Jordan watched the glass disk in the street very carefully. He was pretty sure it had not been there a couple of minutes before, and he was also sure that he hadn’t looked away from the pavement.

Finally he nudged it with a dirty sneaker. It looked awfully thin, and he was afraid to break it, but when he touched it with the edge of his shoe, it didn’t seem to budge. He squatted down and looked into it. It wasn’t glass like a windowpane. It looked more like that piece of volcanic glass that Mrs. Gubner had brought to school, except bluish, and with weird spots in it, that swirled and rippled even though he couldn’t see them move. He just knew they did.

After a while he remembered that he had to go to school, and realized that he was looking up at the houses along the street with great relief—they are still here, they aren’t rotted away and gone like in a time travel movie, came the thought. So he walked over to his skateboard and his backpack and kept going.

After a minute or two the glass disk rose as if someone underneath it were opening a hatch, which was pretty much the case; a man and a woman emerged, wearing orange business suits.

“Well, that was close,” said the man. The woman examined the street.

“Still using asphalt. We should go forward about a century,” she announced.

“You know best,” said the man, and they lifted the glass disk and climbed under it again.

A house finch swooping down to look at the shiny thing was rather startled to find it gone at swoop’s bottom.