by Greg Egan
Amanda said, “There’s that burst again. A ‘stop what you were doing’ signal?”
“That’s what it looks like.”
“We should get that on tape,” she suggested.
Carlo agreed. They spent the next bell and a half capturing the signals that initiated and halted dozens of different movements, trying to exhaust all the possibilities while the probe was in place and the recorder was still working. They ran out of paper before Carlo was entirely satisfied, but by then he was glad of any excuse to extract the probe and resorb his abused limb.
Amanda left him; she had two pairs of voles ready to mate in the pathway suppression experiments. Carlo stayed harnessed to the bench, looking over the recordings.
The patterns for all the repetitive motions he’d tried were, gratifyingly, roughly periodic. In fact, if he coiled each strip into a broad helix of just the right width he could place each cycle right beside its successor, and see the same instructions arriving again and again. Then the pattern faded out until the “stop” signal came—and that was virtually identical in every case.
On a finer scale, though, the sequences remained mysterious. The brightness and duration of the individual pulses varied enormously, and there were no obvious recurring motifs. So how did his flesh interpret these instructions? Were there detailed commands for each muscle fiber, spelling out every contraction? Or was this more like a sequence of symbols or sounds, strung together to form words in some ancient somatic language?
Tosco had conducted an ingenious study where he’d dyed the flesh in a lizard’s extremities, color-coded by its initial position, and shown that after being resorbed it could turn up in any other labile region. The flesh that had comprised a certain toe one day could easily find itself in the middle of a limb the day after. But that didn’t settle the question as to whether the flesh “knew” which role it was playing at any given moment, or whether that responsibility fell entirely to the brain. Each time the body reshaped itself, did the brain tell the new toe-flesh “Now you are a toe”, allowing them both in later conversations to take certain toe-ish understandings for granted? The signals Carlo had recorded for repeated motions—spelled out the first few times, then left to his finger’s own initiative—suggested that the brain didn’t micro-manage everything, but the initial instructions seemed far more detailed and complex than he would have expected if they were merely specifying a selection from a pre-existing repertoire of possible finger movements.
Carlo looked across the workshop toward Tosco’s bench. Nine years after his first dye studies, he was still repeating the experiments—and that wasn’t out of laziness or inertia. He kept refining the techniques and gathering more data, painstakingly building up maps that showed the way flesh moved within a lizard’s body as it adopted various postures.
Nine years was nothing in the history of this field. A lifetime was nothing. Carlo gazed at the streaks of pigment on the paper in front of him, and realized that he still hadn’t solved one simple, practical problem: the paper was darkest when the light had been most bright. If he ever hoped to send these recorded signals back into his body, he’d need a way to modulate the light source in precisely the opposite fashion: making it bright when the paper was dark.
Amanda returned with the preliminary results from her two vole matings. The whole brood in the second suppression test had been stillborn—but as ever it had been a brood of four.
She took one of the strips of paper from the bench and held it up to the light from a nearby lamp.
“So… you’ll run this beside a second, sensitized strip?” she asked. “To duplicate the pattern with the density reversed?”
Carlo stared at her in silence, dumbstruck for a moment. Then he came to his senses and replied, “Of course.”
11
“Air,” said Ivo. “Air is what remains when the fiercest flame has consumed its fuel entirely. There’s nothing safer, nothing more stable. In the worst case imaginable—if the orthogonal rock acts as a liberator for all of our solids—we should still be able to manipulate it with jets of air.”
Tamara looked around the small chamber, wondering if anyone else shared the secret thrill she felt at the prospect Ivo was raising. What could be more terrifying than a universal liberator: a substance that could set anything on fire? And what could be more exhilarating than finding a way to cheat that danger, to grasp the ungraspable in invisible hands?
Massima, the lottery winner, appeared to be growing less at ease with each word she heard. When she’d first put her name down for a chance at this jaunt there’d been a lot less talk of explosions. Ulfa, the chemist appointed by the Council to oversee the project, was as calm and businesslike as ever, raising neat rows of notes on her chest as Ivo spoke. Only Ada, who’d beaten six other astronomers in their own mini-lottery for deputy navigator, showed any sign of excitement.
Ada said, “What if we can’t break a sample free with air alone? If the Object is made of something like hardstone, and there are no loose fragments… you can’t carve hardstone with a jet of air, however high the pressure.”
“If that’s the situation,” Ivo replied, “we’ll have to cut into the surface with airborne dust. If we add a small amount of crushed powderstone to the jet, the reaction between the powderstone and the orthogonal rock will render the jet far more potent.”
“You’re assuming that the rock itself will be consumed, and not just the powderstone,” Ulfa pointed out.
“Do you know of any liberator that isn’t consumed in the flame it creates?” Ivo asked her.
“No,” Ulfa conceded. “But the liberators we know about are fragile plant extracts. We can’t assume that a slab of solid rock will act the same way.”
“If there’s a flame produced at all, the heat should at least weaken the rock,” Ivo said. “And if that’s not sufficient, we could replace the powderstone with hardstone, making the jet more abrasive.”
