On Earth, the glaciers came and went, while above them the changeless Moon still carried its secret from the stars. With a yet slower rhythm than the polar ice, the tides of civilization ebbed and flowed across the Galaxy. Strange and beautiful and terrible empires rose and fell, and passed on their knowledge to their successors.

And now, out among the stars, evolution was driving towards new goals. The first explorers of Earth had long since come to the limits of flesh and blood; as soon as their machines were better than their bodies, it was time to move. First their brains, and then their thoughts alone, they transferred into shining new homes of metal and gemstone. In these, they roamed the Galaxy. They no longer built spaceships. They were spaceships.

But the age of the Machine-entities swiftly passed. In their ceaseless experimenting, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light.

Into pure energy, therefore, they presently transformed themselves; and on a thousand worlds, the empty shells they had discarded twitched for a while in a mindless dance of death, then crumbled into dust.

Now they were Lords of the Galaxy, and could rove at will among the stars, or sink like a subtle mist through the very interstices of space. Though they were freed at last from the tyranny of matter, they had not wholly forgotten their origin, in the warm slime of a vanished sea. And their marvellous instruments still continued to function, watching over the experiments started so many ages ago.

But no longer were they always obedient to the mandates of their creators; like all material things, they were not immune to the corruption of Time and its patient, unsleeping servant, Entropy.