Even when the globular clusters were young and the swirl of the galaxy new-formed, the seeds of life were everywhere. The most ancient and massive stars had long ago exploded into supernovae, their wreckage of heavy elements spilling across the dust-clouds of the Milky Way.
From these shrouds of stardust, nebulae condensed into stars surrounded by discs of dusty clouds, gas and rocky chunks. As time passed the larger masses in the discs swept up the dust and gas, forming planets. In many systems huge gas giants, or still vaster worlds almost as large as stars coalesced from the nebula. The gravity of these massive planets churned the disc, forcing worldlets into collisions, throwing asteroids into the interstellar dark and leaving the warm reaches of the inner system barren realms of rocky debris.
Around a few of the stars, though, small rocky planets formed from metal-rich clouds. The collisions of comets onto these young worlds and the bubbling out of gases from their insides wrapped many of them in oceans of water or ammonia and thick atmospheres of carbon dioxide, ammonia and methane. Many times the atmospheres leaked away into space, the world's gravity too weak or the fierce heat of its sun too great, and the oceans froze or evaporated. On other worlds thick layers of carbon dioxide trapped heat and their oceans boiled.
Between the extremes of freezing or boiling or desiccation, a few of the planets that orbited at just the right distance and had a moderate gravity retained their oceans. Some of these worlds circled yellow and orange dwarfs, warm, stable and long-lived stars, that bathed them in heat and light. The hard, ultraviolet photons of young, vigorous suns and lightning forking across the clouds reacted atmospheric gases into heavy, complex molecules that fell in a constant rain into the churning seas, filling them with a myriad organic taints. Within a few hundred million years chemical replicators swarmed in primeval oceans.
Roughly one in fifty star systems has life-bearing planets.
Billions of years must pass on a world before the emergence of complex, multicellular life. The path from simple PNA-like replicators, through RNA-analogues to sophisticated replicator systems based on intricate chemical pathways within cells is a long one. Most lifebearing worlds have no organisms more complex than bacterial colonies, or algae, or flatworms.
During these long ages, life reworks a world, radically changing the composition of the atmosphere. The reducing atmosphere of carbon dioxide, methane and ammonia is replaced by an oxidizing one of nitrogen and oxygen or, more rarely, chlorine.
When life suddenly explodes into animal diversity it seems likely that progress becomes rapid (on Terra it was only 175 megayears between the first animals with spinal cords and the emergence of fish and 100 megayears later amphibians were common; 75 megayears further years had produced reptiles, a further 50 and dinosaurs were well on the way to world dominance).
Intelligence is much harder to judge. Certainly many mammals are intelligent enough to have a civilization: chimps and cetaceans chief among them, and many others not far off. Birds and dinosaurs are not really that much less intelligent. Also molluscs (which are only very distantly related to mammals) have produced very intelligent species (squid and octopus). Given the enormous advantages of being intelligent, when anim als are large enough to have a big brain, they will probably develop one.
Life on dry land on this planet is doomed over a time scale of 150-250 megayears. (Basically: atmospheric pO2 has been rising steadily for 600 megayears. This is driven by improvements in the photosynthetic efficiency of plants, which is driven by evolutionary selection pressure. If the curve is extrapolated, at some time in the future the pO2 will exceed about 28% (compared to today's 16%), at which point even waterlogged organic matter will burn in air. There are several hundred thousand spontaneous fires per year (caused by lightning strikes), therefore fires will rage out of control across all exposed land areas. And outgassing of CO2 from the fires won 't reduce the partial pressure of oxygen - because the cycle is driven by deep-ocean plant life. Therefore life on land will basically come to an end.
If this scenario holds (what about the large amounts of dust spread by fires, wouldn't they cool off the planet?), what will happen with the oceanic life afterwards? Perhaps it will reach a steady state: some land vegetation (if it grows fast enough or isolated enough it will work despite the fires), much life in the oceans and a cooler climate (more dust and oxygen, less carbon dioxide) which will regulate oceanic plants by lowering the temperature.
Perhaps land-life is transient on most planets?
