For a moment master and pupil regarded each other pensively, each perhaps seeing the other’s point of view more clearly than ever before in his life. Then, with one impulse, they turned together down the long passage from the Council Chamber, with their escort still following patiently in the rear.

This world, Alvin knew, had not been made for man. Under the glare of the fierce blue lights-so dazzling that they pained the eyes-the long, broad corridors seemed to stretch to infinity. Down these great passageways, the robots of Diaspar must come and go throughout their endless lives, yet not once in centuries did they echo to the sound of human feet.

Here was the underground city, the city of machines without which Diaspar could not exist. A few hundred yards ahead, the corridor would open into a circular chamber more than a mile across, its roof supported by great columns that must also bear the unimaginable weight of Power Center. Here, according to the maps, the Central Computer brooded eternally over the fate of Diaspar.

The chamber was there, and it was even vaster than Alvin had dared imagine but where was the Computer? Somehow he had expected to meet a single huge machine, naive though he knew that this conception was. The tremendous but meaningless panorama beneath him made him pause in wonder and uncertainty.

The corridor along which they had come ended high in the wall of the chamber-surely the largest cavity ever built by man-and on either side long ramps swept down to the distant floor. Covering the whole of that brilliantly lit expanse were hundreds of great white structures, so unexpected that for a moment Alvin thought he must be looking down upon a subterranean city. The impression was startlingly vivid, and it was one that he never wholly lost. Nowhere at all was the sight he had expected-the familiar gleam of metal which since the beginning of time man had learned to associate with his servants.

Here was the end of an evolution almost as long as Man’s. Its beginnings were lost in the mists of the Dawn Ages, when humanity had first learned the use of power and sent its noisy engines clanking about the world. Steam, water, wind-all had been harnessed for a little while and then abandoned. For centuries the energy of matter had run the world until it too had been superseded, and with each change the old machines were forgotten and new ones took their place. Very slowly, over thousands of years, the ideal of the perfect machine was approached-that ideal which had once been a dream, then a distant prospect, and at last reality:

No machine may contain any moving parts.

Here was the ultimate expression of that ideal. Its achievement had taken Man perhaps a hundred million years, and in the moment of his triumph he had turned his back upon the machine forever. It had reached finality, and thenceforth could sustain itself eternally while serving him.

Alvin no longer asked himself which of these silent white presences was the Central Computer. He knew that it comprised them all-and that it extended far beyond this chamber, including within its being all the countless other machines in Diaspar, whether they were mobile or motionless. As his own brain was the sum of many billion separate cells, arrayed throughout a volume of space a few inches across, so the physical elements of the Central Computer were scattered throughout the length and breadth of Diaspar. This chamber might hold no more than the switching system whereby all these dispersed units kept in touch with one another.

Uncertain where to go next, Alvin stared down the great sweeping ramps and across the silent arena. The Central Computer must know that he was here, as it knew everything that was happening in Diaspar. He could only wait for its instructions.

The now-familiar yet still awe-inspiring voice was so quiet and so close to him that he did not believe that his escort could also hear it. «Go down the left-hand ramp,» it said. «I will direct you from there.»

He walked slowly down the slope, the robot floating above him. Neither Jeserac nor the proctors followed; he wondered if they had received orders to remain here, or whether they had decided that they could supervise him just as well from their vantage point without the bother of making this long descent. Or perhaps they had come as close to the central shrine of Diaspar as they cared to approach.

At the foot of the ramp, the quiet voice redirected Alvin, and he walked between an avenue of sleeping titan shapes. Three times the voice spoke to him again, until presently he knew that he had reached his goal.

The machine before which he was standing was smaller than most of its companions, but he felt dwarfed as he stood beneath it. The five tiers with their sweeping horizontal lines gave the impression of some crouching beast, and looking from it to his own robot Alvin found it hard to believe that both were products of the same evolution, and both described by the same word.

About three feet from the ground a wide transparent panel ran the whole length of the structure. Alvin pressed his forehead agaipst the smooth, curiously warm material and peered into the machine. At first he saw nothing then, by shielding his eyes, he could distinguish thousands of faint points of light hanging in nothingness. They were ranged one beyond the other in a three-dimensional lattice, as strange and as meaningless to him as the stars must have been to ancient man. Though he watched for many minutes, forgetful of the passage of time, the colored lights never moved from their places and their brilliance never changed.

If he could look into his own brain, Alvin realized, it would mean as little to him. The machine seemed inert and motionless because he could not see its thoughts.

For the first time, he began to have some dim understanding of the powers and forces that sustained the city. All his life he had accepted without question the miracle of the synthesizers which age after age provided in an unending stream all the needs of Diaspar. Thousands of times he had watched that act of creation, seldom remembering that somewhere must exist the prototype of that which he had seen come into the world.

As a human mind may dwell for a little while upon a single thought, so the infinitely greater brains which were but a portion of the Central Computer could grasp and hold forever the most intricate ideas. The patterns of all created things were frozen in these eternal minds, needing only the touch of a human will to make them reality.

The world had indeed gone far since, hour upon hour, the first cavemen had patiently chipped their arrowheads and knives from the stubborn stone.

Alvin waited, not caring to speak until he had received some further sign of recognition. He wondered how the Central Computer was aware of his presence, and could see him and hear his voice. Nowhere were there any signs of sense organs-none of the grilles or screens or emotionless crystal eyes through which robots normally had knowledge of the world around them.

«State your problem,» said the quiet voice in his ear. It seemed strange that this overwhelming expanse of machinery should sum up its thoughts so softly. Then Allvin realized that he was flattering himself; perhaps not even a millionth part of the Central Computer’s brain was dealing with him.

He was just one of the innumerable incidents that came to its simultaneous attention as it watched over Diaspar. It was hard to talk to a presence who filled the whole of the space around you. Alvin’s words seemed to die in the empty air as soon as he had uttered them.

«What am I?» he asked.

If he had put that question to one of the information machines in the city, he knew what the reply would have been. Indeed, he had often done so, and they had always answered, «You are a Man.» But now he was dealing with an intelligence of an altogether different order, and there was no need for painstaking semantic accuracy. The Central Computer would know what he meant, but that did not mean that it would answer him.