“Imagine there is no time. Imagine there is no space…” In the still cold of Callisto, as she described extraordinary ideas, Luru’s voice was a dry rustle.

“Take a snapshot of the universe. You have a static shape, a cloud of particles each frozen in flight at some point in space.” A snapping of fingers. “Do it again. There. There. There. Each moment, each juggling of the particles, gives you a new configuration.

“Imagine all those snapshots, all the possible configurations the particles of the universe can take. In any one configuration you could list the particles’ positions. The set of numbers you derive would correspond to a single point on a mighty multidimensional graph. The totality of that graph would be a map of all the possible states our universe could take up. Do you see? And that map is configuration space.”

“Like a phase space map.”

“Like a phase space, yes. But of the whole universe. Now imagine putting a grain of dust on each point of the map. Each grain would correspond to a single point in time, a snapshot. This is reality dust, a dust of the Nows. Reality dust contains all the arrangements of matter there could ever be…”

Slowly, as Luru explained and Nilis tried to clarify, Pirius began to understand.

Configuration space was not Pirius’s world, not his universe. It was a map, yes, a sort of timeless map of his own world and all its possibilities, a higher realm. And yet, according to Luru Parz, it was a universe in itself, a place you could go, in a sense. And it was filled with reality dust. Every grain of sand there represented an instant in his own universe, a way for the particles of his universe, atoms and people and stars, to line themselves up.

But this was a static picture. What about time? What about causality?

If you lined up reality dust grains in a row you would get a history, of a sort, Luru Parz said. But it might not make sense as a history; nothing like causality might emerge, just a jumble of disconnected snapshots one after another. But the sand grains attracted each other. If they came from neighboring points in the greater configuration space, the graph of all possible instants, the moments they mapped must resemble each other. And so the grains lined up in chains, each line of grains representing a series of instants which, if you watched them one after another, would give you the illusion of movement, the illusion of time passing — perhaps, if the grains were similar enough, even the illusion of causality.

Something like that.

And configuration space, he slowly understood, was where Luru Parz wanted to send Pirius.

It was beyond his imagination. “You want me to go into a map? How is that possible?”

Luru said, “Reth Cana discovered that, constrained in this space and time, the endoliths found a way into configuration space — and Reth Cana found a way for humans to follow. He could download a human consciousness into this abstract realm.”

“I can see the appeal of that for pharaohs,” Nilis said with dark humor. “An abstract, static, Platonic realm — a place of morbid contemplation, a consolation for ageless pharaohs as they sought to justify the way they administered the suffering of their fellow creatures.”

Luru Parz smiled thinly. “Of course it is a realm beyond our experience. So Reth constructed metaphors, a kind of interface to make its features accessible to human minds. There is an island — a beach. You’ll see a mountain, Pirius, and a sea. The mountain is order, and at its peak is that special dust grain that represents the initial singularity: the Big Bang, the unique event when all the universe’s particles overlaid each other.”

Pirius said, “And the sea?”

“The sea is the opposite. The sea is disorder — maximal entropy — the ocean of meaninglessness to which everything washes, in the end.”

Pirius stood before the doorway, set up in the abandoned laboratory of Reth Cana. It looked as if it led nowhere. In fact, Luru Parz was saying, it led to a different realm of reality altogether. “And if I walk through this door—”

“You will split in two,” Luru said. “You will still be here, walking out the other side. But a copy of you will be made.”

“Like a Virtual.”

“Yes. It will feel like you, have your memories. But it will not be you.”

“And this copy will be in configuration space.”

“Yes.”

“But why must I go there?”

“Because that is the place the pharaohs went. The pharaohs flocked there, from all over Sol system and beyond,” Luru Parz said. “Their knowledge — some of it preserved from long before the Qax Occupation — went with them, too. Configuration space is a black library — the final library — and it contains much we have lost.”

Nilis said, “You chose not to follow these undying refugees into configuration space, Luru Parz.”

Her face was blank. “Unfinished business,” she said.

Pirius said, “And this lost knowledge is what you want me to bring back.”

“Yes. The ancients had considerable powers. Don’t forget it was human action that turned Jupiter into a black hole. Perhaps they even knew how to land punches on the supermassive monster at the center of the Galaxy.”

He understood. “You want me to find a weapon in there. A weapon to strike at Chandra, in this hideous old library of yours.”

“Yes… but there’s a catch.”

“A catch?”

“Once in there, the refugees didn’t stay human for long. Which is somewhat inconvenient. Try to hold onto yourself, Ensign. Your identity. And stay away from the sea.”

Pirius peered at the portal. “Will I be able to come back? I mean, uh, he — the Virtual copy.”

Nilis strode up to him and took his shoulders. Pirius had never seen Nilis look so grave. “Pirius, I have taken you far from your home, your duty. I have asked you to face many extraordinary situations — and many dangers. But this is by far the most difficult thing I have ever asked you to do.”

Pirius said slowly, “I can’t come back.”

Luru Parz laughed. “But it doesn’t matter. Sentient or not, it will only be a copy, like a Virtual. And it won’t last long. It has to be you, Ensign.” She smiled, showing her blackened teeth. “You’re the only suitable resource we’ve got. I’m worn smooth with time, Nilis here is too aged… only you have the strength to endure this.”

Pirius looked at the frame. He felt numbed, not even afraid; perhaps his imagination was exhausted. He shrugged. “There are already two copies of me running around the Galaxy. I suppose I’m used to being split in half. When shall we do this?”

Luru Parz said, “The equipment is ready.”

Nilis gaped. “Now? Just like that?”

“Why delay?” She stepped close to Pirius, so close he could smell her musty odor through the chill tang of the ice. “Do it, Pirius. Step through and it will be over. Don’t think about it. Just step through…” She was grotesquely seductive. He felt oddly compelled to obey. It was as if he had a gun in his hand, pointed to his head; no matter how rational he was there was always a trace of a compulsion to pull the trigger — and that self-destructive compulsion was what Luru Parz was working on now. “Do it,” she whispered, like a voice in his own head.

Nilis said, “Oh, but this is so — I wish I could spare you this ordeal!”

“It will only be a copy,” Luru said. “Not you. What does a copy matter?”

Enough. Pirius turned away from Nilis. Luru Parz was right. If he had to do this -

He stepped into the frame. There was a flare of light, electric blue, blinding him. He pushed forward further, into the light.

He staggered. Gravity clutched at him, stronger than the ice moon’s wispy pull, as if inertial shielding had failed. The ground under his feet felt soft, dusty, like asteroid regolith.