The Arrows of Time

by Greg Egan

  Azelio feigned shock. ‘The shape of the cosmos is at stake . . . and you want to swindle me out of my rations?’

  ‘Who’s swindling you? You can check all the data yourself. You can ask Ramiro to audit the software.’

  Azelio considered the offer. ‘If the light goes straight, you pay me; if Lila’s predictions are confirmed, you win. Anything else – including Vittorio’s theory – is a draw.’

  ‘Agreed.’

  ‘Two loaves, then,’ Azelio confirmed. ‘You’re on.’

  ‘Is there something that needs monitoring while you’re waiting for the stars to align?’ Ramiro asked Agata. ‘I’m on watch all night – it wouldn’t be any trouble.’

  ‘There’s nothing like that,’ she replied.

  ‘Then why not get some rest?’

  Agata looked up from her console. ‘I can’t just shut off my mind in the middle of this.’

  Ramiro stretched his shoulders and swivelled around to face her. ‘The star trails will still be there when you wake. And we’ll be following the same orbit whether you’re sitting here fretting, or fast asleep in bed.’

  ‘That’s true.’

  ‘But . . . ?’

  Agata said, ‘Why would I wait six years for the chance to do this, and then sleep through half of it?’

  Ramiro buzzed. ‘Fair enough.’

  ‘I used to hold vigils outside the voting halls,’ Agata recalled. ‘I’d watch the people come and go, watch the tallies rising.’

  He said, ‘So when you take something seriously, you try to make the most of it?’

  ‘Yes. Is that so strange?’ Agata tried to judge his mood, and decided to take a chance. ‘Isn’t that what you and Tarquinia are doing? Making the most of your friendship?’ Ever since Azelio had confided his own suspicions about the pair’s activities to her, Agata had suffered bouts of curiosity, but she’d never had the courage to ask the participants themselves about the experience.

  Ramiro didn’t seem angered by the question, or embarrassed. ‘In a way,’ he said. ‘If I was back on the mountain, I’d be worried that I was doing the opposite: taking the drive to raise children and wasting it on something trivial. Here, I can tell myself that I have no chance of becoming a father, so it’s not a waste at all.’

  Agata said, ‘Everyone but the Starvers accepts that it makes sense to have children without fission – so why not refine the process even further and select precisely the effects we want from it?’

  ‘Why not?’ Ramiro agreed. ‘As an abstract proposition, it sounds as sensible as separating out the parts of a plant instead of blindly eating the whole thing. We don’t have to swallow the poisonous roots when it’s the stem that actually tastes good.’

  ‘But why as an abstract proposition?’ Agata pressed him.

  Ramiro hesitated. ‘The trouble is, even when the body can’t put things back together, it never forgets how they used to be joined.’

  ‘What do you mean?’

  ‘It makes me want children more than ever,’ he said. ‘It takes that ache that might have faded with time, and reminds me, over and over again, that it’s never going to be fulfilled.’

  While they were in free fall the Surveyor could be oriented any way they liked, and Tarquinia had chosen to set the window facing the rim of the hemisphere of home-cluster star trails. As Agata’s vigil stretched on, she left Ramiro in peace, ignored the clock on her console, and just stared out through the window, waiting for the first sign that something solid and invisible had moved between her and the ordinary stars.

  Despite the lights of the cabin, after a few lapses her eyes began picking out a faint grey disc against the deeper blackness of the dark hemisphere. Esilio’s sun scattered ordinary starlight, so she could have checked its progress through the telescope without even switching to the time-reversed camera, but she was content to let the image remain elusive, coming and going as her concentration faltered, or as Ramiro shifted in his harness and drew her focus back to the reflected interior.

  When a bite appeared in the rim of the bowl, all ambiguity vanished from the scene. Agata felt a tingling of excitement, and beneath it a churning sense of disruption. When the Surveyor had altered its velocity the star trails themselves had stretched and shrunk, but she’d seen the same predictable deformation when the Peerless turned around, and in the end it amounted to little more than holding up a distorting mirror to the sky. This was different: before her eyes, an orthogonal star was leaving its hemisphere and crossing the border, obscuring the ancestors’ stars behind it.

