英语时差：原子理论和空间（下）

But wait! What about the protons and neutrons and stuff? Well, they’re in there, but only in the very center. That’s called the nucleus. An atom’s nucleus is surrounded by a cloud of orbiting electrons. Virtually all the mass of the atom — the stuff and not the fluff — is in the nucleus. And the nucleus is incredibly tiny compared to the overall size of the atom. In fact, it’s about a hundred thousand times smaller. It’s like a speck of dust floating around inside a cathedral. In between the dust speck and the cathedral walls is nothing but space. So you are made up of things that are mostly empty space, with occasional specks floating in them. Does it make you feel kind of empty, too? Don’t worry. Every other object in the world, from a pebble to Mount Everest, is the same way.