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"I understand you so far," said Dors, sounding a little surprised

"Well then, we know that sos are easy to sirow more and more complex they become harder to simulate until finally they become impossible to simulate But at what level of complexity does si use of a mathematical technique first invented in this past century and barely usable even if one ee and very fast computer, our Galactic society falls short of that mark It can be represented by a simulation simpler than itself And I went on to show that this would result in the ability to predict future events in a statistical fashion-that is, by stating the probability for alternate sets of events, rather than flatly predicting that one set will take place"

"In that case," said Hummin, "since you can profitably si so Why is it impractical?"

"All I have proved is that it will not take an infinite time to understand Galactic society, but if it takes a billion years it will still be impractical That will be essentially the sa it would take? A billion years?"

"I haven’t been able to work out how long it would take, but I strongly suspect that it will take at least a billion years, which is why I suggested that number"

"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"

Hureat 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"

Huht 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 reain "Tellthat’s totally marinated in mathematics"

"Nohistory in the library reminded me that Galactic society was less coo, when the E established, the Galaxy contained only about ten o, the pre-Iether Still deeper in the past, who kno society shrinks down? Perhaps even to a single world as in the legends you yourself once mentioned, Huht be able to work out psychohistory if you dealt with a much simpler Galactic society?"

"Yes, it seeht 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 froht happen a thousand years after the formation of the Empire-you could then check the actual situation at that time and see how near thethat 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 GE very well and ould have to dig After all, that was eleven o"

Seldon’s face turned into a picture of dismay "What do you mean we don’t know the situation in 1,000 GE very well? There were computers then, weren’t there, Dors?"

"Of course"

"And s of ear and eye? We should have all the records of 1,000 GE as we have of the present year of 12,020 GE"

"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 GE, 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 Anytime, eventually drowns in accumulated noise They say that fully one third of the records in the Iibberish, 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-governh for thousands of years, so that many of the essential points of Galactic history remain known even if they took place in pre-Io, the less there is preserved"

"I can’t believe that," said Seldon "I should think that new copies would beHow could you let knowledge disappear?"

"Undesired knowledge is useless knowledge," said Dors "Can you iy 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 so so carelessly disposed of"

"A particular iteht 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 priravitation 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 rows smaller, a useful psychohistory becoe dwindles even more rapidly than size, so psychohistory becohs the en Sector," said Dors,

Hummin looked up quickly "So there is and that would be the perfect place to put Seldon I should have thought of itfroen Sector?"

"Hari, please, I’ll tell you later Right now, I have preparations to ht"

33

Dors had urged Seldon to sleep a bit They would be leaving halfway between lights out and lights on, under cover of "night," while the rest of the University slept She insisted he could still use a little rest

"And have you sleep on the floor again?" Seldon asked

She shrugged "The bed will only hold one and if we both try to crowd into it, neither of us will get rily for a moment and said, "Then I’ll sleep on the floor this time"

"No, you won’t I wasn’t the one who lay in a coma in the sleet"

As it happened, neither slept Though they darkened the rooh the perpetual hum of Trantor was only a drowsy sound in the relatively quiet confines of the University, Seldon found that he had to talk He said, "I’ve been so much trouble to you, Dors, here at the University I’ve even been keeping you from your work Still, I’m sorry I’ll have to leave you"

Dors said, "You won’t leavea leave of absence for me"

Seldon said, dismayed, "I can’t ask you to do that"

"You’re not Huuard you After all, I faded in connection with Upperside and should make up for it"

"I told you Please don’t feel guilty about that-Still, I must admit I would feel more comfortable with you atwith your life"

Dors said softly, "You’re not, Hari Please go to sleep"

Seldon lay silent for a while, then whispered, "Are you sure Hu, Dors?"

Dors said, "He’s a reot influence here at the University and everywhere else, I think If he says he can arrange for an indefinite leave for me, I’m sure he can He is a most persuasive man"

"I know," said Seldon "Sometimes I wonder what he really wants of me"

"What he says," said Dors "He’s aand idealistic ideas and dreah you know him well, Dors"

"Oh yes, I know him well"

"Intimately?"

Dors , Hari, but, assu the most insolent interpretation- No, I don’t know him intimately What business would that be of yours anyway?"

