# Confused in Chapter 3 of RF's QED

1. Mar 11, 2010

### soup_

Hello,

I'm reading through Richard Feynman's QED (for the first time) and I'm at Chapter 3. At the bottom of page 102 (2006 edition), he says, "So the timer we used for the 'imaginary stopwatch' was the monochromatic source:--in reality, the angle of the amplitude for a given path depends on what time the photon is emitted from the source. Once a photon has been emitted, there is no further turning of the arrow as a photon goes from on point to another in space-time."

From what I read from these sentences, he seems to be saying that in Chapters 1 and 2, all the times where he talked about the "stopwatch hand" spinning as the photon traveled through space-time, that he was using it as a simplification.