Greg Egan - The Arrows of Time

He was woken by Tarquinia’s voice and her hand on his shoulder. ‘Your turn for the watch,’ she said.

Ramiro looked up at her in the dim light. ‘I thought I’d lost you,’ he said.

‘But you didn’t.’

He unstrapped himself and reached out to embrace her. She was still wearing her own cooling bag; he opened the fastening behind her neck and pulled it down over her shoulders and arms. When she was bare he pressed himself against her chest; an urgent pleasure affirmed the rightness of it, and then he felt their skin adhering.

He looked down and saw the light passing between them. He tried to pull free, but Tarquinia stopped him.

‘You can’t hurt me,’ she said. ‘After shedding two children, I can’t fission.’

Ramiro wanted to believe her, but he was afraid that they’d reached the point where they could talk each other into anything. ‘How do you know?’

‘We’re not the first people to put it to the test.’

Tarquinia eased them together onto the bed, then she brought the straps around them and pulled them tight. The sense of being confined in this state made Ramiro dizzy with joy; he closed his eyes and sank into the warmth suffusing their bodies.

He didn’t care any more what the truth was: if the woman he loved had made him her co-stead, that was her choice. And if she went the way of women, he’d happily raise her children. He couldn’t understand how he’d ever feared that. It was what he was meant for.

Tarquinia shook him awake a second time.

‘Ramiro? It’s been half a bell. Someone should be on watch.’

He shifted against the cool sand. She’d loosened the straps, but their bodies were still touching.

‘What happened?’

She said, ‘We exchanged light. And I’m still here.’

‘It could have gone wrong.’ Ramiro felt himself shivering. ‘I could have killed you.’ Leaving the Surveyor with no pilot, and four newborn children to care for. ‘I must have been insane.’

Tarquinia said, ‘I’ve known a dozen women who’ve survived this. Believe me, if I hadn’t been sure I would have fought you off.’

Ramiro didn’t doubt her, but it didn’t change the fact that he hadn’t been sure himself.

He found the catches on the straps and released himself from the bed, then he grabbed a rope and dragged himself away. In the end he’d let his instincts rule him; he’d become the contemptible animal he’d been warned of all his life.

Tarquinia watched him struggling into his cooling bag. ‘People do this,’ she said. ‘We both enjoyed it, and no one got hurt. It’s not some terrible crime.’

‘If it’s so ordinary,’ he retorted, ‘why don’t they talk about it? Why isn’t it in the biology course taught to every child?’

Tarquinia took the question seriously. ‘I suppose they want men to concentrate on rearing their sister’s children, instead of getting distracted chasing after women whose brothers are already doing the right thing.’

Ramiro turned to face her. ‘ I wanted you to fission . While we were together, I didn’t care if you lived or died.’

Tarquinia met his gaze, unperturbed. ‘And I felt the same way, Ramiro. I wanted exactly what you wanted. Our bodies don’t hand out rewards to people who merely go through the motions. To steal the most pleasure from this, you have to come as close as you can to believing that it’s the real thing.’

As the Surveyor drew closer to Esilio’s sun, Agata willed the days to stop slipping away so quickly, robbing her of precious time to work.

It had taken her four years to reshape the foundations of field theory into a form that made sense to her: a kind of dissection of the behaviour of fundamental particles into a series of simple diagrams. When a photon moved from one place to another, the first diagram of the series showed this happening entirely uneventfully. But in the second diagram, the photon was shown giving up its energy to the luxagen field to create a pair of disturbances with positive and negative source strength, which travelled for a while before recombining into a replacement for the original photon.

In a sense it was just like the old double-slit experiment that Yalda’s teacher, Giorgio, had used to convince people that light was a wave: light couldn’t be passing through one slit or the other, because the pattern of bright and dark lines it made could only be understood by adding contributions due to the light taking paths through both slits. But in Agata’s version the set of ‘paths’ included not only a variety of routes, but all manner of transmogrifications along the way.

She had baulked at this, at first: a lone photon couldn’t turn into a pair of luxagens – each with just a third of the photon’s mass – because whatever the velocities of those luxagens, it would be impossible to satisfy the laws of conservation of energy and momentum. But she’d finally understood that each of the diagrams on its own was just a kind of fiction, expressing a narrow sliver of the true history, and any characters that came and went without being present at the start and end of each story were mere flights of fancy, subject to very different rules compared with those that endured. Every part was needed to make up the whole, but only the totality was real.

With any process the variations were endless, but the more complex the diagram the smaller its contribution, allowing the sum to remain finite. And in this scheme, the vacuum itself was simply the sum of all diagrams that started and ended with no particles at all, its energy due entirely to disturbances that came and went of their own accord, with no connection to anything persistent.

Agata had been gratified to discover that, in flat space at least, these diagrams rendered the vacuum manageable. But if the vacuum energy curved space, then flat space was actually impossible – and if curvature modified the vacuum energy, the two could only be in harmony at some elusive fixed point that remained beyond the reach of her methods.

Having come so far, she ached to complete the story. She wanted to return to the Peerless with everything solved: the vacuum energy tied to the curvature of space and the topology of the cosmos – determining once and for all whether the entropy gradient that had enabled life was a stupendously improbable fluke, or simply an unavoidable consequence of a few simple principles.

When she lifted her gaze up from her desk, the prospect of the Surveyor ’s planetfall was glorious and thrilling, the purpose of their journey finally to be fulfilled. But when she looked down at her unfinished calculations, she thought: glorious – but please, not yet.

Gathered with the rest of the crew around Tarquinia’s console, Agata compared the two images on the screen. One was a grey disc faintly mottled with reds and browns, weakly but uniformly lit, grainy and poorly resolved as the photodetectors struggled at the limits of their sensitivity. The other was a disc of the same size, and two-thirds of it lay in the deepest black night, but the crescent of dayside revealed an impossibly vivid landscape of jagged grey mountains, dusty red plains and twisted brown valleys, sharp enough to touch.

Esilio by the light of the home cluster’s stars, and Esilio by the light of its sun. Esilio as they’d see it with their own eyes, and Esilio through the time-reversed camera. Esilio as it had been a few chimes ago – and Esilio as it would be a few chimes in the future.