3 ms·

This reminds me of Feynman’s QED, which is a must read for laymen who want to know more about things like why shadows have fuzzy edges and other ways light does

by User23 7y ago

This reminds me of Feynman’s QED, which is a must read for laymen who want to know more about things like why shadows have fuzzy edges and other ways light doesn’t exactly travel in a straight line.

whatshisface 7y ago
You don't need QED for that, only Maxwell's equations. QED is necessary if you want to explain how those effects jive with the fact that you can count individual photons.
- Judgmentality 7y ago
  If I am wrong, please correct me: but I don't believe traditional electromagnetism can explain the fuzziness (which I think is better described as noisiness) of shadows.
  - yorwba 7y ago
    That's just diffraction. Any kind of wave spreads slightly into the shadow behind an obstacle; the waves described by Maxwell's equations are no exception.
  - Groxx 7y ago
    I suspect "fuzziness" here is something specific? E.g. fuzzy-edged shadows from the sun seems pretty obvious - it's not a point light source. So this is referring to... nano-scale edge fuzziness or something? Or the shenanigans needed to do sub-wavelength features (like we do for silicon lithography)?
  - thisrod 7y ago
    It depends what you mean by "traditional" and "fuzziness". In ray optics, shadows from point sources are black and white. (If half of the sun is obscured, the surface it illuminates is half as bright, but that's pretty obvious.) That's very old school. Newton could get it right, even though he got particles and waves entirely wrong. In wave/electromagnetic optics, shadows are shades of grey. Just like water waves can be ripples at one end of a beach, crashing surf at the other, and vary continuously in between. In quantum optics, shadows are a superposition of different shades of grey, due to shot noise from the photons. That matters if you're doing very precise interference measurements, but not when you're taking photographs, no matter how short the exposure.
- deleted 7y ago
  [deleted]
- leftyted 7y ago
  The previous poster is referring to this book [0], which is a series of pop science lectures. [0] https://en.wikipedia.org/wiki/QED%3A_The_Strange_Theory_of_Light_and_Matter https://en.wikipedia.org/wiki/QED%3A_The_Strange_Theory_of_L...
IshKebab 7y ago
This doesn't actually take advantage of the wave-like nature of light. There's no diffraction or refraction happening.
darkmighty 7y ago
> why shadows have fuzzy edges ? Shadows have fuzzy edges in geometric optics as well (unless you're mentioning usually micrometer-scale diffraction effects). It's because illuminators are not point-like, so when viewed near an edge your light source progresses in size until it disappears (penumbra to umbra) https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra

by User23 7y ago

whatshisface 7y ago

You don't need QED for that, only Maxwell's equations. QED is necessary if you want to explain how those effects jive with the fact that you can count individual photons.

Judgmentality 7y ago
If I am wrong, please correct me: but I don't believe traditional electromagnetism can explain the fuzziness (which I think is better described as noisiness) of shadows.
- yorwba 7y ago
  That's just diffraction. Any kind of wave spreads slightly into the shadow behind an obstacle; the waves described by Maxwell's equations are no exception.
- Groxx 7y ago
  I suspect "fuzziness" here is something specific? E.g. fuzzy-edged shadows from the sun seems pretty obvious - it's not a point light source. So this is referring to... nano-scale edge fuzziness or something? Or the shenanigans needed to do sub-wavelength features (like we do for silicon lithography)?
- thisrod 7y ago
  It depends what you mean by "traditional" and "fuzziness". In ray optics, shadows from point sources are black and white. (If half of the sun is obscured, the surface it illuminates is half as bright, but that's pretty obvious.) That's very old school. Newton could get it right, even though he got particles and waves entirely wrong. In wave/electromagnetic optics, shadows are shades of grey. Just like water waves can be ripples at one end of a beach, crashing surf at the other, and vary continuously in between. In quantum optics, shadows are a superposition of different shades of grey, due to shot noise from the photons. That matters if you're doing very precise interference measurements, but not when you're taking photographs, no matter how short the exposure.
deleted 7y ago
[deleted]
leftyted 7y ago
The previous poster is referring to this book [0], which is a series of pop science lectures. [0] https://en.wikipedia.org/wiki/QED%3A_The_Strange_Theory_of_Light_and_Matter https://en.wikipedia.org/wiki/QED%3A_The_Strange_Theory_of_L...

IshKebab 7y ago

This doesn't actually take advantage of the wave-like nature of light. There's no diffraction or refraction happening.

darkmighty 7y ago

> why shadows have fuzzy edges ? Shadows have fuzzy edges in geometric optics as well (unless you're mentioning usually micrometer-scale diffraction effects). It's because illuminators are not point-like, so when viewed near an edge your light source progresses in size until it disappears (penumbra to umbra) https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra https://en.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra