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  Convergent Series

  Charles Sheffield

  This is a work of fiction. All the characters and events portrayed in this book are fictional, and any resemblance to real people or incidents is purely coincidental.

  Summertide copyright © 1990 and Divergence © 1991, both by Charles Sheffield

  All rights reserved, including the right to reproduce this book or portions thereof in any form.

  A Baen Books Original

  Baen Publishing Enterprises

  P.O. Box 1403

  Riverdale, NY 10471

  ISBN: 0-671-87791-7

  Cover art by Gary Freeman

  First printing, July 1997

  Distributed by Simon & Schuster

  1230 Avenue of the Americas

  New York, NY 10020

  Typeset by Windhaven Press, Auburn, NH

  Printed in the United States of America

  Summertide

  Book One of

  The Heritage Universe

  For Ann, Kit, Rose and Toria.

  PROLOG

  Expansion

  1086 (3170 A.D.).

  A ninety-seven-year silence was ending.

  For close to a century the ship's interior had heard no human voice and felt no human footstep. The vessel whispered its way between the stars, passengers close to absolute zero in dreamless paradeath. Once a year their bodies warmed to liquid-nitrogen temperatures while shared experiences were fed to them from the ship's central data bank: memories of a hundred years of interstellar travel, for bodies that would age less than one day.

  As the final weeks of deceleration began it was time to start the awakening. When the destination was reached, decisions might be needed that went beyond machine judgment—a notion that to the ship's main computer, the first of its kind to be equipped with the Karlan emotional circuits, was both insulting and implausible.

  First warming was initiated. Interior sensors picked up the reassuring flutter of returning heartbeats, the initial sigh and murmur of working lungs. The emergency crew would be awakened first, two by two, on a last-in, first-out basis; only with their approval would others begin emergence.

  The first pair drifted up to consciousness with one question burning in their minds: Was it arrival—or was it override?

  The computer had been programmed to rouse them for only three reasons. They would be disturbed if the ship were closing at last on their destination, Lacoste-32B, a minor G-2 dwarf star that lay three light-years beyond the rose-red stellar beacon of Aldebaran. They would wake if an on-board problem had arisen within the ship's half-kilometer ellipsoid, a disaster too big for the computer to handle without human interaction.

  Or, the final possibility, they would be pulled from hibernation if one of spacefaring humanity's oldest dreams had become reality:

  I/T—Immediate Transfer; Interstellar Transition; Instantaneous Travel; the superluminal transportation system that would end Crawlspace exploration.

  For more than a thousand years the exploration and colony ships had crept outward, widening the sphere of Earth's influence. The millennium had yielded forty colonies, scattered through a Sol-centered globe seventy light-years in diameter. But every inch within that sphere had been traveled at less than a fifth of light-speed. And every colony, no matter how small and isolated, had a research program that sought the superluminal . . .

  The first two wakened were one man and one woman. They fought a century-long lassitude, queried the ship's internal status panels, and shared their relief. No on-board disaster had occured. The message center held no urgent incoming file, no news of a great breakthrough. There would be no party of superluminal travelers waiting to welcome late-arrival colonists at Lacoste.

  Ahead of the ship the target star already showed a visible naked-eye disk. Gravitational perturbations of the star had long predicted the presence of at least two orbiting giant planets. Now their existence could be confirmed by direct observation, together with five smaller bodies closer to the primary.

  The woman was recovering faster than the man. It was she who first left the Schindler hibernation unit, stood up shakily in the one-tenth-gee field, and moved to stare at the external displays. She uttered a low sound, a grunt of satisfaction from sluggish vocal cords, followed by an experimental clearing of her throat.

  "We made it! There it is."

  And there it was. The molten-gold disk of Lacoste lay at the exact center of the forward screen. Two minutes later the man had eased his way to her side, still wiping protective gel from his face. He touched her arm in congratulations, relief, and love. They were life-partners.

  "Time to waken the others."

  "In a few minutes," she said. "Remember Kapteyn. Make sure we've got something."

  The example of Kapteyn's Star was written in every explorer's memory: eight planets, all apparently with wonderful potential; and all, on close inspection, useless for human habitation or for supplies. The early colony ship that had arrived at Kapteyn had been too depleted to reach any second target.

  "We're only two light-days out," she went on. "We can start scanning. Let's take a look for oxygen atmospheres before we wake anyone else."

  The on-board computer picked up her command and responded to it. One oxygen world, said its soft voice. Life probability 0.92. The field of view zoomed and swung so that Lacoste first grew rapidly in size and then disappeared from the top of the screen, while a new pinpoint of light appeared at the screen center and swelled to fill it.

  Fourth planet, the computer said. Overall figure of merit for Earth isomorphism, 0.86. Mean distance, 1.22; mean temperature range, 0.89 to 1.04; axial tilt—

  "What the devil is that?"

  The computer paused. The man's question had no meaning.

  The screen held a planet at its center, a blue-gray sphere already seen in enough detail to reveal the broad bands and swirls of atmospheric circulation patterns. But it also showed a web of hazy lines and bright spirals surrounding the planet and cradling it in multiple strands of light.

