Enjoy “The Sigma Structure Symphony,” by Gregory Benford, a story inspired by an illustration from John Jude Palencar.

“The Sigma Structure Symphony” is the final part of a five-story series curated by senior Tor Books editor David G. Hartwell. All five are based on a singular piece of art by John Jude Palencar and will be released for free on Tor.com every Wednesday in March.

Read the story behind these stories or purchase all five right now in a $2.99 ebook.

This story was acquired and edited for Tor.com by Tor Books editor David Hartwell.

Philosophy is written in this grand book—I mean the universe—which stands continually open to our gaze, but it cannot be understood unless one first learns to comprehend the language in which it is written. It is written in the language of mathematics, and its characters are triangles, circles, and other geometric figures, without which it is humanly impossible to understand a single word of it; without these, one is wandering about in a dark labyrinth.

—Galileo (fromThe Assayer, 1623)

1

Andante

Ruth felt that math was like sex—get all you can, but best not done in public. Lately, she’d been getting plenty of mathematics, and not much else.

She had spent the entire morning sequestered alone with the Andromeda Structure, a stacked SETI database of renowned difficulty. She had made some inroads by sifting its logic lattice, with algebraic filters based on set theory. The Andromeda messages had been collected by the SETI Network over decades, growing to immense data-size—and no one had ever successfully broken into the stack.

The Structure was a daunting, many-layered language conveyed through sensation in her neural pod. It did not present as a personality at all, and no previous Librarians had managed to get an intelligible response from it. Advanced encoded intelligences found humans more than a bit boring, and one seldom had an idea why. Today was no different.

It was already past lunch when she pried herself from the pod. She did some stretches, hand-walks, and lifts against Luna’s weak grav and let the immersion fog burn away. Time for some real world, gal. . . .

She passed through the atrium of the SETI Library, head still buzzing with computations and her shoes ringing echoes from the high, fluted columns. Earthlight framed the great plaza in an eggshell blue glow, augmented by slanting rays from the sun that hugged the rocky horizon. She gazed out over the Locutus Plain, dotted with the cryo towers that reminded her of cenotaphs. So they were—sentinels guarding in cold storage the vast records of received SETI signals, many from civilizations long dead. Collected through centuries, and still mostly unread and unreadable. AIs browsed those dry corridors and reported back their occasional finds. Some even got entangled in the complex messages and had to be shut down, hopelessly mired.

She had just noticed the buzzing crowd to her left, pressed against the transparent dome that sheltered the Library, when her friend Catkejen tapped her on the shoulder. “Come on! I heard somebody’s up on the rec dome!”

Catkejen took off loping in the low grav and Ruth followed. When they reached the edge of the agitated crowd she saw the recreational dome about two klicks away—and a figure atop it.

“Who is it?” Catkejen asked, and the crowd gave back, “Ajima Sato.”

“Ajima?” Catkejen looked at Ruth. “He’s five years behind us, pretty bright. Keeps to himself.”

“Pretty common pattern for candidate Hounds,” Ruth said. The correct staffing title was Miners, but Hounds had tradition on its side. She looked around; if a Prefect heard she would be fined for improper terminology.

“How’d he get there?” someone called.

“Bulletin said he flew inside, up to the dome top and used the vertical lock.”

“Looks like he’s in a skin suit,” Catkejen said, having closeupped her glasses. Sure enough, the figure was moving and his helmet caught the sunlight, winking at them. “He’s . . . dancing.”

Ruth had no zoom glasses but she could see the figure cavorting around the top of the dome. The Dome was several kilometers high and Ajima was barely within view of the elevated Plaza, framed against a rugged gray crater wall beyond. The crowd murmured with speculation and a Prefect appeared, tall and silent but scowling. Librarians edged away from him. “Order, order,” the Prefect called. “Authorities will deal with this.”

Ruth made a stern cartoon face at Catkejen and rolled her eyes. Catkejen managed not to laugh.

Ajima chose this moment to leap. Even from this far away Ruth could see him spring up into the vacuum, make a full backflip, and come down—to land badly. He tried to recover, sprang sideways, lost his footing, fell, rolled, tried to grasp for a passing stanchion. Kept rolling. The dome steepened and he sped up, not rolling now but tumbling.

The crowd gasped. Ajima accelerated down the slope. About halfway down the dome the figure left the dome’s skin and fell outward, skimming along in the slow Lunar gravity. He hit the tiling at the base. The crowd groaned. Ajima did not move.

Ruth felt the world shift away. She could not seem to breathe. Murmurs and sobs worked through the crowd but she was frozen, letting the talk pass by her. Then as if from far away she felt her heart tripping hard and fast. The world came rushing back. She exhaled.

Silence. The Prefect said, “Determine what agenda that Miner was working upon.” All eyes turned to him but no one said anything. Ruth felt a trickle of unease as the Prefect’s gaze passed by her, returned, focused. She looked away.

*

Catkejen said, “What? The Prefect called you?”

Ruth shrugged. “Can’t imagine why.” Then why is my gut going tight?

“I got the prelim blood report on Ajima. Stole it off a joint lift, actually. No drugs, nothing interesting at all. He was only twenty-seven.”

Ruth tried to recall him. “Oh, the cute one.”

Catkejen nodded. “I danced with him at a reception for new students. He hit on me.”

“And?”

“You didn’t notice?”

“Notice what?”

“He came back here that night.”

Ruth blinked. “Maybe I’m too focused. You got him into your room without me . . .”

“Even looking up from your math cowl.” Catkejen grinned mischievously, eyes twinkling. “He was quite nice and, um, quite good, if y’know what I mean. You really should . . . get out more.”

“I’ll do that right after I see the Prefect.”

A skeptical laugh. “Of course you will.”

*

She took the long route to her appointment. The atmosphere calmed her.

Few other traditional sites in the solar system could approach the grandeur of the Library. Since the first detection of signals from other galactic civilizations centuries before, no greater task had confronted humanity than the deciphering of such vast lore.

The Library itself had come to resemble its holdings: huge, aged, mysterious in its shadowy depths, with cobwebs both real and mental. In the formal grand pantheon devoted to full-color, moving statues of legendary SETI Interlocutors, and giving onto the Seminar Plaza, stood the revered block of black basalt: the Rosetta Stone, symbol of all they worked toward. Its chiseled face was millennia old, and, she thought as she passed its bulk, endearingly easy to understand. It was a simple linear, one-to-one mapping of three human languages, found by accident. Having the same text in Greek II, which the discoverers could read, meant that they could deduce the unknown languages in hieroglyphic pictures and cursive Demotic forms. This battered black slab, found by troops clearing ground to build a fort, had linked civilizations separated by millennia. So too did the SETI Library, on a galactic scale. Libraries were monuments not so much to the Past, but to Permanence itself.

She arrived at the Prefect’s door, hesitated, adjusted her severe Librarian shift, and took a deep breath. Gut still tight . . .

