“Of course you’d never detect anything that small,” said Carlos. He seemed almost cheerful. I wondered why…and then I knew. He’d been right about the way the ships were disappearing. It must compensate him for being tied to a pillar.

“But,” said Forward, “black holes of all sizes could have formed in that explosion, and should have. In more than seven hundred years of searching no quantum black hole has ever been found. Most cosmologists have given up on them, and on the big bang, too.”

Carlos said, “Of course there was the Tunguska meteorite. It could have been a black hole of, oh, asteroidal mass—”

“—and roughly molecular size. But the tide would have pulled down trees as it went past—”

“—and the black hole would have gone right through the Earth and headed back into space a few tons heavier. Eight hundred years ago there was actually a search for the exit point. With that they could have charted a course—”

“Exactly. But I had to give up that approach,” said Forward. “I was using a new method when the Institute, ah, severed our relationship.”

They must both be mad, I thought. Carlos was tied to a pillar and Forward was about to kill him, yet they were both behaving like members of a very exclusive club…to which I did not belong.

Carlos was interested. “How’d you work it?”

“You know that it is possible for an asteroid to capture a quantum black hole? In its interior? For instance, at a mass of ten to the twelfth kilograms—a billion metric tons,” he added for my benefit, “a black hole would be only one point five times ten to the minus fifth angstroms across. Smaller than an atom. In a slow pass through an asteroid it might absorb a few billions of atoms, enough to slow it into an orbit. Thereafter it might orbit within the asteroid for eons, absorbing very little mass on each pass.”

“So?”

“If I chance on an asteroid more massive than it ought to be, and if I contrive to move it, and some of the mass stays behind…”

“You’d have to search a lot of asteroids. Why do it out here? Why not the asteroid belt? Oh, of course. You can use hyperdrive out here.”

“Exactly. We could search a score of masses in a day, using very little fuel.”

“Hey. If it was big enough to eat a spacecraft, why didn’t it eat the asteroid you found it in?”

“It wasn’t that big,” said Forward. “The black hole I found was exactly as I have described it. I enlarged it. I towed it home and ran it into my neutronium sphere. Then it was large enough to absorb an asteroid. Now it is quite a massive object. Ten to the twentieth power kilograms, the mass of one of the larger asteroids, and a radius of just under ten to the minus fifth centimeters.”