“Damn right,” Yugo said.

 “The theory fits.”

 “Yup. Psychohistory works.”

 Hari stared at the flexing colors. “I never thought…”

 “It could work so well?” Dors had walked behind his chair and now rubbed his scalp.

 “Well, yes.”

 “You have spent years including the proper variables. It must work.”

 Yugo smiled tolerantly. “If only more people shared your faith in mathists. You’ve forgotten the sparrow effect.”

 Dors was transfixed by the shimmering data-solids, now rerun­ ning all Trantorian history, throbbing with different-colored schemes to show up differences between real history and the equations’ post-dictions. There were very few. What’s more, they did not grow with time.

 Not taking her eyes from the display, Dors asked slowly, “Spar­ row? We have birds as pets, but surely—”

 “Suppose a sparrow flaps its wings at the equator, out in the open. That shifts the air circulation a tiny amount. If things break just right, the sparrow could trigger a tornado up at the poles.”

 Dors was startled. “Impossible!”

 Hari said, “Don’t confuse it with the fabled nail in the shoe of a horse, that a legendary beast of burden. Remember?—its rider lost a battle and then a kingdom. That was failure of a small, critical component. Fundamental, random phenomena are democratic. Tiny differences in every coupled variable can produce staggering changes.”

 It took a while to get the point through. Like any other world, Trantor’s meteorology had a daunting sensitivity to initial condi­ tions. A sparrow’s wing-flutter on one side of Trantor, amplified through fluid equations over weeks, could drive a howling hurricane a continent away. No computer could model all the tiny details of real weather to make exact predictions possible.

 Dors pointed at the data-solids. “So—this is all wrong?”

 “I hope not,” Hari said. “Weather varies, but climate holds steady.”

 “Still…no wonder Trantorians prefer indoors. Outdoors can be dangerous.”

 “The fact that the equations describe what happened—well, it means that small effects can smooth out in history,” Hari said.

 Yugo added, “Stuff on a human scale can average away.”

 She stopped massaging Hari’s scalp. “Then…people don’t mat­ ter?”

 Hari said carefully, “Most biography persuades us that people—that we—are important. Psychohistory teaches that we aren’t.”

 “As a historian, I cannot accept—”

 “Look at the data,” Yugo put in.

 They watched as Yugo brought up detail, showed off features. For ordinary people, history endured through art, myth, and liturgy. They felt it through concrete examples, close up: a building, a cus­ tom, a historical name. He and Yugo and the others were like sparrows themselves, hovering high over a landscape unguessed by the inhabitants below. They saw the slow surge of terrain, glacial and unstoppable.

 “But people have to matter.” Dors’ voice carried a note of forlorn hope. Hari knew that somewhere deep in her lurked the stern dir­ ectives of the Zeroth Law, but over that lay a deep layer of true human feeling. She was a humanist who believed in the power of the individual—and here she met blunt, uncaring mechanism, in the large.

 “They do, actually, but perhaps not in the way you want,” Hari said gently. “We sought out telltale groups, pivots about which events sometimes hinge.”

 “The homosexuals, f’instance,” Yugo said.

 “They’re about one percent of the population, a consistent minor variant in reproductive strategies,” Hari said.

 Socially, though, they were often masters of improvisation, fashioning style to substance, fully at home with the arbitrary. They seemed equipped with an internal compass that pointed them at every social novelty, early on, so that they exerted leverage all out of proportion to their numbers. Often they were sensitive indicators of future turns.

 Yugo went on, “So we figured, could they be a crucial indicator? Turns out they are. Helps out the equations.”

 Dors said severely, “Why does history smooth out?”

 Hari let Yugo carry the ball. “Y’see, that same sparrow effect had a positive side. Chaotic systems could be caught at just the right instant, tilted ever so slightly in a preferred way. A well-timed nudge could drive a system, yielding benefits all out of proportion to the effort expended.”

 “You mean control?” She looked doubtful.

 “Just a touch,” Yugo said. “Minimal control—the right nudge at the right time—demands that the dynamics be intricately under­ stood. Maybe that way, you could bias outcomes toward the least damaging of several finely balanced results. At best, they could drive the sys­ tem into startlingly good outcomes.”

 “Who’s controlling?” Dors asked.

 Yugo looked embarrassed. “Uh, we…dunno.”

 “Don’t know? But this is a theory of all history.”

 Hari said quietly, “There are elements, interplays, in the equations that we don’t grasp. Damping forces.”

 “How can you not understand?”

 Both men looked ill at ease. “We don’t know how the terms in­ teract. New features,” Hari said, “leading to…emergent order.”

 She said primly, “Then you don’t really have a theory, do you?”

 Hari nodded ruefully. “Not in the sense of a deep understanding, no.”

