In Hackett’s day humans had threatened life on Earth; now they had saved the last of it.

  The sky too was sparse.

  Even the Sun itself was star-like now in the sky above Earth, rather than sun-like. It had become a white dwarf, eking out the last residual heat bequeathed by its glory days of fusion burning. Hackett found it hard to believe that that shrunken relic had once been a red giant that had almost reached all the way out to the orbit of Earth itself.

  And he was startled to learn that the shrivelled Sun was the only star visible to the naked human eye. That was despite the great late burst of star-making caused by the collision of the galaxies, of the human Galaxy and Andromeda. Hackett remembered predictions that the combined super-galaxy would have begun to dim even five billion years after Andromeda arrived, as the brightest, fast-burning stars started to fade. Fifty billion years further on the stuff of which stars were made itself would be running out – all across the cosmos. And now, with the universe ten or twenty times older still, little remained of its former glory, of the age of light.

  But he was surprised to learn that the Sun retained all its planets – all save Mercury, destroyed in the red giant phase. Venus would have been lost too if not for the intervention of mankind, a heroic relocation in itself, even if it had only been a rehearsal for the shifting of Earth. Someday, still long in the future, random perturbations would dislodge the surviving planets from their star – the orbits of the planets had only ever been quasi-stable – and passing stars too could dislodge worlds, though such events had always been rare. But for now, the planets lingered.

  And if the natural environment was sparse and dark and inert now, so was the human world – to the naked eye at least. Aside from the crawling industries on the surface of the Earth, there was only a dim constellation of space habitats and other craft orbiting the planet – including, now, the relic of the Perseus, brought back from its long drift in deep intergalactic space.

  Taiva Lapic, once citizen of Mars, seemed to know little of these habitats and ships. Hackett guessed that the deep bifurcation of Earth-dwellers and space-dwellers had only deepened from ancient times.

  Indeed if this had gone on for so long it would have been no surprise if there had been some kind of speciation event, Hackett mused, evolution despite the apparent conservatism of intelligence. Sturdy troglodytic Earth-dwellers versus their spidery, big-eyed gravity-free cousins. He studied records and news feeds to investigate.

  It hadn’t happened – any more than it had happened across the meagre five million years that separated him from Icsoba’s ice-cavern people. As with other aspects of the culture of this late age, it seemed clear that the huge blurring of Substrate sleep had imposed a stifling continuity on humanity, a kind of cultural, even evolutionary inertia. The only significant difference to the naked eye was that there were a whole lot more short people than before – short and spindly, often. He guessed these were characteristics adaptive to crowded, zero-gravity environments such as cramped space habitats or to caves deep in the Earth. But given that Icsoba and her people had adapted in the same way in their icebound settlements in a mere five million years – mere, he thought – such changes were pretty minor.

  Which suited Hackett and his fellow travellers, he supposed; at least they might fit in, more or less.

  After maybe a month of this – anyhow after thirty old-style Earth-rotation days, which were still counted as a unit of time if months were not – Taiva Lapic gathered the Perseus crew together, Hackett, Rava and Sabin, and told them their various appeals to land on Earth had been successful.

  ‘As archaics, emanating from a time before the terrestrial and spacefaring branches of humanity had diverged in law, you deserved the benefit of the doubt. Also you are of scientific interest yourselves.’ She shrugged. ‘Plus, what harm could you do?’

  ‘Nothing like a warm welcome,’ Hackett said.

  Taiva studied him, eyed them all. ‘You joke. This is a serious issue. Remember, for most of the lifespan of humanity – which by now means most of the history of this aged universe – it has been clear that the only refuge we humans can count as safe, as ours, is Earth itself. Let it be overwhelmed – let it fail – and we could face extinction. That’s what we are planning to avert.’

  Rava seemed prepared to scoff. But Sabin Roos, who had held responsibility for species-wide issues herself, seemed to understand. ‘After all our travels, it’s strange to think a journey of only a couple of hundred kilometres, from orbit down to the ground, is so significant.’

