"The idea is, how do physical laws act themselves out?" Wright asked in his lecturer voice. "Of course, atoms do not know their own differential equations." A polite chuckle. "But to find where the moon should be in the next instant, in some fashion the universe must calculate where it must go. We can do that, thanks to Newton."

The Astronomer Royal saw that Wright was humoring Geoffrey with this simplification, and suspected that it would not go down well. To hurry Wright along he said, "To make it happen, to move the moon-"

"Right, that we do not know. Not a clue. How to breathe fire into the equations, as that Hawking fellow put it-"

"But look, nature doesn"t know maths," Geoffrey said adamantly. "No more than I do."

"But something must, you see," Professor Wright said earnestly, offering them another plate of the little cut sandwiches and deftly opening a bottle of sherry. "Of course, I am using our human way of formulating this, the problem of natural order. The world is usefully described by mathematics, so in our sense the world must have some mathematics embedded in it."

"G.o.d"s a b.l.o.o.d.y mathematician?" Geoffrey scowled.

The Astronomer Royal leaned forward over the antique oak table. "Merely an expression."

"Only way the stars could get out of whack," Geoffrey said, glancing back and forth between the experts, "is if whatever caused it came from there, I"d say."

"Quite right." The Astronomer Royal pursed his lips. "Unless the speed of light has gone off, as well, no signal could have rearranged the stars straight after doing the moon."

"So we"re at the tail end of something from out there, far away," Geoffrey observed.

"A long, thin disturbance propagating from distant stars. A very tight beam of... well, error. But from what?" The Astronomer Royal had gotten little sleep since Geoffrey"s appearance, and showed it.

"The circle of distorted stars," Professor Wright said slowly, "remains where it was, correct?"

The Astronomer Royal nodded. "We"ve not announced it, but anyone with a cheap telescope-sorry, Geoffrey, not you, of course-can see the moon"s left the disturbance behind, as it follows its...o...b..t."

Wright said, "Confirming Geoffrey"s notion that the disturbance is a long, thin line of-well, I should call it an error."

"Is that what you meant by a checkable idea?" the Astronomer Royal asked irritably.

"Not quite. Though that the two regions of error are now separating, as the moon advances, is consistent with a disturbance traveling from the stars to us. That is a first requirement, in my view."

"Your view of what?" Geoffrey finally gave up handling his small sherry gla.s.s and set it down with a decisive rattle.

"Let me put my philosophy clearly," Wright said. "If the universe is an ongoing calculation, then computational theory proves that it cannot be perfect. No such system can be free of a bug or two, as the programmers put it."

Into an uncomfortable silence Geoffrey finally inserted, "Then the moon"s being ahead, the stars-it"s all a mistake?"

Wright smiled tightly. "Precisely. One of immense scale, moving at the speed of light."

Geoffrey"s face scrunched into a mask of perplexity. "And it just-jumped?"

"Our moon hopped forward a bit too far in the universal computation, just as a program advances in little leaps." Wright smiled as though this were an entirely natural idea.

Another silence. The Astronomer Royal said sourly, "That"s mere philosophy, not physics."

"Ah!" Wright pounced. "But any universe that is a sort of a.n.a.log computer must, like any decent digital one, have an error-checking program. Makes no sense otherwise."

"Why?" Geoffrey was visibly confused, a craftsman out of his depth.

"Any good program, whether it is doing accounts in a bank, or carrying forward the laws of the universe, must be able to correct itself." Professor Wright sat back triumphantly and swallowed a Jesus College sandwich, smacking his lips. The Astronomer Royal said, "So you predict-?"

"That both the moon and the stars shall snap back, get themselves right-and at the same time, as the correction arrives here at the speed of light."

"Nonsense," the Astronomer Royal said.

"A prediction," Professor Wright said sternly. "My philosophy stands upon it."

The Astronomer Royal snorted, letting his fatigue get to him. Geoffrey looked puzzled and asked a question that would later haunt them.

Professor Wright did not have long to wait.

To his credit, he did not enter the media fray with his prediction. However, he did unwisely air his views at High Table, after a particularly fine bottle of claret brought forward by the oldest member of the college. Only a generation or two earlier, such a conversation among the Fellows would have been secure. Not so now. A junior Fellow in political studies proved to be on a retainer from the Times, and scarcely a day pa.s.sed before Wright"s conjecture was known in New Delhi and Tokyo.

The furor following from that had barely subsided when the Astronomer Royal received a telephone call from the Max Planck Inst.i.tute. They excitedly reported that the moon, now under continuous observation, had shifted instantly to the position it should have, had its...o...b..t never been perturbed.

So, too, did the stars in the warped circle return to their rightful places. Once more, all was right with the world. Even so, it was a world that could never again be the same.

