How Does Feynman Explain Reflection in Light and Time?

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Discussion Overview

The discussion centers on Richard Feynman's explanation of light reflection as presented in "The Strange Theory of Light and Matter." Participants explore the mechanics of how Feynman illustrates the directionality of light paths and the implications of different types of reflecting surfaces on the visibility of reflections.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how Feynman determines the directions of arrows in his diagrams, noting that while paths take different times to reach the detector, the rationale behind their spatial direction is unclear.
  • Another participant explains that the arrows start from the source in an arbitrary direction and rotate at a constant speed, suggesting that their final direction is determined by the distance traveled over time.
  • Concerns are raised about the applicability of Feynman's explanation to different types of reflecting surfaces, with one participant noting that the nature of the surface affects whether the detector will see a reflection.
  • It is mentioned that the properties of the reflecting surface influence the interaction of light, affecting transmission, reflection, and absorption.
  • A participant expresses gratitude for the clarification and indicates a need to revisit the full text for better understanding.
  • One participant provides links to lectures that may further elucidate Feynman's explanation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the rationale behind the direction of the arrows or the implications of different reflecting surfaces, indicating that multiple views and uncertainties remain in the discussion.

Contextual Notes

Participants acknowledge missing parts of Feynman's explanation, which may affect their understanding of the concepts discussed, particularly regarding the interaction of light with different surfaces.

Saw
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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...
 
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Saw said:
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.
 
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Nugatory said:
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.

Nugatory said:
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...
 

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