Dark as Day

by Charles Sheffield

  “Here we are,” said Paul. “The famous Diabelli Omnivores. Fusion drives that have transformed travel around the whole system.”

  “Those things?” Jan asked.

  “These things.” Paul patted one of the blue cylinders. “I’m sorry if you’re not impressed.”

  “Maybe if they were working I would be.” And then Jan realized her error. Since the ship was decelerating, the drive must be on, and these engines had to be working.

  Instead of replying, Paul took her wrist in his hand. His fingers were soft and smooth, not like someone who had spent the past week fiddling with engines. He moved her hand until it lay palm-down on the surface of one of the blue cylinders. “Feel anything?”

  She did. The cylinder transmitted a gentle throb to her flat palm, a thrum-thrum-thrum so faint that it felt like the tingle of a weak electric discharge.

  “Tuned as well as we could do them,” Paul said. “Ninety-nine point nine-eight efficiency. One hundred percent isn’t possible, even in theory.”

  “What’s going on inside? If they’re called Omnivores, they ought to be eating something.”

  “It’s probably not the best name for them.” Paul patted the bulbous cylinder, then left his hand to lie alongside Jan’s. “If you were inside—which thank heaven you can’t ever be—you’d find that nuclear fusion is taking place right here, inside this section. At the moment we are fusing hydrogen to helium to power the drive. We can do that with an internal temperature as low as ten million degrees. But if we ever ran short of hydrogen we could fuse helium to make carbon, or anything all the way up to iron. That’s why these are called Omnivores, because they can fuse lots of different elements. But most fusion reactions need at least a hundred million degrees before they start to produce useful net power. We try to avoid it, because the higher temperatures are harder on the engines.”

  Jan pressed her hand down on the cylinder. It was quite cool, but her fingers were just a few centimeters from a roaring fusion furnace. Paul might speak casually of “as low as ten million degrees,” but that sounded more than enough to her.

  Paul was watching closely. “Scary?”

  “No, not at all. Kind of exciting.” It was, too. So much pent-up power, vibrating under her fingers and responding to human control—it gave her a definite lift, an odd kind of turn-on.

  “I hoped you would like it.” Paul again patted the blue cylinder. “I think of this as a kind of test of people. A visit to the engine room produces one of two reactions. Some are terrified at being close to so much raw power—they don’t seem to realize that if the engines ever did blow, they’d be no safer at the other end of the ship than they are standing here. Other people are stirred by what they see as the power that humans have gained over nature. We are doing things inside the Diabellis that once took place only in the middle of stars. I find that impressive and exciting.” He turned away from the Omnivore cylinder. “Let me know if you’d like to come here again. Meanwhile, we’d better be getting back forward. Mars orbit rendezvous in an hour or two. Dr. Bloom will be sitting there itching to get at you.”

  “I think she wants Sebastian more than she wants me.”

  “Even so, it doesn’t sound like much fun for either of you. But I hope you enjoyed this visit.”

  “Very much.”

  That was quite true, and it left in Jan’s mind one question: Why had Paul Marr singled her out, from all the passengers, for the guided tour? Or maybe there was a second question, too: Had Paul Marr singled her out, or was she one on a list of a dozen?

  Jan preferred not to ask. Something told her that she would find out in due course. And if she did, and the answer proved to be that he was interested in Jan alone, there was one other question that she still had to ask herself.

  12

  The control room was cold, and Alex was sweating. In one hour, he and Kate—which in practice probably meant he alone—had to give the most important briefing of his life. It was also likely to be the most difficult. He had insisted that the computing and data resources of the Seine were all that he needed to make his model into a practical prediction tool. Kate had told him that was bullshit, because the model was producing nonsense. He wasn’t sure he believed her. He was sure that he had no idea what might be going wrong.

  Calm, stay calm.

  First, run the model for the decades preceding the Great War. As before, it predicted the occurrence of the war to the year and to the month. Beyond the war that run of the model offered no prediction, but that was as it should be. Such a traumatic event was a singularity of the timeline, beyond which prediction was impossible.

  So what about the runs that Kate had completed while he was, in her words, “diddling little Lucy”? He wasn’t sure it had been Lucy-Maria, but it wouldn’t help with Kate to explain that uncertainty.

  The model automatically stored every parameter of every run. Alex called on the Seine to perform in parallel all the runs that Kate had tried, one after another, the previous night. It would take months to track every variable, so for the moment he wouldn’t try. He settled for gross aggregates. The crucial number for the moment was total solar system population. He asked for that value, averaged over all the runs that he and Kate had performed, to be displayed as a function of time.

  And here it came, the number of humans in the whole solar system, for every year in the coming century and a half.

  The starting value, for the year 2097, was today’s actual count of 5.2 billion. The number was rounded, to two significant figures, but Alex had demonstrated, over and over, that his results were not sensitive to small errors in inputs or minor changes in initial conditions. The value for 2098, 5.3 billion, came five seconds later than he expected. The amount of computation that Alex’s model required was enormous, but nowhere near enough to tax the capacity of the Seine. However, he did not command the system’s highest priority. That went to emergency real-time missions, and to the often-meaningless (in Alex’s humble opinion) computational demands of other government programs.

