‘Perhaps you understand that the universe has more dimensions than the macroscopic, the three spatial and one of time. Most of the extra dimensions are extremely small.’ A technical sidebar translated this for Hex as ‘Planck scale’. ‘But one extra dimension is rather larger, perhaps as much as a millimetre. You must think of the universe, then, as a blanket of spacetime, stretching thirteen billion years deep into the past and some twelve billion light years across—’

‘And a millimetre thick,’ said Hella.

‘There are believed to be many such universes, stacked up’ - the translator boxes hesitated, searching for a simile - ‘like leaves in a book. Also our own universe may be folded back on itself, creased in the thin dimension.’

Engineer Jul said, ‘So what? We know about the extra dimensions. We use them when we hyperdrive.’

‘But,’ said the Ghost, ‘your applications are not currently on the scale of ours.’

‘Tell us about g-waves,’ Teel commanded.

The Ghost said that all forms of energy were contained within the ‘blanket’ of the universe - all save one. Gravity waves could propagate in the extra dimensions, reaching out to the other universes believed to be stacked out there. The Ghosts had learned to focus the gravitational energy raining into their own universe from another.

‘The energy source in the other universe is necessarily large,’ the Integumentary said. ‘Alternatively it may be a remote part of our own universe, an energy-rich slice of spacetime - the instants after the initial singularity for instance, folded back. We aren’t sure. You understand that this weapon offers us a virtually unlimited source of power. It’s just a question of tapping it. Beyond weaponry, many large-scale projects become feasible.’

Hella said, ‘I wonder what “large-scale” might mean for a species of universe-botherers like the Silver Ghosts.’

Teel said, ‘Even when we were friendly with them the Ghosts scared us, I think.’

Hex had had enough of awe. ‘Let’s talk about the target. This weapon system is in the control of the Black Ghost . . .’

Recently the Ghosts had suddenly been scoring victories against the human forces. Their tactics had undergone a revolution that must reflect a change in their command structure, perhaps their very society.

‘Humans work in hierarchies,’ Teel said. ‘Chains of command. All large-scale military organisations in the past have done so. We tend to think it’s the only way to operate, but in fact it’s a very human way to work.’

‘An evolutionary legacy of your past,’ the Integumentary said. ‘When you were squabbling apes in some dismal forest, in thrall to the strongest male—’

‘Shut up,’ Teel said without emotion. ‘Ghosts, however, have always worked differently. Their organisation is more fluid, bottom-up, with distributed decision-making. The whole of their society is self-organising.’

‘Like a Coalescence,’ Borno said with disgust.

‘Like a hive, yes.’