A thermodynamic approach to spontaneous emission

[frankchen]

any isolated macroscopic system, like a large group of atoms, always tends to reach a state that has the maxium entropy. if the electrons in this group of atoms are excited, they will give out their energy so that more degrees of freedom are activated, hence the entropy of the whole system increase. that's why spontaneous emission happens, is that right?

 

[Andrew Mason]

any isolated macroscopic system, like a large group of atoms, always tends to reach a state that has the maxium entropy. if the electrons in this group of atoms are excited, they will give out their energy so that more degrees of freedom are activated, hence the entropy of the whole system increase. that's why spontaneous emission happens, is that right?

Maybe it is just me, but I don't find entropy to be particularly useful in explaining why things happen.

One could also look as spontaneous emission as a consequence of the progression of time. Since the probability that an excited atom will remain in the excited state declines exponentially as a function of time, the probability that excited atoms as a group will undergo spontaneous emission, eventually, approaches certainty. Spontaneous emission, being random, progresses in only one direction because there are many ways that a large system of excited atoms can undergo energy decay and only one way to remain in the original state.

Neither approach really tells us why it occurs.

AM