In the Bering Strait two islands sit about two and a half miles apart, Little Diomede on the American side and Big Diomede on the Russian, and the International Date Line runs down the water between them. From the smaller one, on a clear day, you can look across at tomorrow. People call them Yesterday Island and Tomorrow Island, which is wrong in an interesting way: both are having exactly the same afternoon, under the same sun and the same weather, and only the calendars disagree. Some winters the sea freezes between them, and the distance from today to tomorrow becomes a walk across the ice that nobody is allowed to take.