quantum electrodynamics

Question

When In quantum electrodynamics when using a stopwatch to “time” the movement of a photon to find the direction of its arrow representing the probability amplitude, why does the stopwatch have to start at 3 o’clock and travel anti-clockwise?

Answer 1

In quantum electrodynamics, when using a stopwatch to "time" the movement of a photon, the stopwatch pointing at the the 3 o'clock position is considered the "zero" position and anti-clockwise is actually the direction of positive rotation in the spherical 3-D polar system.