A monk begins his day at sunrise at the bottom of a mountain path. He winds his way to the top — taking several rest breaks along the way — arriving at the summit around sunset.
He meditates throughout the night.
At sunrise the next morning he begins his journey home on the same pathway. (Indeed, there is only one way up, and one way down the mountain, unless one jumps and subsequently dies. The monk chooses not to jump that day.) He arrives an hour or so before dusk — since it is far less laborious going down the hill than up it. Besides, he has just become enlightened.
Now to the question: Is there a specific place on the path where the monk was at the exact same location at the exact same time of day on both days? Please explain your answer.
Ok, two days and 20 posts later, here's the first installment
of my two part answer : The Feynman diagram: