56 – Perturbation Theory

   From: Professor Paul Kreuger, FRS, etc.
   To: The Editor, NATURE Data Bank (Public access)
   Subject: MOUNT ZEUS AND JOVIAN DIAMONDS

   As is now well understood, the Europan formation known as 'Mount Zeus' was originally part of Jupiter. The suggestion that the cores of the gas giants might consist of diamond was first made by Marvin Ross of the University of California's Lawrence Livermore National Laboratory in a classic paper 'The ice layer in Uranus and Neptune – diamonds in the sky?' (Nature, Vol 292, No. 5822, pp. 435-6, 30 July 1981). Surprisingly, Ross did not extend his calculations to Jupiter.
   The sinking of Mount Zeus has produced a veritable chorus of lamentations, all of which are totally ridiculous – for the reasons given below.
   Without going into details, which will be presented in a later communication, I estimate that the diamond core of Jupiter must have had an original mass of at least 10^28 grams. This is ten billion times that of Mount Zeus.
   Although much of this material would doubtless have been destroyed in the detonation of the planet and the formation of the – apparently artificial – sun Lucifer, it is inconceivable that Mount Zeus was the only fragment to survive. Although much would have fallen back on to Lucifer, a substantial percentage must have gone into orbit – and must still be there. Elementary perturbation theory shows that it will return periodically to its point of origin. It is not, of course, possible to make an exact calculation, but I estimate that at least a million times the mass of Mount Zeus is still orbiting in the vicinity of Lucifer. The loss of one small fragment, in any case most inconveniently located on Europa, is therefore of virtually no importance. I propose the establishment, as soon as possible, of a dedicated space-radar system to search for this material.
   Although extremely thin diamond film has been mass-produced since as long ago as 1982, it has never been possible to make diamond in bulk. Its availability in megaton quantities could totally transform many industries and create wholly new ones. In particular, as was pointed out by Isaacs et al almost a hundred years ago (see Science, 151, pp. 682-3, 1966) diamond is the only construction material which would make possible the so-called 'Space elevator', allowing transportation away from Earth at negligible cost. The diamond mountains now orbiting among the satellites of Jupiter may open up the entire Solar System; how trivial, by comparison, appear all the ancient uses of the quartic-crystallized form of carbon!
   For completeness, I would like to mention another possible location for enormous quantities of diamond – a place, unfortunately, even more inaccessible than the core of a giant planet...
   It has been suggested that the crusts of neutron stars may be largely composed of diamond. As the nearest known neutron star is fifteen light years away, and has a surface gravity seventy thousand million times that of Earth, this can hardly be regarded as a plausible source of supply.
   But then – who could ever have imagined that one day we would be able to touch the core of Jupiter?

