Q&A: General Astronomy and Space Science

Q:
What keeps electrons moving? Why don't they slow down?

A:
These are questions physicists were asking at the beginning of the last century, before the development of the quantum theory. The discovery that the atom consists of a massive, positively charged nucleus surrounded by light, negatively charged electrons led naturally to a picture of the atom in which it was similar to a planetary system, with electrons in orbit around the nucleus.

However, it was soon realized that an atom should collapse due to radiative losses by the electron, but it obviously doesn't. This, and other work led to the idea of quantum states, and the concept that electrons bound in atoms act, not like particles, but like confined waves.

When an electron is confined to a limited region around the nucleus, the wave properties of the electron permit only certain special, predetermined states of motion. This behavior is very similar to waves set up by the vibration of air in an organ pipe, or strings on a violin. Because of its wavelike nature, the electron bound to an atom cannot change its state continuously: it must change abruptly from one allowed state, or wave pattern, to another.