by Greg Egan
One vaguely cruciform constellation lay almost flat in the hyperal plane: every one of the four stars shared roughly the same altitude above the horizon, and the same left-right azimuthal bearing, and yet they were not bunched together in the sky; the hyperal directions kept them as far apart as the stars of the Southern Cross. Orlando struggled to attach labels to them: sinister and dexter for the quadral pair, gauche and droit for the quintal. It was completely arbitrary, though, like assigning compass points to a fictitious map drawn on a circular piece of paper.
Several degrees away to the left-up-dexter-gauche, he could see another four stars; these lay in the lateral-vertical plane, the plane of the “ordinary” sky. Mentally extending the two planes and visualizing their intersection was a very peculiar experience. They met in a single point. Planes were supposed to intersect along lines, but these ones refused to oblige. A quadral line running between the sinister and dexter stars of the Hyperal Cross pierced the vertical plane at right angles to both arms of the Vertical Cross ... but so did the quintal line. There were four lines in the sky — or in his head — that were all mutually perpendicular.
And the sky still looked flat.
Nervously, Orlando let his gaze drop. Stars were visible below the horizon — not through the ground, but around it, as if he was standing on a narrow, jutting cliff, or a sharp pillar. He’d chosen to have no power to twist his head or body out of the usual three dimensions of the scape, though his eyes bulged literally out of his skull, hyperally, to capture a broad swath of extra information. He pictured a vertical Flatlander with two eyecircles, one above the other, suddenly made spherical, their axes still confined to swivel within the planar world but their lenses, their pupils, their field of view, protruding beyond it. As well as being a ludicrous anatomical impossibility, this compromise was now beginning to induce a giddy mixture of vertigo and claustrophobia. The Island had negligible width in the extra dimensions, and he could see clearly that the slightest hyperal movement of his body would send him plummeting into space like a drunken cosmic stylite. At the same time, the physical confinement that prevented this made him feel like he was wedged between two sheets of glass, or afflicted by some bizarre neurological disease that robbed him of the ability to move in certain directions.
“Restore me.”
His visual field collapsed to a relative pinhole, and for a moment he felt so infuriatingly diminished that he shook his head wildly, trying to cast off the blinkers. Then abruptly his vision seemed gloriously normal, and the macrosphere’s wide sky was like a fading memory of a disorienting optical illusion.
He wiped the sweat from his eyes. It was a start. A small taste of reality. Maybe he’d work up the courage eventually to wander a fully five-dimensional scape wearing a five-dimensional anatomy. Apart from the alarming possibility of glancing down and catching a glimpse of his own internal organs — like a Flatlander who twisted vis head out of the plane — unless he added two dimensions to his simulated flesh he’d have the balancing skills of a paper doll, once he was free to fall quadrally and quintally.
But even gaining the anatomy and instincts to navigate five dimensions would only be scratching the surface. There’d always be more to adapt. In the flesh, he’d been scuba-diving dozens of times, but he’d barely been able to communicate with amphibious exuberants. The Transmuters had been here for at least a billion years — or a roughly comparable period of macrosphere time, in terms of the rates of the most likely biochemical or cybernetic processes. Of course, they were sentient creatures in control of their own destiny, not beached fish required to have the right mutations in order to survive. They might not have changed at all. They might have clung like good realists — or good abstractionists — to simulations of the old world.
But over the eons, they might easily have decided to acclimatize to their new surroundings. And if they had, communication could prove impossible, unless someone in the expedition was prepared to meet them halfway.
Unless someone was prepared to bridge the gap.
The Flight Deck was crowded, making it a perfect environment in which to practice negotiating unpredictable obstacles, but Orlando found himself spending most of his time transfixed by the view. One entire wall of the penteractal scape was given over to a giant window, and the magnified image of Poincaré behind it offered a perfect excuse to do nothing but stand and stare. Moving about in public 5-scapes still made Orlando intensely self-conscious, less out of any fear of falling flat on his face than from a strong sense that he could take no credit for the fact that he didn’t. His 5-body came equipped with numerous invaluable reflexes, as any real macrospherean body almost certainly would, but relying on these alien instincts made him feel like he was operating a telepresence robot programmed with so many autonomous responses that any instructions he gave it would be superfluous.
