Shipstar

by Benford, Gregory

  Details. The tortured landscapes below passed before his eyes like an unending scroll. He thought of how the decisions that seem momentous in the moment, or even over a lifetime, were flickering instants in the life of the Bowl. These matters were too small to be observed by the Ice Minds, just single passing lives.

  The Bowl had made them look back across a gulf of not mere centuries or millennia, but on the grand scale of evolution itself. Maybe that was the true deep purpose of coming out here among the stars. To see times that glowed and shimmered in memory’s flickering light.

  He had a thought. Was there more than one Bowl, coasting around the galaxy? Maybe such things were a technological niche that others thought of and inhabited—very-long-view things, hard to quite grasp for humans. Maybe if alien species had the right precursor society—that of those smart dinosaurs, who loved warmth and sun and stillness—then their love of a forever summer would make them build such contraptions. If so, the blunt hammer of evolution gave another strategy to gain the stars, one different from smart, talky primates.

  Whatever waited at Glory, in its stacked levels, there was a biosphere on top, a place to love beneath a star that had a sunset every day. Beings who lived in layers would be strange indeed, and humanity would have to adapt. Redwing smiled. If the Bowl had taught him anything, it was about human versatility. He would be alert when he reached Glory after a long sleep, and he liked his odds.

  It couldn’t be stupid to voyage out in small vessels, to distant worlds where beauty and happiness would get redefined again and again. Even if Earth became a distant and perhaps wistful memory—as all his crew and himself would inevitably be, for sure—the expansion of human horizons was an ultimate good. Whatever built the Bowl had believed that, too. There was something comforting in that thought alone.

  Time for bed.

  AFTERWORD

  BIG SMART OBJECTS

  I. HOW WE BUILT THE BOOKS

  Gregory Benford’s take—

  In science fiction, a Big Dumb Object is any immense mysterious object that generates an intense sense of wonder just by being there. “The Diamond as Big as the Ritz” by F. Scott Fitzgerald is a non-SF example. They don’t have to be inert constructs, so perhaps the “dumb” aspect also expresses the sensation of being struck dumb by the scale of them.

  Larry said to me at a party, “Big dumb objects are so much easier. Collapsed civilizations are so much easier. Yeah, let’s bring them up to speed.”

  So we wrote Bowl of Heaven, deciding that we needed two volumes to do justice to a Big Smart Object. The Bowl has to be controlled, because it’s not neutrally stable. His Ringworld is a Big Dumb Object since it’s passively stable, as we are when we stand still. (Or the ringworld would be except for nudges that can make it fall into the sun. Those are fairly easy to catch in time. Larry put active stabilizers into the second Ringworld novel.)

  A Smart Object is statically unstable but dynamically stable, as we are when we walk. We fall forward on one leg, then catch ourselves with the other. That takes a lot of fast signal processing and coordination. (We’re the only large animal without a tail that’s mastered this. Two legs are dangerous without a big brain or a stabilizing tail.) There’ve been several Big Dumb Objects in SF, but as far as I know, no smart ones. Our Big Smart Object is larger than Ringworld and is going somewhere, using an entire star as its engine.

  Our Bowl is a shell more than a hundred million miles across, held to a star by gravity and some electrodynamic forces. The star produces a long jet of hot gas, which is magnetically confined so well, it spears through a hole at the crown of the cup-shaped shell. This jet propels the entire system forward—literally, a star turned into the engine of a “ship” that is the shell, the Bowl. On the shell’s inner face, a sprawling civilization dwells. The novel’s structure doesn’t resemble Larry’s Ringworld much, because the big problem is dealing with the natives.