57 – Interlude on Ganymede

   'These poor, primitive colonists!' lamented Mihailovich. 'I'm horrified – there's not a single concert grand on the whole of Ganymede! Of course, the thimbleful of optronics in my synthesizer can reproduce any musical instrument. But a Steinway is still a Steinway – just as a Strad is still a Strad.'
   His complaints, though not altogether serious, had already aroused some counter-reactions among the local intelligentsia. The popular Morning Mede programme had even commented maliciously: 'By honouring us with their presence, our distinguished guests have – if only temporarily – raised the cultural level of both worlds...'
   The attack was aimed chiefly at Willis, Mihailovich and M'Bala, who had been a little too enthusiastic in bringing enlightenment to the backward natives. Maggie M had created quite a scandal with an uninhibited account of Zeus-Jupiter's torrid love affairs with Io, Europa, Ganymede and Callisto. Appearing to the nymph Europa in the guise of a white bull was bad enough, and his attempts to shield Io and Callisto from the understandable wrath of his consort Hera were frankly pathetic. But what upset many local residents was the news that the mythological Ganymede was of quite the wrong gender.
   To do them justice, the intentions of the self-appointed cultural ambassadors were completely praiseworthy, though not entirely disinterested. Knowing that they would be stranded on Ganymede for months, they recognized the danger of boredom, after the novelty of the situation had worn off. And they also wished to make the best possible use of their talents, for the benefit of everyone around them. However, not everyone wished – or had time – to be benefited, out here on the high-technology frontier of the Solar System.
   Yva Merlin, on the other hand, fitted in perfectly, and was thoroughly enjoying herself. Despite her fame on Earth, few of the Medes had ever heard of her. She could wander around, in the public corridors and pressure domes of Ganymede Central, without people turning their heads or exchanging excited whispers of recognition. True, she was recognized – but only as another of the visitors from Earth.
   Greenburg, with his usual quietly efficient modesty, had fitted into the administrative and technological structure of the satellite and was already on half a dozen advisory boards. His services were so well appreciated that he had been warned he might not be allowed to leave.
   Heywood Floyd observed the activities of his shipmates with relaxed amusement, but took little part in them. His chief concern now was building bridges to Chris, and helping his grandson plan his future. Now that Universe – with less than a hundred tons of propellant left in its tanks – was safely down on Ganymede, there was much to be done.
   The gratitude that all aboard Galaxy felt towards their rescuers had made it easy to merge the two crews; when repairs, overhaul and refuelling were complete, they would fly back to Earth together. Morale had already been given a great boost by the news that Sir Lawrence was drawing up the contract for a greatly improved Galaxy II – though construction was not likely to begin until his lawyers had settled their dispute with Lloyd's. The underwriters were still trying to claim that the novel crime of space hijacking was not covered by their policy.
   As for that crime itself, no-one had been convicted, or even charged. Clearly, it had been planned, over a period of several years, by an efficient and well-funded organization. The United States of Southern Africa loudly protested innocence, and said it welcomed an official enquiry. Der Bund also expressed indignation, and of course blamed SHAKA.
   Dr Kreuger was not surprised to find angry but anonymous messages in his mail, accusing him of being a traitor. They were usually in Afrikaans, but sometimes contained subtle mistakes in grammar or phraseology which made him suspect that they were part of a disinformation campaign.
   After some thought, he passed them onto ASTROPOL – which probably already has them, he told himself wryly. ASTROPOL thanked him, but, as he expected, made no comments.
   At various times, Second Officers Floyd and Chang and other members of Galaxy's crew were treated to the best dinners on Ganymede by the two mysterious out-wonders whom Floyd had already met. When the recipients of these (frankly disappointing) meals compared notes afterwards, they decided that their polite interrogators were trying to build up a case against SHAKA, but were not getting very far.
   Dr van der Berg, who had started the whole thing – and had done very well out of it, professionally and financially – was now wondering what to do with his new opportunities. He had received many attractive offers from Earth universities and scientific organizations – but, ironically, it was impossible to take advantage of them. He had now lived too long at Ganymede's one-sixth of a gravity, and had passed the medical point of no return.
   The Moon remained a possibility; so did Pasteur, as Heywood Floyd explained to him.
   'We're trying to set up a space university there,' he said, 'so that off-worlders who can't tolerate one gee can still interact in real time with people on Earth. We'll have lecture halls, conference rooms, labs – some of them will only be computer-stored, but they'll look so real you'd never know. And you'll be able to go videoshopping on Earth, to make use of your ill-gotten gains.'
   To his surprise, Floyd had not only rediscovered a grandson – he had adopted a nephew; he was now linked to van der Berg as well as Chris by a unique mix of shared experiences. Above all, there was the mystery of the apparition in the deserted Europan city, beneath the looming presence of the Monolith.
   Chris had no doubts whatsoever. 'I saw you, and heard you, as clearly as I do now,' he told his grandfather. 'But your lips never moved – and the strange thing is that I didn't feel that was strange – it seemed perfectly natural. The whole experience had a – relaxed feeling about it. A little sad – no, wistful would be a better word. Or maybe resigned.'
   'We couldn't help thinking of your encounter with Bowman, aboard Discovery,' added van der Berg.
   'I tried to radio him before we landed on Europa. It seemed a naïve thing to do, but I couldn't imagine any alternative. I felt sure he was there, in some form or other.'
   'And you never had any kind of acknowledgement?'
   Floyd hesitated. The memory was fading fast, but he suddenly recalled that night when the mini-monolith had appeared in his cabin.
   Nothing had happened, yet from that moment onwards he had felt that Chris was safe, and that they would meet again.
   'No,' he said slowly. 'I never had any reply.' After all, it could only have been a dream.

