The pair lumbered across the street; the protector and the girl. He was a segmented conglomeration of self-building, self-repair robotic parts, who ate ancient asphalt for energy. His body was a fortress of welded rebar and chunks of concrete; all steel wheels and steel legs and a matrix of interlocking levels that the girl lived within. There used to be others, but she was the only one left. His segments could separate, and had different functions: welding, cleaning, debriding, greasing, collecting resources; but they were all him and under his control. He lazily followed the old roads, chewing with a maw of rusted iron.
The girl was young, more than weaned or she wouldn't be alive living alone, but neared to infant than adult. She was freckled, gangly, and usually sunburnt. The protector did not know her age. He called her 'Gee' because that was the first syllable she made when they met. There were other roamers, groups of protectors and their people, but they met fewer and fewer as they passed into the north.
Gee carefully peeled the bark from a twig and shoved it into her teeth. She laid back in her hammock just below the top level and looked up at clouds in the sky, through the metal grate of the floor above, happily scraping plaque from dental crevices.
"What's on the other side of the blue, or is it all just blue?" she asked.
"Stars," he said.
"What are stars?"
"They are suns."
"How come we can't see them? Or are they really tiny? Is the blue solid? Are they behind the blue? How could you poke a hole in the blue?"
"They are far away," he said, "so they look tiny."
"But you can't see them."
"If we travel to the night, you could see them."
"Yes. They would look like tiny dots of light. You can see thousands of them, but there are billions?"
"Billions?" she asked, then burst out into laughter.
"Why is that funny?"
"That's just sooo many." She settled back and was quiet for a few minutes. Then she said "Could we travel to the night?"
"It would take a long while. But it will be here in a few years anyway."
"Really? Was it here before?"
"Yes, when you were younger, but you don't remember it."
"No. I think I'd remember something like the sky being black."
"It used to come every day. Half the day was bright, and half the day was dark, more or less."
"Do you remember that?"
"Yes. But that was hundreds of years ago, before the exodus."
"You said that's when there were more people."
"Yes, billions," he said. Gee burst into laughter again.
"Can I have some water?" she asked.
"Yes, but we're running low. We need to find a new source."
"Okay," she said. She hopped off the hammock, and jumped down the staircase, propelling herself from her arms on the railings. She ran across the rough wooden floor, leapt to the adjacent segment, and banged into the plastic water tank. There was a hollow reverberation and the contents sloshed around the bottom. She bent down and wrapped her lips around the spigot, then pulled the lever. She drank deeply.
"That's enough for now," said the protector.
"Umn, okay," she said wiping her lips. "It's just so hot."
"It's always hot," said the protector.
"Well, it doesn't bother you. You don't need water."
"Be glad we are at this latitude," he said. She swung absently from a pipe. She pulled herself up and let her legs swing free into the void below.
"I hope the winds come soon."
"When its windy you complain of the cold."
"But I think it's getting hotter. I think I'd rather be cold."
"It's possible. We will be tidally locked soon. Maybe in another century or two."
"What does that mean?"
"It means that soon one side of the planet will constantly be facing the sun, and the other side will constantly be facing away. The sun side will be completely burnt and dry, just like it is at the equator now, and the dark side will be completely frozen over. There probably will no longer be precipitation. That means rain or snow. For awhile, life might survive on the border between the two, where it will permanently be twilight."
"It's where the sun is low in the sky, about to be obscured by the Earth. It is darker."
"Is it blue or black?"
"Often it's purple or pink or orange."
"What?! Really?" She leapt down to the floor and ran up the segments to where the protector's speaker was. She sat cross-legged next to it. "Why is pink?"
"The color of the sky is an illusion. The light from the sun has to travel through the atmosphere to get to us. When the sun is high in the sky, the light has less distance to travel through the air than when it is low in the sky."
"I don't understand. What does distance have to do with it?"
"A longer distance means thicker air. The air filters the light, and it does a better job at filtering out short wavelengths. Blue is a shorter wavelength."
Gee sighed heavily and held her head in her hands.
"I don't get it! What's a wavelength?" she exclaimed.
