“Very well. That is a reasonable, and defensible, position. It is based on an implicit assumption that twin Histories, after their split, do not affect each other in any way. Technically speaking, you are assuming that Quantum-Mechanical Operators are linear… But,” and now that note of excitement returned to his voice, “it turns out there may be a way to talk to the other History — if, on some fundamental level, the universe and its twin do remain entangled. If there is the smallest amount of Nonlinearity in the Quantum Operators — almost too small to detect—”

“Then such communication would be possible?”

“I have seen it done… in the Sea, I mean… the Constructors have managed it, but only on the smallest of experimental scales.”

Nebogipfel described to me what he called an “Everett phonograph” — “after the twentieth-century scientist, of your History, who first dreamed up the idea. Of course the Constructors have another label — but it is not easily rendered into English.”

The Nonlinearities of which Nebogipfel spoke worked at the most subtle of levels.

“You must imagine that you perform a measurement — perhaps of the spin of an atom.” He described a “Nonlinear” interaction between an atom’s spin and its magnetic field. “The universe splits in two, of course, depending on the experiment’s outcome. Then, after the experiment, you allow the atom to pass through your Nonlinear field. This is the anomalous Quantum Operator I mentioned. Then — it turns out you can arrange affairs so that your action in one History depends on a decision taken in the second History…”

He went into a great deal of detail about this, involving the technicalities of what he called a “Stem-Gerlach device,” but I let this wash past me; my concern was to grasp the central point.

“So,” I interrupted him, “is it possible? Are you telling me that the Constructors have invented such inter-History communication devices? Is our table one such?” I began to feel excitement at the thought. All this chatter of billiard balls and spinning atoms was all very well; but if I could talk, by some Everett phonograph, to my selves in other Histories — perhaps to my home in Richmond in 1891…

But Nebogipfel was to disappoint me. “No,” he said. “Not yet. The table utilizes the Nonlinear effect, but only to — ah — to highlight particular Histories. At least some selection, some control, over the processes is displayed, but… The effects are so small, you see. And the Nonlinearities are suppressed by time evolution.”

“Yes,” I said with impatience, “but what is your guess? By placing this table here, is our Constructor trying to tell us that all this stuff — Nonlinearity, and communication between Histories — that it’s all important to us?”

“Perhaps,” Nebogipfel said. “But it is certainly important to him.”

Nebogipfel reconstructed something of the history of Humanity, across fifty million years. Much of this picture was tentative, he warned me — an edifice of speculation, founded on the few unambiguous facts he had been able to retrieve from the Information Sea.

There had probably been several waves of star colonization by man and his descendants, said Nebogipfel. During our journey through time in the car, we had seen the launch of one generation of such ships, from the Orbital City.

“It is not difficult to build an interstellar craft,” he said, “if one is patient. I imagine your 1944 friends in the Palaeocene could have devised such a vessel a mere century or two after we left them. One would need a propulsion unit, of course — a chemical, ion or laser rocket; or perhaps a solar sail of the type we have observed. And there are strategies to use the resources of the solar system to escape from the sun. You could, for instance, swing past Jupiter, and use that planet’s bulk to hurl your star-ship in towards the sun. With a boost at perihelion, you could very easily reach solar escape velocity.”

“And then one would be free of the solar system?”

“At the other end a reverse of the process, the exploitation of the gravity wells of stars and planets, would be necessary, to settle into the new system. It might take ten, a hundred thousand years to complete such a journey, so great are the gulfs between the stars…”

“A thousand centuries? But who could survive so long? What ship — the supply question alone—”

“You miss the point,” he said. “One would not send humans. The ship would be an automaton. A machine, with manipulative skills, and intelligence at least equivalent to a human’s. The task of the machine would be to exploit the resources of the destination stellar system — using planets, comets, asteroids, dust, whatever it could find — to construct a colony.”

“Your ’automatons,’ “ I remarked, “sound rather like our friends, the Universal Constructors.”

He did not reply.

“I can see the use of sending a machine to gather information. But other than that — what is the point? What is the meaning of a colony without humans?”

“But such a machine could construct anything, given the resources and sufficient time,” the Morlock said. “With cell synthesis and artificial womb technology, it could even construct humans, to inhabit the new colony. Do you see?”

I protested at this — for the prospect seemed unnatural and abhorrent to me — until I remembered, with reluctance, that I had once watched the “construction” of a Morlock, in just such a fashion!

Nebogipfel went on, “But the probe’s most important task would be to construct more copies of itself. These would be fueled up — for example, with gases mined from the stars — and sent on, to further star systems.

“And so, slow but steady, the colonization of the Galaxy would proceed.”

“But,” I protested, “even so, it would take so much time. Ten thousand years to reach the nearest star, which is some light years away—”

“Four.”

“And the Galaxy itself—”

“Is a hundred thousand light years across. It would be slow,” he said. “At least at first. But then the colonies would begin to interact with each other. Do you see? Empires could form, straddling the stars. Other groups would oppose the empires. The diffusion would slow further… but it would proceed, inexorably. By such techniques as I have described, it would take tens of millions of years to complete the colonization of the Galaxy — but it could he done. And, since it would be impossible to recall or redirect the mechanical probes, once launched, it would be done. It must have been done by now, fifty million years after the founding of First London.”

He went on, “The first few generations of Constructors were, I think, built with anthropocentric constraints incorporated into their awareness. They were built to serve man. But these Constructors were not simple mechanical devices — these were conscious entities. And when they went out into the Galaxy, exploring worlds undreamed of by man and redesigning themselves, they soon passed far beyond the understanding of Humanity, and broke the constraints of their authors… The machines broke free.”

“Great Scott,” I said. “I can’t imagine the military chaps of that remote Age taking to that idea very kindly.”

“Yes. There were wars… The data is fragmented. In any event, there could be only one victor in such a conflict.”

“And what of men? How did they take to all this?”

“Some well, some badly.” Nebogipfel twisted his face a little and swiveled his eyes. “What do you think? Humans are a diverse species, with multiple and fragmented goals — even in your day; imagine how much more diverse things became when people were spread across a hundred, a thousand star systems. The Constructors, too, rapidly fragmented. They are more unified as a species than man has ever been, by reason of their physical nature, but because of the much greater Information pool to which they have access — their goals are far more complex and varied.”