Greg Egan: The Arrows of Time

An inset opened in the navigation screen and Tarquinia spoke from the observatory on the peak. ‘I’ve made sightings of six beacons and estimated the rate of change of the Peerless ’s spin. Everything’s within the expected range.’

Ramiro thanked her and she closed the link. For all the built-in redundancy in his own system, an independent manual check was a welcome proof that the software was faithfully reporting reality.

The Councillors filed out, with Greta following. Ramiro leant back in his harness and stretched his shoulders, chirping softly with relief. In principle, the program controlling the photonics could do everything now without further intervention: kill the spin, turn the mountain so the giant engines at the base were aimed in the right direction, then start those engines and keep them glowing with exactly the right power and frequency, until they’d fully reversed the travellers’ original velocity with respect to the home world. Ramiro could see himself sitting at his console watching the script playing out day by day. But if it was too much to hope that the Peerless really would drive itself for the next three years, he’d be satisfied if the program managed to detect and describe any problems it was unable to circumvent.

‘Ramiro?’

He looked up; Tarquinia had reappeared on the navigation screen.

‘What’s happening?’ he asked, surprised that she’d have anything more to report so soon.

‘Don’t panic,’ she said. ‘The spin-down’s going perfectly.’

‘But?’

‘I just saw the latest snapshot of the halo.’

Ramiro’s anxiety deepened. The navigators used ultraviolet images of the region around the Object as a way of measuring the density of interstellar gas, traces of which could be seen being annihilated as it struck the orthogonal asteroid’s dust halo.

Tarquinia read the look on his face and buzzed softly. ‘The gas is as rarefied as ever; the corridor should still be safe to traverse. But there was something unexpected on the image. I think it was a gnat moving away from the Station.’

Ramiro struggled to make sense of this claim. ‘I heard there was a gnat left behind; the last shift didn’t have enough pilots to fly them all back. It should have been tied up, but I suppose it could have sprouted some kind of air leak that pushed it away—’

‘I don’t mean drifting ,’ Tarquinia interjected. ‘It was firing its engines. Some of the flare came our way – that’s the only reason it showed up on the snapshot.’

‘But the Station’s empty. Everyone’s been evacuated.’

Tarquinia knew what she’d seen. ‘Do you think someone could have automated the gnat?’ she asked. ‘To start flying on its own, after they’d left the Station?’

‘It’s possible,’ Ramiro conceded. ‘But why would they?’

‘I have no idea. But it’s either that, or someone’s managed to stay behind.’

‘What are you suggesting? Some disappointed voters from Pio’s faction have decided that they’re going to get their way after all… at the Station ?’ Ramiro didn’t know whether he should be amused or horrified. The ambition was comical, but if there really were holdouts who’d concluded that the safest life they could make for their children lay in an abandoned research habitat, there’d be nothing funny when they starved to death.

‘This image shows a gnat using its engines,’ Tarquinia replied. ‘I’m not going to try to guess if there are people inside, let alone what their motives could be.’

‘Do you want me to chase down the Councillors?’ Ramiro didn’t know whose job it had been to ensure that every last traveller was inside the Peerless before the spin-down commenced, but he was glad it fell entirely outside his own domain.

Tarquinia said, ‘You’d better do that.’

Ramiro loosened his harness. ‘If we had cameras in all the corridors,’ he mused, ‘and programs for recognising invariant anatomy…’

‘We could have done an automated census before starting up the engines?’ Tarquinia suggested.

‘Ah, good idea.’ Ramiro hadn’t been thinking on quite that scale. ‘I was just picturing a way of getting messages to people when they were wandering around the mountain.’ But Greta and her guests would not have gone far. ‘Are you certain this isn’t a false alarm?’

‘No,’ Tarquinia admitted. ‘But if we fire the main engines and there are people left behind, do you want to be the one who takes responsibility?’

Ramiro said, ‘I’ll find the Councillors.’

Ramiro was roused by a discordant clanging of his own design, impossible to mistake for anything else. It was not a pleasant way to wake, but experience had shown him that no gentler sound could penetrate his sleep. He dragged himself out from beneath the tarpaulin of his sand bed and over to the communications link. The walls’ red moss-light had been gentle on his eyes, but when he switched on the display the sudden brightness was painful.

‘I’m going to need you to go outside,’ Greta said.

‘Why?’ Ramiro asked, baffled. ‘Is someone waiting in the corridor?’

‘I’m not talking about your apartment.’

Ramiro massaged his skull, hoping to conjure up a third interpretation.

‘The census results are in,’ Greta said. ‘There’s no one missing from the Peerless .’

‘Good! We can fire the main engines with a clear conscience.’

Greta hummed impatiently. ‘The observatories are tracking the gnat, but we still have no idea what it’s doing.’

‘Why should we care?’ Ramiro was mildly curious, but chasing a moving target across the void when no one’s life was at stake, and the environs in which the whole strange prank was playing out would soon be left far behind, struck him as a little disproportionate.

Greta said, ‘Who understands automation better than you do?’

‘Appeals to my vanity will get you nowhere.’

‘That wasn’t a rhetorical question,’ she retorted. ‘The gnats aren’t meant to be able to do this. But it looks as if someone else knows your field well enough to make it happen.’

‘It’s a trivial modification,’ Ramiro stated flatly. ‘If you want to get me interested you’re going to have to do better than that.’

Greta fell silent.

‘What?’ he pressed her. ‘You can trust me to automate the turnaround, but you can’t tell me the Council’s paranoid theory about a self-driving gnat?’

‘We think the intention might be to exploit the Object as some kind of weapon,’ she confessed.

Ramiro’s skin tingled strangely. He had never even been close to the Object, but since childhood he’d heard stories of Carla and Ivo’s near-fatal first approach, when even the faint wind leaking from their cooling bags had set the rock below them on fire.

‘We could always start the main engines ahead of schedule,’ he suggested. ‘Before this gnat can finish doing whatever it’s trying to do.’

‘And what about the farms?’

‘Some soil spills down the walls, to the place we were moving it anyway.’

Greta said, ‘It’s only the wheat fields that have been left fallow for the changeover. There are timber plantations, medicinal gardens and a dozen different crops we use for fibres and resins that all need careful transplantation.’

Ramiro doubted that anyone would have cared about a few upended trees if it had been clear that the whole mountain was at stake. But if the cost to agriculture seemed too great in the face of an undetermined threat, there were other routes to certainty.

‘Why not just destroy the gnat?’ he suggested. ‘How hard could that be?’

‘The Council wants it intercepted, undamaged,’ Greta insisted. ‘We need to inspect the navigation system and find out exactly what the plan was.’