The Arrows of Time

by Greg Egan

  When he reached the hull he could see Tarquinia clearly through the front window, already busy at the navigator’s console. A moment later the first warning light blinked out on the panel beside the airlock: the inner door was closed. He waited for the pressure to be pumped down; with a finite amount of sunstone to gasify, they weren’t going to throw away any more air than was necessary.

  The second warning light went out. Ramiro gripped the crank with his feet and began turning it. Once he passed through this hatch, he’d have nowhere to escape to for the next six years. But he’d been forced here by his own nature, as much as by his circumstances; he wasn’t merely exchanging one prison for another. And once he’d passed through these temporary constrictions, there’d be infinitely more elbow room in the end – for himself, and for everyone who followed him to Esilio.

  In the cabin, the sense of familiarity he’d gained from the rehearsals reimposed itself. Ramiro sealed the inner hatch, then clambered down a rope ladder to the nearest of the three couches behind Tarquinia’s. The couches were shaped to make more sense once the gravity was at right angles to its present direction, but for now he had to lie on his back with his legs bent and raised, his feet brushing the floor-to-be.

  As he strapped himself into place, his jetpack and helmet felt like absurd encumbrances, but when he plugged his corset’s cable into the console in front of him the panel lit up in acknowledgement. When the automation could read any pattern he raised on his skin, it didn’t matter how mobile his limbs were.

  ‘A full crew?’ Tarquinia lamented, mock-disappointed. ‘I was hoping for an increase in my rations.’

  Azelio said, ‘I’ll see what I can do once we make planetfall.’

  Ramiro glanced at Agata on the couch to his left; it was hard to read her face through her helmet. ‘Agata gets first call on any extra food.’

  ‘Why?’ she demanded.

  ‘When the Surveyor breaks down and we’re stranded on Esilio, someone will have to populate the planet.’

  Tarquinia said, ‘Don’t worry, Ramiro: by then, the Peerless will have so much knowledge from the future that they’ll be able to send us detailed instructions for triggering division in males.’

  Before he could think of a suitable riposte his console beeped and began displaying the countdown. Three lapses remained to the launch. Ramiro tried to relax; he trusted Verano and his team. And even if the hull broke apart they’d stand a fair chance of surviving – so long as it happened sooner rather than later.

  Two lapses. As Ramiro watched the symbols flickering towards zero, his anxiety vanished. He’d already crossed the point of no return. To get under way now would be nothing but a relief.

  One lapse.

  Eleven pauses. Ten. Nine. Eight.

  Tarquinia said, ‘Commenced burning support ropes.’ The cables holding them to the mountain were as thick as Ramiro’s arms; even a dozen high-powered coherers couldn’t slice the Surveyor free in an instant.

  Three. Two. One.

  ‘Released.’ Tarquinia’s announcement was redundant: they were weightless, and the mountain was receding.

  Through the window, the Peerless began drifting off-centre, perversely moving to the right; they’d been flung from the rim moving right themselves, but the tiny spin they’d inherited from the mountain had at first cancelled, and was now overtaking, the effect of their changing perspective.

  ‘Firing engines.’

  The thrust from the rebounders rose up smoothly, then levelled off. Ramiro sank into the seat of the couch. He was heavier than he’d been before the ropes were cut – and the jetpack felt like more of a burden, tugging down on the narrow shoulder straps. But the acceleration itself was no different from that of the Peerless during the turnaround.

  The mountain had disappeared from sight completely. Through the window in front of him the blazing rim of the home-cluster star trails appeared horizontal as the Surveyor ascended towards the dark hemisphere.

  ‘Everyone all right?’ Tarquinia enquired.

  ‘I’m fine,’ Azelio replied.

  Agata said, ‘Can I leave my jetpack on?’

  ‘As long as you want to.’

  ‘Then I’m fine, too.’

  ‘Ramiro? Any special requests?’

  He said, ‘I’ll be happy once we can see where we’re going.’

  Tarquinia buzzed curtly. ‘When I agreed to the confidentiality conditions, Greta stressed that you were the last person I should let in on the secret.’