  2099: the rounded average over all runs remained at 5.3 billion. Alex spot-checked the exact value, which showed an increase. 2100: sure enough, the number was up slightly again, to 5.4. Alex was aware of Kate at his shoulder, watching not the display but Alex himself. The years moved on steadily, the population count crept higher.

  Maybe nothing was wrong. Maybe Kate had screwed up. Alex’s models were different from all earlier predictive models. He was still struggling to find a way to explain those differences in a way that Kate’s chosen test subject, moronic Macanelly, could understand, but every conceivable model had certain things in common. It had endogenous variables, computed within the model and used to produce future values of those same variables; and it had exogenous variables, values that must be fed into the model from some external source.

  Any model needed both.

  2105: 5.6 billion; 2106: 5.7 billion; 2107: 5.7 billion….

  Endogenous variables were easy, you simply provided their present-day values and the model ran with them to estimate their future values. The big question was always, where do you get values for exogenous variables? In a model designed to predict the development of the solar system for a century or more, the one thing you knew for certain was that there would be surprises.

  2110: 5.9 billion; 2111: 6.0 billion; 2112: 6.1 billion….

  The increase in solar system population, averaged over all model runs, was accelerating.

  By definition, a surprise was something that no one could hope to predict. And since surprises were inevitable, in this sense Alex’s model runs were all bound to be wrong. Cheap faster-than-light travel, true immortality as opposed to today’s longevity treatments, the arrival of aliens in the solar system; any of these might happen, in any future year. Alex’s model could assume any one of them, and still make predictions. However, none of the runs that Kate had made assumed any such thing.

  2117: 6.5 billion; 2118: 6.6 billion; 2119: 6.7 billion….
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  What Alex had learned, over years of experience, was that futures in which no surprise exogenous variables were introduced tended to be conservative futures. They had slower growth, and better stability.

  But what about war, all-out combat like the Great War that had torn the solar system apart thirty years ago? That produced huge effects, but it was not an exogenous variable, introduced from outside. It arose directly from a steady series of changes in human activities. It was a prediction of the model—the main prediction, in fact, that motivated all of Alex’s work. If your model could predict that a war was on the way, you had a chance to explore changes in exogenous variables to make the war disappear.

  2124: 7.6 billion; 2125: 7.8 billion; 2126: 8.0 billion….

  But suppose that, without future surprises or another great war, humanity over the span of centuries dwindled and faded and vanished? What did the modeler do then? If Kate were correct, and the model runs all went that way, Alex had better have some kind of an answer ready for the meeting with Mischa Glaub. Kate thought Glaub might have a couple of other people with him, members of the project review committee.

  2134: 9.2 billion; 2135: 9.5 billion, 2136: 9.9 billion.

  They had come to the year of the model run where Alex had left last night—the place where he had dragged himself away from the displays and headed off with his mother to meet Cyrus and Lucy-Maria Mobarak. At this point Kate had taken over. Now he had to pay extra attention to other variables, while continuing to monitor population growth.

  2137: 10.0 billion. Running along smoothly, except that the rate of population growth was suddenly down. Now he recognized another complication. The model was set up to accept inputs, where appropriate, from other sources. Before the Seine came into operation those other sources were limited and well-defined. Now, suddenly, a million new data sources could feed the model. They included other predictive models whose outputs Alex did not trust.

  “How did you limit exogenous variable inputs?” He snapped the question to Kate, without taking his eyes off the display.

  “I cut them out.” She was standing very close to him, where she could see everything he saw. Her breath on his cheek was as warm as her voice was cold. “You left without telling me how to pick them, or what values to use. I didn’t take any that you hadn’t included.”

  Alex nodded. New exogenous variables were a source of possible instability. Kate had made the conservative choice, by prohibiting new ones. All the macroscopic measures looked good to him. He could see no sign of the precursors of war, the ominous indicators that had popped up all over when he did simulations of System activity for forty years ago.

  But something odd was happening. The model was now forty-five years out, and although the population count continued to creep up, two other variables had reversed their trend. The index for Outer System activity was down, with the cancellation of three development projects among the moons of Neptune. Just as disturbing, no new extra-solar probes had been launched for the past seven years in any of the model’s predicted futures.

  “Can you see it?” Kate didn’t sound angry anymore. She was just tense.

  “Yes.”

  “Do you know what’s causing it?”

  “No idea.”

  “What are we going to tell Mischa Glaub and the review committee?”

  A good question, but not one to concern Alex at the moment. He had too much else on his mind. Sixty-five years out, with no hint of coming war; but transportation cargo volume and inter-world passenger traffic were down. So were terraforming activities, Oort Cloud exploration, free-space research stations, and what Alex thought of as “inverse terraforming”—the genetic modification of Earth’s plants and animals to match the geography and physiography of other worlds.

  And now, in 2140, the population curve was totally flat and he thought the fitted curve showed the first hint of a downward slope. Why, when the solar system was peaceful and stable?

