“What is it?”
“Gravitational lensing. Bent light. That means… It must be…” He scrolled through expert system interpretations, speed-reading. “We’re looking at a black hole. A giant.
“This is probably the remnant of a supercluster. Just as what’s left of a Galaxy after star evaporation collapses into the central hole, so galactic clusters will collapse in turn, and then the superclusters.
“That hole might have a mass of anything from a hundred trillion to a hundred thousand trillion solar masses, an event-horizon radius measured in hundreds of light-years.”
“I don’t understand,” said Emma. “Where did the Galaxy go?”
“Our Galaxy hole was surely carried to the heart of the local galactic cluster black hole, and then the supercluster.”
“And we were dragged along with it.”
“If it’s a hole it has no accretion disc,” Malenfant said.
“Malenfant, this thing is ancient. It ate up everything a hell of a long time ago.”
“So how come those motes haven’t been dragged down?” Malenfant said.
“Life,” Emma said. “Even now. Feeding off the great black holes. Right?”
“Maybe,” Cornelius said, grimly. “Maybe. But if so they aren’t doing enough. Even gravity mines can be exhausted.”
“Hawking radiation,” Malenfant said.
“Yes. Black holes evaporate. The smaller the hole, the faster they decay. Solar mass holes must have vanished already. In their last seconds they become energetic, you know. Go off with a bang, like a nuke.” He smiled, looking tired. “The universe can still produce occasional fireworks, even this far downstream. But ultimately even this, the largest natural black hole, is going to evaporate away. What are the downstreamers going to do then? They should be planning now, working. There will be a race between the gathering and management of energy sources and the dissipative effects of the universe’s general decay.”
Malenfant said, “You’d make one hell of an after-dinner speaker, Cornelius.”
The camera had panned again, and it found the Sheena in her beach ball.
“I think her movements are getting labored,” Emma said.
Cornelius murmured, “There’s nothing we can do. It’s cold out there, remember, in the far downstream. Her heater will surely expire before long. Maybe she won’t even suffocate.”
They watched in silence.
Sheena’s firefly, tethered to the beach ball, jerked into motion. It floated toward Emma’s viewpoint, across the eerily smooth surface of the liquefied asteroid.
It drifted to a halt and reached out with a grabber arm to touch its human-controlled cousin. In the softscreen image, the arm was foreshortened, grotesquely huge.
Then the firefly turned and drifted out of shot, toward the portal, towing the beach ball.
“Onward,” Emma whispered.
Another transition, another blue flash.
The camera performed a panorama, panning through a full three hundred and sixty degrees. The portal, a glaring blue ring still embedded in the asteroid ground, slid silently across the softscreen. There was the Sheena’s bubble, resting on the surface, lit only by the robot’s lights and by the soft blue glow of the portal itself. The Sheena tried to swim, a dim dark ghost behind the gold. But she fell, languidly, limbs drifting.
And then, beneath a black sky, there was only the asteroid surface, smooth: utterly featureless, rubbed flat by time.
“It’s just like the last stop,” Emma said. “As if nothing will ever change again.”
“Not true,” Cornelius said. “But this far downstream, the river of time is flowing broad and smooth—”
“Down to a sunless sea,” Emma said.
“Yes. But there is still change, if only we could perceive it.”
The camera tipped up, away from the asteroid, and the softscreen filled up with black sky. At first Emma saw only darkness, unrelieved. But then she made out the faintest of patterns: charcoal gray on black, almost beyond her ability to resolve, a pattern of neat regular triangles covering the screen.
When she blinked, she lost it. But then she made out the pattern again. Abruptly it blurred, tilted, and panned across the screen.
Now the triangles showed up pinkish white, very blurred but regular, a net of washed-out color that filled space.
“The firefly is using false color,” Cornelius said.
The pattern slid across the screen jerkily as the remote firefly panned its camera. And beyond the net Emma saw a greenish surface, smoothly curved, as if the netting contained something.
“It must cut the universe in half,” Emma said.
More of the framework slid through the screen, blurring as the camera’s speed outstripped the software’s ability to process the image.
“It looks like a giant geodesic dome,” Malenfant said.
Cornelius said, “I think it is a dome. Or rather, a sphere. Hundreds of thousands of light-years wide. A net. And there’s only one thing worth collecting, this far downstream.” He pointed to the complex, textured curtain of greenish light visible through the interstices of the dome. “Look at that. I think we’re seeing black hole event horizons in there. Giant holes, galactic super-cluster mass and above. They are orbiting each other, their event horizons distorting. I think the holes have been gathered in there, deliberately. They are being merged, in a hierarchy of more and more massive holes. I imagine by now the down-streamers can manage hole coalescence without significant energy loss.”
“How the hell do you move a black hole? Attach a tow rope?”
