atmosphere – which would have made it more noticeable, and easier to trace back to its source.
Within minutes, the microprobes had reported six more eruptions, from underwater sites scattered around the planet. It made no sense to Azar; these gigatonnes of water were rising into orbits about a thousand kilometers up, but if they were meant as weapons, who were they aimed at? The microprobes were much lower down, and Mologhat was a hundred times further away. A direct hit with a solid iceberg could have done a lot of damage to any intruder, but these glistening snowballs weren’t even holding together; Tallulah was just shrouding itself with a tenuous halo of tiny ice crystals.
“This isn’t warfare!” she declared. “They don’t think they’re under attack. They saw the gamma rays, and thought: antimatter. They’re afraid they’re drifting into a cloud of antimatter. The ice is to tell them if there’s any more around.”
Shelma considered this. “I think you’re right. They picked up a flash of annihilation radiation, and jumped to the conclusion that it was a natural source.”
Never mind that there was no natural source of bulk antimatter anywhere in the galaxy; if you’d spent a billion years in space without encountering another civilization, perhaps a small cloud of antihydrogen seemed like a far less extravagant hypothesis than alien visitors using proton-antiproton gamma rays for communications.
“So they still don’t even know we’re here?” Azar wondered. “All those radio messages came to nothing. What do we have to do to get noticed – tattoo the binary digits for pi across the stratosphere?”
Shelma said, “I wouldn’t advise that. But it’s not even clear to me that there’s anyone home; this might just be a non-sentient device that’s outlived the people it’s meant to be protecting.”
The water missiles had stopped; the absence of any answering flash of radiation must have made it clear that if there was antimatter around, it was far too thinly spread to pose any kind of hazard.
Azar tried calling Mologhat again, but it was still not responding. “They must have hit it,” she said. “Whatever they thought it was, they must have launched something small and fast, and knocked it out before the ice storm even started.” She felt numb. So much for the doorway to the stars.
Shelma touched her arm reassuringly. “It might yet reply – but even if it’s gone, we’re not stranded.”
“No?” The microprobes had nowhere near enough power for interstellar transmissions, or even the raw materials to build the kind of hardware they’d need. And the data-ferrying balloon couldn’t send them anywhere; their return path to Mologhat would have involved a gamma-ray mirror on the balloon, modulating and reflecting radiation coming down from the station itself.
Azar slumped into her seat. How had she ever imagined she could do this? Travel fifteen hundred light years as if it was nothing? There was no magic gate leading home, just fourteen quadrillion kilometers of vacuum.
Shelma said, “We have plenty of resources down here.”
Azar rubbed her eyes and tried to concentrate. “That’s true.” Given time, the nanotech could build them almost anything – and they didn’t even have to reach all the way back to Hanuz or Bahar; they just had to connect to the Amalgam’s network. Still, the nearest node was seven hundred light years away; getting a signal that far was a daunting prospect. “Can we do this from the ground?”
“Well ... we could build a radio dish a few hundred kilometers across,” Shelma replied, deadpan. “Factoring in suitable error correction for the signal-to-noise ratio, it might only take two or three centuries to complete the transmission.”
Azar got the message. “OK: better to build a rail gun and launch a transmitter into orbit. But even if we can power a rail gun, how do we power the transmitter? We don’t have any antimatter. There’s virtually no deuterium here; are we going to try to build a hydrogen-boron fusion reactor?” The most efficient way to produce gamma rays was from antimatter – that would certainly make for the lightest power source to loft into orbit – but trying to create even a few micrograms of antihydrogen with nothing but plant carbohydrates as the energy source made Shelma’s giant radio dish sound like a good idea. Whatever was guarding Tallulah might be a tad obtuse, but it was difficult to imagine a particle accelerator powered by industrial-scale deforestation slipping under the radar.
“What’s the point of this transmission anyway?” she said bitterly. “To arrive home empty handed, with no news worth hearing? If it comes to that, I’d rather let my backup wake.”
“So would I,” Shelma said, “but I think you’re missing something.”
“Yeah?”
“The news worth hearing,” she said, “and the energy source we need in order to send it, are the very same thing. Whatever’s keeping this planet warm is just a few kilometers beneath our feet. If we can reach it, study it, understand it and harness it, we’ll have both the means to get home, and the reason.”
4
A few kilometers beneath our feet was an encouraging way of putting it; from where they stood the actual distance was twenty-seven thousand meters. The nanotech built some robot moles, powered by long thermoelectric tails, and sent them on their way. They would reach the heat source in about two hundred days.
The oceanic crust was much thinner in places. Azar did some calculations. It wasn’t clear what kind of food there’d be in the water, but she thought it was worth finding out. Shelma agreed, and they set out for the coast.
The insect made good time, averaging about thirty kilometers an hour, but when they reached the edge of the jungle food became more sparse and the scattered plants less nutritious. Flying across the flat, monotonously glowing savannah, Azar ached for sunrise to come and banish the interminable night. But she fought down the pang of homesickness and tried to find the beauty in this upside-down world.
Other explorer insects were already fanning out from a dozen sites where the spores had landed, building up a picture of the continent’s geochemistry. A tentative analysis of the data suggested that the surface had only been above sea level for about a quarter of a billion years.
“Before that, there might have been no dry land at all,” Shelma suggested. “That would explain why the ecosystem here is so young.”
“So where did all the water go?” Azar wondered. “Unless their antimatter detectors have a lot of false alarms.” Even the modest amount that they’d seen thrown skywards would mostly rain back down again.
“A collision?” Shelma frowned and withdrew the suggestion. “No, the odds would be very low out here, to hit something big enough.” The current estimate of Tallulah’s galactic orbit suggested that it hadn’t even crossed another system’s Oort cloud in the last billion years.
They reached the shoreline. Waves lapped gently on a lifeless beach; the infrared glow of the placid ocean made Azar think of liquid metal, but if she’d been wearing her body this water would have made a luxurious warm bath.
In the waves they found only single-celled creatures, living off a very thin soup of organic debris. They flew out a kilometer and took another sample, sending scout mites a few hundred meters down.The soup was thicker here; with a little tweaking, the insect would be able to make use of it.
There was a trench some six hundred kilometers off the coast, where the mysterious neutrino source was just nine thousand meters below the ocean floor. They set out across the waves, stopping every couple of hours to dive and feed.
Each time they plunged into the water, Azar noticed Shelma tensing. She wondered about the propriety of commenting on this; if she’d been looking at Shelma’s true self-image – a Bahari body with five limbs and five tails, like the rear end of a cat caught in a kaleidoscope – she would not have been able to distinguish tranquility from terror. Still, it was not as if the scape was reading Shelma’s mind; it was merely translating information that she had chosen to make public.
As they approached the trench, Azar finally spoke. “You don’t have to do this if you don’t want to.” The trench was three thousand meters deep; if Shelma had retained a primal fear of drowning, Azar had no wish to see her suffer. “We can split the processor, and you can stay up here.”
Shelma shook her head, a little puzzled by this offer. “No, I’ll go with you. But first I want to bring in as much of the library as we can fit.”
“Oh.” Azar understood now; this was nothing to do with how Baharis felt about getting their fur wet. Once they were underwater they’d lose radio contact with everything, including the balloon-borne library.
