Hans Rebka had spent a lot of time studying Paradox. He knew the history of the artifact's discovery, and all about the effects of its interior on incident radiation (little) and intruding sapient species (disastrous). So far as the spiral arm was concerned, Rebka qualified as a Paradox expert.
Whereas . . .
He hung in space staring back toward the inaccessible outside, then ahead to the ominous-looking central region, and was filled with a sobering thought: he really knew next to nothing about the structure, nature, or origin of Paradox.
There had certainly been changes—nothing in Paradox's history spoke of irreversible movement within it, or of an isolated torus at the center. But changes how, when, and why?
Another couple of attempts showed that any attempt to move toward the outer surface was a waste of fuel and energy. He turned off his suit's thrust. That was when he realized that the situation was worse than he had thought. In principle he should be hovering at a fixed location within Paradox. In practice he was drifting, slowly but steadily, toward the center. He could move tangentially without any problem, but always there was a small radial component carrying him farther inward.
His next action was instinctive, the result of twenty years of hard experience. He did not think about it or try to explain it, although E.C. Tally, had he been present, could have done so in his own terms. When a computing problem of exceptional size and urgency was encountered, all subsidiary computation should be halted. Peripheral activities must go into complete stand-by mode, in favor of work on the single central problem.
Of course, Tally regarded humans as very handicapped by virtue of inefficient design. A major part of human central nervous activity went into simple maintenance work, so that total power-down of peripherals or unwanted memory banks was not feasible.
But given those built-in limitations, Hans Rebka came pretty close to E.C. Tally's ideal. Rebka did not give a thought to Tally, or his own situation, or to anything that might be happening outside Paradox. He did not waste time with more experiments in tangential movement, or futile back-up attempts, or even in speculation as to the reason for his forward motion. Every scrap of his attention focused on the fat donut-disk twenty kilometers ahead of him. Unless something changed, he would be arriving there in an hour or so. Better be ready.
The outside of the donut was studded with dark markings, possible openings. They indicated that the disk was slowly rotating. At first they seemed no more than tiny pock marks, but as Hans came closer he could see a shape to each of them. They were like scores of little black diamonds, irregularly spaced around the disk, the long diagonal of each parallel to the disk's main axis. What had appeared from a distance to be a central hole right through the disk, making it into a plump torus, now was of more ambiguous nature. There was certainly a darkness at the center, but the black was touched with cloudiness and a hint of structure that did not match Rebka's concept of empty space.
He stared until his vision blurred. What could give that impression, of simultaneous presence and absence? Nothing in his experience.
No matter. Unless something changed, he would soon be able to find out by direct experience. His inward progress had not slowed. If anything, he was moving faster. Maybe ten more minutes to the center.
Now his ability to move tangentially
was
important—because he suddenly had a choice. Not much of one, in normal terms, but he could aim for one of the diamond-shaped openings on the side of the disk, or else head for the black swirl at the center.
Which?
Assume that his inability to move farther from the center continued. Then he could enter one of the diamonds, and if that proved useless he might still be able to go on and see what lay in the darkness at the disk's center. Explore the black region first, and there would be no later chance to visit the diamonds.
Maximize your number of options.
Decision made.
The disk was rotating, but very slowly. Rendezvous should present no problem. He could count half a dozen different diamonds along the edge, each looking as good as any other. Rebka picked one at random and used his suit thrustor to match angular velocity with it. Then it was only a matter of watching and waiting, making sure that no anomalous increase in his own radial speed threw him off target.
The opening was bigger than it had seemed from a distance, maybe twenty meters on the diamond's long axis and fifteen on the short. Rebka aimed right for the middle, wondering in the final seconds if he was about to be dissociated to individual atoms, squeezed to a pinpoint of nuclear density matter, or spun a hundred thousand light-years out of the spiral arm to intergalactic space.
