Convergent Series

by Charles Sheffield

  She sipped a few drops from her palm. It was brackish, not quite sea-salt. Rather like the taste of her own blood.

  The complicated chemical balance of a planet like Opal made her sit back on her haunches and think. In a world without continents, streams and rivers could not perform their steady leaching of salts and bases from upthrust deep structures. Microseepage of primordial methane and the higher hydrocarbons must occur on the seabed, with absorption taking place through the water column. The whole land-water balance had to be radically different from the world that she knew. Was it truly a stable situation? Or were Opal and Quake still evolving from their condition before that traumatic hour, forty-odd million years ago, when they had been cast into their wild new orbit around Mandel?

  She walked a hundred meters inland and squatted cross-legged on a hummock of dark green.

  The parent star showed as a bright patch, high in the cloud-covered sky. There would be at least another two hours of daylight. Now that she had taken a closer look at Opal, she saw it as a warm and friendly world, not at all the raging fury of her imagination. Surely humans could thrive there, even at Summertide. And if Opal was so pleasant, could its twin, Quake, be all so different?

  But it would have to be very different, if her own conclusions had any validity. She stared at the gray horizon, unmarked by boats or other land, and reviewed for the thousandth time the train of analysis that had brought her to Dobelle. How persuasive were those results, of minimal least-square residuals? To her, there was no way that such a precise data fit could occur by coincidence. But if the results were so persuasive and indisputable to her, why had others not drawn the same conclusions?

  She came up with only one answer. She had been helped in her thinking because she was a stay-at-home, a person who had never traveled between the stars. Humanity and its alien neighbors had become conditioned to think of space and distances in terms of the Bose Drive. Interstellar travel employed a precise network of Bose Nodes. The old measure of geodesic distance between two points no longer had much significance; it was the number of Bose Transitions that counted. Only the Ark dwellers, or perhaps the old colonists creeping along through Crawlspace, would see a change in a Builder artifact as generating a signal wavefront, expanding out from its point of origin and moving across the galaxy at the speed of light. And only someone like Lang, fascinated by everything to do with the Builders, might ask if there were single places and times where all those spherical wavefronts intersected.

  Each piece of the argument felt weak, but taken together they left Darya fully persuaded. She felt a new anger. She was in the right place—or would be, if she could just leave Opal and get herself over to Quake! But instead she was stuck in a sleepy dreamland.

  Sleepy dreamland. Even as those words formed in her mind there came a grating whirr from behind. A figure from a nightmare flew through the air and landed right in front of her, its six jointed legs fully extended.

  If Darya did not cry out, it was only because her throat refused to function.

  The creature standing in front of her lifted two of its dark-brown legs off the ground and reared up to tower over her. She saw a dark-red, segmented underside, and a short neck surrounded by bands of bright scarlet-and-white ruffles. That was topped by a white, eyeless head, twice the size of her own. There was no mouth, but a thin proboscis grew from the middle of the face and curled down to tuck into a pouch on the bottom of the pleated chin.

  Darya heard a high-pitched series of chittering squeaks. Yellow open horns in the middle of the broad head turned to scan her body. Above them a pair of light-brown antennas, disproportionately long even for that great head, unfurled to form two meter-long fans that quivered delicately in the moist air.

  She screamed and jumped backward, stumbling over the grassy tussock that she had been sitting on. As she did so a second figure came in a long, gliding leap to crouch down before the carapace of the first. It was another arthropod, almost as tall but with a sticklike body no thicker than Darya's arm. The creature's thin head was dominated by lemon-colored compound eyes, without eyelids. They swiveled on short eyestalks to examine her.

  Darya became aware of a musky smell, complex and unfamiliar but not unpleasant, and a moment later the second being's small mouth opened. "Atvar H'sial gives greetings," a soft voice said in distorted but recognizable human speech.

  The other creature said nothing. As the first shock faded Darya was able to think rationally again.

  She had seen pictures. Nothing in them had suggested such a size and menacing presence, but the first arrival was a Cecropian, a member of the dominant species of the eight-hundred-world Cecropia Federation. The second animal must be an interpreter, the lower species that every Cecropian was said to need for interaction with humankind.

  "I am Darya Lang," she said slowly. The other two were so alien that her facial expressions probably had little meaning to them. She smiled anyway.

  There was a pause, and again she was aware of the unfamiliar odor. The Cecropian's twin yellow horns turned toward her. She could see that their insides were a delicate array of slender spiral tubes.

  "Atvar H'sial offers apologies through the other." One of the jointed arms of the silent Cecropian waved down to indicate the smaller beast by its feet. "We think perhaps we startled you."

  Which had to be the understatement of the year. It was disconcerting to hear words that had originated in the mind of one being issuing from the mouth of another. But Darya knew that the seed world for the Cecropian clade, their mother planet as Earth had been the mother-planet for all humans, was a cloudy globe circling the glimmer of a red dwarf star. In that stygian environment the Cecropians had never developed sight. Instead they "saw" through echolocation, using high-frequency sonic pulses emitted from the pleated resonator in the chin. The return signal was sensed by the yellow open horns. As one side benefit, a Cecropian knew not only the size, shape, and distance of each object in the field of view, it could also use Doppler shift of the sonic return to tell the speed with which targets were moving.

  But there were disadvantages. With hearing usurped for vision, communication between Cecropians had to be performed in some other way. They did it chemically, "speaking" to each other via the transmission of pheromones, chemical messengers whose varying composition permitted them a full and rich language. A Cecropian not only knew what her fellows were saying; the pheromones also allowed her to feel it, to know their emotions directly. The unfurled antennas could detect and identify a single molecule of many thousands of different airborne odors.

  And to a Cecropian, any being that did not give off the right pheromones did not exist as a communicating being. They could "see" them all right, but they did not feel them. Those nonentities included all humans. Darya knew that early contacts between Cecropians and humans had been totally unproductive until the Cecropians had produced from within their federation a species with both the capability for speech and the power to produce and sense pheromones.

  She pointed to the other creature, which had disconcertingly swiveled its yellow eyes so that one was looking at her and one at the Cecropian, Atvar H'sial. "And who are you?"

  There was a long, puzzling silence. Finally the small mouth with its long whiskers of sensing antennas opened again.

  "The name of the interpreter is J'merlia. He is of low intelligence and plays no part in this meeting. Please ignore his presence. It is Atvar H'sial who wishes to speak with you, Darya Lang. I seek discussion concerning the planet of Quake."

  Apparently Atvar H'sial used the other in the same way as the richer worlds of the Alliance employed service robots. But it would require a very complex robot to perform the translation trick that J'merlia was doing—more sophisticated than any robot that Darya had heard of, except for those on Earth itself.

  "What about Quake?"

  The Cecropian crouched lower, placing its two forelegs on the ground so that the blind head was no more than four feet from Darya. Thank God it does
n't have fangs or mandibles, Darya thought, or I couldn't take this.

  "Atvar H'sial is a specialist in two fields," J'merlia said. "In life-forms adapting to live with extreme environmental stress, and also in the Artificers—the vanished race whom humans choose to call the Builders. We arrived on Opal only a few short time units ago. Long since we sent request for permission to visit Quake near to Summertide. That permission had not yet been granted, but at Opal Spaceport we spoke to a human person who told that you plan to go to Quake also. Is this true?"

  "Well, it's not quite true. I want to go to Quake." Darya hesitated. "And I want to be there close to Summertide. But how did you find me?"

  "It was simple. We followed the emergency locator on your car."

  Not that, Darya thought. I mean, how did you know that I even existed?

  But the Cecropian was continuing. "Tell us, Darya Lang. Can you arrange permission for Atvar H'sial's visit to Quake also?"

  Was Darya's meaning being lost in translation? "You don't understand. I certainly want to visit Quake. But I don't have any control of the permits to go there. That's in the hands of two men who are on Quake at the moment, assessing conditions."

  There was a brief glint of Mandel through the cloud layers. Atvar H'sial reflexively spread wide her black wing cases, revealing four delicate vestigial wings marked by red and white elongated eyespots. It was those markings, the ruffled neck, and the phenomenal sensitivity to airborne chemicals that had led the zoologist examining the first specimens to dub them fancifully "Cecropians"—though they had no more in common with Earth's cecropia moth than with any other Terran species. Darya knew that they were not even insects, though they did share with them an external skeleton, an arthropod structure, and a metamorphosis from early to adult life-stage.

  The dark wings vibrated slowly. Atvar H'sial seemed lost in the sensual pleasure of warmth. There were a few seconds of silence, until the cloud gap closed and J'merlia said, "But men are males. You control them, do you not?"

  "I do not control them. Not at all."

  Darya wondered again about the accuracy with which she and Atvar H'sial were receiving each other's messages. The conversion process sounded as though it could never work, moving from sounds to chemical messengers and back through an alien intermediary who probably lacked a common cultural data base with either party. And she and Atvar H'sial also lacked common cultural reference points. Atvar H'sial was a female, she knew that, but what in Cecropian culture was the role played by males? Drones? Slaves?

  J'merlia produced a loud buzzing sound, but no words.

  "I have no control over the men who will make the decision," Darya repeated, speaking as slowly and clearly as she could. "If they deny me access to Quake, there is nothing that I can do about it."

  The buzzing sound grew louder. "Most unsatisfactory," J'merlia said at last. "Atvar H'sial must visit Quake during Summertide. We have traveled far and long to be here. It is not thinkable to stop now. If you cannot obtain permission for us and for yourself, then other methods must be sought."

  The great blind head swung close, so that Darya could see every bristle and pore on it. The proboscis reached out to touch her hand. It felt warm and slightly sticky. She forced herself not to move.

  "Darya Lang," J'merlia said. "When beings possess a common interest, they should work together to achieve that interest. No matter what obstacles others attempt to put in their way, they should not be deterred. If you could guarantee your cooperation, there is a way that Darya Lang and Atvar H'sial might visit Quake. Together. With or without permission."

  Was J'merlia misinterpreting Atvar H'sial's thoughts, or was Darya herself misunderstanding the Cecropian's intention? If not, then Darya was being recruited by this improbable alien to join a secret project.