Shelma began communing with the library, trying to choose a selection of its contents that would fit inside the insect without leaving them ill-equipped in the face of some crucial problem or opportunity. “I don’t want to meet the Ground Heaters and then find we can’t even make sense of their language!”
“If they’re so smart,” Azar replied, “let them make sense of ours.” Then again, if they’d spent a billion years living alone on the ocean floor, it would probably be unwise to expect too much of their communications skills.
Hanuz had sent no travelers out into the galaxy for a hundred thousand years, and that had been long enough. Though Tallulah had been an enticing destination, Azar had left home less for the sake of the orphan’s secrets than for the sake of breaking the curse. As the window for joining Mologhat had approached, she’d thought: If we don’t do this now, it will only grow harder. And she’d finally stopped waiting for someone else to volunteer.
Shelma announced that she’d completed her selection, then she changed her mind and dived back into the interface. Azar thought of her great-great-granddaughter, Shirin, struggling to pack for an overnight trip. Shirin would be ancient when Azar returned; she’d have left all her toy animals behind.
“This is it now,” Shelma declared. “We’re prepared for anything.” Her avatar wasn’t quite hyperventilating, but Azar could imagine her letting a breeze of random skills and factoids play through her mind, soaking her tissues with the oxygen of information before the conduit slammed shut.
“I could always give myself amnesia, if you want a little more room,” Azar suggested. Shelma actually looked tempted for a moment, before smiling thinly at the joke.
Azar took the joystick and the insect dived beneath the waves.
Their infrared vision wasn’t quite useless here; if they tuned to a wavelength a little shorter than the peak thermal emissions around them, they could see the shadows that nearby objects cast against the glow of the warmer water below. Augmented with the strobe flashes of sonar, the vague shadows became fluttering vertical ribbons, drifting in the current but maintaining their orientation. Azar sent in the scout mites, who found the ribbons to be packed with tiny buoyancy chambers that exchanged gases in a complex cycle, eking a few microwatts out of the temperature gradient. The ribbon-weed’s C3 sequence made it a close cousin of the land plants; in fact, it had probably changed very little from the ancestor whose other offspring had invaded the continents.
Five hundred meters down, they saw the first animals: small, segmented worms about a millimeter long, feeding off the ribbon-weed. The scout mites grabbed a few cells from the worms’ skin for analysis. As Azar watched the data coming through, she felt a sense of disorientation to rival anything since she’d stepped on to Mologhat. The worms had no C3 in their cells; they were no more related to the weed they were munching on than she was to Shelma. Their replicator was P2, a polypeptide. What’s more, their genome had been the subject of some blatantly artificial modifications, probably less than a million years ago.
“Introduced?” Shelma suggested.
“They must be,” Azar replied. Colonists from a P2 world must have come to Tallulah, bringing a few species from their home planet and tweaking them in order to survive here. It was a curious strategy; almost all interstellar travelers were digital in transit, not biological, and even if – like the founders of Hanuz – they had a fetish for recreating their original biochemistry upon arrival, such travelers tended to colonize sterile worlds. But then, nobody traveled to an orphan world for the sake of its real estate value. “It looks as if someone else came treasure-hunting long before we did.”
“Apparently,” Shelma concurred. “But if Tallulah is such old news, why isn’t the heating process known halfway around the galaxy by now?”
As they descended further the ribbon-weed grew larger, the soup of microbes thicker, and the P2 creatures more numerous and diverse. There were shrimp-like animals straining microbes from the water, floating gas bladders with poisonous tentacles, and sinuous, muscular fish of every size, feeding on each other, the ribbon-weed and the shrimp.
A vast forest came into sonar range, rising up from the ocean floor. Azar had already been impressed by the size of the free-floating ribbon-weed, but its anchored cousins were giants, fifty or sixty meters high. With convection currents in the water sweeping heat away more efficiently than air, the temperature gradient was far less steep here than on land, but the water also made it easier for taller structures to support themselves. The scout mites counted eighty species of animals in the forest’s upper reaches alone; some were P2, but there were C3 species as well, the first such animals the mites had found. And some were N3, with their genome encoded in nucleic acid.
“This place really has been popular,” Shelma observed dryly. “It’s enough to bring out the biograffitist in anyone. You sprinkle some N2 microbes in the water; I’ll add the C1.” N2 was DNA, Azar’s ancestral replicator.
The N3 species, like the P2, had been engineered, but the best estimates put the date of intervention much earlier, between two and three hundred million years ago. Azar checked their local copy of the library; there was no previous archaeological evidence for an interstellar civilization with N3 ancestry in that epoch – and this was not one of the databases Shelma had trimmed. How could a civilization reach such a difficult target as Tallulah, but leave no trace anywhere else?
As they descended slowly into the forest, the insect announced a discovery that had nothing to do with Tallulah’s polyglot biology. The robot’s mass spectrometer was constantly analyzing samples from the water around them, and it had just stumbled across an extraordinary find. The object in question had a mass of 40.635 atomic units; this far-from-integral figure might have made sense as an average for a sample containing a mixture of calcium-40 and its heavier isotopes – but it wasn’t an average, it was the mass of a single ion. Stranger still, when stripped of all its electrons the thing had a charge, not of twenty or so, but two hundred and ten. This was double the charge of any known stable nucleus, and ten times greater than its atomic weight implied.
“Who ordered that?” Azar quipped. Shelma didn’t even smile; the depleted library wasn’t up to providing the scape with the context for a proper translation.
“It’s femtotech,” Shelma declared.
Azar hesitated, then agreed. It was a staggering notion, but what else could it be? A new fundamental particle ... with a charge of two hundred and ten? Femtotech – the engineering of matter on the scale of atomic nuclei – was still a primitive art within the Amalgam; there had been some ingenious creations but they all had to do their job quickly, before they blew apart in a few trillionths of a second. The insect’s find had endured for at least three hundred seconds, and counting.
“How do you create a femtomachine with a binding energy equal to ninety percent of its mass?” she wondered. The most stable nuclei, nickel and iron, weighed about one percent less than the sum of their parts, thanks to the potential energy associated with the strong nuclear force. But increasing that effect by a factor of ninety was almost unimaginable.
The insect measured the ion’s magnetic moment. The result was orders of magnitude higher than that which a nucleus of atomic number 210 would be expected to possess if it was sitting quietly in its ground state; to generate such a strong magnetic field, it would need to be spinning at relativistic speeds. This only made the overall picture even stranger: the kinetic energy from this rotation should have added substantially to the ion’s total mass, rendering the actual forty-something value even more bizarre. The one thing that made a warped kind of sense was the failure of the ion to tear itself apart from centrifugal force. How could it explode, when the fragments would need to possess ten times more energy than the whole?
Azar said, “I take it this is ash from the heating process?”
Shelma managed a dazed smile. “If it’s not, it certainly should be. Ninety percent mass-to-energy conversion. No wonder it’s still going strong after a billion years!”
