Incandescence

Roi found it difficult to follow the details of Zak's calculations, but if she stepped back and looked at the overall picture, it was a startling idea. Weight is the difference between preferred and actual motion. What her body felt as it pressed against the floor of a tunnel was a kind of struggle against falling, a struggle she could only perform with the aid of the rock beneath her. What she felt now, the absence of that struggle, only seemed dangerous because in a more normal place any such lapse would be punished with serious injury if it lasted more than a heartbeat or two.

„All right,“ she said. „The principle you're asserting is simple enough, and I think I understand what's happening with the spinning tube. How can this explain the pattern of weights across the whole Splinter?“

Zak said, „For that, we need another experiment.“

He led her across the web, to a tube anchored firmly to several wires. „The axis of this cylinder runs from shomal to junub; the midpoint is precisely on the Null Line.“ He took two stones from his carapace, then placed one gently in the mouth of the tube, and the other beside the tube's midpoint. Both floated where he left them, showing no immediate evidence of motion.

„What do you think will happen?“ he asked Roi.

She thought carefully. „The stone that's a little bit shomal will have a little bit of weight, slowly pulling it toward the Null Line. So given time, it will fall down to the Null Line.“

„So let's wait and see.“

To help pass the time, Zak asked Roi to recount the details of her journey, and they chatted about the different work teams she'd seen, the changes in vegetation from place to place, the rumors of food shortages. As they talked, the first stone did indeed gradually descend into the tube, while the second one remained where Zak had placed it.

As the moving stone approached the fixed one at the midpoint of the tube, Roi said, „I was right, wasn't I?“

„Keep watching,“ Zak insisted.

The stone didn't stop at the center. It kept traveling slowly down the tube, away from the Null Line.

„But there is no weight at the Null Line!“ Roi said. „If you're exactly at the Null Line, you should go nowhere. You don't start falling junub!“ She gestured at the other stone, which continued to float where Zak had left it.

„Move away from the Null Line, and throw a stone across it,“ Zak suggested. He pointed to the slender wire that marked the invisible line, then handed her a projectile.

Roi complied, bracing herself on a cross-wire. The stone didn't quite touch the wire, but it came close before sailing smoothly past it.

„It kept going,“ she mused. That didn't surprise her; she hadn't really expected the Null Line to magically rob the missile of its velocity. So why had she been surprised that the stone that had fallen under its own weight, rather than being tossed, had also kept moving?

She went back to watching the stone in the tube. Eventually, it reached the mouth opposite the one where Zak had placed it. She waited for it to emerge from the tube, but again her guess proved ill-founded. Moving just as slowly as it had at the start, it now reversed its motion and began to fall back into the tube.

„A little junub,“ she said, „means a little weight back toward the Null Line again. And somehow, it all balances out. When the stone first crosses the Null Line, the weight begins to act in reverse, but not enough to halt it completely, only to begin to slow it down. Only when it reaches as far junub as it began shomal does it halt completely. And then it starts the very same motion again, in reverse."

«Right,» said Zak. «But where does this beautiful pattern come from? The weight, the motion, two stones coming together and moving apart?»

«I have no idea,» Roi confessed.

«What comes back to itself, over and over? What repeats itself, endlessly?»

Roi was blank for a moment. «A circle?»

«Yes.»

«I don't see any circle.»

Zak rummaged in his right cavity and fished out a loop of wire. «When we throw a stone here, it looks as if it follows a straight line. But how can we really be sure? Before long it hits the wall of the chamber, and we can't know where it would have gone if it hadn't been stopped. So imagine that the way things move when there's nothing to interfere with them isn't always a perfectly straight line. Suppose that if they're tossed in the right direction, they travel around and around, in a very big circle.»

Roi was perplexed. «How big? As big as the Splinter?»

«Much bigger than that. Imagine a circle so big that you could follow a part of it from one side of the Splinter to the other and not even notice the curve, not even see that it was not a straight line.»

Roi's mind reeled. Crossing from one side of the Splinter to the other. then stretching out far into the Incandescence?