It showed him a long line of incredibly old-fashioned-looking cars in front of a gas station just as far out-of-date. The history teacher went on, “Things only got worse as time went on. By the time we reached the 2040s, our oil reserves really did start running dry, the way people had said they would for years. Nobody knew what to do. Many feared that civilization would collapse from lack of energy, lack of transport, lack of food.”

The desktop showed skinny people plundering a truck outside a supermarket. Jeremy's grandfather talked about those days, too. Jeremy hadn't taken him too seriously till he found out on his own how bad things had been. The video on the desktop looked a lot better than the stuff from the 1970s. It had started out digital. It wasn't so grainy, and the color and sound were better. Jeremy felt more as if he were really there, not watching something from ancient history.

“What caused the change?” Ms. Mouradian asked. “Why don't we have troubles like those now?”

A dozen hands shot into the air at the same time. Jeremy's was one of them. Behind him, a girl said, “Why doesn't she ask easy ones like that all the time?”

Two or three people couldn't stand knowing and not saying. Before Ms. Mouradian could call on anybody, they shouted out the answer: “The alternates!”

She nodded. “That's right. The alternates. Without the work of Galbraith and Hester, the world would be a very different place.” When she suddenly smiled, she didn't look a whole lot older than the kids in her class. “And that's what the alternates are all about, isn't it? Look at your desktops, please.”

Jeremy did, even though he'd already seen this video a million times. There were Samaki Galbraith and Liz Hester announcing their discovery to a startled world. He was tall and black and dignified. She was a little redhead who bounced and squeaked, excited at what they'd found. Considering what it was, she'd earned the right, too.