Abruptly the camera angle swung again. The smoothed-out asteroid, the portal, tilted crazily.

The beach ball was moving, half bouncing, half rolling toward the portal. It left a trail of pits and scrapes in the smooth metallic-dust surface of the asteroid.

Emma said sadly, “So Sheena hasn’t yet found peace.”

The camera swung around once more, and Emma got a last glimpse of the mighty, broken empire of the black hole engineers.

It was magnificent, she thought, and it would last an unimaginable time, zoom factors beyond puny human scales. But it was an epic of futility.

“What now?” Malenfant muttered. “What is left?”

Emma didn’t know. But, she found, she welcomed the obliter-

ating blue flash.

Once more, emptiness.

A.piton, trailing a tether, was drifting across the field of view. The little gadgets were lit up brightly by the firefly’s floods, a brightness that only contrasted with the illimitable darkness beyond.

Malenfant growled, “So why can’t we see the asteroid?”

“Because we aren’t on a solid surface. The firefly’s accelerome-ters show it is rolling, tumbling in space.”

Now there was something new in the frame, beyond the writhing tether. It was a blue circle, suspended in the darkness, glowing bright, turning slowly. And alongside it was a slack golden ball, oscillating in space, returning languid highlights.

Emma said, “That’s the artifact. And Sheena. Is she—”

The camera zoomed in on the ball until it filled the screen. The squid within was turning slowly, gently drifting. The only light falling on her, save for the soft blue glow of the portal, was from the firefly’s dimming flood.

“She’s receding,” Emma said. “Moving away from the firefly, and the portal.”

“Yes,” Cornelius said. “Her momentum, as she came through the hole, is taking her away.”

Malenfant asked, “So what happened to the asteroid?”

“Proton decay,” Cornelius said immediately. “I’ve been expecting this.” He checked his expert systems for details. “There are three quarks inside a proton, you know; if you wait long enough you’ll see them come together to form a miniature black hole that immediately explodes… Well. The details of the mechanism don’t matter.”

“Are you saying that matter itself is unstable?”

“On the longest time scales, yes. But it’s slow. The fact that you’re standing there — that you can survive your own mass — tells us proton decay must take at least a billion billion years. Your body contains so many protons and neutrons that any faster decay rate would give rise to enough energetic particles to kill you by cancer. Now we’ve seen that the rate is a lot slower than that.”

Malenfant said, “So the asteroid just evaporated.”

“Yes. It got smaller and smaller, warmed gently by the annihilation of electrons and positrons in its interior, a thin smoke of neutrinos drifting out at light speed.”

Emma asked, “How long this time?”

“The theories are sketchy. If you want me to put a number on it, I’d say ten to power a hundred and seventeen years.” Even Cornelius looked bewildered now. “More zoom factors.”

The cephalopod hab dwindled in the softscreen image, turning, receding.

“So where is everybody?” Malenfant snapped.

Cornelius turned to him, looking lost. “You’re not listening. There is no more. When proton decay cuts in, nothing is left: no dead stars, no rogue asteroids like Cruithne, no cold planets, no geodesic empires. This far downstream, all the ordinary matter has disappeared, the last black holes evaporated. The universe has swollen, its material stretched unimaginably thin.

“Even if the black hole farmers had tried to gather more material to replace what decayed away, they would have been beaten by the time scales. Matter was decaying faster than it could be gathered and used to record information, thoughts, life. And when their structure failed, the last black hole must have evaporated.” He looked misty. “Of course they must have tried. Fought to the last. It must have been magnificent.”

Emma studied Malenfant. “You’re disappointed. But we’ve seen so much time. So much room for life—”

“But,” Malenfant said, “I hoped for eternity.”

Cornelius sighed. “The universe will presumably expand forever, on to infinity. But we know of no physical processes that will occur beyond this point.”

Emma said, “And all life, of any form, is extinct. Right?”

“Yes.”

“In that case,” Emma said softly, “who is Sheena talking to?”

Sheena was blurred with distance now, her habitat a golden planet only dimly visible in the light of the robot’s failing lamps. Maybe Emma’s imagination was projecting something on her, like the face of the man in the Moon.

But still—

“I’m sure I can see her signing,” she said.

“My God,” Malenfant said. “You’re right.”

Emma frowned. “There must be someone here. Because the portal’s here. And it called to us — right? — through a relay of portals, upstream through the zoom factors, to the present. Maybe it called to Sheena, and brought her here.”

“She’s right,” Cornelius said, wondering. “Of course she’s right. There has to be an entity here, a community, manipulating the neutrino bath and sending signals to the past.”

“So where are they getting the energy from, to compute, to think?”

Cornelius looked uncomfortable; obsessively he worked his softscreen, scrolling through lists of references. “It’s very speculative. But it’s possible you could sustain computation without expending energy. We have theoretical models…

“What actually uses up energy during computation is discarding information. If you add two numbers, for instance, clearing out the original numbers from your memory store eats up energy. But if your computation is logically reversible — if you never discard information — you can drive down your processing costs to arbitrarily small values.”

“There has to be a catch,” Malenfant said. “Or somebody would have patented it.”

Cornelius nodded. “We don’t know any way of interacting with the outside universe without incurring a loss. No way of inputting or outputting data. If you want to remain lossless, you have to seal yourself off, in a kind of substrate. But then, nothing significant is going to change, ever again. So what is the use of perception?”

“Then what’s left?”

“Memory. Reflection. There is no fresh data. But there may be no end to the richness of understanding.”

Malenfant said, “If these ultimate downstreamers are locked into the substrate, how can Sheena talk to them?”

“Sheena is a refugee from the deepest past,” Cornelius said. “Perhaps they feel she is worth the expenditure of some of their carefully hoarded energy. They must be vast,” he said dreamily. “The last remnant particles orbit light-years apart. A single mind might span the size of a Galaxy, vast and slow as an empire. But nothing can hurt them now. They are beyond gravity’s reach, at last immune to the Heat Death.”

Emma said, “And these are our ultimate children? These wispy ghosts? The manipulation of structures spanning the universe, the endless contest of ingenuity versus entropy — was

it all for this?”

“That’s the deal,” Cornelius said harshly. “What else is there?”

“Purpose,” Emma said simply. “We’re losing her.”

Sheena was drifting out of the picture.

Cornelius tapped his console. “The firefly is nearly out of attitude-control gas.”

Every few minutes the beach ball drifted through the frame of the softscreen as the firefly’s helpless roll carried it around. The image was dim, blurred, at the extreme range of the failing camera. Emma took to standing close to the softscreen frame, staring at the squid’s image, trying to read any last signs.

It’s like a wake, she thought.