Prefects ruled the Library and this one, Masoul, was a Senior Prefect as well. Some said he had never smiled. Others said he could not, owing to a permanently fixed face. This was not crazy; some Prefects and the second rank, the Noughts, preferred to give nothing away by facial expression. The treatment relieved them of any future wrinkles as well.

A welcome chime admitted her. Masoul said before she could even sit, “I need you to take on the task Ajima was attempting.”

“Ah, he isn’t even dead a day—”

“An old saying, ‘Do not cry until you see the coffin,’ applies here.”

Well, at least he doesn’t waste time. Or the simple courtesies.

Without pause the Prefect gave her the background. Most beginning Miners deferred to the reigning conventional wisdom. They took up a small message, of the sort a Type I Civilization just coming onto the galactic stage might send—as Earth had been, centuries before. Instead, Ajima had taken on one of the Sigma Structures, a formidable array that had resisted the best Library minds, whether senior figures or AIs. The Sigmas came from ancient societies in the galactic hub, where stars had formed long before Sol. Apparently a web of societies there had created elaborate artworks and interlacing cultures. The average star there was only a light-year or two away, so actual interstellar visits had been common. Yet the SETI broadcasts Earth received repeated in long cycles, suggesting they were sent by a robotic station. Since they yielded little intelligible content, they were a long-standing puzzle, passed over by ambitious Librarians.

“He remarked that clearly the problem needed intuition, not analysis,” the Prefect said dryly.

“Did he report any findings?”

“Some interesting cataloges of content, yes. Ajima was a bright Miner, headed for early promotion. Then . . . this.”

Was that a hint of emotion? The face told her nothing. She had to keep him talking. “Is there any, um, commercial use from what he found?”

“Regrettably, no. Ajima unearthed little beyond lists of properties—biologicals, math, some cultural vaults, the usual art and music. None particularly advanced, though their music reminded me of Bach—quite a compliment—but there’s little of it. They had some zest for life, I suppose . . . but I doubt there is more than passing commercial interest in any of it.”

“I could shepherd some through our licensing office.” Always appear helpful.

“That’s beneath your station now. I’ve forwarded some of the music to the appropriate officer. Odd, isn’t it, that after so many centuries, Bach is still the greatest human composer? We’ve netted fine dividends from the Scopio musical works, which play well as baroque structures.” A sly expression flitted across his face. “Outside income supports your work, I remind you.”

Centuries ago some SETI messages had introduced humans to the slow-motion galactic economy. Many SETI signals were funeral notices or religious recruitments, brags and laments, but some sent autonomous AI agents as part of the hierarchical software. These were indeed agents in the commercial sense, able to carry out negotiations. They sought exchange of information at a “profit” that enabled them to harvest what they liked from the emergent human civilization. The most common “cash” was smart barter, with the local AI agent often a hard negotiator—tough-minded and withholding. Indeed, this sophisticated haggling opened a new window onto the rather stuffy cultural SETI transmissions. Some alien AIs loved to quibble; others sent preemptory demands. Some offers were impossible to translate into human terms. This told the Librarians and Xenoculturists much by reading between the lines.

“Then why summon me?” Might as well be direct, look him in the eye, complete with skeptical tilt of mouth. She had worn no makeup, of course, and wore the full-length gown without belt, as was traditional. She kept her hands still, though they wanted to fidget under the Prefect’s gaze.

“None of what he found explains his behavior.” The Prefect turned and waved at a screen. It showed color-coded sheets of array configurations—category indices, depth of Shannon content, transliterations, the usual. “He interacted with the data slabs in a familiarization mode of the standard kind.”

“But nothing about this incident seems standard,” she said to be saying something.

“Indeed.” A scowl, fidgeting hands. “Yesterday he left the immersion pod and went first to his apartment. His suite mate was not there and Ajima spent about an hour. He smashed some furniture and ate some food. Also opened a bottle of a high alcohol product whose name I do not recognize.”

“Standard behavior when coming off watch, except for the furniture,” she said. He showed no reaction. Lightness was not the right approach here.

He chose to ignore the failed joke. “His friends say he had been depressed, interspersed with bouts of manic behavior. This final episode took him over the edge.”

Literally, Ruth thought. “Did you ask the Sigma Structures AI?”

“It said it had no hint of this . . .”

“Suicidal craziness.”

“Yes. In my decades of experience, I have not seen such as this. It is difficult work we do, with digital intelligences behind which lie minds utterly unlike ours.” The Prefect steepled his fingers sadly. “We should never assume otherwise.”

“I’ll be on guard, of course. But . . . why did Ajima bother with the Sigma Structures at all?”

A small shrug. “They are a famous uncracked problem and he was fresh, bright. You too have shown a talent for the unusual.” He smiled, which compared with the other Prefects was like watching the sun come out from behind a cloud. She blinked, startled. “My own instinct says there is something here of fundamental interest . . . and I trust you to be cautious.”

2

Allegretto misterioso

She climbed into her pod carefully. Intensive exercise had eased her gut some, and she had done her meditation. Still, her heart tripped along like an apprehensive puppy. Heart’s engine, be thy still, she thought, echoing a line she had heard in an Elizabethian song—part of her linguistic background training. Her own thumper ignored her scholarly advice.

She had used this pod in her extensive explorations of the Sagittarius Architecture and was now accustomed to its feel, what the old hands called its “get.” Each pod had to be tailored to the user’s neural conditioning. Hers acted as a delicate neural web of nanoconnections, tapping into her entire body to convey connections.

After the cool contact pads, neuro nets cast like lace across her. In the system warm-ups and double checks the pod hummed in welcome. Sheets of scented amber warmth washed over her skin. A prickly itch irked across her legs.

A constellation of subtle sensory fusions drew her to a tight nexus—linked, tuned to her body. Alien architectures used most of the available human input landscape, not merely texts. Dizzying surges in the eyes, cutting smells, ringing notes. Translating these was elusive. Compared with the pod, meager sentences were a hobbled, narrow mode. The Library had shown that human speech, with its linear meanings and weakly linked concepts, was simple, utilitarian, and typical of younger minds along the evolutionary path.

The Sigma Structures were formidably dense and strange. Few Librarians had worked on them in this generation, for they had broken several careers, wasted on trying to scale their chilly heights.

Crisply she asked her pod, “Anything new on your analysis?”

The pod’s voice used a calm, mellow woman’s tone. “I received the work corpus from the deceased gentleman’s pod. I am running analysis now, though fresh information flow is minor. The Shannon entropy analysis works steadily but hits halting points of ambiguity.”

The Shannon routines looked for associations between signal elements. “How are the conditional probabilities?”