He glanced down at the bottom of the window. The most trivial details in a 5-scape could still be hypnotic; the tesseract of the window met the tesseract of the floor along, not a line, but a roughly cubical volume. That he could see this entire volume all at once almost made sense when he thought of it as the bottom hyperface of the transparent window, but when he realized that every point was shared by the front hyperface of the opaque floor, any lingering delusions of normality evaporated.
With Poincaré, delusions of normality were untenable from the start; even its outline confounded his old-world notions of curvature and proportion. Orlando could see at a glance that the star’s four-dimensional disk filled only about one third of the tesseract he imagined framing it — far less than a circle inscribed within a square — and this made some ill-adapted part of him expect it to sag inward as it arced between the eight points of contact with the tesseract. It didn’t, of course. And since the polis had come close enough for the star’s continents to be resolved, he’d been bedazzled. The borders of these giant floating slabs of crystallized minerals were intricate beyond the possibilities of three-dimensional nature; no wind-carved landscape, no coral reef could have been as richly convoluted as this silhouette of dark rock against glowing magma.
“Orlando?”
He moved slowly, consciously, thinking it through, following his body’s suggestions but refusing to act on autopilot. Paolo was to his rear-left-dexter-gauche, and he turned first in the horizontal plane, then the hyperal. Orlando was blind to signatures, but his visual cortex had been rewired to grant five-dimensional facial cues the same significance as the old kind, and he recognized the approaching four-legged creature immediately as his son.
Bipeds in the macrosphere would have been even less stable than pogo sticks on Earth; with sufficient resources devoted to dynamic balancing, anything was possible, but no one in C-Z had opted for such an unlikely 5-body. Quadrupeds on a four-dimensional hypersurface had just one degree of instability; if the left and right pairs of feet defined orthogonal lines in the hyperal plane, it created a kind of cross-bracing, leaving only the problem of swaying forward or backward — no more than bipeds faced on two-dimensional ground. Six-legged macrosphereans would be as stable as Earth’s quadrupeds, but there was some doubt as to whether they could mutate into an upright species with two arms; eight limbs seemed to allow an easier transition. Orlando was more interested in the choices available to the Transmuters than the dynamics of natural selection, but like Paolo he’d opted for four arms and four legs. No centaurlike extensions to their trunks had been required; the hyperal space around their hips and shoulders provided more than enough room for the extra joints.
Paolo said, “Elena’s been looking at absorption spectra around the coastal regions. There’s definitely some kind of local, catalyzed chemistry going on there.”
“‘Catalyzed chemistry’? Why isn’t anyone willing to say the word ‘life’?”
“We’re on uncertain ground. In the home universe, we could say confidently which gases could only be present if they were biogenic. Here, we know which elements are reactive, but we’re just guessing when
it comes to whether or not they could be replenished by some inorganic process. There is no simple chemical signature that screams ‘life.’”
Orlando turned back to the view of Poincaré. “Let alone one that screams ‘Transmuters, not natives.’”
“Who needs a chemical signature for that? You just ask them. Or do you think they’ll have forgotten who they are?”
“Very funny.” He felt a chill, though. As acclimatized as he was — able to stand four-legged in the middle of a penteract without collapsing into gibbering insanity — he couldn’t imagine forgetting his own past, his own body, his own universe. But the Transmuters had been here a billion times longer.
