The Eternal Flame

by Greg Egan

  Tamara hung back and let Carla and Ivo take their turns at the telescope first. She didn’t mind waiting, listening to their descriptions before she saw the image; it was like savoring the odor of a seasoned loaf for as long as possible before finally taking a bite.

  “The more variegated the better,” Ivo said, squinting through the eyepiece. “Ah… wouldn’t it be perfect if just one of these minerals set calmstone on fire, and the others were inert? Then Silvano could have his new farms out here, alongside the liberator mines.”

  He moved aside, and Tamara prepared to take his place. From the Peerless, the best view of the Object had given them its rough dimensions but little else. For two days now, she and Ada had been tracking it through their theodolites, treating successive locations of the blurred ellipse as one more set of navigational data, their sightings building up to a family of lines that would complete the elegant geometrical construction that made the rendezvous possible. But now they were close enough for the Gnat’s largest telescope—barely the size of Tamara’s own body—to show her the whole point of the exercise.

  Tamara closed three eyes and pressed the fourth to the instrument. The ellipse was now a crisply rendered, idiosyncratic oval with a pinched and tilted waist. About a third of one lobe was as red as firestone, but the rest bore patches of brown, of gray and of white. Everything was pale and subdued in the starlight—and any comparisons she made with the sight of mineral samples in a well-lit workshop or storeroom would be unreliable—but the brown outcrops more or less matched the calmstone slopes of the Peerless, viewed under similar conditions. There was a sprinkling of small impact craters everywhere—structures Tamara had only ever seen before as sketches in astronomy books, recorded by the ancestors when they’d observed the inner planet Pio.

  “We finally have our own sister world,” she said.

  “Sister or co?” Ada replied.

  “It almost matches us in size,” Carla pointed out. “A co should be smaller.”

  Ivo said, “It’s what happens when the two come together that counts.”

  “Either way,” Tamara said, “it doesn’t look like a stranger.” After three generations alone in the void, the travelers could hardly dismiss any companion as mundane. But these rocks did appear to be ordinary rocks, old and pitted as they were after a long journey. If their origins really could be traced all the way around the history of the cosmos, back to the primal world’s past-directed disintegration, that only made their similarity to the stuff of the Peerless all the more striking. Matter was matter, shaped by the same rules and forces everywhere—and it looked no different even when you encountered it backward.

  Two small burns nudged the Gnat’s trajectory toward the rendezvous point. The crew kept returning to the telescope as the Object’s slow spin revealed its whole surface: more of the same minerals, more small craters.

  “The only thing missing is life,” Carla said. “Not one patch of weed, not one speck of moss.”

  “Pio, Gemma and Gemmo were dead worlds too,” Tamara reminded her. “Chemistry might be universal, but life must still be rare.”

  Ivo took his turn at the eyepiece. “Forget life,” he said. “I’d be happy with any sign of rubble.”

  Tamara felt the same. If the Object had been nothing but a loose pile of stones then they would have had no hope of altering its trajectory—but enough fragmentation to save Ivo from having to chip off samples himself would be a huge advantage. The Object’s spin was slow enough that even its weak gravity could, in theory, maintain a tenuous grip on pebbles scattered across its surface, but the creation and persistence of such things would depend on the whole detailed history of the body. Over time, the radiation pressure of starlight should have pushed away the very tiniest dust grains, but that was no loss: anything too small to see and avoid would only have posed a hazard.

  While Tamara had been locked away on the farm, Ivo had been working on his sampling techniques. By now he was able to get decent results with powderstone as the target and pure air as the blade, and with calmstone as the target and traces of hardstone in the airflow to act as an abrasive. The first was easy enough, but the second could take more than a day.

  He had also tried to carve firestone using air flecked with its liberator. Burning furrows into the firestone hadn’t been a problem, but getting an intact sample free of the main body had proved impossible.

  People had been studying firestone since antiquity. But if Ivo had to hack a piece of the Object loose using its own kind of fire as his only cutting tool, he would need to learn to do it in a matter of days.