In the earliest days the worlds were low in heavy elements, with smaller, cooler cores and mantles with less active magma. Without the heat of radioactive decay to drive the drifts of the continental plates their crusts were much more uniform. As a result many of these worlds were almost completely covered in oceans. Although life arose in many of those oceans, only rarely did it move onto the land and rarer still was intelligence and technology.
Intelligence does not make civilization inevitable. Members of intelligent species may be solitary, or confined to a narrow niche and so incapable of forming a high population civilization. This is especially true for carnivores: the population must to low for there to be enough prey, but such a situation inhibits the development of complex societies.
Technology is only acquired by cultural toolmakers: species that start a memetic evolution in which ideas and inventions are passed from one individual to another by communication. To become toolmakers, a species must possess the means to manipulate objects with precision; this skill is far from ubiquitous. Even then the most rapid routes to technology rely o n fire, an invention almost impossible for the aquatic species that are the most common sentients in the Galaxy.
Culture does not inevitably lead to technology. There are many unimaginably ancient cultures across the Galaxy that are highly advanced in philosophy and art, but with preindustrial technology. Often these cultures exist in technological stasis for millenia between notable advances.
Nevertheless, the galaxy is immense and at many times and in many places amongst its hundreds of billions of stars cultural toolmakers arose and even moved into space. Thus begins the Secret History of the Galaxy.
The development of most technological civilizations that develop in isolation follows a common pattern. This consists of four distinct phases: a brush with extinction, interstellar travel, contraction to a tightly bound postbiological core and then transcendence.
Typically technological development begins slowly, but at some point (perhaps hundreds of thousands or even millions of years) after the beginning of a culture it explodes, leading rapidly to high technology. Unfortunately behaviour patterns associated with non-technological cultures persist, leading to a rapidly increasing population and ever higher competition for resources. This leads to massive environmental damage caused by industrialisation and usually to self-inflicted destruction by fusion fire, nanotech plague, asteroidal bombardment, or more general environmental collapse. This then is the Toolmaker Koan: travelling to the stars requires a highly developed industrial infrastructure, but development of technology leads to nuclear war and extinction. In milder cases a species passes through many cycles of industrial development followed by almost total self-destruction, or achieves limited interstellar travel first, but only rarely is the Crash completely avoided.
The aftermath of such a Crash is bleak. Most of the world's non-renewable resources are consumed, making the emergence of other technological species highly unlikely for extended periods of time.
When species first turn their telescopes on the skies, the stars seem unimaginably far apart; even travel to the nearest planets is a very difficult problem. As technology advances many systems are invented to bridge the interstellar abyss: light sails, nuclear pulse drives, antimatter rockets, interstellar ramjets and others. The distance to the stars seems much reduced. Typically species that survive the Crash begin interstellar colonisation when the time taken to reach the stars is shorter than the average lifespan of an individual.
If the species spreads out into the galaxy whilst still facing an imminent Crash then the results are often devastating for the local region. The older, more established colonies on the interior of the specie s' sphere collapse, leaving ravaged worlds and plundered star systems. A thin shell of civilization between the frontier and the devastated core spreads out across the galaxy. Any other less advanced species encountered on the frontier are absorbed into the civilization and have their worlds stripped of resources. Invariably the species eventually becomes extinct (dying out in each of hundreds of systems), makes a phase transition to a more sustainable way of life, or is stopped by conflict with other civilizations. The result is a sphere of totally depleted worlds littered with decaying industrial relics. In such a wasteland, technological species cannot emerge for tens of millions of years or longer.
Interstellar colonisation occurs at a time of great technological progress. As technology advances the stars begin to seem farther away again. This occurs because the species carks itself into post-biological bodies, vastly speeding up thought. If one can think a million times faster, then the stars seem a million times farther away. Also the advance of technology tends to lead to much greater rates of communication between individuals, sometimes leading to individuality being totally dissolved. This increased thinking speed and connectivity between members of the species makes even being a light second from the centre of civilization seem like being isolated and alone. The more closely connected an individual is to the rest of the species, the less likely it is to want to travel to some place far away.
