Time, it has been joked, is what keeps everything from happening all at once. It is the clock on our wall, the watch on our wrist, perhaps even the beat of our heart. Time seems to flow forward like a steady stream. We live in time, and time washes over us whether we like it or not.

And yet, time appears to be very different from that other entity in which we live, space. Space, the air and land and seas around us, the sky overhead and the universe beyond, is a more comfortable concept. We can move forward or backward in space, at our will. (The only requirement is that we must stay in our universe.) We can return to a place visited earlier, we can live or walk or run in more places than another, we know how to navigate through space. We might say, "I...