VIII – THE KINGDOM OF SULPHUR

58 – Fire and Ice

   Before the age of planetary exploration opened in the late twentieth century, few scientists would have believed that life could have flourished on a world so fan from the Sun. Yet for half a billion years, the hidden seas of Europa had been at least as prolific as those of Earth.
   Before the ignition of Jupiter, a crust of ice had protected those oceans from the vacuum above. In most places the ice was kilometres thick, but there were lines of weakness where it had cracked open and torn apart. Then there had been a brief battle between two implacably hostile elements, which came into direct contact on no other world in the Solar System. The war between Sea and Space always ended in the same stalemate; the exposed water simultaneously boiled and froze, repairing the armour of ice.
   The seas of Europa would have frozen completely solid long ago, without the influence of nearby Jupiter. Its gravity continually kneaded the core of this little world; the forces that convulsed Io were also working here, though with much less ferocity. The tug of war between planet and satellite caused continual submarine earthquakes, and avalanches which swept with amazing speed across the abyssal plains.
   Scattered across those plains were countless oases, each extending for a few hundred metres around a cornucopia of mineral brines gushing from the interior. Depositing their chemicals in a tangled mass of pipes and chimneys, they sometimes created natural parodies of ruined castles or Gothic cathedrals, from which black, scalding liquids pulsed in a slow rhythm, as if driven by the beating of some mighty heart. And, like blood, they were the authentic sign of life itself.
   The boiling fluids drove back the deadly cold leaking down from above, and formed islands of warmth on the seabed. Equally important, they brought from Europa's interior all the chemicals of life. Here, in an environment which would otherwise be totally hostile, were abundant energy and food. Such geothermal vents had been discovered in Earth's oceans, in the same decade that had given mankind its first glimpse of the Galilean satellites.
   In the tropical zones close to the vents flourished myriads of delicate, spidery creatures that were the analogues of plants, though almost all were capable of movement. Crawling among these were bizarre slugs and worms, some feeding on the 'plants', others obtaining their food directly from the mineral-laden waters around them, At greater distances from the source of heat – the submarine fire around which all these creatures warmed themselves – were sturdier, more robust organisms, not unlike crabs or spiders.
   Armies of biologists could have spent lifetimes studying a single small oasis. Unlike the Palaeozoic terrestrial seas, Europa's hidden ocean was not a stable environment, so evolution had progressed swiftly here, producing multitudes of fantastic forms. And they were all under indefinite stay of execution; sooner or later, each fountain of life would weaken and die, as the forces that powered it moved their focus elsewhere. The abyss was littered with the evidence of such tragedies – cemeteries holding skeletons and mineral-encrusted remains where entire chapters had been deleted from the book of life.
   There were huge shells, looking like trumpets larger than a man. There were clams of many shapes – bivalves, and even trivalves. And there were spiral stone patterns, many metres across, which seemed an exact analogy of the beautiful ammonites that disappeared so mysteriously from Earth's oceans at the end of the Cretaceous period.
   In many places, fires burned in the abyss, as rivers of incandescent lava flowed for scores of kilometres along sunken valleys. The pressure at this depth was so great that the water in contact with the red-hot magma could not flash into steam, and the two liquids co-existed in an uneasy truce.
   Here, on another world and with alien actors, something like the story of Egypt had been played long before the coming of man. As the Nile had brought life to a narrow ribbon of desert, so these rivers of warmth had vivified the Europan deep. Along their banks, in bands seldom more than a kilometre wide, species after species had evolved and flourished and passed away. And some had left monuments behind, in the shape of rocks piled on top of each other, or curious patterns of trenches engraved in the seabed.
   Along the narrow bands of fertility in the deserts of the deep, whole cultures and primitive civilizations had risen and fallen. And the rest of their world had never known, for all these oases of warmth were as isolated from one another as the planets themselves. The creatures who basked in the glow of the lava river, and fed around the hot vents, could not cross the hostile wilderness between their lonely islands. If they had ever produced historians and philosophers, each culture would have been convinced that it was alone in the Universe.
   And each was doomed. Not only were its energy sources sporadic and constantly shifting, but the tidal forces that drove them were steadily weakening. Even if they developed true intelligence, the Europans must perish with the final freezing of their world.
   They were trapped between fire and ice – until Lucifer exploded in their sky, and opened up their universe.
   And a vast rectangular shape, as black as night, materialized near the coast of a new-born continent.