He felt a slight resistance as he entered the opening, as though he was passing through a thin film of sticky material. Then he was inside, tensed and quiveringly ready for whatever life-preserving action might be necessary. A sharp note within his helmet told him to glance at the monitors. He observed that the temperature outside his suit had gone instantly from the bleak frigidity of interstellar space to that of a pleasant spring morning on Sentinel Gate.
What else had changed?
Speculation ahead of time would have been a waste of effort, so before entering the diamond he had not allowed himself the indulgence of wondering what he might find inside. In spite of that, he must have carried somewhere in the back of his head a list of things he definitely did
not
expect to encounter when he went through the opening. Otherwise, there would have been no reason for his astonishment at what he saw when he emerged into the interior.
He was in a room like a misshapen cube. One dimension was the full width of the disk, with curved ceiling and floor that followed the shape of the torus. On either side the plane walls stretched away, to make a chamber at least forty meters across. Every square inch of those walls was occupied by cabinets, nozzles, troughs, gas supply lines, faucets, and hoses. Thousand after thousand of them, in all shapes and sizes.
Rebka moved to the far wall of the chamber, closest to the center of Paradox. It was rock-solid, seamless, and resonated a deep boom under a blow from his fist. No way out through that.
He went to inspect the wall on his right. The first units he came to were apparently a line of gas dispensers. There were no dials, indicators or instructions, but it was hard to mistake the turncocks for anything else. Rebka cautiously cracked one open. He waited for his suit's sensors to sample what came out, then turned the gas stream off at once. Fluorine! Poisonous, highly reactive, and no knowing how much of it the unit would supply. Maybe enough to fill the whole chamber, assuming the membrane at the entrance was able to hold an atmosphere.
Hans moved along the line, trying each dispenser. Chlorine, helium, nitrogen, neon, hydrogen, methane, carbon dioxide, ammonia. Oxygen. He might starve here or die of thirst, but he was not going to asphyxiate. He could recharge the air supply of his suit, matching it to any preferred proportion of gases. In fact—he eyed the line of units, stretching away in both directions—it would not be surprising if some dispensers offered mixtures of gases. Certainly he saw far more dispensers than were needed to offer the gaseous elements and their simplest compounds.
It was tempting to test that idea. Instead, he turned his attention to smaller units farther along the wall. These provided liquids instead of gases. His suit was able to identify only the simplest as he permitted small samples of each to touch the sensors. Methyl alcohol, acetone, ethyl alcohol, benzene, ether, toluene, carbon tetrachloride.
Water.
He paused for a long time when that sample was identified.
Drink me.
Except that in this case he almost certainly could, and with no ill-effects. His suit pronounced the water pure and potable.
Far more purposefully, he headed for the cabinets and nozzles. It was no particular surprise to find that he could travel freely in that direction, even though it took him away from the center of Paradox. Something had restricted his movement before, but apparently it now had him where it wanted him. It was also no surprise to find that the things that looked like supply cabinets and feeding nozzles were exactly that. The variety of foods dispensed was bewildering, and most of it was certainly not to human tastes. But that was natural. Somewhere along these walls he could probably find a food supply suitable for any species in the spiral arm. It was just a matter of seeking out the ones designed for humans.
Rebka didn't bother. He had suit supplies for several days. He hovered in position close to the wall and banged on it with a gloved fist. Solid, although without the resonant feeling of the inner wall.
Time to start thinking again, and of more than mere survival. The "old" Paradox had permitted explorers to enter or leave, but wiped their minds clear of all memories before they left. The "new" Paradox did not affect the mind, since Rebka certainly felt normal, but it steered anyone entering to the central region. Where, unless something changed, they would stay.
And do what?
The ways of the Builders were a mystery, even to specialists like Darya Lang and Quintus Bloom. But who could accept the idea of carefully herding a man to the middle of an artifact, providing all the physical necessities of life, and then leaving him alone until he died? That was not merely not logical, it was
anti
-logical.
