Greg Egan: Incandescence

They'd reached a junction in the tunnel. Roi moved toward the left branch, which she knew was a cul-de-sac ending in some comfortable crannies.

«Before we part,» Zak said, «can I show you something?» He opened his carapace and reached into the empty seed bed to remove a rolled-up sheet of cured skin, which he proceeded to spread out before her. «This is my favorite map of the Splinter.»

Roi was unimpressed. The single cross-section portrayed was covered with an absurdly regular hatching of short, straight lines which bore no resemblance to any routes she knew. And there was no hint of anything really useful, such as vegetation patterns or the lodes of dense, sheltering rock.

«Are you telling me I can get from here to here?» she asked, gesturing at two endpoints of one of the peculiar markings. But it wasn't even clear where these points were meant to be, since there were no cues to indicate how far along the Null Line, rarb or sharq, the cross-section was taken.

«It's not a map of tunnels,» Zak replied. «It's a map of weights.»

It took a moment for his meaning to become clear. The longest lines were drawn at the edge of the Splinter, where the weight was greatest. The lines' varying lengths, and the way they gradually rotated as you followed them around the center of the map, offered a plausible rendering of the way weight changed from place to place. A small crossbar on each one distinguished the bottom end from the top.

«You drew this yourself?» she asked.

«No, I copied it from a map I found in a library. That had nothing to indicate its provenance, though, and it could easily have been a copy itself. For all I know this could be the seventh or eighth generation.»

Roi pondered the strange task the original cartographer had embarked upon. «Everybody knows that weight increases as you move away from the Null Line. What's the need for a map like this?»

«In what manner does it increase?» Zak demanded. «How quickly, as you move in different directions? And which way, exactly, is down, as you move between the quarters?»

Roi couldn't imagine why anyone would need to know these things with more precision than she already knew them herself. Still, there was something compelling about the stretching and shrinking and rolling of the lines. Each individual mark conveyed nothing new to her, but seeing the totality displayed in this way was curiously satisfying.

«It's pleasing to the eye,» she conceded. «Like the pattern of seeds on a leaf.»

«Oh, it's far simpler than that,» Zak replied. «I can characterize it very easily. Suppose you travel three hundred spans shomal or junub from the Null Line. The weight there will be one vazn, back toward the Null Line. If you travel twice as far, the weight will be two vazn; three times as far, three vazn; and so on, in proportion to the distance.»

«If you travel garm or sard instead, your weight will point away from the Null Line, and it will grow three times as fast. You only need to go one hundred spans before it reaches one vazn.»

«What if you travel in none of those directions?» Roi gestured at the map. «The weight twists around. It's no longer so simple.»

«It remains simple,» Zak insisted, «if you know one more trick. Think of weight as a line, as it is on this map. Put aside for a moment the length and direction of that line, and ask instead for its extent along two axes: shomal-junub, and garm-sard. However far you are shomal or junub of the Null Line determines the weight line's extent along the shomal-junub axis. However far you are garm or sard determines its extent along the garm-sard axis. That's all you need to know in order to draw the line. Its extent in each direction has a simple prescription, and that fixes the line as a whole.»

Roi absorbed this, then re-examined the map, which seemed to bear out Zak's claim. But if his recipe for combining the effect of travel in different directions seemed simple enough to be inevitable, it was the basic ingredients that now struck her as puzzling. Why did being garm or sard of the Null Line add three times more to your weight than being shomal or junub? Why not four times, or five? And why did «garm-sard weight» push you away from the Null Line, while «shomal-junub weight» pulled you back to it? She couldn't even guess at the answers, but she could understand now why Zak was pursuing this strange, lonely task. These patterns demanded an explanation.

«When you find what you're looking for,» she said, «I hope to hear of it.»

The shadow of Zak's heart grew visibly faster, as if she'd hefted a large rock on to his carapace. He said, «Why not help me in my search?»

Roi looked around again, but he was still alone. Did he honestly believe he could recruit her, unaided? She said, «I've told you the work I do.»

«I don't expect you to leave your team,» he replied.

«That's wise of you.» Roi felt a stab of pity for him, followed by a treacherous thrill of disloyalty. It wouldn't have been the worst fate in the world if Zak had had forty team-mates waiting to ambush her, a throng of eccentric questioners to lure her away from the worthy monotony of the crops.

«What I'm asking won't interfere with your work. I only want you to take some measurements, as you travel around the edge.»

«Measurements?»

«To confirm the weights.» Zak began rolling up the map. «I have no idea who drew this. I can only guess about the scales they used to represent distances and weights. And what if it's not accurate? I can't just take it on faith! Even if it was correct when it was drawn, what if something has changed since then?»

Roi was still trying to wrap her mind around the notion of a solo, partial recruitment, but this last comment electrified her. «Someone told me a story once,» she said, «about the weights growing stronger.»

«So strong that they tore the world to pieces. Hence our name for what remains.»

Roi said, «Do you believe that's true?»

Zak hesitated. «Who can say? Maybe it's simply in our nature to imagine a larger, more glorious world in the past. To console ourselves, as we confront our limitations, with the idea that we were once part of something greater.»

Roi joked, «I think I'd find more consolation by imagining a larger world in the future .»

Zak took her words perfectly seriously. «Exactly, but how? Should we hope to catch up with our mythical cousins who went tumbling away into the Incandescence?»

This was becoming too strange for Roi. «You said something about measurements.»

«Yes.» Zak opened his carapace again, and removed a long tube wrought from susk cuticle. As he offered it to her, the shifting light revealed a coil of metal inside, with a small, smooth stone attached to the end of it.

Roi took it, trying not to show her astonishment at how casually he was handing over this extraordinary device. «See the numbers carved along the side?» Zak asked her.

«Yes.»

«The greater the weight, the further the spring stretches.»

«Of course.» That principle was clear, but how would she measure the exact direction? There were a number of slender rods lying against the side of the tube; Roi tugged gently on one of them, and it unfolded into a spindly leg. There were three legs, and a system of shorter rods as well.

«You need to take sights of some reference points,» Zak explained. «And then record the angles between the legs and the weight tube.»

«This is beginning to sound complicated.»

In fact, it was beginning to sound like work. What she felt about Zak's plans, though, was nothing at all like the buzz of camaraderie. He wasn't competing with her team; he was offering her something entirely different.