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  Beyond the forward end of the cylinder, on the bow of your new terrarium, attach a forward unit at the point of the long axis. Eventually your terrarium will be spinning at a rotational rate calculated to create the effect of gravity on the inner surface of the interior cylinder so that when you are inside, you will be pulled to the floor as if in a gravity field. This is the g equivalent, or gequivalent. The forward unit will then be connected to the bow of the terrarium by a geared axle, to allow the forward unit not to spin but instead to stay fixed. It will be nearly weightless in this bowsprit chamber, but many functions of the terrarium will go better without the spinning, including docking, viewing, navigating, etc.

  It is possible to build an interior cylinder that spins freely inside an asteroid that does not spin—the so-called prayer wheel configuration—and this does give you both an interior with g effect and a non-spinning exterior, but it is expensive and finicky. Not recommended, though we have seen some good ones.

  When stern and bow are properly installed and configured, and the asteroid is set spinning, the interior is ready to be terraformed.

  Begin with a light dusting of heavy metals and rare earths, as specified for the biome you are trying to create. Be aware that no Terran biome ever began with the simple ingredients you will be starting with on an asteroid. Biospheres need their vitamins right from the start, so be sure to arrange for the importation of the mix you want, usually including molybdenum, selenium, and phosphorus. These are often applied in “puff bombs” set off along the axis of the cylindrical space. Don’t poison yourself when you do this!

  After that, string the axis of the cylinder with your terrarium’s sunline. This is a lighting element, on which the lit portion moves at whatever speed you choose. The lit portion of the sunline usually starts the day in the stern of the cylinder, after a suitable period of darkness (during which any streetlights overhead will serve as stars). The lit portion of the line, appropriately bright, then traverses the sunline from stern to bow (or east to west, as some describe it), taking usually the same time as a Terran day, as measured by the latitude of your biome on Earth. Seasons inside your terrarium will be rendered accordingly.

  Now you can aerate the interior to the gas mix and pressure you desire, typically somewhere between 500 and 1100 millibars of pressure, in something like the Terran mix of gases, with perhaps a dash more oxygen, though the fire risk quickly rises there.

  After that, you need biomass. Naturally you will have in your spice rack the complete genetic codes of all the creatures you intend to introduce into your biome. Generally you will be either recreating some Terran biome, or else mixing up something new, hybrid biomes most people call Ascensions, after Ascension Island on Earth, the site of the first such hybrid (started inadvertently by Darwin himself!) All the genomes for all the species of your particular biome will be available for print on demand, except for the bacteria involved, which are simply too numerous and too genetically labile to categorize. For them you will have to apply the appropriate inoculant, usually a muck or goo made of a few tons of the bacterial suite that you want.

  Luckily bacteria grow very fast in an empty ecological niche, which is what you now have. To make it even more welcoming, scrape the interior wall of your cylinder, then crumble the rock of the scrapings finely, to a consistency ranging from large gravel to sand. Mixed with an edible aerogel, this then becomes the matrix for your soil. Put all the ice gathered in your scraping aside, except for enough when melted to make your crumbled rock matrix moist. Then add your bacterial inoculant and turn up the heat to around three hundred K. The matrix will rise like yeasted dough as it becomes that most delicious and rare substance, soil. (Those wanting a fuller explanation of how to make soil are referred to my bestselling All About Dirt.)

  With a soil base cooked up, your biome is well on its way. Succession regimens at this point will vary, depending on what you are looking for at climax. But it’s true to say that a lot of terraria designers start out with a marsh of some kind, because it’s the fastest way to bulk up your soil and your overall biomass. So if you are in a hurry to occupy, this is often a good way to start.

  When you’ve got a warm marsh going, either freshwater or salt, you are already cooking good. Smells will rise in your cylinder, also hydrological problems. Fish, amphibian, animal, and bird populations can be introduced at this point, and should be if you want maximum biomass growth. But here you have to watch out for a potential danger: once you get your marsh going, you may fall in love with it. Fine for you, but it happens a bit too often. We have too many estuarine biomes now, and not enough of the other biomes we are hoping to cook out here.

  So try to keep your distance at this point; keep a depopulate marsh, or stay away from it during this part of the process. Or join a trading scheme in which you trade asteroids when they are at the marsh point, so that you come into a new one wanting to change things, unattached to what’s already there.

  With the hefty biomass created by a marsh, you can then build up land using some of your excavated materials, saved on the surface of the asteroid for this moment. Hills and mountains look great and add texture, so be bold! This process will redirect your water into new hydrologies, and this is the best time to introduce new species, also to export species you no longer want, giving them to newer terraria that might need them.

  Thus over time you can transform the interior of your terrarium to any of the 832 identified Terran biomes, or design an Ascension of your own making. (Be warned that many Ascensions fall as flat as bad soufflés. The keys to a successful Ascension are so many that I have had to pen another volume, How to Mix and Match Biomes!, now available.)

  Ultimately you will need to make many temperature, landscape, and species adjustments, to get to the kind of stable climax community you want. Any possible landscape is achievable; sometimes the results are simply stunning. Always the entire landscape will be curving up around you, rising on both sides and meeting overhead, so that the look of the land will envelop you like a work of art—a goldsworthy inscribed on the inside of a rock, like a geode or a Fabergé egg.