  The deceleration was planned to take place in three stages. Tamara put aside every distraction and devoted herself to the navigator’s arts. She didn’t care about the jagged beauty of their companion world any more; all that mattered was the geometry and timing of the encounter.

  The first and longest burn rid the Gnat of most of its velocity relative to the Object—but it was impossible to aim the engines perfectly, and observations soon revealed that in slowing the craft they’d also pushed it slightly off course.

  Tamara tweaked the second burn to compensate. It would add its own errors, but the thrust would be less and the consequences smaller.

  Before the third burn, she and Ada spent half a day sighting and re-sighting beacons and following the Object’s slow drift against the stars. Their target was growing visibly larger by the bell now, and though they were aiming for a suitable offset a small mistake could see them slam right into the rock. Tamara was duly meticulous—but it was hard to resist a kind of sneaking pride in the thought that it wouldn’t be the worst way to go. For the Gnat to become lost in the void would have been humiliating—quite apart from the unpleasantness of hyperthermia—but if they actually hit this lonely speck after crossing such a vast distance, their demise would at least be a testament to their almost perfect navigation.

  Tamara set the clockwork for the burn, and when Ada had checked the dials she checked them again herself. She strapped herself into her couch and, for the first time, closed her front eyes.

  The couch pushed against her back, the shuddering of the engines penetrated her bones. The glare of the exhaust came through her eyelids, two giant gray stars blossoming in the darkness where the windows would have been.

  The gray stars faded. Tamara opened her eyes, took off her helmet and unstrapped herself from the couch. As she crossed the cabin, the Object’s now familiar terrain filled the view through the window on the left—neither approaching nor retreating, giving every appearance of perfect stillness.

  That was impossible, but inasmuch as any one moment could be called an arrival, this was it. Trying to steer the Gnat into a well-defined orbit once and for all would have been too ambitious; the tug of the Object was so weak that orbital velocity and escape velocity were just two different kinds of brisk walking pace. But with careful observations and the odd gentle push from the air jets, they ought to be able to weave back and forth between a safe altitude and an unintended departure.

  It was Carla who rose first to join her, chirping with delight at the landscape suspended below. “Well done!” she said, turning to include Ada.

  Ada said, “Now that we’re here… why not just rest for a while, then go back and break the news that the Object was inert?”

  She was joking, but the proposal did have a certain mischievous appeal. “We could probably get away with it,” Tamara replied. “Silvano might try to send a follow-up mission, but I doubt he could persuade the Council to back it. Dragging some giant self-contained engine, big enough to capture this by brute force…?” She swept an arm across the alarming arc the Object now subtended.

  Ivo said, “They’d never do it, you can be sure of that. Our own plans are quite insane enough.”

  24

  Carla helped Ivo attach his spectrograph to the telescope, then watched him load the first sample into the catapult beside the window: the first small irritant with which they hoped to goad the Object
into a revelatory response. The Gnat had no airlock as such—nothing large enough for the crew to come and go without depressurising the whole cabin—but Marzio had designed a miniature version, equipped with lever-operated scoops and pincers, that allowed them to move these tiny samples the short distance through the hull and into the catapult’s launch tube.

  Back when the surface of the Peerless had been suffering the sporadic flashes attributed to orthogonal dust, no one had ever managed to observe—let alone record—the light’s spectrum. Before the centrifugal force of the mountain’s spin put an end to those displays, people had proposed spectrographs with such a wide angle of view that the inability to know precisely where the light would be coming from would cease to matter. The problem they’d never solved, though, had been the question of timing: no one could react quickly enough to open a shutter just as the flash occurred, and a prolonged wide angle exposure, even if it encompassed one of the rare events, would bury any signal from the flash itself in the accumulated background of reflected starlight.

