As with most ideas in physics, the concept of the atom has evolved over time. The left panel has links to the progression of theories, in chronological order, that best described, at the time, what we knew about atomic structure.

Some people look at the list and scoff, "Ha! You see! All of physics is just a Theory has two definitions: 1) something provisional or not quite real, 2) a systematic framework of concepts that describe a natural phenomenon. Scientists use definition 2 when they use the word theory, whereas lay persons tend to be thinking of definition 1 when they use the word theory. Thus, the jeer, "It's only a theory."theory, and scientists are always changing their minds!" Others of us listen to those sorts of comments and say, "Yes, thank you for the compliment!" For we can only do our best with the limited facts we know. The cool part is that as we discover new facts, we modify our thinking to accomodate them! The alternative is mental stagnation and creative dysfunction...

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