Tallulah’s crust was generating heat at a rate of about two petawatts, stabilizing the planet’s temperature by replacing the energy that leaked out of the greenhouse blanket. At ninety percent mass conversion, that would consume less than eight hundred tonnes of fuel each year, so in principle the process could continue for about ten-to-the-eighteenth years: a billion times longer than it had been running so far. Unlike fission or fusion, even if the starting point for the femtotech process had to be one particular kind of nucleus, it really didn’t matter how rare it was in nature, since the energy required to synthesize it from anything else would be trivial in comparison.
If each tonne of the Ground Heaters’ “gold” burned so fiercely that it could power the transmutation of a hundred tonnes of nickel or iron into yet more fuel, then Tallulah’s bonfire would easily outlive the stars.
Technology like this could transform the Amalgam. Antimatter had never been more than a wonderfully compact storage device, costing as much energy to make as it released. The most exquisitely efficient fusion systems extracted about half a percent of their fuel’s mass as usable energy. There were some unwieldy tricks with black holes that could do better, but they weren’t very practical, let alone portable. If everyone could harness the Ground Heaters’ femtotech, it would be like a magic wand that could turn nine parts in ten of anything into energy, leaving nothing behind but this strange spinning ash.
Azar said, “This is a lot to conclude from one weird ion. Are we sure it’s not an instrument error?”
Before the insect touched the ocean floor it picked a second speck of ash out of the water. Azar had the nanotech rebuild the relevant instruments from scratch and repeat the analysis. There had been no error; all the properties were the same.
5
The nanotech built more moles and sent them down into the rock, but even here where the crust was thinner, Azar knew she would have to be patient.
“Sixty days?” she lamented, pacing the flight deck. She didn’t expect to be able to unravel the nucleon-by-nucleon details of the femtotech in a hurry, but if they could obtain a sample of the deep crust and observe the way its composition was changing as energy was released, that would at least confirm that their overall picture of the Ground Heaters’ process was correct.
Until they had some of this white-hot rock to play with, the practicalities of harnessing the femtotech remained obscure, but Azar’s sense of anxiety at their isolation had almost vanished. To be stranded for nothing, with little to be gained if they managed to return, had been a dismal prospect, but now that the stakes were so high the situation was exhilarating. Prometheus, eat your heart out.
While they waited for the moles to hit pay dirt they continued to explore the ribbon forest, building up a catalog of the three kinds of life that Tallulah’s mysterious fire sustained. Perhaps unsurprisingly, the P2 animals – the newest – were by far the most numerous, having been engineered to be able to digest everything that had come before them. To the older N3s, and the even rarer C3s, the P2s were unpalatable – though not indestructible; the scouts witnessed cases of N3 fish killing off their P2 rivals, even though they were useless as food. What’s more, a few of the C3 creatures were able to feed on N3 flesh; evolution had finally granted them a belated revenge on the first wave of invaders. In another hundred million years, who knew who would be eating whom?
When they first came across the colony of P2 “lizards”, Azar thought that they were charming animals. Spread across a dozen square kilometers of the forest floor, their network of burrows was entwined with the giant ribbon-weeds’ roots, which they tapped for food.
The lizards had two eight-clawed limbs that they used for digging and grasping objects; all their motive force came from their powerful tails. They sensed the world around them with a mixture of IR vision and sonar. Glands in their cheeks excreted complex molecular cocktails, which they squirted at each other almost constantly. Olfactory signaling within a colony of social animals was nothing surprising; the shock came when the scout mites caught some of them squirting the chemicals at inanimate objects in certain chambers within their burrows – and the inanimate objects squirted back replies. On closer examination, the devices turned out to be sophisticated chemical transceivers, linked by a fiber optic network.
“So these are our predecessors,” Shelma said. “They came all the way to Tallulah, in the middle of nowhere, to solve the mystery of its warmth. But they must have found the femtotech long ago, so why are they still here? Why not take the treasure home? Why not spread it across the galaxy?”
“Why leave a world that will keep you warm for a million times longer than any star?” Azar replied.
“Why not build a hundred more worlds just like it?” Shelma countered.
“Let’s ask them.”
The scouts set to work sampling the chemical signals that comprised the lizards’ language, and trying to correlate them with elements in the environment and the creatures’ behavior. It was an impertinent level of eavesdropping, but they had to bootstrap communications somehow, and with no culture or biology in common they couldn’t simply march up to the lizards and start playing charades. Ideally the scouts would have included children as their subjects, in order to share in any lessons they received, but in the entire colony of fifty thousand there were currently no young at all – which suggested that the lizards had cut back their fertility to stabilize the population, while living more or less as long as they wished.
Fiber optic trunk lines connected the colony to others around the planet, and all the data traffic passing through appeared to conform to a single language. If there were any intelligent N3 creatures still around, either they weren’t plugged into the same network, or there’d been a radical assimilation of cultures in one direction or the other.
Fed by the forest and served by their own rudimentary nanotech, the lizards seemed to pass the time socializing. The chemical transceivers granted them access to libraries, but most of the content being summoned appeared very similar to their habitual person-to-person exchanges, suggesting that it was closer to narrative history or fiction than anything more specialized and technical. Then again, even the most naturalistic dialogues might have encoded subtle themes that remained elusive at this stage of the analysis.
The lizards had no apparent social hierarchies, and as hermaphrodites they exhibited no sexual dimorphism, but the scouts identified one curious form of division. Many of the lizards identified themselves as belonging to one of three groups, which were named for the actions of spiraling inward, spiraling outward, and, the clear majority, following a circle. Since this was not a description of anyone’s actual swimming style, it had to be a metaphor, but for what? The scouts had failed to observe anything tangible that correlated with this classification.
After thirty days Shelma declared, “It’s time to introduce ourselves.”
“Are you sure?” Azar was impatient for answers, but it seemed as if the scouts could easily spend another month piecing together further subtleties of the lizards’ language.
“We’ve reached the point where we can greet them politely and explain who we are,” Shelma said. “The way to get more reliable language acquisition now is through dialogue.”
Shelma instructed the nanotech to build two facsimile lizard bodies. These robots would beobvious caricatures, functional but not such perfect imitations that the lizards could mistake them for fellow colonists.
The insect communicated with the robot lizards by line-of-sight laser pulses with a range of just a few meters. Azar and Shelma kept their software on the insect’s processor and operated the lizards by telepresence, monitoring the robots’ points of view without becoming fully immersed in their sensoria or giving up the feeling of being located on the insect’s flight deck.
With her lizard body swimming toward the edge of the colony, weaving its way between the ribbon-weeds, Azar was overwhelmed with happiness. She was more than just a traveler now; she was about to become an ambassador to a hitherto unknown culture. And however physically isolated she was at this moment, she did not feel cut off from her roots in Hanuz. In her mind’s eye, she could almost see the faces of the people she hoped to regale with her adventures.
A lizard approached, seemingly unafraid. The puff of chemicals it squirted through the water was barely visible, but Azar heard the translation loud and clear. “Who are you?”
“We come in peace from another world,” Azar announced proudly. The lizards had not been seen discussing astronomy, but they did have a word for the planet as a whole, and a general inflection for “not this thing, but another of its kind”.
The lizard turned and fled.
On the flight deck, Azar turned to Shelma. “What did I do wrong?” She’d half-expected her claim to be greeted with skepticism – their robot bodies were well within reach of the lizards’ own technology, after all – but perhaps the gamma rays that had triggered the ice halo had served as an ominous calling card.