 Models followed the gritty, experienced world, he reflected. They echoed their times. Clockwork planetary mechanics came after clocks. The idea of the whole universe as a computation came after computers. A worldview of stable change came after nonlinear dy­ namics…

 He had a glimmering of a metamodel, which would look at him and describe how he would then select among models for psycho­ history. Peering down from above, it could see which was likely to be favored by Hari Seldon…

 “Who plans this control?” Dors persisted.

 Hari caught at the idea he had, but it slipped away. He knew how to coax it back: ease up. “Remember that joke?” he said. “How do you make God laugh?”

 She smiled. “You tell him your plans.”

 “Right. We will study this result, sniff out an answer.”

 She smiled. “Don’t ask you for predictions about the progress of your own predictions?”

 “Embarrassing, but yes.”

 His desksec chimed. “An Imperial summons,” it announced.

 “Damn!” Hari slapped his chair. “Fun’s over.”

 2.

 Not quite time for the Specials to arrive, Hari thought. But getting any work done was impossible while he was on edge.

 He jiggled coins in his pocket, distracted, then fished one out. A five cred piece, amber alloy, a handsome Cleon I head on one side—treasuries always flattered emperors—and the disk of the Galaxy seen from above on the other. He held it on edge and thought.

 Let the coin’s width represent the disk’s typical scale height. To be correct, the coin would have to bulge at its center to depict the hub, but overall it was a good geometric replica.

 In the disk was a flaw, a minute blister in an outer spiral arm. He did the ratio in his head, allowing that the galaxy was about 100,000 light-years across, and…blinked. The speck portrayed a volume about a thousand light years across. In the outer arms, that would contain ten million stars.

 To see so many worlds as a fleck adrift in immensity made him feel as though Trantor’s solidity had opened and he had plunged helplessly into an abyss.

 Could humanity matter on such a scale? So many billions of souls, packed into a grainy dot.

 Yet they had spanned the whole incomprehensible expanse of that disk in a twinkling.

 Humanity had spread through the spiral arms, spilling through the wormholes, wrapping itself around the hub in a mere few thousand years. In that time the spiral arms themselves had not revolved a perceptible angle in their own gravid gavotte; that would take half a billion years. Human hankering for far hori­ zons had sent them swarming through the wormhole webbing, popping out into spaces near suns of swelling red, virulent blue, smoldering ruby.

 The speck stood for a volume a single human brain, with its primate capacities, could not grasp, except as mathematical nota­ tion. But that same brain led humans outward, until they now strode the Galaxy, mastering the starlit abyss…without truly knowing themselves.

 So a single human could not fathom even a dot in the disk. But the sum of humanity could, incrementally, one mind at a time, knowing its own immediate starry territory.

 And what did he desire? To comprehend all of that humanity, its deepest impulses, its shadowy mechanisms, its past, present, and future. He wanted to know the vagrant species that had man­ aged to scoop up this disk, and to make it a plaything.

 So maybe one single human mind could indeed grasp the disk, by going one level higher—and fathoming the collective effects, hidden in the intricacies of the Equations.

 Describing Trantor, in this proportion, was child’s play. For the Empire, he needed a far grander comprehension.

 Mathematics might rule the galaxy. Invisible, gossamer symbols could govern.

 So a single man or woman could a matter.

 Maybe. He shook his head. A single human head.

 Getting a little ahead of ourselves, aren’t we? Dreams of godhood…

 Back to work.

 Only he couldn’t work. He had to wait. To his relief, the Imper­ ial Specials arrived and escorted him across Streeling University. By now he was used to the gawkers, the embarrassment of plowing through the crowds which now accumulated everywhere, it seemed, that he might frequent.

 “Busy today,” he said to the Specials captain.

 “Got to expect it, sir.”

 “You get extra duty pay for this, I hope.”

 “Yessir. ‘Digs,’ we call them.”

 “For extra risk, correct? Dangerous duty.”

 The captain looked flustered. “Well, yessir…”

 “If someone starts shooting, what are your orders?”

 “Uh, if they can penetrate the engaging perimeter, we’re to get

 between them and you. Sir.”

 “And you’d do that? Take a gauss pulse or a flechette?”

 He seemed surprised. “Of course.”

 “Truly?”

 “Our duty, y’know.”

 Hari was humbled by the man’s simple loyalty. Not to Hari Seldon, but to the idea of Empire. Order. Civilization.

 And Hari realized that he, too, was devoted to that idea. The Empire had to be saved, or at least its decline mitigated. Only by fathoming its deep structure could he do that.

 Which was why he disliked the First Minister business. It robbed him of time, concentration.

 In the Specials’ armored pods he salved his discontent by pulling out his tablet and working on some equations. The captain had to remind him when they reached the palace grounds. Hari got out and there was the usual security ritual, the Specials spreading out and airborne sensors going aloft to sniff out the far perimeter. They reminded him of golden bees, buzzing with vigilance.

 He walked by a wall leading into the palace gardens and a tan, round sheet the size of his fingernail popped off the wall. It stuck to his neck. He reached up and plucked it off.