“If you were on a bus trying to go east in a maze of dirt roads in a large valley, you might not be able to tell your direction from moment to moment. If someone took a series of snapshots, sometimes the bus might be facing north, or south, or even west, even though all the while this is a journey to the east.”

“If you were on a bus trying to go east in a maze of dirt roads in a large valley, you might not be able to tell your direction from moment to moment. If someone took a series of snapshots, sometimes the bus might be facing north, or south, or even west, even though all the while this is a journey to the east.”

— Steven C. Hayes