A Hole In Space, page 13
What some science fiction writers have been calling a Dyson sphere is something else: a hollow spherical shell, like a ping pong ball with a star in the middle. Mathematically at least, it is possible to build such a shell without leaving the solar system for materials. The planet Jupiter has a mass of 2 x lO^30 grams, which is most of the mass of the solar system excluding the sun. Given massive transmutation of elements, we can convert Jupiter into a spherical shell 93 million miles in radius and maybe ten to twenty feet thick. If we don't have transmutation, we can still do it, with a thinner shell. There are at least ten Earth masses of building material in the solar system, once we throw away the useless gasses.
The surface area inside a Dyson sphere is about a billion times that of the Earth. Very few galactic civilizations in science fiction have included as many as a billion worlds. Here you'd have that much territory within walking distance, assuming you were immortal.
Naturally we would have to set up a biosphere on the inner surface. We'd also need gravity generators. The gravitational attraction inside a Uniform spherical shell is zero. The net pull would come from the sun, and everything would gradually drift upward into it.
So. We spot gravity generators all over the shell, to hold down the air and the people and the buildings. "Down" is outward, toward the stars.
We can control the temperature of any locality by varying the heat-retaining properties of the shell. In fact, we may want to enlarge the shell, to give us more room or to make the permanent noonday sun look smaller. All we need do is make the shell a better insulator: foam the material, for instance. If it holds heat too well, we may want to add radiator fins to the outside.
Note that life is not necessarily pleasant in a Dyson sphere. We can't see the stars. It is always noon. We can't dig mines or basements. And if one of the gravity generators ever went out, the resulting disaster would make the end of the Earth look trivial by comparison.
But if we need a Dyson sphere, and if it can be built, we'll probably build it.
Now, Dyson's assumptions (expanding population, expanding need for power) may hold for any industrial society, human or not. If an astronomer were looking for inhabited stellar systems, he would be missing the point if he watched only the visible stars. The galaxy's most advanced civilizations may be spherical shells about the size of the Earth's orbit, radiating as much power as a Sol-type sun, but at about 1O angstroms wavelength-in the deep infrared...
...assuming that the galaxy's most advanced civilizations are protoplasmic. But beings whose chemistry is based on molten copper, say, would want a hotter environment. They might have evolved faster, in temperatures where chemistry and biochemistry would move far faster. There might be a lot more of them than of us. And their red-hot Dyson spheres would look deceptively like red giant or supergiant stars. One wonders.
In The Wanderer, novelist Fritz Leiber suggested that most of the visible stars have already been surrounded by shells of worlds. We are watching old light, he suggested, light that was on its way to Earth before the industrial expansion of galactic civilization really hit its stride. Already we see some of the result: the opaque dust clouds astronomers find in the direction of the galactic core are not dust clouds, but walls of Dyson spheres blocking the stars within.
I myself have dreamed up an intermediate step between Dyson spheres and planets. Build a ring 93 million miles in radius—one Earth orbit—which would make it 600 million miles long. If we have the mass of Jupiter to work with, and if we make it a million miles wide, we get a thickness of about a thousand meters. The Ringworld would thus be much sturdier than a Dyson sphere.
There are other advantages. We can spin it for gravity. A rotation on Its axis of 770 miles/second would give the Ringworld one gravity outward. We wouldn't even have to roof itover. Put walls a thousand miles high at each rim, aimed inward at the sun, and very little of the air will leak over the edges.
Set up an inner ring of shadow squares—light orbiting structures to block out part of the sunlight—and we can have day-and-night cycles in whatever period we like. And we can see the stars, unlike the inhabitants of a Dyson sphere.
The thing is roomy enough; three million times the area of the Earth. It will be some time before anyone-complains of the crowding.
