On Wet Stars 5; Visit to a Wet Star

    5. Visit to a Wet Star

    My starship rehiggsed when sensors pinged an infrared emitter. With higgs-field normalized and ship mass regained, ship and I were at rest, far from any star but only a light-year from a small, intense heat source. I aimed at the object and dehiggsed. Massless, ship and I propagated at lightspeed.
    Ship and I rehiggsed a light-hour away from a small planetoid, 1578  kilometers in radius, glowing bright in infrared at the triple point of water. Spectroscope showed water, carbon dioxide and nitrogen, with traces of oxygen and helium.
    I had stumbled upon a rogue world, glowing from its own heat. The sunless slushball was hurtling from one dense nebula to another one, each ten light-years away, with a hundred thousand years to the encounter. It had 1/3 the mass of Europa, 1/24 gee surface gravity, and an escape velocity of 1179 m/s. By composition it had to be mostly water. It was a small waterworld, with liquid, vapor and ice at the surface. Which made no sense, without some sort of internal heat source.

    A Steppenwolf? A rogue water-world, with a hot radioactive core? Lifebearing? Interesting… but that slushball was too small and light for much of a metal core. It also had a magnetosphere, a Van Allen belt, and polar auroras. But how? What was it?
    I had to explore. First things first; I collected all data so far, saved the file, entangled it with a cache on Earth, and chirped Earth the key. Then I aimed my ship and dehiggsed.
    My ship rehiggsed ten radii away from the object, and I knew right away that the planetoid was artificial and inhabited. My scopes showed megastructures; several skyhook cables; a ringlike habitat spanning the planetoid’s icy equator. The equator was icebound,  but the poles were liquid and at 30 degrees C; rather the reverse of the norm! Also it had a moon of its own, covered with mass drivers and ion drives.
    I saw all of this in infrared. There was no sunlight; the rogue world was deep in the night between the stars; only starlight lit the tops of its clouds. The planetoid had an active weather system, with constant precipitation near the equator. The equatorial belt flickered blue with lightning.
    The sea and the icebelt were dark… except for the city-ship lights. The water of Wet Star Nemo (for so they named it to me later) glowed from within like bioluminescent surf; which in a sense it was. The sight was magical. It’s always night on Nemo; but its seas are as spangled with lights as stars in the sky; for the city-ships are, in a sense, small stars.
    The Nemoites spotted me right away. They radioed greetings and docking orders. Tractor beams gripped my ship and carried it to the tip of one of the orbital towers. That’s where they have their docks; and also their observatories.
    What transpired then would take far more time and space to recount than this brief blog can contain; in fact the Nemoites prolonged my visit for reasons of their own. This is but a brief sketch of notes from a visit to a miniaturized type I civilization. Nemo has a trillion inhabitants, mostly in millions of megacities, each in a diamond-hulled deep-water 3-kilometer-wide fusion-powered arcology ship. Nemo has the population of a civilization covering every world in a star-system, but in a smaller region, for it populates volume, not area; and the short distances allows the entire megaswarm of megacities to be wired up in small-planetoid time. Nemo has a real-time cyberspace.
    The design philosophy of Nemo is: fusion power; distributed intelligence; self-sufficiency; self-maintenance; recycling and scavenging; scale power to infrastructure, not vice versa; webs, not hubs; robust persistent natural flows. Nemo is an artificial star, an ecology, a city-of-cities and a noosphere.
    This they told me when they ferried me and my ship down the tower to the equatorial Ring. The Ring is a 10-kilometer wide torus, 9914 kilometers around, buried kilometers under the equatorial icebelt, connected to skyhook towers, mass-driver outlets, and particle-accelerator ports. The Nemoites showed this to me.
    They also pointed out Nemo’s tug moon, covered with with ion drives and microwave rectenna. Nemo’s Ring and ships beam microwave power to the tug, which powers its ion drive, which holds it at a fixed position near Nemo; a gravity tug. That, plus slingshotting past large planets, is Nemo’s motility system.
    The Ring contains a superconducting loop, charged with enough permanent current to sustain the planetoid’s magnetosphere. It also has mass-drivers, particle accelerators, fleets of spaceships, dry-docks for Nemo’s ship-cities, equatorial monorails, servers for the planetary internet, other big equipment, parklands, towns, and cities. It is of course fusion-powered, by a mixture of tokamak, Bussard polywell and inertial-confinement fusors.
     The Ring is Nemo’s Port-World; a mega-habitat. It alternates parkland, wilderness and cities for a population of about a billion inhabitants. It fell into uninhabitable disrepair about a hundred million years ago (same time as the freezing-over) but civilization re-arose and fixed the problem; for though sometimes the Ring breaks, the city-ships endure.
    Nemo’s ocean and its Ring form two quite distinct technozones; Nemo’s yin and yang, so to speak. Most of the people of Nemo inhabit 3 kilometer-wide diamond-hulled deep-ocean fusion-powered arcology ships. Who needs a star when you have a fusor and you’re swimming in fuel?

