The Arrows of Time

by Greg Egan

  When he’d finished, Ramiro brushed the crumbs from his gloves. ‘What happens if we get this wrong?’ he asked. ‘If we scare the rogue into some kind of evasive manoeuvre that changes its trajectory, but it’s still not enough to stop it hitting the Station . . . could that skew things so that the plume ends up aimed at the Peerless?’

  Tarquinia had already thought it through. ‘Any collision at this speed is going to give the Station so much energy that it will be oblivious to the Object’s gravity: it will be travelling on a virtually straight line, not whipping around in an eccentric orbit. So even if the impact’s skewed, either the Station will crash on the side where it was meant to crash, or it will miss the Object completely and fly off into the void.’

  ‘So the worst that can happen is that the saboteurs get what they want: a delay in the turnaround.’ Worse was possible for the two of them, but Ramiro was trying to calm himself for the task ahead, not give himself a reason to back out completely.

  Tarquinia said, ‘As far as I can see. But the problem then is how people will respond.’

  ‘You mean . . . retribution?’ Ramiro hadn’t been thinking that far ahead. ‘The migrationists will be in trouble just for trying this stunt, whether or not we manage to stop it.’

  ‘I think a lot of travellers will be a great deal more displeased if the turnaround is actually postponed for a generation than they would have been by the mere effrontery of the attempt.’ Tarquinia sounded bemused: hadn’t Ramiro invested a third of his life preparing for the event?

  ‘I’d be disappointed,’ he confessed. ‘But it’s not as if everything I’ve done will have been wasted. Even if the delay is so long that they decide to replace the whole system with something more modern, they’ll still end up using a lot of my ideas.’

  ‘Hmm.’ Tarquinia was surprised, but she wasn’t going to try to argue him out of his position. ‘Most people have been looking forward to this for a long time, though – and for someone who hasn’t directly contributed to it, it’s living through the turnaround that would make all the difference. You get to take some pleasure in having made it possible, whenever it happens. The rest of us will just be robbed of the biggest thing we hoped to see in our lives.’

  ‘Three years of arduous gravity, and some changes in the appearance of the stars?’

  ‘It’s not the novelty, or the spectacle,’ Tarquinia replied. ‘It’s the proof that what we’ve been through might be worth it. It’s seeing the mountain heading back towards the home world – seeing the plan finally enacted, not just promised. We can’t take part in the reunion, but a whole generation’s been clinging to the hope that at least we’d be here for the turnaround.’

  ‘That’s all a bit teleological for me.’ Ramiro had no wish to offend her, but the idea of anyone’s sense of worth being reduced to their role as witness to the Great Project just dismayed him. ‘I hope our descendants can help the ancestors. But why should everything we do derive its meaning from that?’

  Tarquinia buzzed incredulously. ‘So you don’t care why we’re turning around?’

  ‘I never said that,’ Ramiro protested. ‘I think the turnaround will be a good thing for everyone. If I felt otherwise, I would have joined the migrationists. But day to day? I just like solving problems and doing my job well. That’s enough. There’s no need for all this grandiose posturing.’

  Tarquinia fell silent. Ramiro felt a twinge of guilt: ‘grandiose posturing’ might have been a bit too strong.

  ‘Anyway, forget it,’ he said. ‘We’re not going to mess this up, so any consequences are hypothetical.’

  ‘One kind are hypothetical,’ Tarquinia allowed. ‘But don’t forget the rest.’

  ‘The rest?’

  ‘Most travellers will be happy if we succeed,’ she said, ‘and I hope they’ll forgive the migrationists, out of sheer relief at their ineffectuality.’

  ‘But?’ Ramiro shifted uneasily in his cooling bag, hoping his meal was going to stay down.

  Tarquinia said, ‘Whoever did this, they’re not going to give up. If they’re certain that the Peerless is heading for oblivion, what else can they do but keep on trying to save us?’

