A Hole In Space

STEP TWO: Pick a planetoid. Ideally, we need an elongated chunk of nickel-iron, perhaps one mile in diameter and two miles long.

STEP THREE: Bore a hole down the long axis.

STEP FOUR: Charge the hole with tanks of water. Plug the openings, and weld the plugs, using the solar mirror.

STEP FIVE: Set the planetoid spi

STEP SIX: The axis would be the last part to reach melting point. At that point the water tanks explode. The pressure blows the planetoid up into an iron balloon some ten miles in diameter and twenty miles long, if everybody has done their jobs right.

The hollow world is now ready for tenants. Except that certain things have to be moved in: air, water, soil, living things. It should be possible to set up a closed ecology. Cole and Cox suggested setting up the solar mirror at one end and using it to reflect sunlight back and forth along the long axis. We might prefer to use fusion power, if we've got it.

Naturally we spin the thing for gravity.

Living in such an inside-out world would be odd in some respects. The whole landscape is overhead. Our sky is farms and houses and so forth. If we came to space to see the stars, we'll have to go down into the basement.

We get our choice of gravity and weather. Weather is easy. We give the asteroid a slight equatorial bulge, to get a circular central lake. We shade the endpoints of the asteroid from the sun, so that it's always raining there, and the water runs downhill to the central lake. If we keep the gravity low enough, we should be able to fly with an appropriate set of muscle-powered wings; and the closer we get to the axis, the easier it becomes. (Of course, if we get too close the wax melts and the wings come apart...)

Macro-Life

Let's back up a bit, to the Heinlein "Universe" ship. Why do we want to land it?

If the "Universe" ship has survived long enough to reach its target star, it could probably survive indefinitely; and so can the nth-generation society it now carries. Why should their descendants live out their lives on a primitive Earthlike world? Perhaps they were born to better things.

Let the "Universe" ship become their universe, then. They can mine new materials from the asteroids of the new system, and use them to enlarge the ship when necessary, or build new ships. They can loosen the population control laws. Change stars when convenient. Colonize space itself, and let the planets become mere way-stations. See the universe!

The concept is called Macro life. Macro-life is large, powered, self-sufficient environments capable of expanding or reproducing. Put a drive on the inside-outside asteroid bubble and it becomes a Macro life vehicle. The ring-shaped flying city can be extended indefinitely from the forward rim. Blish's spindizzy cities were a step away from being Macro-life; but they were too dependent on planet based society.

A Macro-life vehicle would have to carry its own mining tools and chemical laboratories, and God knows what else. We'd learn what else accidentally, by losing interstellar colony ships. At best a Macro-life vehicle would never be as safe as a planet, unless it was as big as a planet, and perhaps not then. But there are other values than safety. An airplane isn't as safe as a house, but a house doesn't go anywhere. Neither does a world.

Worlds

The terraforming of worlds is the next logical step up In size. For a variety of reasons, I'm going to skip lightly over it. We know both too much and too little to talk coherently about what makes a world habitable.

But we're learning fast, and will learn faster. Our present pollution problems will end by telling us exactly how to keep a habitable environment habitable, how to keep a stable ecology stable, and how to put it all back together again after it falls apart. As usual, the universe will learn us or kill us. If we live long enough to build ships of the "Universe" type, we will know what to put inside them. We may even know how to terraform a hostile world for the convenience of human colonists, having tried our techniques on Earth itself.

Now take a giant step.

Dyson Spheres

Freeman Dyson's original argument went as follows, approximately.

No industrial society has ever reduced its need for power, except by collapsing. An intelligent optimist will expect his own society's need for power to increase geometrically, and will make his plans accordingly. According to Dyson, it will not be an impossibly long time before our own civilization needs all the power generated by our sun. Every last erg of it. We will then have to enclose the sun so as to control all of its output.

What we use to enclose the sun is problematic. Dyson was speaking of shells in the astronomical sense: solid or liquid, continuous or discontinuous, anything to interrupt the sum light so that it can be turned into power. One move might be to convert the mass of the solar system into as many little ten-by-twenty-mile hollow iron bubbles as will fit. The smaller we subdivide the mass of a planet, the more useful surface area we get. We put all the-little asteroid bubbles in circular orbits at distances of about one Earth orbit from the sun, but differing enough that they won't collide. It's a gradual process. We start by converting the existing asteroids. When we run out, we convert Mars, Jupiter, Saturn, Uranus ... and eventually, Earth.

Now, aside from the fact that our need for power increases geometrically, our population also increases geometrically. If we didn't need the power, we'd still need the room in those bubbles. Eventually we've blocked out all of the sunlight. From outside, from another star, such a system would be a great globe radiating enormous energy in the deep infrared.

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 thi

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 i

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.