Instantiation

by Greg Egan

  Fatima felt light-headed. She left her study and walked to the back door, then she stepped out into the courtyard. There was a streetlight nearby, but she found a place where it was hidden by a neighbor’s tree, then she stood there waiting for her eyes to adapt and the stars to come into view.

  The Pane was twice as wide as a full moon now, still smaller than the Magellanic Clouds but far more eye-catching with its circular geometry. It really did look as if someone had taken a coin-sized piece of the Milky Way and slid it across the sky to a new position.

  She heard the door open, and she turned to see Salif approaching. “Sorry I woke you,” she said.

  “Don’t be sorry. I just want to know what’s troubling you.”

  Fatima hesitated, as if speaking the words might be enough to make everything she’d imagined true, but holding her peace would see the possibility dissipate into the night like a dream.

  But that wasn’t how the world worked.

  “I think we’ve already gone through the Pane,” she said.

  “Okay.” Salif rubbed his arms against the chill. “If you want me to say something sensible about that, I might need a bit more information.”

  Fatima explained the geometry of the time lag. Salif frowned, but then he got it.

  “So you’re telling me that all of this,” he gestured with a wide sweep of his hand that took in every part of the sky but the Pane, “is the view looking back through the portal at our old neighborhood?”

  “Yes. Or you could say the view’s come with us. We’ve gone through, but enough light has followed us that it still looks almost like home, for now.”

  Salif was skeptical. “If we’re only seeing the Pane as it was 140 years ago, how can you be sure we really did pass through it? If it was off to the side a bit, just enough to miss us, would we even notice the difference?”

  Fatima said, “If it was going to miss us, it would look like it was moving sideways as it grew bigger – enough that successive snapshots of the rim wouldn’t nest around each other; they’d intersect. But they do nest, almost concentrically. We might not have scored a bull’s eye, but we didn’t miss the dart-board entirely.”

  Salif laughed and shook his head. “I don’t know what to say! If you’re right, we just traveled thousands of light-years, and no one even noticed?”

  “No one noticed because the short cut we took was over flat terrain. If we’d hit the rim, that might have been disastrous, but I think the Pane itself is just ordinary vacuum. So in a sense, nothing ‘happened’ to us – nothing that a purely local measurement could have detected. The topology around us just turned out to be different than we expected.”

  “That’s got to be the understatement of the millennium.” Salif hugged himself; it really was getting cold. “So we’ve survived the journey, but are we in any danger now that we’ve arrived?”

  “I don’t see why we would be,” Fatima replied. “There’s no reason to expect we would have ended up on the verge of colliding with anything. None of the new stars seem especially close, and to some extent the sheer size of the Pane means we’ve brought our old elbow room with us.”

  “But you think this is a natural event? We haven’t been … caught in some alien butterfly net?”

  Fatima wasn’t sure if he was gently mocking her, but she took the question at face value. “If the Pane is a topological defect, it could date back to the Big Bang. I can’t explain how it would have formed, but it’s even harder to believe it could be created artificially.”

  “Okay.” Salif fell silent for a while, as if he was trying to put the whole picture together to his own satisfaction. Then he said, “How sure are you, of any of this?”

  “Not sure at all,” Fatima conceded. “It fits what we’re seeing better than anything else I’ve heard, but that doesn’t mean much. I can make some predictions and see if they’re borne out over the next few months.”

  “But sooner or later, you’re going to tell the world that we’ve already fallen through the looking glass?” Salif sounded more worried now than when they’d been discussing the event itself.

  Fatima said, “That’s what I’m trying to decide. I don’t want to sow panic. But if I’m right, things are only going to get more frightening: the Pane will just keep growing bigger in the sky – and the more stars that vanish behind it, the closer it will seem to be. What better way to undercut the fear that hitting the Pane might destroy the Earth than announcing that we’ve already come through without a scratch?”

  Salif remained apprehensive. “What if you’re wrong, though? What if this thing just fizzles out? Do you want to be remembered as the woman who claimed that while we were asleep one night, the sky fell down? And when people pointed out the familiar constellations – all still in place, exactly where they’d always been – she insisted that they were only a mirage?”

  Fatima couldn’t help feeling wounded, but he was right to drag her back to Earth. “I’ll talk to my colleagues first,” she said. “Maybe Gabrielle can find some flaw in my reasoning, and prove that it’s all nonsense.”

  Salif stepped forward and embraced her. “You know I trust you,” he said. “I just don’t want to see you get hurt.”

  “I know.” Fatima extricated herself from his arms. “We’d better go inside, or we’re both going to freeze to death.”

  7

  As Gabrielle listened, an expression of pure delight spread across her face – along with a hint of impatience as she joined the dots herself and waited for Fatima to stop talking.

  “The geometry all makes sense now!” she proclaimed elatedly. “At light-speed, the most symmetric shape is a disk moving perpendicular to itself; there is no rest frame in which it could be spherical. And that explains why we’re not seeing it at an angle – it’s not like a frisbee or a manhole cover that could approach us edge-on. To any observer, it’s a circular disk moving perpendicular to itself at light-speed.”

