The Arrows of Time

by Greg Egan

  In Gineto’s apartment, Vala spent a chime scrupulously copying Agata’s posture and learning to mimic her gait.

  ‘No one would mistake our faces,’ Vala admitted, ‘but if I hold this box of books on my shoulder to obscure my face from the camera . . .’ She demonstrated.

  Agata had carried Medoro’s real books home in more or less the same way; a second instalment need not attract suspicion. She handed Vala the key to her apartment. ‘Happy reading.’

  She waited with Serena and Gineto, practising her imitation of Vala but hoping that no one would even be watching the camera feeds. Let them all be busy following Ramiro and Tarquinia.

  Serena checked the clock on her belt. ‘Time to go.’

  Gineto said, ‘Good luck.’

  Agata followed Serena out of the apartment, trying to appear suitably motherly: mildly affectionate but mostly aloof. Vala had always seemed bemused that two lumps of flesh shed from her body had grown into fully functioning creatures, with no further intervention on her part. The corridor wasn’t too busy, so Serena took the adjoining rope, never concealing Agata entirely from the cameras they passed, but often obscuring part of the view. Anyone with access to the feeds would be able to reconstruct every party’s true movements easily enough, in retrospect – or long before the event, if the information was recognised as important enough to send back – so their not being caught out now would be largely contingent on their not being caught out later. From their position of ignorance, success and failure seemed balanced on a knife edge, but from a cosmic point of view the two slabs of self-consistent events had been utterly distinct for at least the last three years.

  As they drew nearer to the utility shaft, Agata could see a camera gazing straight down at the entrance portal. They hung back, and Serena glanced at her clock. ‘Where are they?’ she muttered. A moment later Agata heard a group of people approaching, talking and buzzing.

  ‘Now,’ Serena whispered. They advanced together. There were a dozen people coming the other way, spread out between the two guide ropes. Some of them, politely, tried to shift ropes to let Serena and Agata pass, but they were packed too close together along both ropes for them to all fit on either one. As the impasse clumsily sorted itself out, two women who looked like mother and daughter managed to break out of the throng and move away. Agata followed Serena down into the shaft and pulled the portal cover closed behind her. If the security sensors here hadn’t been dealt with, they wouldn’t be the first ones to trigger them: the portal’s lock had been snapped a few bells before, and most of the team was meant to have come through before them.

  As they descended the ladder in the red-tinged gloom, Agata could hear the muffled hiss of gas in the tunnel beside them. No one came here on regular cleaning shifts; the warm air was inimical to moss.

  When they arrived at the bottom of the shaft the darkness was impenetrable. Serena said quietly, ‘It’s us,’ and someone switched on a coherer. Agata squinted into the glare and counted two dozen and nine figures squeezed around them, already wearing their corsets, cooling bags and jetpacks. Many of them had never used the jetpacks; they should all have had one-on-one briefings earlier from their more experienced friends, but it was Agata’s job now to go through the safety checks and remind them of everything they’d forgotten.

  ‘If you get into trouble,’ she began, climbing two steps back up the ladder to make herself visible to everyone, ‘just draw a stop line: a straight horizontal line across your chest.’ She demonstrated. ‘The rock will still be moving below you, but don’t let that confuse you: the pack will bring you to a halt relative to the mountain’s axis, so you won’t go flying off into the void.’

  There was no time for more than the basics, but if they could retain it, it ought to keep them alive. Agata put on her own equipment.

  ‘Does everyone understand what we need to do with the occulters?’ The protocol she’d written had been copied discreetly from skin to skin, and some of the volunteers would not have received it until they’d reached this assembly point. In a perfect world they would have rehearsed the manoeuvre daily for a stint or two, but at least the jetpacks would handle most of the navigation.

  ‘Can the machines drill into our bodies?’ a young man asked anxiously.

  ‘Not intentionally,’ Agata assured him. ‘They’re not that sophisticated; they have no defensive strategies as such. The only danger is if they’re so confused that they mistake you for rock, but if you get out of their way they won’t pursue you.’

  Serena passed Agata a helmet. They were aiming not to use the links; this would probably be their last chance to talk until they were back in the mountain again.

  ‘Happy Travellers’ Day,’ Serena said.

  ‘Happy Travellers’ Day,’ Agata replied. She put on her helmet and turned towards the maintenance hatch.

  A succession of shutters sealed off portions of the final length of the cooling tunnel, opening in sequence to allow air to pass from chamber to chamber at ever lower pressures until it was expelled into the void. The maintenance hatch wasn’t meant to open unless the whole cycle had been stopped and all the chambers had reached the ambient pressure of the mountain’s interior, but Serena’s technician friends had managed to fake the sensor data to convince the hatch that it was safe to operate. The only catch was that it had been too complicated to try to lock it against any real part of the cycle. It would be up to each person exiting to synchronise their access with a time when the shutter below them wasn’t open to the void.

  Agata pressed her helmet to the hatch and listened to the sequence of clanks and hisses until the rhythm was embedded in her mind. The last time she’d dealt with machinery in the tunnels it hadn’t ended well, but at least she’d had the timing right.