“Nothing,” Shelma assured her. “Summoning other witnesses is a common response.” Shelma had no prior experience of first contact, but the library confirmed her claim.
Azar said, “What if they’ve forgotten that there are other worlds? They’ve been here for a million years. They might not even remember their own history.”
Shelma was not persuaded. “There’s too much technology around; even if they fell into a dark age at some point, they would have reconstructed everything by now.” The lizards’ nanotech maintained their health; it could easily have sequenced all the plants and animals around them, just as the Amalgam nanotech had done. Still, without the right context – without libraries of replicator sequences from a thousand other worlds – would they know how to interpret the data?
Azar saw bodies darting through the fronds. The first lizard had returned, with ten, twelve, fourteen friends. She could never have distinguished one from the other unaided, so she invoked software to track their features and assign phonetic names to them all.
Shelma said, “Please accept our good wishes. We come in peace from another world.”
Omar, the first lizard they’d met, replied, “How can that be? It’s not time.”
His companion Lisa added, “You’re not taking Tallulah from us. We’ll never accept that.”
Suddenly all fourteen lizards were speaking at once. Azar’s robot’s senses had no problem following their words; the chemical emissions were tagged with individual markers, so there was no chance of confusing one lizard’s words for another’s. Azar had the audio translation untangled into separate streams.
Some of the lizards were expressing surprise and skepticism, not at the notion of visitors from another world, but at the timing of their arrival. Others seemed to think that she and Shelma were the vanguard of an army of colonists who had come to seize Tallulah, and they defiantly expressed their intention to resist.
Shelma said, “We’re not colonists, we’re merely explorers. We saw Tallulah and became curious.”
“Where is your own world?” a lizard dubbed Caleb demanded.
“My companion and I come from different worlds,” Shelma explained. “Both more than a thousand light-years away.” The software would translate this into the local measure of distance, but with no units suitable for astronomical scales the number attached would be awfully large.
The lizards broke into a fresh cacophony. Such a journey was inconceivable.
Omar said, “Please come with us.”
The crowd pressed around them from all sides, urging them forward. Shelma said privately, “Just go where they ask, don’t resist.”
The lizards seemed unaware of the tiny insect hovering between the larger robots; certainly its laser flashes were outside their visible spectrum. “You think they’re taking us prisoner?” Azar said. It was hard to decide which was more bizarre: the fact that someone might wish to do this, or the fact that they believed it could be done.
“More or less,” Shelma replied. “But at this point I’d rather cooperate than escape. If we can clear up a few misunderstandings, everything should be fine.”
Azar let the pack of lizards guide her through the ribbon-weeds, then down into a burrow. Watching events through the flight deck’s dome made her feel much less claustrophobic than the impression she got from her jostled robot’s senses, but when the narrowing tunnels and the ever tighter crush meant the insect risked becoming conspicuous, they had it crawl inside Shelma’s body. The line of sight between the two larger robots came and went, so Azar put her own lizard on autopilot, meekly complying with the flow of the crowd, and changed the insect’s flight deck scape to show her an external view rather than the innards of its host.
They were taken to a small, bare chamber with a single entrance. After six of the lizards piled in with them, there was little room to spare.
Omar resumed the interrogation, his skepticism undiminished. “Your star must be very dim,” he declared. “We believed that we had many more years.”
Azar thought she was beginning to understand. Tallulah would not come close to another star for a very long time; the lizards had somehow fixed on that event as the most likely occasion for visitors.
“Our stars are very bright, but very distant,” she insisted. “Why do you doubt that? Didn’t your own ancestors travel far to reach this world?”
Omar said, “Their journey took half a year.”
Half a year? Perhaps the real story had degenerated into myth, retold with cozy, domesticated numbers to replace the terrifying reality of interstellar distances.
“At the speed of light?” asked Shelma.
The chamber erupted with expressions of mirth and derision. “Only light travels at the speed of light,” Lisa explained.
The scouts had found no evidence of the lizards digitizing themselves. Had they lost that technology, or had they never possessed it? Could their ancestors really have crossed the light years as flesh?
“So how far would they have traveled,” Azar asked, “in that half-year?”
“Perhaps a billion kilometers,” Omar replied.
Azar said nothing, but the claim was absurd; a billion kilometers was the size of a small planetary system. The lizards had spent too long dozing away the centuries at the bottom of this warm ocean; not only had they forgotten their own history, they had forgotten the true scale of the universe around them.
Shelma persisted. “When we follow the path of Tallulah back in time, it doesn’t come that close to the path of any star for a billion years. Have you been here for a billion years?”
Omar said, “How can you know Tallulah’s path? How long have you been watching us?”
“Thirty thousand years,” Shelma replied. “Not me personally, but people I trust.”
Mirth again. Why was this claim so laughable?
“Thirty thousand years?” Omar said. “Why did you imagine that would tell you the whole story?”
Shelma was bewildered now. “We’ve tracked your position and your speed,” she said. “We know the motion of the stars. What else is there to account for?” Tallulah’s galactic orbit was sparsely populated; chaos would eventually make retrodiction impossible, but the confidence levels over a billion years were still quite tight.
“Eight times since we arrived on Tallulah,” Omar explained, “this world has changed course. Eight times, the heat rose from the ground to bring our path closer to our destination.”
6
An argument broke out among the lizards; they withdrew from the discussion and left the chamber, leaving their guests with only two taciturn sentries. The insect probably could have slipped past these guards, or even burrowed its way back to the surface if necessary, but Shelma insisted that it was better to try to keep the dialogue open, and on consideration Azar agreed.
“So our orphan is a tourist,” Shelma mused. “It steered its way right into the lizards’ home system, and now it’s heading for a new destination. But did the Ground Heaters arrange that, or did the N3 colonists bolt on the engines later?”
“Maybe that’s where the water went,” Azar suggested. The eruptions they’d seen earlier would have no long term effect on the planet’s motion, but a hotter jet that reached escape velocity would do the trick.
Shelma said, “Water would be a strange choice of propellant. Photonic jets would be more efficient.”
“If it was the N3ers doing it,” Azar said, “maybe they didn’t have fine enough control over the femtotech.”
“Maybe. But the N3ers left no biological presence on the land, so they must have been ocean dwellers. Would ocean dwellers throw so much water into space that they lost thirty percent of their real estate?”
“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 hundred thousand 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 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 weeven 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.
“You should join the Amalgam,” Azar said, “and use their network to migrate. The kind of world you’re looking for is not in high demand; a frozen planet tidally locked to a faint brown dwarf is of no interest to most space-faring cultures.”
“And it’s no use to us either,” Jake replied, “unless we can enliven it. We can’t send the deep rock through your network, can we?”
“No, but if you spent a century or two manufacturing antimatter from geothermal energy, you could build an engine to carry samples of rock at a significant fraction of lightspeed. And even if for some reason you didn’t have enough spare power to do that, I guarantee that you could find a partner in the Amalgam who’d trade you a few tonnes of antimatter for some deep rock samples of their own. And I mean a few tonnes on arrival at Tallulah, not a few tonnes when it left home!”