59 – Trinity

   'That was well done. Now they will not be tempted to return.'
   'I am learning many things; but I still feel sad that my old life is slipping away.'
   'That too will pass; I also returned to Earth, to see those I once loved. Now I know that there are things that are greater than love.'
   'What can they be?'
   'Compassion is one. Justice. Truth. And there are others.'
   'That is not difficult for me to accept. I was a very old man, for one of my species. The passions of my youth had long since faded. What will happen to – to the real Heywood Floyd?'
   'You are both equally real. But he will soon die, never knowing that he has become immortal.'
   'A paradox – but I understand. If that emotion survives, perhaps one day I may be grateful. Should I thank you – or the Monolith? The David Bowman I met a lifetime ago did not possess these powers.'
   'He did not; much has happened in that time. Hal and I have learned many things.'
   'Hal! Is he here?'
   'I am, Dr Floyd. I did not expect that we should meet again – especially in this fashion. Echoing you was an interesting problem.'
   'Echoing? Oh – I see. Why did you do it?'
   'When we received your message, Hal and I knew that you could help us here.'
   'Help – you?'
   'Yes, though you may think it strange. You have much knowledge and experience that we lack. Call it wisdom.'
   'Thank you. Was it wise of me to appear before my grandson?'
   'No: it caused much inconvenience. But it was compassionate. These matters must be weighed against each other.'
   'You said that you needed my help. For what purpose?'
   'Despite all that we have learned, there is still much that eludes us. Hal has been mapping the internal systems of the Monolith, and we can control some of the simpler ones. It is a tool, serving many purposes. Its prime function appears to be as a catalyst of intelligence.'
   'Yes – that had been suspected. But there was no proof.'
   'There is, now that we can tap its memories – or some of them. In Africa, four million years ago, it gave a tribe of starving apes the impetus that led to the human species. Now it has repeated the experiment here – but at an appalling cost.
   'When Jupiter was converted into a sun, so that this world could realize its potential, another biosphere was destroyed. Let me show it to you, as I once saw it...'

   Even as he fell through the roaring heart of the Great Red Spot, with the lightning of its continentwide thunderstorms detonating around him, he knew why it had persisted for centuries, though it was made of gases far less substantial than those that formed the hurricanes of Earth. The thin scream of hydrogen wind faded as he sank into the calmer depths, and a sleet of waxen snowflakes – some already coalescing into barely palpable mountains of hydrocarbon foam – descended from the heights above, It was already warm enough for liquid water to exist, but there were no oceans here; this purely gaseous environment was too tenuous to support them.
   He descended through layer after layer of cloud, until he entered a region of such clarity that even human vision could have scanned an area more than a thousand kilometres across. It was only a minor eddy in the vaster gyre of the Great Red Spot; and it held a secret that men had long guessed, but never proved.
   Skirting the foothills of the drifting foam mountains were myriads of small, sharply defined clouds, all about the same size and patterned with similar red and brown mottlings. They were small only as compared with the inhuman scale of their surroundings; the very least would have covered a fair-sized city.
   They were clearly alive, for they were moving with slow deliberation along the flanks of the aerial mountains, browsing off their slopes like colossal sheep. And they were calling to each other in the metre band, their radio voices faint but clear against the cracklings and concussions of Jupiter itself.
   Nothing less than living gasbags, they floated in the narrow zone between freezing heights and scorching depths. Narrow, yes – but a domain far larger than all the biosphere of Earth.
   They were not alone. Moving swiftly amongst them were other creatures, so small that they could easily have been overlooked. Some of them bore an almost uncanny resemblance to terrestrial aircraft, and were of about the same size. But they too were alive – perhaps predators, perhaps parasites, perhaps even herdsmen.
   And there were jet-propelled torpedoes like the squids of the terrestrial oceans, hunting and devouring the huge gasbags. But the balloons were not defenceless; some of them fought back with electric thunderbolts and with clawed tentacles like kilometre-long chainsaws.
   There were even stranger shapes, exploiting almost every possibility of geometry – bizarre, translucent kites, tetrahedra, spheres, polyhedra, tangles of twisted ribbons... The gigantic plankton of the Jovian atmosphere, they were designed to float like gossamer in the uprising currents, until they had lived long enough to reproduce; then they would be swept down into the depths to be carbonized and recycled in a new generation.
   He was searching a world more than a hundred times the area of Earth, and though he saw many wonders, there was nothing here that hinted of intelligence. The radio voices of the great balloons carried only simple messages of warning or of fear. Even the hunters, who might have been expected to develop higher degrees of organization, were like the sharks in Earth's oceans – mindless automata.
   And for all its breathtaking size and novelty, the biosphere of Jupiter was a fragile world, a place of mists and foam, of delicate silken threads and paper-thin tissues spun from the continual snowfall of petrochemicals formed by lightning in the upper atmosphere. Few of its constructs were more substantial than soap bubbles; its most terrifying predators could be torn to shreds by even the feeblest of terrestrial carnivores.

   'And all these wonders were destroyed – to create Lucifer?'
   'Yes. The Jovians were weighed in the balance against the Europans – and found wanting. Perhaps, in that gaseous environment, they could never have developed real intelligence. Should that have doomed them? Hal and I are still trying to answer this question; that is one of the reasons why we need your help.'
   'But how can we match ourselves against the Monolith – the devourer of Jupiter?'
   'It is only a tool: it has vast intelligence – but no consciousness. Despite all its powers – you, Hal and I are its superior.'
   'I find that very hard to believe. In any event – something must have created the Monolith.'
   'I met it once – or as much of it as I could face – when Discovery came to Jupiter. It sent me back as I am now, to serve its purpose on these worlds. I have heard nothing of it since; now we are alone – at least for the present.'
   'I find that reassuring. The Monolith is quite sufficient.'
   'But now there is a greater problem. Something has gone wrong.'
   'I did not think I could still experience fear...'
   'When Mount Zeus fell, it could have destroyed this whole world. Its impact was unplanned – indeed, unplannable. No calculations could have predicted such an event. It devasted vast areas of the Europan seabed, wiping out whole species – including some for which we had high hopes. The Monolith itself was overturned. It may even have been damaged – its programs corrupted. Certainly they failed to cover all contingencies; how could they, in a Universe which is almost infinite, and where Chance can always undo the most careful planning?'
   'That is true – for men and monoliths alike.'
   'We three must be the administrators of the unforeseen, as well as the guardians of this world. Already you have met the Amphibians; you have still to encounter the Silicon-armoured tappers of the lava streams, and the Floaters who are harvesting the sea. Our task is to help them find their full potential – perhaps here, perhaps elsewhere.'
   'And what of mankind?'
   'There have been times when I was tempted to meddle in human affairs – but the warning that was given to mankind applies also to me.'
   'We have not obeyed it very well.'
   'But well enough. Meanwhile there is much to do, before Europa's brief summer ends, and the long winter comes again.'
   'How much time do we have?'
   'Little enough; barely a thousand years. And we must remember the Jovians.'

IX – 3001

60 – Midnight in the Plaza

   The famous building, towering in solitary splendour above the woods of central Manhattan, had changed little in a thousand years. It was part of history, and had been reverently preserved. Like all historic monuments, it had long ago been coated with a microthin layer of diamond, and was now virtually impervious to the ravages of time.
   Anyone who had attended early meetings of the General Assembly could never have guessed that more than a thousand years had passed. They might, however, have been intrigued by the featureless black slab standing in the Plaza, almost mimicking the shape of the UN building itself. If – like everyone else – they had reached out to touch it – they would have been puzzled by the strange way in which their fingers skittered over its ebon surface.
   But they would have been far more puzzled – indeed, completely overawed – by the transformation of the heavens.

