Greg Egan - The Arrows of Time

‘If you think that the Peerless is going to hit something, why not build an extra channel far away?’ Ramiro mused. ‘Ah – that would require some new engineering, wouldn’t it? The first plan put the light path running along the axis, making use of the rigidity of the mountain to stabilise the mirrors. So all you’ve been able to do is repeat that. Ordinarily, the instrument builders would have found a way to keep the mirrors aligned out in the void – but if they’d managed to do that someone would have heard about it long before the event. With twelve separate teams all spying on each other, they can’t even keep a secret from themselves when that’s their only real hope of success.’

‘You know a great deal less than you imagine,’ Greta said flatly.

‘Really? If only you hadn’t had to know everything yourself. You didn’t just turn traveller against traveller: you’ve turned the mere possibility of knowledge into a kind of stupefying drug.’

‘There are some flaws in the system,’ Greta conceded. ‘We’ll learn from them. After the disruption, certain things will be reorganised.’

‘ Reorganised? ’ Ramiro buzzed. ‘Will you put all the scientists and engineers in isolation, incommunicado, in the hope that that will solve the problem?’

‘Just be patient,’ she said. ‘You’ll see how things turn out.’

‘Tell me one thing, then,’ Ramiro asked solemnly. ‘Tell me there’s a pact between the Councillors to shut down all their channels voluntarily. Tell me the disruption’s nothing more than that.’

‘I can’t lie to you,’ Greta replied. ‘The disruption is not a voluntary shutdown, it’s proof of a grave threat to the integrity of the Peerless . Knowing that it’s coming will help minimise the danger and ensure the continuity of governance – but beyond that, I know no more than you do.’

Agata brought a basket of loaves from the pantry and passed it around. ‘I don’t know why everyone’s so gloomy,’ she said, breaking the silence. ‘The whole idea of a collision makes no sense to me.’

Ramiro approached the subject warily. ‘What if the Councillors and their entourage are prepared to travel to Esilio? They wouldn’t have an easy life there, but over time they might be able to build up their resources to the point where their descendants could protect the home world. There needn’t be a contradiction.’

‘I’m not talking about the inscription,’ Agata replied. ‘Whatever hit the Peerless would have to be large enough to disrupt the messaging system immediately, or there’d be a message describing the initial effects of the impact: a fire on the slopes, a breach of the hull – even if people didn’t have time to narrate it, there’d be instrument readings sent back automatically. But anything that large ought to be visible as it approached. Even if it was travelling at infinite speed, it would cast a shadow against the orthogonal stars that we could pick up with time-reversed cameras.’

Azelio was hanging on her words, desperate for reassurance. ‘What if it comes in from the wrong direction?’ he asked.

‘There is no wrong direction if you deploy the cameras properly,’ Agata insisted. ‘Suppose this meteor is approaching with infinite speed from the home cluster side. That would render it invisible from the mountain, but if it passed a swarm of time-reversed cameras looking back towards the mountain , they’d see the meteor’s shadow against the orthogonal stars before it was actually present.’

Ramiro wasn’t persuaded. ‘That all sounds good in theory, but the surveillance network certainly wasn’t that sophisticated when we left. There’d be some serious technical challenges with processing the data fast enough and getting the result back to the Peerless before the impact. It wouldn’t be trivial.’

‘And that’s the measure of things now?’ Azelio was incredulous. ‘You’re saying that everything we do to protect ourselves is only possible if it’s trivial ? I thought this was all down to probabilities! How likely is it that people who desperately want to solve these problems could just sit at their desks fretting about it, while making no progress at all?’

He turned to Agata for support, but her confidence was wavering. ‘I spent years in that state myself,’ she admitted. ‘It’s not that difficult to achieve.’

Azelio lowered his gaze. ‘We should start our own evacuation, then. Bring as many people as we can on board.’

‘I’d have no objection to that,’ Tarquinia said. ‘But once we dock, whatever happens to the Surveyor will be out of my hands.’ Ramiro had a brief fantasy of the Surveyor orbiting the mountain at a safe remove while evacuees jetted across the void to join them – but unless they were lugging six years’ worth of food there wouldn’t be much point. And even then it could only end badly, once the lucky few had to start turning the rest away.

Azelio’s expression changed abruptly. He buzzed with a kind of pained relief, as if he’d just decided that his fears were not only groundless but embarrassingly naïve. ‘Whatever else we’re missing,’ he said, ‘we know the Peerless ’s location when the disruption takes place. If we were going to be hit by something, we could avoid that just by changing course: we wouldn’t happily steer straight for the meteor.’

Ramiro said, ‘Maybe they will change course. Maybe they already did. Either way, the disruption still happens.’

‘Exactly!’ Azelio replied. ‘So it can’t be down to a collision. If changing the location were enough to stop it happening… it couldn’t happen. On Esilio, we were never forced to do anything against our will, so how could a mountain full of people with no intention of dying be forced to choose a fatal trajectory? Stumbling blindly into a collision would be one thing – but how could it happen with foreknowledge?’

Agata considered this. ‘I think your argument would hold if we knew the cause with certainty. But it’s not so clear-cut when we’re less informed – when we’re not sure that the disruption will be fatal, and we’re not sure that it involves a collision at all.’

Azelio scowled. ‘So because we can’t know that it’s a collision… it’s more likely that it is?’

‘Is that really so strange?’ Agata replied. ‘If everyone on the Peerless was confronted with the certain knowledge that the course they were on was suicidal, then there’s no way they’d persist with it – unless some freakishly unlikely set of events undermined the efficacy of their intentions. With three years’ warning to achieve the necessary swerve, what could possibly stop them? The engines would need to drop off, and every last person capable of improvising any kind of substitute would need to die of some convenient affliction. I don’t believe for a moment that the cosmos contains anything so unlikely.

‘But taking an unknown risk is different. If we don’t know exactly what would make us safe, there’s no need for an endless barrage of misfortune to keep us from finding the right solution.’

Azelio abandoned the argument and the cabin fell into a despondent silence. Ramiro almost wished he hadn’t argued against Agata’s first, cheerful verdict. He couldn’t imagine what Azelio was going through, but even his own brief, hallucinatory experiences of fatherhood offered a hint. Nothing could be more harrowing than being forced to contemplate the death of the children you’d promised to protect.

‘Maybe the Councillors are going to shut down the system themselves,’ he suggested. ‘Just because Greta denied it doesn’t mean they won’t do it.’

‘But why would they?’ Tarquinia asked irritably.