“That sounds horrible,” Mardina said, and Beth could feel the grip of her hand tighten. “It doesn’t even make any sense. How could a single thought last a million years? I can’t imagine it.”
“But experiences of time can differ,” the ColU said. “In my Culture there was a Christian scholar called Thomas Aquinas—I wasn’t able to trace him in your history, Titus. He distinguished three kinds of time, or perhaps perceptions of time. Tempus was human time, which we measure by changes in the world around us—the swing of a pendulum, the passage of a season. A Titanian ice giant would experience a slower tempus than a human. Aevus was angel time, measured by internal changes—by the development of thoughts, understanding, moods. For the angels, you see, stood outside the human world. And then there was aeternitas, God’s time, for God and only God could apprehend all of eternity at once. The electron-positron minds would not be God, but in the timeless twilight of the universe they might have been like angels . . .”
“Might have been,” Mardina said, almost bitterly. “Might have been.”
The ColU said, “The positronium angels will never exist. Our universe won’t last long enough for that. And the reason our universe is not eternal is because of the existence of other universes. And we know they exist because we, all of us, have visited several of them.”
“Aye, and fought in them,” Titus said, stirring from his space and pushing back blankets. “But in this universe my bladder’s full. Anybody want more tea? Chu, maybe you could put another pot of ice on the fire . . .”
• • •
It took an hour before they were settled again.
When they took their places Beth thought they seemed calmer, more attentive—more ready to take in this strange news from the sky. The break had been a smart bit of people management by Titus Valerius, she thought. Who in the end hadn’t really needed a piss at all.
“So,” Titus said now, slurping the last of his tea, “as if the fate of this universe wasn’t bad enough, you have to talk about all the other ones.”
Stef smiled. “All right, Titus, I know we are leading you on a march you’d rather not be following . . . It’s all about logic, though. When all else fails, ask a philosopher. Sorry. Old physicist’s joke.
“Look, we all know from personal experience that other universes exist, with histories more or less similar to this one—or to the one into which each of us was born. And in my Culture our philosophers had predicted the existence of those universes. Our laws of nature were well founded, you see, but they did not prescribe how the universe had to be. Many universes were possible—an infinite number. It is just as our science would have predicted the sixfold symmetry of a snowflake, which comes from the underlying geometry of ice crystals, but within that sixfold rule set, many individual snowflakes are possible, all different from each other.”
“Universes as numerous as snowflakes,” Beth said. “That’s wonderful. Scary.”
Stef said, “But what are these universes? Where are they? You know that the science of my Culture was more advanced than in any other we’ve yet encountered—”
The ColU said, “And Earthshine would say that was because we had been the least deflected into efforts to build Hatches for his Dreamers.”
“We did have some models of the multiverse—I mean, of a super-universe that is a collection of universes. After centuries of study we never came to a definitive answer. We probably never got far out enough into our own universe to be able to map the truth.
“Still, we believed our universe had expanded from a single point, out of a Big Bang. Expanded, cooled, awash with light at first, atoms and stars and planets and people condensing out later. But our universe was like a single bubble in a bowl of boiling water, like a pot we put on the fire.” She gestured at the clay pot, within which water was languidly bubbling. “You see? There is a substrate, something like the water in the pot. And out of that heated-up substrate emerges, not just one bubble, but a whole swarm of them, expanding, popping . . . They are the other universes we’ve been visiting.
“And what’s inside those universes is going to be different, one universe to the next—a little or a lot. Some could differ wildly from the others, not just in historical details. Suppose gravity were stronger—I mean, the force that gives us weight. Then stars would be smaller, and would burn out more quickly. Everything would be different. And if gravity were weaker, there might be no stars at all. And of course some universes are going to be more similar than others.”
It seemed to be Chu who understood most readily. Not for the first time, Beth wondered what kind of scholar he might have become, given the chance. “All the universes we have seen are similar. They all have planets, suns, people. They even have the same people, up to a point.”
“Yes,” Stef said eagerly. “You’ve got it. When you think about it the differences are pretty small. I mean, whether Rome falls or not would be a big deal for us,” and she smiled as Titus scowled ferociously, “but from Per Ardua, say, you wouldn’t even notice it.”
The ColU said, “We believe that the Dreamers can somehow reach out to other universes that are—nearby. There is no good term for it. What is nearness in a multiverse? Beginning in one universe, they reach out into another that is similar, yet that contains a human Culture that is more—conducive—to Hatch-building. And we, our small lives, are swept along in the process.”
Beth found herself frowning. “But why? Why would they do that?”
Stef said, “We need to find that out. In fact I suspect Earthshine may already be learning that secret. What’s important now is that we know the multiverse exists. OK? We’ve been there. Now, the multiverse is big. Surely that’s true. But it can’t be infinite.”
