When I hit the ten-minute mark, the pendulum is barely moving anymore, so I decide that’s long enough. Grand total: 346 full cycles in exactly ten minutes.

Onward to phase two.

I measure the distance from the hatch handle to the floor. It’s just over two and a half meters. I go back downstairs to the “bedroom.” Again, the ladder is no problem. I’m feeling so much better now. That food really did the trick.

“What’s your name?” the computer asks.

I look down at my sheet toga. “I am the great philosopher Pendulus!”

“Incorrect.”

I hang the pendulum on one of the robot hands near the ceiling. I hope it’ll stay still for a while. I eyeball the distance between the robot hand and the ceiling—I’ll call it a meter. My pendulum is now four and a half meters lower than it was before.

I repeat the experiment. Ten minutes on the stopwatch, and I count the total cycles. The result: 346 cycles. Same as upstairs.

Golly.

Thing is, in a centrifuge, the farther you get from the center, the higher the centripetal force will be. So if I were in a centrifuge, the “gravity” down here would be higher than it was upstairs. And it isn’t. At least, not enough to get a different number of pendulum cycles.

But what if I’m in a really big centrifuge? One so huge that the force difference between here and the lab is so small it doesn’t change the number of cycles?

Let’s see…the formula for a pendulum…and the formula for the force of a centrifuge…wait, I don’t have the actual force, just a cycle count, so there’s a one-over-x factor involved…this is actually a very instructive problem!

I have a pen, but no paper. That’s okay—I have a wall. After a lot of “crazy prisoner scribbling on a wall”–type stuff, I have my answer.

Let’s say I’m on Earth and in a centrifuge. That would mean the centrifuge provides some of the force with the rest being supplied by Earth. According to my math (and I showed all my work!), that centrifuge would need a 700-meter radius (which is almost half a mile) and would be spinning at 88 meters per second—almost 200 miles per hour!

Hmm. I think mostly in metric when doing science stuff. Interesting. Most scientists do, though, right? Even scientists who grew up in America.

Anyway, that would be the largest centrifuge ever built…and why would anyone build it? Plus, something like that would be loud as heck. Whizzing through the air at 200 miles per hour? At the very least there’d be some turbulence here and there, not to mention a lot of wind noise. I don’t hear or feel anything like that.

This is getting weird. Okay, what if I’m in space? There wouldn’t be turbulence or wind resistance, but the centrifuge would have to be bigger and faster because there’s no gravity to help out.

More math, more graffiti on the wall. The radius would have to be 1,280 meters—close to a mile. Nothing anywhere near that big has ever been built for space.

So I’m not in a centrifuge. And I’m not on Earth.

Another planet? But there isn’t any planet, moon, or asteroid in the solar system that has this much gravity. Earth is the largest solid object in the whole system. Sure, the gas giants are bigger, but unless I’m in a balloon floating around the winds of Jupiter, there’s just nowhere I could go to experience this force.

How do I know all that space stuff? I just know it. It feels like second nature—information I use all the time. Maybe I’m an astronomer or a planetary scientist. Maybe I work for NASA or ESA or—

* * *

—

I met Marissa every Thursday night for steak and beer at Murphy’s on Gough Street. Always at six p.m., and because the staff knew us, always at the same table.

We’d met almost twenty years ago in grad school. She dated my then-roommate. Their relationship (like most in grad school) was a train wreck and they broke up within three months. But she and I ended up becoming good friends.

When the host saw me, he smiled and jerked his thumb toward the usual table. I made my way through the kitschy décor to Marissa. She had a couple of empty lowball glasses in front of her and a full one in her hand. Apparently, she’d gotten started early.

“Pre-gaming, eh?” I said, sitting down.

She looked down and fidgeted with her glass.

“Hey, what’s wrong?”

She took a sip of whiskey. “Rough day at work.”

I signaled the waiter. He nodded and didn’t even come over. He knew I wanted a rib-eye, medium, mashed potatoes on the side, and a pint of Guinness. Same thing I ordered every week.

“How rough could it be?” I asked. “Cushy government job with the DOE. You probably get, what, twenty days off a year? All you have to do is show up and you get paid, right?”

Again, no laugh. Nothing.

“Oh, come on!” I said. “Who pooped in your Rice Krispies?”

She sighed. “You know about the Petrova line?”

“Sure. Kind of an interesting mystery. My guess is solar radiation. Venus doesn’t have a magnetic field, but positively charged particles might be drawn there because it’s electrically neutral—”

“No,” she said. “It’s something else. We don’t know exactly what. But it’s something…else. But whatever. Let’s eat steak.”

I snorted. “Come on, Marissa, spill it. What the heck is wrong with you?”

She mulled it over. “Why not? You’ll hear it from the president in about twelve hours anyway.”

“The president?” I said. “Of the United States?”

She took another gulp of whiskey. “Have you heard of Amaterasu? It’s a Japanese solar probe.”

“Sure,” I said. “JAXA has been getting some great data from it. It’s really neat, actually. It’s in a solar orbit, about halfway between Mercury and Venus. It has twenty different instruments aboard that—”

“Yeah, I know. Whatever,” she said. “According to their data, the sun’s output is decreasing.”

I shrugged. “So? Where are we in the solar cycle?”

She shook her head. “It’s not the eleven-year cycle. It’s something else. JAXA accounted for the cycle. There’s still a downward trend. They say the sun is 0.01 percent less bright than it should be.”

“Okay, interesting. But hardly worth three whiskeys before dinner.”

She pursed her lips. “That’s what I thought. But they’re saying that value is increasing. And the rate of the increase is increasing. It’s some sort of exponential loss that they caught very, very early thanks to their probe’s incredibly sensitive instruments.”