She looked up towards the sun, towards invisible Earth. I just want a sky clear of alien ships, she thought. And to achieve that, perhaps we will have to sacrifice much.
Reth Cana began to describe where the Callisto bugs had ‘gone’, seeking room to grow.
‘There is no time,’ he whispered. ‘There is no space. This is the resolution of an ancient debate – do we live in a universe of perpetual change, or a universe where neither time nor motion exist? Now we understand. Now we know we live in a universe of static shapes. Nothing exists but the particles that make up the universe – that make up us. Do you see? And we can measure nothing but the separation between those particles.
‘Imagine a universe consisting of a single elementary particle, an electron perhaps. Then there could be no space. For space is only the separation between particles. Time is only the measurement of changes in that separation. So there could be no time.
‘Imagine now a universe consisting of two particles…’ Gemo nodded. ‘Now you can have separation, and time.’ Reth bent and, with one finger, scattered a line of dark dust grains across the floor. ‘Let each dust grain represent a distance – a configuration of my miniature two-particle cosmos. Each grain is labelled with a single number: the separation between the two particles.’ He stabbed his finger into the line, picking out grains. ‘Here the particles are a metre apart; here a micron; here a light year. There is one special grain, of course: the one that represents zero separation, the particles overlaid. This diagram of dust shows all that is important about the underlying universe – the separation between its two components. And every possible configuration is shown at once, from this god-like perspective.’
He let his finger wander back and forth along the line, tracing out a twisting path in the grains. ‘And here is a history: the two particles close and separate, close and separate. If they were conscious, the particles would think they were embedded in time, that they are coming near and far. But we can see that their universe is no more than dust grains, the lined-up configurations jostling against each other. It feels like time, inside. But from outside, it is just – sequence, a scattering of instants, of reality dust.’
Gemo said, ‘Yes. “It is utterly beyond our power to measure the changes of things by time. Quite the contrary, time is an abstraction at which we arrive by means of the changes of things.”’ She eyed Hama. ‘An ancient philosopher. Mach, or Mar-que…’
‘If the universe has three particles,’ said Reth, ‘you need three numbers. Three relative distances – the separation of the particles, one from the other – determine the cosmos’s shape. And so the dust grains, mapping possible configurations, would fill up three-dimensional space – though there is still that unique grain, representing the special instant where all the particles are joined. And with four particles—’
‘There would be six separation distances,’ Hama said. ‘And you would need a six-dimensional space to map the possible configurations.’
Reth glared at him, eyes hard. ‘You are beginning to understand. Now. Imagine a space of stupendously many dimensions.’ He held up a dust grain. ‘Each grain represents one configuration of all the particles in our universe, frozen in time. This is reality dust, a dust of the Nows. And the dust fills configuration space, the realm of instants. Some of the dust grains may represent slices of our own history.’ He snapped his fingers, once, twice, three times. ‘There. There. There. Each moment, each juggling of the particles, a new grain, a new coordinate on the map. There is one unique grain that represents the coalescing of all the universe’s particles into a single point. There are many more grains representing chaos – darkness – a random, structureless shuffling of the atoms.
‘Configuration space contains all the arrangements of matter there could ever be. It is an image of eternity.’ He waved a fingertip through the air. ‘But if I trace out a path from point to point—’
‘You are tracing out a history,’ said Hama. ‘A sequence of configurations, the universe evolving from point to point.’
‘Yes. But we know that time is an illusion. In configuration space, all the moments that comprise our history exist simultaneously. And all the other configurations that are logically possible also exist, whether they lie along the track of that history or not.’
Hama frowned. ‘And the Callisto bugs—’
Reth smiled. ‘I believe that, constrained in this space and time, the Callisto lifeforms have started to explore the wider realms of configuration space. Seeking a place to play. Life will find a way.’
Nomi toiled up the gentle slope of the ridge that loomed above the settlement. This was one of the great ring walls of the Valhalla system, curving away from this place for thousands of kilometres, rising nearly a kilometre above the surrounding plains.
The land around her was silver and black, a midnight sculpture of ridges and craters. There were no mountains here, none at all; any created by primordial geology or the impacts since Callisto’s birth had long since subsided, slumping into formlessness. There was a thin smearing of black dust over the dirty white of the underlying ice; the dust was loose and fine-grained, and she disturbed it as she passed, leaving bright footprints.
‘…Do you understand what you’re looking at?’
The sudden voice startled her; she looked up.
It was Sarfi. She was dressed, as Nomi was, in a translucent protective suit, another nod to the laws of consistency that seemed to bind her Virtual existence. But she left no footprints, nor even cast a shadow.
Sarfi kicked at the black dust, not disturbing a single grain. ‘The ice sublimes – did you know that? It shrivels away, a metre every ten million years – but it leaves the dust behind. That’s why the human settlements were established on the north side of the Valhalla ridges. There it is just a shade colder, and some of the sublimed ice condenses out. So there is a layer of purer ice, right at the surface. The humans lived off ten-million-year frost … You’re surprised I know so much. Nomi Ferrer, I was dead before you were born. Now I’m a ghost imprisoned in my mother’s head. But I’m conscious. And I am still curious.’
Nothing in Nomi’s life had prepared her for this conversation. ‘Do you love your mother, Sarfi?’
Sarfi glared at her. ‘She preserved me. She gave up part of herself for me. It was a great sacrifice.’
Nomi thought, You resent her. You resent this cloying, possessive love. And all this resentment bubbles inside you, seeking release. ‘There was nothing else she could have done for you.’
‘But I died anyway. I’m not me. I’m a download. I don’t exist for me, but for her. I’m a walking, talking construct of her guilt.’ She stalked away, climbing the slumped ice ridge.
Gemo started to argue detail with her brother. How was it possible for isolated bacteria-like creatures to form any kind of sophisticated sensorium? – but Reth believed there were slow pathways of chemical and electrical communication, etched into the ice and rock, tracks for great slow thoughts that pulsed through the substance of Callisto. Very well, but what of quantum mechanics? The universe was not made up of neat little particles, but was a mesh of quantum probability waves. – Ah, but Reth imagined quantum probability lying like a mist over his reality dust, constrained by two things: the geometry of configuration space, as acoustic echoes are determined by the geometry of a room; and something called a ‘static universal wave function’, a mist of probability that governed the likelihood of a given Now sharing configuration space with a given other…