    There are about a million ships in Nemo, each with about a million inhabitants, for a total of a trillion people. The city-ships are mostly self-sustaining; they exchange mostly people and information. They plasma-torch all waste down to atoms, to recycle with almost 100% efficiency. The heat output of those millions of city-ships are what keeps most of Nemo liquid.

    The waterworld’s liquid volume  is 1.649 * 10^10 km^3; when divided among a million ships, is 1.649 * 10^4 km^3 per ship, for an average distance of 25 kilometers between ships.

    That’s not too crowded, they say... but traffic control is a constant necessity. You don’t want to crack your city’s diamond hull, or damage its external engines. The ships display swarming behavior, like birds or fish; and this is facilitated by the planetary Internet; the Wet Net, they called it.
   
    The city-ships are in constant communication, for traffic, current, temperature and pressure reports. For they are not entirely in control of their water-world; it has a way of its own which city-ships, Ring, and Eggs must respect.

     Nemo’s ocean convects in a double-donut, with warm water rising to the poles, flowing to the equator, cooling and sinking there. Therefore warm open ocean at the poles and ice at the equator. But other convection patterns could prevail, such as single-donut convection; to avoid this, the Nemo ships cooperate to manipulate heat generation and currents.

    The city-ships coordinate, via Wet Net, power output to ensure that their world neither boils nor freezes over. The latter had happened in the past once, the Nemoites said; but they overcame that and put in safeguards. It wasn’t that long ago, only a hundred million years. What’s time to a Wet Star? 

    The Nemoites figure that there is sufficient water-fuel on Nemo to keep its civilizations running for a trillion years. Civilizations, plural, for the city ships are born, flourish, and eventually fail and break, mostly independently. And this process had been going on continuously, with hundreds of thousands of city-ships always at each phase of the process, for a billion years. So the waterworld has hosted some form of civilization, hosted by some breed of Nemoite (of which there are many species) for astronomical times. Or so the Wet Net said.

    Nemo’s immediate travel-plans (meaning; for the next billion years) were this spiral galaxy, then the Magellenic Clouds, then Andromeda, then  leave the Local Group and head for the Virgo Cluster.

    The Nemoites persuaded me to park my ship in the Ring while I took a tour via city-ship down to the Eggs at the Core, then up to a Pole, then a surface cruise to the icebelt, then onto the Ring and by monorail back to my ship. Again, more than I can tell in this short blog.

    Conditions at the Core are strange; gigapascal pressure and microgravitation. The Ship Eggs there serve as city-ship drydocks. They also process fragments of broken ship debris, which constantly accumulates at the core due to Nemo’s weak gravitation and strong convection.

    They let me tour the ship docks. Too much to tell here. Docking at gigapascal is like docking at vacuum but in reverse. They even tell the same jokes that spacers do, comparing docking to sex; for in both cases vessels must exchange vulnerable small organisms across a hostile medium. There are packet-exchange systems, like Scorpiod sex (the Scorpoids themselves don’t use it, they find it vulgar) and cloacal systems (avoided by the Aves) and of course docking-tube systems. Nemoites told these jokes, and they admired my news about Scorpoids and Aves. Fortunately their tales about my having to dress up in a white sperm suit was more Nemoite joking.
   
    That tour through the shipyards took so long that I should have figured out that something was up. I did later, just before they threw me away, by checking the Wet Net about what they had been calling me behind my back.  I didn’t know any of that at the time.
   
