But before it had traveled more than a few hundred meters, the ball of distortion swelled up, burst silently, and dissipated.

There was a rustle of movement in the corvette, a collective sigh of disappointment.

Darc clapped Nilis on the back. “Scratch another run. Never mind, Commissary. We’re not done yet.”

“Indeed not.”

Torec said to Pirius, “Timing is everything. The implosion in the center is what we’re trying to design. If the amplitude is large enough, you get nonlinearity—a shock wave, its profile distorting as it travels, what the techs call a ‘classical scalar wave.’ I think we’ve got the amplitudes right, but not the timing. If the waves don’t converge right at the center, they just pass through each other harmlessly.”

Pirius said, “And if the timing is right—what’s supposed to happen?”

Torec stared at him, the first time she’d looked at him directly since he had got here. “You were on Callisto, and you don’t know?”

Pirius said helplessly, “I just did my job there.”

“This is a design from the Occupation era. It’s a black-hole cannon, Pirius.” She smiled faintly. “Can you believe that? We’re making a cannon to fire black holes at the Xeelee. And you know what else? It was designed by Friends. Friends, just like Enduring Hope!”

Pirius, stunned, stared at the battered test rig. The techs and drones were already going back to work.

Nilis asked Pirius to spend some time with him.

They sat together in Nilis’s cabin. It was clear to Pirius that the Commissary wanted something. But Nilis was still guilty about how Pirius had been “used” on Callisto, and he seemed to want to make it up to him by talking to him.

He said his “Callisto weapon” did indeed date from the time of the Qax Occupation. Pirius was amazed that the Friends of Wigner, in his day an illegal fringe cult out on Arches, had roots that deep.

Back then the Friends had been a group of rebels on Earth. During the early phase of the Occupation, the control of the Qax had been relatively light—and remarkably enough, the Friends had been able to assemble a whole spacecraft, equipped with black-hole cannons, under the noses of Earth’s occupiers.

The Friends had known that a wormhole bridge to the deeper past was soon to be opened; spanning fifteen centuries, this audacious stunt had been set up by none other than Michael Poole. When the bridge opened, the Friends hurled themselves and their ship into the past. Ignoring the humans of Poole’s time, they had set to work preparing their battery of black holes—but their purpose was not to use their cannon as weapons. Their target was Jupiter. In the guts of the gas giant these grenades of twisted spacetime would collide and merge, each collision sending out pulses of gravitational waves. By programming this sequence, the Friends hoped to shape the collapse of Jupiter, and so sculpt the final black hole that would result.