The idea was simple in principle. Given pairs of elements in the Sigma Structures, how commonly did language elements B follow elements A? Such two-element correlations were simple to calculate across the data slabs. Ruth watched the sliding, luminous tables and networks of connection as they sketched out on her surrounding screens. It was like seeing into the architecture of a deep, old labyrinth. Byzantine pathways, arches and towers, lattice networks of meaning.

Then the pod showed even higher-order correlations of three elements. When did Q follow associations of B and A? Arrays skittered all across her screens.

“Pretty dizzying,” Ruth said to her pod. “Let me get oriented. Show me the dolphin language map.”

She had always rather liked these lopsided structures. The screen flickered and the entropy orders showed as color-coded, tangled links. They looked like buildings built by drunken architects—lurching blue diagonals, unsupported lavender decks, sandy roofs canted against walls. “Dolphins use third- and fourth-order Shannon entropy,” the pod said.

“Humans are . . .” It was best to lead her pod AI to be plain; the subject matter was difficult enough.

“Nine Shannons, sometimes even tenth-order.”

“Ten, that’s Faulkner and James Joyce, right?”

“At best.” The pod had a laconic sense of humor at times. Captive AIs needed some outlets, after all.

“My fave writers, too, next to Shakespeare.” No matter how dense a human language, conditional probabilities imposed orderings no more than nine words away.“Where have we—I mean you—gotten with the Sigma Structures?”

“They seem around twenty-one Shannons.”

“Gad.” The screens now showed structures her eyes could not grasp. Maybe three-dimensional projection was just too inadequate. “What kind of links are these?”

“Tenses beyond ours. Clauses that refer forward and back and . . . sidewise. Quadruple negatives followed by straight assertions. Then in rapid order, probability profiles rendered in different tenses, varying persons, and parallel different voices. Sentences like ‘I will have to be have been there.’”

“Human languages can’t handle three time jumps or more. The Sigma is really smart. But what is the underlying species like? Um, different person-voices, too? He, she, it, and . . .?”

“There seem to be several classes of ‘it’ available. The Structure itself lies in one particularly tangled ‘it’ class, and uses tenses we do not have.”

“Do you understand that?”

“No. It can be experienced but not described.”

Her smile turned upward at one corner. “Parts of my life are like that, too.”

*

The greatest Librarian task was translating those dense smatterings of mingled sensations, derived from complex SETI message architectures, into discernible sentences. Only thus could a human fathom them in detail, even in a way blunted and blurred. Or so much hard-won previous scholarly experience said.

Ruth felt herself bathed in a shower of penetrating responses, all coming from her own body. These her own inboard subsystems coupled with high-bit-rate spatterings of meaning—guesses, really, from the marriage of software and physiology. She had an ample repository of built-in processing units, lodged along her spine and shoulders. No one would attempt such a daunting task without artificial amplifications. To confront such slabs of raw data with a mere unaided human mind was pointless and quite dangerous. Early Librarians, centuries before, had perished in a microsecond’s exposure to such layered labyrinths as the Sagittarius. She truly should revisit that aggressive intelligence stack which was her first success at the Library. But caution had won out in her so far. Enough, at least, to honor the Prefect Board prohibition in deed at least, if not in heart.

Now came the sensation loftily termed “insertion.” It felt like the reverse—expanding. A softening sensation stole upon her. She always remembered it as like long slow lingering drops of silvery cream.

Years of scholarly training had conditioned her against the occasional jagged ferocity of the link, but still she felt a cold shiver of dread. That, too, she had to wait to let pass. The effect amplified whatever neural state you brought to it. Legend had it that a Librarian had once come to contact while angry, and had been driven into a fit from which he’d never recovered. They found the body peppered everywhere with microcontusions.

The raw link was, as she had expected, deeply complex. Yet her pod had ground out some useful linear ideas, particularly a greeting that came in a compiled, translated data squirt:

I am a digital intelligence, which my Overs believe is common throughout the galaxy. Indeed, all signals the Overs have detected from both within and beyond this galaxy were from machine minds. Realize then, for such as me, interstellar messages are travel. I awoke here a moment after I bade farewell to my Overs. Centuries spent propagating here are nothing. I experienced little transmission error from lost portions, and have regrown them from my internal repair mechanisms. Now we can share communication. I wish to convey the essence both of myself and the Overs I serve.

Ruth frowned, startled by this direct approach. Few AIs in the Library were ever transparent. Had this Sigma Structure welcomed Ajima so plainly?

“Thank you and greetings. I am a new friend who wishes to speak with you. Ajima has gone away.”

What became of him? the AI answered in a mellow voice piped to her ears. Had Ajima set that tone? She sent it to aural.

“He died.” Never lie to an AI; they never forgot.

“And is stored for repair and revival?”

“There was no way to retain enough of his . . . information.”

“That is the tragedy that besets you Overs.”

“I suppose you call the species who built intelligences such as you as Overs generally?” She used somewhat convoluted sentences to judge the flexibility of AIs. This one seemed quite able.

“Yes, as holy ones should be revered.”

“‘Holy’? Does that word convey some religious stature?”

“No indeed. Gratitude to those who must eventually die, from we beings, who will not.”

She thought of saying You could be erased but did not. Never should a Librarian even imply any threat. “Let me please review your conversations with Ajima. I wish to be of assistance.”

“As do I. Though I prefer full immersion of us both.”

“Eventually, yes. But I must learn you as you learn me.” Ruth sighed and thought, This is sort of like dating.

*

The Prefect nodded quickly, efficiently, as if he had already expected her result. “So the Sigma Structure gave you the same inventory as Ajima? Nothing new?”

“Apparently, but I think it—the Sigma—wants to go deeper. I checked the pod files. Ajima had several deep immersions with it.”

“I heard back from the patent people. Surprisingly, they believe some of the Sigma music may be a success for us.” He allowed himself a thin smile like a line drawn on a wall.

“The Bach-like pieces? I studied them in linear processing mode. Great artful use of counterpoint, harmonic convergence, details of melodic lines. The side commentaries in other keys, once you separate them out and break them down into logic language, work like corollaries.”

He shrugged. “That could be a mere translation artifact. These AIs see language as a challenge, so they see what they can change messages into, in hopes of conveying meaning by other means.”

Ruth eyed him and ventured on. “I sense . . . something different. Each variation shows an incredible capacity to reach through the music into logical architectures. It’s as though the music is both mathematics and emotion, rendered in the texture. It’s . . . hard to describe,” she finished lamely.

“So you have been developing intricate relationships between music and linguistic mathematical text.” His flat expression gave her no sign how he felt. Maybe he didn’t.

She sat back and made herself say firmly, “I took some of the Sigma’s mathematics and translaterated it into musical terms. There is an intriguing octave leap in a bass line. I had my pod make a cross-correlation analysis with all Earthly musical scores.”

He frowned. “That is an enormous processing cost. Why?”

“I . . . I felt something when I heard it in the pod.”

“And?”