    After a prolonged Egg tour my cruise city rode convection up to surface at the North Pole. There I visited a surface-ship city, stationed at the pole. From the polar city I saw magnificent auroras, and a view of the Galaxy. It’s always night on Nemo. I learned that the polar city harvests helium from the atmosphere, and from visiting city-ships; it then sends this helium down to the Core Eggs, which uses helium for emptying out new Eggs at gigapascal; and in return the Eggs send the polar city products manufactured in zero-gee. They explained all this at length.

    I eventually returned to my cruise city. We drifted on convection south towards the equator. The sky clouded up; fog turned to rain, and then snow and sleet. My cruise submerged well north of the equatorial hailstorms, and docked at the Ring.

    I rode the monorail, eager to return to my starship. But the ride was long, so I logged onto the Wet Net. That’s when I found out what a trillion minds really thought about  me. They called me “tourist”, “outer barbarian”, “the rube”, and “Specimen Alpha”. My ship they called “his ride”, “the puzzle”, “the prize” and “Prototype Alpha”.

    I also found out what they really did about me. Namely, they disassembled my ship, down to the atom, and reverse-engineered it. While I was on a leisurely grand tour, a million megacities were hastily processing and replicating, within weeks, hundreds of years of my own star-system’s technological progress. That’s what a coordinated teramind fusion-powered noosphere can do. My original ship was vaporized in the nanoscan; what awaited me was a manufactured replica, identical down to the atom. They’d already tested it, and their replica worked.
   
    When I got to my stop, I was boiling mad; but I couldn’t prove anything, the ship looked better than ever (“courtesy maintenance and upgrade”, they said) and all systems were go. Only a fool trusts what you read on the Wet Net; so I kept my mouth shut and  I boarded what they called my ship. They lifted my ship up a skyhook cable and ejected it into space.

    I was out past the tug-moon and the Van Allen belt and about to dehiggs when sensors detected an enormous dehiggsing field forming behind me. It was Nemo, using the technology they stole from me! The entire world, including skyhooks and tug-moon, dehiggsed and propagated away at lightspeed, in its original heading. It’ll reach its destination nebula, for water and mineral restocking, in ten years, not a hundred thousand.
   
    Not that it matters much; what’s time to a Wet Star?

    It’s a world that got away. I don’t blame you if you don’t believe me; all I have to show for the experience is memories, and lots of crappy tourist memorabilia, most of it cast in cheap diamond.

On Wet Stars 4; Conversation between Hellerstein and Nordley

    4. Conversation between N. Hellerstein and G. David Nordley:


NH:
But a 10,000 km torus does provide room for a great big honking particle accelerator; any use for that?

GDN:
On could use it to push small starships up to near relativistic speeds, to deal with external issues.

NH:
To scout out an approaching nebula, I suppose. How much use would the particle beam be for asteroid and meteor defense? Or would that be a misuse of a precision technology? What asteroid defenses do you propose?


***


NH:
Iain Banks noted, in “The Algebraist”, that the core of an all-liquid world will experience microgee. Any use for that?

GDN:
Well, the space station advocates believe there are all sorts of uses for microgee.   A hollow diamond sphere at the center would have essentially zero g throughout its volume, just as the electric field within a charged metal sphere is zero.

NH:
So, a room-temperature shirtsleeve zero-gee drydock. Excellent! I suppose they’ll build ships in it; so call them “Eggs”. But these Eggs need propulsion and Wet Net access to stay at the core despite whatever currents there are.

***

NH:
Speaking of which... I am concerned that the wet star is too light to hold its hydrogen. How badly will it leak? Can keeping sufficient magnetosphere and oxygen keep it wet, or will it constantly have to absorb comets?

GDN:
At the 30K starlight equilibrium temperature (the surface for a thin atmosphere, the tropopause for a thick one) the mean molecular velocity of monatomic hydrogen is 0.852 km/s and molecular hydrogen is 0.6.   So it will leak a little, but not much.   Helium’s is 0.426, so one would expect the atmospher to become helium enriched with time.   Heavier gasses would freeze out before they get high enough to be subject to Jean’s evaporation.   It would lose a lot of this gas, even with a protective magnetic field, in stellar periastron passes, of course.

NH:
Suppose it takes a 1,000,000 year jaunt between stars. How much water will it lose? How does it go about ingesting new water? Earlier versions of the Wet Star were Neptune-sized and didn’t mind plowing into an ice ring one bit. But now that it’s Europa-sized and has vulnerable necessary surface structures, it’ll have to eat more daintily. Dock a comet at the tip of an elevator cable and sip its water down? Or will dropping comets onto the poles do?