"I’m sorry," said Seldon "I just didn’t want, inadvertently, to be invading someone else’s-"

"Property? That’s even o to sleep"

"I’ain, Dors, but I can’t sleep Let e the subject You haven’t explained what the Mycogen Sector is Why will it be good for o there? What’s it like?"

"It’s a small sector with a population of only about two enians cling tightly to a set of traditions about early history and are supposed to have very ancient records not available to anyone else It’s just possible they would be of more use to you in your attempted exaht be All our talk about early history brought the sector to mind"

"Have you ever seen their records?"

"No I don’t know anyone who has"

"Can you be sure that the records really exist, then?"

"Actually, I can’t say The assuenians is that they’re a bunch of madcaps, but that may be quite unfair They certainly say they have records, so perhaps they do In any case, ould be out of sight there The Mycogenians keep strictly to theo to sleep"

And somehow Seldon finally did

34

Hari Seldon and Dors Venabili left the University grounds at 0300 Seldon realized that Dors had to be the leader She knew Trantor better than he did-two years better She was obviously a close friend of Hu at him) and she understood his instructions Both she and Seldon were swathed in light swirling docks with tight-fitting hoods The style had been a short-lived clothing fad at the University (and ah right now itthenizable-at least at a cursory glance

Hummin had said, "There’s a possibility that the event Upperside was coents after you, Seldon, but let’s be prepared for the worst"

Seldon had asked anxiously, "Won’t you come with us?"

"I would like to," said Hummin, "but I et hed He understood

They entered an Expressway car and found a seat as far as possible from the feho had already boarded (Seldon wondered why anyone should be on the Expressways at three in the ht that it was lucky some were or he and Dors would be entirely too conspicuous)

Seldon fell to watching the endless panorama that passed in review as the equally endless line of coaches netic field

The Expressway passed row upon row of dwelling units, few of them very tall, but some, for all he knew, very deep Still, if tens of millions of square kilometers formed an urbanized total, even forty billion people would not require very tall structures or very closely packed ones They did pass open areas, in -but some of which were clearly parklike And there were nuuess Factories? Office buildings? Who knew? One large featureless cylinder struck hiht be a water tank After all, Trantor had to have a fresh water supply Did they sluice rain from Upperside, filter and treat it, then store it? It see to study the vieever

Dorsoff" She stood up and her strong fingers gripped his ar on solid flooring while Dors studied the directional signs

The signs were unobtrusive and there were many of theraphs and initials, which were undoubtedly understandable to native Trantorians, but which were alien to him

"This way," said Dors

"Which way? How do you know?"

"See that? Tings and an arrow"

"Tings? Oh" He had thought of it as an upside-doide and shallow, but he could see where it s of a bird "Why don’t they use words?" he said sullenly

"Because words vary from world to world What an ’air-jet’ is here could be a ’soar’ on Cinna or a ’swoop’ on other worlds The tings and an arrow are a Galactic symbol for an air vessel and the symbol is understood everywhere Don’t you use them on Helicon?"

"Not eneous world, culturally speaking, and we tend to cling to our private ways firhbors"

"See?" said Dors "There’s where your psychohistory ht come in You could show that even with different dialects the use of set sy force"

"That won’t help" He was following her through empty dim alleyways and part of his ht be on Trantor and whether this was a high-crile phenoeneralizations from that That’s what one ht be interpreted only by afor an air-jet?"

She stopped and turned to look at hi the sy to reach a golf course? Are you afraid of air-jets in the way so many Trantorians are?"

"No, no We fly freely on Helicon and I make use of air-jets frequently It’s just that when Hummin took me to the University, he avoided coht ould leave too clear a trail"

"That’s because they knehere you were to begin with, Hari, and were after you already Right now, it may be that they don’t knohere you are and we’re using an obscure port and a private air-jet"

"And who’ll be doing the flying?"

"A friend of Hummin’s, I presume"

"Can he be trusted, do you suppose?"

"If he’s a friend of Hummin’s, he surely can"

"You certainly think highly of Hue of discontent

"With reason," said Dors with no attempt at coyness "He’s the best"

Seldon’s discontent did not dwindle

"There’s the air-jet," she said

It was a s beside it was a s Trantorian colors

Dors said, "We’re psycho"

The pilot said, "And I’m history"

They followed him into the air-jet and Seldon said, "Whose idea were the passwords?"

"Hummin’s," said Dors

Seldon snorted "Somehow I didn’t think Hummin would have a sense of humor He’s so solemn"

Dors smiled