  Azelio was confused. ‘What secret?’

  Agata said, ‘We’re not going to travel all the way to Esilio by dead reckoning. Accelerometers are good, but they’re not that good. And the home-cluster stars aren’t enough, either.’

  Azelio understood. ‘They finished the time-reversed camera, in secret?’

  Ramiro said, ‘I think they had prototypes working before the bombing.’

  Tarquinia shifted uncomfortably in her seat, then made a decision. ‘Since everyone knows the situation, I’m not going to treat you like fools.’ An inset opened on Ramiro’s console showing him a patch of sky lit up with stars. Not the home cluster’s long trails; these images were brief stabs of colour, some of them piling the whole spectrum together into a white smudge. He glanced to his left and saw that Agata and Azelio were being sent the same feed.

  ‘Behold the orthogonal stars, lighting the way into the future.’ Agata sounded bitter, and Ramiro couldn’t blame her: this was proof that even from the killers’ point of view her friend’s murder had been futile.

  ‘This is Esilio’s sun.’ Tarquinia drew a red circle around a bright speck near the centre of the view.

  ‘Greta’s spyware will tell her that you’ve broken your agreement,’ Ramiro predicted. He hadn’t been allowed near the Surveyor’s automation while it was in development, but he was sure that the Peerless would be receiving a constant flow of data from the expedition, far beyond the communications they volunteered.

  ‘I don’t care,’ Tarquinia replied. ‘What’s she going to do about it now?’

  ‘Blow us up?’ Azelio joked.

  Agata said, ‘Not if we keep going. They’ll only kill us if we start to look threatening – if we turn around and start heading back.’

  18

  Agata woke in a state of joyful anticipation, but then she spent a lapse or two lying motionless, wondering if she had the day right. She could see the diurnal clock on her console’s panel, but she’d made a deliberate choice to omit the date from the default display. She’d fooled herself in the past, waking with all kinds of wildly optimistic notions about the phase the mission had reached, but it was important that she settle the matter by consulting her memory, with no other aids.

  Since the link with the Peerless had crackled its last transmission and the flow of messages from Serena and Lila had ceased, time had become a desert out of the sagas: a featureless wasteland of shimmering heat haze and treacherous mirages. But Agata was sure that she’d just passed a full day with a justified belief that the long-awaited event was imminent. If she was wrong about that then she wasn’t just disoriented, she was completely delusional.

  She rose from her sand bed and walked over to the console. She hadn’t been mistaken about the date, but she brought up the flight plan to confirm its significance. It had been a few stints since they’d passed the one-quarter mark in the duration of their outwards journey, but that fractional accomplishment had offered nothing tangible to celebrate. Today, the Surveyor’s progress would finally be made manifest: its history would reach orthogonality with that of the Peerless, and Tarquinia would shut off the engines.

  Agata left her room and walked out into the front cabin. Tarquinia wasn’t up yet; Ramiro was on watch.

  ‘Good morning,’ she said.

  ‘No, it’s not.’ Ramiro swivelled his seat around to face her. ‘Complete weightlessness is tedious,’ he complained. ‘We should have found a way to avoid it.’

  ‘You could always move in with
Azelio’s plants,’ Agata joked.

  ‘I shouldn’t have to. If they get to swing on a tether, why not us?’

  ‘What would you use as the counterweight? Splitting the whole vehicle in two would be too complicated.’

  ‘Yeah, yeah,’ Ramiro sulked. ‘What kind of expert on gravity are you, if you can’t summon it at the flick of a switch?’

  Agata said, ‘The kind who understands enough to be willing to bet that that’s never going to happen. I’ll give you a gross to one that no one will discover such a thing between now and the reunion.’

  Ramiro scowled. ‘To be verified how? I thought your theory was that inventors would always censor the messages they sent into the past – since that’s more probable than their ideas appearing out of nowhere.’

  Agata wasn’t going to let these complications stand in the way of a good bet. ‘I think they could tell us what they’d built. They just couldn’t tell us how it worked.’