Ulfa said, “This is a material we’ve never encountered before. What if it can’t be abraded, even by burning hardstone?”
Ivo emitted a soft hum of frustration. “There’s no reason to believe that orthogonal matter will be endowed with magical powers of durability! Reversing the arrows of its luxagens might influence its chemical properties with respect to ordinary matter, but it can’t make the rock itself harder, or more resistant to heat.”
Tamara had to side with him on that: it was basic rotational physics. For a rock to be rendered tougher just because its “future”—according to Nereo’s arrow—had ended up facing their past was as absurd as expecting a rope to become stronger if you turned around and traversed it in the opposite direction.
Ulfa remained calm, but unswayed. “I understand that, Ivo. But it’s my job to ask what will happen if these assumptions are wrong.”
“If the rock can’t be cut by any method at all… then we won’t cut it,” Ivo replied. “What else can I say?”
“And if you can’t take a sample,” Ulfa pressed him, “how will you calibrate the process that you’re hoping to use to capture the Object?”
Ivo was silent for a few pauses. Then he said, “We’ll have no choice but to perform the reaction in the wild. We’ll throw calmstone at the Object and observe the effects—scaling up the quantity gradually so we don’t take undue risks.”
“But you’ll have no way to measure the force you’re producing,” Ulfa said.
“Not immediately,” Ivo agreed. “Not until it starts to change the Object’s trajectory. We’ll simply have to work by trial and error, incrementally: dropping calmstone on the site where we want to deliver a push, until the cumulative effect is large enough to observe.”
Ulfa paused to dust her chest with dye and press a sheet of paper to her skin. Then she addressed Tamara. “Do you think that’s feasible?”
“It will be difficult,” Tamara admitted. “Each beacon will only be visible once a bell, so if we’re going to have to nudge the Object repeatedly and check its motion each time, it will be a
slow process. We could be there for as long as a couple of stints.”
“So you’ll need more cooling air, more food,” Ulfa said. “What’s that going to do to your flight plan?”
“The mass of any extra food would be negligible,” Tamara said, resisting a joke about the proportion of women on the crew. “But it might be worth making allowances to bring more cooling air. Hyperthermia is a horrible way to go.”
Massima said, “Forgive me for interrupting.”
At the sound of her voice everyone turned to face her. In all the planning meetings she’d attended, she’d barely spoken a word.
Tamara tried to counter the alarm she’d inadvertently created. “I only meant that we needed to be sure of our air supplies. I promise you, we won’t be taking any foolish risks—”
Massima raised a hand to silence her. “I accept that. But the truth is, I have no expertise to contribute to this task, so why should I be there with you, using up precious air? It was generous of you to offer a place on the Gnat to an onlooker. This could have been the experience of a lifetime, the perfect story to leave to my children. But in all conscience, after what I’ve heard these last few stints I can’t take that role any more. I wish you luck, but I’ll have to hear about the journey upon your return.”
Tamara didn’t know how to respond. Imploring the woman to reconsider would only embarrass her.
Ada said, “I respect your decision, Massima. And I’ll be happy to tell you everything as soon as we get back.”
As Massima left the chamber, Tamara wondered if the Council would insist that they draw another name from the lottery entrants. If not, they’d have a chance to bring another crew member. If it was prudent to appoint two navigators, why not a second chemist in case something befell the first?
Ivo went on to describe the machinery he wished to commission from the instrument builders, to equip the Gnat with hands of air should it need them. Ulfa quibbled over some details, but eventually agreed that he could take his sketches to Marzio and have prototypes made.
When the meeting was over, Tamara caught up with Ada in the corridor.
“I can’t believe I frightened off our passenger,” Tamara lamented.
“It’s not your fault,” Ada replied. “She made her own judgment.”
“So how’s your co taking this?” Tamara asked her.
“He’s a little jealous,” Ada admitted. “But he’ll survive.”
“He’s not worried about you?”
Ada thought for a while as they dragged themselves along the ropes. “Maybe he is. But he knows I won’t get another chance like this. I mean, I’m not going to be guiding the Peerless home, am I? And I’m never going to spot anything in the sky that really matters.”
Tamara buzzed admonishingly. “You have more years as an observer ahead of you than I do!”
“Maybe. But what could surpass the Object?”
“Something that surprises us completely,” Tamara suggested. “We’ve barely started making use of infrared.”
“At the launch of the Peerless,” Ada mused, “everyone must have felt some pride to be bearing the world on their shoulders. And if we ever return, I expect the whole generation who make it back will be treated like heroes. But when you’ve been born into this mess halfway, with no say in it, what can you do? If you’re vain enough you could spend your life imagining you’re going to discover the Eternal Flame. As for the rest of us… we get to starve ourselves as best we can, make some tiny contribution to the Great Project, and try to remain contented while we pass the time until we have children.”
Tamara thought that was putting it rather bleakly. “Except for the starving, would things have been so different if we’d been born back home, before the Hurtlers?”