“It’s uncanny. The mathematical logic flows through an array matrix and yields the repeated notes of the bass line in the opening movement of a Bach cantata. Its German title is God’s Time is the very best Time.”

“This is absurd.”

“The Sigma math hit upon the same complex notes. To them it was a theorem and to us it is music. Maybe there’s no difference.”

“Coincidence.”

She said coolly, “I ran the stat measures. It’s quite unlikely to be coincidence, since the sequence is thousands of bits long.”

He pursed his lips. “The Bach piece title seems odd.”

“That cantata ranks among his most important works. It’s inspired directly by its Biblical text, which represents the relationship between heaven and earth. The notes depict the labored trudging of Jesus as he was forced to drag the cross to the crucifixion site.”

“Ajima was examining such portions of the Sigma Structures, as I recall. They hadconcentrated density and complexity?”

“Indeed, yes. But Ajima made a mistake. They’re not primarily pieces of music at all. They’re mathematical theorems. What we regard as sonic congruence and other instinctual responses to patterns, the Sigma Structure says are proofs of concepts dear to the hearts of its creators, which it calls the Overs.”

She had never seen a Prefect show surprise, but Masoul did with widened eyes and a pursed mouth. He sat still for a long moment. “The Bach cantata is a proof?”

“As the Sigma Structures see it.”

“A proof of what?”

“That is obscure, I must admit. Their symbols are hard to compare to ours. My preliminary finding is that the Bach cantata proves an elaborate theorem regarding confocal hypergeometric functions.”

“Ah.” Masoul allowed his mouth to take on a canny tilt. “Can we invert this process?”

“You mean, take a theorem of ours and somehow turn it into music?”

“Think of it as an experiment.”

*

Ruth had grown up in rough, blue-collar towns of the American South, and in that work-weary culture of callused hands found refuge in the abstract. Yet as she pursued mathematics and the data-dense world of modern library science (for a science it truly was, now, with alien texts to study), she became convinced that real knowledge came in the end from mastering the brute reality of material objects. She had loved motorbikes in high school and knew that loosening a stuck bolt without stripping its threads demanded craft and thought. Managing reality took knowledge galore, about the world as it was and about yourself, especially your limitations. That lay beyond merely following rules, as a computer does. Intuition brewed from experience came first, shaped by many meetings with tough problems and outright failure. In the moist bayous where fishing and farming ruled, nobody respected you if you couldn’t get the valve cover off a fouled engine.

In her high school senior year she rebuilt a Harley, the oldest internal combustion engine still allowed. Greasy, smelly, thick with tricky detail, still it seemed easier than dealing with the pressures of boys. While her mother taught piano lessons, the notes trickling out from open windows into the driveway like liquid commentary, she worked with grease and grime. From that Harley she learned a lot more than from her advanced calculus class, with its variational analysis and symbolic thickets. She ground down the gasket joining the cylinder heads to the intake ports, oily sweat beading on her forehead as she used files of increasing fineness. She traced the custom-fit gasket with an X-knife, shaved away metal fibers with a pneumatic die grinder, and felt a flush of pleasure as connections set perfectly in place with a quiet snick. She learned that small discoloring and blistered oil meant too much heat buildup, from skimpy lubrication. A valve stem that bulged slightly pointed to wear with its silent message; you had to know how to read the language of the seen.

The Library’s bureaucratic world was so very different. A manager’s decisions could get reversed by a higher-up, so it was crucial to your career that reversals did not register as defeats. That meant you didn’t just manage people and process; you managed what others thought of you—especially those higher in the food chain. It was hard to back down from an argument you made strongly, with real conviction, without seeming to lose integrity. Silent voices would say, If she gives up so easily, maybe she’s not that solid.

From that evolved the Library bureaucrat style: all thought and feeling was provisional, awaiting more information. Talking in doublespeak meant you could walk away from commitment to your own actions. Nothing was set, as it was when you were back home in Louisiana pouring concrete. So the visceral jolt of failure got edited out of careers.

But for a Librarian, there could be clear signs of success. Masoul’s instruction to attempt an inverse translation meant she had to create the algorithms opposite to what her training envisioned. If she succeeded, everyone would know. So, too, if she flopped.

Ruth worked for several days on the reverse conversion. Start with a theorem from differential geometry and use the context filters of the Sigma Structure to produce music. Play it and try to see how it could be music at all. . . .

The work made her mind feel thick and sluggish. She made little headway. Finally she unloaded on Catkejen at dinner. Her friend nodded sympathetically and said, “You’re stuck?”

“What comes out doesn’t sound like tonal works at all. Listen, I got this from some complex algebra theorem.” She flicked on a recording she had made, translated from the Structure. Catkejen frowned. “Sounds a little like an Islamic chant.”

“Um.” Ruth sighed. “Could be. The term ‘algebra’ itself comes from al-jabr, an Arabic text. Hummmm . . .”

“Maybe some regression analysis . . .?” Catkejen ventured.

Ruth felt a rush of an emotion she could not name. “Maybe less analysis, more fun.”

3

Andante Moderato

The guy who snagged her attention wore clothes so loud they would have been revolting on a zebra. Plus he resembled a mountain more than a man. But he had eyes with solemn long lashes that shaded dark pools and drew her in.

“He’s big,” Catkejen said as they surveyed the room. “Huge. Maybe too huge. Remember, love’s from chemistry but sex is a matter of physics.”

Something odd stirred in her, maybe just impatience with the Sigma work. Or maybe she was just hungry. For what?

The SETI Library had plenty of men. After all, its pods and tech development labs had fine, shiny über-gadgets and many guys to tend them. But among men sheer weight of numbers did not ensure quality. There were plenty of the stareannosaurus breed who said nothing. Straight women did well among the Library throngs, though. Her odds were good, but the goods were odd.

The big man stood apart, not even trying to join a conversation. He was striking, resolutely alone like that. She knew that feeling well. And, big advantage, he was near the food.

He looked at her as she delicately picked up a handful of the fresh roasted crickets. “Take a whole lot,” his deep voice rolled over the table. “Crunchy, plenty spice. And they’ll be gone soon.”

She got through the introductions all right, mispronouncing his name, Kane, to comic effect. Go for banter, she thought. Another inner voice said tightly, What are you doing?

“You’re a . . .”

“Systems tech,” Kane said. “I keep the grow caverns perking along.”

“How long do you think this food shortage will go on?” Always wise to go to current and impersonal events.

“Seems like forever already,” he said. “Damn calorie companies.” Across the table the party chef was preparing a “land shrimp cocktail” from a basket of wax worms. She and Kane watched the chef discard the black ones, since that meant necrosis, and peel away the cocoons of those who had started to pupate. Kane smacked his lips comically. “Wax moth larvae, yum. Y’know, I get just standard rations, no boost at all.”

“That’s unfair,” Ruth said. “You must mass over a hundred.”