  Half a chime before the expected encounter, Ramiro slipped on the ultraviolet goggles. It was impossible for the astronomers on the Peerless to measure the rogue’s position down to the last saunter, so Tarquinia had decided that the only reliable way to synchronise the next stage of the process was to allow the rogue to overtake them. The goggles didn’t leave Ramiro blind – the photonics aimed to overlay an image of any incident UV on an ordinary view – but the result was an imperfect compromise and he could understand why Tarquinia didn’t want to try to read the navigation console while wearing the things herself.

  ‘After this, every new gnat will have UV cameras built in,’ he predicted.

  ‘Then we’re lucky no one thought it was worth it before.’ Tarquinia gave a curt hum of displeasure. ‘What next? Weapons built in? Everything we make from now on designed with the worst in mind?’

  Ramiro adjusted the straps on his goggles. He wasn’t going to fret about some hypothetical escalation of the conflict. There was a problem right in front of them; they had to focus on it completely now.

  ‘Three lapses to go,’ Tarquinia announced.

  Ramiro tensed, willing himself to vigilance. He turned slightly to the left. If the rogue arrived later than they’d anticipated, sticking rigidly to the flight plan would leave them perpetually ahead of it. Only by cutting their engines completely could they guarantee that the rogue would pass them, revealing itself through its flare.

  ‘Two lapses.’

  Ramiro fixed the pattern of the stars in his mind, noting each trail’s extension in artificial white beyond the usual violet. The rogue might pass them in the distance, and he did not want to be confused about the significance of some pale white streak.

  ‘One lapse.’ Tarquinia waited, then counted down the last pauses. ‘Five. Four. Three. Two. One.’

  Ramiro said, ‘Nothing.’ He was weightless now; the engines had cut off automatically. He strained his eyes, wondering if the trajectories could have been so misaligned that the rogue had already passed them by, completely out of sight.

  Something moved in the corner of his vision; before he could turn towards it there was a light in front of him, vanishing into the distance. ‘Now!’ he shouted. Tarquinia restarted the engines, at a lower thrust intended to match the rogue’s acceleration.

  Magically, the white speck stopped fading.

  ‘It’s stable,’ Ramiro marvelled. In all these cubic severances of void – and the further three dimensions of velocity in which they might have gone astray – they’d actually succeeded in crossing paths with their foe and keeping pace with it.

  Tarquinia raised the acceleration slightly; the speck grew brighter and slid off-centre. ‘It’s going left,’ Ramiro warned her. Tarquinia eased the thrust down, turned the gnat fractionally for a few pauses, then turned it back again. As far as Ramiro could tell, the rogue was dead ahead now.

  By trial and error they whittled away the distance between the two gnats. Tarquinia advanced cautiously; if they overshot the rogue its engines would become invisible. Instead, the light grew gratifyingly intense, to the point where Ramiro had to lower the gain on the goggles.

  Tarquinia said, ‘I can see the hull now.’

  Ramiro took off the goggles and waited for his eyes to adjust. Ahead of them and slightly to the left, the rogue gnat’s dome glistened in the starlight above its grey hardstone shell. In visible light, the blazing beacon he’d been following was reduced to a black patch at the rear of the hull.

  Tarquinia brought them closer. ‘I’m going to depressurise,’ she said. As the air hissed out of the cabin, Ramiro opened the valve on the tank attached to his cooling bag. Tarquinia put on her helmet, but Ramiro deferred; it would be awkward trying to aim the coherer with his face covered, and with the heat being drawn off most of his body he’d be co
mfortable for a while yet.

  When the rogue was suspended a couple of saunters away, he unstrapped his harness, found the release handle under the dome on his left and pulled open the exit hatch. He slithered around on the couch until he was facing out. Tarquinia handed him the coherer. He held the scope to his eye; there was nothing between him and the rogue but void now. He searched the hull for the two dark circles of the proximity sensors; he knew more or less where they had to be, but it still took three sweeps to find them.

  Ramiro reached up and set the coherer to blue – far enough from infrared that it wouldn’t trigger the sensors – and checked that the spot was falling on his first target. Then he slid the tuner further along, to a point he’d marked earlier with a speck of adhesive resin: an ultraviolet frequency that would permanently damage the lattice structure of the photodetector.

  The dark circle showed no visible change, but he’d expected none. He’d just have to trust the physics. He shifted his attention to the second sensor.