  "Somebody got here ahead of us . . ." The woman's voice faded before the sentence was completed. The information network among inhabited planets was in continuous operation. It was limited to light-speed, but even so she could not believe that some exploring ship had also been sent to Lacoste, unknown to them. And if another ship had arrived here, the scale of what they were seeing went beyond anything that an exploring colony might accomplish in a few years.

  Or in a few centuries.

  "Pan view."

  The computer heard her words and adjusted the image. The planet shrank to pea size, a bright bead of light at the middle of the screen. The surrounding nimbus of intensive in-space construction was revealed, a gleaming nacreous setting within which the planet nestled like a pearl in an oyster. Slender tendrils of construction stretched out endlessly, thinner and thinner, until they fell below the resolution of the observing sensors.

  "Not our kind, Tamara," the man said softly. "That's not us."

  No human works, not even the ring cities that surrounded Earth itself, came close in size and complexity. Some of the spiraling filaments around the planet had to be over four hundred thousand kilometers long and many kilometers across. They should have been unstable to gravitational forces from the planet, to tidal perturbations, and to their own interactions. And yet clearly they were not.

  "Time to wake the others," Tamara said.

  "And then?"

  "And then . . ." She sighed. "And then, I don't know what. We finally did it, Damon. We found another intelligent species. A technologically advanced one, too. But if they could build that"—she gestured at the dazzling structure on the screen, and her voice became husky— "why didn't they find us? Well
, I guess we'll know the answer to that in a few more days."

  Three weeks later the ship's pinnaces were roving the veins and arteries of the space artifact. For fifteen days the main vessel had hovered five million kilometers away, waiting for and expecting contact from the planet in response to radio and laser signals. They had been met with total silence. Finally they had approached and begun direct exploration.

  The misty filaments on the screen resolved themselves to the interlocking network of a colossal artifact. They stretched down to the surface of the planet, an uninhabited world apparently well suited to human colonization; but the tendrils also reached far out into space, for purposes that could not even be guessed at.

  And those purposes could not be found out from their creators. Like the planet, the artifact was uninhabited.

  Tamara and Damon Savalle found themselves cruising in their pinnace along one of the filaments, a metal-and-polymer tube three kilometers wide and fifty thousand long. Maintenance machines crept along the inner surface, moving so slowly that their motion was hardly perceptible. The machines ignored the little pinnace completely.

  Tamara was at the communications panel, in contact with the main ship. "They confirm our analyses of meteorite pitting," she said. "At least ten million years old, uninhabited for more than three. And I don't see anything to grin at."

  "Sorry." Damon did not look it. "I was thinking of the old paradox from before Expansion. If there are aliens, where are they? Twenty days ago we thought we had the answer: no aliens. Now we're asking it all over again. Where are they, Tammy? Who built all this stuff? And where are the builders?"

  She shrugged. Damon's question would remain unanswered for more than three thousand years.

  But while they stared and marveled, a weak incoming signal was reaching the main ship from a small and struggling colony on Eta Cassiopeiae A. It told of an intriguing new physical theory involving Bose-Einstein statistics, along with a suggestion for a subtle and complex deep-space experiment far beyond the limited resources of the little colony.

  With everyone at Lacoste focused on the Builders, the new message received no attention at all.

  But the Builders were long gone; and superluminal travel was on the way.

  ARTIFACT: COCOON

  UAC#: 1

  Galactic Coordinates: 26,223.489/14,599.029/+112.58

  Name: Cocoon Star/planet association: Lacoste/Savalle

  Bose Access Node: 99 Estimated age: 10.464 ± 0.41 Megayears

  Exploration History: Cocoon holds a special place in human history, as the first artifact to be discovered by human explorers, just as Cusp (see Entry 300) was the first to be discovered by the Cecropian clade. Cocoon was found in E. 1086 by a Crawlspace colony ship seeking habitable planets in the Lacoste system.

  Physical Description: The form of Cocoon is a three-dimensional development of the familiar ring cities in place around many inhabited worlds. However, it goes far beyond the standard equatorial-plane assemblies, in both extent and presumed function. This artifact employs forty-eight Basal Stalks connecting Cocoon to the equatorial planetary surface and reaching up to the continuous ring structure at stationary altitude. Four hundred and thirty-two thousand exterior filaments stretch five hundred thousand kilometers from the planet. No two filaments are identical, but typical dimensions of the hollow cylindrical tubes are from two to four kilometers, exterior radius. Viewed from many locations, the surface of Savalle is completely obscured by Cocoon.

  The corridors of Cocoon's interior are extensively patrolled by Phages (see Entry 1067). Explorers must monitor continuously for their presence.

  Physical Nature: Construction of Cocoon employs the standard superstrength polymers used in most Builder artifacts. The absence of a second satellite for Savalle, even though the fossil record clearly shows that double-satellite tides occurred until twelve million years ago, suggests a now-vanished moon as the main source of Cocoon's construction materials.

