Energy Excitation: Why Electron Emits Radiation

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Discussion Overview

The discussion revolves around the reasons why an excited electron in an atom emits radiation and transitions back to a lower energy level rather than remaining in the excited state. It explores concepts from quantum mechanics, including the nature of isolated atoms and the probabilities associated with energy state transitions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the atom is not isolated and can interact electromagnetically, leading to decay from an excited state.
  • Others argue that every possible process will eventually occur, questioning why an electron would prefer to stay in a higher energy level.
  • One participant notes that the transition from excited to ground state has a certain probability and a corresponding lifetime, which is generally short for most atoms.
  • There is a discussion about the meaning of "isolated atoms," with some clarifying that it refers to a system without coupling to the electromagnetic field.
  • Concerns are raised about the implications of using a Hamiltonian that does not account for electromagnetic coupling, which may lead to misconceptions about the lifetime of excited states.
  • Participants question how quantum mechanics accounts for the non-zero probability of decay from an excited state to the ground state.

Areas of Agreement / Disagreement

Participants express differing views on the nature of isolated atoms and the implications of quantum mechanics on energy state transitions. There is no consensus on the reasons behind the emission of radiation or the conditions affecting the lifetime of excited states.

Contextual Notes

The discussion highlights limitations in understanding due to the dependence on specific Hamiltonians and the assumptions made in quantum mechanics regarding energy measurements and state transitions.

Rahma Al-Farsy
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Why doesn't an electron which has been excited not keep the energy gained and stay in a higher quantum level? Why does it prefer to emit radiation and return to a lower energy level?
 
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It can do so, and every process that is possible will happen at some point. Why should it stay in a higher level? This is true for isolated atoms as well.
 
What do you mean by isolated atoms?
 
Well the transition from the excited state to the ground state has some probability to happen (and so some lifetime during which the atom stays excited).
Now the lifetime is pretty short for most of the atoms I know, and so they eventually end up in the ground state. If the lifetime happened to be relatively long, you would expect the atom to prefer being at an excited state (although I don't have such an example at hand).
 
Rahma Al-Farsy said:
What do you mean by isolated atoms?
isolated atoms: I think they mean the quantum mechanical system of the atom where there is no term in the Hamiltonian to account for the coupling of the atom to the radiation (EM) field... pretty much "classical quantum mechanics" (I guess)
 
Rahma Al-Farsy said:
What do you mean by isolated atoms?
A system with only the atom in it... i.e. no possibility there is a state which consists of an atom and a photon.
The atomic model does not include the coupling with the EM field... did you read the link?

ChrisVer said:
Well the transition from the excited state to the ground state has some probability to happen
Doesn't that just change the wording of the question to "how come there is a non-zero probability of decay?"
I think OP would like to know how this gets accounted for in QM.

mfb said:
Why should it stay in a higher level?
Is key... the reason students may come to believe the lifetime of an excited atomic state is infinite is because they have usually been taught to work out the states by using a hamiltonian that does not include the coupling to the EM field. This is the level where students are taught that if a measurement of energy of the system gets you, say, the 1st excited state ... then all subsequent measurements of energy should return the 1st excited state (provided certain other things don't get measured in between energy measurements). So how does the QM learned so far allow that a subsequent measurement of energy may (eventually and inevitably will) get you the ground state?
 

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