Ada tipped her head, conceding the point. “The big cities had many more people than the Peerless, but how many people can you meet in a lifetime? And if I was traveling from town to town by truck or train, instead of reveling in my freedom I might have spent the journey gazing up at the sky, wishing I could go flying in a rocket instead.”
“And you’ll be traveling from town to town soon enough,” Tamara joked. The Object was unlikely to be populated, but the latest measurements suggested that it was comparable in size to the Peerless. “You have the best of both worlds.”
“I know!” Ada said. “Believe me, I realize how lucky I am. Not only will I escape this prison for a while, the journey might even turn out to be useful. Addo understands that, which is why he’d never ask me to give it up.”
Tamara was silent. They’d reached the junction where they’d have to go their separate ways.
Ada said, “So your co’s not the same?”
“I’m working on it,” Tamara said. “Right now all he can see is the danger, but I’m sure I’ll bring him round in the end.”
12
Carla was reaching behind the textbooks for her stash of groundnuts when she heard someone moving on the ropes near the entrance to the classroom. She closed the cupboard quickly, embarrassed. She should have been strong enough to deal with her hunger without playing these stupid games.
Patrizia appeared in the doorway. “Do you have a moment, Carla? I need to ask you about something.”
“Of course.” Carla’s gut was squirming, cheated of the imaginary meal she’d promised it, but she kept her voice even and her face composed.
Patrizia dragged herself to the front of the room. “I know I made a fool of myself, with what I said about the tarnishing,” she began.
“That’s not true,” Carla insisted. “I asked for wild ideas, and you were brave enough to offer one. Just because it didn’t hold up doesn’t make you foolish.”
“Well, I’ve had another wild idea,” Patrizia admitted. “But this time, I was wondering if you’d hear it in private.”
“Of course.”
“I hope I’m not wasting your time,” Patrizia said. “Sometimes it’s so hard to concentrate that I start making stupid mistakes. Things I ought to know just… go into hiding.”
The misery in that last phrase was painful to hear, but Carla didn’t know what she could do about it. It wasn’t her place to tell the poor girl to put off the famine for another year or two—trading the risk that she’d face a much more arduous struggle, later, for a little more youthful energy and clarity when she really needed it.
“We all make mistakes,” she said. “Tell me your idea, I’ll be happy to hear it.”
Patrizia began haltingly. “The first part is just elementary mechanics, really. But I wanted to check it with you before I go any further.”
Carla did her best to hide her dismay. She’d been thinking of the groundnuts all through the lesson, but if she could survive her cravings for a whole bell she could remain polite for another few lapses.
She said, “Go ahead.”
“Suppose you have a motionless particle, and it’s struck by another particle that’s about three times as heavy,” Patrizia said. “I think their energy-momentum vectors before and after the collision would be something like this:”
“That looks fine to me,” Carla replied. The first diagram portrayed the history of the collision, while the second repositioned the same four vectors to make the geometrical rules that governed them visible at a glance. “You’re just using the triangle law, right? The sum of the two energy-momentum vectors has to be conserved, and their individual lengths are just the masses of the particles, which don’t change. So the vectors will form two sides of a triangle whose shape is left unchanged by the collision, and whose third side—the total energy-momentum—remains fixed.”
Patrizia seemed relieved, but still far from confident. “And all the possibilities for a collision like this can be found by rotating that triangle around its third side?”
“Yes.”
“That will give you the off-axis collisions as well? You just swing the triangle out…?” She sketched some examples, showing what happened to the particles’ momenta if they glanced of
f each other during the impact, scattering to either side of the original axis, bringing in another dimension of space.
“That’s all correct,” Carla assured her, letting a hint of impatience into her voice. Wherever Patrizia was taking this, she had the basics right, she could move on.
Patrizia said, “On the same assumptions, I calculated the final energy for the heavy particle, for a few different starting energies.” She opened a pocket, pulled out a sheet of paper and unrolled it.
Carla hesitated now. Though she’d surely made a similar plot once herself—as part of some long-forgotten exercise when she’d first been studying mechanics—this had gone past the obvious-at-a-glance stage. “The angle here is measuring how far the heavier particle ends up off-axis?” she asked.
“Yes,” Patrizia said. “The details of the collision itself—whether it’s glancing or head-on—would determine that angle, but I’m just trying to be clear about the final outcome, about the possible combinations of angles and energies allowed by the conservation laws. The really striking thing about these curves is the way the greatest angle of deflection always turns out the same! So long as the lighter particle starts off at rest, there’s a maximum angle at which the heavier particle can end up being knocked off course, and it only depends on the ratio of the masses—the energy of the collision doesn’t come into it.”
“Hmm.” Carla couldn’t recall ever being aware of that result, and she couldn’t see any simple geometrical reason why it had to be true, so she worked through the algebra on her chest. The claim turned out to be perfectly correct: the maximum angle of deflection was the same, regardless of the energy.
Carla’s impatience was tempered by curiosity now. Was Patrizia going to try to rescue her tarnishing theory by adding a second luxagen, three times heavier than the first?
Patrizia said, “I can put curves with exactly the same form as this through the data we measured in the light scattering experiment.” She dug out a second plot.