  When he was done, Ramiro righted himself on the couch. The navigation console was predicting an impact with the Station in less than four chimes.

  He put on his helmet. ‘We’re too late to use the explosives, aren’t we?’

  Tarquinia’s voice came through the link, but he could hear a muffled version through the couch as well. ‘I’m sorry,’ she said. ‘It took me longer to catch up than I thought it would.’

  ‘Don’t worry about it.’ On balance, Ramiro was relieved; the whole idea had sounded like a dangerous gamble.

  The rogue was drawing closer now; Tarquinia was using the manoeuvring engines to ease the gnat sideways. Ramiro waited for the rogue to turn skittish, but their presence had no effect on it at all. Either he really had killed the proximity sensors, or the saboteurs hadn’t even tried to make use of them.

  Ramiro slid into a safety harness attached to a short rope. Tarquinia had brought the two gnats to within about three stretches of each other; Ramiro could see right through the rogue’s dome now, into its empty cabin. If he’d been weightless he would happily have attempted to jump straight for the rogue’s hull, but under this much acceleration he doubted that he would have made it a quarter of the way.

  He poked his legs out through the hatch and reached around with his right foot for the panel that covered the boarding rope. He slid it aside and groped for the hook on the end of the rope. He’d chosen a cooling bag that left his feet uncovered, allowing him to re-form them easily into hands. He took hold of the hook, released the brake on the reel, then unwound what he judged to be a little more rope than he’d need.

  Seated on the rim of the hatch with his legs dangling down into the void, leaning a little so he could watch himself through the dome, Ramiro tossed the hook. When it struck the other gnat’s dome he cringed, expecting the worst; if the rogue’s software was monitoring sound in the cabin, this would be the time for it to scupper the attempted boarding.

  The rogue stayed put. Ramiro was puzzled, but he was beginning to suspect that the saboteurs had baulked at the idea of trying to automate a response to every contingency. Their overriding aim would have been to keep the rogue on course and on schedule; with the Station deserted and the Peerless so far away they had hardly been guaranteed visitors, and any extra layers of complexity in the software aimed at dealing with that possibility would have carried some risk of jumping at shadows. It was just bad luck for them that their plan had been detected so early; if he and Tarquinia had left the Peerless half a bell later, this whole encounter would have been impossible.

  Ramiro gathered up the rope and tried again. On his fourth attempt, the hook passed through the ring beside the rogue’s hatch. The boarding rope hung down into the void; he didn’t want to tighten it so much that any jitter in the engines would snap it, but as it was the catenary looked dauntingly steep. He wound some rope back onto the reel, until the dip at the centre was no more than a couple of strides.

  ‘How long have we got?’ he asked Tarquinia.

  ‘A bit more than three chimes.’

  Ramiro removed his safety harness. The rope that tied it to the cabin’s interior was too short for the crossing, but if he’d substituted a longer rope that would have put him in danger of swinging down into the gnat’s ultraviolet exhaust. Having had no training in using a jetpack, he’d decided that the bulky device would just be a dangerous encumbrance. If he lost his grip, or if the boarding rope snapped or came loose, the safest outcome would be for him to plummet straight down away from both vehicles and await rescue.

  Tarquinia said, ‘Be careful.’

  ‘I intend to.’ Ramiro clambered out of the hatch and took hold of the boarding rope, swinging his legs up to share the load. He was more used to dealing with ropes in low gravity – as antidotes to drift rather than weight-bearing structures – but with four limbs in play he had no trouble supporting himself. With his rear eyes he gazed down at the stars beneath him; if he was going to react badly to the infinite drop it would be better to do it now than when he was halfway across. But though the sight was discomfiting, he didn’t panic or seize up. A long fall could only harm him if there was something below on which to dash open his skull. Nothing made for a softer landing than the absence of any land at all.