Professor Wright was not smug. He received the news from the Astronomer Royal, who had brought along Geoffrey to Jesus College, a refuge now from the inst.i.tute. "Nothing, really, but common sense."

He waved away their congratulations.

Geoffrey sat, visibly uneasily, through some talk about how to handle all this in the voracious media glare. Philosophers are not accustomed to much attention until well after they are dead. But as discussion ebbed Geoffrey repeated his probing question of days before: "What sort of universe has mistakes in it?"

Professor Wright said kindly, "An information-ordered one. Think of everything that happens-including us talking here, I suppose-as a kind of a.n.a.log program acting out. Discovering itself in its own development. Manifesting."

Geoffrey persisted, "But who"s the programmer of this computer?"

"Questions of first cause are really not germane," Wright said, drawing himself up.

"Which means that he cannot say," the Astronomer Royal allowed himself.

Wright stroked his chin at this and eyed the others before venturing, "In light of the name of this college, and you, Geoffrey, being a humble bearer of the message that began all this..."

"Oh, no," the Astronomer Royal said fiercely, "next you"ll point out that Geoffrey"s a carpenter."

They all laughed, though uneasily.

But as the Astronomer Royal and Geoffrey left the venerable grounds, Geoffrey said moodily, "Y"know, I"m a cabinet maker."

"Uh, yes?"

"We aren"t b.l.o.o.d.y carpenters at all," Geoffrey said angrily. "We"re craftsmen."

The distinction was lost upon the Royal Astronomer, but then, much else was, these days.

The j.a.panese had very fast images of the moon"s return to its proper place, taken from their geosynchronous satellite. The transition did indeed proceed at very nearly the speed of light, taking a slight fraction of a second to jerk back to exactly where it should have been. Not the original place where the disturbance occurred, but to its rightful spot along the smooth ellipse. The immense force needed to do this went unexplained, of course, except by Professor Wright"s Computational Principle.

To everyone"s surprise, it was not a member of the now quite raucous press who made the first telling gibe at Wright, but Geoffrey. "I can"t follow, sir, why we can still remember when the moon was in the wrong place."

"What?" Wright looked startled, almost spilling some of the celebratory tea the three were enjoying.

Or rather, that Wright was conspicuously relishing, while the Astronomer Royal gave a convincingimpression of a man in a good mood.

"Y"see, if the error"s all straightened out, why don"t our memories of it get fixed, too?"

The two learned men froze.

"We"re part of the physical universe," the Astronomer Royal said wonderingly, "so why not, eh?"

Wright"s expression confessed his consternation. "That we haven"t been, well, edited..."

"Kinda means we"re not the same as the moon, right?"

Begrudgingly, Wright nodded. "So perhaps the, ah, "mind" that is carrying out the universe"s computation cannot interfere with our-other-minds."

"And why"s that?" the Astronomer Royal a little too obviously enjoyed saying.

"I haven"t the slightest."

Light does not always travel at the same blistering speed. Only in a vacuum does it have its maximum velocity.

Light emitted at the center of the sun, for example-which is a million times denser than lead-finds itself absorbed by the close-packed ionized atoms there, held for a tiny sliver of a second, and then released. It travels an infinitesimal distance, then is captured by yet another hot ion of the plasma, and the process repeats. The radiation random-walks its way out to the solar surface. In all, the pa.s.sage from the core takes many thousands of years. Once free, the photon reaches Earth in a few minutes.

Radiation from zones nearer the sun"s fiery surface takes less time because the plasma there is far less dense. That was why a full three months elapsed before anyone paid attention to a detail the astronomers had noticed early on and then neglected.

The "cone of chaos" (as it was now commonly called) that had lanced in from the distant stars and deflected the moon had gone on and intersected the sun at a grazing angle. It had luckily missed Earth, but that was the end of the luck.

On an otherwise unremarkable morning, Geoffrey rose to begin work on a new pine cabinet. He was glad to be out of the media glare, though still troubled by the issues raised by his discovery. Professor Wright had made no progress in answering Geoffrey"s persistent questions. The Astronomer Royal was busying himself with a Royal commission appointed to investigate the whole affair, though no one expected a commission to actually produce an idea. Geoffrey"s hope-that they could "find out more by measuring," seemed to be at a dead end.

On that fateful morning, out his bedroom window, Geoffrey saw a strange sun. Its lumpy shape he quickly studied by viewing it through his telescope with a dark gla.s.s clamped in place. He knew of the arches that occasionally rose from the corona, vast galleries of magnetic field lines bound to the plasma like bunches of wire under tension. Sprouting from the sun at a dozen spots stood twisted parodies of this, snaking in immense weaves of incandescence.

He called his wife to see. Already voices in the cobbled street below were murmuring in alarm.

Hanging above the open marsh lands around the ancient cathedral city of Ely was a ruby sun, its grand purple arches swelling like blisters from the troubled rim.

His wife"s voice trembled. "What"s it mean?"

