Greg Egan: The Arrows of Time

Greta said, ‘Absolutely not!’

Tarquinia gave the idea some thought. ‘We don’t know the rogue’s trajectory with enough precision to ensure that we’d hit it, but I suppose we could use the explosives to make a near miss almost as good. The only trouble is… it wouldn’t take much of a course change by the rogue to ruin the whole plan. Even if you reprogrammed our navigation system so they could tweak the trajectory from the Peerless , the explosive isn’t that sophisticated: once we set the time delay, it would be impossible to change it remotely.’

Ramiro was prepared to accept this argument, but Greta felt obliged to add her own reasons. ‘The Council still wants the rogue’s navigation system analysed,’ she said. ‘The trajectory might be obvious now, but there could be other information about the perpetrators that can be gleaned by studying what they’ve done.’

‘Yeah, I’m sure they signed their names in the software.’ Ramiro didn’t doubt that there was such a thing as programming style, but the idea of identifying a saboteur on the basis of anything so vague was ludicrous. ‘I’ll be happy if we manage to keep the Station from being hit, but once that’s guaranteed I’m not risking my life humouring the Councillors.’

Greta didn’t reply; she knew better than to push him now.

‘So… we’re going ahead with the interception?’ Tarquinia asked tactfully.

Ramiro stared at the flight plan: the map of their future for the next five bells. As far as he knew, on every other occasion when two gnats had come together in the void they’d had cooperating pilots, and their main engines had been shut off for the approach. But here were the trajectories, meeting up perfectly right before his eyes.

‘Why not?’ he said. ‘What could possibly go wrong?’

At Ramiro’s request, Tarquinia showed him a version of the flight plan with their acceleration marked. Translating between the standard maps and the starry emptiness around her might have been second nature to Tarquinia, but the only way Ramiro could hope to stay oriented was by knowing which direction would feel like ‘up’ to him for the various stages along the route.

They’d already acquired a substantial velocity towards the Station on their way from the Peerless , and now they were veering sideways, bringing them closer to the rogue’s trajectory. But in a bell and a quarter they’d begin to swing the engines around, until they were using all their power to reverse. Ramiro found it utterly perverse that they could have caught up with the rogue much sooner if it had been fleeing from them, rather than heading their way: the need to match velocities wouldn’t have forced them to waste time going backwards.

‘Do you have a tuneable coherer in your toolbox?’ he asked Tarquinia.

‘Of course. Why?’

‘I think we’ll need to burn the proximity sensors, before we get too close.’ For long-range navigation the gnats relied on beacons, but to dock they picked up the reflections of their surroundings in infrared. The rogue had no hope of seeing them coming from afar, but once they tried to sidle up to it, it would know that it had company.

Tarquinia said, ‘It won’t have a lot of freedom for evasive action; if it delays its arrival too much, the Station will have moved around in its orbit. And it can’t make up lost time later; the engines are running at full power as it is.’

‘It could still shift sideways with the manoeuvring engines,’ Ramiro suggested. ‘There’d be nothing to stop it recovering from that – and it would be enough to make our job impossible.’ Once they were beside the rogue any sudden change in the main engines’ thrust would see it plummet out of sight, but it would only take the tiniest swerve to snap a boarding rope slung between the vehicles.

‘True enough,’ Tarquinia conceded. ‘But we’ll need to combine the coherer with some kind of sighting scope.’

She unplugged the photonic cable from her corset, then clambered down into the hold. As she rummaged around for the parts she needed, Ramiro contemplated her empty couch and unattended console. He’d happily imagined the Peerless driving itself for years – but in this fragile craft, rushing towards a near-collision, even the briefest absence of the pilot was enough to unsettle him.

‘How about this?’ Tarquinia handed him a scope, three clamps and a coherer. ‘The range of the sensors would be about a saunter. Through this, you should be able to see them at twice that distance.’

Ramiro said, ‘We’ll need to calibrate the alignment.’

‘Of course. Put it together, then I’ll get the optics workbench.’

‘You have an optics workbench ?’

‘A small one.’

The bench was half the size of Ramiro’s torso, but it let them measure the angle between the scope’s axis and the coherer’s beam. By the time he had the crude weapon aligned, he looked out through the dome to see that the gnat had rotated again without him even noticing. The engines were dragging them backwards now, giving them a trajectory much like the parabola of a ball thrown under gravity – albeit in some very strange game where the skill lay more in controlling the direction of the ongoing force than in the initial toss.

‘Do you have children?’ he asked Tarquinia.

‘No.’

‘So what did your brother say, when you told him about this?’

‘He wished me a safe journey,’ Tarquinia replied.

Ramiro said, ‘If I’d told my uncle, I probably wouldn’t be here at all.’

‘Hmm.’ Tarquinia sounded sympathetic, but reluctant to take sides. ‘So let’s neither of us do anything reckless,’ she said. ‘If we play this right, your family need never even know that you were out here.’

The gnat reached the top of its parabola and started falling back towards the Station. Ramiro glanced up from the navigation console, unable to dismiss a stubborn intuition that the event ought to be visible somehow, but nothing in the view through the dome had changed.

The Peerless was still tracking the rogue and sending updates; the thing was five dozen severances away, off to Ramiro’s left and ‘below’ him – in the sense of ‘down’ rammed into his body by the engines, the opposite of that in his tossed-ball analogy. He slid his head past the edge of the couch and examined the sky with his rear gaze, knowing full well that there was nothing he could hope to see. Even if he’d slipped on the ultraviolet goggles that Tarquinia had given him from her trove of gadgets, the rogue’s engines were pointed away from him. A similarly equipped passenger on the rogue might have seen the UV flare from the gnat ahead of them, but Ramiro was hoping that the saboteurs had had no chance to augment the vehicle with extra hardware.

‘We need to eat now,’ Tarquinia declared, tugging at the lid on the store beside her couch.

‘I don’t have much appetite,’ Ramiro protested.

‘That’s not the point,’ Tarquinia said flatly. ‘You’ve only had half a night’s sleep, and you’re going to need to be alert for this. It’ll take a bell for the loaves to be digested, so this is mealtime.’

Ramiro buzzed at her presumptuousness. ‘Yes, Uncle.’

‘I’m your pilot, that’s worse. Can your uncle toss you out into the void?’

He took the loaf that she handed him and bit into it dutifully. It was a struggle to force the chewed food down his oesophagus; half the flesh that usually helped him to swallow had been ossified.

When he’d finished, Ramiro brushed the crumbs from his gloves. ‘What happens if we get this wrong?’ he asked. ‘If we scare the rogue into some kind of evasive manoeuvre that changes its trajectory, but it’s still not enough to stop it hitting the Station… could that skew things so that the plume ends up aimed at the Peerless ?’