And as for excess helium; give that as reaction mass to the gravity tug?

***

NH:
And let’s not forget the gravity-tug. How big should it be?

GDN:
I thought I gave you a point design for that.   What kind of delta V do you want, and how fast do you want to get it?

NH:
Okay, here’s the mission: Nemo was built in Kuiper Belt orbit (or to be precise it was melted and stocked): lately its inhabitants, all 100 billion of them, want out from solar system politics. They plan to slingshot past Jupiter and head out into interstellar space; and they’re willing to take 100 Earth years until encounter. How big a tug would they need? And can they keep the tug after Jupiter encounter?

So they slingshot past Jupiter and are heading to Alpha Centauri. How long will it take them to get there? Suppose that half-way there they see that Alpha’s boring, Proxima’s the star to visit. How big a tug moon do they need to change course?

On Wet Stars 3; Wet Star Nemo

    3. Wet Star Nemo



    The previous blog described a Wet Star as an enhanced Steppenwolf. This is a simple form; but perhaps more advanced models exist.

    So consider Nemo, a Wet Star. It has no iron core; it is almost entirely liquid, and heated by artificial fusion. It incorporates megastructures, and also a swarm of deep-ocean ship-arcologies. Its water radius is 1578 km; its ocean (well-mixed by convection) averages 30 degrees C; pressure at the core is 1.04 gigapascals; it has about 1/3 the mass of Europa, 1/24 gee surface gravity (and zero-gee at the core!), and an escape velocity of 1179 m/s.

     Nemo’s ocean convects in a double-donut, with warm water rising to the poles, flowing to the equator, cooling and sinking there. Therefore open ocean at the poles and ice at the equator. But perhaps other convection patterns could prevail, such as single-donut convection; to avoid this, the Nemo ships will cooperate to manipulate heat generation and currents.

    I have been assuming that a million fusion-powered ships holding a hundred billion people will generate enough waste heat to keep the wet star liquid and convecting. I have not done the numbers, and indeed have no idea how to do such numbers; so the basic idea of the Wet star may be entirely invalid. Will it freeze over? Will it boil? What is the correct power output per ship?

    Nemo has a magnetosphere, generated by a superconducting loop spanning Nemo’s equator. This loop is housed in a megastructure; the Ring, a tunnel 1 km wide and 9914 km long, buried under the equatorial icebelt. The Ring contains the superconducting loop, dry dock for the ships, monorail, particle accelerator, servers for the planetary internet, other big equipment, parklands, towns, and cities. The Ring is a classic mega-habitat; if you populate it at New York City density (about 68380 people/km^2) then the Ring has about 678 million people. A proper nation! And just for the planetary port!

    If you make the Ring ten km wide, then New York City density gets you 6.78 billion people; a properly Trantorian world-city! I recommend alternating cities, towns, and wilderness, for a billion people. The Ring as Port World!

    The Ring is buried kilometers under the equatorial icebelt (for meteor protection) and has bits poking out; including at least one elevator cable to geosynch, for cheap planetary access to space. Also the exit ports for the particle beam, and maybe for the mass-drivers. (Though perhaps mass-drivers and elevator cables don’t mix.)

    Nemo is accompanied by a small moon covered with with ion drives and microwave rectenna. Nemo’s Ring and ships beam microwave power to the tug, which powers its ion drive, which holds it at a fixed position near Nemo; a gravity tug. This, plus slingshotting past large planets, is Nemo’s motility system.

    Nemo’s ocean and its Ring form two quite distinct technozones; Nemo’s yin and yang, so to speak. Most of the people of Nemo inhabit 1 km-wide diamond-hulled deep-ocean fusion-powered arcology ships. I wanted a million ships in Nemo, but I worried that this might crowd a water sphere merely 1578 km in radius. Not to worry; that’s a volume of 1.649 * 10^10 km^3  ; if that is divided among a million ships, that’s 1.649 * 10^4 km^3 per ship. I here assume that the average distance between ships is the cube root of that number - though perhaps I am off by a factor of the square root of three or something. If not, then there’s about 25.4 km distance between ships.

    That’s not too crowded, I think... but I suppose that traffic control will be a constant necessity. You don’t want to crack your diamond hull. No doubt the ships will exhibit swarming behavior, like birds, or fish!

