"Father, what makes the light of day shine?" Nem crouched on one knee to address his son.

"The engines. Deep inside the floor of the ship they make power. And that light in the sky is a burning tube of plasma that runs on power from the engines."

"Who put it there?"

"Our ancestors. Three hundred years ago they built this ship so that they could be part of a great adventure, an adventure to the stars."

"What are stars?" Nem frowned. This was always the hard part to explain.

"Close your eyes and think about the ship. What do you see?"

"I see the walls. When you look down along the spin axis, you see them curling up from the ground to meet the sky. If you walk long enough, you can go all the way around it."

"What does it look like from the outside?"

"Outside?"

"Let me try something else. If you dig down into the ground, how far can you go?"

"Hmm. Well, I don’t think you can dig on forever, so there must be some sort of boundary, and then… what else?"

"Then you hit space. There is no air in space, it’s real nothingness."

"How far does space go?"

"Forever. It goes on and on and on and then, we think, it comes back around to the other side."

"So it’s like here, just a lot bigger."

"You know, I think you’re right. The real problem is that it’s so much bigger that it takes a hundred thousand years to get even across a tiny part of it. We are going through space in an attempt to get from one star to another. But it takes a thousand years to get from one star to another, so our ancestors built this ship. The world."

"Wow. What’s so great about the other star?"

"It’s somewhere other than our star. Our ancestors were explorers."

"Then what are we?"

"I have no idea."