Greg Egan - The Arrows of Time

After a lapse or two, her body and everything around her was imbued with stillness. The view through the window was unchanged; the stars were indifferent to the sudden straightening of the Surveyor ’s history. The susurrations of the cooling system grew quieter; Agata had grown accustomed to the old sound, and the new silence made the room feel dead.

‘What now?’ she asked Tarquinia.

Tarquinia unplugged her corset. ‘That’s it. Everything’s done.’

‘What about the plants?’

Azelio said, ‘There’s no hurry. A few days without gravity isn’t going to harm them. Ramiro will help me set up the tether soon.’

‘All right.’

Agata dragged herself back to her cabin and harnessed herself to her desk. She looked up at the pictures she’d brought: Medoro, Serena, Gineto, Vala and Arianna, scattered among the colourful childish sketches that Azelio was sharing with her. If she’d commandeered the Surveyor she could have flown in a loop right back to Ancestors’ Day on the Peerless . So far as she could tell there was nothing in the physics that would forbid it – so long as she didn’t try to cut corners and make do with a semicircular route, arriving as antimatter and spoiling the party. But she hadn’t seen herself anywhere else in the crowd that day, staring longingly at her friends – and if a visitor from the future really had joined them in her absence, Medoro had done a very good job of keeping it a secret.

She looked away. Nostalgia passed the time, but it needed to be rationed. And if no one else was celebrating the Surveyor ’s parallelism with the home world, she might as well forget it and focus on her work. Though Lila had given the vacuum-energy problem to one of her students, Pelagia, Agata had decided to pursue it independently, in the hope of preventing her brain ossifying from disuse. With a wildly unfair eight-year advantage over her rival it wasn’t impossible that she’d return with a worthwhile contribution of some kind, but she hadn’t told Lila about her plans, sparing herself the weight of any expectations.

So far, she was still grappling with the notion of the vacuum. She’d read the definitive treatment by Romolo and Assunto, who’d adapted Carla’s wave mechanics to the study of fields, but all they’d really cared about was predicting the results of particle collisions. They’d deliberately sidestepped all the distracting cosmological issues, and – apart from Yalda’s insight that the cosmos had to be finite in order to prevent exponential surges in the light field – it did make sense that none of the results of any small-scale experiment should depend on whether the cosmos was a torus, a sphere, or some four-dimensional analogue of a thrice-knotted pastry.

Since all of the old-school field theorists’ measurements depended on changes in energy, rather than any absolute scale, Romolo and Assunto had been free to set the vacuum energy to zero by decree. They’d certainly understood that the true value was a difficult quantity to pin down – so they’d vaguely sketched its origins, and then subtracted it out of all their other formulas so they could concentrate on the remaining parts that were more mathematically tractable and contributed to nice, tangible things like the rate at which positive and negative luxagens annihilated each other in their experiments at the Object.

But even their formal, mathematical expression for the vacuum state was a bizarre sleight of hand: they’d imagined taking the simpler vacuum of a more pristine theory – one where all particles stood aloof from each other, refusing to interact – and writing it as a sum of pieces that each corresponded to a different energy level of the true theory. If you followed that sum over a long time, you could pick out the least rapid oscillations that represented the lowest energy level. So in all of Romolo and Assunto’s calculations, they’d pretended that everything happened in an infinitely old cosmos that had started – infinitely long ago – with the simple vacuum, from which a mathematical trick extracted the true vacuum before they set to work adding particles to it in the here and now.

Amazingly, all of this nonsense had worked well enough for their purposes, with the quantities they’d predicted confirmed by experiment again and again. But the real cosmos with its own real history and topology couldn’t be understood by grafting on an infinitely long run-up from a state that had never actually existed.

Someone knocked on the door of the cabin. Agata dragged herself over and opened it.

‘Are you busy?’ Azelio asked.

‘Not really.’

‘Do you want to help me set up the tether?’

Agata felt a surge of excitement, but then she realised that it was premature. ‘You think Tarquinia will let me do it?’

‘Didn’t she give you your void proficiency certificate?’

‘Only because she doubted that anyone else would.’

Azelio frowned. ‘Ramiro doesn’t have much more experience than you. If you’re willing to ask Tarquinia, I’ll support you.’

The two of them approached the pilot in her couch, and Tarquinia heard them out politely.

‘My job is to try to keep you all alive,’ she said. ‘This might not be an especially dangerous task, but Ramiro has the edge on you in confidence.’

Agata said, ‘If the worst comes to the worst, I’m expendable. Ramiro isn’t. If something goes seriously wrong with the automation, no one else will be able to fix it.’

‘I can get us home without automation,’ Tarquinia replied.

‘Of course.’ Agata hoped she hadn’t inadvertently insulted her. ‘But you have to admit that a lot of things would become more difficult if we were forced to do them manually.’

‘Hmm.’

Azelio said, ‘Everyone needs experience to get used to working in the void. The engines are switched off, and we’d both be wearing jetpacks; how much safer could it be? And if Agata does this now, it could make all the difference to the kind of task she can manage in an emergency.’

Tarquinia inclined her head, conceding his point. ‘But she did tell me once that she’d rather not have anyone relying on her.’

‘I was joking!’ Agata insisted. She wasn’t sure that she had been, but she certainly didn’t feel that way now.

Tarquinia said, ‘You can go out with Azelio and set up the tether, but that’s all: install it, but leave it motionless. Ramiro will go out for the spin-up. Half the task for each of you. What could be fairer?’

Sanctified by the ancestors’ gaze or not, the sky unsettled Agata. When she’d trained with Tarquinia around the Peerless , the contrasting hemispheres had made it easy to stay oriented. There were bright stars now that caught her eye, and constellations that she could commit to memory, but it took much more effort to seek out these relatively subtle cues than it had to distinguish between an empty black bowl and a riot of colour.

Azelio seemed to be focused on the Surveyor itself, so Agata followed his lead and tried to think of the disc of the hull as her horizon. Still clinging to the hand rings outside the airlock she turned her body until it was perpendicular to the disc, then she released her grip and drew a short arrow on her chest that pointed towards her head. The jetpack obliged with a gentle push in that direction; when she’d ascended half a stride above the hull she drew a stop-line that killed her velocity. The jetpack was keeping track of all the acceleration it delivered – along with any bumps and pushes she inflicted on herself – and it knew how to return her to her initial state of motion.

She followed Azelio to the rear of the hull, opposite the main cabin and its window, and halted beside him. The two agronomy pods mounted here were roughly cubical, each about as broad as Agata was tall. Azelio grasped a ring to brace himself, lit the scene with the coherer mounted on his helmet, then began turning the first of the eight wide, hollow bolts that held the first pod in place. Agata had arrived upside down for the task; she secured herself with her foot through a ring, then squatted down so she could grip another with a hand and right herself. She switched on her own coherer and squinted at the disc of brightness she’d imposed on the starlit hull; it was strange to see the sharp details summoned out of the grey shadows, as if the Surveyor of the void had become the Surveyor of the workshop again. Then she reached into the bolt closest to her and took hold of the crossbar within. The crossbar needed a twist around its own axis to disengage the spring-loaded pins that locked it in place, then it served as a handle to turn the bolt.