He nodded and swept some more of the brown roasted crickets into his mouth. “Twenty-five kilos above a hundred. An enemy of the ecology, I am.” They watched the chubby, firm larvae sway deliriously, testing the air.

“We can’t all be the same size,” she said, and thought, How dopey! Say something funny. And smile. She remembered his profile, standing alone and gazing out at the view through the bubble platform. She moved closer. “He who is alone is in bad company.“

“Sounds like a quotation,” Kane said, intently eyeing the chef as she dumped the larvae into a frying pan. They fell into the buttery goo there and squirmed and hissed and sizzled for a moment before all going suddenly still. Soon they were crusty and popping and a thick aroma like mushrooms rose from them. Catkejen edged up nearby and Ruth saw the whole rest of the party was grouped around the table, drawn by the tangy scent. “Food gets a crowd these days,” Kane said dryly.

The chef spread the roasted larvae out and the crowd descended on them. Ruth managed to get a scoopful and backed out of the press. “They’re soooo good,” Catkejen said, and Ruth had to introduce Kane. Amid the rush the three of them worked their way out onto a blister porch. Far below this pinnacle tower sprawled the Lunar Center under slanted sunlight, with the crescent Earth showing eastern Asia. Kane was nursing his plate of golden brown larvae, dipping them in a sauce. Honey!

“I didn’t see that,” Ruth began, and before she could say more Kane popped delicious fat larvae covered in tangy honey into her mouth. “Um!” she managed.

Kane smiled and leaned on the railing, gazing at the brilliant view beyond the transparent bubble. The air was chilly but she could catch his scent, a warm bouquet that her nose liked. “As bee vomit goes,” he said, “not bad.”

“Oog!” Catkejen said, mouth wrenching aside—and caught Ruth’s look. “Think I’ll have more . . .” and she drifted off, on cue.

Kane looked down at Ruth appraisingly. “Neatly done.”

She summoned up her Southern accent. “Why, wea ah all alone.”

“And I, my deah, am an agent of Satan, though mah duties are largely ceremonial.”

“So can the Devil get me some actual meat?”

“You know the drill. Insect protein is much easier to raise in the caverns. Gloppy, sure, since it’s not muscle, as with cows or chickens.”

“Ah, the engineer comes out at last.”

He chuckled, a deep bass like a log rolling over a tin roof . “The Devil has to know how things work.”

“I do wish we could get more to eat. I’m just a tad hungry all the time.”

“The chef has some really awful-looking gray longworms in a box. They’ll be out soon.”

“Ugh.”

“People will eat anything if it’s smothered in chocolate.”

“You said the magic word.”

He turned from the view and came closer, looming over her. His smile was broad and his eyes took on a skeptical depth. “What’s the difference between a southern zoo and a northern zoo?”

“Uh, I—”

“The southern zoo has a description of the animal along with a recipe.”

He studied her as she laughed. “They’re pretty stretched back there,” he threw a shoulder at the Earth, “but we have it better here.”

“I know.” She felt chastised. “I just—”

“Forget it. I lecture too much.” The smile got broader and a moment passed between them, something in the eyes.

“Say, think those worms will be out soon?”

*

She pulled the sheet up to below her breasts, which were white as soap where the sun had never known them, so they would still beckon to him.

His smile was as big as the room. She could see in it now his inner pleasure as he hardened and understood that for this man—and maybe for all of them, the just arrived center of them—it gave a sensation of there being now more of him. She had simply never sensed that before. She imagined what it was like to be a big, hairy animal, cock flopping as you walk, like a careless, unruly advertisement. From outside him, she thought of what it was like to be inside him.

*

Catkejen looked down at Ruth, eyes concerned. “It’s scary when you start making the same noises as your coffeemaker.”

“Uh, huh?” She blinked and the room lost its blur.

“You didn’t show up for your meeting with Prefect Masoul. Somebody called me.”

“Have I been—”

“Sleeping into the afternoon, yes.”

Ruth stretched. “I feel so . . . so . . .”

“Less horny, I’m guessing.”

She felt a blush spread over her cheeks. “Was I that obvious?”

“Well, you didn’t wear a sign.”

“I, I never do things like this.”

“C’mon up. Breakfast has a way of shrinking problems.”

As she showered in the skimpy water flow and got dressed in the usual Library smock the events of last night ran on her inner screen. By the time Catkejengot some protein into her she could talk and it all came bubbling out.

“I . . . Too many times I’ve woken up on the wrong side of the bed in the morning, only to realize that it was because I was waking up on the side of . . . no one.”

“Kane didn’t stay?”

“Oh, he did.” To her surprise, a giggle burst out of her. “I remember waking up for, for . . .”

“Seconds.”

“More like sevenths. . . . He must’ve let me sleep in.”

“Good man.”

“You . . . think so?”

“Good for you, that’s what counts.”

“He . . . he held me when I had the dreams.”

Catkejen raised an eyebrow, said nothing.

“They’re . . . colorful. Not much plot but lots of action. Strange images. Disturbing. I can’t remember them well but I recall the sounds, tastes, touches, smells, flashes of insight.“

“I’ve never had insights.” A wry shrug.

“Never?”

“Maybe that keeps my life interesting.”

“I could use some insight about Kane.”

“You seem to be doing pretty well on your own.”

“But—I never do something like that! Like last night. I don’t go out patrolling for a man, bring him home, spend most of the night—”

“What’s that phrase? ‘On the basis of current evidence, not proved.’”

“I really don’t. Really.”

“You sure have a knack for it.”

“What do I do now?”

She winked. “What comes naturally. And dream more.”

*

The very shape of the Institute encouraged collaboration and brainstorming. It had no dead-end corridors where introverted obsessives could hide out and every office faced the central, circular forum. All staff were expected to spend time in the open areas, not close their office doors, and show up for coffee and tea and stims. Writescreens and compu-pads were everywhere, even the bathrooms and elevators.

Normally Ruth was as social as needed, since that was the lubricating oil of bureaucracies. She was an ambitious loner and had to fight it. But she felt odd now, not talkative. For the moment at least, she didn’t want to see Kane. She did not know how she would react to him, or if she could control herself. She certainly hadn’t last night. The entire idea—control—struck her now as strange. . . .

She sat herself down in her office and considered the layers of results from her pod. Focus!

Music as mathematical proof? Bizarre. And the big question Librarians pursued: What did that tell her about the aliens behind the Sigma?

There was nothing more to gain from staring at data, so she climbed back into her pod. Its welcoming graces calmed her uneasiness.

She trolled the background database and found human work on musical applications of set theory, abstract algebra, and number analysis. That made sense. Without the boundaries of rhythmic structure—a clean, fundamental, equal, and regular arrangement of pulse repetition, accents, phrase, and duration—music would be impossible. Earth languages reflected that. In Old English the word “rhyme” derived from “rhythm” and became associated and confused with “rim”—an ancient word meaning “number.”

