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Spontaneous emission

  1. Apr 19, 2015 #1
    By Spontaneous emission it is said that the electron jumps to the higher energy state and then after some time "spontaneously" falls to the lower state.

    It is still not clear to me, what makes the electron to "fall" back to the lower state, if higher state is also allowed state and excitation does not violate transition rules, therefore "spontaneously" falling contradicts 1 Newton's law, or it is due to the acting Columb's forces and interactions between electrons in the atom? And what determines time at which electron stays at excited state, I assume it is somehow Fermi statistics?

    I am in a master level.

    Thank you.
    Last edited: Apr 19, 2015
  2. jcsd
  3. Apr 19, 2015 #2
    The thermodynamically irreverisble transition to the lower energy state is due to the much larger number of large degrees of freedom carried by the photon than the excited molecule.

    Fermi's Golden Rule determines the transition rate.
  4. Apr 19, 2015 #3


    Staff: Mentor

    It really requires Quantum Field Theory to explain. Basically its not in an eigenstate when the electron and its coupling to the quantised EM field is considered. The usual hand-wavey explanation is its caused by random fluctuations of virtual particles in the vacuum. Its a bit hand-wavey because virtual particles dont really exist - but that is by the by - there is a long thread discussing that at the moment if you want to delve into it.

    If you do an internet search there are some papers that go into the detail eg:

    I am pretty sure Craigi got what he said from Wikipedia:

    I don't think the large degrees of freedom per-se is the reason.

    Last edited: Apr 19, 2015
  5. Apr 20, 2015 #4
    Thank you very much!
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