  She slid the hatch open. Air blew in from behind her, but it only took a flicker for the pressure to equalise. She climbed into the tunnel and braced herself against the walls with her hands and feet. Serena closed the hatch behind her.

  Agata waited in the dark, mentally composed but still viscerally terrified: there was absolutely nothing about the situation that her body found acceptable. She heard the creaking of the shutters above her and the sibilance of expanding gas drawing nearer.

  A span from her head, the rotating disc of the shutter above her finally swung its aperture around to coincide with the tunnel. Agata felt the air rising up across her cooling bag, moving the opposite way to the usual cycle now that she’d wrecked the pressure gradient. But the sensors had been numbed – the anomaly would pass unnoticed.

  When the shutter closed there was nothing to feel, and in the perfect darkness no way to be sure that it had happened. But then the exiting wind rustled the fabric on her limbs and starlight entered the tunnel from below. Agata didn’t look down for confirmation; she just brought her limbs together and let herself fall.

  Half a dozen strides from the outlet she drew a circle on her chest and the jetpack eased her to a halt, supporting her as she followed the rotation of the Peerless. She sketched an upwards arrow and ascended, until a safety handle set into the rock for maintenance workers came within reach. Wide-field cameras on the slopes monitored the space around the mountain, with their feeds analysed automatically to detect anyone in trouble falling away into the void, but as long as the team remained close to the hull they’d be out of view.

  Agata waited for Serena to emerge, and for two more of their companions to join them. They couldn’t stay to watch the whole team exit; there were only four handles, and hovering would waste too much air. Agata gestured to the others and they set off for the base.

  The starlit slopes turned beneath them, the pale brown calmstone sliding past ever faster as they moved further from the axis, making their straight-line trajectories seem like giddy spirals. Agata kept watch for sudden changes in the topography ahead; the jetpacks knew the basic shape and motion of the Peerless, but they carried neither detailed surface maps nor proximity sensors. No one had ever intended the wea
rers to skim the slopes at high speeds, so if she slammed into an unexpected rise she’d only have her failing eyesight to blame.

  The jetpack overshot the rim of the base, and the rock below her fell away to be replaced by black emptiness then a sudden, shocking dawn. She could see the blazing lights of the half of the transition circle that the mountain had been blocking, just peeking above the distant horizon. Agata sketched a down-arrow and the jetpack brought her closer to the rock; the dawn ahead vanished, but she still had the other half of the circle behind her. The base was slightly convex, so, however low she dropped, the Peerless wouldn’t hide the entire transition circle, plunging her into complete darkness.

  She looked around for the others; she could just make out Serena away to her left and another anti-saboteur to her right. The jetpacks had been programmed to take the volunteers to equally spaced points above the rim, but from here it was up to each of them to choose their path on a sweep in towards the axis.

  The rock below her was a blur, moving past at more than a saunter every pause, but if she tried to match its velocity she’d be constantly using her jets to provide the necessary centripetal force – which would empty her air tank long before she got halfway to the axis. In all her training exercises with Tarquinia, in all the manoeuvres she’d performed around the Surveyor, she’d never faced anything like this.

  The occulters could be waiting almost anywhere; in their final flight they could cover a lot of distance quickly. She couldn’t assume that they’d all crawled close to their targets. So she had to find a compromise: she had to slow the relative motion of the rock just enough so she’d be sure to notice one of the machines sweeping by, and then try to move closer to the axis as quickly as she could, lessening the drain on the jets.

  Agata turned herself around so she was facing the surface at an angle where she caught the reflection of the stars. The grey blur shimmered with colour now, the texture visible if still mysterious. She sketched a double arrow to begin reducing her relative motion; the jetpack complied, though it sent a warning message through her corset, alerting her to the cost.

  She waited anxiously, afraid that this unrehearsed strategy would get her nowhere, but then the transition came in an instant: suddenly, the shimmer from the rock was comprehensible. Agata could see the small bumps and concavities, the fine crevices, an endless parade of details rushing by beneath her. The occulters had been clad well enough to blend in with the stone around them from a distance, but she was only a couple of strides from the surface. If she kept her concentration, the machines ought to be unmissable.

  The mountain completed each rotation in less than seven lapses; her motion was stretching that out threefold, but rather than hanging back to witness a full turn at every radius she had to trust her companions to cover their own portions of the territory. Agata wished she could have made it a mathematical certainty that no square scant would go unsearched, but before she’d been out here and seen the conditions she’d been in no position to make binding plans. All she could do now was hope that most of the team found their own workable strategies, and between the symmetry of their initial placement and the shared conditions that prompted their individual actions they’d end up executing a combined sweep without too many gaps.

  She began moving steadily in towards the axis.

  The change below her was so stark and it came so abruptly that Agata almost began chasing it, but she caught herself in time. The smooth black expanse of the engine’s rebounders was unmistakable, and the visual jolt of entering it was followed by near-perfect homogeneity. The idea of the occulters drilling into this precious lode was shocking – and it would also be the place where their camouflage was the least effective – but Agata decided not to speed past the region. However strong the argument for the machines avoiding it, she couldn’t trust her adversaries not to exploit that presumption.

