Why electron enters the lowest potential possible?

[Tahmeed]

Why electron and overall an atom is most stable in lowest potential energy? There is a concept of stable equilibrium in classical physics, does it apply here as well? but electron is never in an equilibrium state, neither an atom is.

Then why it tries to be in lowest potential?

 

[stevendaryl]

Why electron and overall an atom is most stable in lowest potential energy? There is a concept of stable equilibrium in classical physics, does it apply here as well? but electron is never in an equilibrium state, neither an atom is.

Then why it tries to be in lowest potential?

In nonrelativistic quantum mechanics, if you disregard the electromagnetic field, then there are a discrete number of possible (bound) states for an electron, and they are all stable. What makes the higher-level states unstable is the interaction between the electron and the electromagnetic field. Roughly speaking, if $\delta E$ is the energy difference between the current state of the electron and the ground state, then the interaction with the electromagnetic field will result in "sharing" that energy between the electron and photons. The reason that it all goes to photons is a counting argument: the set of possible states with that energy given to photons is so much huger than the set of possible states with that energy given to the electron. For the electron to radiate the energy away is the most entropy-increasing solution, so it's just the second law of thermodynamics at work.