Titus scratched his head. “Here we go again . . . Dare I ask, why not?”
“The trouble is, Titus,” the ColU said, “some scholars have always believed that nature does not contain infinities. Infinities are just a useful mathematical toy invented by humans, with no correspondence to reality. Unlike the number three, say, which maps on to collections of three objects: three people, three potatoes . . .”
Stef said, “Infinities can make sensible questions meaningless. Titus, start with the number one.”
“I think I can grasp that.”
“Add another one.”
“I have two.”
“Subtract one.”
“I have one again.”
“Add one.”
“Two.”
“Subtract one.”
“One!”
“Add one!”
“Two!”
“Subtract one!”
“One!”
She held up her hands. “OK, that’s enough. You get the idea. Now if I asked you to stop doing that after some finite number of steps—twelve or twenty-three or five hundred and seventy-eight—what answer would you get?”
“That’s easy. Either two or one.”
“Definitely one or the other?”
“Of course.”
“But if I asked you to go on forever, what answer would you end up with?”
“I—ah . . . Oh.”
“You see?” Stef said. “The answer can’t be determined. The question becomes absurd, once you bring infinity into it.”
Titus said, “I can feel my brain boiling like the water in that pot.”
“Physics—my philosophy—is about asking sensible questions and expecting sensible answers. About being able to predict the future from the past. When you bring in infinities, sensible questions have dumb answers. The whole system breaks down.”
The ColU said, “So the point is, the multiverse—the collection of the universes we visit—must be finite. Because nature won’t allow infinities.”
Mardina scowled. “Well, so what? What do I care if there is one reality, or ten or twenty or a million?”
The ColU said, “Given that one simple fact—that the multiverse must be finite—and knowing how old the universe is, or was in the age we came from—it has always been possible to make an estimate of how long the universe was going to last. How long it was likely to be before we hit the multiverse wall. Probabilistic only, but . . .”
Titus snapped, “How long, then?”
The ColU said, “My latest estimate, based on my inspection of the sky as far back as our time on the Malleus Jesu, is three and a half billion years after the age of mankind.”
Titus shook his head, growling under his breath. “An absurd number.”
“Not to an astrophysicist,” Stef said with a smile. “That is, a philosopher who knows the stars, Titus. In my Culture we were pretty sure that the universe was a bit less than fourteen billion years old. So why should the universe last longer than a few billion more? You see? Not trillions or hundreds of trillions of years, or beyond the age of proton decay . . . In my Culture we used to call this the Doomsday Argument. Why should the future be so dissimilar to the past? Shouldn’t we expect to find ourselves somewhere in the middle of its life span, not in its first few instants?”
Mardina was touching her belly again, as if trying to shield her baby from all this. “Three point five billion years. You’re saying the universe will die, three point five billion years after the year I was born. If I understand these numbers at all—that’s still an immense stretch of time.”
“Of course,” Stef said. “But here’s the catch, Mardina. We have been brought to the end of that stretch. That’s what we’ve determined—what the ColU has established definitively from his study of the sky.”
“It isn’t just the aging of the stars, the position of the galaxies,” the ColU said. “That would be enough for a rough estimate. There are also distortions in the background glow of the sky, the fading relic of the Big Bang explosion. Distortions caused by events from the future.”
Titus tapped the pot with a fingernail. “Because of the proximity of this wall of yours.”
“Which is a tremendously energetic horizon that sends back signals, back through time. Signals that show up as distortions in the background radiation. That is why I am able to be so precise. This, the age in which we find ourselves, is the End Time—”
“I don’t want to hear it.” Mardina stood, suddenly, pulling away from Beth, the weight of her blankets almost making her stumble into the fire. “I don’t want to hear any more.” She clamped her hands over her ears, and stomped out.
Beth half rose. “She needs her boots, her cloak, if she’s going out there—”
“No.” Chu was already on his feet, and grabbing his own boots. “Let me. It is our problem.”
Beth nodded to the rest. “Let him go. It will be harder for them, to be so young, to have to face this. We must let them find their way.”
Beth longed to go after her daughter, but she made herself sit still. “You’re a wise man, Titus Valerius.”
He smiled, looking tired. “No. Just an old one, and a survivor. So, Collius. Here we are in the far future, as I understand it. How long until we encounter this—edge?”
The ColU said simply, “A year. No more.”
Titus nodded. “And what then? What will happen?”
Stef said, “A wall of light.”
Titus heaved a huge sigh. “Very well. From the ethereal to the practical. Shall we consider our route for tomorrow? And then we all need sleep, if Morpheus grants it tonight.”
68
The antistellar was the place where all the gravity-train tunnel mouths converged.