  The occulted region grew larger, slowly revealing with clarity and precision the shape she’d squinted and guessed at. Agata savoured the delay still to come: she’d chosen reference points on the star trails well clear of the clutter of the rim, so it would be a bell or so before she could start making measurements.

  Ramiro said, ‘I wonder what the settlers will call it: that day of the year when the sun starts its passage across the stars.’

  Azelio and Tarquinia joined them, and the four of them ate breakfast together as they watched the black disc become whole. Then Agata turned to her console and summoned up the image through the telescope.

  She guided the software as it tracked the celestial markers she’d chosen. Some were transitions in the perceptually defined hue of a single star trail: the point where orange turned to red, easy to find by eye though there was no discontinuity in the light’s actual wavelength. Others were points where two trails crossed, and were not so much fixed beacons as sites where she expected some complicated but illuminating slippage. The colours of the two trails were never the same where they met, so two beams that were initially travelling side-by-side would be bent by different amounts depending on their speed, leaving a slightly different pair of hues to meet up in their place.

  Agata didn’t expect any telltale distortion to leap out at her from the screen; the changes would be measured in arc-flickers. All she could do was check that the software had latched on to the correct features, and watch closely to ensure that nothing went awry as the black disc encroached on the field of view.

  She did not take her eyes from the telescope’s feed until the last of the markers had vanished behind the sun. Then she summoned the analysis: a plot of measurements compared to predictions.

  ‘Azelio?’ she called.

  ‘Yes?’

  ‘Prepare to skip lunch; I’ll be eating for both of us.’

  Azelio dragged himself over to take a look at the results, soon followed by Ramiro and Tarquinia. The measurements with their spread of errors wove a course that hewed closely to Lila’s predictions – and ruled out Vittorio’s theory entirely.

  ‘Space is curved!’ Tarquinia exclaimed delightedly. She’d taken no prior position on Lila’s theory, but the sheer strangeness of the notion seemed to please her now that it could finally be justified.

  ‘Very slightly,’ Azelio conceded. ‘It’s barely measurable.’

  ‘This might seem like a tiny, obscure effect now,’ Tarquinia replied, ‘but I guarantee that in a couple of generations, every astronomer will be making use of it somehow.’

  Ramiro squeezed Agata’s shoulder. ‘Congratulations.’

  She said, ‘It was Lila’s prediction, not mine.’

  ‘And yet I don’t see Lila here making the measurements.’

  ‘When I told her I was going to be doing this,’ Agata recalled, ‘she said: “If the results aren’t what my equations dictate, all we can do is pity the poor cosmos – because true or not, the theory will be the more beautiful of the two by far.“ ’

  ‘So you’ve proved that the cosmos is beautiful,’ Azelio concluded. ‘But you still can’t tell us its shape.’

  ‘The beauty is that it’s comprehensible,’ Agata declared. ‘Even if its shape is unknown.’

  ‘Unknown to you,’ Ramiro said provocatively.

  ‘Yes.’ Agata frowned. ‘But why the distinction? Have you been working with Lila’s equations yourself, on all th
ose long watches?’

  ‘Ha! I wish I were that smart.’

  ‘Then who . . . ?’

  ‘If the messaging system’s been operating on the Peerless since a year or so after we left,’ Ramiro reasoned, ‘then Lila and her students will have had a year by now to think over all the results we bring back. So who knows how far they might have taken things?’

  ‘That doesn’t bother me,’ Agata said firmly. ‘I’ve stolen an advantage over everyone on the Peerless, squeezing three years into each year that passed for them. If they end up deriving some beautiful corollaries from my results by the time I return, that will give me the best of both worlds: I’ll get to see what other people make of my work – and I won’t even have to wait around while they do it.’

  It was a nice idea in principle; maybe she really could live up to it. But whether or not her competitors had already had the last word, she was hungry to return to her calculations, reinvigorated by this proof that her efforts so far had not been wasted.

