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B Spontaneous increase in energy level

  1. Dec 8, 2017 #1
    i know there is a certain probability for an electron to fall to a lower energy level,without an exciting event,like a collision. Is the reverse also true I.e that a electron could jump to a higher level,without absorbing any extraneous energy..if so are the lifetimes in the new state the same for both processes?
  2. jcsd
  3. Dec 8, 2017 #2


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    It does not just fall. The leftover energy needs to be expelled, usually in the form of a photon, or energy would not be conserved.

    Just as you need to expell energy to go to a lower energy level, you need to add energy to go to a higher one.
  4. Dec 8, 2017 #3
    Actually, it's not immediately obvious that the probability for an electron to "fall" to a lower energy state should be nonzero, assuming that the electron occupies a bound state far away from any perturbing electromagnetic fields. Normally, states with well-defined energy in quantum mechanics are "stationary," meaning that they do not change with time. When we introduce a perturbation to the region around a bound state--for example, by shining a light on an electron bound to an atom--we can induce transitions between the stationary states. This is what causes stimulated emission and absorption of radiation by atomic electrons--basically, an electron can absorb a stray photon and "jump" to a higher energy level, or can be "stimulated" by passing photons to jump down to a lower one. (The latter process is not at all intuitive from the point of view of classical physics, and is the mechanism responsible for light amplification in a laser.)

    The reason electrons sometimes "fall" even without the presence of a perturbation--in a process called "spontaneous emission"--has to do with quantum electrodynamics. Essentially, the theory tells us that the electromagnetic field is always nonzero--it is literally impossible for a region of space to be free of electromagnetic "perturbations." In particular, spontaneous emission is really just a special case of stimulated emission.

    So the answer to your question is no--any transition from a stationary state to a higher-energy one involves the absorption of a photon, just as a transition from a higher-energy state to a lower one involves the emission of a photon.
  5. Dec 8, 2017 #4
    I was thinking of the uncertainty between time and energy,that there is a non zero probability to jump higher for a very short time. As posted on another thread,someone said the atom is never really isolated from any em field,can it “borrow “ this energy from itself?
  6. Dec 8, 2017 #5
    I think I just found the answer, it involves the combination of the states of an em field combined with the states of the electron,and phase space. It seems almost like the law of entropy in operation. So where by spontaneous emmision is possible the reverse is almost impossible.
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