The Eternal Flame

by Greg Egan

  Assunto sketched two examples on his chest.

  “Are there particles of light in this picture?” he mused. “Not if you think a ‘particle of light’ is something like a tiny grain of sand. The number of photons associated with each wave is really just a label for its energy level, found by counting the steps up from the lowest level. It’s not a count of things you could hold in your hand.”

  “The lowest level, with zero photons, doesn’t have zero energy,” Carla protested. “That’s…”

  “Strange?” Assunto suggested. “I agree. But the same kind of thing is true of your luxagen in a solid: you can’t make it lie still at the bottom of the valley.”

  “Yes, but at least there’s something there in the valley,” Carla replied. “You’re claiming that the void itself has energy—with a contribution from every possible mode of the light field!” Every frequency, every direction, every polarization that any light wave could possess would each leave the vacuum with a trace of energy—without the need for the light waves themselves to be present at all.

  Assunto said, “Only changes in energy are detectable. The actual value is a meaningless concept: if you redefine every energy level by adding or subtracting the same amount, that won’t change anything you can measure. So it doesn’t bother me at all if a theory gives a non-zero value for empty space… but if you prefer to subtract that value from everything in sight, bringing the vacuum energy down to zero, go ahead and do that. It won’t make any difference.”

  Carla fell silent. The result still struck her as preposterous, but she couldn’t yet see how to argue against it.

  “Where has this taken us?” Assunto continued. “We started with Yalda’s light field, which has a precise value at every point in space and every moment in time. But now Patrizia’s principle has given us a theory where we can no longer think that way. Just as a luxagen in a solid lacks a precise location and is spread out across its valley, the amplitude of a light wave must also be spread out across a range of values. In a strong enough light wave, the spread of values can be much less than the peak amplitude of the light, so this need not contradict the way we use waves in conventional optics. But when a single luxagen ‘scatters a photon’—when it lowers by one the photon count for light of a certain frequency and direction, and then raises by one the photon count for light of a different frequency and direction—we should neither expect conventional optics to apply, nor assume that the failure of the old laws means that we’re describing something akin to colliding grains of sand.”

  Assunto spread his arms in a gesture of finality. There’d be more details in the paper itself, but his presentation was finished. “Questions?”

  Most people in the room looked as if they were still struggling to absorb what they’d heard, but Onesto responded immediately.

  “What about luxagens?” he asked Assunto.

  “What about them?”

  “Can they fit into the same framework? If photons are really just steps in the energy levels of a light wave, can you account for luxagens the same way?”

  Assunto said, “When a luxagen wave in a solid rises to a higher energy level, that doesn’t amount to making a new luxagen. It just means the original luxagen has more energy than before.”

  “I understand that,” Onesto replied. “But I’m not talking about the energy levels in a solid. You took a light wave traveling through empty space, and showed that the energy levels of each mode amounted to what Carla and Patrizia would have called the number of photons in the wave. So why can’t you do the same thing with a luxagen wave in empty space, finding energy levels for each mode of that wave that correspond to the number of luxagens?”

  “Because they’re completely different kinds of waves!” Assunto said. “A light wave isn’t all that different from a wave on a string: the higher its peaks, the more energy it carries. Given that relationship between energy and wave size, we can come along and apply Patrizia’s principle, which forces the energy to take on discrete values.

  “But to get luxagen waves in the first place, we’ve already applied Patrizia’s principle to the energy of a single particle. A luxagen wave’s energy has nothing to do with the size of the wave; its overall size is meaningless, only its shape and its frequency matter. How could you apply Patrizia’s principle for a second time, to a wave like that? It would make no sense.”

  “I see.” Onesto clearly wasn’t satisfied—but his personal sense of nature’s symmetry would have to defer to these annoying technicalities for now.

  Patrizia turned to Carla. “You should be happy! Assunto wasn’t trying to dispute our results; he just found a better way to think about photons.”

  “It’s an interesting theory,” Carla admitted begrudgingly. The truth was, it still felt like trespass to her: Assunto had snuck into her room and rearranged the guide ropes, and it didn’t matter whether or not he’d left them tidier than he’d found them. “We should have spotted the same pattern ourselves,” she said. The formula for the energy in a light wave was elementary optics, generations old. If she and Patrizia hadn’t been half-dazed by hunger when they’d come up with the whole idea of energy levels, they might have noticed the analogy and pursued it, long before Assunto had paid the slightest attention to their results.

  “So what now?” Patrizia asked eagerly. “Maybe we could write a new paper together, re-analyzing the scattering experiment with the photons treated Assunto’s way.”

  “Maybe when I get back,” Carla replied.

  “Oh, of course.” In her excitement, Patrizia had forgotten about the Gnat. “In six days you’ll be—”

  “Traveling through the void,” Carla said. She watched the other physicists filing out of the room, reverently collecting their copies of Assunto’s paper. “So I’ll let you know if empty space turns out to be full of some mysterious, ineradicable energy.”