These technological effects mean that for many toolmaking species there is only a narrow window for interstellar travel (at least by small subsets of the species): too early and there is not the infrastructure to make such travel possible, too late and nobody wants to be cut off from civilization. On passing into postbiological existence most species forsake extensive interstellar colonisation and communication as the 'subjective horizon' closes in to smaller than a single system.
The species has become a lesser Power, confined to a small region of space, but wielding the advanced, almost godlike, technologies of the Singularity. Lesser powers often display complex topologies of consciousness, with element-streams separating as autonomous agents and then recombining. Such separations sometimes lead to Intervention Events, occurences that have profound effects on the histories of regions of the galaxy. Even across the small space occupied by the core Mind there can be large enough variations in thought that the Power can seem almost fragmented, with processes thinking about many things at once.
Interaction between biological and postbiological civilizations seems so impossibly slow to the postbios that in most cases it is not even attempted. The vastly accelerated thinking of such Singular entities means that such civilzations may change beyond recognition in an afternoon. Sometimes, however, such postbiologicals construct simulations of lesser intelligences running at high speed to enable some form of communication.
The increasing rate of technological development eventually leads toolmaking species to cark their intelligences into exotic machineries: dyson shells of nanocomputers submerged in stars, magnetic fluxes pinned in the accretion discs of black holes, nucleonic computers in the crusts of neutron stars, and other more bizarre and less comprehensible things. These species, the greater Powers, have entered the deep regions of the Singularity and are heading towards Transcendence.
At last the species transcribes itself into dark matter, leaving behind interaction with the bright froth of baryons that make up the mundane universe. Finally, even the possibilities of photinos and axions are too constraining and the consciousness of the civilization exists as swarms of virtual particles, dancing ghostlike across the seething geometries of spacetime.
The relics left behind by transcending civilizations are often so advanced that any use of them by emerging species is impossible. Indeed in some cases the construction is so subtle that they are not even recognised as artifacts.
The history of the galaxy is largely the history of tens of thousands of species developing in isolation, heading towards extinction or transcendence. Tiny bubbles of civilization expand and contract across the stars, separated by vast gulfs of space and time. Sometimes, though, these separate stories intersect, forming a web of consequences that stretch from today back into the barely remembered depths of time, and beyond.
High tech societies occur with moderate frequency, but none go on to form 'galactic empires' as they are too busy wiping each oth er out over misunderstandings or old-fashioned xenophobia. The galaxy is in equilibrium at a tech-level only slightly higher than humanity. Species simply do not get time to advance any more before falling prey to some rival. The emergence of new species keeps the number of starfaring races approximately constant. This model has the disadvantage that there is no sign of any major war having occurred over Sol system, nor has humanity yet been attacked by a hostile and powerful alien foe.
Species which survive the initial threats of ecocide and nuclear destruction by placing strict controls on their populations do not spread colonies rapidly across the stars. Instead they are driven mostly by curiosity and so send out exploratory missions and not colonists. This leaves very little sign of their presence. Unfortunately we should by now have encountered one of their probes (unless they are being deliberately stealthy), and would in any case would not stop the rapid spread of other species.
The species has long since given up on using planets, living instead in gigantic space habitats. Any star system showing a biosphere is carefully avoided (or perhaps discreetly monitored). The vast majority of the population live in otherwise uninhabited systems, making use of asteroids as raw materials. This society may be forced to fight terrible wars against encroaching Moties or others.
An early supercivilization colonised the entire galaxy billions of years ago and then wiped itself out/graduated to higher things, leaving a network of wormholes covering many systems throughout the galaxy. Over time the natural movement of stars has ejected wormholes from the plane of the galaxy or formed CTCs, thus destroying them. Today there are dozens of mini-networks across the Milky Way. Later races have quickly stumbled upon these wormhole networks and used them for their colonisation efforts in preference to constructing their own. This has lead to the surviving civilizations making use of the networks and fighting over them. Our own local region has long since had its network collapse and so is a backwater, unvisited by any 'higher' civilizations. The generation rate of new starfaring civilizations is low enough that in this particular region we are the first starfarers.
