Greg Egan - The Arrows of Time

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 to 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.

More experienced now, she dared to let the rock below her blur a little, trading off perfect clarity for less costly centripetal force. Agata didn’t want to grow complacent, but the numbers were already better than she’d dared hope. While the majority of the team had barely been into the void before, five people had done maintenance work out on the hull. If those five alone had dealt with two bombs each, as she had, the job would already be completed.

The amorphous blur below her was broken by a sharp edge spinning by. Agata went in pursuit, astonished by her luck. She was beginning to pity all the searchers who must have come just as far with no result; everyone would understand that that might happen to them, but three times now she’d seen the signs that their collective effort was heading for victory, while others would still be wondering if the whole endeavour had been misconceived.

The third occulter came into view. The cargo was attached in exactly the same manner as it had been on the last one. Agata didn’t delay her assault; she grabbed one of the posts, shut off the jetpack and began applying her coherer. But as she worked, she sifted through the possibilities.