Greg Egan - The Arrows of Time

‘Why not? The collectors gather light from all directions – and they can’t discriminate between ordinary light and time-reversed light. If we can shift the explosions far enough away from the surface that there’s no risk of them breaching the tubes, they could still be the cause of the disruption. They don’t even need to damage the cameras permanently – they just have to overwhelm the photonics long enough for the time-reversed light that’s in transit to be lost.’ The original plan for the occulters had been to blind each channel to a single star, but the design that made that impossible rendered this new plan far less demanding: it didn’t matter where in the sky the explosions appeared. The collectors would funnel all the photons in and dazzle the cameras, regardless.

Serena said, ‘What if there’s a sensor that can bring down a shutter if the ambient light gets too bright? I mean, the light that’s meant to do this damage will be bouncing back and forth between the mirrors before it gets to the camera. There’ll be plenty of time for news of the danger to reach the camera by a shorter route.’

She was right, Agata realised. But it might not matter. ‘They can bring down a shutter to protect the camera from permanent damage… but that shutter will block the time-reversed light, too. So it will all come down to the timing: whether the flash from the explosions forces the shutter to close for so long that the signal is lost.’

Serena was quiet for a moment. ‘So how do we divert the saboteurs’ bombs? Go out there and physically move them?’

‘Maybe,’ Agata replied. ‘But I don’t know how we can get out undetected.’

Serena was incredulous. ‘You think the Council will try to stop us protecting the mountain ?’

‘Not as such – but if we’re going to tell them our plan, they’ll have known about it for the last three years. So why wouldn’t they have modified their own defences at the base to take account of what we tell them about the occulters and the explosives?’

Serena said, ‘Because we don’t tell them. Because we’re afraid that they’d find a way to prevent the explosions from causing the disruption – which would bring us back to a meteor as the cause.’ She put a hand over her eyes and massaged her temples. ‘Just when I’d stopped getting messages from myself, the future finds a new way to order me around.’

‘Has it told you how to get into the void unseen? Or do some of your army of waking sleepers happen to be airlock guards?’

‘No airlock guards,’ Serena replied, ‘but we have technicians capable of splicing photonic cables and disabling sensors.’

‘That’s not enough,’ Agata said ruefully. ‘There’ll be people at all the airlocks, from now to the disruption.’

Serena hummed angrily. ‘So do you believe we’re going to do this, or do you think we’re going to cower in our rooms and wait for whatever unfolds?’

‘I don’t know.’ Agata hadn’t been able to bring herself to reveal what Ramiro had told her about the inscription. The only certainty they had now was the disruption; there was no promise of any kind of triumph to follow.

‘Are you still working in the cooling tunnels?’ Serena asked.

‘No.’

‘But you’re familiar with the whole system?’

‘I’ve done the induction – it was fairly detailed. Why?’

Serena said, ‘Cooling air leaves the mountain – and there won’t be people guarding every vent. If my technician friends can disable the sensors, we can go out with the air and start looking for these bombs.’

Agata began buzzing softly. ‘You think they’ll let a mob of saboteurs congregate at an air vent? There are cameras in every corridor, there are people watching every move we make.’

‘Maybe your moves,’ Serena conceded. ‘The mere fact that you were on the Surveyor with the anti-messager Ramiro taints you a little. But who am I? Who are my friends? There aren’t enough people in the entire security department to watch everyone, and the software never got smart enough to take over the job. We’re not saboteurs, we’re not known dissidents. While they’re watching the usual suspects, all we have to do is avoid setting off the kind of alarms that can’t be ignored.’

In Gineto’s apartment, Vala spent a chime scrupulously copying Agata’s posture and learning to mimic her gait.

‘No one would mistake our faces,’ Vala admitted, ‘but if I hold this box of books on my shoulder to obscure my face from the camera…’ She demonstrated.

Agata had carried Medoro’s real books home in more or less the same way; a second instalment need not attract suspicion. She handed Vala the key to her apartment. ‘Happy reading.’

She waited with Serena and Gineto, practising her imitation of Vala but hoping that no one would even be watching the camera feeds. Let them all be busy following Ramiro and Tarquinia.

Serena checked the clock on her belt. ‘Time to go.’

Gineto said, ‘Good luck.’

Agata followed Serena out of the apartment, trying to appear suitably motherly: mildly affectionate but mostly aloof. Vala had always seemed bemused that two lumps of flesh shed from her body had grown into fully functioning creatures, with no further intervention on her part. The corridor wasn’t too busy, so Serena took the adjoining rope, never concealing Agata entirely from the cameras they passed, but often obscuring part of the view. Anyone with access to the feeds would be able to reconstruct every party’s true movements easily enough, in retrospect – or long before the event, if the information was recognised as important enough to send back – so their not being caught out now would be largely contingent on their not being caught out later. From their position of ignorance, success and failure seemed balanced on a knife edge, but from a cosmic point of view the two slabs of self-consistent events had been utterly distinct for at least the last three years.

As they drew nearer to the utility shaft, Agata could see a camera gazing straight down at the entrance portal. They hung back, and Serena glanced at her clock. ‘Where are they?’ she muttered. A moment later Agata heard a group of people approaching, talking and buzzing.

‘Now,’ Serena whispered. They advanced together. There were a dozen people coming the other way, spread out between the two guide ropes. Some of them, politely, tried to shift ropes to let Serena and Agata pass, but they were packed too close together along both ropes for them to all fit on either one. As the impasse clumsily sorted itself out, two women who looked like mother and daughter managed to break out of the throng and move away. Agata followed Serena down into the shaft and pulled the portal cover closed behind her. If the security sensors here hadn’t been dealt with, they wouldn’t be the first ones to trigger them: the portal’s lock had been snapped a few bells before, and most of the team was meant to have come through before them.

As they descended the ladder in the red-tinged gloom, Agata could hear the muffled hiss of gas in the tunnel beside them. No one came here on regular cleaning shifts; the warm air was inimical to moss.

When they arrived at the bottom of the shaft the darkness was impenetrable. Serena said quietly, ‘It’s us,’ and someone switched on a coherer. Agata squinted into the glare and counted two dozen and nine figures squeezed around them, already wearing their corsets, cooling bags and jetpacks. Many of them had never used the jetpacks; they should all have had one-on-one briefings earlier from their more experienced friends, but it was Agata’s job now to go through the safety checks and remind them of everything they’d forgotten.

‘If you get into trouble,’ she began, climbing two steps back up the ladder to make herself visible to everyone, ‘just draw a stop line: a straight horizontal line across your chest.’ She demonstrated. ‘The rock will still be moving below you, but don’t let that confuse you: the pack will bring you to a halt relative to the mountain’s axis, so you won’t go flying off into the void.’