  No one had managed to find so much as a single tiny crater or other blemish left behind by the strange ignitions. With no more empirical clues, three generations of travelers had been left to speculate about the collisions. That the modest spin of the Peerless had been enough to brush the encroaching specks of dust aside ruled out sheer speed of impact as an explanation for the flashes, in favor of some kind of chemical reaction with the rock of the mountain itself. But no theory of chemical luminescence, no theory of fuels and liberators, no theory of light and luxagens, had ever offered a believable account of the events.

  Ivo said, “One scrag of calmstone, delivered to the northern gray flats.”

  He released the catapult.

  Carla glanced across the cabin at Ada, who was resting a hand on the emergency lever that would fire the engines immediately to propel the Gnat out of harm’s way if the Object did a Gemma and began to transform itself into a star. Tamara, clinging to the rope beside Ada, was wearing a heavy blindfold. If the Object burned so fiercely that its radiance became injurious, this macabre precaution might at least spare the sight of one of their navigators.

  Carla bent down and peered through the theodolite in front of her—willingly putting one eye at risk in order to cover the opposite contingency, that the flash might be too weak to see any other way—while her fingertips brushed the dials of the adjacent clock. They believed they knew how long it would take the speck of calmstone to reach the surface, but if the reaction itself was delayed the exact timing would be a valuable further datum.

  “Opening the shutter,” Ivo said softly.

  Carla stared at the starlit gray surface, expecting an anticlimax. The secret that had eluded generations couldn’t give itself up with the first grain of sand they tossed. She felt the dials reach the estimated impact time and move on: one pause beyond, two, three—

  A dazzling point of light blossomed against the grayness, like a sunstone lamp seen through a pin-hole. Carla dutifully transcribed the precise time of the event onto her thigh even as she waited for the pin-hole to burst open, for the barrier between the realms to be torn apart and chaos to come spilling through.

  The light faded and died. Carla quickly turned around and put an undazzled rear eye to the theodolite. There was no wildfire spreading from the impact site. The surface appeared completely unchanged.

  Ivo said, “Tell me I didn’t hallucinate that.”

  “Hallucinate what?” Tamara asked impatiently.

  “It was bright but… contained,” Carla managed. “Just as they described it in the old fire-watch reports!” Just as Yalda herself had first seen it—looking back on the Peerless from the void, when a construction accident during the building of the spin engines had almost sent her to her death.

  Ivo pulled the strip of paper out of the spectrograph. Carla lit a lamp so they could examine it properly. The paper had been darkened across the entire range of frequencies, showing a spectrum similar to that of the light from any burning fuel. But superimposed on this was a feature so sharp that Carla at first mistook it for a calibration mark on the paper—a line Ivo might have drawn for the purpose of alignment. It was no such thing. The paper had been blackened by the flash itself, along a narrow band corresponding to an ultraviolet wavelength of one gross, eight dozen and two piccolo-scants.

  Tamara was keeping her blindfold on, so Carla explained the results to her.

  “What could produce that?” Tamara asked. “A single, sharp ultraviolet line?”

  “I’ve never seen anything like it,” Ivo declared. “No ordinary rock burns with a narrow peak brighter than all the other light from the flame.”

  “Let alone just one peak,” Carla added. “The total amount of energy a luxagen needs to gain in order to escape from calmstone would be something like two dozen times greater than the jump corresponding to that ultraviolet line. You’d expect a liberator for calmstone to modify the energy levels so the total gap was bridged in a lot of small steps—but there’s no reason why all of those steps should turn out to be identical in height!”

  Ada said, “And yet, there it is: one lonely peak.”

  Ivo launched a second scrag of calmstone, this time at the red-tinged portion of the Object’s southern lobe. The terrain here looked as if it was covered in firestone; watching through the theodolite, Carla braced herself for the sight of a wildfire, if not a full-blown Gemma event.

  Three pauses and five flickers after the impact, there was a single, brief pinprick of radiance.

  When Ivo extracted the paper from the spectrograph, there were some minor differences across the visible frequencies but the spectrum was dominated by exactly the same ultraviolet peak as before.