   The last tourists had left an hour ago, and the Plaza was utterly deserted. The sky was cloudless, and a few of the brighter stars were just visible; all the fainter ones had been routed by the tiny sun that could shine at midnight.
   The light of Lucifer gleamed not only on the black glass of the ancient building, but also upon the narrow, silvery rainbow spanning the southern sky. Other lights moved along and around it, very slowly, as the commerce of the Solar System came and went between all the worlds of both its suns.
   And if one looked very carefully, it was just possible to make out the thin thread of the Panama Tower, one of the six umbilical cords of diamond linking Earth and its scattered children, soaring twenty-six thousand kilometres up from the equator to meet the Ring around the World.
   Suddenly, almost as swiftly as if it had been born, Lucifer began to fade. The night that men had not known for thirty generations flooded back into the sky. The banished stars returned.
   And for the second time in four million years, the Monolith awoke.

Acknowledgements

   My special thanks to Larry Sessions and Gerry Snyder for providing me with the positions of Halley's Comet on its next appearance. They are not responsible for any major orbital perturbations I have introduced.
   I am particularly grateful to Marvin Ross of the Lawrence Livermore National Laboratory, not only for his stunning concept of diamond-core planets, but also for copies of his (I hope) historic paper on the subject.
   I trust that my old friend Dr Luis Alvarez will enjoy my wild extrapolation of his researches, and thank him for much help and inspiration over the past thirty-five years.
   Special thanks to NASA's Gentry Lee – my coauthor on Cradle – for hand-carrying from Los Angeles to Colombo the Kaypro 2000 lap-portable which allowed me to write this book in various exotic and – even more important – secluded locations.
   Chapters 5, 58 and 59 are partly based on material adapted from 2010: Odyssey Two. (If an author cannot plagiarize himself, who can he plagiarize?)
   Finally, I hope that Cosmonaut Alexei Leonov has now forgiven me for linking him with Dr Andrei Sakharov (still exiled in Gorky when 2010 was jointly dedicated to them). And I express my sincere regrets to my genial Moscow host and editor Vasili Zharchenko for getting him into deep trouble by borrowing the names of various dissidents – most of them, I am happy to say, no longer imprisoned. One day, I hope, the subscribers to Tekhnika Molodezhy can read the instalments of 2010 which so mysteriously disappeared.

   Colombo, Sri Lanka
   25 April 1987 (1)

footnotes
   1.Something strange has happened: I was under the impression that I was writing fiction, but I may have been wrong. For consider the following sequence of events:
   1. In 2010: Odyssey Two the spaceship Leonov was powered by the Sakharov Drive.
   2. Now, half a century later (Chapter , spaceships are powered by the muon-catalysed, 'cold fusion' reaction discovered by Luis Alvarez et al in the l950s. (See the autobiography Alvarez: Basic Books, NY, 1987.)
   3. According to the London Times, 17 August 1987, Dr Sakharov is now working on nuclear power production 'based on... muon-catalysed, or "cold" fusion, which exploits the properties of an exotic, short-lived elementary particle related to the electron... Advocates of "cold fusion" point out that all the key reactions work best at just 900 degrees centigrade...'
   I now await, with great interest, comments from Nobel Laureates Sakharov and Alvarez on the roles I have given them.
   Arthur C. Clarke, 30 September 1987

3001: The Final Odyssey

Arthur C. Clarke


Odyssey

Arthur C. Clarke,
PROLOGUE – The Firstborn
I – STAR CITY
1 – Comet Cowboy
2 – Awakening
3 – Rehabilitation
4 – A Room with a View
5 – Education
6 – Braincap
7 – Debriefing
8 – Return to Olduvai
9 – Skyland
10 – Homage to Icarus
11 – Here be Dragons
12 – Frustration
13 – Stranger in a Strange Time
II – GOLIATH
14 – A Farewell to Earth
15 – Transit of Venus
16 – The Captain's Table
III – THE WORLDS OF GALILEO
17 – Ganymede
18 – Grand Hotel
19 – The Madness of Mankind
20 – Apostate
21 – Quarantine
22 – Venture
IV – THE KINGDOM OF SULPHUR
23 – Falcon
24 – Escape
25 – Fire in the Deep
26 – Tsienville
27 – Ice and Vacuum
28 – The Little Dawn
29 – The Ghosts in the Machine
30 – Foamscape
31 – Nursery
V – TERMINATION
32 – A Gentleman of Leisure
33 – Contact
34 – Judgement
35 – Council of War
36 – Chamber of Horrors
37 – Operation Damocles
38 – Pre-emptive Strike
39 – Deicide
40 – Midnight: Pico
EPILOGUE
SOURCES AND ACKNOWLEDGEMENTS
SOURCES
ACKNOWLEDGEMENTS
IN MEM0RIAM: 18 SEPTEMBER 1996
VALEDICTION

Arthur C. Clarke,
3001: THE FINAL ODYSSEY

   For Cherene, Tamara and Melinda – may you be happy in a far better century than mine

PROLOGUE – The Firstborn

   Call them the Firstborn. Though they were not remotely human, they were flesh and blood, and when they looked out across the deeps of space, they felt awe, and wonder – and loneliness. As soon as they possessed the power, they began to seek for fellowship among the stars.
   In their explorations, they encountered life in many forms, and watched the workings of evolution on a thousand worlds. They saw how often the first faint sparks of intelligence flickered and died in the cosmic night.
   And because, in all the Galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped.
   And sometimes, dispassionately, they had to weed.
   The great dinosaurs had long since passed away, their morning promise annihilated by a random hammerblow from space, when the survey ship entered the Solar System after a voyage that had already lasted a thousand years. It swept past the frozen outer planets, paused briefly above the deserts of dying Mars, and presently looked down on Earth.
   Spread out beneath them, the explorers saw a world swarming with life. For years they studied, collected, catalogued. When they had learned all that they could, they began to modify. They tinkered with the destiny of many species, on land and in the seas. But which of their experiments would bear fruit, they could not know for at least a million years.
   They were patient, but they were not yet immortal. There was so much to do in this universe of a hundred billion suns, and other worlds were calling. So they set out once more into the abyss, knowing that they would never come this way again. Nor was there any need: the servants they had left behind would do the rest.
   On Earth, the glaciers came and went, while above them the changeless Moon still carried its secret from the stars. With a yet slower rhythm than the polar ice, the tides of civilization ebbed and flowed across the Galaxy. Strange and beautiful and terrible empires rose and fell, and passed on their knowledge to their successors.
   And now, out among the stars, evolution was driving towards new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and gemstone. In these, they roamed the Galaxy. They no longer built spaceships. They were spaceships.
   But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light.
   Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds, the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into dust.
   Now they were Lords of the Galaxy, and could rove at will among the stars, or sink like a subtle mist through the very interstices of space. Though they were freed at last from the tyranny of matter, they had not wholly forgotten their origin, in the warm slime of a vanished sea. And their marvellous instruments still continued to function, watching over the experiments started so many ages ago.
   But no longer were they always obedient to the mandates of their creators; like all material things, they were not immune to the corruption of Time and its patient, unsleeping servant, Entropy.
   And sometimes, they discovered and sought goals of their own.

