by Greg Egan
“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 the thermocouple 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 as Shelma; 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 atmos
phere,” 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 lying around 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 anywa
y. 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.
