Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

FAQ says refraction isn’t from absorption and emission

  1. Feb 11, 2009 #1
    I find now that there are several effects on light that are not explained by QED. This surprises me since Feynman was so fond of saying that it covered nearly all the physics we experience. So I expected to get an explanation for reflection when I watched his lectures or read his book on QED.

    Feynman also said QED is all about absorption and emission. Yet our FAQ dispels the myth of light slowing down in glass that way. That QED type interaction explains Raman Scattering. But that’s for a small fraction (.00001%) of the light that passes through.

    1 – How does aluminum foil reflect light at the quantum level? (Or any other shiny metal.)
    2 – How does glass slow down light at the quantum level? (The FAQ says what it’s not but not what it is.)
    3 – Why can I see things under an ultraviolet light (black light)? (Maybe this one is QED.)
    4 – What other light effects are not explained by QED. (I want to know everything!)
  2. jcsd
  3. Feb 11, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2018 Award

    I think you have several misunderstanding here.

    1. The conduction electrons displays what are known as "plasmons". These interacts with the electric field of the photon but then retransmit it back with the same momentum, but shifted by pi. You learn this not from QED, but from Condensed Matter Physics.

    2. I'm not sure which part of the FAQ you did not understand. It clearly explained the mechanism on why light appears to slow down. In actuality, it doesn't. The only reason why we say it does is because if you compare the phase of the light that doesn't pass through the glass versus the one that does, the one that does appears to have the phase shifted later. This is how we then say that the light took longer to travel through the same distance in glass.

    3. You can't see UV light. Your eye does not have the sensitivity for that range. However, you can see the EFFECT that UV has on other object, and this include fluorescence of the object due to the impinging UV light. I do laser alignment of a UV laser, which would be impossible since I can't see it. But I can certainly detect its path if I use a piece of paper that fluoresces when the UV light hits it.

    4. How do you know there is? In #1, the reason why you don't get such explanation out of QED is because it involves a material that has a collective behavior.

  4. Feb 11, 2009 #3
    This is great! Thanks, ZapperZ.

    Can you tell me what topics to research to learn more about refraction from a quantum physics point of view?
  5. Feb 11, 2009 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Try the Feynman Lectures on Physics, vol 2, and start from the beginning of the book.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook