"But you don't really know."
"I've been trying to work it out."
"Without success?"
"Without success."
"The University library does not help?" Hummin cast a look at Dors as he asked the question.
Seldon shook his head slowly. "Not at all."
"Dors can't help?"
Dors sighed. "I know nothing about the subject, Chetter. I can only suggest ways of looking. If Hari looks and doesn't find, I am helpless."
Hummin rose to his feet. "In that case, there is no great use in staying here at the University and I must think of somewhere else to place you."
Seldon reached out and touched his sleeve. "Still, I have an idea."
Hummin stared at him with a faint narrowing of eyes that might have belied surprise-or suspicion. "When did you get the idea? Just now?"
"No. It's been buzzing in my head for a few days before I went Upperside. That little experience eclipsed it for a while, but asking about the library reminded me of it."
Hummin seated himself again. "Tell me your idea-if it's not something that's totally marinated in mathematics."
"No mathematics at all. It's just that reading history in the library reminded me that Galactic society was less complicated in the past. Twelve thousand years ago, when the Empire was on the way to being established, the Galaxy contained only about ten million inhabited worlds. Twenty thousand years ago, the pre-Imperial kingdoms included only about ten thousand worlds altogether. Still deeper in the past, who knows how society shrinks down? Perhaps even to a single world as in the legends you yourself once mentioned, Hummin."
Hummin said, "And you think you might be able to work out psychohistory if you dealt with a much simpler Galactic society?"
"Yes, it seems to me that I might be able to do so."
"Then too," said Dors with sudden enthusiasm, "suppose you work out psychohistory for a smaller society of the past and suppose you can make predictions from a study of the pre-Imperial situation as to what might happen a thousand years after the formation of the Empire-you could then check the actual situation at that time and see how near the mark you were."
Hummin said coldly, "Considering that you would know in advance the situation of the year 1,000 of the Galactic Era, it would scarcely be a fair test. You would be unconsciously swayed by your prior knowledge and you would be bound to choose values for your equation in such a way as to give you what you would know to be the solution."
"I don't think so," said Dors. "We don't know the situation in 1,000 G.E. very well and we would have to dig. After all, that was eleven millennia ago."
Seldon's face turned into a picture of dismay. "What do you mean we don't know the situation in 1,000 G.E. very well? There were computers then, weren't there, Dors?"
"Of course."
"And memory storage units and recordings of ear and eye? We should have all the records of 1,000 G.E. as we have of the present year of 12,020 G.E."
"In theory, yes, but in actual practice- Well, you know, Hari, it's what you keep saying. It's possible to have full records of 1,000 G.E., but it's not practical to expect to have it."
"Yes, but what I keep saying, Dors, refers to mathematical demonstrations. I don't see the applications to historical records."
Dors said defensively, "Records don't last forever, Hari. Memory banks can be destroyed or defaced as a result of conflict or can simply deteriorate with time. Any memory bit, any record that is not referred to for a long time, eventually drowns in accumulated noise. They say that fully one third of the records in the Imperial Library are simply gibberish, but, of course, custom will not allow those records to be removed. Other libraries are less tradition-bound. In the Streeling University library, we discard worthless items every ten years.
"Naturally, records frequently referred to and frequently duplicated on various worlds and in various libraries-governmental and private-remain clear enough for thousands of years, so that many of the essential points of Galactic history remain known even if they took place in pre-Imperial times. However, the farther back you go, the less there is preserved."
"I can't believe that," said Seldon. "I should think that new copies would be made of any record in danger of withering. How could you let knowledge disappear?"
"Undesired knowledge is useless knowledge," said Dors. "Can you imagine all the time, effort, and energy expended in a continual refurbishing of unused data? And that wastage would grow steadily more extreme with time."
"Surely, you would have to allow for the fact that someone at some time might need the data being so carelessly disposed of."
"A particular item might be wanted once in a thousand years. To save it all just in case of such a need isn't cost-effective. Even in science. You spoke of the primitive equations of gravitation and say it is primitive because its discovery is lost in the mists of antiquity. Why should that be? Didn't you mathematicians and scientists save all data, all information, back and back to the misty primeval time when those equations were discovered?"
Seldon groaned and made no attempt to answer. He said, "Well, Hummin, so much for my idea. As we look back into the past and as society grows smaller, a useful psychohistory becomes more likely. But knowledge dwindles even more rapidly than size, so psychohistory becomes less likely-and the less outweighs the more."
"To be sure, there is the Mycogen Sector," said Dors, musing.
Hummin looked up quickly. "So there is and that would be the perfect place to put Seldon. I should have thought of it myself."