  As he dragged himself out along the rope, Ramiro’s confidence increased. He wasn’t going to lose his grip for no reason, and the two gnats remained in perfect lockstep, their engines running as smoothly as he could have wished. His thoughts turned from the mechanics of the approach to the task ahead. With only three chimes remaining, it had passed the point where all he’d have to do to spare the Station was shut off the rogue’s engines. Its sheer momentum now would be enough to carry it to the impact point with only a few pauses’ delay – not long enough for the Station’s orbit to move it out of harm’s way. But the saboteurs might have made it difficult to change the flight plan quickly, so his best bet would be to plug his corset directly into the engine controller. That was not a smart way to try to fly a gnat to a specific destination, but all he had to do was swerve sharply enough to avoid both the Station and the Object. Once he was clear of both, he could kill the engines and Tarquinia would come and find him.

  Ramiro felt the rope tilting disconcertingly as he approached the rogue feet first. He’d been looking up into the star trails, but now he raised his head; the hatch was just a few strides away. Clambering upside down into the cabin was going to be awkward, but he didn’t think it was worth trying to turn his body around. When the hatch came within reach, he took his right foot from the rope and stretched it towards the handle.

  His leg jerked back before he was aware of the reason, then the pain arrived, driving everything else from his mind. He was seared flesh and a bellowing tympanum, skewered to an endless, unbearable present, begging for relief that never came.

  ‘Ramiro?’ Tarquinia repeated his name half a dozen times before he could form a reply.

  ‘I’m burnt,’ he said.

  Tarquinia was silent for a moment. ‘They must have sabotaged the cooling system,’ she concluded. ‘Do you want me to come and get you?’

  Ramiro had closed his eyes; he opened them now, and realised that he’d managed to hang onto the rope despite the shock. ‘No.’ His damaged foot was useless, but he still had three good limbs. ‘Can we pump some of our own air through?’

  ‘There isn’t time,’ Tarquinia said flatly.

  ‘No.’ It would take at least a chime just to set up the hoses, let alone for the air to have any effect.

  ‘I’m going to try pushing the rogue, hull to hull,’ Tarquinia announced. ‘How quickly can you get back here?’

  ‘I don’t know. Let me try.’

  Ramiro braced himself and began. Even with his injured foot touching nothing, his body complained about the effort and the motion; it wanted to curl up where it was. He tried bribing it with images of the safety of the cabin: the rogue was fatal, and the rope was precarious, but once he was in the cabin he co
uld rest.

  Halfway back, Ramiro felt his foot growing mercifully numb. He looked down to see a swarm of tiny yellow globules spilling from the ruined flesh, glowing like the sparks from an old-fashioned lamp as they fell into the void.

  ‘Tarquinia?’

  ‘Do you need help?’

  He could ask her to bring out a knife and amputate his foot, but that would take too long. ‘The wound isn’t stable,’ he said. ‘I’d better not come back into the cabin.’

  ‘What do you mean, it isn’t stable?’

  ‘The burn’s denatured the tissue to the point where it might be explosive. You’d better start the manoeuvre, and I’ll drop out here.’

  ‘You can’t drop, Ramiro.’ Tarquinia presented the verdict as if she’d brook no contradiction.

  ‘I trust you,’ he said. ‘If I survive this, I know you’ll come and get me.’

  ‘If we were clear of obstacles, you can be sure I would,’ Tarquinia replied. ‘But if you let go of that rope now, I won’t have time to deal with the rogue and pick you up before you come to grief.’

  Ramiro felt himself scowling in disbelief; his pain-addled brain was proffering an image of him tumbling away into the safety of the void. With no rock beneath him, what was there to fear? But if he insisted on taking the gnats’ frame of reference and its fictitious gravity seriously, to complete the description he’d need to include the two things above him: the Station and the Object, falling straight down. Letting himself fall, too, wouldn’t protect him: those giant battering rams had already gained too much velocity. Turning his air tank into an improvised jet to push himself sideways might just get him clear of the Station in time, but the Object was too large, his aim too unreliable.

  He stared down at the sparks escaping from his foot. ‘Maybe this won’t go off – but if it does I don’t want us both dying.’

  ‘Then stay where you are!’ Tarquinia insisted. ‘It’s the shock wave in air that kills bystanders; if anything happens, the dome and the void will protect me. Look, we don’t have time for a debate! I’m going to start the manoeuvre now. If you get into trouble, shout.’