  Taiva smiled thinly. ‘Oh, you’re going a lot deeper than that, my friend. Didn’t you know? And you have had some assistance with your permissions. Somebody down there has asked to see you, John Hackett.’

  64

  Three days later, after, it seemed, various detailed final clearances had been confirmed, Hackett and his companions were loaded into a small, stubby, three-legged landing craft docked by its nose to the habitat.

  Within they found chairs with seat belts, a small washroom, a smaller kitchen area where drinks and packet foods were available. Some things never changed.

  Taiva accompanied them aboard, a little irritably, Hackett thought. With her own, ancient, personal links to the crew she had clearly been the right person to welcome them to this new age, but she no doubt had her own priorities to pursue, her own projects to get back to. He supposed they ought to be grateful she wasn’t still more reluctant – if she had refused this baby-sitting chore, who would have taken her place? Evidently they had no friends here, and evoked little curiosity.

  It was hard, awkward, to remember that he had had a sexual relationship with this woman. Neither of them mentioned it; Hackett rarely thought of it. Even love did not endure in this universe, it seemed.

  With the group strapped in, the automated lander popped free of its docking port, swivelled, and pulled briskly away from the habitat.

  As the lander descended, Hackett looked out of the small ports at desolate, unrecognisable rocky landscapes drifting below.

  ‘Strange experience,’ he said. ‘For sure this is more like landing on the Moon used to be, when you stood on a flaring rocket all the way down to the surface. Whereas on Earth you would use the atmosphere, batter your way in with a heatshield, and maybe glide down to the surface – or plunge into the sea. Now, no atmosphere, no seas—’

  Taiva Lapic said, ‘Look, I got here the long way round. If you people are going to grouse about how it’s all gone downhill since the good old days of the stelliferous era I’m going back into the Substrate.’

  ‘No, no,’ said Rava. ‘We’ll be good.’

  They fell dutifully silent, and followed the view.

  They were coming down over the day side of Earth – a day nearly as dark as the night, given the dim glow of the aged Sun. It was a dull ride, the scenery only slowly changing – the featureless black sky, the ground below bare, shadowed save for a few scatterings of lights – yes, it was like the Moon, the inhabited Moon, much more than the human Earth Hackett remembered. It was sad.

  He had, he reminded himself, set out on his long journey to the stars – and, it turned out, to the future – because of a loss, the loss of his niece. And now he was dealing with a branch of mankind which had lost everything – its whole future, its dreams of a place in the cosmos – leaving only this, the hulk of the Earth, the patient, enduring mother. He felt his heart break, a little.

  At least it was home, he thought.

  The final landing was easy, seamless – imperceptible rather than gentle.

  Once down Hackett immediately unbuckled and stood up, bouncing on his toes. ‘Earth gravity,’ he said. ‘Nothing like it. Nothing feels so good, even if I did have to have that course of injections to withstand it.’ Some kind of nanobot reinforcement of his antique, much-abused muscular-skeletal structures.

  Rava Pogee said sourly, ‘People have lived away from the Earth across times many orders of magnitude longer than they ever had lived on Earth in your day. But still, maybe some lizard relic in the back of your primordial brain realises it’s come home.’

  Hackett grinned. ‘Thanks. So what now?’

  ‘I told you,’ Taiva said. ‘The descent from orbit is only the start. We’ve a way to go yet. A long way further down to go …’

  The module grew dark, and there were a couple of rumbles and bangs outside. Hackett had the impression of massive pieces of machinery moving around the exterior hull. A hiss of air.

  Then the door swung open.

  Taiva stood, led the way to the door, passed through. Wordless, the others followed.

  Hackett found himself in a kind of expanded version of the lander’s main cabin – the same hotel-room chic, the bathroom, the drinks dispenser. But here there was more than one room, others visible through open doors. Hackett glimpsed beds.

  ‘You said, further down to go. This is an elevator?’

  ‘An elevator,’ Taiva said.

  Destined to take him deep into the planet itself. An elevator like a hotel suite. An elevator with beds. A long way deep.

  ‘We’ll be moving in five minutes,’ Taiva said. ‘The journey to the edge of the core will take around twenty-four hours. Choose a room, if you think you’re going to need it.’