Juhi said, “We need to be careful. It’s one thing to hand Tallulah over to the Next Passengers, as the Builders intended, but we don’t want a million strangers flocking here just to mine the planet.”
“Nobody’s going to do that,” Shelma assured her. “If deep rock has any value at all in theAmalgam, it will come from the ability to graft it, or the ability to reverse-engineer it. In either case, a few kilograms would be enough.”
Rahul said, “Whether we choose to join the Amalgam or not, you need antimatter for your own journey, don’t you?”
“A few micrograms would come in handy,” Shelma admitted.
The transceiver sprayed out a chemical ringtone and Rahul replied with a command for it to speak. Azar found the conversation that followed cryptic – and she suspected that parts of it were literally in code – but when it was over Rahul announced, “Someone spotted you in the forest with Jake. The Circlers have destroyed your puppets, but they know more or less what happened now. I think we need to move from here.”
Azar was dismayed. “Can’t you talk to them? Explain the situation? None of our plans should be any threat to them.” The Amalgam would happily leave the Circlers in peace, sending no travelers and no further explorers, but the Spiral Out faction were entitled to emigrate, and to trade a few small pieces of Tallulah’s exotic legacy with the wider galaxy.
Rahul said, “They’re convinced that you’re the New Passengers, and that the fight to retain Tallulah has begun. In the past they’ve viewed Spiral Out as timid fatalists, but now that we’ve come to your aid we’re something worse. We’re traitors.”
On the flight deck Shelma muttered a string of obscenities. “We’re not going to spark a civil war,” she told the lizards. “We’ll surrender ourselves. It doesn’t matter if they destroy us; we’ll make backups.”
Jake said, “But they understand now that you can do that. You could surrender a thousand machines to them – or one pair of living creatures, and call them your true form – but it won’t be enough to convince them that they’ve put an end to your plans.”
Azar wanted to contest this bleak verdict, but from what she’d seen of the Circlers firsthand it rang true. Whatever the original intention of Tallulah’s creators, it had sounded like a beautiful story: a chariot traveling between faint, forgotten stars, rescuing the inhabitants of dying worlds, offering them a safe, warm home for a few million years so they could build up their strength then fly from the nest – or, if they wished, dive into its depths, into a femtoscale mansion of a quadrillion rooms. In a way, she admired the Circlers for their determination to tear up the script, to scream at their long-vanished benefactors that they would make their own decisions and not just meekly come along for the ride. But the irony was that they were so intent on rebelling against the Builders that they seemed blind to anything that didn’t conform to their own version of the scenario. It was chiseled in stone that one day they would fight the New Passengers for Tallulah, and they had spent so long rehearsing this play that you couldn’t even tap them on the shoulder and suggest a different ending without being dragged into the plot and cast as the villain.
Shelma had their mock-lizard body destroy itself, and found a dim but agile P2 fish for the insect to parasitize and modify. A talking fish would attract suspicion, but with some help from the library they managed to engineer speech glands for it that created rapidly decaying words; if they swam up close to a chosen confidante they could emit some short-range chemical whispers with little chance of beingoverheard. Unfortunately, the lizards’ own medical nanotech wasn’t flexible enough to do the same for them, and Jake and the others recoiled from a friendly offer to let the aliens tweak their speech organs.
Shelma said privately, “This is going to get messy.”
“So how do we fix it?” Azar replied.
“I wish I knew.”
They agreed on a place and time to rendezvous, then Jake, Rahul and Juhi scattered.
Shelma said, “I think we should go back to the surface for a while.”
They took the fish as high as it could go, then left it parked and rode the insect alone for the last few hundred meters. When they broke the water, Azar found herself almost weeping with relief. She was still as far from home as ever, but just a glimpse of the stars after so long without them made her feel that she was back in the right universe again.
Neither the balloon nor the orbiting microprobes had experienced any form of aggression, or noticed anything else unusual. It seemed that the Circlers, for all their paranoia, had been too complacent to create a world bristling with sensors and weapons while Tallulah’s next stop was still so far from sight.
Shelma said, “We should bring the balloon down on the ground somewhere and replicate the library a few times. I think we’re already carrying everything vital, but if our backups have to take over from us we want to be sure that they’re not disadvantaged.” Their backups in the jungle were already receiving incremental memory updates, by radio via the microprobes.
Azar agreed, and they sent the instructions. She paced the flight deck, rubbing her eyes. She had given up the need for sleep, but there was still something irredeemably strange about the feeling of unpunctuated consciousness stretching back into the distance.
“I screwed up,” Shelma said. “I rushed to make contact. We didn’t even know what the factions’ names meant.”
“And I let you do it,” Azar replied. “We’re both at fault. But I don’t believe the situation’s irretrievable. The Circlers have killed some alien zombies, but according to Jake the philosophies have been at peace for millennia; it could still be a step too far for them to start harming each other.”
“How do we defuse their anxiety,” Shelma said, “when there’s no invading army for them to defeat? Do we offer them the microprobes as sitting ducks? I doubt that they could hit targets that small, and even if they could they’d just assume that there were ten thousand more.”
Azar looked up at the stars again, and tried to see them as a hostile, threatening sight. “They need some theater. They need some catharsis.” Clearly Shelma thought the same way too, but then neither of them were exactly experts in the lizards’ psychology. “And we need to talk to Jake again.”
“What do you have in mind?”
“The microprobes are too small, and Mologhat is already gone. So maybe we should think about launching a bigger target.”
Only Juhi turned up at the rendezvous point in a remote stretch of ribbon-weed forest. “Jake andRahul are safe,” she said, “but they’re too far away at the moment.”
“What’s been happening?” Azar asked her.
“We’ve been in contact with most of Spiral Out, and they’ve made a decision. They want to send a delegation with you to the closest world in the Amalgam, to make contact with this culture and report back on the possibilities for trade and migration.”
Azar was encouraged; at least Spiral Out had proved willing to break from its preconceptions.
“We’re prepared to start manufacturing antimatter,” Juhi continued. “But we should compare notes on the process first; if you have a more efficient method we should adopt that.”
Shelma said, “What kind of power sources do you have access to?” The everyday lizard culture they’d seen was based on plant thermoelectrics.
“There are some deep-bore geothermal turbines that are used for specialized research projects,” Juhi replied. “Obviously we can’t tap the whole output, but we should be able to siphon some off discreetly.”
“What if you just built your own turbine?” Azar said. “Would the Circlers do anything to stop you?”
“Right now,” Juhi said, “I don’t think it would be wise to find out.”
Azar turned that statement over in her mind. If people were about to begin clandestine antimatter production, what would happen to them if they were caught?
“We’ve had an idea,” she said, “but I don’t know if it will make sense to you. The Circlers believe we’ve come from a nearby planet, from a star too dim to see. What if we built a spacecraft that might have made a short journey like that ... and then let the Circlers shoot it down?”
Juhi said, “How are you going to power this spacecraft?”
“The azide bulbs you eat when you travel; enough of them could actually get a small craft into low orbit. The Circlers accept that we’re digitized, so they don’t expect the invasion force to be a fleet of thousand-tonne arks.”