"Light travels in waves, like ripples in a puddle. Those ripples are waves, and they have a low part, called a trough, and a high part, called a crest. The distance from crest to crest or trough to trough is called a wavelength."
"Oh," said Gee. "So blue light travels faster than pink light."
"No," he said, "but that's an interesting conclusion. Its unintuitive, but all light travels at the same speed. Mostly."
"Ugh, forget I asked," said Gee. She got up and went to the stairs down to the next level. There was an ancient sofa and she flopped down on it.
"Are you tired?" he asked.
"Yeah," she said, yawning.
"We should rest then," he said.
"You can keep going. I'll just take a nap maybe." There was a long silence between them, then the protector spoke.
"Gee, I have to tell you something," he said.
"Mmmn," she muttered.
"Are you sleeping?"
"No," she said.
"I think my network is going to fail. I need a new hub. It's been giving me trouble."
"I thought you had two?" she asked.
"The other one died."
"Oh. That's bad then, right?"
"Yes. I need it so that all my parts can work together."
"Can't you make one?"
"It's too complicated. No one makes them anymore."
"Is that why the protectors are dying out?"
"So that's going to happen to you?"
Gee sat up and pulled her knees to her face. Even in the heat, her skin became gooseflesh.
"But I can still talk to you, if that happens?"
"Yes, you could. But you will need to find another protector in better shape. That's the reason why you came to me in the first place, with your people."
"Them," she said, staring off into the distance. "I don't want to leave you. I don't want to be alone."
"You could find more people to be with. Then it wouldn't be lonely."
"But we haven't seen another protector or people in ages!" Gee was breathing hard. "What if I don't find any?!"
"You have to believe you can," he said.
"But what if believing isn't enough? And we've been going to the north, where there are less and less! Where it's hotter and hotter! Where there's less water."
"There are more resources here, that haven't been picked over. I was hoping to find a new hub by now, but that hasn't happened. I'm sorry. I should have told you before now. I should have asked you."
"I'm just a kid!" She ran down the segments, away from the protector's voice, out of earshot on his own body. She huddled in the back storage area, sweating and holding back tears. The protector stopped. He curled back, and moved the head segment towards the tail segment.
"I'm sorry," he said.
"I don't know what to do," she said, sobbing. "I don't know."
"You know more than you think you know," he said.
"I'm just little," she said.
"You're bigger than you think you are," he said.
"And I don't know anything like you do. You always know everything."
"You're smarter than you think you are."
"No I'm not," she said, wiping at her eyes angrily.
"Yes you are," he said.
"No," said Gee. There was a pause.
"We should rest here," he said. "We still have time together. And I've decided to turn back south so you won't have to walk as far to find a new protector."
"I'm sorry," he said. "But that's part of life."
"Do you get scared?"
"What are you scared about?"
"Things you haven't thought about yet."
"Like what?" she asked. He took a long time to answer.
"I worry about you. I worry about life ending on this planet. I don't want to see it, but I probably will. I worry that the humans who left forgot us here. They probably don't even care."
"They scavenged the moon to make their ships, for one thing. When the Earth was depleted, they didn't try hard to repair it, they just left because they could. Like a virus bursting forth from the cell that incubated it."
"I shouldn't think about those things. I should think about the present."
"What's a moon?" asked Gee.
"It was a little planet that spun around our own. It was smaller, and didn't have any life on it."
"Wow. What did it look like?"
"It was round and white in the sky. Not like the sun, it didn't produce light, just reflected the sunlight. It had craters and mountains and valleys."
"Did it have oceans?"
"No, it was all rock. Mostly silicon."
"What was so wrong that they took it?"
"It gave the Earth its day and night. It was part of the Earth once."
"But we have day and night?"
"It gave every part of the Earth its day and night. Mostly."
"Do you think I'll ever see night? Do you think I'll ever see the stars?"
"I hope you do Gee," he said. She hopped from the tail to the head segment and climbed up to the speaker box. She put her cheek next to it, and listened to the quiet thrum of the electronics inside.
"I hope you do too," said Gee.