Cornelius shrugged. “I don’t know. Maybe you use Hawking radiation as a rocket. The details hardly matter. The dome seems to be an energy collector. Like a Dyson sphere. Anything still alive must be living on those struts, feeding off the last free energy: the slow Hawking radiation of the black holes. But it’s a damn thin trickle.” He glanced at his softscreen. “We can postulate strategies for survival. Maybe they eke out their dilute resources by submitting to long downtimes: hibernation, slow computation rates, stretching an hour of awareness across a million years…”
Perhaps, Emma thought. Or perhaps they are conscious continually even now, in this ruin of a universe. Frozen into their black hole cage, unable to move, trapped like Judas in the lowest circle of Hell.
Cornelius said, “It may seem strange to you how much we can anticipate of this remote time. But the downstreamers are walled in by physical law. And we know they will have to manage their black hole resources. The supercluster holes are the largest to have formed in nature, with masses of maybe a hundred trillion suns. But even they are evaporating away.
“So they have to harvest the holes. If you combine two holes you get a more massive hole—”
“Which will be cooler.” Malenfant nodded. “It will evaporate more slowly. So you can stretch out its lifetime.”
“They’re probably coalescing holes in hierarchies all over the reachable universe. This site, immense as it is, might be just a rung on the ladder.
“The engineering details are tricky. You have to bring the holes together fast enough that they don’t evaporate away before you’ve harvested them. On the other hand it mustn’t be so rapid that you form a hole so huge it evaporates too slowly and you are starved of usable energy… Remarkable,” Cornelius breathed, staring at the dim, ghostly images. “To think that mind has now encompassed the universe — that the future evolution of the universe actually depends on conscious choices — made by our descendants.”
Cooperation, Emma thought, spanning a universe, projects lasting millions, even billions of years. Whatever these people
have become, she thought, they are not human.
“Oh, Jesus. Look at that.”
Emma turned back to the screen, where Malenfant was staring.
Across a broad circular region the geodesic network was disrupted. It looked as if some immense fist had punched through it from the inside, ripping and twisting the st
ruts. The tips of the damaged struts were glowing a little brighter than the rest of the network; perhaps there was some form of repair effort under way.
And beyond the damaged network she could see the event horizons of giant coalescing black holes — each, perhaps, the mass of a supercluster of galaxies or more — the horizons distorted, great frozen waves light-years long visible in their cold surfaces.
“What do you think?” Emma said. “Some kind of breakdown?”
“Or war,” Malenfant said.
“War? Here, so far downstream? That’s insane.”
“Maybe not,” said Cornelius. “These people have responsi-
bility for the whole of the future. They are managing the last
of the universe’s energy resources. With responsibility comes
tension, disagreement. Conflict.”
Malenfant said, “To have come so far, to see this. How depressing.”
“No,” Cornelius said irritably. “We have no idea what kind of minds inhabit these giant structures. They may inhabit hierarchies of consciousness far above us. Their motivations are probably so far removed from ours that we can’t even guess at them—”
“Maybe.” Malenfant growled. “But I’m just a poor H Sap. And if I lived in that dome, I’d want to survive,-no matter how huge my brain was. And it seems to me they are doing a damn poor job.”
Reluctantly, Emma asked, “How far have we come?”
Cornelius studied his softscreens again. “Even the e-systems
are giving up on me now.
“Suppose we’ve taken another scale-factor jump downstream of the same kind of size as last time. That puts us at around ten to power one hundred years remote. What does that mean?” He rubbed his forehead. “To these downstreamers, the early days of their empire — zoom factors often or a hundred or ten thousand back, maybe, when even medium-sized black holes could still exist — those days were the springtime of the universe. As for us, we’re a detail, back in the detail of the Big Bang somewhere, lost in the afterglow.
“Malenfant, I once asked you if you understood, really understood, what it would mean to carry your off-Earth colonization project through to its final conclusion: to challenge eternity. This is what it means, Malenfant. This.
“And the immensity of the responsibility. We have to spread across the universe, make it possible for human descendants of the far downstream to have the power to do this, to survive the winter as long as possible. Because this is the last refuge.”
“But this is a process without limit.” Malenfant frowned. “This is a strategy that offers the prospect of eternal life… doesn’t it?”
“No,” Cornelius said sadly. “At least we don’t think so. There’s a paradox. You have to have some kind of framework, a structure to gather your energy, house your souls.”
“The Disneyland sphere.”
“Yes. The structure grows with time. And even if matter is stable, which it may not be, the structure has to be upgraded, repaired. The maintenance requirements go up with time, because the structure is getting bigger, but the energy available is going down with time.
“It’s a squeeze, Malenfant. And it isn’t possible to win. This black hole management policy is a good idea — the last, best idea — but in the end, it’s doomed to fail.”
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.”
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