  She felt wary, but caution was mixed with a thrill of anticipation. The Cecropian could almost have been reading Darya's own earlier thcughts. If Rebka and Perry agreed to let her go to Quake, all well and good. But if not . . . there might be another project in the making.

  And not just any project; an enterprise designed to take her to her objective—at Summertide.

  Darya could hear the whistle of air as it was pumped continuously through the Cecropian's spiracles. The proboscis of Atvar H'sial was oozing a dark-brown fluid, and the eyeless face was a demon taken from a bad childhood dream. By Darya's side, the black, eight-legged stick figure of J'merlia was drawn from the same nightmare.

  But humans had to learn to ignore appearance. No two beings who shared common thinking processes and common goals should be truly alien to each other.

  Darya leaned forward. "Very well, Atvar H'sial. I am interested to hear what you have to say. Tell me more."

  She was certainly not ready to agree to anything; but surely there could be no harm in listening?

  CHAPTER 6

  Summertide

  minus twenty-nine.

  The Umbilical and the capsules that rode along it had been in position for at least four million years when humans colonized Dobelle. Like anything of Builder construction, it had been made to last. The system worked perfectly. It had been studied extensively, but although the analyses told a good deal about Builder fabrication methods, they revealed nothing about Builder physiology or habits.

  Did the Builders breathe? The cars were open, built of transparent materials, and lacking any type of airlock.

  Did the Builders sleep and exercise? There was nothing that could be identified as a bed, or a place to rest, or a means of recreation.

  Then surely the Builders at least had to eat and to excrete. Except that although the journey from Opal to Quake took many hours, there were no facilities for food storage or preparation, and no facilities for the evacuation of waste products.

  The only tentative conclusion that human engineers could reach was that the Builders were big. Each capsule was a monster, a cylinder over twenty meters long and almost that much across, and inside it was all empty space. On the other hand, there was no evidence that the cars had been used by the Builders themselves— maybe they had been intended only as carriers of cargo. But if that were true, why were they also equipped with internal controls that permitted changes to be made in speed along the Umbilical?

  While students of history argued about the nature and character of the builders, and theoreticians worried about inexplicable elements of Builder science, more practical minds went to work to make the Umbilical of use to the colonists. Quake had minerals and fuels. Opal had neither, but it possessed living space and a decent climate. The transportation system between the two was much too valuable to be wasted.

  They began with the amenities necessary to make a comfortable journey between the components of the planetary doublet. They could not change the basic size and shape of the capsules; like most Builder products, the cars were integrated modules, near-indestructible and incapable of structural modification. But the cars were easily made airtight and fitted with airlocks and pressure adjustment equipment. Simple kitchens were installed, along with toilets, medical facilities, and rest areas. Finally, in recognition of the discomfort of planet-based humans with great heights, the transparent exteriors were fitted with panels that could be polarized to an opaque gray. The main observation port lay only at the upper end of the capsule.

  Rebka was cursing that last modification as their car came closer to Quake. While they were ascending to Midway Station and beyond he had enjoyed an intriguing view of the planet ahead of them—enough to be willing to leave for a later occasion an exploration of the Builder artifact of Midway Station itself. He had assumed that he would continue to see more and more details of Quake until they finally landed. Instead, the car inexplicably swung end-over-end when they were still a few hundred kilometers above the surface. In place of Quake he was suddenly provided with an uninformative and annoying view of Opal's shifting cloud patterns.

  He turned to Max Perry. "Can you swing us back? I can't see a thing."

  "Not un
less you want us to crawl the rest of the way." Perry was already jumpy in anticipation of their arrival. "We'll be entering Quake's atmosphere any minute now. The car has to be bottom-down for aerodynamic stability, or we have to crawl. In fact . . . He paused, and his face became taut with concentration. "Listen."

  It took a moment for Rebka to catch it; then his ears picked up the faintest high-pitched whistle, sounding through the capsule's walls. It was the first evidence of contact with Quake, of rarefied air resisting the passage of the plunging capsule. Their rate of descent must already be slowing.

  Five minutes later another sensory signal was added. They were low enough for pressure equalization to begin, and air from Quake was being bled in. A faintly sulfurous odor filled the interior. At the same time the capsule began to shake and shiver with the buffeting of winds. Rebka felt an increased force pushing him down into the padded seat.

  "Three minutes," Perry said. "We're on final deceleration."

  Rebka looked across at him. They were about to land on the planet that Perry described as too dangerous for visitors, but there was no sign of fear in Perry's voice or on his face. He showed nervousness, but it could just as well be the excitement and anticipation of a man returning home after too long a time away.

  How was that possible, if Quake was so dangerous a death trap?

  The car slowed and stopped, and the door silently opened. Rebka, following Perry outside, felt that his suspicions were confirmed. They were stepping out onto a level surface, a blue-gray dusty plain sparsely covered with dark green shrubs and a low-profile ochre lichen. It was certainly dry and hot, and the smell of sulfur in the midafternoon air was stronger; but less than a kilometer away Rebka could see the gleam of water, with taller plants on its boundary, and near them stood a herd of low, slow-moving animals. They looked like herbivores, quietly grazing.