  Cocoon's filaments are held in stable position by a balance of gravity, rotating reference frames, and stellar radiation pressure. No unfamiliar science is needed to explain that stability, although the system design calls for the solution of large, discrete optimization problems beyond the best computers available within the Clades. Elephant (see Entry 859) was applied to the problem and reached a constrained solution (the so-called Cocoon Restricted Problem) in four standard years of computation time.

  Intended Purpose: There are few secrets to Cocoon, if we except the need for such a massive system. The Basal Stalks permit materials to pass to and from the planetary surface of Savalle at negligible cost; the Exterior Filaments allow economical payload transfer to any point of the Lacoste stellar system, using the momentum-bank principle. The capacity of Cocoon is enormous: one fifty-thousandth of the mass of Savalle could in principle be transferred to space each year, enough to slow the planetary rotation rate appreciably and change Savalle's day by two seconds.

  —From the Lang Universal Artifact Catalog, Fourth Edition.

  CHAPTER 1

  Expansion

  4135 (6219 A.D.).

  Where am I?

  A man who had seen fifty planets and succeeded in a hundred difficult jobs ought to be like a cat, turning instinctively to land on his feet in any situation. But recently he seemed to be just the opposite, more disoriented with every new task.

  Hans Rebka came fully awake and lay with eyes closed, waiting for memory of place and function to seep into his brain. As that came, confusion was replaced by anger.

  A week earlier he had been in orbit around Paradox, preparing for one of the most challenging assignments of his life. He and three companions were to enter the Paradox sphere, carrying with them new shielding and a completely new type of recording sensor. If they succeeded they would bring back for the first time information from the Paradox interior—perhaps new information about the Builders themselves.

  To Rebka, Paradox was the most enigmatic and intriguing of all Builder structures. The dark, spherical bubble, fifty kilometers across, permitted ready entry but on exit removed all memories, organic or inorganic. Computers emerged with no recording on any storage medium. Humans who had reached the interior returned with the minds of newborn infants.

  Exploration efforts had finally been abandoned; but lately visitors to the region of Paradox had been reporting changes. The bubble was different in external appearance, and possibly in internal status. A new effort might succeed.

  It was a dangerous mission, but Hans Rebka had been looking forward to it. He had volunteered, and he had been accepted as team leader.

  And then the call had come, just one day before the descent into Paradox.

  "An alternative assignment . . ." The voice was thin and whispering, reduced in frequency spectrum by its passage through the Bose communications network. " . . . to the double-planet of Dobelle. You must leave without delay . . ."

  The space-thinned voice sounded in no way imperious, but the command emanated from the highest government level of the Phemus Circle. And it was an assignment for Rebka alone; his companions would proceed to explore Paradox. At first it sounded like an honor, a privilege that he should be singled out in that way. But as the assignment was explained to him, Rebka's confusion began.

  He knew his talents. He was a doer and a fixer, and a damned good one. He could think on his feet and improvise solutions in real-time to tough problems; he was a typical product of his home world, Teufel.

  "What sins must a man commit, in how many past lives, to be born on Teufel?" Half the spiral arm knew that saying. Like all the planets of the Phemus Circle, Teufel was resource-poor and metal-poor. Settled in despair and dire necessity as the life-support systems of an early colony ship faltered and failed, it was also an outcast planet, too hot, too small, and with a barely breathable atmosphere. The life expectancy of a human who grew to maturity on Teufel—most did not—was less than half the average for the Phemus Circle, and less than a third of that for
an inhabitant of any world of the Fourth Alliance. All those born and raised on Teufel found an instinct for self-preservation before they could talk—or they never lasted long enough to talk.

  Rebka was a slight, large-headed man with hands and feet too big for his body. He had the wan, slightly deformed look of someone who had suffered persistent childhood malnutrition and trace-element deficiency. But that early privation had affected his brains not at all. He had learned the odds early, when at eight years old he had seen a set of images from the wealthy worlds of the Alliance bordering the Phemus Circle. Strong anger was born within him. He learned to use it, to channel and control it to fuel his progress, at the same time that he learned to hide his feelings with a smile. By the time he was twelve years old he had worked his way off Teufel and was in a Phemus Circle government training program.

  Rebka was proud of his record. Starting with less than nothing, he had risen steadily for twenty-five years. He had run massive terraforming projects, taking the harshest and most inhospitable planetary bodies and converting them to human paradises (someday he would do as much for Teufel); he had led dangerous expeditions to the heart of the mirror-matter comet region, far from any chance of help if things went wrong; he had flown so close to stellar surfaces that communications were impossible in the roar of ambient radiation, and his returning ship was ablated and melted past hope of further use. And he had led a crew on a near-legendary trip through the Zirkelloch, the toroidal space-time singularity that lay in the disputed no-man's land between the worlds of the Fourth Alliance and those of the Cecropia Federation.

  All that. And suddenly—at the thought, confusion was replaced by anger; anger was still his friend—he was demoted. Stripped, without a word of explanation, of all real responsibilities and sent to a distant, unimportant world to act as nursemaid or father-confessor for someone ten years his junior.