As with most of these structures, our landscape is optional, a challenge to engineer and artist alike. A look at the outer surface of a Ringworld or Dyson sphere would be most instructive. Seas would show as bulges, mountains as dents. River beds and river deltas would be sculpted in; there would be no room for erosion on something as thin as a Ringworld or a Dyson sphere. Seas would be flat-bottomed—-as we use only the top of a sea anyway—and small, with convoluted shorelines. Lots of beachfront. Mountains would exist only for scenery and recreation.
A large meteor would be a disaster on such a structure. A hole in the floor of the Ringworld, if not plugged, would eventually let all the air out, and the pressure differential would cause storms the size of a world, making repairs difficult.
The Ringworld concept is flexible. Consider:
(1) More than one Ringworld can circle a sun. Imagine many Ringworlds, noncoplanar, of slightly differing radii—or of widely differing radii, inhabited by very different intelligent races.
(2) We'd get seasons by bobbing the sun up and down. Actually the Ring would do the bobbing; the sun would stay put. (One Ring to a sun for this trick.)
(3) To build a Ringworld when all the planets in the system are colonized to the hilt (and, baby, we don't need a Ringworld until it's gotten that bad!) pro tem structures are needed. A structure the size of a world and the shape of a pie plate, with a huge rocket thruster underneath and a biosphere in the dish, might serve to house a planet's population while the planet in question is being disassemb1ed. It circles the sun at 770 miles/second, firing outward to maintain its orbit. The depopulated planet becomes two more pie plates, and we wire them in an equilateral triangle and turn off the thrusters, evacuate more planets and start building the Ringworld.
Dyson Spheres 2
I pointed out earlier that gravity generators look unlikely. We may never be able to build them at all. Do we really need to assume gravity generators on a Dyson sphere? There are at least two other solutions.
We can spin the Dyson sphere. It still picks up all the energy of the sun as planned; but the atmosphere collects around the equator, and the rest is in vacuum. We would do better to reshape the structure like a canister of movie film; it gives us greater structural strength. And we wind up with a closed Ringworld.
Or, we can live with the fact that we can't have gravity. According to the suggestion of Dan Aiderson, Ph.D., we can built two concentric spherical shells, the inner shell transparent, the outer transparent or opaque, at our whim. The biosphere is between the two shells.
It would be fun. We can build anything we like within the free fall environment. Buildings would be fragile as a butterfly. Left to themselves they would drift up against the inner shell, but a heavy thread would be enough to tether them against the sun's puny gravity. The only question is, can humanity stand long periods of free fall?
Hold it A Minute
Have you reached the point of vertigo? These structures are hard to hold in your bead. They're so flipping big It might help if I tell you that, though we can't begin to build any of these things, practically anyone can handle them mathematically. Any college freshman can prove that the gravitational attraction inside a spherical shell is zero. The stresses are easy to compute (and generally too strong for anything we make). The mathematics of a Ringworld are those of a suspension bridge with no-endpoints.
Okay, go on with whatever you were doing.
The Disc
What's bigger than a Dyson sphere? Dan Alderson, designer of the Alderson Double Dyson Sphere, now brings you the Alderson Disc. The shape is that of a phonograph record, with a sun situated in the little hole. The radius is about that of the orbit of Mars or Jupiter. Thickness: a few thousand miles.
Gravity is uniformly vertical to the surface (freshman physics again) except for edge effects.. Engineers do have to worry about edge effects; so we'll build a thousand-mile wall around the inner well to keep the atmosphere from drifting into the sun. The outer edge will take care of itself.
This thing is massive. It weighs far more than the sun. We ignore problems of structural strength. Please note that we can inhabit both sides of the structure.
The sun will always be on the horizon, unless we bob it, which we do. (This time it is the sun that does the bobbing.) Now it is always dawn, or dusk, or night.