  Fatima had no argument with any of this, but it wasn’t quite the response she’d expected. “You don’t seem too unsettled by the thought that we might have…”

  “Gone through already?” Gabrielle shrugged. “To be honest, I’ve had it at the back of my mind since yesterday, but I wasn’t sure if you’d believe that the curvature could be so low that we wouldn’t feel a thing.”

  “I see.”

  “Can I help you write the paper?” Gabrielle pleaded.

  Fatima was taken aback. “Of course.” So much for having her ideas torn to shreds, but maybe if they sat down together and worked through all the calculations carefully, they’d find a weak spot and the whole thing would unravel.

  By early afternoon, they’d finished their first draft. The geometry itself was very simple, and they had enough data to fix the radius of the Pane to within a few percent. The only wiggle room that remained was in the impact parameter: the distance between the Earth and the axis of the cylinder the Pane had swept out. Without that, they could not make firm predictions for the way the Pane’s apparent shape would evolve in the coming weeks, but they could at least constrain the possibilities for the progression of ellipses that ought to manifest as their off-center viewpoint finally made its mark.

  “One more read-through, then we should post it on the arXiv,” Gabrielle suggested.

  “How long have you been up now?” Fatima asked.

  “Eighteen hours.”

  “Maybe we should leave it till tomorrow.”

  Gabrielle was horrified. “What if someone beats us to it? They’re not all trying to shoe-horn the Pane into standard wormhole models.”

  Fatima was torn, but it was true that anyone could stumble on the same insights at any moment. Whatever they did, the possibility that the planet had relocated was going to start seeping into the public conversation sooner or later. If she and Gabrielle published first, they’d own the story. Maybe if they put the right spin on it, they could soften the blow.

  Still …

  “What if we’re wrong?” s
he replied. “This is a big claim to make, after less than three days’ worth of observations.”

  Gabrielle said, “We still have a chance to falsify the theory.”

  “How?”

  “You didn’t check with Cerro Tololo yet, did you?”

  “No.” Fatima had completely forgotten about the impending event.

  She brought up the web site. While they’d been busy writing, HD 184039, nine hundred light-years away, had disappeared behind the Pane.

  Gabrielle cheered. “Do you want to wait three months for Proxima Centauri?” she asked.

  “No.” Fatima still felt anxious, but she did not want to cede priority for the idea. And if she was wrong, she might not be in the best company, but she certainly wouldn’t be alone. Seven hundred new papers had appeared on the arXiv in the last forty-eight hours – most of them positing exotic new physics to explain the Pane.

  Gabrielle proof-read the manuscript and corrected a couple of typos. Fatima posted it, though it wouldn’t appear online for a few more hours.

  “I’d better go home and grab some sleep,” Gabrielle said. “No rest until we’ve answered the second question.”

  “The second question?” Fatima was a long way from letting go of the first.

  “We’re probably not in Kansas any more,” Gabrielle replied. “So the question is: where exactly are we?”

  8

  When Fatima emailed the draft press release to Daniel, he phoned her back in less than a minute. “Is this a joke?” he asked.

  “Of course not.”

  “The entire solar system passed through a wormhole three days ago?”

  “I don’t want to use the world ‘wormhole,’” Fatima insisted. “It has too many misleading connotations.”

  Daniel said, “I think terminology is the least of your problems.”

  “What I’ve described is just one of several competing theories,” she conceded. “And it might be a while before we know which one’s correct. But you wanted my take on the Pane as soon as possible, and this is it.”

  Daniel sighed, resigned to the situation. “Are you willing to do interviews, defending this theory?”

  “If I have to.”

  “Here’s a tip, then: prepare some graphics illustrating what you’re saying, or the TV people will choose their own. Probably from some bad science fiction movie.”

  Fatima made a short animation, showing how the light grazing the edge of the Pane would lag behind the Pane itself, determining its apparent size at any moment. She resisted the urge to add the Pythagorean formula, and just had the hypotenuse swing down across the diagram so its length could be visually compared with the distance to the center. Then she grabbed a passing undergraduate for an opinion.

  “It’s kind of text-booky,” he complained. “You should show some actual stars.”

  Fatima collected a sequence of exposures of the Pane, and then overlaid an expanding red circle showing her model’s prediction for the size of the effective window. The match was almost eerily perfect – as any linear fit to this linear data would have been.

  She passed the animation on to Daniel, and he sent it out with the press release. Then she sat at her desk and waited, re-reading the paper she’d written with Gabrielle, checking and re-checking every equation.

  The first interview request came from local Canberra radio. The journalist was polite, but a tad incredulous, and not a little confused; she seemed to think that if they’d already crossed through the Pane, but it looked as if they hadn’t, then at some point they must have traveled back in time. “We’re only seeing the past,” Fatima stressed. “That’s how it is, when you look into the sky. We’re always looking back in time.”

  It was after five o’clock; Daniel had been clear that they’d probably missed the deadline for most Australian coverage. But Europe was just waking up, and a German breakfast TV program wanted to Skype her. “We’ll record the segment in English, then play it later with subtitles for your parts,” the producer explained.

  “All right.”

