I imagined moon-men: Selenites, as we might call them, themselves descended from Humanity. The Selenites must have watched the lethal progress of the great fires which broke across the crust of the oxygen-choked earth. The Selenites had known that men still lived on the earth — but they were men fallen from civilization, men living as savages, even as animals once more, sliding back into some pre-rational state. Perhaps the collapse of the earth impacted them too — for it may be that Selenite society could not survive without provision from Mother Earth.

The Selenites could grieve for their cousins on the Mother World, but could not reach them… and so they attempted to signal. They built their immense mirror — it must have been half a mile across, or more, to be visible across inter-planetary distances.

The Selenites may even have had some more ambitious aim in mind than simple inspiration from the sky. For example, they may have sent — by making the mirror flicker, using some equivalent of Morse — instructions on crop-rearing, or engineering — the lost secrets of the steam engine, perhaps — something, at any rate, rather more useful than mere good-luck messages.

But in the end it was to no avail. In the end, the fist of Glaciation closed about the land. And the great lunar mirror was abandoned, as men disappeared from the earth.

Such, at any rate, was my speculation, as I stood gazing through the windows of my tower; I have no means of knowing if I was right — for Nebogipfel was unable to read this new History of Humanity in such detail — but in any event the gleam of that isolated mirror on the moon became, for me, a most eloquent symbol of the collapse of Humanity.

The most striking feature of our night sky was not the moon, however, nor even that absence of stars: it was the great, weblike disc, a dozen times Luna’s width, that I had noticed on our first arrival. This structure was extraordinarily complex and alive with motion. Think of a spider-web, perhaps lit from behind, with drops of dew glistening and rolling over its surface; now envisage a hundred tiny spiders crawling over that surface, their motion slow but quite visible, evidently working to strengthen and extend the structure — and then cast your vision across many miles of inter-planetary space! — and you will have something of what I saw.

I made out the web-disc most clearly in the early hours of the morning — perhaps around three o’clock — and at such times I was able to make out ghostly threads of light — tenuous and thin — which reached up, from the far side of the earth, and out through the atmosphere towards the disc.

I discussed these features with Nebogipfel. “It’s quite extraordinary… it’s as if those beams make up a kind of rigging of light, which attach the disc to the earth; so that the whole affair is like a sail, towing the earth through space on some spectral wind!”

“Your language is picturesque,” he said, “but it captures something of the flavor of that enterprise.”

“What do you mean?”

“That it is a sail,” he said. “But it is not towing the earth: rather, the earth is providing a base for the wind which drives the sail.”

Nebogipfel described this new type of space yacht. It would be constructed in space, he said, for it would be much too fragile to haul upwards from the earth. Its sail consisted, essentially, of a mirror; and the ’wind’ which filled the sail was light: for particles of light falling on a mirrored surface deliver a pushing force, just as do the molecules of air which make up a breeze.

“The ’wind’ comes from beams of coherent light, generated by earthbound projectors as wide as a city,” he said. “It is these beams which you have observed as ’threads’ joining planet to sail. The pressure of the light is small but insistent, and it is extraordinarily efficient in transferring momentum — especially as light speed is approached.”

He imagined that the Constructors would not sail upon such a ship as discrete entities, as had the passengers of the great ships of my day. Rather, the Constructors might have disassembled themselves, and allowed their components to run off and knit themselves into the ship. At the destination, they would reassemble as individual Constructors, in whatever form was most efficient for the worlds they found there.

“But where is the space yacht’s destination, do you think? The moon, or one of the planets — or—”

In his flat, undramatic Morlock way, Nebogipfel said: “No. The stars.”

Nebogipfel continued his experiments with the billiards table. Repeatedly the ball would encounter that peculiar clattering I had observed about the middle of the table, and several times I thought I saw billiard balls — more copies of our original — appearing from nowhere and interfering with the trajectory of our ball. Sometimes the ball emerged from these collisions and continued along the path it might have followed regardless of the clattering-about; sometimes, though, it was knocked onto quite a different path, and — once or twice — we observed the type of incident I described earlier, in which a stationary ball was knocked out of its place, without my, or Nebogipfel’s, intervention.

This all made for an entertaining game — and clearly something fishy was going on — but for the life of me I could not see it, despite that hint of Plattnerite glow about the pockets. My only observation was that the slower the ball traveled, the more likely it was to be diverted from its path.

The Morlock, though, grew gradually more excited about all this. He would immerse himself in the hide of the patient Constructor, delving once more into the Information Sea, and emerge with some new fragment of knowledge he’d fished up — he mumbled to himself in that obscure, liquid dialect of his kind — and then he would hurry straight to the billiards table, there to test his new understanding.

At last, he seemed ready to share his hypotheses with me; and he summoned me from my steam bath. I dried myself on my shirt and hurried after him to the Billiards Room; his small, narrow feet pattered on the hard floor as he half-ran back to the table. He was as excited as I could remember seeing him.

“I think I understand what this table is for,” he said, breathless.

“Yes?”

“It is — how can I express it? — it is only a demonstration, little more than a toy but it is a Multiplicity Generator. Do you see?”

I held up my hands. “I fear I don’t see a thing.”

“You are familiar enough with the idea of the Multiplicity of Histories, by now…”

“I should be; it’s the basis of your explanation of the divergent Histories we have visited.”

At every moment, in every event (I summarized), History bifurcates. A butterfly’s shadow may fall here or there; the assassin’s bullet may graze and pass on without harm, or lodge itself fatally in the heart of a King… To each possible outcome of each event, there corresponds a fresh version of History. “And all of these Histories are real,” I said, “and — if I understand it right they lie side by side with each other, in some Fourth Dimension, like the pages of a book.”

“Very well. And you see, also, that the action of a Time Machine — including your first prototype — is to cause wider bifurcations, to generate new Histories… some of them impossible without the Machine’s intervention — like this one!” He waved his hands about. “Without your machine, which started off the whole series of events, humans could never have been transported back to the Palaeocene. We should not now be sitting on top of fifty million years of intelligent modification of the cosmos.”

“I see all that,” I said, my patience wearing thin. “But what has it to do with this table?”