"What do you mean physics isn't holding it up?" Jesse said. "Believe me, this is not what I want to hear right at this moment."

Harry smiled. "Sorry. Let me rephrase. Physics is involved in holding up this beanstalk, certainly. But the physics involved aren't of the garden variety. There's a lot going on here that doesn't make sense on the surface."

"I feel a physics lecture coming on," I said.

"I taught physics to teenagers for years," Harry said, and dug out a small notepad and a pen. "It'll be painless, trust me. Okay, now look." Harry began drawing a circle at the bottom of the page. "This is the Earth. And this"—he drew a smaller circle halfway up the page—"is Colonial Station. It's in geosynchronous orbit, which means it stays put relative to the Earth's rotation. It's always hanging above Nairobi. With me so far?"

We nodded.

"Okay. Now, the idea behind the beanstalk is that you connect Colonial Station with the Earth through a 'beanstalk'—a bunch of cables, like those out the window—and a bunch of elevator platforms, like the one we're on now, that can travel back and forth." Harry drew a line signifying the cable, and a small square, signifying our platform. "The idea here is that elevators on these cables don't have to reach escape velocity to get to Earth orbit, like a rocket payload would. This is good for us, because we don't have to go to Colonial Station feeling like an elephant had its foot on our chests. Simple enough.

"The thing is, this beanstalk doesn't conform to the basic physical requirements of a classic Earth-to-space beanstalk. For one thing"—Harry drew an additional line past Colonial Station to the end of the page—"Colonial Station shouldn't be at the end of the beanstalk. For reasons that have to do with mass balance and orbital dynamics, there should be additional cable extending tens of thousands of miles past Colonial Station. Without this counterbalance, any beanstalk should be inherently unstable and dangerous."

"And you're saying this one isn't," I said.

"Not only is not unstable, it's probably the safest way to travel that's ever been devised," Harry said. "The beanstalk has been in continuous operation for over a century. It's the only point of departure for colonists. There's never been an accident due to instability or matériel failure, which would be related to instability. There was the famous beanstalk bombing forty years ago, but that was sabotage, unrelated to the physical structure of the beanstalk itself. The beanstalk itself is admirably stable and has been since it was built. But according to basic physics, it shouldn't be."

"So what is keeping it up?" Jesse said.

Harry smiled again. "Well, that's the question, isn't it."

"You mean you don't know?" Jesse asked.

"I don't know," Harry admitted. "But that in itself should be no cause for alarm, since I am—or was—merely a high school physics teacher. However, as far as I know, no one else has much of a clue how it works, either. On Earth, I mean. Obviously the Colonial Union knows."

"Well, how can that be?" I asked. "It's been here for a century, for God's sake. No one's bothered to figure out how it actually works?"

"I didn't say that," Harry said. "Of course they've been trying. And it's not like it's been a secret all these years. When the beanstalk was being built, there were demands by governments and the press to know how it worked. The CU essentially said 'figure it out,' and that was that. In physics circles, people have been trying to solve it ever since. It's called 'The Beanstalk Problem.'"

"Not a very original title," I said.

"Well, physicists save their imagination for other things." Harry chuckled. "The point is, it hasn't been solved, primarily for two reasons. The first is that it's incredibly complicated—I've pointed out the mass issues, but then there are other issues like cable strength, beanstalk oscillations brought on by storms and other atmospheric phenomena, and even an issue about how cables are supposed to taper. Any of these is massively difficult to solve in the real world; trying to figure them all out at once is impossible."

"What's the second reason?" Jesse asked.

"The second reason is that there's no reason to. Even if we did figure out how to build one of these things, we couldn't afford to build it." Harry leaned back. "Just before I was a teacher, I worked for General Electric's civil engineering department. We were working on the SubAtlantic rail line at the time, and one of my jobs was to go through old projects and project proposals to see if any of the technology or practices had application to the SubAtlantic project. Sort of a hail-Mary attempt to see if we could do anything to bring down costs."

"General Electric bankrupted itself on that, didn't they?" I asked.

"Now you know why they wanted to bring down costs," Harry said. "And why I became a teacher. General Electric couldn't afford me, or much of anyone else, right after that. Anyway, I'm going through old proposals and reports and I get into some classified stuff, and one of the reports is for a beanstalk. General Electric had been hired by the U.S. Government for a third-party feasibility study on building a beanstalk in the Western Hemisphere; they wanted to clear out a hole in the Amazon the size of Delaware and stick it right on the equator.

"General Electric told them to forget it. The proposal said that even assuming some major technological breakthroughs—most of which still haven't happened, and none of which approach the technology that has to be involved with this beanstalk—the budget for the beanstalk would be three times the annual gross national product of the United States economy. That's assuming that the project did not run over budget, which of course it almost certainly would have. Now, this was twenty years ago, and the report I saw was a decade old even then. But I don't expect that the costs have gone down very much since then. So no new beanstalks—there are cheaper ways of getting people and material into orbit. Much cheaper."

Harry leaned forward again. "Which leads to two obvious questions: How did the Colonial Union manage to create this technological monstrosity, and why did they bother with it at all?"

"Well, obviously, the Colonial Union is more technologically advanced than we are here on Earth," Jesse said.

"Obviously," Harry said. "But why? Colonists are human, after all. Not only that, but since the colonies specifically recruit from impoverished countries with population problems, colonists tend to be poorly educated. Once they get to their new homes, you have to assume they're spending more time staying alive than they are thinking up creative ways to build beanstalks. And the primary technology that allowed interstellar colonization is the skip drive, which was developed right here on Earth, and which has been substantially unimproved for more than a century. So on the face of it, there's no reason why the colonists should be any more technologically advanced than we are."

Something suddenly clicked in my head. "Unless they cheat," I said.

Harry grinned. "Exactly. That's what I think, too."

Jesse looked at me, and then Harry. "I'm not following you two," she said.

"They cheat," I said. "Look, on Earth, we're bottled up. We only learn from ourselves—we make discoveries and refine technology all the time, but it's slow, because we do all the work ourselves. But up there—"

"Up there humans meet other intelligent species," Harry said. "Some of which almost certainly have technology more advanced than ours. We either take it in trade or reverse engineer it and find out how it works. It's much easier to figure out how something works when you've got something to work from than it is to figure it out on your own."