  Tarquinia said, ‘Make sure everything’s secure in your cabins. I’ll need to run the engines hard for a while; we still have a lot of velocity to shed before we can go into orbit around the planet.’

  Agata said, ‘Right.’ The shape of the cosmos would have to wait; there was still the small matter of Esilio.

  21

  While Azelio and Tarquinia debated the merits of different landing sites, Ramiro clung to a rope beside the window and gazed down at the starlit world below. How could he understand Esilio? Of all the sciences he’d studied as a child, geology had been the least developed – and at the time, he’d imagined, the least likely ever to be of use to him. Of the little that he remembered, he remained unsure what he should trust. The ancestors had had no idea what a rock was actually made of, while their successors, with all their superior knowledge, had never set eyes on a planet.

  ‘We need to be within walking distance of four or five different kinds of soil, or what will the crop tests be worth?’ Azelio said heatedly.

  ‘I appreciate that,’ Tarquinia replied. ‘But if we don’t come down on flat, stable ground, we could damage the Surveyor irreparably.’

  Over the eons, Ramiro had been taught, every kind of rock exuded traces of gas, and for a body with sufficient gravity this gas would accumulate into an atmosphere. If the body also happened to orbit a star, winds driven by the temperature difference between day and night eroded the rock, and once there was airborne dust and sand that accelerated the process. The routes of the dust-flows carved out valleys and mountains, shaped as well by the differing durability of the underlying rock. But where had those various minerals come from? As far as he recalled, no one even knew for sure whether they dated all the way back to the entropy minimum, had formed over cosmic time from the sedate decay of some primordial substance, or had been forged in the core of a giant ur-world where liquid fires – contained for a while by its unimaginable gravity – thrashed and churned until the whole thing finally split apart and scattered.

  Tarquinia brought an image of the next candidate onto her console, taken in full sunlight with the time-reversed camera. Ramiro struggled to interpret it, but the combination of near-smoothness and suspiciously delicate ridges suggested a plain of wind-ruffled dust into which the Surveyor might sink and vanish.

  ‘Can’t we just settle for the safest-looking ground?’ he proposed. ‘If it turns out that there’s a problem with the soil, we can always ascend and come down somewhere else.’

  Azelio turned to stare at him angrily. ‘I’m not spending years hopping from site to site! That’s not what we agreed to!’

  ‘All right. Forget it.’ Ramiro regretted speaking so carelessly; Azelio had his niece and nephew to think of.

  Tarquinia summoned another image. ‘Why do we only have two probes?’ she fretted. They could send one down in advance of the Surveyor, and the second if their first choice proved unsuitable, but that was the limit: the probes weren’t sophisticated enough to explore more than one location each.

  ‘Perhaps we could extend the survey for a few more days,’ Ramiro suggested. The planet was turning beneath them as they circled from pole to pole; each successive orbit carried them over a different meridian, and though they’d sampled a wide variety of terrain they were still far short of seeing everything. ‘There has to be a perfect site down there.’

  ‘Exactly!’ Azelio replied. He gestured at the console. ‘None of these are acceptable.’

  ‘We can keep looking,’ Tarquinia agreed. ‘A few more days is nothing.’

  Azelio excused himself to check on the plants. Weightlessness wasn’t good for them, but it wasn’t worth setting up the tether again – not unless the selection process was going to stretch out into stints, rather than days.

  Tarquinia switched to the live feed from the time-reversed camera: dawn was breaking over a red plain criss-crossed by brown fissures.

  ‘Look at all that land!’ Ramiro marvelled. If every field of wheat in the Peerless were laid out here side by side, they would pass by in a flicker, lost in the vastness. The sagas were full of journeys on foot that had crossed ancient empires and lasted for years, but nothing he’d read or imagined had prepared him for the scale of the world below. ‘How could the first travellers ever give up so much freedom?’

  ‘I think the Hurtlers might have helped,’ Tarquinia suggested.

