Emma saw the turning wheels reflected in Mane’s broad, glistening eyes. “What is a world engine?”
“Can you not see? Look deeper.”
“…Ah,” Nemoto said.
At the heart of the turning rings, there was a world.
It was like Earth, but it was not Earth. Turning slowly in the light of an off stage sun, it was wrapped in a blanket of thick, ragged cloud. Emma glimpsed land that was riven by bright-glowing cracks and the pinpricks of volcanoes. Plumes of black smoke and dust streaked the air, and lightning cracked between fat purple clouds.
“Not a trace of ocean,” Nemoto murmured. “Too hot and dry for that.”
“Do you think it is Earth? — or any of the Earths?”
“If it is, it is a young Earth, an Earth still pouring out the heat of its formation…”
“The sky,” Mane said, her voice quavering, “is full of rock.”
Emma glanced up.
…And for an instant she saw what the Daemon saw: a different point of view, as if she were standing on that burnt, barren land, on bare rock so hot it glowed, close to a river of some sticky, coagulating lava. She looked up through rents in fat, scudding clouds — into a sky that was covered by a lid of rock, an inverted landscape of mountains and valleys and craters.
She gasped, and the vision faded.
Emma saw again the hot young world, and another beside it now, a Moon-like world, evidently cooler than Earth, but large, surely larger than Mars, say. The two planets sat side by side, like an orange and an apple in a still-life.
But they were approaching each other.
“I think we are watching the Big Whack,” Nemoto murmured. “The immense collision that devastated young Earth, but created the Earth-Moon system…”
The planets touched, almost gently, like kissing. But where they touched a ring of fire formed, shattering the surface of both worlds, a spreading splash of destruction into which the smaller body seemed to implode, like a fruit being drained of its flesh.
“The collision took about ten minutes,” Nemoto said softly. “The approach speed was tens of thousands of miles per hour. But a collision between such large bodies, even at such speeds, would look like slow motion.”
A vast fount of material, glowing liquid rock, gushed into space from the impact. Emma glimpsed the impacting planetesimal’s grey curve, a last fragment of geometric purity, lost in the storm of fire. A great circular wave of fire spread out around the Earth from the impact point.
A ring of glowing light began to coalesce in Earth orbit. As it cooled it solidified into a swarm of miniature bodies. And then spiral arms formed in the glowing moonlet cloud. It was a remarkable, beautiful sight.
“This is how the Moon was born,” Nemoto said. “The largest of those moonlets won out. The growing Moon swept up the remnant particles, and under the influence of tidal forces rapidly receded from Earth. Earth itself, meanwhile, was afflicted by huge rock tides, savage rains as the ocean vapour fell back from space. It took millions of years before the rocks had cooled enough for liquid water to gather once more.”
“You know a lot about this stuff, Nemoto.”
Nemoto turned, her face underlit by the glow of Earth’s violent formation. “A few months ago a new Moon appeared in Earth’s sky. I wanted to know how the old one had got there. I thought it might be relevant.”
Emma glanced at Mane. The Daemon stood with her knuckles resting lightly on invisibility. Her eyes were closed, her face blank. Julia’s eyes were closed too.
“What do they see?” she whispered to Nemoto. “What do they hear?”
“Perhaps more than this show-and-tell diorama. Manekato said this place, this tunnel in the Moon, was information-rich. Julia is as smart as we are, but different. Manekato is smarter still. I don’t know what they can apprehend, how far they can see beyond what we see.”
“…Hey. What happened to the Earth?”
The glowing, devastated planet had blown apart. Fragments of its image had scattered to corners of the chamber — where the fragments coalesced to new Earths, new Moons, a whole family of them. They hung around the chamber like Christmas-tree ornaments, glowing blue or red or yellow, each lit by the light of its own out-of-view sun.
Other Earths:
Emma saw a fat, solitary world, banded with yellow cloud.
Here was another cloud-striped world, but the clouds swirled around a point on its equator — no, it was a world tipped over so that its axis pointed to its sun, like Uranus (or was it Neptune?).
Here was an Earth like Venus, with a great shroud of thick clouds that glowed yellow-white, nowhere broken.
Here was a world with a fat, cloud-shrouded Moon that seemed to loom very close. This Earth was streaked by volcanic clouds. It lacked ice caps, and its unrecognizable continents were pierced by shining threads that must have been immense rivers. This world must be battered by the great tides of air, water and rock raised by that too-close companion.
Most of the Earths seemed about the size of Earth — of the Earth, Emma’s Earth. But some were smaller — wizened worlds that reminded her of Mars, with huge continents of glowering red rock and brooding weather systems squatting over their poles. And some of the Earths were larger. These monster planets were characteristically wreathed in thick, muddy atmospheres and drowned in oceans, water that stretched from pole to pole, with a few eroded islands protruding above the surface, rooted on some deep-buried crust.