  The virtues of any Big Object, whether dumb or smart, are energy and space. The collected solar energy is immense, and the living space lies beyond comprehension except in numerical terms. While we were planning this, my friend Freeman Dyson remarked, “I like to use a figure of demerit for habitats, namely the ratio R of total mass to the supply of available energy. The bigger R is, the poorer the habitat. If we calculate R for the Earth, using total incident sunlight as the available energy, the result is about twelve thousand tons per watt. If we calculate R for a cometary object with optical concentrators, traveling anywhere in the galaxy where a zero magnitude star is visible, the result is one hundred tons per watt. A cometary object, almost anywhere in the galaxy, is 120 times better than planet Earth as a home for life. The basic problem with planets is that they have too little area and too much mass. Life needs area, not only to collect incident energy but also to dispose of waste heat. In the long run, life will spread to the places where mass can be used most efficiently, far away from planets, to comet clouds or to dust clouds not too far from a friendly star. If the friendly star happens to be our Sun, we have a chance to detect any wandering life-form that may have settled here.”

  This insight helped me think through the Bowl, which has an R of about 10−10! The local centrifugal gravity avoids entirely the piling up of mass to get a grip on objects, and just uses rotary mechanics. So of course, that shifts the engineering problem to the Bowl’s structural demands.

  Big human-built objects, whether pyramids, cathedrals, or skyscrapers, can always be criticized as criminal wastes of a civilization’s resources, particularly when they seem tacky or tasteless. But not if they extend living spaces and semi-natural habitat. This idea goes back to Olaf Stapledon’s Star Maker:

  Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy.

  Our smart Bowl craft is also going somewhere, not just sitting around, waiting for visitors like Ringworld—and its tenders live aboard.

  We started with the obvious: Where are they going, and why?

  Answering that question generated the entire frame of the two novels. That’s the fun of smart objects—they don’t just awe, they also intrigue.

  My grandfather used to say, as we headed out into the Gulf of Mexico on a shrimping run, A boat is just looking for a place to sink.

  So heading out to design a new, shiny Big Smart Object, I said, An artificial world is just looking for a seam to pop.

  You’re living just meters away from a high vacuum that’s moving fast, because of the Bowl’s spin (to supply centrifugal gravity). That makes it easy to launch ships, since they have the rotational velocity with respect to the Bowl or Ringworld … but that also means high seam-popping stresses have to be compensated. Living creatures on the sunny side will want to tinker, try new things.…

  “Y’know, Fred, I think I can fix this plumbing problem with just a drill-through right here. Uh—oops!”

  The vacuum can suck you right through. Suddenly you’re moving off on a tangent at a thousand kilometers a second—far larger than the 50 km/sec needed to escape the star. This makes exploring passing nearby stars on flyby missions easy.

  But that easy exit is a hazard, indeed. To live on a Big Smart Object, you’d better be pretty smart yourself.

  Larry Niven’s take—

  “The Enormous Big Thing” was my friend David Gerrold’s description of a plotline that flowered after the publication of Ringworld. Stories like Orbitsville, Ring, Newton’s Wake, John Varley’s Titan trilogy and Rendezvous with Rama depend on the sense of wonder evoked by huge, ambitious endeavors. Ringworld wasn’t the first; there had been stories that built, and destroyed, whole universes. These objects often become icons of larger issues implying unknowable reaches and perspectives. Their governing question is usually, “Who built this thing? And why?” They had fallen out of favo
r.

  I wasn’t the first to notice that a fallen civilization is easier to describe than a working one. Your characters can sort through the artifacts without hindrance until they’ve built a picture of the whole vast structure. Conan the Barbarian, and countless barbarians to follow, found fallen civilizations everywhere. I took this route quite deliberately with Ringworld. I was young and untrained, and I knew it.

  A fully working civilization, doomed if they ever lose their grasp on their tools, is quite another thing. I wouldn’t have tried it alone. Jerry Pournelle and I have described working civilizations several times, in Footfall, Lucifer’s Hammer, and The Burning City.

  With Greg Benford, I was willing to take a whack at a Dyson-level civilization. Greg shaped the Bowl in its first design. It had a gaudy simplicity that grabbed me from the start. It was easy to work with: essentially a Ringworld with a lid, and a star for a motor. We got Don Davis involved in working some dynamite paintings.

