Electrons

I'm reading Andy Weir's Project Hail Mary and he's messing about with light and spectroscopy and I was just reading about that for my post about the Keanu Reeves movie Siberia and all this got me to thinking about electrons.

I think the problem I have is that there are two forms of heat and I don't understand how they are connected. There is the gross form of heat where atoms vibrate. As I recall, all atoms are vibrating all the time. The higher the temperature, the stronger the vibration. The only time they stop vibrating is when they are cooled all the way down to absolute zero. No vibration, no motion, no temperature. 

Atoms at peace don't vibrate much, they are content with their lot, locked into fixed relationships with their neighbors. Everybody minds their own business, but they all talk to each other, neighborly like. No hot-rodders tearing through our town, least not since that Packer kid's girl dumped him.

Heat things up and the vibrations get stronger and all those friendly, neighborly bonds aren't quite so strong, or maybe they've just move out of reach. It's like our fence has been doubled and our lots are drifting apart.

But then there's the other kind of heat where the electrons get excited. A photon comes blasting in from out of town, hits one of our happy little atoms and one of the electrons gets boosted to a higher orbit. Okay, it's not an orbit, it's a higher state, you know, closer to nirvana. But then, after a while, the electron returns to its previous, normal state and in the process emits a photon. 

Now we come to the crux of the matter - what is 'after a while'? What determines when that electron decides to return to its previous, lower state? Does it take a while to figure our that nirvana isn't all it's cracked up to be? Yeah, somethin's goin' on that I do not understand.

P.S. Andy Weir also wrote The Martian, which got made into a movie, and Artemis, about a moon base. The movie was pretty great. Artemis was entertaining.