Re: What force or energy keeps subatomic particles moving?

Hello Teri,

That's a very good question. Niels Bohr asked the same question, in the early 20th century: why don't the electrons inside atoms, which seem to move very fast, eventually slow down? He didn't need to worry about the fact that "matter has existed since creation": the equations of classical physics seemed to predict that electrons should slow down really quickly - nanoseconds or microseconds, I think - and fall into the nucleus! If these equations (which were derived from "macroscopic" experience, studying balls and bullets and planets) were correct, then all atoms would have "worn down" a long time ago.

Atomic electrons do not slow down, not at all, not over the lifetime of the Universe, so clearly the equations governing bullets and planets are not the same as the ones governing atoms. Bohr came up with a new theory, which correctly describes hydrogen atoms. In the Bohr model, the electrons in atoms are not free to move in any which way; they are confined to one of several quantum states. The electron can stay in any quantum state forever, without losing energy; it can jump from one state to another. But it cannot live "between" states. This means that it cannot slow down gradually; it can only change from one state to another in discrete jumps, and each such jump requires that the atom emit or absorb light. Also, there is one particular state which is called the "ground state". In this quantum state, the electron has the least amount of energy possible; you cannot slow it down any further. So, in a nutshell, ground-state atoms cannot "wear out" or slow down because there is nothing possible to change into.

Most of the atoms around you on Earth are already in their ground state (well, most molecules are in a ground state, and most atoms are bound up in molecules). Almost every time you see matter emitting light, it is because electrons are jumping from one discrete state to another: candle flames, computer screens, fluorescent light bulbs. If you build an amateur spectrometer, you can look at different types of light sources, and see how specific colors come from specific atoms; each color is associated with a particular "jump" in a particular molecule. Stars (like the Sun) are a somewhat different story; most atoms in the sun are "ionized" - the electrons and nuclei are all wandering around freely, so the sun is not really made of atoms at all; it's an electron-proton plasma. (If the sun's plasma were to cool down to Earth's temperature, the electrons would quickly pair up with the protons, and eventually end up in the ground state.)

You should read more about the "Bohr Model" of the atom, which (though incomplete) is easy to understand, and about quantum mechanics in general, which explains why Bohr's model works at all. here is a good easy explanation of the whole business.

Good question. If you had asked this question in 1910, no one would have known the answer! (If you had answered it, you might well have won the Nobel prize!)

-Ben