In our normal experiences we know that every event is caused by something else. If a window breaks, it happened because a ball went through it, which happened because a kid threw it, and so on.
However, if the history of science teaches us anything, it is that our “normal experiences” have often been wrong.
The Earth is not flat, although it looks pretty flat (especially on the prairies). The Earth moves, although it seems like everything else does. Things tend to stay in motion, even though everything experiences some friction around us and eventually slows down. And not every event has a cause.
An atom can undergo three processes when emitting or absorbing light. First in can experience stimulated absorption, when a photon of light hits an electron in the atom and bumps it to a higher energy level. This is like coming along and picking up a pencil and putting it on a higher shelf – the overall energy is increased. It can also undergo stimulated emission, this is the key to what happens in lasers. A photon comes along, “bumps” the electron (that’s in its excited state) and the electron drops to a lower state, releasing its energy as another photon (1 photon in, 2 photons out). Basically it’s like coming along and knocking the pencil back down to a lower shelf, and as the pencil falls, rather than picking up speed with energy it emits energy in the form of light. These two processes fit our mold of having a nice explainable cause, and there isn’t anything to weird about them.
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