  Obviously it is also possible to make interiors that are all liquid. Some of these aquaria or oceanaria include archipelagoes; others are entirely water, even their walls, which are sometimes refrozen transparently so that in the end when you approach them, they look like diamonds or water droplets floating in space. Some aquaria have no air space in their middles.

  As for aviaries, every terrarium and most aquaria are also aviaries, stuffed with birds to their maximum carrying capacity. There are fifty billion birds on Earth, twenty billion on Mars; we in the terraria could outmatch them both combined.

  Each terrarium functions as an island park for the animals inside it. Ascensions cause hybridization and ultimately new species. The more traditional biomes conserve species that on Earth are radically endangered or extinct in the wild. Some terraria even look like zoos; more are purely wilderness refugia; and most mix parkland and human spaces in patterned habitat corridors that maximize the life of the biome as a whole. As such, these spaces are already crucial to humanity and the Earth. And there are also the heavily agricultural terraria, farmworlds devoted to producing what has become a very large percentage of the food feeding the people of Earth.

  These facts are worth noting and enjoying. We cook up our little bubble worlds for our own pleasure, the way you would cook a meal, or build something, or grow a garden—but it’s also a new thing in history, and the heart of the Accelerando. I can’t recommend it too highly! The initial investment is nontrivial, but there are still many unclaimed asteroids out there.

  WAHRAM AND SWAN

  Although no doubt they were simply the result of an engineering response to an engineering problem, regarded as an aesthetic matter the Mercurial launching gyres were interesting. A maglev tube twisted in a cone set on its point, increasing in size as it rose. The tip of the cone was secured to a platform that moved in a circle, about the size
of the widest part of the cone. The movement of the platform exaggerated very effectively the force of acceleration on the ferries as they were being magnetically thrown up the tube. Thus the ferry they were in had them seated sideways to the ground, but as it careened around and up, their floor became most definitely down, and then with dizzying speed they were launched into space, going so fast that if there had been an atmosphere they would have burned to a crisp the moment they left the tube. The effect as seen from the spaceport resembled some kind of antique carnival ride. From inside the ferry it proved to be a quite serious acceleration, very near the maximum allowed in commercial travel, which was 3.5 g.

  Swan Er Hong had strapped herself into the seat beside Wahram just before takeoff, grimacing apologetically at the cliché of her lateness. Now she leaned toward him to look out the little window at the rapidly receding craterscape of her home world. Quickly the land changed from a plane to a ball, a thin crescent of it bathed in sunlight, the gibbous nightside black. Mercury was an interesting place, but Wahram was not unhappy to leave; despite the locals’ best efforts to spruce it up with art, the landscape was a cindery clinker. And the truth was that when he was inside its marvelous gliding city, the sudden blink of illumination on high points to the west always reminded him of the sun, following them relentlessly, always about to burst over the horizon and torch everything.

  Their ferry was going to catch the terrarium Alfred Wegener, which was moving so fast that the ferry would have to make another long three-g burn to catch up. During this time, Wahram shifted his seat into bed mode and endured like everyone else. Across the room Swan groaned and curled around herself on her bed. Wahram forbade himself to think about the studies that had been made on the effect of g-forces on the human brain, delicate goo that it was, trapped without much padding inside its hard prison walls. Then the Wegener caught them and reeled them in with a final little squish of g, as if to emphasize the problem.

  After that Wahram and the other passengers had to adjust to the sudden weightlessness, and pull themselves from the ferry into the terrarium’s dock, then through the neck and down broad padded stairs to the cylinder floor.

  The interior space in the Wegener was pretty substantial, about twenty kilometers long and five across, spun to a one-g equivalent. The great majority of the interior space was park, with a few small towns scattered mostly fore and aft. The mix of savanna and pampas was very attractive, Wahram thought as he walked toward the first village, looking up at the land overhead. Grass prairie and patches of forest arched like a giant Sistine Chapel overhead, a Sistine on which Michelangelo had painted a version of Eden—a savanna, the first human landscape, appealing to something very deep in the mind. Although terrarium topology always made Wahram feel as if he were inside a map that had been rolled into a tube. As one looked along the longitude line one occupied, the land always appeared as a long U-valley, with nearby trees topped by higher, more distant trees, tilting toward the valley bottom in a curve of ever-steepening parkland, up to vertical side walls, as in certain great glacial U-valleys—but then the walls continued up and folded over, breaking past verticality in a manner very distinct to the eye. Above that line the landscape was simply overhead, and quite undeniably upside down. As now, for instance, when beyond a cloud he saw the tops of a sheet of flocking birds, flying over the surface of a lake hanging directly over his head.

  Wahram went to a little Saturn House in the first town, called Plum Lake, and checked in. They kept a restaurant in the ground floor, so he signed up for kitchen duties (he liked all the simplest chores), and after showering he took a walk around the town. It was a handsome place, with a lakefront and a hill, and a tram station at its eastern end. Trams ran through parkland to the other towns. The central plaza was full of Venusians, presumably on their way home: tall broad-shouldered young Chinese, for the most part, with intent eyes and big smiles. They were working on Venus hip deep in dry ice, doing dangerous things. Wahram engaged in similar work when he was home on Titan, but Titan had only .14 g, and this had often saved him from little accidents; Venus, at .9 g, impressed him as dangerous.

