“Okay, so now give me Gil Hodges’s home run total, multiplied by Pee Wee Reese’s batting average. And don’t use paper and pencil. You can do it in your head.”

“You’re nuts,” Nate told him. “That’s probably a ten-digit number.”

“What’s life without challenges? Get it right and you’ve earned yourself a licorice whip.”

Soon they were in the foothills of the Rockies. Then the Rockies themselves, jutting up into the clouds, their craggy peaks covered in snow. Nate tried to picture what it would be like to be on one of them—like Ernest Shackleton, carrying a pack, with nothing but rations of dried meat and nuts to keep you going.

They passed a station wagon, Minnesota plates, with a family inside: mother, father, and four kids in the back, suitcases on top. As they drove by they did their special car trick. They each put one arm out the window, making a perfectly synchronized waving motion, like they were one giant bird, with a truck cab for a body.

Sometime in the afternoon they stopped for a bowl of chili at a diner alongside the highway, and one more time just after darkness fell, near the Idaho border. Then they set out on the highway again, the lights of the truck cutting through the dark, hardly another vehicle in sight.

“Funny, isn’t it?” his dad said, looking out at the desolate stretch of blacktop, lit by a nearly full moon. “At this very moment our bodies are taking in tiny amounts of cosmic radiation.”

Nate didn’t have to ask, What are you talking about? He knew his father would tell him.

“Tiny particles of alpha, beta, and gamma rays emitted into the atmosphere as a result of radioactive decay,” he went on. “We can’t see them, but they’re here, all around us, all the time.”

“We studied radioactivity in science.”

“Ah, science class,” his dad said with a long sigh. “If you want to know what’s what, see things for your own self. Never trust your teachers to tell you the whole story.

“Right here in Idaho, for instance. Experimental nuclear reactor over in Idaho Falls had an accident a few years back. Three men were killed instantly from the radiation. They had to bury them in lead coffins, their bodies were so heavily contaminated. The government put concrete over their graves, just so the relatives could come and visit them without getting radiated themselves. You think they tell us that stuff on the news? Not likely.

“See this watch face?” Dad continued, holding out his wrist. “Radioactive. It’s radium-based paint that makes the hands glow in the dark. The factory workers who used to paint the dials would have the habit of licking the tips of their brushes, to keep the bristles together, and darned if they didn’t come down with cancer from the stuff.”