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Quick Question

  1. Feb 12, 2008 #1
    I know that as space expands it cause light to force itself to increase its wavelength, but I can't seem to remember how it relates to a decrease in energy, and thus a decrease in temperature. I know that in this respect energy is related to wavelength as opposed to how it classically related to amplitude.

    Thanks, I hope I've got that much right so far =]
  2. jcsd
  3. Feb 12, 2008 #2


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    From quantum mechanics, the energy of a photon is given by


    where h is a constant (Plancks constant) and f is the frequency of the wave. Using the basic wave equation

    [tex] v=f\lambda[/tex]

    where [tex]\lambda[/tex] is the wavelength, and taking the velocity of light to be c we get


    So, as the 'classical' wavelength increases, the energy of the photon decreases.

    I hope that helps, let me know if I'm being too equationy!
  4. Feb 12, 2008 #3
    Perfect thanks =]
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