“It’s an interesting idea,” Juhi said, “but the hardest part would be contriving their success in destroying the craft. Since your arrival they’ve been dredging up plans for weapons that our ancestors constructed for the last close approach, two hundred thousand years ago. But nobody’s sure now that they still understand those designs.”
Shelma said, “What about surveillance? Are they already monitoring what’s happening in near space?”
“Yes. You can be sure of that.”
“Then the problem,” Shelma said, “is that they’d see us taking off. It would be better to convince them that something new is coming in from deep space.”
Juhi paused, the front of her body twitching from side to side, a motion that Azar now recognized as a sign of anxiety. “I don’t see how we can do that. But let me take this to the others.”
Shelma had the insect’s nanotech construct a sample of a solid-state antimatter factory, and passed it to Juhi for the lizards to copy. It was the Amalgam’s most efficient design, but nothing could get around the fact that it would still need thousands of times more power than any ordinary burrow consumed.
After parting from Juhi they stayed away from Jute and the other colonies, but the scout mites had placed intercepts on some of the inter-colony trunk fibers long ago. The lizards had no infrastructure in place for quantum encryption, and their standard communication codes were easily cracked; clearly this wasn’t a culture with an entrenched history of bitter enmities and closely held secrets. It was a culture polarized by sudden panic, and Azar clung to the hope that cooler heads would soon prevail.
The tapped conversations were discouraging, though. The idea of Spiral Out as traitors was spreading throughout the Circlers, many of whom were urging each other to keep a close watch on their treacherous neighbors and erstwhile friends. The claim that the alien visitors were benign explorers with no territorial ambitions was largely discounted; two previous examples of Tallulah being colonized were, apparently, sufficient to render other motives unlikely. Azar began to wonder if the best course would be to lie low for a century or two and simply wait for the non-arrival of the trumpeted invasion force to leave the prophets of doom looking like fools.
Rahul met them for the next rendezvous. “Jake’s disappeared,” he said. “I think he’s been imprisoned, but nobody will admit to holding him.”
Azar was speechless. For all the bad news she’d heard from the taps, she’d never believed it would come to this.
“We can send machines to hunt for him,” Shelma said.
“If you can, please,” Rahul replied. “But they will have moved him to another colony, so I don’t know exactly where you should start.”
Azar came to her senses. She instructed the scouts that were already hovering near the fish; they would spread out and replicate, following the fiber trunk lines from colony to colony, spawning search parties as they went.
“We have an idea to placate the Circlers,” Rahul said. “To give them the triumph they think they need.”
“Go on,” Shelma urged him.
“We can’t get a craft into deep space, unseen,” he said. “And even if we could, I doubt the Circlers could hit it. But the Old Passengers’ machines are still working very well after all this time – as you know, to your cost. If they were seen to repel the would-be New Passengers, I think the Circlers would treat that victory as their own.”
Shelma said, “But how do we get the target up there? And how do we guarantee that the machines strike it?”
“We cheat,” Rahul said. “We hack into the Old Passengers’ network, and make it respond with as much sound and fury as possible to something that isn’t really there.”
Azar said, “Do you know how to do that?”
“Not quite,” Rahul admitted. “This is where we need your help.”
The lizards had mapped parts of the Old Passengers’ network long ago. It was bioengineered from native C3 plants, and used a modified form of the conductive polymers that Azar had first seen in thethermocouple bush. There were sensors of various kinds scattered across the continents, processing hubs on land and in the water, and dozens of geothermal cannons on the ocean floor.
Every thousand years or so someone had tried tapping into the network, but the protocols had always eluded them. There had been talk of trying to decommission the whole eccentric, unpredictable system, but the contrary view – that the Old Passengers had known what they were doing, and always had the interests of Tallulah at heart – had prevailed. Certainly the system had been benign enough to allow the lizards themselves to cross from their home world unmolested, and if the cannons sometimes spat steam and ice at phantoms that was a small price to pay.
Armed with Rahul’s map, Azar and Shelma returned to the surface and sent instructions to the other explorer insects, which had now reached every continent. As the insects tapped into the network, the microprobes monitored the flashes of Cherenkov radiation that incoming cosmic rays created in the upper atmosphere. Whatever else might elicit a response from the system, radiation was a proven irritant.
As they waited for the data to accumulate, Azar couldn’t stop thinking about Jake. What would his captors do? Torture him? While the lizards had engineered senescence away, and pumped their bodies full of medical nanotech that could combat the subtlest toxins and parasites, a simple metal blade could still be as painful, or as fatal, as it would have been for their earliest ancestors.
In three days, the insects had cracked the protocol: they knew how the Old Passengers’ network represented the atmospheric flashes, and how the data was cross-checked and confirmed. Though the system was moderately robust against errors, if the lizards’ anecdotes meant anything it was prone to the occasional false positive, and it certainly hadn’t been designed with resistance to tampering as a high priority. Azar was beginning to suspect that the Old Passengers had never actually contemplated an invasion; all of their concerns had revolved around natural hazards.
Would the Circlers understand as much, and know that they were being had? Or would they seize upon the evidence as vindication of their fantasies?
They dived to meet Rahul again, and Shelma told him that the network was now in their hands.
“Make it happen,” he said. “Shoot down the invaders.”
Azar communed with the scout mites. There was still no news of Jake.
9
The insect glided in a gentle helix a few meters above the ocean, but Azar locked the flight deck scape to the stars, banishing the perceived rotation. She fixed her gaze on the horizon and waited.
Data was being fed into the Old Passengers’ network, painting an elaborate mirage: a cloud of antihydrogen heading straight for Tallulah, three million kilometers away and closing fast. Interstellar gas and dust colliding with the cloud was creating highly energetic gamma rays; in turn, these gamma rays were striking nitrogen molecules in Tallulah’s stratosphere and generating particle-antiparticle pairs. None of this exotic radiation would be getting close to the ground, so the whole hallucination was being played out in terms of flashes of light from high in the atmosphere.
Shelma said, “Given their proclivities, you’d think they would have put satellites in orbit: gamma-ray telescopes at least.”
“Maybe they did,” Azar replied, “but the orbits were destabilized when Tallulah entered the lizards’ system. Or maybe they were just corroded away.” A quarter of a billion years was a long time; deep rock in the satellites might have provided a constant trickle of power, and nanotech could have carried out repairs, but if they lost material to abrasive dust or cosmic ray ablation, however slowly, nothing could have kept them intact forever.
“There she blows!” Shelma cried out happily; with the full library now accessible to the scape, the translations Azar heard of her speech were much more evocative. In infrared, the distant column of superheated steam glowed like an electric arc, rising out of the ocean and stretching into the sky. The ascending tip grew dim and faded into the distance, but when Azar added an overlay with visible frequencies amplified she could see the end of the icy spear glistening in the starlight as it hurtled into space.
This time there was no planet-shrouding halo needed to flush out the danger; the target was all too clear. The microprobes were tracking the ice missiles, and would feed their interaction with the imaginary antimatter cloud into the models that were generating the hoax atmospheric light show for the network, ensuring that all the data continued to reflect a consistent scenario. Of course, if the Circlers also happened to be looking for atmospheric flashes they would see no such thing, but that shouldn’t matter, since they had no way of knowing exactly what the Old Passengers’ defenses thought they were firing at.