  Greg kept seeing implications. The Bowl’s history grew more and more elaborate. Ultimately I knew we’d need at least two volumes to cover everything we’d need to show. That gave us time and room.

  II. FUN WITH HIGH TECH

  Warning: some plot spoilers lurk here.

  Our first book, Bowl of Heaven, set up reader expectations and introduced the Folk who ran the place—or thought so. That let us wrap up storylines in the sequel, Shipstar, in part by undermining the expectations built up in Bowl of Heaven. We chose to write all this in two volumes because it took time to figure out. The longer time also let us process what many readers thought of Bowl of Heaven, its problems and processes.

  Much of this comes from the intricacies of how the Bowl came to be built. Plus its origins.

  We supposed the founders made its understory frame with something like scrith—a Ringworld term, grayish translucent material with strength on the order of the nuclear binding energy, stuff from the same level of physics as held Ringworld from flying apart. This stuff is the only outright physical miracle needed to make Ringworld or the Bowl work mechanically. Rendering Ringworld stable is a simple problem—just counteract small sidewise nudges. Making the Bowl work in dynamic terms is far harder; the big problem is the jet and its magnetic fields. This was Benford’s department, since he published many research papers in The Astrophysical Journal and the like on jets from the accretion disks around black holes, some of which are far bigger than galaxies. But who manages the jet? And how, since it’s larger than worlds? This is how you get plot moves from the underlying physics.

  One way to think of the strength needed to hold the Bowl together is by envisioning what would hold up a tower a hundred thousand kilometers high on Earth. The tallest building we now have is the 829.8 m (2,722 ft) tall, Burj Khalifa in Dubai, United Arab Emirates. So for Ringworld or for the Bowl, we’re imagining a scrith-like substance 100,000 times stronger than the best steel and carbon composites can do now. Even under static conditions, though, buildings have a tendency to buckle under varying stresses. Really bad weather can blow over very strong buildings. So this is mega-engineering by master engineers indeed. Neutron stars can cope with such stresses, we know, and smart aliens or even ordinary humans might do well, too. So: let engineers at Caltech (where Larry was an undergraduate) or Georgia Tech (where Benford nearly went) or MIT (where Benford did a sabbatical) take a crack at it, then wait a century or two—who knows what they might invent? This is a premise and still better, a promise—the essence of modern science fiction.

  Our own inner solar system contains enough usable material for a classic Dyson sphere. The planets and vast cold swarms of ice and rock, like our Kuiper belt and Oort clouds—all that, orbiting around another star, can plausibly give enough mass to build the Bowl. For alien minds, this could be a beckoning temptation. Put it together from freely orbiting substructures, stick it into bigger masses, use molecular glues. Then stabilize such sheet masses into plates that can get nudged inward. This lets the Builders lock them together into a shell—for example, from spherical triangles. The work of generations, even for beings with very long life spans. We humans have done such, as seen in Chartres cathedral, the Great Wall, and much else.

  Still: Who did this? Maybe the Bowl was first made for just living beneath constant sunshine. So at first the Builders may have basked in the glow of their smaller sun, developing and colonizing the Bowl with ambitions to have a huge surface area with room for immense natural expanses. But then the Bowl natives began dreaming of colonizing the galaxy. They hit on the jet idea, and already had the Knothole as an exit for it. Building the Mirror Zone took a while, but then the jet allowed them to voyage. It didn’t work as well as they thought, and demanded control, which they did by using large magnetic fields.

  The system had virtues for space flight, too. Once in space, you’re in free fall; the Bowl mass is fairly large, but you exit on the outer hull at high velocity, so the faint attraction of the Bowl is no issue. Anyone can scoot around the solar system, and it’s cleared of all large masses. (The Bowl atmosphere serves to burn any meteorites that punch through the monolayer.)

  The key idea is that a big fraction of the Bowl is mirrored, directing reflected sunlight onto a small spot on the star, the foot of the jet line. From this spot the enhanced sunlight excites a standing “flare” that makes a jet. This jet drives the star forward, pulling the Bowl with it through gravitation.

