by Greg Egan
Orlando appeared. The scape software didn’t seem to know quite what to do with his exhalations; the Lilliput dome was maintained at high vacuum, and at first a faint cloud of ice crystals materialized and fell in front of him as his breath expanded and cooled, but after a moment some subsystem changed its mind and started magicking the apparent contamination out of existence as soon as it left his mouth.
After raising a lattice of scaffolding, the bay’s nanomachines began work on the analyzer, drawing up threads of barium, copper, and ytterbium from the reservoirs and spinning them into delicate gray coils of superconducting wire for the magnetic beam splitter — an odd name for the component, when the “beam” in this case would consist of a single neutron. Orlando regarded their handiwork dubiously. “You really think the Transmuters were relying on someone doing an experiment as subtle as this?”
Yatima shrugged. “What’s subtle? The shift between the spectrum of deuterium and hydrogen is a few parts in ten thousand, but we can’t imagine anyone missing it.”
Orlando said dryly, “Deuterium at six thousand times the normal abundance isn’t subtle. Water vapor weighing twenty percent extra isn’t subtle. But particles that behave exactly like neutrons until you split them into two quantum states, rotate one by more than 720 degrees, then recombine them to check their relative phase? Somehow I think that might qualify.”
“Maybe. But the Transmuters didn’t have much choice; you can’t make neutrons twenty percent heavier. All they could do was wrap them in other layers that would draw attention to them. What makes Swift special? The heavy isotopes in the atmosphere. What makes those isotopes special? The extra neutrons they contain. What makes those neutrons special? There’s only one thing you can change about a neutron, without turning it into something else entirely. The length of the wormhole.”
Orlando seemed about to object, but then he raised his hands in a gesture of resignation. There was no point arguing; they’d soon have an answer, one way or the other.
In Blanca’s extension of Kozuch Theory, as in the traditional version, most elementary particle wormholes were as short as they were narrow; the two mouths, the two particles, shared the same microscopic 6-sphere. That was the most probable state for a wormhole created out of the vacuum, and unlike traversable wormholes they weren’t free to adjust their length once they were formed. But there was no theoretical reason why longer ones couldn’t exist: chains of short ones joined end-to-end, a string of linked microspheres looping out into the extra six macroscopic dimensions. Once created, they’d be stable; it was just a matter of knowing how to make them in the first place. Ordinary splicing methods — brute-force collisions — simply merged the two microspheres into one.
Sinclair had tested a few trillion electrons, protons, and neutrons, and found no long ones at all, but that didn’t prove that they were physically impossible, it merely confirmed that they were naturally rare. And if the Transmuters had wished to leave behind a single, enduring scientific legacy, Yatima could think of no better choice. Long neutrons had the potential to illuminate a fundamental question that might otherwise take an infant civilization millennia to resolve. Locked up in stable isotopes on a planet orbiting a slow-burning sun, they’d remain accessible for thirty or forty billion years. It was even possible that they’d shed some light on the diametrically opposite problem to their own creation: keeping traversable wormholes short, the secret to bridging the galaxy.
The nanomachines moved on from the beam splitter to a second set of coils, designed to rotate one quantum state of the neutron when it traveled simultaneously down two alternative paths. At first glance, there was no obvious way to tell a long particle from a short one; neither possessed a traversable wormhole, so you couldn’t send a signal through and time it. But Sinclair had realized that the usual classification of particles into fermions and bosons became slightly more complex when long particles were allowed. The classical properties of a fermion were having a spin of half a unit, obeying the Pauli exclusion principle (which kept all the electrons in an atom, and neutrons and protons in a nucleus, from falling together into the same, lowest-energy state), and responding to a 360-degree rotation by slipping 180 degrees out of phase with its unrotated version. A fermion needed two full rotations, 720 degrees, to come back into phase. Bosons needed only one rotation to end up exactly as they began.
Any long particle made up of an odd number of individual fermions would retain the first two fermionic properties, but if it also included any bosons, their presence would show up in the pattern of phase changes when the particle was rotated. A long particle with a wormhole sequence of “fermion-boson-fermion-fermion” would go out of phase and back like a simple fermion after one and two rotations, but a third rotation would bring it back into phase again immediately. Successive rotations could probe the wormhole’s structure at ever greater depths: for each individual fermion in the chain it would take two rotations to restore the particle’s phase, while for each boson it would take just one. As Orlando had put it — groping for a three-dimensional analogy when Yatima had started spouting group theory and topology — it was like sliding down into the particle’s wormhole on the banister of a spiral staircase. Sometimes after going full circle, a twist in the banister left you upside down, so you had to go round once more before the staircase appeared right-way up again. Other times, a single turn left everything looking normal.
As the nanomachines put the finishing touches to the apparatus, wiring the neutron source and detectors to the bay’s data link, Yatima thought of contacting Blanca. But the one time they’d met, the Voltaire clone had shown no interest whatsoever in vis dead Fomalhaut-self’s ideas. Blanca had declined, everywhere, to rush at flesher equivalent — the de facto post-arrival standard adopted throughout the Diaspora — and as a consequence ve’d become rather isolated. Sinclair might have liked to witness the experiment, but he’d have to wait 82 years; he hadn’t taken part in the Diaspora at all.
