“Since you can’t find your way to your own time,” you say, “perhaps we can find my time.” You lead her back a short distance, until you come to an unusually wide tunnel. You stop, and Louisa looks at you inquiringly. “Let’s try this one,” you say.

After traveling almost an hour, the two of you smile with joy to see light ahead, and you soon come out of the tunnel and stand on reddish sandy ground, surveying a saucer-shaped terrain. The air is as fresh and clear as on a crisp, fall day. You guess that you may be in the crater of an extinct volcano. Suddenly, there is a thundering roar behind you. Louisa and you run from a landslide that buries the tunnel leading back to the Cave of Time.

“I wonder what year it is?” Louisa asks, after the two of you have collected your wits.

For the first time you look up at the sun. It is four times as large as the sun you knew, though not as bright. It is almost directly overhead, yet its color is a rusty red.

“I don’t know the answer,” you reply, “but from what I’ve read about astronomy, I would guess it’s the year 2,000-plus about four billion years.