    So let’s say a million ships fit into Nemo with reasonable comfort. I had originally wanted to put a million people in each ship, but on second thought 100,000 people is a perfectly fine city, and I think they will fit comfortably into a kilometer-wide sphere with room for equipment. A million ships times a hundred thousand people per ship is a hundred billion people.

    100,000,000,000 people! That’s a flock of type I civilizations, all wired together! And in such a small volume, too!

             And if you want a trillion people, then let each ship be 2.2 kilometers across; that’ll accommodate cities of a million each.

On Wet Stars 2; Steppenwolf

     2. Steppenwolf


    The trouble with Dyson Sphere and Ringworld and Orbital is that they attempt to capture a significant fraction of a star’s energy output; the Sphere all of it, the Ringworld a few percentage, the Orbital a few percent of a percent. But a star is so enormous, on the human scale, that even an Orbital is monstrously big. I submit that it is bad engineering to build a habitat up to the size of your power source; far sounder to scale power source down to the size of your habitat.

    This blog series describes “Wet Stars”. These are habitats as populous as a Ringworld, but robust enough to shrug off a volley of asteroid strikes. A Wet Star is a kind of “Steppenwolf”, or habitable rogue water-world. A sunless world can harbor an under-ice ocean if it is a bit larger than Earth, or has a thicker atmosphere; fission in the rocky core keeps the ocean liquid and out of thermodynamic equilibrium for gigayears; plenty of time to form a biosphere.

    I like this; it means that you don’t need stars for life. Stars are wasteful; we barely use ours; once we master fusion then stars will be obsolete. Who needs a star when you have a polywell fusor?

    The universe has already made 95% of all the stars it will ever make; so stars are not an expanding niche. But there’s plenty of material left to make rogue planets from.

    A Wet Star is an enhanced Steppenwolf. It is a sunless inhabited planet, powered by its own nuclear energy; but where the Steppenwolf is powered by its core’s dumb fission, fading with time, the Wet Star is powered by its biosphere’s smart fusion, constant over time.

    The Wet Star’s structure is as follows: its core is a Moon-sized sphere of magnetized iron, for gravity and for a magnetosphere; this is surrounded by a thick shell of high-pressure ices; surrounded by a deep ocean, surrounded by an atmosphere. It is mostly dirty ice and dirty water, four to five times the radius of Earth, with 1 gee surface gravity. The deep ocean is heated by the waste heat of millions of fusion-powered deep-sea vessels. Each vessel is a fusion-powered submarine arcology; each with up to millions of inhabitants; making a possible population of trillions. This is comparable to a single Ringworld, or a flock of Orbitals, but much smaller in size, because it populates volume not area. I said the Wet Star has a ‘biosphere’, but really it has a ‘technoshell’.

    Because distances in a Wet Star are less than a light-second (unlike Orbital or Ringworld or Dyson Sphere) it’s possible for the millions of vessels to communicate quickly, and thus form a planetary internet, or nooshell, for exchanging information about positions, currents, traffic, temperature, chemical composition, and much else.

    We, on Earth, now have a planetary information system, but that system is not a Multivac, not a benevolent Hub, nor a tyrannical Colossus. It’s not a Personality set above us; it’s a Network, it’s made by us, it is us. So, too, is the Wet Star’s Net; the Wet Net.

    The basic design intuitions of the Wet Star are: 1) webs, not hubs;  2) simple robust liquid flows, not complex fiddly solid structures; 3) deep ocean for food, fuel, gravitation, and shielding; and above all 4) who needs a star when you have a Bussard polywell?

    The Wet Star’s biggest problems are; motility, magnetosphere, and technoshell coordination, especially in heat regulation. How to get a million independent city-states to burn just enough hydrogen to keep the ocean liquid, but not boil it off? That’s where the Wet Net comes in.

    The Wet Net also make the Wet Star able to react as a unit in the case of collision, radiation or other threat. The vessels usually react simply by retreating to the bottom of the deep ocean; sufficient shielding against asteroid or supernova blast; but they have other resources too.

    The vessels reproduce, age, die, and are broken up for parts, inhabitants and material. They share language, math, information and inhabitants but are otherwise independent. The vessels can meet to exchange materials or inhabitants.

