Ramiro had already entered the coordinates of the nearest cache into the software. He tapped a key on the console and a tight burst of UV erupted from the link. The confirmation came back immediately: the occulter had received the message and was proceeding to act on it.
‘Perfect!’ Tarquinia declared.
‘So far.’ It would take the occulter three days to crawl across the mountain to its first rendezvous. Ramiro pictured the prototype clanking down the plank towards him, back on the Surveyor. They’d made allowances for the machines losing their footing and needing to recover, but the complex manoeuvres required to pick up the cargo would cut into the air supply, and the extra mass being lugged around would shrink the margin for error even further.
Tarquinia said, ‘Next target.’
Their run of luck continued for a while, but the fifth occulter failed to reply. Ramiro rechecked the direction of the link, then broadened the transmission, but it made no difference.
When they’d released the occulters from the Surveyor each one had been given preassigned coordinates, but if the composition of the rock proved unsuitable they were to try again at a number of adjacent sites. A pseudo-random algorithm varied the coordinates; knowing the seed for it they could match the sequence exactly.
After a dozen steps, Ramiro gave up. If the occulter hadn’t found a secure purchase by then, it would not have had enough air left to be of any use to them even if they could locate it.
‘One in five,’ Tarquinia said. ‘We can live with that.’
By the end of the day they’d set a dozen and three occulters in motion and given up on three.
‘If Giacomo had stayed in touch with us,’ Tarquinia mused, ‘he could have spared his people the trouble of planting three of those caches.’
Ramiro said, ‘Maybe. Or maybe we’ll fumble the pick-ups on three of the others and have to go back and use the ones that seemed superfluous.’
‘That’s true.’ Tarquinia reached across and squeezed his shoulder. ‘We’re doing well.’
Ramiro was exhausted. He stared across the room and tried not to think of the machines scuttling along the slopes; the more he visualised them, the harder it became to avoid picturing a cog jamming or a drill bit coming loose. ‘At the turnaround, all our biggest problems had been solved,’ he said. ‘Every traveller before us had put up with far more hardship and uncertainty than we were facing then. So how did it come to this? Why are we the idiots who could lose it all?’
‘Stop thinking about it.’ Tarquinia took him by the arm and led him through into the bedroom.
When they’d finished, Ramiro clung to her body angrily. He’d wasted half his life on this imitation of fatherhood. If he hadn’t wanted the real thing, why did he keep chasing this shadow? He was as much a slave now as if he’d meekly followed his uncle’s commands.
Tarquinia eased herself out of his embrace.
‘What happens afterwards?’ he asked her. ‘After the disruption.’
‘After the disruption,’ she said, ‘life goes back to normal.’
28
Agata ascended the stairs slowly, her gaze cast down at the moss-lit rock, hoping that if anyone was watching her she’d appear suitably distracted: a moody theorist wandering the mountain, oblivious to her surroundings. Though every ordinary resident of the Peerless surely knew the size of the excluded zone around the axis, she hadn’t been able to bring herself to ask Serena or Gineto to tell her. There was no way to phrase the question innocently: whoever she consulted, however obliquely, would be instantly burdened with the knowledge that she was contemplating sabotage. Which might have led nowhere, or might have taken her rapidly to a place she didn’t want to be: finding a way to reassure an alarmed friend that she hadn’t gone over to the side of Medoro’s killers, but was actually striving to undermine them.
To make any progress on that task, she needed a rough idea of the dimensions of the messaging system. It was safe to assume that the designers had made every channel as long as possible, running close to the full height of the mountain, so once she knew how close to the axis the public were permitted to travel she’d have some sense of the mirrors’ width and the volume of each enclosed light path.
As Agata’s weight diminished, she continued upwards, using the guide rope beside her. The ancestors couldn’t tell her how to halt the system, but they must have chosen her for a reason – and the only hint they could give her had to be encoded in that choice itself. She had measured the bending of light by Esilio’s sun, hadn’t she? There was no prospect of using gravity to distort the light paths in the messaging system, but gravity wasn’t the only way to modify light’s passage.
A woman passed her, descending, murmuring a casual greeting. Agata had chosen the stairwell at random; she had no reason to believe that she was heading for an entrance to the facility itself. The usual tiers of apartments here should simply come to an end a little sooner than they had before the system was built.
Above her, less than a saunter away, the twelve long tubes would run from mirror to distant mirror, carrying messages from the future in beams of densely modulated time-reversed starlight. The tubes would be sealed against contamination – against dust or smoke that might scatter the light – and perhaps the Council had made an effort to render them vacuum-safe, in case the ends were breached and they were opened to the void. But that would be a matter of structural reinforcement to limit the damage from a sudden pressure difference, not a matter of impermeability. There was no such thing as a hermetic seal on a container of that size. At the very least, particles of air would be constantly diffusing in and out of the tubes.
For most purposes, air was air. So long as it was chemically inert and dense enough to serve the crucial role of carrying heat away from bodies and machinery, any finer details were of secondary importance. When the cooling system had switched from using the old engines’ exhaust to the gas produced by cold decomposition of sunstone, no one would have much cared that the range of particle sizes was different. But there were countless variations on the basic theme of a stable ball of luxagens, and different mixtures had different properties. The speed of each frequency of light was slightly different in air than in a vacuum, and the precise value depended on the precise composition of the air.
Agata reached the top of the stairs. A sign right in front of her spelt it out: LAST EXIT. She left the stairwell and dragged herself along the corridor, past the doors of the apartments. The Council would have left a large enough buffer above this unrestricted area so that a bomb planted here could not have breached the nearest of the tubes. But she had a number now, good enough to feed into an order-of-magnitude estimate: how fast could she expect a change in the air to diffuse through a resin seal into the tubes that contained the light paths?
Air was air, no one would feel a thing. But if she could make it happen, there’d be no need to damage a single component of the messaging system. The exquisitely calibrated timing of the data fed into each tube would include allowances for ordinary variations in the ‘delay’ created by the light bouncing from mirror to mirror, but once it drifted beyond that range and the signal was scrambled beyond recovery, there’d be nothing that the system could do about it – least of all send a message into the past to warn the operators of the nature of the problem.
Back in her apartment, Agata sat at her desk and worked through the calculations. If she could add a component to the air that was significantly lighter than the smallest particles in the present mixture, it would naturally rise towards the axis and diffuse into the imperfectly sealed tubes. Though a particle of air in isolation had almost no external field, each light wave that passed over it distorted its shape sufficiently to spoil the usual cancellation between the luxagens, and the secondary wave generated by that process combined with the first to slow it down.