  The jet passes through a Knothole at the “bottom” of the Bowl, out into space, as exhaust. Magnetic fields, entrained on the star surface, wrap around the outgoing jet plasma and confine it, so it does not flare out and paint the interior face of the Bowl—where a whole living ecology thrives, immensely larger than Earth’s area. So it’s a huge moving object, the largest we could envision, since we wanted to write a novel about something beyond Niven’s Ringworld.

  For plausible stellar parameters, the jet can drive the system roughly a light-year in a few centuries. Slow but inexorable, with steering a delicate problem, the Bowl glides through the interstellar reaches. The star acts as a shield, stopping random iceteroids that may lie in the Bowl’s path. There is friction from the interstellar plasma and dust density acting against the huge solar magnetosphere of the star, essentially a sphere 100 astronomical units in radius.

  So the jet can be managed to adjust acceleration, if needed. If the jet becomes unstable, the most plausible destructive mode is the kink—a snarling knot in the flow that moves outward. This could lash sideways and hammer the zones near the Knothole with virulent plasma, a dense solar wind. The first mode of defense, if the jet seems to be developing a kink, would be to turn the mirrors aside, not illuminating the jet foot. But that might not be enough to prevent a destructive kink. This has happened in the past, we decided, and lives in Bowl legend.

  The reflecting zone of mirrors is defined by an inner angle, Θ, and the outer angle, Ω. Reflecting sunlight back onto the star, focused to a point, then generates a jet which blows off. This carries most of what would be the star’s solar wind, trapped in magnetic fields and heading straight along the system axis. The incoming reflected sunlight also heats the star, which struggles to find an equilibrium. The net opening angle, Ω minus Θ, then defines how much the star heats up. We set Ω = 30 degrees, and Θ = 5 degrees, so the mirrors subtend that 25-degree band in the Bowl. The Bowl rim can be 45 degrees, or larger.

  The K2 star is now running in a warmer regime, heated by the mirrors, thus making its spectrum nearer that of Sol. This explains how the star can have a spectral class somewhat different from that predicted by its mass. It looks oddly colored, more yellow than its mass would indicate.

  For that matter, that little sun used to be a little bigger. It’s been blowing off a jet for many millions of years. Still, it should last a long time. The Bowl could circle the galaxy itself several times.

  III. BOWL DESIGN

  As the book says, the Bowl star is

  K2 STAR. SIMILAR TO EPSILON ERIDANI (K2 V). INTERMEDI
ATE IN SIZE BETWEEN RED M-TYPE MAIN-SEQUENCE STARS AND YELLOW G-TYPE MAIN-SEQUENCE STARS.

  So its light is reddish and a tad less bright than Sol. There is a broad, cylindrical segment of the Bowl at its outer edge, the Great Plain. This is huge, roughly the scale of Ringworld, with centrifugal gravity Earth normal times 0.8, so humans can walk easily there. Beyond that is the bowl curve, a hemisphere that arcs inward toward the Knothole. On the hemisphere, the Wok, the centrifugal gravity varies with latitude, and is not perpendicular to the local ground. To make a level walking surface, the Bowl has to have many platforms that are parallel to the jet axis, so gravity points straight down.

  The local apparent centrifugal gravity has two vector components:

  A: Centrifugal gravity that is perpendicular to the local level surface on the bowl, vs angle Ψ (in radians). Here Ψ is measured away from the polar bowl axis—that is, the jet axis. The curve peaks at 90 degrees, where the Great Plain has a local g of 1 in this plot. (It’s 0.8 of Earth’s.)

  B: Below shows the magnitude of centrifugal gravity that is parallel to the local level surface on the bowl, vs angle Ψ—thus, it’s the felt force pushing away from the pole where the Knothole lies, along the local level.

  So the pushing-away force is largest at the mid-latitudes, then falls away because the total force is small at the poles. This component also vanishes on the Great Plain.