Yatima gestured at a switch on the side of the neutron source; it was just a scape object grafted onto their view of the machine, but throwing it would transmit a signal down to Lilliput to cycle the first neutron through. “Do you want to do the honors?”
Orlando hesitated. “I’m still not sure what I’m hoping for. Exotic physics from the Transmuters ... or the entertainment value of seeing you try to squirm out of this if you’re wrong.”
Yatima smiled serenely. “The wonderful thing about hope is that it has absolutely no effect on anything. Just throw the switch.”
Orlando stepped forward and did it. The display screen beside it — another scape object — was instantly filled with symbols scrolling past in an unreadable blur. Yatima had been expecting a short pattern, recurring after five or six rotations at most — or if the neutrons were sadly normal, just two. A few segments would have been enough to prove the point, but maybe the Transmuters had had no control over the total length.
Orlando said, “Is this equipment failure, or wild success?”
“Wild success. I hope.”
Yatima sent the screen gestalt instructions to rewind. The start of the data showed the neutron slipping in and out of phase with repeated rotations:
- + + - + - + + + - + - + - + + + + - + - + - + - + + + + + ...
Directly below was the interpretation:
F b F F b b F F F b b b F F F F b b b b ...
Orlando read aloud, “Fermion, boson, fermion, fermion, boson, boson...”
Yatima said, “It’s not a hoax, I swear.”
“I believe you.” The counting went up to 126, then the pattern stopped and something far less decipherable took over. Orlando looked almost fearful. “It’s a message. They’ve left us a message.”
“We don’t know that.”
“It could be the equivalent of their whole polis library. Tied on a single neutron wormhole, like knots on a string.” He was beaming unsteadily now; Yatima wondered if his embodiment software would let him pass out from shock.
>
“Or it might just be proof of artificiality. An improbable sequence, so no one mistakes this for a natural phenomenon and screws up their physics trying to explain it that way. Don’t jump to conclusions.”
Orlando nodded, and wiped his forehead with his palm. He gestured at the screen to scroll forward to the latest data; the torrent continued, but it was visibly slower. Each test for a different number of rotations had to be performed several times to get reliable statistics — and after a billion rotations and an interference measurement, you couldn’t just rotate the neutron one more time for test one-billion-and-one, you had to start again from scratch.
They waited for the pattern to recur. After twenty-two minutes, the neutron decayed without repeating itself. In theory, the resulting proton should have retained the same hidden structure, but Yatima hadn’t made any provision to capture it, and the whole machine would have had to be rebuilt to handle a charged particle.
Ve instructed the analyzer to shift to a much higher rotation frequency. The second neutron rapidly yielded exactly the same sequence as the first, and survived long enough to start repeating, after six times ten-to-the-eighteenth segments. Six exabytes of data wasn’t exactly a polis library, but it left room for a lot more than a maker’s imprint or some idle subatomic graffiti.
The screen translated the sequence into Orlando’s stylized spiral staircase, a twisted ribbon reminiscent of DNA, but far longer than any genome or mind seed. Until this moment, Yatima had never really felt the hand of an alien civilization here; the isotope signature was unambiguous, but too amorphous to convey anything more than its own artificiality. They’d found no ruins, no monuments, no shards — and it was impossible to say whether the oasis life had been the Transmuters’ biological cousins, their artificial pets, or just an accident with no connection to them at all. But now the planet was revealed to be dense with artifacts older than any skyscraper or pyramid, richer than any papyrus or optical disk. And every picogram of atmospheric carbon dioxide held three hundred billion of them.
Ve turned to Orlando. “Do we spread the news now, or try for an interpretation first?” The library was bursting with pattern analysis software, three millennia’s worth of attempts to be prepared for this moment. People had already run most of it on various Swift genomes, looking for hidden messages without success.
Orlando managed a conspiratorial grin. “It’s not like breaking into a tomb. We can’t damage this just by looking at it.”
Yatima jumped to the xenolinguistics indexscape, a room full of display cases holding mock Rosetta stones, fragile scrolls and manuscripts, and quaint electromechanical code-breaking machines. Ve built a pipeline from the store of neutron data to a string of these analysis programs. Orlando had followed ver, and they stood in the carpeted room watching silently as a swarm of blue-white fireflies, representing the data, moved from icon to icon.
The twelfth icon in the chain was an ancient cathode-ray tube display, representing an absurdly naive program that Yatima had only included because it would take so little time to run. The instant the fireflies alighted on its bakelite case, the screen burst into life.
The image began with a single, short vertical line, then zoomed out slowly to reveal dozens, then hundreds, of similar lines. Yatima didn’t recognize the pattern, but the software had: the bottom end points of the lines marked the positions of stars — Voltaire and its backdrop from a certain angle, about fifty million years ago. Oddly enough, it wasn’t a perspective view but an orthogonal projection. Did that say something about the Transmuters’ perceptual system? Yatima caught verself; maps of the Earth had been made looking like everything from flattened orange peel to a reflection of the planet in a giant distorting mirror. None of them revealed a thing about fleshers’ ordinary vision.