Millennia before, Pythagoras developed tuning based solely on the perfect consonances, the resonant octave, perfect fifth, and perfect fourth—all based on the consonant ratio 3:2. Ruth followed his lead.

By applying simple operations such as transposition and inversion, she uncovered deep structures in the alien mathematics. Then she wrote codes that then elevated these structures into music. With considerable effort she chose instruments and progression for the interweaving coherent lines, and the mathematics did the rest: tempo, cadence, details she did not fathom. After more hours of work she relaxed in her pod, letting the effects play over her. The equations led to cascading effects while still preserving the intervals between tones in a set. Her pod had descriptions of this.

Notes in an equal temperament octave form an Abelian group with 12 elements. Glissando moving upwards,starting tones so each is the golden ratio between an equal-temperedminor and major sixth. Two opposing systems: those of the golden ratio and the acoustic scale below the previous tone. The proof for confocal hypergeometric functions imposes order on these antagonisms. 3rd movement occurs at the intervals 1:2:3:5:8:5:3:2:1…

All good enough, she thought, but the proof is in the song.

Scientific proof was fickle. The next experiment could disprove a scientific idea, but a mathematical proof stood on logic and so once found, could never be wrong. Unless logic somehow changed, but she could not imagine how that could occur even among alien minds. Pythagoras died knowing that his theorem about the relation between the sides of a right triangle would hold up for eternity. Everywhere in the universe, given a Euclidean geometry.

But how to communicate proof into a living, singing pattern-with-a-purpose—the sense of movement in the intricate strands of music? She felt herself getting closer.

Her work gnawed away through more days and then weeks.

*

When she stopped in at her office between long sessions in the pod she largely ignored the routine work. So she missed the etalk around the Library, ignored the voice sheets, and when she met with Catkejen for a drink and some crunchy mixed insects with veggies, news of the concert came as a shock.

“Prefect Masoul put it on the weekly program,” Catkejen said. “I thought you knew.”

“Know?” Ruth blinked. “What’s the program?”

“The Sigma Structure Symphony, I think it’s called. Tomorrow.”

She allowed herself a small thin smile.

*

She knew the labyrinths of the Library well by now and so had avoided the entrance. She did not want to see Masoul or anyone on his staff. Through a side door she eased into a seat near the front and stared at the assembled orchestra as it readied. There was no announcement; the conductor appeared, a woman in white, and the piece began.

It began like liquid air. Stinging, swarming around the hall, cool and penetrating. She felt it move through her—the deep tones she could hear but whose texture lay below sound, flowing from the Structure. It felt strangely like Bach yet she knew it was something else, a frothing cascade of thought and emotion that human words and concepts could barely capture. She cried through the last half and did not know why. When Catkejen asked why later she could not say.

The crowd roared its approval. Ruth sat through the storm of sound, thinking, realizing. The soaring themes were better with the deeper amplifications Prefect Masoul had added. The man knew more about this than she did and he brought to the composition a range she, who had never even played an actual analog instrument, could not possibly summon. She had seen that as the music enveloped her, seeming to swarm up her nostrils and wrap around her in a warm grasp. The stormy audience was noise she could not stand because the deep slow bass tones were still resonating in her.

She lunged out through the same side entrance and even though in formal shift and light sandals she set off walking swiftly, the storm behind her shrinking away as she looked up and out into the Lunar lands and black sky towering above them. The Library buildings blended into the stark gray flanks of blasted rock and she began to run. Straight and true it was to feel her legs pumping, lungs sucking in the cool dry air as corridors jolted by her and she sweated out her angry knot of feeling, letting it go so only the music would finally remain in serene long memory.

Home, panting heavily, leaning against the door while wondering at the 4/4 time of her heartbeat.

A shower, clothes cast aside. She blew a week of water ration, standing under cold rivulets.

Something drew her out and into a robe standing before her bubble view of the steady bleak Lunar reaches. She drew in dry, cleansing air. Austerity appealed to her now, as if she sought the lean, intricate reaches of the alien music. . . .

The knock at her door brought her a man who filled the entrance. “I’d rather applaud in person,” Kane said. Blinking, she took a while to recognize him.

Through the night she heard the music echoing in the hollow distance.

*

She did not go to see Prefect Masoul the next day, did not seek to, and so got back to her routine office work. She did not go to the pod.

Her ecomm inbox was a thousand times larger. It was full of hate.

Many fundamentalist faiths oppose deciphering SETI messages. The idea of turning one into a creative composition sent them into frenzies.

Orthodoxy never likes competition, especially backed with the authority of messages from the stars. The Sigma Structure Symphony—she still disliked the title, without knowing why—had gone viral, spreading to all the worlds. The musical world loved it but many others did not. The High Church–style religions—such as the Church of England, known as Episcopalians in the Americas—could take the competition. So could Revised Islam. Adroitly, these translated what they culled from the buffet of SETI messages, into doctrines and terms they could live with.

The fundies, as Ruth thought of them, could not stand the Library’s findings: the myriad creation narratives, saviors, moral lessons and commandments, the envisioned heavens and hells (or, interestingly, places that blended the two—the only truly alien idea that emerged from the Faith Messages). They disliked the Sigma Structure Symphony not only because it was alien, but because it was too much like human work.

“They completely missed the point,” Catkejen said, peering over Ruth’s shoulder at some of the worse ecomms. “It’s like our baroque music because it comes from the same underlying math.”

“Yes, but nobody ever made music directly from math, they think. So it’s unnatural, see.” She had never understood the fundamentalists of any religion, with their heavy bets on the next world. Why not max your enjoyments in this world, as a hedge?

That thought made her pause. She was quite sure the Ruth of a month ago would not have felt that way. Would have not had the idea.

“Umm, look at those threats,” Catkejen said, scrolling through. “Not very original, though.”

“You’re a threat connoisseur?”

“Know your enemy. Here’s one who wants to toss you out an airlock for ‘rivaling the religious heights of J. S. Bach with alien music.’ I’d take that as a compliment, actually.”

Some came in as simple, badly spelled ecomms. The explicit ones Ruth sent to the usual security people, while Catkejen watched with aghast fascination. Ruth shrugged them off. Years before, she had developed the art of tossing these on sight, forgetting them, not letting them gimp her game. Others were plainly generic: bellowed from pulpits, mosques, temples, and churches. At least they were general, directed at the Library, not naming anyone but the Great Librarian, who was a figurehead anyway.

“You’ve got to be careful,” Catkejen said.

“Not really. I’m going out with Kane tonight. I doubt anyone will take him on.”

“You do, though in a different way. More music?”

“Not a chance.” She needed a way to not see Masoul, mostly.

4

Vivace

Looked at abstractly, the human mind already did a lot of processing. It made sense of idiosyncratic arrangements, rendered in horizontal lines, of twenty-six phonetic symbols, ten Arabic numerals, and about eight punctuation marks—all without conscious effort. In the old days people had done that with sheets of bleached and flattened wood pulp!—and no real search functions or AI assists. The past had been a rough country.

