How Does Feynman Explain Reflection in Light and Time?

[Saw]

I have been reading the explanation of reflection that Feynman provides in The strange theory of light and matter.

There are two things I do not understand:

a) How does he choose the directions of the little arrows below the diagram? I understand that each path is different in that it takes more or less time to get to the target (the detector). But on which grounds does he associate to this magnitude (time) one or another spatial direction for the arrows?

b) It seems as if the explanation applied regardless the nature of the reflecting surface, i.e., whether it is specular (a mirror) or not. But the fact is that depending on that factor the detector at point P will actually see or not a reflection of the object at point S...

 

[Nugatory]

a) How does he choose the directions of the little arrows below the diagram? I understand that each path is different in that it takes more or less time to get to the target (the detector). But on which grounds does he associate to this magnitude (time) one or another spatial direction for the arrows?

They all start at the source pointing in the same (arbitrary) direction, and they all rotate at a constant speed like the hands of a clock, so the direction they're pointing after traveling for a given distance and hence given time is completely determined.

b) It seems as if the explanation applied regardless the nature of the reflecting surface, i.e., whether it is specular (a mirror) or not. But the fact is that depending on that factor the detector at point P will actually see or not a reflection of the object at point S...

The properties of the reflecting surface come into the picture through the "shrink and turn" behavior of the interaction at the surface; differences here will affect the transmission, reflection, and absorption of the incident light.

 

[Saw]

They all start at the source pointing in the same (arbitrary) direction, and they all rotate at a constant speed like the hands of a clock, so the direction they're pointing after traveling for a given distance and hence given time is completely determined.

Thanks. That is very clear.

The properties of the reflecting surface come into the picture through the "shrink and turn" behavior of the interaction at the surface; differences here will affect the transmission, reflection, and absorption of the incident light.

More thanks. I was reading an extract and hence missing that part of the explanation. Will retake the full text now and try to understand...

 

[meBigGuy]

He explains it in this lecture. Maybe it will help.

http://vega.org.uk/video/programme/46

You might watch http://vega.org.uk/video/programme/45 first (or not)