'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 godlike 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 change 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 a 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 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.'
