The wormhole did seem to shrink, and the light arch fluoresced. Curious brilliant rainbows rimmed the dark mote. Soon Rachel lost the image among the intertwining, restless strands. Claire fidgeted.

Mark!—survey run complete.

“Great. Our bots deployed?”

Of course. There remain 189 seconds until separation from our shield. Shall I begin sequence?

Claire let out a whoop. “Go!”

Whoooomp! went the release of the magnetic clamps. On a screen Rachel watched the mass drift aside—then a blaze of full fusion fury. The screen went blank, saturated.

Meanwhile, I have an explanation for the anomalous shrinking of the image. The wormhole has negative mass, and so—

“Antimatter?” Claire broke in.

No. Its spacetime curvature is opposite to normal matter.

“I… don’t get it.”

Rachel realized Claire really had been zoned out when they’d gone over the physics Fraq grudgingly gave them.

Admittedly, it was hard to fathom. A wormhole connected at least two regions of space, sometimes points many light-years apart—that she knew going in; everybody did. Some of the most ancient of Library Messages referred to them. A linked set termed the Maze was apparently a closely kept secret. What Fraq termed the Worms were leftovers from the primordial hot universe, wrinkles that even the universal expansion had not ironed out. Matter could pass through one end of the worm and emerge out the other an apparent instant later. Presto, faster-than-light travel.

Rachel watched the screens as the shield fell behind and their target approached. Odds were that one end of the worm ate more matter than the other. If one end got stuck inside a star, it swallowed huge masses, so it got more massive.

But the matter that poured through the mass-gaining Mouth spewed out the other end. Nobody followed Fraq’s terminology logic, since that would mean calling the other the Ass. Locally, that looked as though the mass-spewing one was losing mass. Spacetime around it curved oppositely than it did around the end that swallowed.

So it looked like a negative mass, rejecting matter, and had the opposite spacetime curvature.

Rachel called to Erma, “Why didn’t it shoot out from the sun, then?”

It would, and be lost in interstellar space. But the magnetic arch holds it.

“How come we know it’s got negative mass? All I saw was—”

Erma popped an image onto the wall screen.

Negative mass acts as a diverging lens, for light passing nearby. That was why it appeared to shrink as we flew over it.

Ordinary matter focused light, Rachel knew, like a converging lens. In a glance she saw that a negative-ended wormhole refracted light oppositely. Incoming beams were shoved aside, leaving a dark tunnel downstream.

They had flown across that tunnel, swooping down into it so that the apparent size of the wormhole got smaller. Just what you’d not expect…. Rachel said, “But it takes a whole star to focus light very much.”

True. Wormholes are held together by exotic matter, however, which has properties far beyond our experience.