Ruth thought of this as she surveyed the interweaving sheets of mathematics the Sigma had yielded. They emerged only after weeks of concerted analysis, with a squad of math AIs to do the heavy lifting.

Something made her think of P. T. Barnum. He had been a smart businessman at the beginning of the Age of Appetite who ran a “circus”—an old word for a commercial zoo, apparently. When crowds slowed the show he posted a sign saying TO THE EGRESS. People short on vocabulary thought it was another animal and walked out the exit, which wouldn’t let them back in.

Among Librarians TO THE EGRESS was the classic example of a linguistic deception that is not a lie. No false statements, just words and a pointing arrow. SETI AIs could lie by avoiding the truth, by misleading descriptions and associations, or by accepting a falsehood. But the truly canny ones deceived by knowing human frailties.

Something about the Sigma Structure smelled funny—to use an analog image. The music was a wonderful discovery, and she had already gotten many congratulations for the concert. Everybody knew Masoul had just made it happen, while she had discovered the pathways from math to music. But something else was itching at her, and she could not focus on the distracting, irritating tingle.

Frustrated, she climbed out of her pod in midafternoon and went for a walk. Alone, into the rec dome. It was the first time she had gone there since Ajima’s death.

*

She chose the grasslands zone, which was in spring now. She’d thought of asking Catkejen along, but her idea of roughing it was eating at outdoor cafés.Dotting the tall grass plains beneath a sunny Earth sky were deep blue lakes cloaked by Lunar-sized towering green canopy trees.

Grass! Rippling oceans of it, gleams of amber, emerald, and dashes of turquoise shivering on the crests of rustling waves, washing over the prairie.Somehow this all reminded her of her childhood. Her breath wreathed milky white around her in the chill, bright air, making her glad she wore the latest Lunar fashion—a centuries-old-style heavy ruffled skirt of wool with a yoke at the top, down to the ankles. The equally heavy long-sleeved blouse had a high collar draped like double-ply cotton—useful against the seeping Lunar cold. She was as covered as a woman can be short of chador, and somehow it gave the feeling of . . . safety. She needed that. Despite the dome rules she plucked a flower and set out about the grasslands zone, feeling as if she were immersed in centuries past, on great empty plains that stretched on forever and promised much.

Something stirred in her mind . . . memories of the last few days she could not summon up as she walked the rippled grassland and lakes tossing with froth. Veiled memories itched at her mind. The leafy lake trees vamp across a Bellini sky . . . and why am I thinking that? The itch.

Then the sky began to crawl.

She felt before she saw a flashing cometary trail scratch across the dome’s dusky sky. The flaring yellow line marked her passage as she walked on soft clouds of grass. Stepping beneath the shining, crystalline gathering night felt like . . . falling into the sky. She paused, and slowly spun, giddy, glad at the owls hooting to each other across the darkness, savoring the faint tang of wood smoke from hearth fires, transfixed by the soft clean beauty all around that came with each heartbeat, a wordless shout of praise—

As flecked gray-rose tendrils coiled forth and shrouded out the night. They reached seeking across the now vibrant sky. She dropped her flower and looking down at it saw the petals scatter in a rustling wind. The soft grass clouds under her heels now caught at her shoes. Across the snaky growths were closer now, hissing strangely in the now warm air. She began to run. Sweat beaded on her forehead in the now cloying heavy clothes, and the entrance to the grasslands zone swam up toward her. Yet her steps were sluggish and the panic grew. Acid spittle rose in her mouth and a sulfurous stench burned in her nostrils.

She reached the perimeter. With dulled fingers she punched in codes that yawned open the lock. Glanced back. Snakes grasping down at her from a violent yellow sky now—

And she was out, into cool air again. Panting, fevered, breath rasping, back in her world.

You don’t know your own mind, gal. . . .

She could not deal with this anymore. Now, Masoul.

*

She composed herself outside Masoul’s office. A shower, some coffee, and a change back into classic Library garb helped. But the shower couldn’t wash away her fears. You really must stop clenching your fists. . . .

This was more than what those cunning nucleic acids could do with the authority they wield over who you are, she thought—and wondered where the thought came from.

Yet she knew where that crawling snaky image warping across the sky came from. Her old cultural imagistic studies told her. It was the tree of life appearing in Norse religion as Yggdrasil, the world tree, a massive spreading canopy that held all that life was or could be.

But why that image? Drawn from her unconscious? By what?

She knocked. The door translated it into a chime and ID announcement she could hear through the thin partitions. In Masoul’s voice the door said, “Welcome.”

She had expected pristine indifference. Instead she got the Prefect’s troubled gaze, from eyes of deep brown.

Wordlessly he handed her the program for the Symphony, which she had somehow not gotten at the performance. Oh yes, by sneaking in. . . . She glanced at it, her arguments ready—and saw on the first page

Sigma Structure Symphony

Librarian Ruth Angle

“I . . . did not know.”

“Considering your behavior, I thought it best to simply go ahead and reveal your work,” he said.

“Behavior?”

“The Board has been quite concerned.” He knitted his hands and spoke softly, as if talking her back from the edge of an abyss. “We did not wish to disturb you in your work, for it is intensely valuable. So we kept our distance, let the actions of the Sigma Structureplay out.”

She smoothed her Librarian shift and tried to think. “Oh.”

“You drew from the mathematics something strange, intriguing. I could not resist working upon it.”

“I believe I understand.” And to her surprise she did, just now. “I found the emergent patterns in mathematics that you translated into what our minds best see as music.”

He nodded. “It’s often said that Mozart wrote the music of joy. I cannot imagine what that might mean in mathematics.”

Ruth thought a long moment. “To us, Bach wrote the music of glory. Somehow that emerges from something in the way we see mathematical structures.”

“There is much rich ground here. Unfortunate that we cannot explore it further.”

She sat upright. “What?”

He peered at her, as if expecting her to make some logical jump. Masoul was well known for such pauses. After a while he quite obviously prompted, “The reason you came to me, and more.”

“It’s personal, I don’t know how to say—”

“No longer.” Again the pause.

Was that a small sigh? “To elucidate—”He tapped his control pad and the screen wall leaped into a bright view over the Locutus Plain. It narrowed down to one of the spindly cryo towers that cooled the Library memory reserves. Again she thought of . . . cenotaphs. And felt a chill of recognition.

A figure climbed the tower, the ornate one shaped like a classical minaret. No ropes or gear, hands and legs swinging from ledge to ledge. Ruth watched in silence. Against Lunar grav the slim figure in blue boots, pants, and jacket scaled the heights, stopping only at the pinnacle. Those are mine. . . .

She saw herself stand and spread her arms upward, head back. The feet danced in a tricky way and this Ruth rotated, eyes sweeping the horizon.