    (These encounters resemble sexual encounters, for docking and sex must solve the same technical problem of getting vulnerable small organisms from one hospitable vessel to another, through a hostile environment. It’ll be easy for a writer to play this for laughs; for instance if you want to go from one vessel to another then you have to wear one of those white Woody Allen sperm suits.)

    The Wet Star’s ocean is heated from within, and cooled at the surface; therefore it convects. The water wells up at both poles, then circulates towards the frozen equatorial belt, then descends and circulates poleward. The equatorial ice-belt is the wet star’s only solid surface. Taken as a whole, the wet star is fixed at the triple point of water. Its atmosphere is water vapor, CO2 and other greenhouse gases; but also some oxygen and helium; these being left over from fusing the hydrogen from ocean water. The helium is light and warm enough to escape the wet star; it outgasses helium constantly, and in consequence the wet star slowly loses mass. Trillions of years from now that might cause trouble; but by that time a wet star could ‘refuel’ by plowing into a Saturn-like world’s ice ring.

    The wet star’s atmosphere also convects, and it has weather. There are constant thunderstorms at the equatorial icebelt.

    The wet star’s magnetic core gives it a magnetosphere; but perhaps that would not remain magnetized for the terayears I see possible. Perhaps the Wet Star’s technoshell could cooperatively manipulate ionic currents in its constantly-convecting deep ocean to generate a truly organic magnetosphere. It’s a trillion-year continuous maintenance chore, but necessary in a radiologically hazardous Galaxy.

    Of course a Wet Star doesn’t need a Galaxy any more than it needs a
star. So it could just up and leave... given motility. But how to mount an effective engine on an inhabited slushball as big as Neptune? Perhaps... give each of those billions of vessels a neutralino beam, which they all fire continuously in unison? Or maybe hook a cable to geosynch at the ice belt, and fire an ion drive from geosynch? It may take a while to change course, but what’s time to a wet star?

    The above are my speculations to date. I have mentioned this to Pournelle, friend of Niven, and he put it on his website. I also sent it to Iain Banks. Of course this is just a rough sketch; numbers and feasibility need checking.


    G. David Nordley wrote me to say:

    “The ‘fast’ way of giving delta-v to such an object would be to perform a parabolic trajectory around a much more massive object that happens to be moving in the right direction.   Looked at from a great distance, it is as if the objects “bounce” off each other, like billiard balls.   It could pick up some mass at the same time, of course.   The object will be too massive and too cold to lose mass by evaporation, indeed it will need to get rid of accreted mass from time to time if one is thinking in terms of multibillion year time scales.”  
    “For low acceleration course adjustments, a nuclear powered rocket could hover out in ‘front’ of an Earth-mass planet (one of the asteroid-moving schemes, scaled up by about 20 orders of magnitude).   Let us imagine an ion rocket array with a thrust of 20 million kN, (about 2 million kg force) and an exhaust velocity of 100 km/s with a continuous supply of mass and energy from the planet. It would change the planet’s  velocity by about 1m/s in a million years and consume about 6.2 E16 metric tons of mass (about that of an asteroid or small moon).   Also, the planet’s magnetic field could interact with the galactic field to steer the planet. While ‘new physics’ may come into play, especially at that time scale, I like to confine my imaginings to the physics we know; it’s almost always adequate.”

    “The magnetosphere is less of a problem than you might think.   Build a pipeline full of superconductors around the world on the sea floor and pump current into it.   A loop that big gives you a nice magnetic field with large but manageable currents.”

    “Even with no internal power source, one will get liquid water temperatures powered only by starlight, if one’s atmosphere is deep enough.   Starlight in this part of the galaxy gives one an effective temperature of about 25K.   Start with an effective temperature of about 20-30 K at the tropopause, then with a lapse rate of   6.5K/km one gets to 280 to 290K at about 40 km deep.”

On Wet Stars 1; Critique of the Rickety Big House

               On Wet Stars

               and Sustainable Astroengineering

               A blog in five parts:

1. Critique of the Rickety Big House

2. Steppenwolf

3. Wet Star Nemo

4. Conversation between Hellerstein and Nordley

5. Visit to a Wet Star

               1. Critique of the Rickety Big House

               This series of five blogs is a critique of astroengineering as a fantasy of control. This includes Dyson spheres and Ringworlds. This series also suggests an alternative astroengineering project. I call it the “Wet Star”; and I post it here for people to check and critique.