  “Mineral deficiencies?” He hit the sequence to provide figures on population breakdown. “Maybe reduced fertility?”

  “You think?—” Kate was crowding him, almost sitting in his seat.

  But Alex had an answer before she could complete a question. The available minerals and trace elements needed for human existence were on the increase. The fertility indices were fine, general health was better than ever, longevity was increasing—and still the figures for total System population were declining. As the model moved forward, ticking ahead another five years, the gentle decrease was turning into a nosedive.

  “What’s happening, Alex? What’s causing it?”

  “I don’t know.” He wanted to say, this is impossible, it can’t be happening. Either you have a steady human expansion, or you have a war. Humans just don’t die out, with no reason. That had never happened before in any of the models he had seen—his own, or other people’s.

  2152: 7.1 billion; 2153: 6.4 billion; 2154: 5.7 billion; 2155: 5.0 billion; 2156: 4.3 billion….

  The population prediction wasn’t just decreasing, it was plummeting. Alex waited and watched, but in his mind he had already extrapolated the curve. They were losing seven hundred million people a year. Unless the curve flattened, in a little more than six years the projected human population of the solar system would be zero.

  A plague, a major universal plague which left no survivors? That was the only thing he could think of. Such a disaster could certainly occur, as one of the surprises which any real future might contain. But from the point of view of the model, the plague would have to be fed in as a new exogenous variable. Neither he nor Kate had introduced any such event.

  “Alex …” Kate said.

  She didn’t need to say more. The year index read 2160. The population count was 1.5 billion. As they watched, the year advanced to 2161 and the count fell below a billion. 2162, 2163, 2164 … The count slowed, steadied, hovered around the one hundred million mark. And then—2165, 2166, 2167, 2168—the number began a final and implacable downward run.

  By 2170 it was over. In that year, and in every year beyond, the human population of the solar system was a steady, flat zero.

  They stared at the display in silence. Finally, Kate said, “Well, it is only a model.”

  Normally those would have been fighting words. To Alex’s mind, provided that you fed the model reasonable inputs and possessed enough computer power, the results you got back were a possible future. And more than possible; plausible. Not the only conceivable future, certainly, because of surprise factors that no model could include. A future, however, that was far more than an assembly of random predictions.

  Now a hundred different runs, with a hundred different sets of initial conditions, pointed to the same melancholy conclusion: No humans by the year 2170. Alex was reluctant to believe the results, but he could see no basis for rejecting them.

  Population zero; and two years before that, all transportation, development, and outward expansion had ended. He was still staring at the flat-lined results when Kate made the day’s discomfort complete.

  “Come on,” she said. “We’re running out of time. In half an hour we have to brief Mischa Glaub. I hope you have something sensible to say. Because I sure as hell don’t.”

  * * *

  Kate had warned of a tough review session. Alex decided in the first thirty seconds that the real thing was going to be worse than her fears.

  It began as soon as Kate led Alex into a small conference room flanked by modern display panels and old-fashioned pictures. The latter were of stern-faced individuals, presumably past members of review committees.

  Seated at the table were four people—Kate had promised at most three—no less stern-faced than the images on the wall. Alex had met Mischa Glaub before. He was a short broad man with a shaved head, a sour expression, and a permanently angry disposition. Old hands in the Department of Planning made it a point to avoid meetings with Mischa in the morning. Food, it was said, softened his ire. Unfortunately this sessio
n was starting an hour before lunch, and it would run until the committee members were satisfied.

  Alex had also met, at least briefly, two of the others. They were Glaub’s boss, Tomas de Mises, and Ole Pedersen, head of the Methods and Logistics Directorate which sat at the same organizational level as Mischa Glaub’s empire. It was no surprise to find them here, though Pedersen’s presence might be a problem. Kate had warned Alex that Ole Pedersen was wily and ambitious, always promoting his own group’s products and critical of anyone else’s. Tomas de Mises was less of a worry. He was older, close to retirement, and reluctant to say or do anything likely to cause trouble.

  The final person at the table, however, was the real shocker. She was a middle-aged brunette, whose white skirt and floral blouse broke the rule for office uniform. Rules were for lower level staff. Alex recognized her as Magrit Knudsen, Tomas de Mises’s boss. She was a major force, already a Jovian Worlds’ cabinet member and tipped to become a leader in the Outer Planets’ Development Council.

  Why was she here, for a routine progress review meeting?

  The way that Kate had explained the procedure, Alex, or possibly Alex and Kate, would brief Glaub and a couple of staff assistants. They would brief de Mises, and de Mises would in turn provide summaries for people farther up the chain of command. Apparently normal procedure didn’t apply today. Alex was expected to brief the whole ladder at once, from top to bottom. Magrit Knudsen seemed to be studying him with special interest.

  Kate’s raised eyebrow said, “Don’t blame me. I didn’t know she’d be here, either.” But there was no time for discussion, because Kate and Alex were barely in the room before Mischa Glaub snapped, “All right, let’s get on with it. And keep it short. We’ve all got other business to attend to.”