The Galaxy is too vast and ancient to have a simple history. Amongst the star-strewn arms and molecular clouds, the cinders of dead worlds and the steep spaces of collapsed masses are scattered wonders and terrors. There are myriads of stories, pearl-events strung on stacked geodesics. Great chains of causality twisting and separating. Threads weaving the tapestry of the Secret History.
This tale cannot be told. So step back, build a simple model. Imagine the Milky Way embedded in a virtual space in which a metre represents 1 000 light years and one second 50 000 years. Mark populations of sentient beings with coloured dots, the brightness representing the total level of sentience. Start the view from about six billion years ago.
The Galaxy is a great wheel hanging before you in space, a whirlpool of stars. The galactic disc measures 100m across, but only a metre thick, with a central bulge 20m in diameter. In the disc there are only one or two stars in each cubic centimetre, but in the central bulge there are many more. The core is stained orange-yellow and the spiral arms blaze blue-white with the vigour of massive, young stars. Ancient, red globular clusters form a diffuse spherical halo around the galactic disc. The swirl of stars spins slowly about the central black hole, the outer spiral arms taking over an hour for one rotations and the inner reaches much less. Occasionally a star dies in the flash of a supernova, its shell of light racing across the disc in a few seconds and out into the intergalactic abyss.
For a long time there are no points of light representing civilizations. Suddenly points of dull blue begin to appear, maybe as frequently as one every five minutes. Mostly they burn softly for a long time, but perhaps one in ten glows faintly for as long as a minute then begins to grow brighter over a second or less, becoming a brilliant fleck of sapphire and then vanishing. A species of cultural toolmakers has died. Less often, the increase in intensity continues, leaving a laser-bright point that burns in transcendent brilliance for many seconds.
In rare cases, a number of faint points move away from one of those suddenly brightening points towards nearby star systems. A small clus ter of blue specks forms stretching across a rough sphere five or ten centimetres in diameter. In a hundreth of a second these too burn out. The little explosion of civilization is a shell: the inner systems flare up to brilliance and die, leaving those on the outside to live a few hundred milliseconds more. If the intensity increase of the initial point was slow the sphere is often larger and fainter; in very rare cases it stretches to almost a metre across over as long five or ten seconds.
Sometimes the burning out of a coloured point is rapidly followed by another and the pattern is repeated in the same system: the species has recovered from near disaster, or another related toolmaking species has arisen. These events often mean that the first species transcended.
Look more closely and some of the population-points are green rather than blue. These are chlorine-breathing species. The green points, apart from their greater rarity, act much like the blue.
This pattern continues for about eight turns of the outer spiral arms, the emergence of new civilizations becoming slowly more common with time. Then, almost nine hours into the history, something different happens. Dim points of green begin to travel out from around an ordinary-looking yellow star on the edge of the core. Within ten seconds there are specks of pale green across the disc of the galaxy, glinting like emerald dust.
Many seconds later a short white line appears near one of the green points. It lengthens, heading towards another nearby speck. More of these appear, spreading out from the core into the spiral arms. Within a few seconds the great disc of the Galaxy is permeated by a pale, ghostly network of lines: a spider's web of wormholes that link a hundred million stars. Faint green points race along the softly glowing lines. For the first time a civilization spans the Milky Way.
Suddenly the Galaxy lights up like a beacon, the emerald motes flaring into dazzling brilliance. The points converge into a single mass, flashing across the Web, becoming blinding.
Description of transcendence/migration/whatever of wormhole builders.
Description of colonization by wormhole, continuing for another day.
For many hours the pattern continues, the great swirl stars rotating slowly about its core. Look closely and the stars are churned and mixed, passing through the bright spiral arms and the darker rifts; the pattern is constantly shifting, old clusters breaking and new ones forming. Even the stars themselves die, and the dense clouds of cold hydrogen condense, and new stars are born. The Web becomes tangled as the stars carry its intersections on their complex and turbulent paths. The beautiful pattern frays, its threads breaking as timelike curves close on themselves.
1.25 hours ago mass extinctions occur.
-225my Mass extinctions at Terra, Elysium and others
-8my Supernova chain in galactic core
The future of Ad Astra