Azar said, “If someone had told me that I’d be faking a battle for Tallulah between an extinct species and an imaginary invader, I would never have walked through that gate.”
“Oh, this is nothing,” Shelma scoffed. “One day I’ll tell you about the time—”
A message from the microprobes half a world away cut off the boast in mid-sentence. Something was emerging from the middle of a continent on the other side of the planet, and it wasn’t a fountain of steam. A narrow beam of gamma rays was rising up from the ground, just millimeters thick but energetic enough to have wrapped itself in a radiant cylinder of plasma as it punched its way out of the atmosphere.
Azar let out an anguished moan. “What have we done now?” Her skin crawled as one alarming possibility crossed her mind: someone could be messing with the microprobes, feeding them a vision of non-existent radiation. But that was just paranoid; who would gain anything from hoaxing the hoaxer? Perhaps the insects had screwed up their analysis of the Old Passengers’ protocols and inadvertently injected a second phantom target into the data – one that had elicited a far harsher response.
For several long seconds Shelma was frozen, either in shock or in contemplation. Then she declared, “It’s a photonic jet. We’ve triggered an unscheduled course correction.”
“What?”
“The steam jet is exceeding escape velocity, which means it’s pushing Tallulah off course, very slightly. So the Builders, the Ground Heaters, are compensating.”
Azar wasn’t sure yet what she believed, but she hoped the Circlers reached the same conclusion asShelma; they’d have no reason, then, to question their interpretation of the steam jet as a defensive measure. The photonic jet was just a technical detail, an anti-recoil device for Tallulah’s big guns. In any case, the Old Passengers’ network seemed to know that such a response was only to be expected; it wasn’t treating it as yet another interstellar hazard that needed to be dispelled by its own separate fire hose.
But assuming it wasn’t a counter-hoax, this beam of radiation was infinitely more substantial than the non-existent hazard that was being pummeled. “There are now real gamma rays blasting through the atmosphere,” Azar said. “Hitting nuclei, undergoing pair production. The photonic jet will be surrounded by antimatter.”
Shelma said, “I believe you’re right.”
They instructed the closest insects to fly up near the beam and investigate. The central cylinder of plasma was rich in antiprotons, and though they weren’t lasting long before annihilating, the annihilation gamma rays themselves were in turn striking nitrogen nuclei and creating more proton- antiproton pairs, giving rise to a long cascade before the energy was converted into heat, or escaped into space at the top of the beam.
Nanotech in the insects took just minutes to construct the necessary magnetic harvesters, which plucked the slowest antiprotons from the relatively cool margins of the plasma. There were only a few dozen insects in range, and they could only sip from a small part of the beam, but the bounty here dwarfed the travelers’ needs. The task that might have taken their Spiral Out accomplices months of furtive, dangerous work would now be complete in less than an hour.
Azar felt an intense surge of relief. The Amalgam was almost within reach now, and no one else would need to put themselves at risk to make the journey possible.
Shelma said, “I think I know where the water went.”
“Yeah?”
“When Tallulah came into the Old Passengers’ system, the Ground Heaters were nowhere in sight; they were either dead or they’d gone femto. So the Old Passengers had no one to negotiate with, no one to learn from, no one to spell out the rules. They’d simply found this luxurious abandoned lifeboat, and they wanted to take control. But it takes a long time to evacuate a planet physically, building and launching thousands of spacecraft; it’s possible that there were still millions of people who wanted to make the crossing even as Tallulah was going out of range of their ships.”
“So they built the geothermal cannons,” Azar said, “to try to bring it back in range. They were so desperate to let the stragglers come on board that they were willing to pump half the ocean into the sky.”
“To no avail. The ghosts of the Ground Heaters – or some insentient navigation system – fought them every step of the way. The femtotech couldn’t shut off the cannons; even if it switched off the heating process locally, the rocks would have stayed hot for thousands of years. But the photonic jets it already used for steering could easily compensate for the momentum of the steam.” Shelma hesitated, then added, “That could also explain why the Old Passengers ended up allergic to antimatter. An ordinary course change would have taken Tallulah clear of any debris from its own jets, but after a series of long, complicated tussles, there might have been clouds of antimatter lyingaround that really were worth sweeping aside.”
Azar said, “What drives me crazy is that if the deep rock can be grafted, it was all for nothing. The Old Passengers could have brought a sample back to their own world and solved all their problems without anyone leaving.”
“That was probably the Ground Heaters’ original plan,” Shelma said. “To travel the galaxy handing out deep rock, to reheat dying worlds. But to the Old Passengers, grafting rock would probably have sounded as ridiculous as trying to re-ignite a dead star with a spoonful of lukewarm helium. By the time they understood the first thing about the femtotech it would have been too late.”
Azar watched the column of luminous steam, still rushing into the sky. “Now we’ve thrown away a few more gigatonnes of water, just to deceive the lizards.”
Shelma said, “If you want it to sound slightly less tawdry when you tell your great-great-grandchildren, I recommend the version where we were doing it for the antimatter all along.”
“I don’t mind lying if it saves people’s lives,” Azar replied, “but I’d like to return to Hanuz with some prospect that we’re not leaving behind a civil war.”
“Yeah. We need to find out how far this charade has gone in cleaning up our mess.” Shelma inhaled deeply. “Let’s dive.”
At the rendezvous point, Rahul explained that the Circlers were still debating the significance of the steam jet. The ice halo had been written off as a false alarm until Azar and Shelma had introduced themselves, but this time nobody doubted that such an intense, sustained effort from the Old Passengers’ machines had something to do with encroaching aliens.
When Azar told him that they’d now harvested enough antimatter to make a transmission, Rahul confessed that the photonic jet hadn’t taken him entirely by surprise. “Some people have always believed that the Old Passengers fought against the Builders to control Tallulah’s path. That’s been enough to keep the Circlers from trying to do the same thing themselves; they take it as given that they can’t steer the world, and their only choice is to fight to defend it.”
Shelma said, “Why not trade to defend it? Why not offer any would-be invaders a few kilograms of deep rock grafts?”
“Because grafting is unproven,” Rahul replied. “We’ve done a thousand experiments with different minerals at various temperatures and pressures, and it looks as if there’s a balance we can exploit between the hoop system’s ability to spread and the safety mechanism that stops it running amok ... but the only real proof will come when we try it on a completely new world. Until then, what is there to trade? A handful of warm pebbles that might turn your planet into a fireball, or might do nothing at all.”
As they spoke, a wave of scout mites swam inside the camouflage fish and docked with the insect. They had found Jake; he was being held in an isolated burrow, almost three thousand kilometers away.
Azar gave Rahul the position. He said, “We have no one close. Do you know how many Circlers are guarding him?”
“Our machines saw twenty.”
“Then I don’t know how to help him,” Rahul confessed. “When he broke you out it was easier, everything was still in a state of confusion. Half the people around you had no declared allegiance; Jake and Tilly were not known as Spiral Out before, it was your presence that forced them to take sides. But all twenty people with Jake now will be resolute Circlers, committed to that philosophy for centuries.”
Shelma said, “The invasion has been repelled! What would the Circlers have to gain now by harming him?”