  22

  Carlo woke so abruptly that for a moment he was sure he must have sensed some imminent danger. That idea quickly faded, but the urgency remained. He could feel the tautness of the tarpaulin above him, trapping grit against his skin, and the coolness of the bed below, the resin-caked sand clumping in places. Between these familiar, superficial sensations a third occupied the whole space of his body, a solid presence coexistent with his flesh, agitating every muscle and bone.

  Eyes still shut, he reached over toward Carla, but then he stopped himself before his hand touched her shoulder. There was no point acting only to be rebuffed. He dug his fingers into his chest, trying to assuage the ache long enough to make a plan.

  You’ve done enough, he could say. You’ve lit the fire with your theories; you can leave it to others to nurture the flames. Why put up with another day’s hunger? Why risk dying out there in the void? This is the time to make yourself immortal: not just loved and remembered, but living on in the flesh of your children. On and on forever, down the generations. The ancestors will hear of your discoveries, your descendants will share in your fame.

  What more do you want? This is the time.

  Carlo opened his eyes. He reached up and took hold of the nearest rope and pulled himself out from beneath the tarp. He stared at the clock in the moss-light until the dials became clear. It was too early to light a lamp and pretend that the day had begun.

  He dragged himself out of the bedroom, then released his hold on the rope and let himself drift. The ache in his chest was as strong as ever, and the voice that spoke for it refused to be silenced. What did he have to be ashamed of? Had he locked up his co, like Tamaro? Had he contemplated a single act that went against her will? If Carla listened—if his words made sense to her—how would he have wronged her?

  His skin brushed the cool stone of the floor. He scrabbled about for a suitable rope, then pulled himself into a corner. If he wasn’t going back to bed, he should at least be touching something solid that could draw away the heat.

  It had been his suggestion that they sleep together, on this last night before the trip. H
e’d argued that the signal to her body from his presence—the reminder that she hadn’t been widowed or abandoned—would help protect her during their separation. The logic of that was impeccable, but it proved nothing about his real intentions. A different message seemed to have reached his own flesh: his co was heading into danger, and she might never return.

  Carlo spread his fingers against the stone. How many times had he silently cursed Silvano’s weakness? You really couldn’t stop yourself? You really couldn’t wait? But what was his own great strength, then—being divided against himself? Despising the one act that would complete his life?

  His father had died young. What if he died, himself, before his children were grown? Before they were even born?

  His father’s death had been down to chance, though, brought on by a harmful influence, not some heritable disposition. He had no reason to expect the same fate. In a year or two—or three, or four—when Carla’s work was done, they’d make the decision. She wasn’t spurning him, she wasn’t leaving him, and she wasn’t going to let herself die in the void.

  Let herself? As if she’d have a choice about it, when the Object lit up like a star and engulfed the Gnat in its flames.

  Carlo reached up and hooked his arm around the rope, then moved his hand through a full circle; the helix of rope bit into his forearm, but he locked his hands together and let the pain drive a spike of clarity into his thoughts. If they’d woken together—side by side, eyes still closed, oblivious to the plans of their waking lives—anything might have happened. He hoped that danger was past now, but at the very least there was still a chance that he might spew out some idiotic plea to Carla to change her mind.

  He would wait here until morning. Wait a bell, then light a lamp, then wake his co to wish her a safe trip and a speedy return.

  The great workshop where the Gnat and the beacons that had gone before it had been built was all but empty now. From the entrance, nothing could be seen rising from the once-crowded floor but a mound of half-disassembled scaffolding. When Marzio called out a greeting from afar, the echoes were so disorienting that Carlo couldn’t stop himself looking around for accomplices in some kind of aural prank. Carla raised a hand, and held off her reply until they were closer.

  “Are we early?” she asked Marzio. No one else was in sight.

  “Everyone’s early,” he said. “The others are down near the airlock.”

  The three of them headed off together. Carlo was glad they had a guide; in the dim light from the ceiling’s moss, this part of the workshop looked as featureless as empty space.

  “Viviana and Viviano spent the last three bells conducting final checks,” Marzio offered reassuringly. “Everything’s in good order, cleaned and calibrated.”

  “Thank you,” Carla replied. Carlo took some comfort in the record of the beacons: of the gross that had been launched, only three had failed to light up after their long periods of dormancy. Marzio and his team knew how to build machinery that could function in the void, and Carlo trusted the astronomers to guide the Gnat to its destination. It was only the behavior of the Object itself that lay beyond anyone’s experience.

  As they approached the airlock, Carlo could see some of the people gathered there, their bodies emerging feet-first from behind the horizon of the convex ceiling. A little nearer, he understood why there were a few more legs than he’d been expecting. The crew had decreed that only their families should see them off, but three Councilors had decided to put in an appearance, regardless.

  Silvano stepped forward to greet Carla effusively. There was no throng of constituents to witness the gesture, no crowd on whose behalf he could claim the Object, but this moment could still feature in later speeches. By the time the next election rolled around, whatever good had come from that lump of rock might well be seen by half the Peerless as Silvano’s personal benison.

  Councilors Prospero and Giusta didn’t hang back for long, either. Carlo was impressed that a full nine of their colleagues had deferred to the crew’s request for a private departure, but then, as incumbents when the Gnat’s construction was approved they probably felt secure already in their ownership of the mission.

