“Students, we’re now in what’s called the ore zone. What you see is a scene of early mining work.”

A few miners came toward us. I knew they were holograms, so I didn’t move out of the way. Some of them passed through me, so I could see them very clearly, and I was astonished.

“Did China hire black people to mine coal?”

“To answer that question,” the teacher said, “we’ll have a real experience of the air of the ore zone. Please take out your breathing masks from your bags.”

We put on our masks, and heard the teacher say, “Please remember that this is real, not a hologram.”

A cloud of black dust came toward us. In the beams from our headlamps I was shocked to see the thick cloud of particles sparkling. Then someone started to scream, and like a chorus, a lot of other kids screamed as well. I turned to laugh at them, but I, too, yelped when I got a look: Everyone was completely black, apart from the portion the masks covered. Then I heard another shout that turned my hair on end: It was the teacher’s voice!

“My god, Seya! You don’t have your mask on!”

Seya hadn’t put on his mask, and now he was as completely black as the holographic miners. “You said over and over in history class that the key goal was to get a feel for the past. I wanted a real feel!” he said, his teeth flashing white on his black face.

An alarm sounded somewhere, and within a minute, a teardrop-shaped micro-hovercar stopped soundlessly in front of us, an unpleasant intrusion of something modern. Two doctors got out. By now, all of the real coal dust had been sucked away, leaving only the holographic dust floating around us, so their white coats stayed spotless as they passed through it. They pulled Seya off to the car.

“Child,” one doctor said, looking straight into his eyes. “Your lungs have been seriously harmed. You’ll have to be hospitalized for at least a week. We’ll notify your parents.”

“Wait!” Seya shouted, his hands fumbling with the rebreather. “Did miners a hundred years ago wear these?”

“Shut your mouth and go to the hospital,” the teacher said. “Why can’t you ever just follow the rules?”

“We’re human, just like our ancestors. Why …”

Seya was shoved into the car before he could finish. “This is the first time the museum has had this kind of accident,” a doctor said severely, pointing at the teacher and adding, before getting into the hovercar, “This falls on you!” The hovercar left as silently as it had come.

We continued our tour. The chastened teacher said, “Every kind of work in the mine was fraught with danger, and required enormous physical energy. For example, these iron supports had to be retrieved after extraction in this zone was completed, in a process called support removal.”