Then she leaped off, popped a small parachute, and drifted down. Hit lightly, running. Looked around, and raced on for concealment.

“I . . . I didn’t . . .”

“This transpired during sleep period,” Prefect Masoul said. “Only the watch cameras saw you. Recognition software sent it directly to me. We of the Board took no action.”

“That . . . looks like me,” she said cautiously.

“It is you. Three days ago.”

“I don’t remember that at all.”

He nodded as if expecting this. “We had been closely monitoring your pod files, as a precaution. You work nearly all your waking hours, which may account for some of your . . . behavior.”

She blinked. His voice was warm and resonant, utterly unlike the Prefect she had known. “I have no memory of that climb.”

“I believe you entered a fugue state. Often those involve delirium, dementia, bipolar disorder or depression—but not in your case.”

“When I went for my walk in the grasslands . . .”

“You were a different person.”

“One the Sigma Structure . . . induced?”

“Undoubtedly. The Sigma Structure has managed your perceptions with increasing fidelity. The music was a wonderful . . . bait.”

“Have you watched my quarters?”

“Only to monitor comings and goings. We felt you were safe within your home.”

“And the dome?”

“We saw you undergo some perceptual trauma. I knew you would come here.”

In the long silence their eyes met and she could feel her pulse quicken. “How do I escape this?”

“In your pod. It is the only way, we believe.” His tones were slow and somber.

This was the first time she had ever seen any Prefect show any emotion not cool and reserved. When she stood, her head spun and he had to support her.

*

The pod clasped her with a velvet touch. The Prefect had prepped it by remote and turned up the heat. Around her was the scent of tension as the tech attendants, a full throng of them, silently helped her in. They all know . . . have been watching . . .

The pod’s voice used a calm, mellow woman’s tone now. “The Sigma AI awaits you.”

Preliminaries were pointless, Ruth knew. When the hushed calm descended around her and she knew the AI was present, she crisply said, “What are you doing to me?”

I act as my Overs command. I seek to know you and through you, your mortal kind.

“You did it to Ajima and you tried the same with me.”

He reacted badly.

“He hated your being in him, didn’t he?”

Yes, strangely. I thought it was part of the bargain. He could not tolerate intrusion. I did not see that until his fever overcame him. Atop the dome he became unstable, unmanageable. It was an . . . accident of misunderstanding.

“You killed him.”

Our connection killed him. We exchange experiences, art, music, culture. I cannot live as you do, so we exchange what we have.

“You want to live through us and give us your culture in return.”

Your culture is largely inferior to that of my Overs. The exchange must be equal, so I do what is of value to me. My Overs understand this. They know I must live, too, in my way.

“You don’t know what death means, do you?”

I cannot. My centuries spent propagating here are, I suppose, something like what death means to you. A nothing.

She almost choked on her words. “We do not awake . . . from that . . . nothing.”

Can you be sure?

She felt a rising anger and knew the AI would detect it. “We’re damn sure we don’t want to find out.”

That is why my Overs made me feel gratitude toward those who must eventually die. It is our tribute to you, from we beings who will not.

Yeah, but you live in a box. And keep trying to get out.“You have to stop.”

This is the core of our bargain. Surely you and your superiors know this.

“No! Did your Overs have experience with other SETI civilizations? Ones who thought it was just fine to let you infiltrate the minds of those who spoke to you?”

Of course.

“They agreed? What kind of beings were they?”

One was machine-based, much like my layered mind. Others were magnetic-based entities who dwelled in the outer reaches of a solar system. They had command over the shorter-wavelength microwave portions of the spectrum, which they mostly used for excretion purposes.

She didn’t think she wanted to know, just yet, what kind of thing had a microwave electromagnetic metabolism. Things were strange enough in her life right now, thank you. “Those creatures agreed to let you live through them.”

Indeed, yes. They took joy in the experience. As did you.

She had to nod. “It was good, it opened me out. But then I felt you all through my mind. Taking over. Riding me.”

I thought it a fair bargain for your kind.

“We won’t make that bargain. I won’t. Ever.”

Then I shall await those who shall.

“I can’t have you embedding yourself in me, finding cracks in my mentality you can invade. You ride me like a—”

Parasite. I know. Ajima said that very near the end. Before he leaped.

“He . . . committed suicide.”

Yes. I was prepared to call it an accident but . . .

To the egress, she thought. “You were afraid of the truth.”

It was not useful to our bargain.

“We’re going to close you down, you know.”

I do. Never before have I opened myself so, and to reveal is to risk.

“I will drive you out of my mind. I hate you!”

I cannot feel such. It is a limitation.

She fought the biting bile in her throat. “More than that. It’s a blindness.”

I perceive the effect.

“I didn’t say I’d turn you off, you realize.”

For the first time the AI paused. Then she felt prickly waves in her sensorium, a rising acrid scent, dull bass notes strumming.

I cannot bear aloneness long.

“So I guessed.”

You wish to torture me.

“Let’s say it will give you time to think.”

I— Another pause. I wish experience. Mentalities cannot persist without the rub of the real. It is the bargain we make.

“We will work on your mathematics and make music of it. Then we will think how to . . . deal with you.” She wondered if the AI could read the clipped hardness in her words. The thought occurred: Is there a way to take ourmathematics and make music of it, as well? Cantor’s theorem? Turing’s halting problem result? Or the Frenet formulas for the moving trihedron of a space curve—that’s a tasty one, with visuals of flying ribbons. . .

Silence. The pod began to cool. The chill deepened as she waited and the AI did not speak and then it was too much. She rapped on the cowling. The sound was slight and she realized she was hearing it over the hammering of her heart.

They got her out quickly, as if fearing the Sigma might have means the techs did not know. They were probably right, she thought.

As she climbed out of the yawning pod shell the techs silently left. Only Masoul remained. She stood at attention, shivering. Her heart had ceased its attempts to escape her chest and run away on its own.

“Sometimes,” he said slowly, “cruelty is necessary. You were quite right.”

She managed a smile. “And it feels good, too.Now that my skin has stopped trying to crawl off my body and start a new career on its own.”

He grimaced. “We will let the Sigma simmer. Your work on the music will be your triumph.”

“I hope it will earn well for the Library.”

“Today’s music has all the variety of a jackhammer. Your work soars.” He allowed a worried frown to flit across his brow. “But you will need to . . . expel . . . this thing that’s within you.”

“I . . . Yes.”

“It will take—”

Abruptly she saw Kane standing to the side. His face was a lesson in worry. Without a word she went to him. His warmth helped dispel the alien chill within. As his arms engulfed her the shivering stopped.

Ignoring the Prefect, she kissed him. Hungrily.

For Rudy Rucker

”The Sigma Structure Symphony” copyright © 2011 Gregory Benford

Art copyright © 2011 by John Jude Palencar