  With Carla monopolized by the other Councilors, Silvano turned to Carlo. “You must be feeling proud.”

  Carlo struggled to suppress his irritation. “You make it sound like she’s a child who just won a school prize. Today I’m more concerned with her safety.”

  “Everything will be fine,” Silvano assured him.

  “Really? How would you know?”

  “I know that a lot of good people have done their best.”

  Carlo gave up on the conversation. He knew that he should have been willing to tolerate a few platitudes from a well-meaning friend, but all he could hear in Silvano’s words these days was Councilor-speak.

  Ivo was off to one side with his son and grandchildren, but he raised a hand in greeting to the new arrivals. Carla dragged Carlo past the politicians to join Ada and Addo, their father Pio, and Tamara.

  “We should meet up at the observatory, just before the rendezvous,” Addo suggested enthusiastically. “Roberto was telling me that we might be able to see some signs of the first experiments.” Carlo listened with an awful fascination. Did he want to watch for those flares of light, and try to judge their significance from a distance? A sequence of orderly, isolated flashes would prove that the crew were still in control, but what would he make of a sustained light, or prolonged darkness? He watched Addo talking and talking, and wondered how peaceful his night had been.

  Tamara said, “We should start boarding now.” The words were like a knife against Carlo’s skin, but there was nothing to be done about it.

  He embraced Carla briefly. “Safe voyage,” he said.

  “Stay happy,” she replied. “I’ll see you soon.”

  As he stepped away, Tamara caught Carlo’s eye. “I’ll bring her back,” she said. Carlo nodded in acknowledgment, but he felt uneasy before her gaze, as if her ordeal might have left her with the power to judge exactly how close other men had come to repeating the sins of her co.

  The crew separated from the onlookers. Carlo watched as the four fitted their cooling bags with practiced movements. Once they’d donned the bulky helmets it was hard to tell the women apart. The airlock was big enough for two people at a time; Ada and Tamara went through first. When it was Carla’s turn she raised a cloth-covered arm in farewell, then stepped through the door with Ivo.

  Marzio touched Carlo’s shoulder. “Come and watch the launch.”

  Everyone gathered around the observation window, an octagonal slab of clearstone a couple of strides wide set in the floor beside the airlock. When Carlo looked down he could see all four travelers still on the ladder, the white fabric that enclosed their bodies catching the starlight. The Gnat itself was directly below the window, a dark silhouette hanging from a dozen thick support ropes. As he watched, Ada or Tamara stepped from the ladder through the vehicle’s open hatch, and a moment later a small lamp lit up inside the cabin.

  Pio said, “Imagine the farewells at the launch of the Peerless. This is nothing.” Carlo wanted to thump him, but he did have a point. Not one traveler who’d marched into the mountain, not one father or child or co left behind, had had the slightest hope of a reunion when the voyage was over. His own generation’s troubles weren’t small, but no one had lived without sorrows.

  As Carla reached the end of the ladder she looked up and waved, sweeping her arm across a wide arc. Her exuberance was unmistakable, and Carlo felt a sudden rush of happiness. This was what she wanted. She had balanced everything against the dangers and wanted it still. Whatever had passed in the night, he hadn’t robbed her of this chance. He was tired of feeling ashamed and fearful. Why couldn’t he just rejoice?

  Carla climbed through the hatch. As Ivo followed her, Carlo leaned back and let Silvano, behind him, get a better look.

  Marzio said, “They’ll pressurize the cabin, but keep their
cooling bags on just in case.”

  In case the vehicle itself sprung a leak, or worse. In case the Gnat fell apart, and the crew had to try to make their way back with air rockets.

  Carlo stepped away from the window and checked the clock beside the airlock, its dials specially calibrated for the launch. A little more than a chime remained.

  “What if they’re not ready?” he asked Marzio.

  “They can delay for a revolution or two,” Marzio replied. “Or a dozen, if it comes to that. The orientation of the Peerless has to be just right, or the boost they get from the spin will be wasted, but they have more than enough fuel to cope with a variation in the timing.”

  “Good.” Carlo made his way back to the window. Everyone in the crew had performed endless safety drills. The two navigators were equally proficient; Ada had been prepared to fly the Gnat herself. And the ancestors had managed to launch a whole mountain into the void; this modest expedition should not be beyond their descendants.

  When Carlo looked down the whole vehicle was dark again. That was a good sign, he remembered: Carla had told him that they’d extinguish the lamps once everything was in place and they were ready for the launch. Ada and Tamara were astronomers, used to working by touch and starlight.

  Marzio counted. “Five. Four. Three. Two. One.”

  Inside the Gnat, the clockwork released the clamps that had been gripping the support ropes. Carlo’s skin tingled with fear and awe as the dark shape fell away into the void. He staggered slightly; Silvano put a hand on his shoulder.

  The silhouette shrank against the star trails, dropping straight toward the bright, gaudy circle that marked the division of the sky. But the rendezvous point didn’t lie in that plane, the Gnat couldn’t simply be flung toward its destination. Marzio began counting again. Carlo braced himself.