The Disc would be a wonderful place to stage a Gothic or a swords-and-sorcery novel. The atmosphere is right, and there are real monsters. Consider: we can occupy only a part of the Disc the right distance from the sun. We might as well share the Disc and the cost of its construction with aliens from hotter or colder climes. Mercurians and Venusians nearer the sun, Martians out toward the rim, aliens from other stars living wherever it suits them best. Over the tens of thousands of years, mutations and adaptations would migrate across the sparsely settled borders. If civilization should fall, things could get eerie and interesting.
Cosmic Macaroni
Pat Gunkel has designed a structure analogous to the Ringworld. Imagine a hollow strand of macaroni six hundred million miles long and not particularly thick—say a mile in diameter. Join it in a loop around the sun.
Pat calls it a topopolis. He points out that we could rotate the thing as in the illustration—getting gravity through centrifugal force—because of the lack of torsion effects. At six hundred million miles long and a mile wide, the curvature of the tube is negligible. We can set up a biosphere on the inner surface, with a sunlight tube down the axis and photoelectric power sources on the outside. So far, we've got something bigger than a world but smaller than a Ringworld.
But we don't have to be satisfied with one loop! We can go round and round the sun, as often as we like, as long as the strands don't touch. Pat visualizes endless loops of rotating tube, shaped like a hell of a lot of spaghetti patted roughly into a hollow sphere with a star at the center (and now we call it an aegagropilous topopolis.) As the madhouse civilization that built it continued to expand, the coil would reach to other stars. With the interstellar links using power supplied by the inner coils, the tube city would expand through the galaxy. Eventually our aegagropilous galactotopopolis would look like all the stars in the heavens had been embedded in hair.
The Megasphere
Mathematically at least, it is possible to build a really big Dyson sphere, with the. heart of a galaxy at its center. There probably aren't enough planets to supply us with material. We would have to disassemble some of the star of the galactic arms. But we'll be able to do it by the time we need to.
We put the biosphere- on the outside this time. Surface. gravity is minute, but the atmospheric gradient is infinitesimal. Once again, we assume that it is possible for human beings to adapt to free fall. We live in free fall, above a surface area of tens of millions of light years, within an atmosphere that doesn't thin out for scores of light years.
Temperature control is easy: we vary the heat conductivity of the sphere to pick up and hold enough of the energy from the stars within. Though the radiating surface is great, the volume to hold heat is much greater. Immustrial power would come from photoreceptors inside the shell.
Within this limitless universe of air we can build exceptionally large structures, Ringworld-sized and larger. We could even spin them for gravity. They would remain aloft for many times the lifespan of any known civilization before the gravity of the Core stars pulled them down to contact the surface.
The Megasphere would be a pleasantly poetic place to live. From a flat Earth hanging in space, one could actually reach a nearby moon via a chariot drawn by swans, and stand a good chance of finding selenites there. There would be none of this nonsense about carrying bottles of air along.
One final step to join two opposing life styles, the Macrolife tourist types and the sedentary types who prefer to restructure their home worlds.
The Ringworld rotates at 770 miles/second. Given appropriate conducting surfaces, this rotation could set up enormous magnetic effects. These could be used to control the burning of the sun, to cause it to fire off a jet of gas along the Ringworld axis of rotation. The sun becomes its own rocket. The Ringworld follows, tethered by gravity.
By the time we run Out of sun, the Ring is moving through space at Bussard ramjet velocities. We continue to use the magnetic effect to pinch the interstellar gas into a fusion flame, which now becomes our sun and our motive power.
The Ringworld makes a problematical, vehicle. What's it for? You can't land the damn thing anywhere. A traveling Ringworld. is not useful as a tourist vehicle, anything you want to see, you can put on the Ringworld itself... unless it's a lovely multiple star system like Beta Lyrae but you just can't get that close on a flying Ringworld.
A Ringworld in flight would be a bird of ill omen. It could only be fleeing some galaxy-wide disaster.
Now, galaxies do explode. We have pictures of it happening. The probable explanation is a chain reaction of novae in the galactic core. Perhaps we should be maintaining a space watch for fleeing Ringworlds ... except that we couldn't do anything about it.