"I"m afraid to ask."

"I thought everything got put back right."

"Must be more complicated, somehow."

"Or a judgment." In his wife"s severe frown he saw an eternal human impulse, to read meaning into the physical world-and a moral message as well.

He thought of the swirl of atoms in the sun, all moving along their hammering trajectories, immensely complicated. The spike of error must have moved them all, and the later spike of correction could not, somehow, undo the damage. Erasing such detail must be impossible. So even the mechanism that drove the universal computation had its limits. Whatever you called it, Geoffrey mused, the agency that made order also made error-and could not cover its tracks completely.

"Wonder what it means?" he whispered.

The line of error had done its work. Plumes rose like angry necklaces from the blazing rim of the starwhose fate governed all intelligence within the solar system.

Thus began a time marked not only by vast disaster, but by the founding of a wholly new science.

Only later, once studies were restored at Cambridge University, and Jesus College was rebuilt in a period of relative calm, did this new science and philosophy-for now the two were always linked-acquire a name: the field of empirical theology.

Glacial

ALASTAIR REYNOLDS.

Alastair Reynolds [www.members.tripod.com/~voxish/Home. html] was born in Barry, South Wales (the birthplace of Bob Hope), raised in Cornwall, educated in Newcastle and St. Andrews, Scotland (Ph.D. in astronomy), and now lives in Noordwijk, Holland, and works for the European s.p.a.ce Agency. He is one of the British s.p.a.ce opera writers to emerge in the mid and late 1990s, and the most "hard SF" of them. To date his stories have been published almost exclusively in Interzone and in Spectrum SF, the ambitious new SF magazine from Scotland. His first novel was Revelation s.p.a.ce (2000) and his second, Chasm City, was published in 2001.

"Glacial," from Spectrum SF, which is now one of the major small press SF magazines, is a sequel to Reynolds" 2000 novella, "Great Wall of Mars." An almost superhuman group of the Conjoiners, a group mind composed of individual humans, is exploring systems nearby in the galaxy humans reached centuries before. And they find one, with one survivor, and a mystery.

Nevil Clavain picked his way across a mosaic of shattered ice. The field stretched away in all directions, gouged by sleek-sided creva.s.ses. They had mapped the largest cracks before landing, but he was still wary of surprises; his breath caught every time his booted foot cracked through a layer of ice.

He was aware of how dangerous it would be to wander from the red path which his implants were painting across the glacier field.

He only had to remind himself what had happened to Martin Setterholm.

They had found his body a month ago, shortly after their arrival on the planet. It had been near the main American base; a stroll from the perimeter of the huge, deserted complex of stilted domes and ice-walled caverns. Clavain"s friends had found dozens of dead within the buildings, and most of them had been easily identified against the lists of base personnel which the expedition had pieced together.

But Clavain had been troubled by the gaps, and had wondered if any further dead might be found in the surrounding ice fields. He had explored the warrens of the base until he found an air-lock which had never been closed, and though snowfalls had long since obliterated any footprints, there was little doubt in which direction a wanderer would have set off.

Long before the base had vanished over the horizon, Clavain had run into the edge of a deep, wide creva.s.se. And there at the bottom-just visible if he leaned close to the edge-was a man"s outstretched arm and hand. Clavain had gone back to the others and had them return with a winch to lower him into the depths, descending thirty or forty meters into a cathedral of stained and sculpted ice. The body had come into view: a figure in an old-fashioned atmospheric survival suit. The man"s legs were bent in a horrible way, like those of a strangely articulated alien. Clavain knew it was a man because the fall had jolted his helmet from its neck-ring; the corpse"s well-preserved face was pressed halfway into a pillow of ice. The helmet had ended up a few meters away.

No one died instantly on Diadem. The air was breathable for short periods, and the man had clearly had time to ponder his predicament. Even in his confused state of mind he must have known that he was going to die.

"Martin Setterholm," Clavain had said aloud, picking up the helmet and reading the nameplate on the crown. He felt sorry for him, but could not deny himself the small satisfaction of accounting for another of the dead. Setterholm had been among the missing, and though he had waited the better part of a century for it, he would at least receive a proper funeral now. There was something else, but Clavain very nearly missed it. Setterholm had lived long enough to scratch out a message in the ice. Sheltered at the base of the glacier, the marks he had gouged were still legible. Three letters, it seemed to Clavain: an I, a V and an F.

IVF.

The message meant nothing to Clavain, and even a deep search of the Conjoiner collective memory threw up only a handful of vaguely plausible candidates. The least ridiculous was in-vitro fertilization, but even that seemed to have no immediate connection with Setterholm. But then again, he had been a biologist, according to the base records. Did the message spell out the chilling truth about what had happened to the colony on Diadem: a biology lab experiment which had gone terribly wrong? Something to do with the worms, perhaps?