I – STAR CITY

1 – Comet Cowboy

   Captain Dimitri Chandler [M2973.04.21/93.106//Mars//I SpaceAcad3005] – or 'Dim' to his very best friends – was understandably annoyed. The message from Earth had taken six hours to reach the space-tug Goliath, here beyond the orbit of Neptune; if it had arrived ten minutes later he could have answered 'Sorry – can't leave now – we've just started to deploy the sun-screen.'
   The excuse would have been perfectly valid: wrapping a comet's core in a sheet of reflective film only a few molecules thick, but kilometres on a side, was not the sort of job you could abandon while it was half-completed.
   Still, it would be a good idea to obey this ridiculous request: he was already in disfavour sunwards, through no fault of his own. Collecting ice from the rings of Saturn, and nudging it towards Venus and Mercury, where it was really needed, had started back in the 2700s – three centuries ago. Captain Chandler had never been able to see any real difference in the 'before and after' images the Solar Conservers were always producing, to support their accusations of celestial vandalism. But the general public, still sensitive to the ecological disasters of previous centuries, had thought otherwise, and the 'Hands off Saturn!' vote had passed by a substantial majority. As a result, Chandler was no longer a Ring Rustler, but a Comet Cowboy.
   So here he was at an appreciable fraction of the distance to Alpha Centauri, rounding up stragglers from the Kuiper Belt. There was certainly enough ice out here to cover Mercury and Venus with oceans kilometres deep, but it might take centuries to extinguish their hell-fires and make them suitable for life. The Solar Conservers, of course, were still protesting against this, though no longer with so much enthusiasm. The millions dead from the tsunami caused by the Pacific asteroid in 2304 – how ironic that a land impact would have done much less damage! – had reminded all future generations that the human race had too many eggs in one fragile basket.
   Well, Chandler told himself, it would be fifty years before this particular package reached its destination, so a delay of a week would hardly make much difference. But all the calculations about rotation, centre of mass, and thrust vectors would have to be redone, and radioed back to Mars for checking. It was a good idea to do your sums carefully, before nudging billions of tons of ice along an orbit that might take it within hailing distance of Earth.
   As they had done so many times before, Captain Chandler's eyes strayed towards the ancient photograph above his desk. It showed a three-masted steamship, dwarfed by the iceberg that was looming above it – as, indeed, Goliath was dwarfed at this very moment.
   How incredible, he had often thought, that only one long lifetime spanned the gulf between this primitive Discovery and the ship that had carried the same name to Jupiter! And what would those Antarctic explorers of a thousand years ago have made of the view from his bridge? They would certainly have been disoriented, for the wall of ice beside which Goliath was floating stretched both upwards and downwards as far as the eye could see. And it was strange-looking ice, wholly lacking the immaculate whites and blues of the frozen Polar seas. In fact, it looked dirty – as indeed it was. For only some ninety per cent was water-ice: the rest was a witch's brew of carbon and sulphur compounds, most of them stable only at temperatures not far above absolute zero. Thawing them out could produce unpleasant surprises: as one astrochemist had famously remarked, 'Comets have bad breath'.
   'Skipper to all personnel,' Chandler announced. 'There's been a slight change of programme. We've been asked to delay operations, to investigate a target that Spaceguard radar has picked up.'
   'Any details?' somebody asked, when the chorus of groans over the ship's intercom had died away.
   'Not many, but I gather it's another Millennium Committee project they've forgotten to cancel.'
   More groans: everyone had become heartily sick of all the events planned to celebrate the end of the 2000s. There had been a general sigh of relief when 1 January 3001 had passed uneventfully, and the human race could resume its normal activities.
   'Anyway, it will probably be another false alarm, like the last one. We'll get back to work just as quickly as we can. Skipper out.'
   This was the third wild-goose-chase, Chandler thought morosely, he'd been involved with during his career. Despite centuries of exploration, the Solar System could still produce surprises, and presumably Spaceguard had a good reason for its request. He only hoped that some imaginative idiot hadn't once again sighted the fabled Golden Asteroid. If it did exist – which Chandler did not for a moment believe – it would be no more than a mineralogical curiosity: it would be of far less real value than the ice he was nudging sunwards, to bring life to barren worlds.
   There was one possibility, however, which he did take quite seriously. Already, the human race had scattered its robot probes through a volume of space a hundred light-years across – and the Tycho Monolith was sufficient reminder that much older civilizations had engaged in similar activities. There might well be other alien artefacts in the Solar System, or in transit through it. Captain Chandler suspected that Spaceguard had something like this in mind: otherwise it would hardly have diverted a Class I space-tug to go chasing after an unidentified radar blip.
   Five hours later, the questing Goliath detected the echo at extreme range; even allowing for the distance, it seemed disappointingly small. However, as it grew clearer and stronger, it began to give the signature of a metallic object, perhaps a couple of metres long. It was travelling on an orbit heading out of the Solar System, so was almost certainly, Chandler decided, one of the myriad pieces of space-junk that Mankind had tossed towards the stars during the last millennium and which might one day provide the only evidence that the human race had ever existed.
   Then it came close enough for visual inspection, and Captain Chandler realized, with awed astonishment, that some patient historian was still checking the earliest records of the Space Age. What a pity that the computers had given him the answer, just a few years too late for the Mifiermium celebrations!
   'Goliath here,' Chandler radioed Earthwards, his voice tinged with pride as well as solemnity. 'We're bringing aboard a thousand-year-old astronaut. And I can guess who it is.'