  Hackett goggled. ‘The core? The core of the Earth?’

  ‘The outer perimeter, yes. The iron core – about three thousand kilometres in radius. Above that you have the mantle, silicates – essentially rock, once liquid. Another three thousand kilometres. And above that the crust, a thick skin which is pretty much what humanity subsisted on before space travel – that and sunlight.’

  ‘In my day. But not any more, right?’

  ‘Once the core was kept liquid by the residual heat of its formation, and through the decay of radioactive materials in there – uranium, thorium, others. All of these have long decayed away. The core solidified when the universe was about a tenth its current age, Hackett. And not long after that, people started drilling down.’

  ‘Makes sense,’ Hackett said, though he felt overwhelmed by more astounding numbers, tremendous stretches of time. ‘If Earth is all you have, then make the most of it.’

  ‘Correct. The core is the most useful, of course – its exotic metals are used to manufacture Substrate webs down there … There are plans for the large-scale rebuilding of the planet itself. Or rather, its dismantling. But for now – well, you’ll see.’

  ‘Twenty-four hours in an elevator,’ he mused. ‘I think I will go take a nap …’

  He was napping again when the journey ground to an end, when this technological bubble reached the boundary of the core.

  He had to be woken to be told that he had a visitor. Someone asking for him. By name.

  65

  Leaving his companions, Hackett walked with Taiva Lapic out of the transport, across an apron of rock – under a coarsely finished, rocky roof, high above – and towards a moving staircase, which took him down to some deeper level. A long staircase, terminating at a floor far below – as much as a half-kilometre?

  ‘Escalator,’ he said now.

  Taiva regarded him. ‘Sorry?’

  ‘Took a while to dig up the archaic term. Archaic even in my day. I once saw a historical drama set in a shopping mall. Multiple levels, shops and boutiques and cinemas and theatres, and all connected by moving stairs. Somewhere between the nineteenth and twenty-second centuries … Although my friend Icsoba and her people rode escalators into their ice caverns. My history is getting hazy.’

  ‘Use the Substrate.’

  ‘Yeah, yeah, where all knowledge resides … It’s more fun trying to remember.’

  They reached the bottom of the escalator. Hackett, with some muscle memory of these things, if of primitive archaic forms, stepped off the moving surface easily; the others were more hesitant.

  They walked forward slowly. There were few people around, Hackett saw, most in the distance. To his right, though, was what looked like a cafeteria – tables, chairs, people talking, eating, drinking.

  Taiva asked, ‘So what do you make of this place?’

  ‘Not sure. Very brightly lit. Lots of energy to spare?’

  She shrugged. ‘We have the whole Earth, remember. And perfectly efficient mass-to-energy conversion.’

  ‘E equals m c squared.’

  ‘I’ll take it that means you understand.’

  ‘I understand that you’re burning up this one world we have, to light up a mall.’

  ‘Mall … I’m logging your language. The history you share. But the energy usage is trivial. The insolation enjoyed by the old Earth – when the Sun shone – was equivalent to the usage of a couple of kilogrammes of Earth rock per second … The universe is a trillion years old. It would take a hundred thousand times as long as that for the mass-energy of Earth to be drained in this way.’

  ‘Point taken … I should have noticed the gravity.’ He stopped, bounced on his toes. ‘Feels like a full Earth gravity. I mean, the surface gravity … Perhaps a little more?’

  ‘The core has about a third of Earth’s total mass, but about half the radius … The numbers work out.’

  Hackett nodded. ‘Of course the layers above exert no gravitational influence. If you’re in a cavity in a solid sphere, there’s no net field. Newton himself told me that.’

  ‘Hackett. Stop teasing the locals.’

  The voice came from that cafeteria. Amidst floating platters and trays, a man was getting up, approaching. He was silhouetted against the light.

  But Hackett was surprised to find he knew him.

  ‘You saved my life. Damn it, I can’t remember your name.’