  Fatima was nervous, but the interviewer, Nora, seemed to have read the press release carefully, and she asked intelligent questions. “The other side of the Pane, the one we’ve emerged from, is now moving away from us at the speed of light?”

  “Yes.”

  “So if you’re right, we have no prospect of using it to get home? Not only have we passed through without warning, we can’t turn around and go back.”

  “That’s true,” Fatima agreed. “You can’t see anything approaching at light-speed, and you can’t catch anything retreating that fast.”

  “Not a very convenient subway system, is it?” Nora joked.

  “No,” Fatima agreed. “If this model bears out, I’d say it’s more unlikely than ever that the Pane could be part of any artificial transport network.”

  The BBC was next, then an NPR station in Boston.

  “I see from your university’s web site that your specialty is exoplanets,” the NPR journalist noted.

  “That’s right. It’s just luck that I got involved with the Pane.”

  “So if we’ve suddenly changed neighborhoods, what happens to all your work on neighboring planets?”

  Fatima laughed. “To be honest, I hadn’t really thought about that. But our techniques have improved so much over the last decade that it should be possible to catch up again pretty quickly. It might even be a boon, in one sense, because we’ll potentially have a whole new population of stars and planets to observe.”

  9

  “I have six hundred and thirty-nine emails,” Fatima told Salif. She hefted her phone up from the bedside table. “I think it actually weighs more than it used to.”

  She opened her inbox.

  “Fan mail?” he asked.

  “Not exactly.” He leaned toward her but she turned the phone away, then she climbed out of bed and headed for the kitchen. “I’ll put the coffee on. You go first in the shower.”

  The first ten messages were wall-to-wall racist abuse, death threats and rape threats. Fatima’s chest tightened, and she could feel her heart racing and her mouth turn dry. She sat down on a stool and steadied herself, then she invoked the mail app’s filter and fed it a few examples of the kind of thing she did not wish to see. It was smart enough to sweep up misspellings, deliberate or otherwise.

  The inbox shrank to twenty-three messages, mostly from media outlets who wanted to follow up on the story. She said yes to five, and politely declined the rest; there were only so many hours in a day.

  When Salif joined her, she tried to look cheerful, but he could read her face. “What is it with these animals?” he asked angrily.

  Fatima shrugged. “They seem to think I’ve somehow harmed their chances for Elon to take them on a ride out to the wormhole, which the aliens are building in order to invite all the least pleasant people on Reddit and 4chan into their galactic empire.”

  When Gabrielle turned up at Fatima’s office for her morning briefing, she seemed subdued.

  “You got hate mail too?” Fatima asked.

  Gabrielle winced sympathetically. “Only a little. I’m lucky: second author on the paper, no TV. It’s the wormhole experts who are getting me down.”

  “How?”

  Gabrielle showed her a few of the blog posts that had appeared in response to their paper. Andrew Jolliffe, a cosmologist at Princeton, had written, “While some of us are working hard to explain how the dynamics of an expanding wormhole can result in the unexpected optical properties we’ve seen, Benga and Chan sweep everything puzzling about the Pane into a massless cosmic string, and then make no effort to justify the existence of such an entity.”

  “That’s true,” Fatima conceded. They’d left the rim unexplained: a magical loop of who-knows-what possessing all the properties needed to make everything else work out. “But it doesn’t mean we’re wrong.” The first step in understanding the Pane was to be clear what the observations implied about its structure, on an astro
nomical scale. Whatever exotic modifications to particle physics might or might not follow was a separate question.

  Gabrielle said, “If we’re right, no one else’s predictions for the growth curve will match ours once it goes non-linear. And no one else is predicting any departure from a circular window.”

  “Yeah.” But the non-linearity in the Pane’s apparent growth would probably remain undetectable for five or six months, and any change in the shape would depend on how far they were off-axis. For now, all they could do was be patient, ride out the backlash … and get on with the rest of their work.

  “How are things going on the second question?” Fatima asked.

  “I’m building up a metallicity profile,” Gabrielle replied. “So far, it looks comparable to the Milky Way. I’ve also spotted a few potential Cepheids, so we might have a chance to get some distances without having to wait for parallax measurements.”

  “Well done!”

  When Gabrielle left, Fatima sat down and steeled herself for the five more interviews she’d promised to do. They all turned out to be tougher than the earlier ones; the journalists had read the dismissive reactions from the experts.

  “Your background isn’t in Einstein’s theory of general relativity, is it?” a reporter from Singapore asked pointedly.

  “It’s not my area of research,” Fatima admitted. “I’m an astronomer, I’ve studied relativity, but I’m a planet hunter, not a cosmologist.”

  “So how seriously should we treat your claim that we’ve all passed through a wormhole, when wormholes aren’t your area of expertise?”

  The question stung a little, but it was not unreasonable. Or unanswerable.

  Fatima said, “The simplest explanation for what we’re seeing isn’t a wormhole at all, in the usual sense; it’s a region of space-time that’s flat almost everywhere, but connects up in an unexpected way. My co-author and I don’t claim to have an account as to how this region formed in the first place, but that doesn’t change the fact that what we’re observing fits our model very well so far. Maybe that will continue to be true over the coming days and weeks, maybe it won’t. Only time will tell.”