Assume that the Builders, even if they recognized a different set of physical laws, followed the same laws of logic. Assume that the events within Paradox had been designed using those laws of logic. Then what was happening now? More important, what would happen next?
Curiously enough, Hans could think of one possibility.
Paradox was millions of years old, but it had not always been like this. A year ago, or half a year ago, or sometime recently, it had changed dramatically. Now it captured anyone who entered, and brought them to the central region. But not to die. The chamber walls showed that any creature of even modest intelligence could survive here for a very long time.
And then?
One of two things. The prisoner would remain here, until something else happened. A disquieting thought, given the huge time scales over which the Builders had operated. Or the prisoner, suit recharged, would be free to leave this chamber, and perhaps fulfill some other function within Paradox.
The second possibility meant that Hans might be able to exit the room that he was in. He wandered slowly along the supply lines, dumping used air and wastes from his suit into disposal hoses, and taking on air, food, reaction mass, and water. When his suit was charged to its maximum level, he headed for the diamond of the entrance. He could see, far off, the shimmering outer barrier of Paradox. A tiny step, in terms of normal space distances. A long, long way, if the restraining field still operated outside this room.
No point in waiting. Hans launched himself toward the opening. He went sailing outward, feeling for a second the tug of the membrane at the entrance. Then he was through, outside and floating free.
Except that he wasn't. He felt no force on him, but after a few seconds he glanced back to the surface of the torus and knew that he was not moving outward. Instead, he was slowly, very slowly, beginning the slide back in toward the waiting diamond.
Cross that one off. Rebka took a last yearning look at the outside before he dropped back into the interior. He saw the glowing surface of Paradox—the shimmering rainbow background—the stars beyond; and outlined there, like a black silhouette, a suited figure.
A suit designed for occupancy by humans. A suit that was diving at enormous speed in toward the center.
A suit that surely didn't—did it?—hold a half-witted, numbskull, embodied computer known as E.C. Tally.
"Hey!" Rebka was shouting and waving, as he slid slowly back down into the depths of the torus. "Tally, is that you? This way. Slow down! I said,
this way
, you idiot!"
The suit communicator was not working—could not be working. Certainly the approaching figure showed no sign of seeing or hearing anything. It went zooming in, on maximum thrust, toward an opening farther around the disk. While Rebka was still screaming and waving and sinking slowly into the diamond entrance, the newcomer vanished from view.
Ten seconds later, Rebka was back inside. E.C. Tally, in terms of physical distance, might be no more than a hundred meters away. In terms of meeting, or even communicating, he could as well have been in another galaxy. And Hans Rebka was face to face with his first alternative: he himself would remain, stuck in this one chamber, until something else happened.
Or?
Or he must somehow find his own way out.
Rebka had been in difficult situations before. To get out of them, you had to think at the extreme limit of your abilities. To make such thinking possible, you began with a few simple rules.
He ate some of the new food. Tolerable. Drank a little water. Perfectly acceptable.
And now the hard part.
Relax. Impossible! No. Hard, but you can do it.
Rebka dimmed his suit visor. He turned his mind inward, and listened to the beat of his own pulse. Three minutes later he was asleep.
E.C. Tally had strangely mixed feelings about his body. On the one hand, he absolutely needed it, otherwise his embodied brain could neither communicate nor move. On the other hand, he recognized that the body itself was an sadly frail vessel. The essential E.C. Tally, contained within the matrix of his computer brain, could function in an acceleration of a thousand gravities, a field which would squash his human form into a shallow pool of mashed bones and liquids. He could handle temperatures of a couple of thousand degrees, enough to leave behind only a few teeth from his surrounding body.
And this was, of course, his
second
body. The second one would never be quite the same. He could not admit it to anyone, but he had felt far more committed to the preservation of his first embodiment. He would treat this one well, of course, and maintain it in working order if he possibly could, but if and when it failed . . .