               Consider the Dyson Sphere, of Kardeshev level 2, which captures all the energy output of a star. It could be a “Dyson swarm” of separate habitats, as originally conceived; or it could be a solid shell. Either design choice is troublesome. If a solid shell, then made of what super-material, and how to keep it stable? And what about maintenance?

               Or is the Sphere instead separately orbiting habitats? What a traffic problem! If habitats collide, then they’ll spew debris which will hit and break up other habitats; a cascade! I suspect that, without continuous traffic monitoring, within a mere megayear the habitat fragments will accrete to form planetesimals.

               Niven downscaled the Sphere to the Ringworld. It’s a solid structure, monstrously big, vulnerable to asteroid strikes. Also you need material with the tensile strength of nuclei. Also its orbit is unstable, and it’ll scrape the sun unless you put in attitude jets; and Niven had these kill a billion neighbors every time they fire. So Niven’s Ringworld is naturally a technofascism. Yuck.

               Iain Banks, who is as unrepentantly utopian-socialist as Teapot-Dome-grandheir Niven is cynical-capitalist, downscales the Ringworld even further to his “Culture” star-civilization’s “Orbitals”. An Orbital is a Ringworld-like band, with the radius equal to that of the Earth-Moon system; a Kardeshev-level 1 cinvilizaton. It rotates in one standard day; with the result that it is at one standard gee. No need for shadow squares for a day-night cycle, just tilt the Orbital’s axis of rotation a bit from its orbital axis. Also no sun-scraping or attitude jets; but you still need super-materials. Banks gives each Orbital a “Hub Mind” - that is, a meddling paternalist posthuman AI running everything.

               These three visions have much in common. They are fantasies of control; they are gigantic. They are also... how shall I put this... brittle. Untopological. Slackless. There’s no blob factor allowed. That Orbital has got to spin just right or it’ll fly into pieces; so naturally it needs a busybody in charge. So naturally, the damn thing’s doomed. Ditto with Ringworld and Dyson Sphere.

               All of these systems must be actively maintained, with constant monitoring, adjustment and repair; which implies a living civilization continuously inhabiting the gigastructure. But civilizations rise and fall; they cannot be continuously maintained for longer than mere millennia; far too brief a timescale for astroengineering!

               I propose that astroengineers must design with a timeframe beyond the lifespans of nations, religions, civilizations, languages or even species. Vital systems must be passively self-maintaining over megayears or even gigayears.

               Astro-engineers, take note: the stars are not just big; they are also old.

The City's True Name 12; The City That Only Kids Can See

            The City That Only Kids Can See

            Sogwa whispered,“Tomorrow,” and the portal opened up all the way. She stepped through, and it sealed shut behind her.

            The portal opened at the sound of the City’s true name; though, as Grandma Marge had pointed out, it has many names. “The Future, Posterity, After My Time,” she had said, “all these names are true! And do you see why only kids can see such a City?”

            “Yes,” Sogwa had said quite meekly, to blue-glowing, see-through Grandma Marge.

            Grandma Marge had smiled, and she’d said, “The specific name you need is ‘Tomorrow’.”

            “Tomorrow?” Sogwa had marvelled.

            “In my case, no exaggeration,” Grandma Marge had noted, “so it makes its point.”

            And indeed it did, for the portal opened, and Sogwa stepped through, into Chaos.

            Chaos was a storm-wind. It was like being blown, whirled, cast up and down and up again, through three twists and a fourth, sucked dizzily through an infinite spiral. All was in chaos, and chaos was in all.

            Chaos was turbulent, yet calm. Moving, it rested. Chaos was, and chaos was not. Chaos was formless and void; neither light nor darkness was on the face of the deep.

            But Liberty was there; and the spirit of Liberty passed over the sea of chaos.

            And Liberty said, “Let there be light.”

            And there was light.

            Why, you ask? How did she do it? What is the secret of her creative power?

            I shall tell you.

            You see, there is no secret to her creative power. There’s no secret because it isn’t power. Liberty did not command; she permitted. She let there be light.

            Liberty allowed the light; thus it arose spontaneously. Blessed be Liberty!

            There was light, so Sogwa opened her eyes. She looked around and saw that she was in bed, in her bedroom, and it was morning.