  Ramiro stretched his arms and buzzed wearily. Most of the cabin lights were off, and behind him the home-cluster stars filled the view. It was Ancestors’ Day all over again – only this time it would last for three years.

  ‘The reunion could be happening right now,’ Agata marvelled. ‘Even as we speak, the Peerless could be approaching the home world.’

  ‘It’s not the first time you could have said that. Or didn’t you notice?’ Ramiro was wearing his corset, so he sent the sketch to the nearest console. ‘About a stint before mid-turnaround, our line of simultaneity would have had just the right slope.’

  ‘It’s the first time it’s “now” by the home world’s reckoning as well as our own,’ Agata replied.

  Ramiro was bemused. ‘Name any two events in the cosmos, and there’s a definition of time that makes them simultaneous. If I can’t actually witness this great moment – let alone take part in it – just how excited do you want me to be?’

  ‘I’m sure the ancestors thought about us at the turnaround,’ Agata argued. ‘What’s wrong with a bit of solidarity?’

  ‘I prefer to reserve that for people I can look in the eye.’

  ‘All right. Forget it.’ They’d exchanged their views and found nothing in common, as usual. There was no point wishing it were otherwise.

  ‘I’m going to go strap myself down and sleep through all this nonsense.’ Ramiro nodded towards the passage behind her; Tarquinia had emerged from her cabin.

  Azelio joined Agata and Tarquinia for breakfast, then the three of them set about putting up the guide ropes and checking that everything inside the Surveyor that might drift free was secured. The tool cupboard took the most work; there were individual straps for every item, but people had grown lazy about using them. Azelio went through the pantry, checking every sack of grain for holes. The sand in their beds was already resin-coated – and hoping to contain it was a tad optimistic whatever steps they took – but Tarquinia insisted on putting tarpaulins in place before the gravity was lost.

  Agata clung to a rope in the front cabin as Tarquinia finally issued the command to the engines. The end of the turnaround for the Peerless had taken place over three full days, out of regard for the effects on the most vulnerable travellers, but the crew of the Surveyor were assumed to be more robust. As Agata’s weight plummeted, she was unable to dispel a conviction that the cabin was plunging down, but then the very idea of that vertical axis lost its meaning.

  After a lapse or two, her body and everything around her was imbued with stillness. The view through the window was unchanged; the stars were indifferent to the sudden straightening of the Surveyor’s history. The susurrations of the cooling system grew quieter; Agata had grown accustomed to the old sound, and the new silence made the room feel dead.

  ‘What now?’ she asked Tarquinia.

  Tarquinia unplugged her corset. ‘That’s it. Everything’s done.’

  ‘What about the plants?’

  Azelio said, ‘There’s no hurry. A few days without gravity isn’t going to harm them. Ramiro will help me set up the tether soon.’

  ‘All right.’

  Agata dragged herself back to her cabin and harnessed herself to her desk. She looked up at the pictures she’d brought: Medoro, Serena, Gineto, Vala and Arianna, scattered among the colourful childish sketches that Azelio was sharing with her. If she’d commandeered the Surveyor she could have flown in a loop right back to Ancestors’ Day on the Peerless. So far as she could tell there was nothing in the physics that would forbid it – so long as she didn’t try to cut corners and make do with a semicircular route, arriving as antimatter and spoiling the party. But she hadn’t seen herself anywhere else in the crowd that day, staring longingly at her friends – and if a visitor from the future really had joined them in her absence, Medoro had done a very good job of keeping it a secret.

  She looked away. Nostalgia passed the time, but it needed to be rationed. And if no one else was celebrating the Surveyor’s parallelism with the home world, she might as well forget it and focus on her work. Though Lila had given the vacuum-energy problem to one of her students, Pelagia, Agata had decided to pursue it independently, in the hope of preventing her brain ossifying from disuse. With a wildly unfair eight-year advantage over her rival it wasn’t impossible that she’d return with a worthwhile contribution of some kind, but she hadn’t told Lila about her plans, sparing herself the weight of any expectations.

