“What if it's big enough to have weather?” I asked. “Wouldn’t that work as well, at least for the water supply issue?”
He nodded slowly. “Yes. Although that scenario would increase the runoff issue. As I said, Will, it's all theoretical. With study and experimentation, we could come up with compromises that would provide the best balance of weight savings and ecological robustness. That's what I mean by not having actual knowledge.”
I took a moment to admire the Bishop ring. “Still, it would open up virtually every stellar system with a reasonably well-behaved star. No one at all has expressed any interest in building one?”
“Not to my knowledge, Will. It's been somewhat a slap in the face for me,” he replied with a chuckle. “As I said, the problem is all the political and economic commitments that would have to be made. Humans have very rarely been able to come together to build anything on this scale, at least since the days of the pyramids.”
I shifted in my seat. “Which brings me to the reason for my visit. You’ve drawn up plans for any number of megastructures over the years, both as serious proposals and as study material for your courses. Have you ever done a topopolis?”
“Yes, certainly. As a megastructure, it has a lot going for it. Effectively infinite land area by simply adding more length. No increase in structural or material strength requirements, no matter how long you make it. No need for inhabitants to ever go outside. And if built with sufficient diameter, no Coriolis force to speak of. And it can be added to at any time, if the initial design is done properly.”
“Really? You'd cut open the loop? How would you keep the air from escaping?”
“First, Will, you don't need to have a closed loop. There’s really no physical reason why you couldn't leave the ends unconnected. It wouldn't have a stable orbit anyway, so in either scenario you'd need some method of orbital adjustment. And you’d build it in segments of some length, with some kind of barrier at the end of each segment. The barrier wouldn't even have to go right to the center, as long as the segments were already rotating. Spillover would be trivial.”
I nodded slowly. Without knowing anything about Heaven’s River, Stephen had described it with amazing accuracy. “Good. Stephen, I wonder if I could ask you to look at some scans and comment?”
His eyebrows went up. I hadn’t given him a lot of detail about the purpose of the meeting, except to say that I wanted to talk about megastructures. He accepted the files as I offered them, and converted them to paper idioms, then started flipping through the stack. He muttered a few sentences, then his eyes grew rounder and wider, and he went silent several times he flipped back to earlier pages. Finally converted the idiom to a 3D image. Hanging between us was a four segment long stretch of Heaven’s River.
“Oh. My. God. Someone built one? Who?”
“They aren’t human, Stephen. We’re still learning about them. Here.” I flipped up an image of a Quinlan, hanging in space beside the engineering segment.
“Have you talked to them?”
“Not openly, no. They have a disturbing tendency to shoot first. We’re trying to figure things out without exposing ourselves.”
“Not the Others all over again though?”
“No, nothing like that. Just ground-level belligerence, I think.”
He nodded and leaned forward to inspect the segment. “So, what would you like to know?”
“Limitations. What they can and can't do. How they're likely to lay it out. Infrastructure were looking for someone in the structure, and any info that could narrow things down would be helpful.”
Stephen glanced at me, then poked at the image. “Well, I see a transportation system right there. Vacuum monorail, or something similar. That would be your long-distance travel option. I love the river concept. Artificial current of course, since there is no downhill along the length. I suppose you could raise one end of the river in each segment and pump the water upward, but then you'd have issues of topography even a 1/10% grade for this implementation would mean a half-mile elevation at the headwaters, and moving all that mass up and down would create issues of angular momentum…” He paused, then pointed. “The hollow mountains every 500 miles or so would be where your maintenance and infrastructure would be.
“Wait, hollow mountains?” I peered more closely at the image. It wasn't obvious from the visual, but it appeared the interior of the mountains was actually void space. “Of course, Will. You wouldn't want mountains of real rock, the mass would place a lot of strain on that segment of the topopolis, and to no purpose. Instead, you build a hollow shell which, being closer to the axis, exhibits less centrifugal weight than average. Then you put all your infrastructure that you don't want people to have to look at inside the hollow. Like a theme park. All the mechanicals are hidden.”
“Oh, for crying…” I zoomed in on the image. At the upper limit of magnification, there was the barest hint of detail under the mountains. “And an entrance?”
“No way to predict how that would be designed, but I'm sure now that you know where to look, you can locate one.”
“Interesting. Something to check out, if we could get a scanning drone into position.” I sat back and made a gesture for him to continue.
Stephen examined the hologram in silence for several more mils, then pointed at one of the impellers under a river segment. “I don't think you've correctly characterized the river system, Will. This isn't one river - it's four. Alternately going in opposite directions. The tributaries and feeders allow the rivers to exchange contents, but if you check the impeller configurations, there are two main flow directions. And note how at the segment
