Conversation had run out after that and Seldon watched the structures of the Streeling Sector as they passed. Some were quite low, while some seemed to brush the "sky." Wide crosspassages broke the progression and frequent alleys could be seen.
At one point, it struck him that though the buildings rose upward they also swept downward and that perhaps they were deeper than they were high. As soon as the thought occurred to him, he was convinced it was true. Occasionally, he saw patches of green in the background, farther back from the Expressway, and even small trees.
He watched for quite a while and then became aware that the light was growing dimmer. He squinted about and turned to Hummin, who guessed the question.
"The afternoon is waning," he said, "and night is coming on."
Seldons eyebrows raised and the corners of his mouth turned downward. "Thats impressive. I have a picture of the entire planet darkening and then, some hours from now, lighting up again."
Hummin smiled his small, careful smile. "Not quite, Seldon. The planet is never turned off altogether--or turned on either. The shadow of twilight sweeps across the planet gradually, followed half a day later by the slow brightening of dawn. In fact, the effect follows the actual day and night above the domes quite closely, so that in higher altitudes day and night change length with the seasons."
Seldon shook his head, "But why close in the planet and then mimic what would be in the open?"
"I presume because people like it better that way. Trantorians like the advantages of being enclosed, but they dont like to be reminded of it unduly, just the same. You know very little about Trantorian psychology, Seldon."
Seldon flushed slightly. He was only a Heliconian and he knew very little about the millions of worlds outside Helicon. His ignorance was not confined to Trantor. How, then, could he hope to come up with any practical applications for his theory of psychohistory?
How could any number of people--all together--know enough? It reminded Seldon of a puzzle that had been presented to him when he was young: Can you have a relatively small piece of platinum, with handholds affixed, that could not be lifted by the bare, unaided strength of any number of people, no matter how many?
The answer was yes. A cubic meter of platinum weighs 22,420 kilograms under standard gravitational pull. If it is assumed that each ............