  ‘Yes, but I still wouldn’t have been able to do it. We never belonged cooped up in a mountain; it’s a wonder we didn’t all lose our minds generations ago.’

  ‘So you’re set on making this your home?’ Tarquinia asked. ‘Esilio’s won you over already?’

  Ramiro buzzed softly. ‘Esilio’s one thing, but twelve more years of travelling will probably finish me off.’ He would have relished defying Greta and staying behind when the Surveyor departed – and it would not have undermined the purpose of the mission if the rest of the crew returned to the Peerless with the news that a colony had already been established. But he couldn’t do it alone.

  Tarquinia said, ‘And wide-open spaces are one thing, but you can’t eat dirt. Before you start picturing the flowers on your grave, let’s see if anything can take root here at all.’

  The probe parted from the Surveyor, separated by a burst of air before it fired its engines to start the descent from orbit. Ramiro peered over Tarquinia’s shoulder to watch the instrumentation feed. Azelio looked on from Tarquinia’s right, and even Agata had left her calculations for a while to cling to the rope beside him.

  As the probe slowed to let gravity bring it down, it didn’t take long to fall back behind the Surveyor’s horizon, cutting the link. ‘Do you want to sleep for the next few chimes?’ Agata teased Ramiro. ‘I promise to wake you when all the results are in.’

  ‘No thanks.’ Ramiro asked Tarquinia to replay the recorded data; something unsettling had caught his eye. ‘Look at how hot it was, just before we lost contact!’

  Azelio said, ‘We were expecting some frictional heating, weren’t we?’

  ‘Not so soon. Not at that altitude.’

  Tarquinia frowned. ‘We’re not suffering any unexplained drag ourselves, so I don’t see how we could have the density profile that wrong.’

  Ramiro didn’t want to argue about the cause; the fact remained that the heating was unexpected. ‘If this thing burns up out of sight, we’re never going to know what happened – or what we need to change when we try again. If we make the wrong guess we could lose the second probe the same way.’

  Tarquinia contemplated this gloomy scenario. ‘Then we’d better move quickly,’ she said.

  Ramiro was already strapped to his couch, but Agata and Azelio had to clamber into place as the Surveyor tilted then ascended rapidly. The cabin window faced the stars, but on the navigation console the land could be seen falling away as Tarquinia widened their horizon to reestablish a line of sight to the probe.

  When the link was restored she cut the engines, letting them continue the upwards a
rc from momentum alone. Ramiro was dizzy after the unaccustomed weight, but when his head cleared he focused on the data feed. The probe’s temperature was still high, but it was less than before.

  ‘It must have been a false reading,’ he decided.

  The image feed was growing shaky, as if the probe was being buffeted by high winds. Greta had only provided the expedition with a single time-reversed camera, and the probe’s sunless view of the landscape below was almost impossible to read. The temperature was dropping steadily now. Maybe there was something going on with the cooling air: a valve had jammed when the flow had been needed to dispose of the engine’s heat, but now it had simply snapped open and was overcompensating.

  As the juddering machine rushed towards the surface, Ramiro felt equal parts fear and exultation. In the history of the Peerless, no one had ever performed a manoeuvre that deserved to be described as a landing. But if this small, robust scout couldn’t survive the process, what chance would there be for the Surveyor?

  The image turned black. Tarquinia said, ‘Side camera might be more informative now.’ She sent an instruction from her corset, and the feed changed to a slanted view of an expanse of sandy ground. In the middle distance a few small grey rocks broke the flatness.

  ‘It’s down! It’s safe!’ Azelio chirped ecstatically, then turned to the instrument feed. ‘And the temperature’s fine. It’s already close to Tarquinia’s estimate for the surface.’

  Agata said, ‘In Esilio’s terms, it’s been there for days. What other temperature should it be?’

  Ramiro struggled to accept this. On one level he understood her reasoning perfectly: according to Esilio’s arrow of time, the probe was about to ascend, with any frictional heating yet to come. And if this was the correct perspective, the high temperature they’d seen when it was still above the atmosphere was due to its earlier heating during its ascent.