  So far, she was still grappling with the notion of the vacuum. She’d read the definitive treatment by Romolo and Assunto, who’d adapted Carla’s wave mechanics to the study of fields, but all they’d really cared about was predicting the results of particle collisions. They’d deliberately sidestepped all the distracting cosmological issues, and – apart from Yalda’s insight that the cosmos had to be finite in order to prevent exponential surges in the light field – it did make sense that none of the results of any small-scale experiment should depend on whether the cosmos was a torus, a sphere, or some four-dimensional analogue of a thrice-knotted pastry.

  Since all of the old-school field theorists’ measurements depended on changes in energy, rather than any absolute scale, Romolo and Assunto had been free to set the vacuum energy to zero by decree. They’d certainly understood that the true value was a difficult quantity to pin down – so they’d vaguely sketched its origins, and then subtracted it out of all their other formulas so they could concentrate on the remaining parts that were more mathematically tractable and contributed to nice, tangible things like the rate at which positive and negative luxagens annihilated each other in their experiments at the Object.

  But even their formal, mathematical expression for the vacuum state was a bizarre sleight of hand: they’d imagined taking the simpler vacuum of a more pristine theory – one where all particles stood aloof from each other, refusing to interact – and writing it as a sum of pieces that each corresponded to a different energy level of the true theory. If you followed that sum over a long time, you could pick out the least rapid oscillations that represented the lowest energy level. So in all of Romolo and Assunto’s calculations, they’d pretended that everything happened in an infinitely old cosmos that had started – infinitely long ago – with the simple vacuum, from which a mathematical trick extracted the true vacuum before they set to work adding particles to it in the here and now.

  Amazingly, all of this nonsense had worked well enough for their purposes, with the quantities they’d predicted confirmed by experiment again and again. But the real cosmos with its own real history and topology couldn’t be understood by grafting on an infinitely long run-up from a state that had never actually existed.

  Someone knocked on the door of the cabin. Agata dragged herself over and opened it.

  ‘Are you busy?’ Azelio asked.

  ‘Not really.’

  ‘Do you want to help me set up the tether?’

  Agata felt a surge of excitement, but then she realised that it was premature. ‘You think Tarquinia will let me do it?’


  ‘Didn’t she give you your void proficiency certificate?’

  ‘Only because she doubted that anyone else would.’

  Azelio frowned. ‘Ramiro doesn’t have much more experience than you. If you’re willing to ask Tarquinia, I’ll support you.’

  The two of them approached the pilot in her couch, and Tarquinia heard them out politely.

  ‘My job is to try to keep you all alive,’ she said. ‘This might not be an especially dangerous task, but Ramiro has the edge on you in confidence.’

  Agata said, ‘If the worst comes to the worst, I’m expendable. Ramiro isn’t. If something goes seriously wrong with the automation, no one else will be able to fix it.’

  ‘I can get us home without automation,’ Tarquinia replied.

  ‘Of course.’ Agata hoped she hadn’t inadvertently insulted her. ‘But you have to admit that a lot of things would become more difficult if we were forced to do them manually.’

  ‘Hmm.’

  Azelio said, ‘Everyone needs experience to get used to working in the void. The engines are switched off, and we’d both be wearing jetpacks; how much safer could it be? And if Agata does this now, it could make all the difference to the kind of task she can manage in an emergency.’

  Tarquinia inclined her head, conceding his point. ‘But she did tell me once that she’d rather not have anyone relying on her.’

  ‘I was joking!’ Agata insisted. She wasn’t sure that she had been, but she certainly didn’t feel that way now.

  Tarquinia said, ‘You can go out with Azelio and set up the tether, but that’s all: install it, but leave it motionless. Ramiro will go out for the spin-up. Half the task for each of you. What could be fairer?’

  Sanctified by the ancestors’ gaze or not, the sky unsettled Agata. When she’d trained with Tarquinia around the Peerless, the contrasting hemispheres had made it easy to stay oriented. There were bright stars now that caught her eye, and constellations that she could commit to memory, but it took much more effort to seek out these relatively subtle cues than it had to distinguish between an empty black bowl and a riot of colour.