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

The Doppler Effect- According to Quantum Mechanics

  1. Feb 13, 2008 #1
    I am just beginning to learn about quantum mechanics and I have already come up with a question regarding it. I know that light is absorbed by an electron at once and I know about the doppler shift. Yet is light emitted at once, or gradually? If at once, how could the wavelength be shifted because of the receding or approaching speed of a planet, and therefore, individual atoms (I know it can be shifted by gravity, but that's besides the point, I think)? If it gets emmitted gradually, then why (I mean, why is it absorbed at once and emmitted gradually)?
    Can anyone offer any suggestions for books or website articles that specifically address quantized energy absorbtion? And as I am just starting and do not know anything about differential equations and calculus, should I try to learn it from a school textbook, wait until I take the class, or read a book that might explain it in easier terms (I am a sophmore in high school)?

    Thank You
     
  2. jcsd
  3. Feb 14, 2008 #2
    The Doppler effect is a macroscopic phenomena, and you are trying to fit it in a quantum model. Don't. Quantum physics doesn't deal with questions like "is the photon emitted at once" or "does the electron jump instantaniously between energy levels". That is taking the model too literally. Unlike classical physics, QP doesn't try and explain what "actually happens"..

    When it comes to Doppler the only reasonable explanation is that the emitted wave is stretched or compressed when continuously emitted by a, relative to observer, moving source.

    If you're looking for a detailed explanation of how an atom absorbs light, I'm sorry to say you'll probably be disappointed. The quantum model goes no deeper than to say that the atom absorbs the photon and an electron increases it's energy level accordingly. The model is mainly mathematical, I believe.
     
  4. Feb 14, 2008 #3
    It's a good question. There must be a quantum mechanical explanation of the doppler effect. I can't think what it is at the moment though.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?