The Arrows of Time

by Greg Egan

  Tarquinia grabbed his wrists, dragging his gaze back into focus. ‘Ssh,’ she said. ‘It’s all right.’ She drew away from him slowly, gently separating their remaining adhesions.

  ‘What happened?’ he asked her.

  ‘Nothing,’ she said. ‘Nothing’s wrong.’

  ‘No.’ He had no children to lose. How many times had he told his idiot body the same beautiful lie? How stupid could it be, that it hadn’t seen through him yet?

  He looked past Tarquinia, to the pale grey wall of his cabin. He knew exactly where he was now. The Surveyor was his second prison, and outside it was the third. ‘How will anyone live here?’ he wondered.

  ‘There’ll be a better place than this for a city,’ Tarquinia promised. ‘No dust storms – just gentle winds to sweep the footprints away.’

  ‘That’s not enough.’

  ‘Then you’ll build machines to plant the wheat and harvest it. No one will ever have to touch the soil.’

  Ramiro turned to her. ‘Who’ll build these machines?’

  ‘You will. You and the other settlers.’

  ‘And where will you be?’

  Tarquinia said, ‘I thought you didn’t want to know the future.’

  22

  Agata pressed the broom down firmly against the floor of her cabin and tried again. ‘How hard can it be?’ she muttered. Dust starts off in a large area. Pressure is applied inwards along successive portions of the border. Dust ends up in a smaller area, ready to be collected and removed. On the face of it, this didn’t even pose a conflict with the local arrow: Esilian dust should have been happy to have its entropy decreased as her own time advanced.

  But as she moved the broom across the floor, duly concentrating the dust ahead of it, other dust began to appear behind it – some of it falling from the air, some sliding over the stone to pile up against the bristles. Its entropy was decreasing too, as it accumulated from whatever scattered reaches of the Surveyor in which it had been lurking. The net result was that the stretch of floor she’d swept remained as dusty as ever.

  Azelio knocked on her open door. ‘I know you’re busy, but Ramiro’s sleeping and Tarquinia’s on watch—’

  ‘I’m not busy,’ Agata assured him. ‘Do you want a hand with the measurements?’

  ‘If you don’t mind.’ Azelio nodded at the broom. ‘Have you found the trick to it?’

  ‘Not really,’ she admitted. ‘Maybe what we need is some kind of covered system of barriers. If we can place it on the floor and then reconfigure it without opening the cover, we ought to able to manipulate the dust inside without any more arriving.’

  ‘That sounds . . . elaborate.’

  Agata put on her corset and tool belt and followed Azelio to the airlock, then waited for him to cycle through. The view through the window showed that the weather was calm, but the Surveyor had become so filthy that Tarquinia now insisted on the protocol, regardless. Agata was beginning to suspect that the only remedy for the dust invasion would be to ascend into the void and flush every room out with clean air – and even that depended on their arrow prevailing and the void not being ready with a conspiracy of pollutants poised to rush in the moment they opened the airlock, in a perfect reversal of the intended purge.

  Outside, she caught up with Azelio at the start of the trail. It was Ramiro who’d noticed the regularly spaced indentations in the ground after the last high winds, and decided to fill them with rocks marking the way to each of the four test plots. Agata hadn’t questioned him too closely on the matter, but she suspected that he’d already been contemplating doing something similar. The idea hadn’t come from nowhere, inspired by nothing but the evidence of its own implementation.

  ‘How are the calculations going?’ Azelio asked her, as they started along the trail.

  ‘Slowly.’

  ‘Just as well. If you finish them, what will you do on the journey back?’

  ‘There’s no risk of that.’ Agata had set aside her efforts to understand the curved vacuum and instead had spent the last two stints attempting to analyse their current situation, using a crude model of a field in which two opposing thermodynamic arrows met. But in the versions that were simple enough to handle, both arrows rapidly decayed away, leading almost immediately to a time-blind equilibrium state. The reality, in which countless slender fingers of opposing time interpenetrated, seemed to depend on details too subtle for her to approximate in any meaningful way.

  ‘It’s Luisa’s fifth birthday today,’ Azelio announced cheerfully. ‘I’ll show you her drawing for it when we get back.’

  ‘Happy birthday, Luisa!’ Agata played her coherer’s beam over the grey stones to her left. ‘You never peek, do you? You never riffle through the pile to see what’s coming up?’

  Azelio buzzed. ‘Of course not! That would defeat the whole point.’

  ‘I know. But that wouldn’t be enough to stop me.’

  When they reached the first plot the plants were all dormant, their flowers closed. Agata glanced up at the sky; she knew from the positions of the stars that the sun was well above the horizon, but she would have had to forego artificial light for a few lapses to have any chance of picking out the faint disc. ‘I was hoping the petals might synchronise to the Esilian day,’ she said. ‘They give out photons, the sun accepts them: what could be more sensible than that?’

  ‘Except that eons of evolution has left them with no skill but waiting for an ordinary night, not a time-reversed day.’

  ‘Maybe the settlers could breed it into them,’ Agata suggested. If detecting the dawn for themselves was too hard, the plants could still be prodded with more conventional signals into following the new cycle. For now, the Esilian sun would be getting its due regardless – from the plants, the ground, and her own skin – but not in any useful way.

  ‘Can you do the heights and the stalk circumferences?’ Azelio asked her.

  ‘Sure.’ Agata knelt by the first plant and reached into her tool belt. In a perfect world some clever instrument builder would have added a data recorder directly to the tape measure, but instead she had to aim her coherer so that she could read the tape by eye, raise the figure on her skin, and have her corset record it. ‘Is one soil type racing ahead yet?’ she asked Azelio. He’d started from the other end of the row, making his own inspection to record the number and condition of the flowers.

  ‘No.’

  ‘So there’s not much difference? The settlers could farm anywhere?’

  Azelio was silent. Agata regretted distracting him; she’d probably made him lose count.

  As he stood to move on to the next plant, he said, ‘Actually, they’ve all stopped growing.’

  Agata was startled; nothing in Azelio’s demeanour had prepared her for this news. ‘All of them? Every single one?’

  ‘Yes.’ Azelio spoke calmly. ‘At first it was only a few cases, and I put it down to transplantation shock. But the numbers just kept getting worse, and three days ago the last exceptions succumbed.’

  Agata struggled to find the least dismaying interpretation of these facts. ‘Do you think it’s the wind?’ They could always improve the windbreaks, or even relocate the whole experiment.

  ‘No. They haven’t lost that many petals, or had roots dislodged.’

  ‘So it’s the soil,’ she concluded. ‘All four kinds are inhospitable.’

  ‘It’s looking that way.’

  ‘Have you told Ramiro?’

  ‘The trial isn’t finished yet,’ Azelio stressed. ‘There’s still a chance that this could be a temporary hiatus.’

  ‘Right.’ Agata understood now why he’d called on her to help him with the measurements: he was trying to keep the results from Ramiro for as long as possible, in the hope that something would change.

  Azelio knelt down and continued his inspection; Agata did the same. As she turned the revelation over in her mind, she was surprised at her own equanimity. After six years away from the mountain the conflict that they’d come her
e to remedy seemed remote and petty. If they really could rid the Peerless of Medoro’s killers by showing that a settlement was viable, she’d certainly relish that victory – but between the light-deflection measurements and her work on the vacuum, she already found it impossible to think of her time here as wasted.

  But Azelio had no such consolations; he was only here in the hope of making the mountain safer for the children he’d promised to protect.

  On their way to the next plot Agata asked him, ‘Is it the composition of the soil? Or is it the arrow?’

  ‘I can’t say for sure,’ Azelio replied.

  ‘Can’t you guess?’ Agata pressed him.

  He said, ‘The spectra suggest that at least two of the soil types should have had everything the wheat needed.’

  ‘So it probably is the arrow?’ There was nothing inimical to life about the mere presence of a conflicting arrow; the crew had survived it perfectly well, thanks to their store of food with its unambiguous origins and their undiminished ability to rid their bodies of excess heat. Esilio even accepted their excrement without complaint, however bizarre the material’s fate would seem to a time-reversed observer. But the plants’ uptake of nutrients relied on interactions between their roots and the native soil at a microscopic level, and there was no guarantee that the two systems, left to themselves, would simply sort out their differences.

  Azelio wasn’t ready to give up hope of a simple agronomic solution. ‘We could try mixing the most promising soils,’ he said. ‘Or we could look for better conditions elsewhere. If it’s the arrow, that’s the end of it.’

  Agata said, ‘I’ll defer to your expertise on soil chemistry – but when it comes to the arrow, let me be the judge. The problem still might not be insurmountable.’

  ‘Really?’ Azelio buzzed sceptically. ‘You can’t even sweep your own floor any more. How are you going to reach into the ground and persuade every speck of dust that it’s mistaken about the route it’s taking away from the entropy minimum?’

  Agata had no answer to that. But if she couldn’t change the brute facts, the cosmos wasn’t taking sides in this clash: it simply had no choice but to reconcile everything it had brought together. If there had to be an accommodation between Esilio’s arrow and the Surveyor’s, the trick would be to find a way to make the crop’s failure even more improbable than its success.

  Ramiro must have made a choice, Agata realised, not to seek constant updates on the state of the crops. Warned that there could be problems at the start as the plants adapted to their new conditions, he’d stepped back and left it to Azelio to monitor their health, and to offer a verdict only once it was warranted.

  But Ramiro wasn’t blind, and as the flowers ceased unfurling and the stalks began to wither, Agata could see that both men were losing hope.

  Bell after bell, day after day, she sketched elaborate diagrams for machines to manipulate the soil’s properties. Chemically, each mineral grain was no different from that of an equivalent on the Peerless or the home world. Physically, the distinction came down to the fact that soil on the home world had once been solid rock, while for Esilian soil, from her own point of view, that fate still lay in the future. Or in Esilio’s terms, the vast bulk of the planet’s soil had been eroded from rock . . . leaving two competing possibilities: that some small portion of it had actually been emitted from the roots of time-reversed stalks of wheat, or that those strange withered plants had failed to contribute anything before finally regaining their health and being carried away by the visitors.

  Still, a plant knew nothing of the past and future of each grain of sand; the whole interaction with the roots had to make sense in the present. If she could find a way to measure the detailed distribution of thermal vibrations in the soil they’d brought with them, and then recreate that in the native soil, it would no longer be statistically reasonable for the plants to fail to absorb it.

  To the naked eye, soil was just soil – and if the differences were microscopic, how hard could they be to erase? But when she took the most promising of her schemes and thought seriously about the practicalities, the measurements were close to impossible, the manipulations impractical, the computations prohibitive and the projected throughput so slow that a cubic scant of soil would have taken eons to process.

  Agata deleted the sketches from her console. She peeled off her corset and lay down on her sand bed. The whole approach was a dead end: she might as well have set out to reverse the motion of every particle of air in the Surveyor in the hope of creating a breeze that would carry all the dust away.

  Anything that sought to inscribe a new arrow into the soil at a microscopic level was doomed; the numbers would always be against her. What she needed was something infinitely less subtle.

  Agata waited until she had a chance to speak to Tarquinia alone. ‘Do you remember telling me once that you believed Greta had put a bomb on the Surveyor?’

  Tarquinia replied warily, ‘No, but I’ll take your word for it.’

  ‘My word that there’s a bomb?’

  ‘No, your word that I told you.’

  ‘So it’s true?’

  Tarquinia struggled to reconstruct some half-forgotten chain of inferences. ‘Verano dropped some hints. He was very apologetic.’

  ‘Is there any way to be sure?’ Agata pleaded. ‘Greta might have put him up to the apology, as a kind of misinformation.’ Even before the launch, the whole crazed-anti-messager-rams-the-Peerless scenario had never struck her as very plausible, and after spending six years with Ramiro – irritating as he could be – Agata had to strive mightily to put herself inside the head of anyone who’d imagined him commandeering the Surveyor and turning it into a weapon.

  Tarquinia was bemused. ‘This is a strange time to start worrying about it,’ she said. ‘If an unexpected bump could set it off, we’d have been dead long ago.’

  ‘If the Council really didn’t trust Ramiro not to turn saboteur,’ Agata reasoned, ‘then they wouldn’t have been content with a bluff, would they? They would have insisted on some genuine means to destroy the Surveyor if it turned rogue.’

  ‘I suppose that’s true,’ Tarquinia agreed. ‘Though over the last six years I’ve become pleasantly accustomed to not having to think about politicians at all, so I don’t know what my judgement is worth now.’

  ‘If there’s a bomb, we need to find it,’ Agata declared. ‘We need to cut it open and extract the explosive.’

  Tarquinia swivelled on her couch, assessing this suggestion. ‘We need to locate the hidden, possibly tamper-proof bomb that’s been obliging enough not to kill us so far, and start prodding and poking at it now . . . because?’

  ‘Because the test plots are failing,’ Agata explained. ‘So we need to take the explosive up into the hills, turn some rock into soil for ourselves – against the Esilian arrow – and see if that imbues the soil with the properties that it needs to support plant growth.’

  ‘If wheat hadn’t failed to grow properly in weightlessness,’ Tarquinia mused, ‘then Yalda never would have ordered the spin-up. And if Yalda hadn’t ordered the spin-up, the Peerless might well have been incinerated by antimatter. So really, I ought to be encouraged by history: anything that starts with crop failure ends well.’ There was a sound of hardstone scraping against hardstone, then slipping.

  ‘Can you see what you’re doing?’ Agata aimed her own coherer down into the maintenance shaft.

  ‘Yes, I can see,’ Tarquinia replied. ‘It’s just that none of these bolts have been turned since the engines were assembled.’

  ‘The bomb’s not going to explode just because you open that panel, is it?’ Agata asked anxiously.

  Tarquinia looked up at her, affronted. ‘However much pressure he was under, Verano would never have done anything so perverse. We’re entitled to inspect our own engines; that hardly amounts to an act of sedition.’

  There was a long silence, followed by a rhythmic squeaking noise that was almost certainly one of the bolt
s being turned. Agata restrained herself from cheering; Ramiro was asleep.

  It took Tarquinia more than a chime to loosen all six bolts and remove the access panel. Agata peered over her shoulder into the exposed cavity, where cooling pipes ran along the back of the rebounders. If one of the banks of rebounders had failed, someone could have squeezed in here to fit a replacement.

  ‘Anything?’ Agata asked hopefully.

  ‘Nothing obvious,’ Tarquinia admitted. ‘I thought this was the last place we hadn’t poked around in, but maybe I should sit down with the maintenance logs to confirm that.’

  ‘Right.’

  Tarquinia lingered, lowering her head partway through the hatch and turning her face sideways. ‘There’s a big stone beam that goes right across the top of the engines, from rim to rim.’

  ‘Could something be attached to it?’ Agata suggested. ‘Out of sight from where you are?’

  ‘I’m just wondering why it’s there at all,’ Tarquinia replied. ‘The floors of the cabins should provide enough bracing for the engines. And why a beam that runs across one particular diameter of the disc, and not another one at right angles to it? Nothing about the stress from the engines picks out one axis like that.’

  ‘No.’

  Tarquinia said, ‘If I don’t come out in six lapses, send in Azelio with a rope.’

  ‘Azelio?’

  ‘No offence to you or Ramiro, but he’s the skinniest. There’s not much point in two people getting stuck.’ Tarquinia climbed head first through the access hatch, slithering deeper and humming softly as the cooling pipes banged against her, until even her feet had disappeared from view.

  Agata waited, listening intently for any cries of discovery or distress. She was starting to wonder if she should have kept her inspiration to herself. Tarquinia trapped in the guts of the Surveyor would not be a happy outcome – and if she actually located the mythical device there could be worse to follow.

  Worrying silences were punctuated with thuds, pings and echoing curses. Finally, Agata heard Tarquinia returning, her steady advance eliciting a resonant hum from the maze of pipes.