 Hello, and welcome to our How Small Is It segment on atoms. The ancient Greeks had two schools of thought on atoms. One was that you could take a substance like water and divide it and divide it and divide it infinitely. The other school said you can divide it and divide it and divide it to a point at which point you have the smallest piece of water, and if you separate that, it's not water anymore. In those days they didn't have any testing capabilities to verify one theory or another. But today we do. This segment is all about the atom and the pieces that go together to form an atom. In our first segment, we saw carbon atoms through the eye of an electron microscope. Their diameter was 0.14 nanometers. That's very small. There are more atoms in the breath of air that I just took than there are stars in the entire visible universe. But what do we really know about atoms? And the parts that go together to make an atom. That's what this segment is all about. We'll start with J.J. Thompson's guess as to the structure of these things, atoms. It's a fascinating story, and it'll put us on a path to understanding elementary particles and the Higgs boson.