Orlando exhaled heavily. “Pixel arrays? It’s that simple?” He sounded almost disappointed, but then he laughed, elated. “Good old two-dimensional images, changing with time! How’s that for an antidote to abstractionism?” After a moment he added, “Even if it is just a fragment of the data.” Yatima was receiving gestalt tags broadcast by the cathode-ray tube icon, packed with supplementary information, but Orlando was tortuously reading the same things in linear text from a translation window pasted into the scape by his exoself.
From the motion of the stars, the time between each frame was determined to be about 200 years; the software displayed 50 frames, 10,000 years, per tau. The whole view was heavily stylized, and the image was binary: not even a gray scale, just black and white. But the software had concluded that the vertical lines attached to each star were a kind of luminosity scale, giving the distance at which the energy density of the star’s radiation fell to 61 femtojoules per cubic meter — coincidentally or not, the same as the cosmic microwave background. For Voltaire, this distance was about one eighteenth of a light year; for the sun, about one seventh. The orthogonal projection enabled the “luminosity lines” for a few hundred stars to be visible simultaneously, all at the same scale; a realistic perspective from anywhere in the galaxy would have shown all but a few diminished by distance to the point of invisibility, making the intended meaning much more obscure.
As the view continued to expand, though, all the stars’ lines were soon reduced to identical, single-pixel specks anyway. Yatima was puzzled, but reserved judgment.
When the whole Milky Way was visible, not quite edge-on, the zoom-out stopped. Then a short vertical line appeared suddenly: twelve hundred light years long, pointing up from the plane of the galactic disk, vanishing after just one frame. Yatima had been wondering how the map would portray sources of radiation that shone for less than 200 years; the simplest method would be to match their total energy to an ordinary star’s output over two centuries. On that basis, a twelve-hundred-light-year luminosity line corresponded to a burst of radiation comparable to the output of the sun over fourteen billion years. The kind of burst produced by two colliding neutron stars.
Neutrons to warn of neutron stars? Was that another level of the isotopes’ multilayered meaning?
Every two or three hundred thousand years, another burst appeared somewhere in the galaxy. Smaller lines flashed up more frequently, most of them probably supernovae; a few corresponded to known remnants. Orlando asked soberly, “So is this history, or prediction?”
“Well, from the pattern of heavy isotopes in the crust, it looks like the Transmuters processed the atmosphere at least a billion years ago.” So if their predictions of these events in their far future were accurate, it would prove that they’d understood the dynamics of neutron star binaries far better than C-Z or gleisner astronomers. It was impossible to judge their record on these ancient bursts, predating even flesher gamma-ray astronomy, but if it turned out that they’d correctly anticipated the time of Lac G-1’s collision, they’d have shown themselves to be extraordinarily trustworthy forecasters.
Yatima glanced at Orlando, his eyes locked on the screen. The Transmuters could promise him a fleshers eternity without another Lacerta. They could guarantee a safe return to Earth, and everything he’d once valued.
Around 100,000 years before the present, the scale began to change again. Yatima watched uneasily as the Andromeda galaxy, the whole Local Group, and then ever more distant galactic clusters came into view. Then at 26,000 BP a line appeared, almost two billion light years long, skewering the tiny Milky Way.
The image zoomed back in rapidly, just in time to show a gamma-ray burst at 2000 BP: Lac G-1. The Transmuters had correctly predicted the time of the burst to the nearest 200-year frame, and its position and energy to the nearest pixel.
Orlando remained silent as the map ran on for another twenty million years. In all that time, it showed no more gamma-ray bursts near enough to Earth to harm the biosphere.
But if the map’s predictions were all equally reliable, then 26,000 years ago there’d been an event in the galactic core that rendered every ordinary burst irrelevant. In a thousand more years, the consequence
s would finally sweep through the region — and even if the Diaspora, the gleisners, and the Earth-based polises began to flee at once, when the pulse of radiation finally washed over them it would be thirty million times more intense than Lacerta.
Paolo said firmly, “It’s not possible. You’d need six or seven billion solar masses undergoing gravitational collapse to release that much energy.”
Yatima had asked to meet him to talk about Orlando, not to debate the meaning of the neutron data for the thousandth time. But Paolo seemed determined to dispose of the core burst itself before he’d listen to a word on any other subject, and maybe that was fair enough. Belief or disbelief in the event formed the ground beneath everything else, now.
“The galactic core contains more than enough mass, depending on where you draw the boundary.”
“Yes, but those stars are all in orbit. They’re not about to fall together into a giant black hole.”
Yatima laughed humorlessly. “Lac G-1’s neutron stars were in orbit, too. They weren’t supposed to fall together for another seven million years. So I wouldn’t stake my life on conservation of angular momentum until I found out where it all went with Lacerta.”
Paolo shrugged dismissively. The burden of proof wasn’t his. Even if it was being read correctly, the Transmuters’ message wasn’t necessarily honest; even if it was honestly intended, that didn’t mean it was infallibly true. And the failure to explain Lacerta hardly meant that conservation laws could be discarded at will. If it had been a purely theoretical argument, Yatima would have happily conceded every point.