  The surface became rough and grey again. Agata forced herself to readjust her expectations: her prey would show much less contrast now. The temptation to look around for her companions was growing, as much out of a longing for the support of their presence as any real fear for their safety. But with her front eyes fixed on the rock below, her rear gaze couldn’t reach beyond the blackness of the orthogonal cluster. She tried to assuage the pangs by rekindling her anger with Ramiro and Tarquinia; at least that made her feel stronger and more focused. But as the pits and cracks in the stone swept by, she thought of Azelio, who believed that all their efforts were in vain. If a meteor had always been on its way, this charade would not deflect it.

  A shape with hints of regular borders passed below her and was gone. Agata raised a triangle on her chest, the preprogrammed symbol to send the jetpack in pursuit. She waited anxiously for the rock to slow, but when it halted there was nothing below her. She edged sideways, stride by stride, and then there it was fixed to the rock: an occulter with a small package dangling from it, held in place by nothing but hooks and strings.

  Ramiro had given her no details, but she’d been expecting some far more robust form of attachment. She took the knife from her tool belt, grabbed hold of the package and cut the strings.

  The bombs would be driven by timers alone; any kind of trigger based on location would be too unreliable to take out all twelve channels simultaneously, and navigation was the occulters’ job. Still, Agata kept the centrifugal weight on her cargo constant as she ascended from the rock, following a helix that kept the surface motionless beneath her. If everything she’d surmised was mistaken and some accelerometer was ready to cry foul, better not to take a piece of the mountain with her.

  When she’d reached a decent altitude she let the jetpack kill her circular motion and spare itself the costly countervailing force. Nothing exploded. Agata was tempted, briefly, to try to prise open the stone box and take a look at the mechanism inside, but the risk of a booby trap seemed to outweigh any prospect of learning something useful.

  She was still ascending slowly, in free fall now. She released her hold on the bomb, then instructed the jetpack to return her to the point where she’d left off. As she watched the package shrink into the darkness, a glorious ache of hope came to her unbidden. There were only a dozen bombs: the volunteers outnumbered them more than two-to-one. If even half the other searchers were as lucky as she’d been, the job would soon be done.

  Back above the rock face, Agata fought to maintain her concentration. Twice she chased features in the stone that turned out to be nothing – perceptual illusions, or wishful thinking. It was better to pursue false alarms that to miss a single bomb, but her air supply wasn’t infinite.

  Looking back towards the rim she caught a glimpse of another searcher, a lonely silhouette against the blaze of the transition circle. By now there was no way of guessing who it was, but the figure looked safe and busy. It was tempting to exchange a few words, to compare counts, to share strategies . . . but even in its tightest directional mode the link was only for emergencies, so Agata did nothing to stop their drift apart.

  The next find was so clear that Agata cursed her stupidity as she formed the triangle; the phantoms on which she’d wasted so much air seemed inexcusable now. As the rock halted, the occulter appeared almost directly below her, but she was surprised to see how different the package looked from the last one.

  She moved closer. There were no strings; the bomb was secured to two posts that rose from the occulter’s arms, lifting the rigid assembly clear of the dodecahedral core that held the air jets. But how had these posts been attached, out on the slopes? Was this the occulter that Tarquinia had repaired – and she’d had to perform some strange modifications in the void?

  Agata was baffled, but she didn’t have time to make sense of it. She took a wrench from her tool belt and set to work; the jetpack braced her with yet more expenditure of air. She tried to turn the post itself, but it was too smooth and she could get no purchase on it. She groped around the attachment point on the arms, but there was no bolt head. The posts seemed t
o be glued in place.

  She closed one hand around the occulter’s arm then shut off her jetpack’s airflow completely, letting herself hang down across the vertical rock face. She took a flat bar and inserted it between the machine’s arm and the rock, then began trying to prise the splayed drill bits out of the holes they’d made. But however hard she strained there was no perceivable effect; the drills were mounted too securely and the rock itself wasn’t going to crack.

  If she’d had more air she could have tried taking the drill assembly apart; she’d put half of them together herself, so she should have been able to reach in and unscrew all the same bolts by touch alone. But not while she was clinging to this sheer drop. She took a high-powered coherer in her free hand and began carving through the posts that held the bomb in place.

  Every few lapses she had to stop and wait for the occulter to cool down; it wasn’t smart enough to use its own air to deal with this unexpected contingency, and the heat was slow to dissipate into the rock. At least her own need to be able to hold onto the frame gave her a clear signal to act; it was unlikely that any temperature she could tolerate on her skin would be high enough to trigger the explosive. When the second post was all but severed, she started up her jetpack to support her and then snapped the post by hand.

  Agata moved quickly into a disposal trajectory, cancelling her motion around the axis as she ascended – rising a little faster than before, now that her cargo would have less time to reach a safe distance. She released the bomb and resumed the search. She was exhausted, but she still had enough air to go farther.