Paolo said, “My Swift-self says they’ve started inscribing a copy of the polis on the surface of Kafka.” There was resigned disgust in his voice; if the core burst turned out to be a misunderstanding, the digging of these giant trenches would go down in history as the crassest act of defilement since the age of barbarism. “Models of the reconstruction robots still look dodgy, though. It’s a pity the Transmuters didn’t mention anything about the neutrino spectrum; a total energy dose for all particles at all frequencies is almost useless for predicting damage, and our own estimates are wildly uncertain, since we have no idea how or why the core’s supposed to collapse.” He laughed dryly. “Maybe they didn’t expect anyone to try riding it out. Maybe they knew it would be unsurvivable. That’s why they left us the keys to the macrosphere, instead of hints for building neutrino-proof machines: once it was too late to flee the galaxy, they knew this would be the only escape route.”
Orlando knew he was being goaded, but he replied calmly, “Even if the core burst’s unsurvivable, this doesn’t have to be the end of the line. The vacuum here is made of four-dimensional universes. Even if it’s impossible to break into them, there must be other singularities, other links already created from within. In all those universes, there must be other species as advanced as the Transmuters.”
“There might. They must be rare, though, or the place would be swarming with them.”
Orlando shrugged. “Then if the whole Coalition has to make a oneway trip into the macrosphere, so be it.” He spoke with defiant equanimity, but the prospect was almost unbearable. He’d always told himself that there’d be a way through: that he’d die in the flesh, with a flesher child to bury him, on a world where he could promise a thousand generations that no fire and no poison would rain from the sky. If the macrosphere was the only true sanctuary, his choice of futures came down to faking the entire fantasy in a 3-scape, or embodying himself in the alien chemistry of this universe and trying to raise a child on a world more surreal than anything in Ashton-Laval.
Paolo managed to display contrition on his altered face, visible to Orlando’s altered eyes. “Forget about one-way trips. If we can talk to the Transmuters at all, they’re more likely to tell us that we misread everything. There was no warning, there’ll be no core burst. We simply got it wrong.”
* * *
Probes were sent ahead to Poincaré on fast, single-pass trajectories. Orlando watched the images accumulate, the curved stripes of instrument footprints barely scratching the star’s hypersurface with medium-resolution topographic and chemical maps. Glimpses of the folded mountain ranges and igneous plains of the continents’ interiors appeared strikingly organic to his old-world sensibilities; there were wind-blasted plateaus whorled like fingerprints, channels carved by lava flows more elaborate than capillary systems, plumes of frozen magma extruding spikes like riotous fungal growths. Poincaré’s sky was permanently dark, but the landscape itself was radiant with heat flowing up from the core, glowing at wavelengths analogous to near-infrared: on the border between the energy levels for lepton transitions and molecular vibrations. There were traces of rings and branched chains based on atom 27 in the absorption spectra of the atmosphere above much of the interior, but the most complex chemical signatures were found near the shores.
There were also tall structures clustered around the coastal regions that did not appear to be plausible products of mere erosion or tectonics, crystallization or vulcanism. These towers were ideally placed to extract energy from the temperature difference between the magma oceans and the relatively cool interiors, though whether they were Poincaré’s equivalent of giant trees or some form of artifact was unclear.
A second wave of probes was placed in powered orbits, pushing themselves in against the outer rim of their angular momentum ridges so that engine failure would see them flung away into deep space, not crashing to the ground. Comparisons of scale with the home universe were slippery, but if the 5-bodies they’d chosen were used as measuring rods, Poincaré’s hypersurface could hold ten billion times as many denizens as the Earth — or conceal a few thousand industrial civilizations in the cracks between its putative forests and vast deserts. Mapping the entire star at a resolution guaranteed to reveal or rule out even a Shanghai-sized pre-Introdus city was a task akin to mapping every terrestrial planet in the Milky Way. The circular band of images collected by one probe as it completed one orbit of the hypersphere amounted to less than a pinprick, and even when the orbit was swept 360 degrees around the star, the sphere it traced out was about as significant, proportionately, as one shot of one location on an ordinary globe.