            A ray of golden sunlight beamed flat across the room and lit a young girl, stirring in bed though still asleep. Sogwa pounced on her and padded all over her chest, saying, “Mew, mew! Wake up, it’s morning! Mew, mew! It’s morning, it’s tomorrow, wake up, Hannah, wake up!”

            That’s the story that Sogwa told me last night, and now I’ve told it to you.

The  End

The City's True Name 11; Mount Auburn

            Mount Auburn

            Sogwa stepped through the portal, to Mount Auburn, Plot Number 10782 / 2 .

            It was late pre-morning, dew-time; the sky was black, with a faint hint of pink towards the east. And right below the eastern horizon, just barely visible to Sogwa’s cat-eyes, was her destination; the City That Only Kids Can See. She needed only its true name to enter.

            All around Sogwa were see-through people, all glowing blue. They chatted to each other:

            “Sun’s coming up soon!”

            “Back to bed then, now, right?”

            “Right! I can’t outshine that!”

            And the blue-glowing see-through people all went back to their plots. They stepped down into the earth like you would get into a tub. Sighing, they laid down and vanished into the ground.

            A blue-glowing see-through person approached. It was Grandma Marge.

            Grandma Marge was as beautiful as ever. Her eyes were sky blue, her hair was brown, with white roots if you looked hard. She wore a  half-smile; her face was grooved deep with smile lines.

            Sogwa said, “Grandma Marge, it’s me.”

            Grandma Marge saw her, and smiled deeper. “Hi, Sogwa.”

            Sogwa said, “I know you have to lie down before the sun comes up, but before you do, please, Grandma Marge, can you tell me the true name? I need it to get home.”

            “The true name of what?”

            “The City That Only Kids Can See,” said Sogwa. “That one over there,” she said, pointing a paw towards the east.

            Grandma Marge squinted towards the east. She said, “I can’t quite make it out.”

            Sogwa said, “I can see it plain as day!”

            “Then tell me what you see.”

            Sogwa said, “Look! Right there! It’s the spaceport! See? A ship just blasted off!”

            “Mm-hm!” Grandma Marge murmured, not seeing.

            “Can’t you see all the hovercabs flitting around? And the monorails? And the bullet trains? And the geodesic domes?”

            Grandma Marge said, “No, I can’t, it’s still too dark.”

            “Look! Over there! It’s the Robot Works!”

            “Who works there?”

            “Robots!”

            “What do they make there?”

            “More robots!”

            Grandma Marge said “Hmph!”

            Sogwa pointed out other sights of the City That Only Kids Can See; the wind farms, tide-mills and sun towers; the recombinant zoo, the gasoline trees, the fusion incinerator, the air-car perch, the cyberspace cafe, the moving-picture-paper mill, the super-telescope, the replicator works, the rejuvenation clinic, the hologram theater, the World Parliament and the Lunar Embassy.

            Sometimes Grandma Marge said “Mm-hmm!” and sometimes “Ahh...” and sometimes “Hmph!”; but each time she smiled, with smile-lines creased deep. All the while Grandma Marge saw not a thing, for it was still too dark for her human eyes, though not for Sogwa’s cat-eyes.

            Finally Grandma Marge said, “So you want the City’s true name.”

            “And the reason why,” Sogwa added.

            “The reason why is clear enough,” said Grandma Marge, “and so’s the name. But really, it has many names.”

            Then Grandma Marge gave Sogwa three true names for the City That Only Kids Can See. Sogwa saw in each name its own explanation.

            Grandma Marge told Sogwa the specific name she needed to get back home. Sogwa marvelled at the name and Grandma Marge noted, “It makes its point.”

            With that, Grandma Marge stepped down into the earth like you would get into a tub. With a sigh she lay down and vanished.

            Sogwa said, “Goodbye, Grandma Marge.”

            Then Sogwa held up a paw and said, “Access web.” One claw on her paw gleamed bright; she whipped her paw around in a circle; this left behind a glowing circle in the air, which flickered one, twice, then blazed blue. The portal sounded a chime, and it said,

            “Welcome to the Web.”

            Sogwa clicked on System, then Tools, then Damons, then Clock Damon.

            The portal opened halfway; from within glittered brass gears, whirling and clattering. The Clock Damon said, “State your destination.”

            And Sogwa whispered the true name of the City That Only Kids Can See.

            She whispered,

            “Tomorrow...”

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