“It would set an example for future collaborators.”
They swam together to the closest intercept point on the trunk line; the scouts were piggy-backing their own data onto the fiber, using methods too subtle for the lizards to detect. Azar and Shelma watched through the scouts’ senses, and passed on the Circlers’ chemical conversation to Rahul. Jake was in one chamber, along with four guards; in a nearby chamber the other Circlers had gathered to discuss the latest news and plan their next move.
Shelma spoke to Azar privately. “I’ve got the nanotech primed to go in and digitize him, if it comes to that. But if we wait for them to kill him it might be too late; if they mutilate the body or use corrosive chemicals we won’t have time to capture him properly.”
Jake hadn’t given them explicit consent to do anything, but Azar swallowed her objections. According to Juhi he had wanted to be part of a delegation to the Amalgam, and if he turned out to be displeased about being snatched into the infosphere without warning, they could always write him back into ordinary flesh once they’d smuggled his software to safety. The real danger here was jumping in too soon or too late. Too soon and they risked re-igniting tensions with an unmistakable alien intervention. Too late and Jake would be dead.
Among the Circlers in the other chamber were two that Azar recognized from their first encounter: Omar and Lisa. Most of the talk here so far had been petty squabbling, but now the subject turned to Jake.
“We should release him,” Omar insisted. “The fleet has been destroyed or turned back; it doesn’t matter what he does now.”
“Spiral Out need to know what happens to traitors,” Lisa replied. “He set New Passengers free among us. He put everyone in danger.”
Another Circler, Silas, said, “You saw their technology; they could have escaped anyway. Whatever Spiral Out do, we’re never going to be sure that we’re safe, that we’re alone. That’s the reality now, and we need to find a way to live with it.”
Half a dozen other Circlers responded to this angrily, swimming around the chamber in tight, anxious loops. “We need to kill him,” Judah declared. “We need to draw a clear boundary between the right of Spiral Out to make their plans to leave Tallulah, and our right to live here safely and defend our own world.”
Omar said, “If we kill him we’ll start another war. Do you know how many people died in the last one?”
“Better a million die than we lose the whole world to the New Passengers,” Lisa replied.
“Better nobody dies,” Omar retorted, “and we spend our efforts on something that can help us all. We’ve been living like fools. We don’t deserve to feel safe, and killing our own people won’t change that. We don’t even know with certainty where the closest world really lies! And we have no idea what kind of life there might be around the bright stars; I doubt that the aliens were telling us the truth, but none of us really know what’s possible.”
“We’ve been caught sleeping,” Judah conceded. “That much is our fault. But what do you suggest we do about it?”
Omar said, “We need to work together with Spiral Out to explore the nearest worlds, before any more of their inhabitants reach us themselves. If we send out small robots to gather information, the results can serve everyone: defenders of Tallulah, and those who want to leave.”
Lisa was scornful. “After this, you’re going to trust Spiral Out as our allies?”
“Jake freed two aliens that you were threatening to kill,” Omar replied. “They had done us no harm, and we don’t even know for sure that they were lying. Because of that, we should slaughter all of Spiral Out? Or treat them all as our enemies? If everything that’s happened wakes them from their sleep the way it should wake us, we can benefit from each other’s efforts.”
Azar looked to Rahul for a reading of the situation, but he was motionless, his posture offering no verdict. Jake’s fate could go either way.
After forty minutes of discussion with no clear consensus, Omar said, “I’m releasing him.” He paused for a few seconds, then left the chamber. Lisa squirted wordless, dissatisfied noise, but nobody moved to stop him.
Omar entered the chamber where Jake was being held and spoke with the Circlers who were standing guard.
“I don’t agree,” said Tarek. “You’ve come alone to demand this. Who else is with you?”
Omar and Tarek went together to the other Circlers. Omar said, “I repeat, I’m releasing Jake. If anyone here wants a war, I will be an enemy of the warmongers, so you’d better kill me now.”
Judah said, “No one’s going to kill you.” He swam with Omar to Jake’s chamber and spoke with the remaining guards. Then all five of them departed, leaving Jake alone.
Jake circled the chamber nervously a few times, then headed out of the burrow. Azar sent a swarm of scouts after him, but they had no data channel back to the fiber, and Jake was soon out of sight.
Almost an hour later, a message came through from the scouts; Jake had reached a nearby colony where the scouts could tap into the fiber again. Azar told Rahul their location.
Rahul said, “He’s safe, he’s with friends. It’s over for now.”
Azar sat on the flight deck weeping, hiding her tears even from Shelma.
10
Launched from a rail gun on Tallulah’s highest mountain, Mologhat 3 spent six seconds plowing through the atmosphere before attaining the freedom of space. Its heat shield glowed brightly as itascended, but if the Old Passengers’ machines noticed it they found no reason to molest this speck of light as it headed out of harm’s way. When it reached an altitude of a thousand kilometers it fired its own tiny photonic jet, but the radiation was horizontal and highly directional; nothing on Tallulah had a hope of detecting it.
Jake, Tilly, Rahul, Juhi and a fifth delegate, Santo, swam across the flooded observation deck, looking down on their world for the first time. Azar swam among them, but not as a lizard in anyone’s eyes. Her words would come to them as familiar chemicals, but they could cope with the sight of her as she really was.
As Azar gazed upon Tallulah, she dared to feel hope. There would be no war, no pogrom, but there was still a daunting task ahead for the millions of Spiral Out who remained. They would need to prepare the Circlers for the truth: for the eventual return of this secret delegation, for trade with the Amalgam, for a galaxy that was not what they’d imagined at all. For a future that didn’t follow their script.
Jake said, “Do you think we’ll ever meet Shelma again?”
Azar shrugged; he wouldn’t recognize the gesture immediately, but he’d soon learn. “She once told me that she could choose for herself between solitude and a connection with her people. If she wants to come back, she’ll make those connections as strong as she can.”
“No one’s ever returned before,” Jake said.
“Did Spiral In ever really want to?”
When the moles finally hit pay dirt beneath the ocean floor, their mass spectrometers had detected more than a hundred billion variants of the hoop, and that was only counting the stable forms. The deep rock was more complex than most living systems; no doubt much of that complexity was fixed by the needs of the heating process, but there was still room for countless variations along the way – and room for a new passenger hitching a ride on the hoops as they turned iron and nickel into heat.
If you had to become deep rock in order to understand it, Shelma had decided, she would become it, and then come back. She’d drag the secrets of the hoops out of the underworld and into the starlight.
“What if you can’t?” Azar had asked her. “What if you lose your way?”
“There’s room in there for a whole universe,” Shelma had replied. “If I’m tempted into staying, don’t think of me as dead. Just think of me as an explorer who lived a good life to its end.”
Jake said, “Tell me more about your world. Tell me about Hanuz.”
“There’s no need,” Azar replied. She gestured at the departure gate. “If you’re ready, I’ll show it to you.”
“Just like that?” Jake twitched anxiously.
“It’s fourteen quadrillion kilometers,” she said. “You won’t be back for three thousand years. You can change your mind and stay, or you can gather your friends and swim it with me. But I’m leaving now. I need to see my family. I need to go home.”