much more than simple computer power.”
“Like what?”
“Like a huge number of external databases, online for the first time. We were careful not to introduce what we thought of as inappropriate exogenous variables into the model, but the Seine doesn’t have that constraint. Anything that is not specifically ruled out is open for consideration. The trouble is, the Seine is so complex that we don’t know what it includes and what it excludes. I believe that we have to do something radically different. We have to introduce our own exogenous variables, things that we believe are possible logical components of the future. We have to see how this affects the computed results.”
Kate, for a change, didn’t act like an ice princess. The lines of her face softened, and she stared directly at Alex. “But there could be a million things in the possible future. How are we supposed to know what to choose?”
“We assess possible events on the basis of our own estimates of their likelihood. We change the model to reflect it, and see what difference it makes to the results.”
“I wouldn’t know where to begin.”
“Well, I think I do. The Seine doesn’t try to predict the future, or make random assumptions. It uses only facts that are present somewhere in the System right now. If the computed future suggests the extinction of humanity, that’s because those factors are already present today.”
“Such as what?”
This was one that Alex wished he could avoid. “Such as the Commensals. They are basically human, but a thousand other life forms have been spliced into them. It occurred to me that the way we have been running the model, neither the computer nor the Seine data banks makes any distinction between a human and Commensal. We don’t know if future population figures refer to humans, or Commensals, or both. If everyone in the System eventually elects to become a Commensal, then the model that we have may be predicting that the future holds no true humans. On the other hand” — Alex had to face an intolerable possibility — “maybe Commensals become the human norm, but they have a built-in flaw that causes them to die out.”
A built-in flaw like guaranteed sterility, so that no one is reproducing anymore.
Kate began to nod agreement, then stared wide-eyed at Alex. “But if that’s the case, then your mother —”
“I’ve already thought of that.”
“Oh, Alex.” She reached out as though to take his hand, then withdrew. “I’m really sorry. I hope that’s not true.”
“So do I.” Alex saw his chance, and jumped in. “And I’m really sorry, too. I don’t mean for my mother and the other Commensals, I mean for what I did. I know I screwed Lucy Mobarak, or Deirdre de Soto, or somebody. Maybe I screwed all of them. But they sabotaged me, I’m sure of it now, down in the Holy Rollers. The drinks were spiked. I had no idea what I was doing — I don’t even remember it. That doesn’t excuse what I did, but maybe it explains it. I want to say again, I’m sorry.”
“Let’s talk about all that later.” But Kate reached out, and this time she did squeeze his hand. “For the moment we have to concentrate on the model. If it’s the Commensals that are causing the trouble…”
…then we are in for a battle royal. The Commensals, and the Sylva Corporation that oversees their creation, between them have tremendous political clout. Kate didn’t need to say that to Alex. His own mother was far from unique in her willingness to do anything to restore and maintain her youth and beauty.
“We’re going to find out.” Alex set to work at the console. “I’m setting up the model to treat Commensals and unmodified humans as separate but interacting populations.” He turned to Kate. “Do you know, can someone who decides to become a Commensal change her mind, and have the process reversed to become a normal human?”
“I don’t think so. I believe it’s one-way only. If it is possible to undo it, I’ve never heard of a case where someone chose that option.”
“So we’ll assume it goes on like that.” Alex set parameters so that any member of the human population could elect to become a Commensal. The human population changed by reproduction, by transfer to Commensal form, or by death. The Commensal population could decrease only through death. An all-Commensal solar system ultimately implied an empty solar system.
He glanced at Kate. His finger hovered over a final key. She nodded. “I can’t think of anything more. Do it, Alex.”
It was the power of a god. Alex pressed. At one touch of his finger, databases all across the System came into play. Within the computer, the separate Faxes that represented more than five billion humans (and now Commensals) began to live, die, love, hate, act and interact, and move around the solar system. Days sped by too fast to follow. As the years rolled on, the full panoply of solar system activity was revealed on the displays.
Most of Alex’s attention focused on just two counts: the ratio of the number of Commensals to the total human population, and the human population itself.
The yearly aggregates came into view. By 2105, System population was a figure familiar from their previous runs: 5.6 billion. Commensals were less than one in ten thousand of humans. But the fraction was creeping up. In 2124, one percent of the human population of 7.6 billion had become Commensals. In 2134, that percentage was close to five percent.
“I think you’re right, Alex.” Kate was crowding close, no longer aloof and standoffish. “It’s the damned Commensals.”
Alex didn’t think so. He could make the extrapolation in his head. The proportion of Commensals was increasing, but nowhere near fast enough to cause problems. With ninety-five percent of the total still human, and still actively breeding, the number of people or Commensals would never start to nosedive by 2150.
But here came 2140, and trouble. The conversion to Commensals were steady at five percent. The trouble lay in the human population. Birth rates were down, along with every other index of activity. Alex and Kate sat and watched in grim silence, right to the bitter end when in 2170 the number of humans hit a flat zero. A small population of Commensals lingered on for a few years, but by 2185 that count was also down to nothing.
“That’s it.” Alex smacked his fist down on the console, ending the run. “Exactly the same results as before. Now we know it’s not the Commensals that cause the problem. Another idea bites the dust.”
“That was just one thing to try.” Kate didn’t mention that in some ways she was relieved. The idea of a solar system filled with Commensals, and only Commensals, did not appeal to her. “We can examine the effect of other important variables.”
“We could.” Alex hesitated. Did he really want to go through with this? “But there’s one other thing I’d like to do before we change variables. There is an alternate way of running the model itself, what I call Snapshot Interactive — SI — mode.”
“I’ve never heard you mention it.”
“That’s because we’ve always stressed the need for repeatable runs. You need results that you can take up the line to Mischa Glaub and Tomas de Mises, and if you have to run again you’ll always want the same answers.”
“Damn right. Alex, I don’t understand you. I know we run with a variety of possible inputs, but each run is deterministic. Except for database changes, we get the same run today as we did yesterday.”
“That’s not guaranteed in SI mode. There can be differences.”
“I think you’d better be specific. Remember, I’ll have the job of explaining all this to Mischa Glaub.”
“I’ll be as clear as I can. As you know, the big difference between my model and the ones developed in Pedersen’s group is that I include a separate piece of code for every single individual in the solar system. Each person is represented by a Fax with some level of decision-making logic of its own. The interaction of all those human-simulator components makes up the complete model. The average properties, such as transportation activity or food needs, are not regarded as independent variables. They are constructed values, built up from all those billions of separate needs.”
“I got that much from your briefing the other day. You’re saying nothing new.”
“I’m about to. When I said that individuals are represented in the model, I meant exactly that. Each person in the solar system census is in there, represented by anything from a Level One to a Level Five Fax. There’s a Mischa Glaub in the model, also a Kate Lonaker, even Cousin Hector, though I bet his Fax is smarter than he is. Most important, there’s an Alex Ligon.”