As Carter-Zimmerman itself moved into a distant powered orbit, Orlando began to find the view from the Flight Deck overwhelming: too detailed and complex to take in, too distracting not to try. Every glance was like a blast of dense atonal music; the only choice was to shut it out, or to listen attentively and still fail to make sense of it. He considered further modifications to his mind; no native, no acclimatized macrospherean would respond to the sight of their world as if it were a drug-induced hallucination, less a vision than a mass-stimulation of networks signaling perceptual breakdown.
He had his exoself enhance his visual cortex further, wiring in a collection of symbols responding to various four-dimensional shapes and three-dimensional borders — all plausible primitive forms, likely to be no more exotic to macrosphereans than a mountain or a boulder was to a flesher. And the view of Poincaré was tamed, parsed into this new vocabulary, though it remained a thousand times denser than any satellite view of the Earth or Swift.
But the Floating Island became unbearable, a straitjacket for his senses, a coffin with a nail-hole of sky. Every 3-scape was the same. Even with his three-dimensional vision fully restored, he couldn’t hack out the new symbols without also losing his memories of Poincaré, and he could feel their lack of stimulation constantly, an absence as oppressive as if the world had turned a uniform white.
He could choose to alternate between sets of symbols, one for 3-scapes and one for 5-scapes, with his exoself holding the untranslatable portion of his memories in storage. In effect, he would become two people, serial clones. Would that be so bad? There were already a thousand of him, scattered across the Diaspora.
But he’d come here to meet the Transmuters in person, not to give birth to a macrospherean twin who’d do it on his behalf. And the Diaspora’s clones would all willingly merge and return to the restored Earth — if that was possible — but what would become of a clone who’d go insane from sensory deprivation in a rain forest, who’d stand beneath a midnight desert sky and scream with frustration at the pinhole view?
Orlando stripped away the enhancements completely, and felt like an amnesiac or an amputee. He stared at Poincaré from the Flight Deck, more stupefied and frustrated than ever.
Paolo asked him how he was coping. He said, “I’m fine. Everything is fine.”
He understood what was happening: he’d come as far as he could travel, while still hoping to return. There were no stable orbits here: you either approached this world at speed, grabbed what you needed, and retreated — or you let yourself be captured, and you spiraled down to collision.
* * *
“It’s a subtle effect, but everywhere I’ve looked the whole ecosystem is slightly skewed in
their favor. It’s not that they dominate in terms of numbers or resource use, but there are certain links in the food chain — all of them ultimately beneficial to this species — that seem too robust, too reliable to be natural.”
Elena was addressing most of U-star C-Z, eighty-five citizens assembled in a small meeting hall: a 3-scape for a change, and Orlando was grateful that someone else felt like a rest from macrospherean reality. The detailed mapping of Poincaré had revealed no obvious signs of technological civilization, but the xenologists had identified tens of thousands of species of plant and animal life. As on Swift, it remained possible that the Transmuters were hiding somewhere in a well-concealed polis, but now Elena claimed to have found evidence of bio-engineering, and the supposed beneficiaries seemed to be camouflaged by nothing more than the modest scale of their efforts.
The xenologists had pieced together tentative ecological models for all the species large enough to be visible from orbit in the ten regions they’d singled out for analysis; microbiota remained a matter for speculation. The giant “towers,” now called Janus trees, grew along much of the coast, powered by the light shining up from the molten ocean. Each individual tree had a lateral asymmetry that looked utterly bizarre to Orlando, with leaves growing larger, more vertical and more sparsely distributed toward the inland side. The same morphological shift continued from tree to tree, between those directly exposed to the ocean light and the four or five less privileged ranks behind them. The leaves of the first rank were a vivid banana yellow on their ocean-facing hypersurface, and bright purple on the back. The second rank used the same purple to catch the waste energy of the first rank, and blue-green to radiate away its own. By the fourth and fifth rank, the leaves’ pigments were all tuned to hues of “near-infrared,” leaving them pale gray in “visible light.” These color translations were faithful to the ordering of wavelengths, but the visible/infrared distinction was necessarily arbitrary, since it was clear that different species of Poincaré life were sensitive to different portions of the spectrum.