The Moons varied too. There seemed to be a spectrum of possible Moons. The smallest were bare grey rock like Luna, those somewhat larger cratered deserts of crimson rock more or less like Mars. Some were almost Earth-like, showing thick air and ice and the glint of ocean — like the Red Moon itself. There were even Earths with pairs of Moons, Emma saw, or triplets. One ice-bound Earth was surrounded, not by a Moon, but by a glowing ring system like Saturn’s.
Emma looked, without success, for a blue Earth with a single, grey, modest Moon.
“The Big Whack collision shaped Earth and Moon,” Nemoto murmured. “Everything about Earth and Moon — their axial tilt, composition, atmosphere, length of day, even Earth’s orbit around the sun — was determined by the impact. But it might have turned out differently. Small, chance changes in the geometry of the collision would have made a large difference in the outcome. Lots of possible realities, budding off from that key, apocalyptic moment.”
“What are we looking at here? Computer simulations?”
“Or windows into other possible realities. It is a glimpse of the vast graph of probability and possibility, of alternates that cluster around the chaotic impact event.” Nemoto seemed coldly excited. “This is the key, Emma Stoney. The Big Whack was the pivotal event whose subtly different outcomes produced the wide range of Earths we have encountered…”
Emma barely understood what she was saying.
Julia grunted. “Grey Earth,” she said. She was pointing to the tipped-over, Uranus-like Earth.
Emma said, “Where you came from.”
“Home,” Julia said simply.
Nemoto said, “I recognize that one.” She pointed to the fat, solitary Earth, banded by Jupiter-like clouds. “A Moonless Earth, an Earth where the great impact did not happen at all. It may be the Earth they call the Banded Earth, which seems to be the origin of these Daemons.”
Mane laid gentle, patronizing hands on their scalps. “Analyse, analyse. Your minds are very busy. You must watch, listen.”
“Ooh.” It was the Nutcracker infant. She was crawling over the invisible floor, chortling at the light show.
Emma glanced down. The various Earths had vanished, to be replaced by a floor of swirling, curdled light.
It was a galaxy.
“Oh, my,” she muttered. “What now?”
The galaxy was a disc of stars, flatter than she might have expected, in proportion to its width no thicker than a few sheets of paper. She thought she could see strata in that disc, layers of structure, a central sheet of swarming blue stars and dust lanes sandwiched between dimmer, older stars. The core, bulging out of the plane of the disc like an egg yolk, was a compact mass of yellowish light; but it was not spherical, rather markedly elliptical. The spiral arms were fragmented. They were a delicate blue laced with ruby-red nebulae and the blue-white blaze of individual stars — a granularity of light and with dark lanes traced between the arms. She saw scattered flashes of light, blisters of gas. Perhaps those were supernova explosions, creating bubbles of hot plasma hundreds of light years across.
But the familiar disc — shining core, spiral arms — was actually embedded in a broader, spherical mass of dim red stars. The crimson fireflies were gathered in great clusters, each of which must contain millions of stars.
The five of them stood over this vast image — if it was an image — Daemon and Ham and humans and Nutcracker baby, squat, ungainly, primitive forms.
“So, a galaxy,” said Emma. “Our Galaxy?”
“I think so,” Nemoto said. “It matches radio maps I have seen.” She pointed, tracing patterns. “Look. That must be the Sagittarius Arm. The other big structure is called the Outer Arm.”
The two major arms, emerging from the elliptical core, defined the Galaxy, each of them wrapping right around the core before dispersing at the rim into a mist of shining stars and glowing nebulae and brooding black clouds. The other “arms” were really just scraps, Emma saw — the Galaxy’s spiral structure was a lot messier than she had expected — but still, she thought, the sun is in one of those scattered fragments.
The Galaxy image began to rotate, slowly.
Emma could see the stars swarming, following individual orbits around the Galaxy core, like a school of sparkling fish. And the spiral arms were evolving too, ridges of light sparking with young stars, churning their way through the disc of the Galaxy. But the arms were just waves of compression, she saw, like the bunching of traffic jams, with individual stars swimming through the regions of high density.
“A galactic day,” Nemoto breathed. “It takes two hundred million years to complete a turn.”
Oh, Malenfant, Emma thought again, you should be here to see this. Not me — not me.
Nemoto said, “But whose Galaxy is it?”
“That is a good question,” Mane said. “It is our Galaxy — that is, it belongs to all of us. The Galactic background is common to the reality threads bound by the Earth-Moon impact probability sheaf—”
“Woah,” Emma said. “Nemoto, can you translate?”
Nemoto frowned. “Think of the Galaxy, a second before the Earth-Moon impact. All those stars have nothing whatsoever to do with the Big Whack, and will not be affected by it. The Galaxy will turn, whether the Moon exists or not, whether humans evolve or not…”
Mane said, “Our Galaxy looks the same as yours. And it is unmodified.”
Emma snapped, “What does that mean?”
