Stef said now, ‘But Titus asked a good question, Earthshine. What meaningful preparations can we make? I think it’s time to stop being enigmatic. Tell us straight what’s on your mind.’ She scowled. ‘Or is this some cruel trick?’

‘No,’ he said earnestly. ‘Not a trick. It is a sliver of hope. Listen, please. We have discussed this many times. You do understand what is to happen? This universe – and all those near it in the multiverse, near in probability space – this universe will intersect a boundary, the edge of the multiverse itself. In essence, time will cease. The End Time – that is a literal description.’

The ColU unit was sitting on a blanket, an honorary human among humans. It said, ‘Imagine that the whole of this world is a simulation, supported in the memory banks of some vast computer – the way Earthshine can project a simulation of a human body. When the boundary comes it will be as if that simulation is frozen. Paused. You would not feel anything. But your stories would be ended, as cleanly as if you had paused some projected virtual show, and never restarted it, leaving the characters in limbo.’

‘Except,’ Earthshine said, ‘we know it won’t be as simple as that. It won’t be a perfectly sharp cut-off. Everything in nature is uncertain – everything is smeared. And so will be the multiverse boundary.’

Stef said, ‘Which is why the kernels work. They are wormholes connecting us to the boundary, and what we find there is a huge outpouring of energy.’

‘That’s it,’ Earthshine said. ‘Every particle in the universe follows a world line, a kind of graph threaded through spacetime. And every world line, every particle, must end at the multiverse boundary. In that way it’s like an event horizon – like the edge of a black hole, but a black hole absorbs. This is like a tremendous mirror, or a furnace, if you like, where every last grain of creation will be thermalised – burned up as heat energy. And as the energies of all the terminating particles pile up there, indeed are reflected back, there will be a last infernal carnival of creation, as that energy nucleates into new particles, which will immediately be swept over by the advancing boundary … ‘

The ColU said now, ‘These huge energies have already had an influence on our universe, observable effects. These were distortions I detected in the cosmic background radiation, as if our universe is recoiling from what is to become of it. That was how I was able to calculate the timing of this event, roughly, long before we got here.’

Earthshine said, ‘The important point now is that the boundary is smeared, just a little. Quantum uncertainty mandates it. The destruction it brings will not be quite instantaneous. And that gives us a sliver of an opportunity—’

‘No,’ Beth said, suddenly understanding. ‘The Dreamers. It’s given the Dreamers an opportunity, to help us.’

‘You understand, Beth Eden Jones,’ the ColU said. ‘You always did have a good intuition about Hatches.’

Mardina frowned. ‘What are you talking about?’

‘The Hatch,’ Beth said, and she took Mardina’s hands. ‘Remember? After Ari and Inguill went through, and Earthshine’s probe. After we opened it again, the Hatch had changed. It’s just like the first Hatch I ever saw, with my father, at the substellar. Buried in the jungle. Grooves appeared in its surface. I was the first to understand – they were grooves to hold the bodies of builders. And when the builders climbed into the grooves, it was like putting a key in a lock. You see?’

‘Ah,’ Titus said. ‘And now in the doorway, when our Hatch was opened up for Ari and Inguill – recesses for hands. Human hands.’

‘I think the Dreamers are telling us something,’ Earthshine said. ‘On some level they know we’re here. I always have the impression that they can’t see us clearly – they don’t understand us, or our nature, or not sufficiently. But they know we’re here.’

Beth said eagerly, ‘Yes, that’s it. They’re saying we can go through the Hatch. We humans. Through to—’

‘The past,’ Earthshine said gravely. ‘It must be someplace else in space, some other world, another history. But it has to be the past, from this point, for there’s no future. And there is plenty of past to choose from. Seventeen billion years of it …’

Chu frowned. ‘How could you even know where you were? In space or time.’

‘Good question,’ Earthshine said. ‘If the travellers remain on Per Ardua, perhaps we could prepare maps of the stars, at different epochs. Even of the position and size of Andromeda. But if you translate through space as well as time … Well, these are details. The journey is the thing.’

Mardina clutched her baby, who stirred and gurgled. ‘Then there’s hope.’

But Stef said gravely, ‘Only three. Remember? That was how he opened this conversation. Only three. Only three of us can do this, pass through the Hatch. Is that what you mean, Earthshine?’

And suddenly the group seemed an enormous crowd: Mardina and her baby, sitting between Chu and her mother Beth; Titus with his daughter clutching his one good hand; Stef sitting alone – and the ColU and Earthshine, two artificial people. Seven of them, or nine, depending on your definition. Of whom only three could survive.

‘Why?’ Mardina found her voice came out as a snarl. ‘Why only three?’

Earthshine sighed. ‘I suspect it is simply because of the world we sit in. Per Ardua. The records show that the builders, using Hatches—’

‘Ah. I remember,’ Beth said. ‘The builders did everything in threes. Their bodies had triple symmetries – three legs. They moved in groups of three, or threes of threes – nine, or twenty-seven.’ She laughed, bitterly. ‘These Dreamers of yours can’t tell how many we are, Earthshine! They can’t tell the difference between us and builders!’

‘Which only shows how remote they are from us,’ Earthshine said. ‘Yet they are trying to be – kind.’

Titus growled, ‘And so we have the game before us – the board set out, and we can’t change the rules. Three to go through, six to remain. And we must decide which three, right now.’

Mardina saw people pull back, as if more shocked by that pronouncement than by Earthshine’s revelations. As for herself, she clutched her baby harder. The sting of hope in her chest was more painful than the despair.

Stef looked small and frail, a blanket over her shoulders. But she said firmly, ‘Titus, it’s too soon. We have a little time left, time to think.’

‘No. In war I have seen similar situations. Some must die so the others can live. We decide this now, and we stick to the decision. Otherwise we will tear ourselves apart. Perhaps literally; we might destroy each other, fighting for a place. Why, I remember once on campaign—’

‘We would not do that,’ Clodia said.

‘We might,’ Stef said ruefully. She turned to Mardina. ‘You, Mardina, and the baby. If nobody else – you. You two are the future of this peculiar little extended family of ours. Of course you must live.’

Mardina felt tears well. ‘But—’

‘No.’ Titus held up his hand. ‘No arguments. Of course she is right; we would not be human if we chose otherwise.’

The ColU said, ‘I am not human at all, and I concur. And as for myself and Earthshine, we should be ruled out. We are created beings, created to serve humanity. And how better can we serve humans now than by saving as many of you as we can? But I speak for myself. Earthshine, your origin is more complicated than mine—’

‘Oh, I’m staying right here,’ Earthshine said. ‘I want to see the End Time firework display. Seventeen billion years in the making – I wouldn’t miss it for the world.’ He seemed to think that over. ‘Ha! I made a joke.’

‘And I will stay,’ Stef said. ‘I’ve done my Hatch-hopping, and I’m too old for babies. Too old even to babysit. And, yes, I admit I’m curious too about the End Time. An entirely novel physical phenomenon. We should work up an observation suite, Earthshine. Do some decent science. Perhaps there will be time to debunk a few theories before the lights go out.’