"What I believe," Jesse said, "is that I want to get something to eat. Care to join me?"
"Belief," Harry Wilson said, and laughed. "Well, maybe belief is holding up this cable. Because it sure as hell isn't fundamental physics."
Harry Wilson had joined Jesse and me at a booth where we were eating. "You two look like you know each other, and that's one up on everyone else here," he said to us as he came up. We invited him to join us and he accepted gratefully. He had taught physics at a Bloomington, Indiana, high school for twenty years, he said, and the beanstalk had been intriguing him the entire time we had been riding it.
"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."