Suzto looked up, too. I expected her to scrunch her face in puzzlement, baffled by Dalt’s words, but instead, near as I could make out in the darkness, she was smiling in wonder.
“Can—can you see the lights, too?” I asked Suzto.
“Sure.”
I was astonished. “How big are they?”
“Tiny. Like this.” She held up her hand, but if there was any space between her finger and thumb, I couldn’t make it out.
“Are they arranged in some sort of pattern?”
Suzto’s vocabulary wasn’t yet as big as Dalt’s. She looked at me, and I tried again. “Do they make shapes?”
“Maybe,” said Suzto. “Some are brighter than others. There are three over there that make a straight line.”
I frowned. “Dalt, please cover your eyes.”
He did so, with elaborate hand gestures.
“Suzto, point to the brightest light in the sky.”
“There’re so many,” she said.
“All right, all right. Point to the brightest one in this part of the sky over here.”
She didn’t hesitate. “That one.”
“Okay,” I said, “now put your hand down, please.”
She drew her arm back in toward her body.
“Dalt, uncover your eyes.”
He did so.
“Now, Dalt, point to the brightest light in this part of the sky over here.”
He lifted his arm, then seemed to vacillate for a moment between two possible choices.
“Not that one, silly,” said Suzto’s voice. She pointed. “This one’s brighter.”
“Oh, yeah,” said Dalt. “I guess it is.” He pointed at it, too. I couldn’t see anything, but it seemed in the darkness that if I could draw lines from the two children’s outstretched fingers, they would converge at infinity.
Dr. Tadders was an old friend, and with both Suzto and Dalt seeing the lights, I decided to join her for lunch. We grew wheat, corn, and other crops under lamps here on the outside of the sphere, and raised chickens and pigs; if you wanted the eggs to hatch, you had to put low roofs over the hens, because they needed to be in constant contact with their clutches, and their own body movements were enough to propel them into flight; chickens really seemed to love flying. Tadders and I both knew that we’d have had more interesting meals if we’d stayed inside the sphere, but the ancient texts said that although the interior was huge, there was still much, much more to the universe.
Most of those on the interior didn’t care about such things; they knew that the sphere’s inner surface could accommodate over a million trillion human beings—a vastly larger number than the current population—and that our ancestors had shut us off from the rest of the universe for a reason. But some of us had decided to venture outside, starting a new settlement on our world’s only real frontier. I didn’t miss much about the inside—but I did miss the food.
“All right, Rodal,” Dr. Tadders said, gesturing with a sandwich triangle, “here’s what I think is happening.” She took a deep breath, as if reviewing her thoughts once more before giving them voice, then: “We know that a long, long time ago, our ancestors built a double-walled shell around our sun. The outer wall is opaque, and the inner wall, fifty bodylengths above that, is transparent. The area between the two walls is the habitat, where all those who still live on the interior of the sphere reside.”
I nodded, and kicked gently off the floor to keep myself afloat. We drifted out of the dining hall, heading outdoors.
“Well,” she continued, “we also know that there was a war generations ago that knocked humanity back into a primitive state. We’ve been rebuilding our civilization for a long time, but we’re nowhere near as advanced as our ancestors who constructed our world were.”
That was certainly true. “So?”
“So, what about that story you translated a while ago? The one about where we supposedly came from?”
I’d found a story in the ancient computers that claimed that before we lived on the interior of the Dyson sphere, our ancestors had made their home on the outer surface of a small, solid, rocky globe. “But that was probably just a myth,” I said.
“I mean, such a globe would have been impossibly tiny. The myth said the homeworld was six million bodylengths in diameter. Kobost”—a physicist in our community—“worked out that if it were made of the elements the myth described, even a globe that small would have had a crushingly huge gravitational attraction: live bodylengths per heartbeat squared. That’s more than ten thousand times what we experience here.”
Of course, the gravitational attraction on any point on the interior of a hollow sphere is zero. When we lived inside the sphere, the only gravity we felt was the pull from our sun, gentiy tugging things upwards. Here, on the outside of the sphere, the gravitational pull is downward, toward the sphere’s surface—and the sun at its center.
I continued. “Although Kobost thinks human muscle could perhaps be built up enough to withstand such an overwhelming gravity, his own studies prove that the globe described in the myth can’t be our homeworld.”
“Why not?” asked Tadders.
“Because of the chickens. There are several ancient texts that show that chickens have been essentially the same since before our ancestors built the Dyson sphere. But with an acceleration due to gravity of five bodylengths per heartbeat squared, their wings wouldn’t be strong enough to let them fly. So that globe in the myth couldn’t possibly have been our ancestral home.” “Well, I agree that’s puzzling about the chickens,” said Tadders, “but wherever our ancestors came from, you have to admit it wasn’t another Dyson sphere. And the inside of a Dyson sphere forms a very special kind of sky. Remember what it was like when we lived in there? Wherever you looked over your head, you saw—well, you saw the sun, of course, if you looked directly overhead. But everywhere else, you saw other parts of the sphere. Some of those parts are a long, long way off—the far side of the sphere is a hundred and fifty billion bodylengths away, isn’t it? But, regardless, wherever you looked, you saw either the sun or the surface of the sphere.”
“So?”
“So the surface of the sphere is reflective—even the dull, grass-covered parts reflect back a lot of light. Indeed, on average the surface reflects back about a third of the light it receives from the sun, making the whole sky glaringly bright.”
People in there did have a tendency to float facing the ground instead of the sky. I nodded for her to go on.
“Well, our eyes didn’t evolve here,” continued Tadders. “If we did come from a rocky world, the sun would have been seen against an empty, non-reflective sky. It must be much, much brighter inside the Dyson sphere than it ever was on the original homeworld.”
“Surely our eyes would have adapted to deal with the brighter light here.”
“How?” asked Tadders. “Even after the great war, we regained a measure of civilization fairly quickly. There was no period during which we were reduced to survival of the fittest. Human beings haven’t undergone any appreciable evolution since long before our ancestors built the sphere. Which means our eyes are as they originally were: suited for much dimmer light. Of course, the ancients may have had drugs or other things that made the interior light seem more comfortable to them, but whatever they used must have been lost in the war.”
“I suppose,” I said.
“But you, me, and everyone else in our settlement who has lived inside the sphere—we’ve damaged our retinas, without even knowing it.”
I saw what she was getting at. “But the children—the children born here, on the outside of the sphere—
She nodded. “The children born here, after we left the interior, have never been exposed to the brightness inside, and so they see just as well in the dark as our distant, distant ancestors did, back on the homeworld. The points of light the children are seeing really do exist, but they’re simply too faint to register on the damaged retinas we adults have.”