  Ivo repeated the experiment, choosing two more regions of the Object with their own distinctive appearance. Then he switched the projectile from calmstone to hardstone, then powderstone, clearstone, mirrorstone, firestone and sunstone. In two dozen and four variations, the delay before the flash was sometimes a little longer or shorter, and the visible part of the spectrum showed clear differences that depended on the particular area being targeted on the surface. But in every case, a single ultraviolet line blackened the paper at exactly the same position.

  Carla could offer no explanation, and Ivo was equally perplexed. Ivo went so far as to aim the spectrograph at a lamp inside the cabin, to see if the ubiquitous line was really just the product of some bizarre flaw in the optics. It wasn’t.

  “Take away the ultraviolet line from this spectrum,” he said, holding up a strip of paper he’d exposed to a flash from the red rock of the southern lobe, “and take away the liberator lines from this one.” He grabbed the test strip he’d made from the lamp. “Apart from those features, they both look the same: burning firestone.”

  “So firestone is firestone, luxagen-swapped or not,” Ada said. “Once it’s actually burning, the light is identical, just as Nereo’s theory would predict.”

  Carla said, “But the process by which the Object’s firestone is being set alight looks nothing like the way a liberator acts on ordinary firestone. And it’s completely indiscriminate: it acts the same way with every mineral. It doesn’t care about the detailed structure of any of these solids—their geometry, their energy levels. It just does its magic trick and pfft…”

  Tamara finally took off her blindfold. “Whether or not we understand the ignition process, surely this is an answer to the fuel problem? Every scrag of the Object can be made to burn! A little too easily for comfort… but if we can slow this thing down enough to keep it in reach, the next generation can deal with the practicalities.”

  “Or the next generation could catch up with it and fetch it back,” Ada suggested. “They’ll have had time to think deeply about the results we’ve seen, and work out what’s really going on. We know the Object’s trajectory with very high precision now. We can’t lose track of it.”

  Tamara almost seemed swayed, but then Ivo interjected angrily, “
We came here to capture the Object! That was the mission the Council approved: to take samples, to do calorimetry, then to trigger a blast that would leave this thing motionless. If we give up now, all we’ll be bequeathing our descendants is a longer journey and a more difficult version of the task we should have done ourselves. We’ve had three generations of theorizing about orthogonal dust, and that’s left us none the wiser. The only way to understand this material is by experiment.”

  Ada said, “You’ve just completed a whole set of experiments! Do you really want to get any closer to something that can set every tool and container you have on fire?”

  “I have the air tools,” Ivo insisted.

  “Which can only carve powderstone,” Ada replied.

  Ivo rummaged through the spectra, then pulled out one strip. “Here! The gray mineral, in the north. As you said, luxagen-swapped or not, the basic properties of a substance are the same. Except for the ultraviolet line, this spectrum is the spectrum of powderstone! To the eye, this rock looks like powderstone! Physically, there is no reason why it shouldn’t be every bit as soft as powderstone.”

  Ada and Tamara looked to Carla. “I can’t argue with that,” she said. “It ought to have the same mechanical properties as the ordinary mineral. But from what we’ve just seen, if a speck of it touches anything—”

  Ivo said, “There’ll be air flowing out of my cooling bag, constantly. The Mite has an air shield around it too. I’ve practiced this: I know I can take a sample of powderstone without touching it.”

  Tamara was silent for a while. “All right,” she said reluctantly. “If you’re still confident that you can do this, I’m not going to stand in your way.”

  She reeled in one of the guide ropes to make some room, then Carla helped Ivo slide the Mite out of its storage bay and bring it to the middle of the cabin. It was less a vehicle in its own right than a kind of chemistry workbench fitted out for the void, with air jets attached. As Ivo’s understudy, Carla had had her own rehearsals with a mock-up of the thing, maneuvering it around the Peerless and practicing the descent from orbit. After a few days she’d become quite comfortable with the way it moved—but she’d lost count of the number of gentle collisions she’d had with the mountain.