  Short, a little plump, with dark hair, dressed in a cape of gold and scarlet, he might have been forty years old, if he was naturally ageing. More likely much older since he had evidently undertaken deep space missions, which were never brief, and subject to time dilation to boot.

  And then Hackett remembered. ‘Cognate. Captain Cognate!’

  The guy grinned broadly. ‘That’s close enough. Glad to see you up and about. When we found you, your ship had been drifting a long time.’

  ‘Yeah, we were lucky—’

  Before they could fit in any more reminiscing, Taiva stepped forward, intervening. She introduced herself, and described herself as Hackett’s mentor, which made Hackett cringe a little.

  ‘And I know you too, of course. Even before your recovery of the Perseus, Captain …’

  ‘Ralom Ssagla.’

  The surname started with a kind of hissing sibilant. Sshth-ag-la.

  ‘Come, sit,’ Taiva said. ‘Eat with us, please. On me. On the government.’

  So they sat, murmured their orders into the air – just fruit juice for Hackett.

  Ssagla turned to Hackett. ‘I’m not surprised your memories are muddled. But you remembered the name of my ship.’

  ‘The Cognate.’

  ‘Indeed. You were barely conscious, the whole time I encountered you. Your automated systems did wake you when I boarded you – some emergency protocol, no doubt. I fixed you up, sent you homeward, trailed you back. And I put you back into the Substrate, of course. Surprising you remember anything at all. I don’t know how much you know of the accident.’

  ‘Little enough,’ Hackett said. ‘It’s kind of embarrassing to talk about. The Perseus is pretty foolproof. Life-support systems were perfected even before I first left Earth – well, save for Substrate tech. And the dark energy ramjet couldn’t be simpler, it’s just a scoop. We were sailing between galaxies, I remember that much. Where the drive is the most efficient; there’s nothing out there but dark energy, except for—’

  ‘Except for an occasional rogue pebble,’ said Ssagla.

  ‘Enough to wreck our ramscoop. Horribly unlucky for us to hit anything.’

  ‘But,’ Ssagla said, ‘the further you travel, the more the odds stack against you. It was going to happen some day.’

  Taiva studied Ssagla. ‘And you have travelled far too, Ralom Ssagla. I looked you up. You don’t make your monumental journeys from some heavily rationalised suicidal impulse. Unlike Hackett here, you aren’t fleeing from anything. You aren’t trying to just stay alive to remember …’

  To remember Sarah. Hackett kept his counsel.

  ‘You, Ssagla, are seeking a goal, however the odds are stacked against success.’

  Ssagla looked confused at this blunt analysis; he said nothing.

  ‘Well, whatever reason he was out there, he found us,’ Hackett said. Now he frowned. ‘We were heading back to Earth. We had already shed some of our velocity – the time dilation was loosening. Then – wham.

  ‘We knew that any rescue was going to be a long time coming. I remember now … I know we even had to shut down our Substrate, to basic storage. Enough to keep our Substrate Descriptions intact, whatever the hell they are. And the Substrate matter printers were keeping the damn hull from sublimating. We were lost in deep intergalactic space for—’

  ‘Most of a trillion years,’ Taiva said gently.

  ‘My God. Still, we drifted back home, we were lost in the Oort cloud. And then you—’

  ‘Driven out there by a dark energy ramscoop of my own—’

  ‘OK, but how did you find us?’

  ‘Because I was already searching. Not for you … I have networks of artificial scouts – oh, networks thousands of light years deep, thousands of scouts, a self-replicating swarm – not looking for you, specifically; you happened to be there to be found. Some of my backers, I can tell you, were disappointed to learn that the discovery was “only” the famous Perseus captained by the immortal Hackett John.’

  ‘Actually it’s John Ha— Never mind.’

  ‘I wasn’t disappointed. At least it proved my search methods work; if there’s something to be found I’ll find it.’ He grinned. ‘Even if it’s only you.’

  ‘So what were you hoping to find?’

  Ssagla nested his fingers, and regarded Taiva cautiously. ‘Do you know, it’s so long I’ve been out there that I’ve quite lost track of whether what I’m doing out there is still legal or not.’