Angular Momentum

Advantages of tumbling pigeons.

“Tell me straight, skipper. What’s wrong?”

“We’re dead. That’s what’s wrong.”


“Even as we stand here, we’re dead men. That last bomb pumped us full of a whole soup of radiation. I’m surprised the hull hasn’t shattered from neutron embrittlement. But the gamma rays are what did us in.”

In the background, someone clutches his abdomen in sudden pain.

“Well, do something!”

“Detonate this warhead in the null-G section amidships.”

“You’re mad!”

“I will be, unless you get on it. I’ve already notified engineering.”

The young lieutenant stands for a moment, petrified.

“Oh fine. Since understanding might make you more obedient. We spin end-over-end for gravity, and right now our plane of rotation is lined up with their vessel. They’re about 15 klicks away, so if we break in half at the right moment, we might get the tail end flung close enough to detonate our atomic drive right next to them before they notice.”

“But! We’ll all die!”

“We’re already dead. Now move it.”


Not exactly diplomacy.

“Lemme get this straight—at the bottom of that mineshaft is a thermonuclear warhead. And at the top of that mineshaft is a steel plate. In 41 seconds, their warship is going to pass by in orbit overhead and we light it off?”

“That’s about the size of it. Any questions?”

“. . .”

“. . .”

“Well, I mean, isn’t the plate kindof . . . you know . . . not aerodynamic?”

“That turns out not to matter. At the speed it will be going, it will be in the atmosphere, oh, only about 130 milliseconds.”

Peter’s mind boggled.

“That’s like a hundred kilometers per second!”

“Yeah. Through their hull. Neat, huh?”

Somewhere in the distance . . .


Orbit Guard

Kratocide or capitalism?

“Don’t tell me you’re busy?”

“Crushingly. Important?”

“No. I’ll be back later.”

The U.F.P. Justice hung in null-G, poised, as its burdened commander labored over the ship’s supercomputer terminal. Two hours ago, the call had come in: “Unauthorized asteroid deflection burn, Dec. -5.419°, R.A. 41.17°, class ξ asteroid 1999 RQ36 ‘Bennu’. Deflection Δv = 0.26±0.03 m/s.”

Small deflections make big changes. Even the emission of absorbed heat makes asteroids move unpredictably, unless their surfaces are mapped in detail. But with literally millions of asteroids, the Yarkovsky effect is not worth the bother.

But now someone has gone and moved one of them. A pretty big one, maybe half a kilometer on edge. That would probably utterly destroy one of Earth’s megacities, should it hit one.

Which means someone landed on it, did a thermographic survey, plotted its orbit to high precision, and then nudged it deliberately, in a particular direction, an exact amount.

So, the question—was it some unhinged terrorist bent on the obliteration of Los Angeles? Or a miner secretly moving a motherlode of priceless volatiles back to base?

In 51 years, he’d know for sure. For now, there’d be only guessing.

A Monte-Carlo Simulation

Because really, how long is “short” for a galaxy?

“We’re alone.”


“Ran a sim. It’s really obvious. I don’t know why I didn’t think of it before. See these green dots?”

The visualization in front of her swam with millions—probably billions—of green fireflies.

“Yeah hmm?”

“Each is a planet in the sim. 1011-ish. Let’s say there are 103 civilizations, starting within 108 years of each other, technologically. Once a civilization attains spaceflight, each of their planets colonizes a vacant one every 500 years.”

“So how long does it take?”

“12 500 years for half the galaxy, and no one else has even started. See where I’m going?”

“Exponential growth is a bitch?”

“Ha. Try again.”

“It seems to me that if you pick a random point in time, chances are, either the galaxy will be empty, or else full. 20 000 years should be enough to colonize the whole thing, and that’s a very short time in galactic terms.”

“Exactly. So the fact we still haven’t heard from anyone?”

“It means either we’re alone, or we’re the first.”