We live on a world: small, immobile, vulnerable, and unprotected. But it will not be so forever.
$16,949.00
When the phone rings late at night, there is a limit to who it can be. I had three guesses as I picked it up: a wrong number (all wrong numbers are the same person), or Lois, or—I didn't bother to think his name. It isn't his anyway.
"Hello?"
"Hello," he said. "You know who this is?"
"Kelsey." It's the name he tells me. "What is it, Kelsey? You're not due for another four months."
"I need an advance. Are you sitting down?"
‘Tm in bed, you son of a bitch." Reading a book, but I didn't tell him that. Better he should be off balance.
"Sorry. I just wanted you braced. I need sixteen thousand—"
"Bug off!" I slammed the phone down.
There was no point in picking up the book. He'd call again. Sometimes he waits a few minutes to make me nervous. This time the phone started ringing almost immediately, and
I snatched it up in the same instant and held it to my ear without saying anything. It's a kind of bluffing game, a game I always lose.
"Kelsey again, and I'm not kidding. I need sixteen thousand, nine hundred and forty dollars. I need it by the end of the week."
"You know perfectly well I can't do that! I can't make that much money disappear without somebody noticing: Lois, the bank, the Bureau of Internal Revenue. Dammit, Kelsey, we've worked this out before."
"The best laid plans of mice and men—"
"Go to hell." Something hit me then. "That's a funny number. As long as I can't pay anyway, why not make it seventeen thousand, or twenty? Why, uh, sixteen thousand nine hundred and forty?"
"It just worked out that way." He sounded defensive.
I probed. "What way?"
"You aren't my only client."
"Client? I'm a blackmail victim! At least be honest with yourself, Kelsey."
"I am. Shall I tell you what you are?"
"No." Someone might be listening, which was the point he was trying to make. "You've got other clients, huh? Go to one of them."
"I did. It was a mistake." He hesitated, then, "Let's call him Horatio, okay? Horatio was a bank teller, long ago. He owns a hardware store now. I've known him about five years. I had to trace him myself, you understand. He embezzled some money while he was a teller."
"What did he do, die on you when the mortgage was due?" I put sarcastic sympathy in my voice.
"I wish he would. No, he waited for my usual call, which I make on April Fools Day. Not my idea; his. I call him once a year, just like you. So I called him and told him he was due, and he said he couldn't afford it any more. He got kind of brave-panicky, you know how it goes—"
"Don't I just, damn you."
"—and he said he wouldn't pay me another red cent if he had to go to prison for it. I got him to agree to meet me at a bar and grill. I hate doing that, Carson. I thought he might try to kill me."
"Occupational hazard. I may return to this subject." I had threatened to kill Kelsey before this.
He sounded disspirited. "It won't help you. I'm careful, Carson. I took a gun, and it was a public place, and I got there first. Besides, there are my files. If I die the cops'll go through those."
I was going to need that information, someday, maybe. But it wasn't fun to hear. "So you met him in this bar and grill. What then?"
"Well," he had the money right with him. He put it right out on the table, and I grabbed it quick because someone might be watching. Someone was, too. I saw the flashbulb go off, and by the time my eyes had stopped watering whoever it was was out the door. Ra—" He caught himself. "Horatio stopped me from getting out. He said, ‘Do you know what the statute of limitations is for embezzlement?"
"I remembered then. It was seven years, and Horatio had me by the balls. Blackmail. He figures I've taken him for sixteen thousand nine hundred dollars and no cents, plus forty bucks for the guy with the camera. He wants it back or he turns me in to the police, complete with photographs."
Kelsey had never heard me laugh before and mean it. "That's hilarious. The Biter Bit bit. If you turn in your files it'll just be more evidence against you. You'll just have to fight it out in court, Kelsey. Tell ‘em it's a first offense."