  At the edge of town he came to a line of trees and a fence. He signed in at a little kiosk and read on a plaque that his new acquaintance Swan Er Hong had designed the biome here some seventy years before. This was a surprise; he had heard she had once been a designer, but she had shown no interest in the Wegener when they arrived.

  Wahram took a little stun gun out of a box of them, put it in the pocket of his coat, and let himself through the gate into the park. He walked at an angle up the curve of the land. The soil was a thick black loam, with a mixed Tanzanian and Argentinian provenance, he had read at the kiosk. A stand of broad-topped acacia trees showed signs of elephant damage on their trunks. Treetops directly overhead looked like round bumps of lichen. Tall clumps of grass obscured the view beyond his immediate locality; one could see more up where the park curved over the nearby treetops. Up to his left, over the trees, a little knoll of rocks looked like a good lookout; although of course that might have occurred to a puma or a hyena, so he was careful as he approached. Most animals were wary of humans, but he didn’t want to surprise anybody. You don’t need danger to get your thrills, his mother used to tell him. That would be decadent, and I don’t like decadence! The rest of his parents had not been so judgmental, perhaps considering that as they were all living around Saturn, their take on danger might be skewed. But his mother had made her point, and Wahram was not decadent; he was continually shocked by the new; and now his heart was pounding a little.

  The knoll was empty, however. The rocks were spotted with actual lichen, as if sprayed with a surfacing of semiprecious stones, yellow and red and pale green. He crouched in a crack and had a look around.

  There were a mother cheetah and two cubs, below him in clumps of bunchgrass. The mother’s attention was focused on some pampas deer grazing in the mid-distance. Wahram wondered what pampas deer made of cheetahs—whether there had been any predator that fast in South America. It seemed unlikely.

  He felt lucky to see cheetahs on their feet, as it seemed they were usually asleep. It looked like this mother was trying to teach her cubs how to hunt; she squashed one down with a forepaw to get it to flatten. The chiral wind was rushing down from the left, so he was crosswind to the cats; they would not smell him. Or so it seemed, although in fact many animals’ senses were so sharp as to make humans seem deaf and dumb.

  He settled down to watch. The cubs, still brindled, were looking confused, as if they didn’t even comprehend the concept of a lesson. They batted each other still, as if wanting to play. The peak point of brain growth was also the peak point of playfulness.

  They were downwind of the deer, who looked unruffled and were coming their way. The mama cheetah crouched in the grass, and now her cubs were doing likewise, their tails twitching uncontrollably.

  Then the mama was off in a burst of grass blades, and the cubs bounded after. The deer dashed away in great pronging leaps, leaving the cheetahs in the dust; but then the deer had to diverge around some trees, and the mother cheetah intercepted the last deer in one group and knocked it over in a tangle of fur that ended with her on top, teeth sunk in the spine at the deer’s neck, holding on. The deer heaved up a little and then was still. The sight of blood was its usual red shock. The cubs arrived late, and Wahram wondered if their lesson had taught them anything but the need to grow up, the need to run fast.

  He found he was standing. And now, looking left at some motion, he saw another person: Swan. Surprised, he waved to her, and she lifted her chin as she continued to watch the cheetah kill. The mother was now teaching the kittens how to eat a deer, not that they needed much instruction there. Wahram surveyed the scene. The lit part of the sunline was now far toward the fore end of the terrarium, its light slanting back with a sunset tint. Masses of grass clumps waved in the wind. It felt like an ancient moment.

  Swan walked over to him and ascended the knoll. It
was going to be a little embarrassing to be found out here alone, which in some parks was not legal, and in general was not considered prudent. Then again, here she was too.

  He nodded his greeting, formal but not unfriendly. “Unusual luck to see such a thing,” he remarked as she approached.

  “Yes,” she said. “Are you out here alone?”

  “I am. And you?”

  “Alone, yes.” She was looking at him curiously. “I’m surprised to find you out here, I must confess. I didn’t know you liked this kind of thing.”

  “Mercury isn’t really where you would find out.”

  She gestured at the cats. “You aren’t worried?”

  “They’re scared of people, I find.”

  “Well, but if they’re hungry…”

  “But they never are, that’s the thing. There’s so much easy prey.”

  “That’s true. But if they have never run into people before, they’ll just think of you as a kind of chimp. Very tasty, no doubt. A delicacy. You hear of it happening. They have no experience of being hunted.”

  “I’m aware we could be prey,” Wahram said. “I carry a little stunner just in case. Don’t you?”

  “I don’t,” she admitted after a pause. “I mean, sometimes I do, but mostly to avoid spending a night in jail.”

  “Indeed.”

  She tilted her head, as if listening to a voice in her ear. She had had her qube implanted, Alex had told him, back when the idea was fashionable. “Speaking of eating,” she said, “shall we get something?”