Does light bend around objects? (Not by gravity or diffraction)

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Discussion Overview

The discussion revolves around the phenomenon of light appearing to bend around objects, specifically in the context of an observation made by a participant involving a metal rod and the full moon. The scope includes conceptual exploration of light behavior, with a focus on whether the observed effect can be classified as diffraction or another phenomenon.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant describes observing a thin line of moonlight parallel to a metal rod, suggesting that light may bend along the surface of the rod.
  • Another participant asserts that the effect is called diffraction.
  • A third participant questions the initial claim of "not by diffraction," seeking clarification on why the original poster dismisses this explanation.
  • The original poster provides reasons for excluding diffraction, citing stronger effects on metals, the defined brightness of the glow, and difficulty finding relevant photographic evidence of diffraction effects.
  • One participant responds by suggesting that the observed effect may involve both diffracted and reflected light due to the reflective nature of metals.
  • This participant also notes that interference patterns require coherent light, which may not be present in the sunlight used in the observation.
  • Another participant explains that diffraction refers to light bending around objects and references Huygen's wavelet model, while also mentioning the Young's two-slit experiment as a notable example of diffraction.

Areas of Agreement / Disagreement

Participants do not reach consensus on whether the observed effect is diffraction or another phenomenon. Multiple competing views remain regarding the nature of the light bending effect.

Contextual Notes

Participants express uncertainty regarding definitions and the specific conditions under which the observed effects occur. There are limitations in the original poster's ability to find photographic evidence and in the clarity of the definitions of diffraction and reflection.

peterparker
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Today I was watching the full moon while I had one eye closed. There was a vertical metal rod which, by moving my head a bit, covered the moon completely, so that no direct light could hit my eye. (Yeah... I do things like that...)
I saw a thin line of moonlight parallel to the rod right at the edge of it.
It looks like the metal would bend the light along its surface for maybe a degree or so.
It doesn't seem to be a property of the metal, because a painted wall has the same effect, but less bright.

Does anyone know how this effect is called?

Thanks for solving this mystery, it puzzles me since I was a child :-D

Kind regards
peterparker
 
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I believe that light bending around objects is called diffraction.
 
Indeed, this is diffraction. Not sure why you put "not by diffraction" in your title? Why do you think this is not diffraction?
 
I didn't take diffraction as an explanation because
A) the effect seems stronger on metals,
B ) the bright glow seems to be too defined, no ripples in intensity are visible (as seen in the slot experiment) and
C) I'm not able to find a photograph of the effect by Googling "visible diffraction". All I can find there is light split up in different wavelengths. And that's not what I see in my little experiment.
 
A) Metals are really reflective, so you are probably seeing both diffracted, as well as reflected light.
B) To see an interference pattern, you need to be looking at coherent light. The light from the Sun is in all wavelengths and different phases and polarizations, so you wouldn't see very much in terms of dimming and brightening.
C) Diffraction just means the light is bending around an object (see Huygen's wavelet model of light). But famously, the Young's two slit diffraction experiment (where the diffraction here means the light bends around the two slits) "proved" light is a wave, and so that's what you're going to see when you look up diffraction.
 

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