At the final destination, as the rest of the party went through the by-now practiced routine of grappling their sled-cart out of the frictionless tube, Stef walked forward, away from the tunnel. The ice under her booted feet was concrete-hard but ridged, crumpled, wind-scoured—evidently old—and was not slick, maybe it was too cold for that; the footing was good. Once, back in her original timeline, she’d skimmed in space over the polar caps of Mars, which were very old accretions of water ice, the deepest layers perhaps a couple of million years old. The ice under her feet now might be a thousand times older than that. She really had been brought to an antique time, an old universe.
And the dark-side cold itself—she seemed to remember that too, from her first experience here. This point furthest from the warmth of the star was the center of a hemisphere of endless night, of ice and dark. Yet there was a limit to the cold, even here; some warmth at least washed around the world from the day side. It was evidently a survivable cold. Still, her breath steamed, and the frigid air plucked at her lungs and nose and eyes.
As she walked she could clearly see, by the light of an Andromeda reduced to a bloated sunset sitting on the horizon, more tunnels, dark gashes in the ground: a network of tunnels lacing this chill hemisphere of the planet, and all converging here, at the antistellar, at this point of geographic symmetry.
And at the precise antistellar point itself, the place all the tunnels seemed to be pointing to—something was there, a kind of flattened dome from which came a glow of pale light, with structures dimly visible within.
Earthshine: it had to be him.
• • •
Stef walked back to her companions. By now they had the cart set up on its runners, ready for the final haul over the ice to the dome. The ColU was in its pack on Chu’s back. Mardina, more visibly pregnant every day despite her layers of cold-weather clothing, stood at Chu’s side, their gloved hands locked together, breath wreathed around their faces.
Titus grunted, pointing to the dome. “So our long journey is over—and there is the obvious destination. We should be ready to defend ourselves.”
The ColU said now, “You may be right, legionary. But consider this. Earthshine needs no such shelter as that dome, whereas you do need shelter. Perhaps the dome itself should be seen as a gesture of welcome.”
Titus nodded cautiously. “I see your reasoning. But consider this, in turn. If we would be welcome, so would Ari and Inguill have been, if they got this far. We should be prepared for whatever they are up to in there. Also, if Earthshine, or his image, could walk around on this ice butt-naked—”
Beth laughed. “Titus, he could fly through the air if he wanted to.”
“Then why isn’t he here now? I’m quite sure he’s as aware of us as we are of him. Why not come out and see us?” Titus glanced around at the group. “It’s clear that there’s much about this situation that we don’t yet understand. We go to the dome. It’s the obvious destination. The only destination. But we go in with our hands open in gestures of peace and friendship, and our weapons sheathed at our backs. Agreed?”
Stef shook her head. “You’re a terrible cynic, Titus Valerius. And I’d like to see you in a knife fight; you’re like an overweight panda in that cold weather gear . . . But you and your instincts have kept us all alive this long. Agreed.”
They formed into a loose party, with Titus, Chu, Clodia and Beth hauling the cart toward the dome, and Mardina walking with Stef at the rear. Titus and Chu were in the front rank, and Stef could see their pugio daggers tucked in the back of their belts, glittering in Andromeda light.
Mardina linked her arm through Stef’s, and they walked cautiously together. Stef peered up. “That sky isn’t what it was when I came this way before, with your grandfather Yuri, in that other timeline. It’s been so long, the stars have swum around the sky, or aged and changed, the constellations have all melted away. I thought I wou
ld still be able to see her, though, up at the zenith. Brilliant she was, and as we walked to the antistellar we saw her steadily rise in the sky unlike any star.”
“‘Her’? Who are you talking about, Stef?”
“A creature called Angelia. A creation of my father.”
“Another artificial person, then. Like the ColU, like Earthshine.”
“Yes. Actually she was also a kind of ship. She and her lost sisters . . . I got to know her. I don’t suppose she could have survived this long. Why, in a billion years or two her very substance would have sublimed away, probably.”
Mardina squeezed her arm. “We’re in another history. She was probably never here at all.”
“Maybe not,” Stef said with a bitterness that surprised her. “Just another story, erased by the Dreamers’ meddling.”
“No, not erased. Not as long as you remember her.”
Stef felt unreasonably touched. She patted Mardina’s hand. “You’re a good person, Mardina.”
Mardina laughed. “Despite my great-grandfather being a criminal mastermind downloaded into a box of metal and glass?”
“Yes. That’s quite a legacy, isn’t it? But Yuri at least was a good man too, your grandfather—I can tell you that much. And you’re going to make a fine young mother.”
But that was the wrong thing to say. Stef could feel Mardina stiffen.
“Well, there’s not going to be the time to find out, is there? Not if the ColU is right that all this,” and she gestured at the starry sky, “is about to roll up like a closing scroll.”
Stef could think of nothing to say.
She was relieved when Titus, in the van of the party, reached the translucent wall of the dome.
Ultima Page 47